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Placentation:- It is defined as the arrangement of ovules within the ovary. several different forms of placentation can be seen in flowering plants.
Types of Placentation:-
i. Marginal:- The ovules develop in rows near the margin on the placenta formed along the ventral suture. It occurs in monocarpellary and unilocular ovary, E.g., Leguminosae.
ii. Parietal:- The placenta is formed by the swelling up of cohering margins, and on the latter develop the ovules in rows. It occurs in bicarpellary or multicarpellary but unilocular ovary, E.g., Papaveraceae.
iii. Axile:- Here, the placentae develop from the central axis which correspond to the confluent margins of carpels. It occurs in bi-to multilocular ovary, E.g., Solanaceae, Malvaceae.
iv. Free-central:- Here, the placenta develop in the centre of the ovary as a prolongation of floral axis and the ovules are attached on this axis. It occurs in multicarpellary but unilocular ovary, E.g., Primulaceae.
v. Superficial or Laminar:- Here, the ovules develop over the entire inner surface of the carpels. It occurs in multicarpellary ovary, E.g., Nymphaea.
vi. Basal:- The placenta develops directly on the thalamus and bears a single ovule at the base of the unilocular ovary, E.g., Compositae.
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Callose:- It is a plant cell wall polysaccharide made primarily of β-1,3-glucan chains with a few β-1,6-linked branches. It is synthesized by callose synthase enzymes in the plasma membrane and degraded by β-1,3-glucanases.
Functions of callose:-
Plant defense:- Rapidly deposited at sites of pathogen attack or wounding, forming a barrier that limits pathogen spread.
Regulation of plasmodesmata:- Callose accumulates around plasmodesmata, reducing their permeability and controlling movement of molecules between cells.
Pollen development:- Essential for the formation of the callose wall surrounding developing pollen mother cells and pollen grains.
Cell plate formation:- Deposited during cytokinesis to support the developing cell plate before it matures into a normal cell wall.
Sieve tube regulation:- Accumulates around sieve pores in the phloem, helping seal damaged sieve elements and regulate transport.
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Self Incompatibility (स्वअनिषेच्यता):-
· जब एक पुष्प के परागकण उसी पुष्प या उसी पौधे के अन्य पुष्प को निषेचित करने में असमर्थ होते हैं तथा अन्य पौधे के पुष्प को निषेचित करने में समर्थ होते हैं तो इसे स्वअनिषेच्यता कहते हैं। लगभग 3000 से भी अधिक पौधों में यह पायी जाती है।
(When pollens of a flower are unable to fertilize the same flower or other flower of the same plant and are able to fertilize the flower of the other plant, it is called self-incompatibility. It is found in more than 3000 plants.)
· जब एक अनिषेच्य परागकण वर्तिकाग्र को परागित करता है तो यह निम्न 4 अवस्थाओं में से किसी एक पर वृद्धि को रोक लेता है जिससे स्व निषेचन असफल हो जाता है:-
(When an incompatible pollen pollinates the stigma, it stops growth at any one of the following 4 stages, causing failure of self-fertilization:-)
i. वर्तिकाग्र पर परागकण अंकुरित नहीं होता है।
(Pollen does not germinate on stigma.)
ii. वर्तिकाग्र पर परागकण अंकुरित होता है परन्तु परागनाल वर्तिकाग्र को भेद नहीं पाती है।
(Pollen germinates on the stigma, but the pollen tube does not penetrate the stigma.)
iii. परागनाल वर्तिकाग्र को भेदने के पश्चात बहुत धीमी गति से वृद्धि करती है।
(The pollen tube grows very slowly after penetrating the stigma.)
iv. निषेचन होने पर भ्रूण अत्यन्त तरुण अवस्था में ही नष्ट हो जाता है।
(Upon fertilization, the embryo is destroyed in a very young state.)
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अपस्थानिक भ्रूणता (Adventive Embryony):- जब भ्रूण का विकास बीजाण्ड की किसी कायिक कोशिका (अध्यावरण या बीजाण्डकाय या निभाग) से बिना भ्रूणकोष बने होता है तो इसे अपस्थानिक भ्रूणता कहते हैं। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- नींबू, आम आदि।
(When the embryo develops from a vegetative cell of ovule (integument or nucellus or challaza) without the formation of embryo sac, it is called adventive embryony. As shown in the diagram below. Examples: Lemon, mango etc.)
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Double fertilization:-
> Both the male garnet present in pollen tube utilises in fertilisation process of angiosperm is known as double fertilisation. It is the characteristic feature of angiosperms except Family Orchidaceae, Podostemaceae and Trapaceae.
> It was first observed by Nawaschin (1898) in Fritilaria and Lilium. It was supported by Guignard (1899).
> It involves two types of fusion –
a. Syngamy (fusion of egg cell and one male gamete):-
- One of the two sperms goes to fertilize the egg cell. This fusion is called syngamy.
- It results in the formation of zygote, which gives rise to proper embryo.
b. Triple fusion (fusion of remaining male garnet and two proper nuclei):-
- The remaining sperm now fuses with the two haploid polar nuclei (present in the centre of embryo sac).
- This fusion is called as triple fusion (as three nuclei i.e., one male garnet and 2 polar nuclei, are fused).
- It results in the formation of triploid endosperm nucleus, which on development (Repeatd mitosis) form the endosperm.
- Endosperm is therefore triploid in angiosperms (It is a characteristic feature of angiosperms)
- Endosperm serves to provide nutrition to the developing embryo.
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Stamen Origin and evolution:- The stamen is the male reproductive organ in angiosperms. It is also known as androecium or microphylls. The stamen composed of slender stalk with a supporting knob. Each anther consists of two lobes connected by a connective. Each anther has two pollen sacs placed longitudinally. The pollen chamber represents a microsporangium that contains many microspores. Each stamen consists of two parts- filament and anther. Some morphologists believed that the stamen consists of three parts-filament, anther and connective. Filament is the midrib, while anther is formed by the union of the margins of the foliage leaves. Various interpretations have been advanced from time to time regarding the morphology of the stamen.
Classical view:- Goethe proposed that flowers are like abbreviated vegetative leaves. De Candolle
further elaborated the theory and stated that the stamens and carpels are all similar to leaves. Thus,
the individual stamen is a leaf which has been modified to form a reproductive organ. The anther
represents the lamina and the filament is the midrib and the whole structure may be a set of
modification of lamina. Arber and many other reported the homology of stamen parts with the foliage
organs.
Telome theory:- Wilson stated that Goethe’s hypothesis is lacking palaeobotanical evidences.
According to him no theory of the origin and morphology can be established based on assumption
without fossil evidences. Various studies led to the view that the body of early land plant was the
branched axis. The proximal portion becomes differentiated into an absorbing organ and the distal
organs evolves a fertile and sterile branched system. These systems probably grow dichotomously,
and sporangia are formed terminally. Based upon the fact, the foliar organs and other parts of the
angiosperms derived from the sterile branched system and the essential parts the flower from the
fertile system. Accordingly, the modern system came into being as a result of extensive reduction and
specialization of fertile dichotomous branched system. The four celled anther of the angiosperm
stamen is explained by he reduction of ultimate and penultimate branch and then by fusion give rise
to paired sporangia. Wilson though believed that the stamen has evolved from dichotomous system,
yet the final evidence is lacking. However, he forwarded his opinion as the Goethe’s hypothesis is
rational.
Revolutionary view:- Thomson put forwarded another views on the ontogeny of the flowers.
According to him the flower is essentially a heterogenous fertile axis bearing floral parts in the torso.
The base is sterile and produces bracteole, bracts and sepals. Rest of the superficial axis is potentially
sporogenous which give rise to petals, staminode, stamens and carpels. Work of Thomson is opened
for memoir of interpretation. According to Hunt, the stamen is not homologous to entire leaf but a part of leaf and the term sporophyll may not be applied to modern stamen.
Note:- Reviewing all the theories proposed so far, the classical theory looks more convincing, as it stated that flower is a modified shoot and the stamen is a part of it.
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Primary Xylem:- Primary development from procambium results in the formation of the primary xylem. It contains protoxylem and metaxylem. Protoxylem grows first, followed by metaxylem and then secondary xylem. Protoxylem lacks tracheids and has narrower vessels than metaxylem.
Structure of Xylem:- Xylem in plants is composed of four different kinds of elements:
i. Tracheids:- Tracheids are tiny conductive elements linked to one another by bordered pits and openings in the secondary cell wall. Tracheids sustain the wood structure in conifers that lack the supporting cells and transport xylem sap. Gymnosperms (conifers) and angiosperms have wood containing a significant amount of tracheids.
ii. Vessels:- The primary conductive cell type in angiosperms is known as a vessel element, which is typically broader in diameter than a tracheid and placed axially, one above the other, to form long tubes known as vessels. Xylem sap is transported by interconduit pits, which permit the lateral flow of solutes across neighbouring conductive elements and the axial transport in tracheary elements. Pits can also connect conduits to the nearby xylem parenchyma cells, which are non-tracheary elements.
iii. Xylem Parenchyma:- Xylem parenchyma cells, which can be positioned either axially or radially, are the last type of wood cells. Although these cells usually have secondary cell walls that are relatively thin and commonly lignified, they conduct various vital functions that are essential for wood and trees.
Xylem Fibre: Xylem fibres are dead cell with a central lumen and lignified walls and provides mechanical support in water transportation.
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In-vitro pollination and its uses:-
Introduction:-
> ‘vitro’ means glass or glassy substances. So, ‘in vitro’ means in glass or glass tube. Cultivation of plant tissue or other organs on artificial media in a test tube or conical flask is called in vitro technique.
> The process of seed formation following stigmatic pollination of cultured pistil has been referred to as in vitro pollination and the development of seed through in vitro fertilization.
History:-
> German Botanist Harberlandt (1902) develops the concept of in vitro culture.
> This in vitro pollination technique was developed at university of Delhi to produce hybrid among species of pavaceraceae and solanece. Barriers during pollination and fertilization of in vitro technique
> Pollination and fertilization under in vitro condition offer an opportunity for producing hybrid embryos among plants that can’t be crossed by conventional method of plant breeding.
> In hybridization programs, transferring viable pollen from one parent to another does not always lead to seed setting.
Types of in vitro pollination:-
i. Ovular pollination:- Application of pollen to excised ovule.
ii. Ovarion pollination:- Application of pollen to excised ovary.
iii. Placental pollination:- Application of pollen to ovules attached to the placenta.
iv. Stigmatic pollination:- Application of pollen to stigma.
Technique in-vitro pollination:-
a. Materials required:-
i. Ovaries which are large and contain many ovules are the best experimental material for in vitro pollination.
ii. Pollen which should be viable and able to germinate.
iii. 1% CaCl2 solution that favour the growth of pollen tube.
b. Disinfection of materials:-
> A reasonable disinfection of ovule and pollen is the principle requirement for in vitro pollination.
> Flower buds are emasculated before anthesis and bagged in order to prevent pollination. The buds are brought to the laboratory for aseptic culture. The whole pistil are sterilized by 70% alcohol surface sterilized with a suitable agent and finally washed with distil water.
> To collect pollen under aseptic condition, anthers removed from the flower are kept in sterile petriplates containing a filter paper until their dehiscence. The pollen is then aseptically deposited on the cultured ovules, placental or stigma depending on the nature of the experiment.
c. Culture of ovules, ovary and stigma:-
i. Culture of Ovules:-
> The growth of pollen tube attached to bare ovules is inhibited by the presence of water on the surface of the ovules.
> This film of water should be dried with filter paper and later the dried ovules covered by the pollen grain.
> In Nicotiana tabacam, Allium cepa, Gynandropsis gynandra seeds are raised from ovules which contain globular or older embryo.
> 6 days after in vitro pollination ovules contain a single celled zygote which requires more complex growth condition.
> For the development of subsequent embryonic stages, ovules which have been self-pollinated are usually kept on the placenta until seed formation while cross pollinated ovules regaine placenta only during the initial 6-8 days of culture.
> Afterwards, they can be transferred to fresh medium without placenta.
> Use:- Ovule culture has proved to be very useful technique for raising inter specific hybrids within genus Gossypium herbacium and Trifalium.
ii. Culture of Ovary:-
> The technique of ovary culture was developed by Nitsch in 1951 by the ovaries of Cucumis and Lycopersicon excised from pollinated flower in vitro to develop into mature fruits.
> Medium:-
- Successful culture excised ovaries from a number of species such as Linaria macroccana, Hyoscymus niger on a medium containing mineral salts and sucrose.
- The addition of vitamin B to the medium resulted in the development of fruits of normal size with viable seeds.
- Further enrichment by IAA or coconut milk induced even larger fruits.
> Floret envelops:- The floret envelops play an important role in the development of the fruit and the embryo of monocots. Ovary excised soon after pollination only when the floret envelop remain intact. E.g. Triticum aestivum and Triticum spelta.
> Hull factor:- This requirement of the floret envelops associating with excised monocot ovules in vitro is known as ‘hull factor’. In the elongation of barely embryo cells can take place but cell division doesn’t occur.
> Use of ovary culture:- Several interspecific and intergeneric hybrids can be produced between sexually incompatible parents in the family Cruciferae with the aid of ovary culture.
iii. Culture of Stigma:-
> The entire placenta or part of it bearing the ovules is used in placenta pollination.
> To perform in vitro stigmatic pollination the excised pistils are carefully surface sterilized without wetting the stigma with the sterilant solution.
> Sometimes the entire pistil in which the placental bearing ovules have been exposed are cultured to study the effect of placental and stigmatic pollination in the same pistil.
> In stigmatic pollination presence of perianth is important factor in dicot.
Application of in vitro pollination:- In plant breeding programs, the technique of in vitro pollination has potential application in different areas-
i. Overcoming self-incompatibility:- Petunia axilaris and Petunia hybrida are self-incompatible species. Germination of pollen is good on self- pollinated pistils but a barrier exists in the zone of the ovary as a result, the pollen tube cannot fertilize the ovule. The barrier of these taxa can be overcome by in vitro pollination.
ii. Overcoming cross-incompatibility:- Successful culture of in vitro pollinated ovules has raised the possibility of producing hybrids which are unknown because of pre-fertilization incompatibility barriers.
iii. Production of haploid plant:- Another application of in vitro pollination reported, is the production of haploids of Mimulus luteus CV. Tigrinus grandiflorus by pollinating its exposed ovules with Torenia fournieri. The haploids of Mimulus luteus developed parthenogenetically, which otherwise could not be obtained through anther culture.
iv. Production of stress-tolerant plant:- Maize plants tolerant to beat stress have been produced through in vitro pollination at high temperature. Additionally these plants exhibited increased vigour and grain yield.
v. Development of young hybrid embryo:- Development of young hybrid embryos can be achieved in extremely widely crosses through in vitro pollination. The efficiency of this technique needs much improvement.
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परागकोष संवर्धन (Anther Culture):-
1. परिचय (Introduction):-
· परिभाषा (Definition):- यह एक कृत्रिम तकनीक है जिसके द्वारा परिवर्धित हो रहे परागकोषों को एक बन्द पुष्प कालिका से एक ठीक व नाजुक अवस्था पर निकाला जाता है और पोषक माध्यम पर संवर्धित किया जाता है। जहाँ परागकोष के अंदर उपस्थित लघुबीजाणु कैलस ऊतक या भ्रूण समान संरचना में विकसित हो जाते हैं जो अंग निर्माण या भ्रूण निर्माण के माध्यम से अगुणित पौधों का निर्माण करते हैं।
(It is an artificial technique by which the developing anthers are collected from a closed floral bud at a fine and delicate stage and cultured on a nutrient medium. Where the microspores develop into callus tissue or embryo like structure, that develop haploid plants through organ formation or embryo formation.)
· अभी तक लगभग 250 पादप जातियों में परागकोष संवर्धन किया गया है। तीन कुलों में अधिक सामान्य है –
(So far anthers have been cultured in about 250 plant species. The three families are more common -)
i. Solanaceae
ii. Criciferae
iii. Poaceae
2. इतिहास (History):-
· W. Tulecke (1953):- इसने सबसे पहले देखा कि अनावृतबीजी पौधे Ginkgo biloba के परिपक्व परागकणों को संवर्धन में अगुणित कैलस निर्माण के लिए प्रेरित किया जा सकता है।
(He first observed that mature pollens of the gymnosperm plant Ginkgo biloba can be induced to form haploid callus in culture.)
· S. Guha and P. Maheshwari (1964):- इन्होने सबसे पहले देखा कि Datura innoxia के निकाले गए परागकोषों के संवर्धन से लघुबीजाणुओं से भ्रूणो का प्रत्यक्ष विकास होता है।
(They first observed that the embryos are developed from the microspores directly in anther culture of Datura innoxia.)
· J. P. Bourgin and J. P. Nitsch (1967):- इन्होने तंबाकू (Nicotiana tabacum) के परागकोष संवर्धन द्वारा पूर्ण रूप से अगुणित पौधे प्राप्त किए।
[They obtained fully haploid plants by the anther culture of tobacco (Nicotiana tabacum).]
· Niizeki and Oono (1968):- ये जापान के वैज्ञानिक थे। इन्होने धान में परागकोष संवर्धन करके पादप प्रजनन के लिए अगुणित पौधे विकसित किए।
(He was a Japanese scientist. He developed haploid plants for plant breeding by anther culture in paddy.)
3. सिद्धान्त (Principle):-
· लघुबीजाणु की पूर्णशक्तता के उपयोग से अगुणित पौधे का निर्माण किया जाता है।
(The haploid plant is produced using the totipotency of the microspore.)
· लघुबीजाणु में गुणसूत्रों का केवल एक समुचय उपस्थित होता है।
(Only one set of chromosomes is present in the microspore.)
· अगुणित पादप निर्माण की प्रक्रिया में लघुबीजाणु का नर युग्मक निर्माण का सामान्य विकास व कार्य रुक जाता है। कायिक कोशिका विभाजन के लिए इसे बलपूर्वक नए उपापचय पथ की ओर मोड़ दिया जाता है।
(In the process of haploid plant development, the normal growth and functioning of the microspore of developing male gametes is halted. It is forced into a new metabolic pathway for somatic cell division.)
· परागकोष संवर्धन में परागकोष के अंदर उपस्थित लघुबीजाणु के प्राकृतिक आवास व वातावरण को परिवर्तित नहीं किया जाता है। संवर्धन परिस्थितियों में माध्यम पर परागकोष का द्विगुणित ऊतक बिना विभाजन किए जीवित रहता है और पोषण प्रदान करके लघुबीजाणु के कायिक विभाजन को प्रेरित करता है।
(Anther culture does not alter the natural habitat and environment of the microspores present inside the anther. In culturing conditions, the diploid tissue of the anther survives on the medium without cell division and induces somatic cell division of the microspore by providing nutrition.)
4. विधि (Procedure):-
· पुष्पन पर तंबाकू की बन्द पुष्पीय कलिकाओं को एकत्रित करते हैं। 17 – 22 mm लंबाई की पुष्पीय कालिका का चयन करते हैं जब बाह्यदलों की लंबाई दलों की लंबाई के बराबर होती है। खुल रही सभी पुष्पीय कलिकाओं को त्याग देते हैं।
(Collect the closed floral buds of tobacco upon flowering. A floral bud of length 17 - 22 mm is selected when the length of the sepals is equal to the length of the petals. Discards all floral buds are to be opened.)
· चयनित पुष्पीय कलिकाओं को LAF कैबिनेट के अन्दर ले जाते हैं। प्रत्येक पुष्पीय कलिका में 5 परागकोष होते हैं और बन्द कलिकाओं के अन्दर इनकी सतह स्वत: निर्जमित होती है। पुष्पीय कलिकाओं के सतही निर्जमीकरण के लिए इन्हें पहले 10 सेकंड के लिए 70% ऐथेनोल में डुबोकर रखते हैं और फिर 10 मिनट के लिए 20% सोडियम हाइपोक्लोराइट विलयन में डुबोकर रखते हैं। अतिरिक्त रसायन को सतह से हटाने के लिए पुष्पीय कलिकाओं को निर्जमित आसुत जल से 3 बार धोते हैं। अंत में इन पुष्प कलिकाओं को निर्जमित पेट्रीडिश में स्थानांतरित कर देते हैं।
(Selected floral buds are carried inside the LAF cabinet. Each floral bud has 5 anther and its surface is sterilized automatically inside the closed buds. For surface sterilization of the floral buds, first of all dip them in 70% ethanol for 10 seconds and then in 20% sodium hypochlorite solution for 10 minutes. To remove excess chemicals from the surface, the floral buds are washed 3 times with sterilized distilled water. Finally these floral buds are transferred to the sterilized patridish.)
· अब एक तीखे चाकू के द्वारा कालिका के एक तरफ कट लगाते हैं और चिमटी की सहायता से दलों व बाह्यदलों को हटा देते हैं। अब एक अन्य चिमटी की सहायता से 5 पुंकेसरों को पुतन्तु सहित उखाड़कर एक अन्य निर्जमित पेट्रीडिश में स्थानांतरित करते हैं। अब 5 पुंकेसरों के पुतन्तुओं को चाकू या ब्लेड से काटकर अलग कर देते हैं जिससे केवल परागकोष रह जाते हैं। क्षतिग्रस्त परागकोषों को भी त्याग देते हैं।
(Now with a sharp knife, cut one side of the floral bud and remove the petals and sepals with the help of forceps. Now with the help of another forceps, collect 5 stamens along with their filaments and transfer them to another sterilized patridish. Now cut the filaments of 5 stamens with a knife or blade, leaving only the anthers. Damaged anthers are also discarded.)
· अब इन स्वस्थ व साबुत परागकोषों को ठोस अगार माध्यम पर स्थापित करते हैं। परागकोष संवर्धन के लिए निम्न में से कोई एक माध्यम उपयोग किया जाता है-
(Now these healthy and intact anthers are placed on solid agar medium. One of the following mediums is used for anther culture -)
i. MS माध्यम (MS medium)
ii. White माध्यम (White's medium)
iii. Nitsch & Nitsch माध्यम (Nitsch and Nitsch medium)
· प्रारम्भ में संवर्धन को अंधेरे में रखा जाता है। 3 – 4 सप्ताहों में परागकोष के अंदर उपस्थित लघुबीजाणु भ्रूणजनन करते हैं और संवर्धित परागकोषों से अगुणित भ्रूण बन जाते हैं। कुछ पौधों में परागकोष के प्रवर्धन द्वारा कैलस ऊतक का निर्माण हो सकता है जिन्हें अगुणित प्लांटलेट्स बनाने के लिए प्रेरित किया जा सकता है।
(Initially the culture is kept in the dark. In 3–4 weeks, the microspores present inside the anther show embryogenesis and haploid embryos are developed from cultured anther. In some plants anther culture can lead to the formation of callus tissue that can be induced to form haploid plantlets.)
· अब इन अगुणित भ्रूणो को नये ताजा अगार माध्यम पर संवर्धन ट्यूब में स्थापित करते हैं। इस अवस्था पर संवर्धनों का 24 – 28°C ताप पर ऊष्मायन किया जाता है। 14 घंटे का प्रकाश व 10 घंटे का अंधकार दिया जाता है। प्रकाश की तीव्रता 2000 लक्स रखी जाती है।
(Now these haploid embryos are established on a new fresh agar medium in culture tube. At this stage the cultures are incubated at 24 - 28 ° C temperature. 14 hours of light and 10 hours of darkness are given. Light intensity is maintained at 2000 lux.)
· जब अगुणित प्लांटलेट्स की लंबाई 50 mm हो जाती है तो अगार माध्यम से स्वतंत्र करने के लिए नल के बहते हुए पानी में धोया जाता है। अब तुरन्त इन्हें औटोक्लेवित कम्पोस्ट युक्त छोटे गमलों में रोपित कर दिया जाता है। शुष्कन को रोकने के लिए प्रत्येक पौधे को काँच के बीकर से ढक देते हैं और आगे के परिवर्धन के लिए नम ग्रीन हाउस में रख देते हैं। कुछ सप्ताहों पश्चात काँच के बीकरों को हटा देते हैं और पौधों को मृदा युक्त बड़े गमलों में रोपित कर देते हैं जहाँ ये पौधे परिपक्व होकर अंत में पुष्पन करते हैं।
(When the length of haploid plantlets becomes 50 mm, they are washed in running tap water to free them from the agar medium. Now they are immediately planted in small pots containing autoclaved compost. To prevent drying, cover each plant with a glass beaker and place it in a moist greenhouse for further growth. After a few weeks, the glass beakers are removed and the plants are planted in large pots containing soil where these plants mature and eventually flowering.)
5. लाभ (Advantages):-
· आधारभूत अनुसंधान के लिए परागकोष संवर्धन की उपयोगिता
(Utility of Anther Culture for Basic Research)
· सरल (Simple)
· कम समय लेता है
(Less Time Consuming)
· उत्तरदायी (Responsive)
· उत्परिवर्तन का अध्ययन (Mutation Study):-
Ø अगुणित पौधों में प्रत्येक जीन का केवल एक ही युग्मविकल्पी पाया जाता है। इसलिए कोई भी अप्रभावी उत्परिवर्तन या लक्षण स्पष्ट रूप से दिखाई देता है।
(In haploid plants, only one allele of each gene is found. Therefore any recessive mutation or trait is clearly visible.)
Ø घातक जीनों युक्त पौधे जीन पूल से निष्कासित हो जाते हैं।
(Plants containing lethal genes are expelled from the gene pool.)
Ø इस प्रकार उत्परिवर्तन का अध्ययन आसानी से किया जा सकता है।
(Thus mutation can be studied easily.)
· क्रायोजेनिक अध्ययन के लिए अगुणितों का उपयोग
(Use of Haploids for Cryogenic Study)
· पादप प्रजनन व फसल सुधार के लिए उपयोग:-
(For Plant Breeding and Crop Improvement:-)
Ø समयुग्मजी वंशक्रमों को उत्पन्न किया जा सकता है। इसके लिए अगुणित पौधों को कोल्चिसीन रसायन से उपचारित किया जाता है।
(Homozygous lines can be produced. For this, haploid plants are treated with colchicine chemical.)
Ø उत्परिवर्तन प्रजनन विधि का उपयोग फसल सुधार में किया जाता है।
(Mutation breeding method is used in crop improvement.)
· बागवानी पौधों के लिए अगुणित संवर्धन का अनुप्रयोग
(Application of Haploid Culture for Horticultural Plants)
· द्वितीयक मेटाबोलाइट्स के अध्ययन के लिए
(For Study of Secondary Metabolites Content)
6. हानियाँ (Disadvantages):-
· बिना क्षति पहुंचाए परागकोषों को निकालने के लिए कौशल की आवश्यकता होती है।
(Skill is required to remove anthers without damage.)
· धान्य फसलों में यह बहुत अधिक सफल विधि नहीं है।
(This is not a very successful method in cereal crops.)
· परागकोष की भित्ति द्विगुणित कोशिकाओं की बनी होती है जिससे द्विगुणित कैलस निर्माण व काइमेरा निर्माण का रिस्क रहता है।
(The anther wall is made up of diploid cells, which has the risk of developing diploid callus and chimera.)
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असंग जनन (Apomixis):- जब जनक पौधे से भ्रूण व बीज का निर्माण बिना निषेचन के होता है तो इसे असंग जनन कहते हैं। बीजांड की कोई भी कायिक कोशिका ज़ाइगोट के समान कार्य करने लगती है। इसके फलस्वरूप बने संतति पौधे अपने जनकों के क्लोन होते हैं। यह तीन प्रकार का होता है -
(When embryo and seed are produced from the parent plant without fertilization, it is called asexual reproduction. Any vegetative cell of the ovule acts as a zygote. The resulting seedlings are clones of their parents. It is of three types -)
a. अपस्थानिक भ्रूणता (Adventive Embryony)
b. अपबीजाणुकता (Apospory)
c. द्विबीजाणुकता (Diplospory)
a. अपस्थानिक भ्रूणता (Adventive Embryony):- जब भ्रूण का विकास बीजाण्ड की किसी कायिक कोशिका (अध्यावरण या बीजाण्डकाय या निभाग) से बिना भ्रूणकोष बने होता है तो इसे अपस्थानिक भ्रूणता कहते हैं। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- नींबू, आम आदि।
(When the embryo develops from a vegetative cell of ovule (integument or nucellus or challaza) without the formation of embryo sac, it is called adventive embryony. As shown in the diagram below. Examples: Lemon, mango etc.)
b. अपबीजाणुकता (Apospory):- जब भ्रूणकोष का विकास बीजाण्ड की किसी कायिक कोशिका (अध्यावरण या बीजाण्डकाय या निभाग) से बिना अर्धसूत्री विभाजन हुए होता है तो इसे अपबीजाणुकता कहते हैं। अर्थात यहाँ गुरुबीजाणु का निर्माण नहीं होता है। भ्रूणकोष की प्रत्येक कोशिका द्विगुणित होती है। भ्रूणकोष की किसी भी एक कोशिका से भ्रूण बन जाता है। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- Crepis
(When the development of the embryo sac occurs without meiosis from any vegetative cell of ovule (integument or nucellus or challaza), it is called as apospory. It means megaspore is not produced here. Each cell of the embryo sac is diploid. An embryo is developed from any one cell of the embryo sac. As shown in the diagram below. Example: - Crepis)
c. द्विबीजाणुकता (Diplospory):- जब भ्रूणकोष का विकास द्विगुणित गुरुबीजाणु से होता है तो इसे द्विबीजाणुकता कहते हैं। गुरुबीजाणु का निर्माण बिना अर्धसूत्री विभाजन के होने के कारण यह द्विगुणित होता है। अत: भ्रूणकोष की प्रत्येक कोशिका भी द्विगुणित होती है। जैसा कि नीचे diagram में प्रदर्शित किया गया है।
(When the embryo sac develops from a diploid megaspore, it is called as diplospory. Megaspore is diploid because it is formed by mitosis instead of meiosis. Therefore, each cell in the embryo sac is also diploid. As shown in the diagram below.)
भ्रूण का विकास निषेचन के बिना होता है। भ्रूण का विकास भ्रूणकोष की कौनसी कोशिका से होता है, इस आधार पर द्विबीजाणुकता 2 प्रकार की होती है-
(Embryo development occurs without fertilization. Depending upon the embryo develops from which cell of the embryo sac, there are 2 types of diplospory -)
i. अनिषेकजनन (Parthenogenesis)
ii. अपयुग्मन (Apogamy)
i. अनिषेकजनन (Parthenogenesis):- जब भ्रूण का विकास अण्ड कोशिका से होता है तो इसे अनिषेकजनन कहते है। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- Taraxacum (घास)
[When the embryo develops from the egg cell, it is called parthenogenesis. As shown in the diagram below. Example: - Taraxacum (grass)]
ii. अपयुग्मन (Apogamy):- जब भ्रूण का विकास प्रतिमुखी कोशिका या सहायक कोशिका से होता है तो इसे अपयुग्मन कहते हैं। जैसा कि नीचे diagram में प्रदर्शित किया गया है। उदाहरण:- प्याज
(When the embryo develops from the antipodal cell or the synergid, it is called apogamy. As shown in the diagram below. Example: - Onion)
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Polyembryony:- Presence of more than one embryo inside the seed is known as polyembryony. It was first reported by A.V. Leuwenhoek (1719) in Citrusi Fam-Rutaceae).This phenomenon is very common in gymnosperm than angiosperm. Besides normal embryoe (develops from Zygote), other embryos are formed inside seed maybe as haploid (n) or Diploid (2n).
Types of Polyembryony:-
i. Induced Polyembryony:- When polyembryony is induced in plants and animals for experiments, it is referred to as induced polyembryony.
ii. Spontaneous Polyembryony:- When polyembryony occurs naturally in plants and animals, it is called natural or spontaneous polyembryony.
iii. True polyembryony:- Many embryos are developed inside single embryo sac.
iv. False polyembryony:- If the ovule carries more then one embryo sac & embryos develop in each embryo sac.
v. Cleavage polyembryony:- In cleavage polyembryony, a single fertilised egg can give rise to multiple embryos. When an embryo divides into several identical parts, each part can develop into a mature embryo. A common example of cleavage polyembryony is seen in Pinus.
vi. Simple polyembryony:- This type of polyembryony occurs when several archegonia are fertilised. When more than one egg is fertilised, it is called simple polyembryony. Adventive polyembryony is the formation of additional embryos through sporophytic budding. It is common in Cycas, lemon, groundnut, mango, Pinus, onion, and orange.
vii. Rosette polyembryony:- In rosette polyembryony, multiple additional embryos are produced from cells known as rosette cells.
Cause of polyembryony in angiosperm:- Polyembryony takes place due to:
i. Cleavage of proembryo:- It is simplest method of polyembryony where zygote divides into many units & each unit develops an embryo.
ii. Development of many embryo from synergid, antipodal cells, endosperm except egg.
iii. Development of many embryo due to presence of more than one embryo sac.
iv. Development of polyembryo from nucellus, integument (outside the embryo sac). According to Haberiandt (1921)” Stimulus for polyembryony is provided by degenerating cells nucelleus Necrohormone theory).
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Carpel evolution:- i. Conduplicate theory:- According to the most widely accepted hypothesis, the carpel constitutes a modified, conduplicate megasporophyll bearing two, adaxial rows of ovules (Figure 6.9D). Recall that a “megasporophyll” is a modified leaf that bears megasporangia, which in the seed plants are components of the ovules and seeds;
ii. Appendicular theory:- This theory was put forwarded by De Candolle, Van Teighem and others and
supported by Eames (1961). According to this theory the inferior ovary has developed as a result of
the fusion of the bases of sepals, petals and stamens and as such appended to the axis of the flower
which has nothing to do with the formation of the ovary wall. Eames stated that due to evolution,
inferior ovary was developed from the superior one by the process of gradual fusion of the bases of
sepals, petals and stamens and adnation of the same to the gynoecium wall which indicate the
superiority of inferior vary over inferior ovary.
iii. Receptacular theory:- According to Schleiden and others, the receptacle of the flower has become
the instrumental in the formation of the inferior condition of the ovary. This has achieved through the
gradual sinking of the ovary to the deep cup shaped receptacle with the process of invagination of the
tip of the thalamus. After sinking down of the ovary the bases of sepals, petals and stamens have been
fused much in the same manner as in case of the appendicular theory.
Specialized carpels:- The most specialized carpels are uniovulate and indehiscent and occur acyclically in great numbers in each flower, with strong trends toward monoecism and even dioecism.
Polycarpous and Syncarpous Ovary:-
i. Apocarpous Ovary:-
Separation:- In apocarpous ovaries, the carpels remain separate from each other, forming individual pistils.
Multiple Ovaries:- Each carpel in an apocarpous ovary has its own distinct ovary.
Varied Arrangement:- The carpels may be arranged in a spiral or whorl pattern, resulting in a diverse floral structure.
Genetic Variation:- The separate pistils in an apocarpous ovary allow for potential variation in seed development and fruit formation.
Examples:- Buttercups and strawberries are examples of plants that exhibit apocarpous ovaries.
ii. Syncarpous Ovary:-
Fusion:- In syncarpous ovaries, the carpels are fused together to form a single pistil.
Shared Ovary:- The fused carpels result in a common ovary that is shared among the carpels.
Coordinated Development:- The fused carpels work together for efficient reproduction and coordinated development of seeds.
Floral Symmetry:- Syncarpous ovaries often contribute to radial symmetry in flowers, creating a balanced and aesthetically pleasing structure.
Examples:- Roses and lilies are examples of plants that possess syncarpous ovaries.
Classification of Ovary:- On the basis of position, the ovary can be classified into three types:
i. Superior Ovary:- When the ovary is attached to the receptacle of the flower, above the other floral whorls, it is known as the superior ovary. Such ovaries are found in fleshy fruits such as berries and drupes. The flower that has a superior ovary is termed as hypogynous. Examples: pea, beans.
ii. Half-inferior Ovary:- When the ovary is embedded and surrounded by receptacles in the flower, it is known as half-inferior ovary. The flowers with half-inferior ovaries are called perigynous. This type of ovary can be seen in the family of Lythraceae in plants such as crape myrtles. In this type, the ovary is half above and half below the insertion point.
iii. Inferior Ovary:- When the ovary is present below the attachment point of other floral parts on the flower, it is called an inferior ovary. This type of ovary can be seen in pome fruits. The flowers which have an inferior ovary are termed as epigynous. Examples: orchids, Fuschia
Evolution and types of placentation:-
Placentation:- It is defined as the arrangement of ovules within the ovary. several different forms of placentation can be seen in flowering plants.
Types of Placentation:-
i. Marginal:- The ovules develop in rows near the margin on the placenta formed along the ventral suture. It occurs in monocarpellary and unilocular ovary, E.g., Leguminosae.
ii. Parietal:- The placenta is formed by the swelling up of cohering margins, and on the latter develop the ovules in rows. It occurs in bicarpellary or multicarpellary but unilocular ovary, E.g., Papaveraceae.
iii. Axile:- Here, the placentae develop from the central axis which correspond to the confluent margins of carpels. It occurs in bi-to multilocular ovary, E.g., Solanaceae, Malvaceae.
iv. Free-central:- Here, the placenta develop in the centre of the ovary as a prolongation of floral axis and the ovules are attached on this axis. It occurs in multicarpellary but unilocular ovary, E.g., Primulaceae.
v. Superficial or Laminar:- Here, the ovules develop over the entire inner surface of the carpels. It occurs in multicarpellary ovary, E.g., Nymphaea.
vi. Basal:- The placenta develops directly on the thalamus and bears a single ovule at the base of the unilocular ovary, E.g., Compositae.
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Embryo Sac:- The embryo sac is the female gametophyte of flowering plants (angiosperms). It develops inside the ovule from a functional megaspore through the process of megagametogenesis.
> A typical mature embryo sac contains 7 cells and 8 nuclei:
1 Egg cell
2 Synergids
3 Antipodal cells
1 Central cell containing 2 polar nuclei
Types of Embryo Sac:- Embryo sacs are classified based on the number of megaspore nuclei participating in their development.
1. Monosporic Embryo Sac:-
> Develops from one megaspore nucleus.
> Most common type.
> Example: Polygonum type (found in many angiosperms).
> Usually 8-nucleate and 7-celled.
2. Bisporic Embryo Sac:-
> Develops from two megaspore nuclei.
> Two nuclei contribute to embryo sac formation.
> Example: Allium type (onion).
3. Tetrasporic Embryo Sac:-
> Develops from all four megaspore nuclei formed after meiosis.
> No cell walls are formed between the megaspores.
> Example: Fritillaria type.
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Development of Endosperm:- The endosperm, a food tissue of varying degree of importance in different species of angiosperm plants, is formed in most cases as a result of fusion of the two polar nuclei and one male gamete. Since all three of die fusing nuclei are haploid, the endosperm is triploid. In the families Orchidaceae and Podostemonaceae, the endosperm formation is completely or partly suppressed.
Types of endosperm formation:- Three types of endosperm formation has been reported in the angiosperms:
1. Free nuclear type of endosperm:-
> The first and usually several of the following divisions of the primary endosperm nucleus are not accompanied by cell wall formation, The endosperm nuclei may either remain free or, in later stages, they may gel separated by cell-walls. The divisions of the endosperm nuclei are quite irregular and, in an endosperm, can be seen in different stages of divisions. As divisions progress, the nuclei are pushed more and more towards periphery that the centre is occupied by a large vacuole.
> Quite frequently, the endosperm nuclei in the chalazal part of the embryo sac have been observed to be larger than those in the micropylar region. The number of free nuclear divisions varies in different species of plants, for example in Primula, Mangifera, Malva, Mains Cannabis etc. several hundred endosperm nuclei may be seen lining the wall of the embryo sac.
> In Asclepias, Rafflesia and Calatropis etc., the cell wall formation starts at the very early stage when only 8 to 16 nuclei have been formed, and in Coffea cell wall formation occurs at the 4-nucleate stage. The cell wall formation starts from the periphery of the embryo sac. Formation of endosperm haustoria has also been reported in several plants e.g., members of family Proteaceae.
2. Cellular type of endosperm:- Here the first division of the primary endosperm nucleus results in the partition of embryo sac into two chambers. The first wall is usually transverse (e.g., Villarsia raniformis, Impatiens roylei, Ruellia etc.,) but sometimes vertical (e.g., Adoxa, Scabiosa, and Circaeastere etc.,) or oblique (e.g., Paperomia, Centranthus, and Helosise to.,), and in few cases the plane of division is variable (e.g., Senecio). Endosperm haustoria may also develop at the micropylar or chalazal ends. In the family Scrophulariaceae, both micropylar and chalazal haustoria are formed.
3. Helobial type of endosperm:- It is an intermediate type between the nuclear and the cellular. Here the first division of the primary endosperm nucleus results in the chambering of the embryosac. The micropylar part of the sac is usually larger than the chalazal part. The endosperm nucleus in the micropylar chamber undergoes several free nuclear divisions, while nucleus in the chalazal region either remains undivided or undergoes only a few divisions, (e.g., Eremurus).
Functions of Endosperms:-
i. An important nutrient medium for the successful development of the embryo.
ii. Rich in fat, carbohydrates and proteins which are used in the establishment of theseedling during seed germination.
iii. At the time of fertilization little nutrition available in the embryo sac. But with theformation of endosperm enough food becomes available for the developing embryo.
iv. The division of zygote usually begins after the endosperm is sufficiently grown. Even ifthe zygote and primary endosperm nucleus divide simultaneously, the endosperm growsmore rapidly.
v. Juice of immature endosperm of a plant is used as nutrition for the developing embryoof the other plant. For example coconut milk is used as nutrient medium in in vitroembryo culture.
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