Nectaries:- These are specialized glands in plants that produce nectar, a sugary liquid that attracts animals such as bees, butterflies, birds, bats, and ants.
Types:- There are two main types:
1. Floral nectaries:-
> Located inside or near flowers.
> Secrete nectar to attract pollinators, helping with pollination and plant reproduction.
2. Extrafloral nectaries:-
> Found on leaves, stems, or petioles, outside the flowers.
> Do not aid pollination directly. Instead, they attract protective insects (especially ants), which defend the plant against herbivores.
Functions of nectaries:-
> Produce nectar rich in sugars (mainly sucrose, glucose, and fructose).
> Attract pollinators for successful fertilization.
> In extrafloral nectaries, provide a food reward to insects that protect the plant from pests.
Examples:-
Floral nectaries:- Sunflower, hibiscus, mustard.
Extrafloral nectaries:- Cotton, castor, passionflower, and many species of acacia.
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Carpel evolution:- 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;
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Sporopollenin:- It is one of the most chemically resistant natural biopolymers known. It forms the outer layer (exine) of pollen grains and spores in land plants, protecting the male gametophyte and spores from environmental damage.
Key characteristics:-
Extremely durable:- Resistant to strong acids, bases, enzymes, high temperatures, and microbial degradation.
Protective:- Shields pollen and spores from ultraviolet (UV) radiation, dehydration, and physical damage.
Chemically complex:- It is a highly cross-linked polymer composed of oxygenated aliphatic compounds and aromatic components. Its exact molecular structure varies among plant species and is still an active area of research.
Functions:-
> Protects pollen during dispersal.
> Prevents water loss (desiccation resistance).
> Provides mechanical strength.
> Contributes to species-specific surface patterns that aid in pollination.
Occurrence:- Sporopollenin is found in:
> The exine of pollen grains in flowering plants and gymnosperms.
> The outer walls of spores in ferns, mosses, and other spore-producing plants.
Importance:-
Paleontology:- Because sporopollenin is highly resistant to decay, fossil pollen and spores are commonly preserved and used to reconstruct ancient climates and vegetation.
Biotechnology:- Empty sporopollenin shells (obtained by removing the internal contents of pollen) are being investigated as natural microcapsules for drug delivery, vaccines, cosmetics, and encapsulation of sensitive compounds.
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Fertilization:- Fertilisation is angiosperms, is unique. It is called double fertilisation. This is because there are two sperms per pollen tube. One of the sperms fertilises the egg cell to form zygote, while remaining sperm fertilises two polar nuclei, resulting in the formation of a triploid endosperm cell. The phenomenon of fertilization was first reported by Strasburger (1884) in Monotrapa. The male gametes are brought to the egg present in female gametophyte by a pollen tube. This phenomenon is called siphonogamy which was discovered by G. B. Amici in Protulaca plant.
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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)
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Embryo:- It is the young, developing plant formed inside the seed after fertilization. It is the future plant in a dormant state and develops into a seedling when conditions are favorable.
Parts of a typical plant embryo:-
i. Radicle:-
> The embryonic root.
> Develops into the primary root after germination.
ii. Plumule:-
> The embryonic shoot.
> Develops into the stem and leaves.
iii. Cotyledon(s):-
> Seed leaves that store or absorb nutrients.
> Dicots have two cotyledons (e.g., bean, pea).
> Monocots have one cotyledon called the scutellum (e.g., maize, wheat).
iv. Hypocotyl:- The part of the embryo below the cotyledons and above the radicle.
v. Epicotyl:- The part above the cotyledons that gives rise to the shoot.
Functions of the plant embryo:-
> Develops into a new plant after germination.
> Contains the genetic information of the next generation.
> Uses stored food from the cotyledons or endosperm until it can photosynthesize.
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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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Monocot Seed:-
Structure:- The monocot seed (e.g., maize/corn grain) consists of the following parts:
i. Seed coat (Testa):- Thin protective outer covering, usually fused with the fruit wall (pericarp) in maize.
ii. Endosperm:- The largest part of the seed, rich in starch, and serves as the food storage tissue.
iii. Embryo:- Located on one side of the seed and includes:
Scutellum (Cotyledon):- A single cotyledon that absorbs nutrients from the endosperm during germination.
Plumule:- The embryonic shoot, protected by the coleoptile.
Radicle:- The embryonic root, protected by the coleorhiza.
Key features:-
> One cotyledon (scutellum)
> Large persistent endosperm stores food.
> Coleoptile protects the plumule.
> Coleorhiza protects the radicle.
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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.)
स्वअनिषेच्यता के प्रकार (Types of Self Incompatibility):- पुष्पों की बाह्य आकारिकी के आधार पर यह दो प्रकार की होती है -
(On the basis of external morphology of flowers it is of two types -)
A. समरूपी स्वअनिषेच्यता (Homomorphic Self Incompatibility)
B. विषमरूपी स्वअनिषेच्यता (Heteromorphic Self Incompatibility)
A. समरूपी स्वअनिषेच्यता (Homomorphic Self Incompatibility):- जब एक किस्म के सभी पौधों के पुष्प बाह्य आकारिकी में एक समान होते हैं तो इसे समरूपी स्वअनिषेच्यता कहते हैं। यह एक जीन S के द्वारा नियंत्रित होती है जिसके बहु युग्मविकल्पी S1, S2, S3, S4 आदि होते हैं।
(When the flowers of all the plants of a variety are similar in external morphology, it is called homomorphic self-incompatibility. It is controlled by a gene S which has multiple alleles S1, S2, S3, S4 etc.)
यह दो प्रकार की होती है -
(It is of two types -)
1. बीजाणुदभिदीय स्वअनिषेच्यता (Sporophytic Self Incompatibility)
2. युग्मकोदभिदीय स्वअनिषेच्यता (Gametophytic Self Incompatibility)
1. बीजाणुदभिदीय स्वअनिषेच्यता (Sporophytic Self Incompatibility):- जब स्वअनिषेच्यता पौधे के जीन प्रारूप द्वारा निर्धारित होती है तो इसे बीजाणुदभिदीय स्वअनिषेच्यता कहते हैं। इसमें मादा जनक पौधे या वर्तिकाग्र के जीन प्रारूप की तुलना नर जनक पौधे के जीन प्रारूप से की जाती है। 50℅ या 100℅ समानता होने पर निषेचन नहीं होता है तथा केवल 100℅ असमानता होने पर ही निषेचन होता है। जैसा कि नीचे diagram में प्रदर्शित किया गया है।
(When self incompatibility is determined by the genotype of the plant, it is called sporophytic self incompatibility. In this, the genotype of the female parent plant or stigma is compared to the genotype of the male parent plant. Fertilization does not occur if there is a 50℅ or 100℅ equality, and fertilization occurs only if there is a 100℅ inequality. As shown in the diagram below.)
उदाहरण (Examples):- सरसों, शलजम, गोभी आदि।
(Mustard, Turnip, Cabage, Cauliflower etc.)
2. युग्मकोदभिदीय स्वअनिषेच्यता (Gametophytic Self Incompatibility):- जब स्वअनिषेच्यता परागकण के जीन प्रारूप द्वारा निर्धारित होती है तो इसे युग्मकोदभिदीय स्वअनिषेच्यता कहते हैं। इसमें मादा जनक पौधे या वर्तिकाग्र के जीन प्रारूप की तुलना परागकण के जीन प्रारूप से की जाती है। समानता होने पर निषेचन नहीं होता है तथा असमान होने पर निषेचन हो जाता है। जैसा कि नीचे diagram में प्रदर्शित किया गया है।
(When self incompatibility is determined by the genotype of pollens, it is called gametophytic self-incompatibility. In this, the genotype of the female parent plant or stigma is compared to the genotype of pollens. Fertilization does not occur when there is equality and fertilization takes place when there is inequality. As shown in the diagram below.)
उदाहरण (Examples):- आलू, टमाटर, तम्बाकू, चुकंदर आदि।
(Potato, Tomato, Tobacco, Beet etc.)
B. विषमरूपी स्वअनिषेच्यता (Heteromorphic Self Incompatibility):- जब एक किस्म के पौधों के पुष्प बाह्य आकारिकी में विषमता दर्शाते हैं तो इसे विषमरूपी स्वअनिषेच्यता कहते हैं। यह दो प्रकार की होती है -
(When the flowers of plants of a variety show asymmetry in external morphology, it is called heteromorphic self incompatibility. It is of two types -)
1. द्विवर्तिकी (Distyly)
2. त्रिवर्तिकी (Tristyly)
1. द्विवर्तिकी (Distyly):- जब पौधों के पुष्पों में वर्तिका की दो प्रकार की लंबाई पायी जाती है तो इसे द्विवर्तिकी कहते हैं। वर्तिका की लंबाई के आधार पर पुष्प दो प्रकार के होते हैं –
(When two types of length of style are found in the flowers of plants, it is called distyly. Depending on the length of the style, there are two types of flowers -)
i. पिन पुष्प (Pin flowers):- इन पुष्पों की वर्तिका लम्बी होती है व पुंकेसर छोटे होते है जैसा की नीचे diagram में प्रदर्शित किया गया है।
(The styles of these flowers are long and the stamens are small as shown in the diagram below.)
ii. थ्रम पुष्प (Thrum flowers):- इन पुष्पों की वर्तिका छोटी होती है व पुंकेसर लम्बे होते है जैसा की नीचे diagram में प्रदर्शित किया गया है।
(The styles of these flowers are small and the stamens are long as shown in the diagram below.)
· किसी भी पौधे पर या तो पिन पुष्प बनते है और या फिर थ्रम पुष्प बनते हैं। दोनों प्रकार के पुष्प एक ही पौधे पर कभी भी नहीं बनते हैं। इस प्रकार पौधों के 2 स्वअनिषेच्य समूह बनते हैं – पिन पुष्प वाले पौधे और थ्रम पुष्प वाले पौधे।
(On any plant, either pin flowers or thrum flowers are formed. Both types of flowers never grow on the same plant. In this way 2 self-incompatible groups of plants are formed - pin flowering plants and thrum flowering plants.)
Øपिन पुष्प वाले पौधे का पिन पुष्प वाले पौधे से क्रॉस करने पर बीज नहीं बनते हैं।
(The pin flower plant do not produce seeds when crossed with the pin flower plant.)
Øथ्रम पुष्प वाले पौधे का थ्रम पुष्प वाले पौधे से क्रॉस करने पर बीज नहीं बनते हैं।
(The thrum flower plant do not produce seeds when crossed with the thrum flower plant.)
Øपिन पुष्प वाले पौधे का थ्रम पुष्प वाले पौधे से क्रॉस करने पर बीज बनते हैं।
(The pin flower plant produce seeds when crossed with the thrum flower plant.)
· यह पद्धति कुछ फसलों में पायी जाती है जैसे – शकरकन्द, Buckwheat (कुट्टू), Primula आदि।
(This method is found in some crops such as sweet potato, buckwheat, primula etc.)
· यह एक जीन S के द्वारा नियंत्रित होती है जिसके दो युग्मविकल्पी S व s होते हैं।
(It is controlled by a gene S, which has two alleles S and s.)
थ्रम पुष्प वाले पौधे = Ss (विषमयुग्मजी)
[Thrum flower plants = Ss (heterozygous)]
पिन पुष्प वाले पौधे = ss (समयुग्मजी)
[Pin flower plant = ss (homozygous)]
· निषेच्य क्रॉसिंग (Compatible Crossing):-
पिन X थ्रम = ss X Ss
थ्रम X पिन = Ss X ss
· अनिषेच्य क्रॉसिंग (Incompatible Crossing):-
पिन X पिन = ss X ss
थ्रम X थ्रम = Ss X Ss
2. त्रिवर्तिकी (Tristyly):- जब पौधों के पुष्पों में वर्तिका की तीन प्रकार की लंबाई पायी जाती है तो इसे त्रिवर्तिकी कहते हैं। वर्तिका की लंबाई के आधार पर पुष्प तीन प्रकार के होते हैं –
(When three types of length of style are found in the flowers of plants, it is called tristyly. There are three types of flowers depending on the length of the style.)
i. लम्बी वर्तिका वाले पुष्प (Long Style Flowers = L):- इन पुष्पों की वर्तिका लम्बी होती है व पुंकेसर छोटे होते है जैसा की नीचे diagram में प्रदर्शित किया गया है।
(The styles of these flowers are long and the stamens are small as shown in the diagram below.)
ii. मध्यम वर्तिका वाले पुष्प (Medium Style Flowers = M):- इन पुष्पों की वर्तिका व पुंकेसर दोनों बराबर व मध्यम लम्बाई के होते हैं जैसा की नीचे diagram में प्रदर्शित किया गया है।
(Both the styles and stamens of these flowers are of equal and medium length as shown in the diagram below.)
iii. छोटी वर्तिका वाले पुष्प (Short Style Flowers = S):- इन पुष्पों की वर्तिका छोटी होती है व पुंकेसर लम्बे होते हैं जैसा की नीचे diagram में प्रदर्शित किया गया है।
(The styles of these flowers are small and the stamens are long as shown in the diagram below.)
· किसी एक पौधे के सभी पुष्पों में वर्तिका की लम्बाई एक समान होती है। भिन्न वर्तिका लम्बाई वाले पुष्प एक ही पौधे पर कभी भी नहीं बनते हैं। एक समान वर्तिका लम्बाई वाले सभी पौधे एक ही स्वअनिषेच्य समूह में आते हैं। इस प्रकार पौधों के 3 स्वअनिषेच्य समूह बनते हैं – L, M व S.
(The length of the styles is the same in all the flowers of a plant. Flowers of different style length never form on the same plant. All plants of equal style length are in the same self-incompatible group. In this way 3 self-incompatible groups of plants are formed - L, M and S.)
ØL समूह के पौधे का L समूह के पौधे से क्रॉस करने पर बीज नहीं बनते हैं।
(Seeds are not formed when the L group plant is crossed up with the L group plant.)
ØM समूह के पौधे का M समूह के पौधे से क्रॉस करने पर बीज नहीं बनते हैं।
(Seeds are not formed when the M group plant is crossed up with the M group plant.)
ØS समूह के पौधे का S समूह के पौधे से क्रॉस करने पर बीज नहीं बनते हैं।
(Seeds are not formed when the S group plant is crossed up with the S group plant.)
ØL समूह के पौधे का M समूह के पौधे से क्रॉस करने पर बीज बनते हैं।
(Seeds are formed when the L group plant is crossed up with the M group plant.)
ØM समूह के पौधे का S समूह के पौधे से क्रॉस करने पर बीज बनते हैं।
(Seeds are formed when the M group plant is crossed up with the S group plant.)
ØS समूह के पौधे का L समूह के पौधे से क्रॉस करने पर बीज बनते हैं।
(Seeds are formed when the S group plant is crossed up with the L group plant.)
· निषेच्य क्रॉसिंग (Compatible Crossing):-
L X M
M X S
S X L
· अनिषेच्य क्रॉसिंग (Incompatible Crossing):-
L X L
M X M
S X S
· यह पद्धति Lythrum salicarea में पायी जाती है।
(This method is found in Lythrum salicarea.)
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Types of ovule:- On the basis of the position of the micropyle with respect to the funiculus, mature ovule can be classified into six main types. These are:
1. Orthotropous ovule:- Orthotropous ovule is also known as atropous. It is upright. In this type the micropyle, chalaza and the funiculus lie in one straight line as in Polygonaceae and Piperaceae.
2. Anatropous ovule:- In this type, the funiculus is long; the body of the ovule becomes completely inverted so that micropyle comes to lie close to the base of the funiculus. This happens due to unilateral growth of the ovule. The nucellus remains straight so micropyle and chalaza lie in one line and funiculus lie parallel to it. It is the most common type of ovule inAngiosperms.
3. Campylotropous ovule:- In campylotropous ovules body of the ovule is not completely inverted, the curvature is less than that in anatropous ovules. The micropyle and chalaza do not lie in the straight line and the funiculus lies at right angle to the chalaza as in Chenopodiaceae and Capparaceae.
4. Amphitropous ovule:- It is similar to campylotropous, but in this case the curvature of the ovule also affects the nucellus/embryo-sac so that it bent like "horse shoe" as in Alismaceae and Butomaceae.
5. Hemianatropous ovule:- Also known as hemitropous. In this type of ovule the funiculus is at right angle to the nucellus and the integuments. Micropyle and chalaza, lie in the same plane as in Ranunculus, Nothoscordum, and Tulbaghia.
6. Circinotropous ovule:- A very peculiar type of ovule is seen in some members of the Plumbaginaceae. Here the nucellar protuberance is at first in the same line as the axis, but the rapid growth on one side causes it to become anatropous. The curvature does not stop but continues until the ovule has turned over completely so that the micropylar end again points upwards. It has been suggested that this kind of ovule, also seen in Opuntia, is distinctive enough to merit a separate name, Circinotropous.
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भ्रूण संवर्धन (Embryo Culture):-
· परिभाषा (Definition):- परिवर्धित हो रहे बीज में से तरुण भ्रूण को निकालकर निर्जमित दशाओं में पोष पदार्थ पर संवर्धित करने की प्रक्रिया को भ्रूण संवर्धन कहते हैं।
(Embryo culture is a process in which young embryo removed from the developing seed and cultured on artificial medium in sterilized conditions.)
· सिद्धान्त (Principle):-
Ø सामान्यतया पोष पदार्थ पर तरुण भ्रूण का परिवर्धन या विकास पूर्ण नहीं हो पाता है और यह सीधे ही पौधे में विकसित हो जाता है। पोष पदार्थ में निम्न में से कोई एक मिलाने से भ्रूण का समय से पहले अंकुरण रोका जा सकता है –
(Generally, the growth or development of the young embryo on the artificial is not complete and it develops directly into the plant. Premature germination of the embryo can be prevented by adding one of the following to the artificial medium-)
i. उच्च सुक्रोज सांद्रता (High sucrose concentration)
ii. उच्च ABA सांद्रता (High ABA concentration)
Ø कुछ पौधों में परिपक्व बीजों के भ्रूणो का भी संवर्धन किया जाता है जैसे – Iris, Orchids आदि।
(In some plants, embryos of mature seeds are also cultured such as - Iris, Orchids etc.)
Ø ग्लोबुलर अवस्था के बाद के भ्रूणो का कृत्रिम संवर्धन अधिक आसान होता है। परन्तु क्रूसिफेरी कुल के कुछ पौधों में केवल कुछ कोशिकाओं वाले भ्रूणो का संवर्धन करना संभव हो सका है।
(Artificial culturing of embryos after the globular stage is easier. But in some plants of the Cruciferae family, it has been possible to culture embryos with only a few cells.)
Ø तरुण भ्रूण को भृणपोष पर संवर्धित कर सकते हैं ताकि इसका पूर्ण विकास व परिवर्धन हो सके।
(Young embryo can be cultured on the endosperm so that it can be fully developed and grown.)
· विधि (Procedure):-
Ø फल से अपरिपक्व बीजों को पृथक करके 10 मिनट के लिए 5℅ Teepol विलयन (एक द्रव डिटरजेंट) में डुबोकर रखते हैं। अब Teepol को हटाने के लिए कर्तोतकों को पानी से धो लेते हैं।
[Separate immature seeds from the fruit and keep them immersed in 5℅ Teepol solution (a liquid detergent) for 10 minutes. Now wash the explants with normal water to remove Teepol from the surface.]
Ø अब इन अपरिपक्व बीजों के सतही निर्जमीकरण के लिए 60 सेकंड के लिए 70℅ Ethanol में डुबोकर रखते हैं। 5 – 10 मिनट के लिए 0.1℅ HgCl2 के विलयन में डुबोकर रखते हैं। अतिरिक्त रसायन को सतह से हटाने के लिए 3 – 4 बार निर्जमित आसुत जल से धो लेते हैं।
(Now for surface sterilization of these immature seeds, immerse them in 70℅ Ethanol for 60 seconds. Then immersed in 0.1℅ HgCl2 solution for 5 - 10 minutes. To remove excess chemical from the surface, wash it 3-4 times with sterilized distilled water.)
Ø अब अपरिपक्व बीज पर चाकू या ब्लेड की सहायता से कट लगाकर सुई की सहायता से तरुण भ्रूण को पृथक कर लेते हैं। जिसे अब कर्तोतक कहा जाता है।
(Now the immature seed is cut with the help of a knife or blade and the young embryos are isolated with the help of a needle. Which is now called explant.)
Ø अब इन पृथक किए गए भ्रूणो को माइक्रो पिपेट या छोटे चमचनुमा स्पैचूला की सहायता से 10 cm पेट्रीडिश में 25 ml ठोस अगार माध्यम पर स्थापित करते हैं। सामान्यतया 6 – 8 भ्रूणो का संवर्धन एक पेट्रीडिश में किया जा सकता है। माध्यम में सुक्रोज या ABA की सांद्रता उच्च रखी जाती है। पेट्रीडिश को सैलो टेप से सील बन्द कर देते हैं ताकि माध्यम के शुष्कन को रोका जा सके।
(Now these isolated embryos are placed on 25 ml solid agar medium in 10 cm patridish with the help of micro pipette or small spoony spatula. Normally 6 - 8 embryos can be cultured in a patridish. The concentration of sucrose or ABA in the medium is kept high. Patridish is sealed with cello tape to prevent drying of the medium.)
Ø अब इस पेट्रीडिश को इंक्यूबेटर में रख देते हैं जहां इसे 25 ±1°C तापमान व 16 घण्टे का प्रकाशकाल दिया जाता है। प्रकाश देने के लिए ठंडी सफ़ेद फ्लोरीसेंट ट्यूब का उपयोग किया जाता है।
(Now put this patridish into an incubator where it is given a temperature of 25 ± 1 ° C and 16 hours of light period. Cold white fluorescent tubes are used in incubator to provide light.)
Ø लगभग 4 सप्ताहों में भ्रूण विकसित हो जाता है और प्ररोह तंत्र व मूल तंत्र बनाना शुरू कर देता है।
(In about 4 weeks, the embryo develops and starts forming the shoot system and root system.)
Øअब इसे नए ताजा माध्यम पर बड़ी संवर्धन ट्यूब में स्थापित करके उप – संवर्धन कर लेते हैं।जिससे नया पौधा विकसित हो जाता है।
(Now sub-culture it by establishing in a large culture tube on a new fresh medium, so that a new plant develops.)
· अनुप्रयोग (Applications):-
i. Embryo Rescue (भ्रूण बचाव):- दूरस्थ संकरण से बना भ्रूण भ्रूणपोष के ह्रास के कारण नष्ट हो जाता है। इसे नष्ट होने से बचाने के लिए तरुण बीजों से भ्रूण को निकालकर कृत्रिम रूप से माध्यम पर संवर्धित करते हैं।
(Embryos formed by distant hybridization are destroyed due to degeneration of endosperm. To protect it from destruction, extract the young embryo from the seeds and artificially grows it on the medium.)
उदाहरण (Example):-
जौं X राई (Barley X Rye)
जौं X गेहूँ (Barley X Wheat)
गेहूँ X राई (Wheat X Rye) = Triticale या Man made Wheat का निर्माण
[Development of Triticale or Man made Wheat]
ii. अगुणित पादप उत्पादन:- अंतराजातीय संकरण में जब जाइगोट से भ्रूण विकसित हो रहा होता है तो एक जाति के गुणसूत्र नष्ट हो जाते हैं तथा भ्रूण अगुणित हो जाता है। इस अगुणित भ्रूण के कृत्रिम संवर्धन से अगुणित पौधे प्राप्त किए जाते हैं।
(In inter-specific hybridization, when the embryo is developing from a zygote, the chromosomes of one species are destroyed and the embryo becomes haploid. The haploid plants are obtained by artificial culturing of this haploid embryo.)
उदाहरण (Example)– Hordeum bulbusum X जौं या गेहूँ (Barley or Wheat)
(इस क्रॉस में Hordeum bulbusum के गुणसूत्र विलुप्त हो जाते हैं।)
(In this cross the chromosomes of the Hordeum bulbusum become extinct.)
iii. Orchid प्रवर्धन:- Orchid के बीजों में भ्रूण तो होता है परन्तु भ्रूणपोष का अभाव होता है। अत: इनके कृत्रिम संवर्धन से पौधे आसानी से विकसित किए जा सकते हैं।
(Orchid seeds contain embryos but lack endosperm. Therefore, plants can be developed easily with their artificial culture.)
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Post-fertilization changes in the flower:- After the process of fertilization, the embryo undergoes a number of mitotic divisions to form a multicellular embryo. The endosperm nucleus also goes through a series of divisions to form a mass of endosperm cells. These endosperm cells provide nutrition to the developing embryo.
After fertilization, the following changes are observed in a flower:
i. There is the formation of a diploid zygote and it develops into an embryo, which forms the future plant.
ii. The endosperm cells serve as a source of nutrition for the developing embryo.
iii. The ovule becomes the seed.
iv. The ovary becomes the fruit.
v. In most plants, the antipodals and synergies disintegrate before, during, or immediately after fertilization.
vi. The outer and inner integuments of the ovule become the testa or the seed coat of the seed.
Petals and sepals fall off.
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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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Tapetum:- Tapetum is the innermost layer of the anther wall that surrounds the developing pollen (microspores). It is a specialized nutritive tissue that plays an essential role in pollen development.
Position:- The anther wall consists of four layers:
i. Epidermis
ii. Endothecium
iii. Middle layers
iv. Tapetum ← Innermost layer
Characteristics:-
> Usually single-layered
> Cells are large and rich in cytoplasm.
> Often binucleate or multinucleate.
> Rich in mitochondria, ER, Golgi bodies, and ribosomes.
> Degenerates as pollen grains mature.
Functions:-
> Provides nutrition to developing microspores.
> Produces enzymes such as callase, which dissolves the callose wall around microspore mother cells.
> Supplies sporopollenin precursors for exine formation through Ubisch bodies (orbicules).
> Synthesizes proteins, lipids, and pollen coat materials.
> Produces pollen kit (especially in insect-pollinated plants).
> Helps in pollen maturation and viability.
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Ovule:- The ovule is the female reproductive structure of flowering plants that develops into a seed after fertilization. It is attached to the placenta inside the ovary by a stalk called the funicle.
Parts of an Ovule:-
i. Funicle:- Stalk that attaches the ovule to the placenta.
ii. Hilum:- Junction where the funicle joins the ovule.
iii. Raphe:- Ridge formed by fusion of the funicle with the ovule body.
iv. Chalaza:- Basal region opposite the micropyle.
v. Integuments:- Protective layers surrounding the nucellus. They later form the seed coat.
vi. Micropyle:- Small opening left by the integuments. Entry point for the pollen tube during fertilization.
vii. Nucellus:- Nutritive tissue enclosing the embryo sac.
viii. Embryo Sac:- Female gametophyte present inside the nucellus. Usually 7-celled and 8-nucleate in angiosperms.
Functions of Ovule:-
> Produces the female gametophyte (embryo sac).
> Protects the embryo sac.
> Receives the pollen tube through the micropyle.
> Site of fertilization.
> Develops into a seed after fertilization.
> Provides nourishment to the developing embryo.
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Embryo sac types:- Depending on how many megaspore nuclei are involved in embryosac formation, the embryosac may be:
1. Monosporic embryo sac:- The chief characteristic of a monosporic embryo sac is that it is derived from only one of the four megaspores. All the nuclei in such an embryo sac are genetically identical because they are derived through mitosis of a single nucleus. There are two types of monosporic embryo sacs:
i. Polygonum Type:- It is the most common type (81% families). It was first time described in Polygonum divaricatum by Strasburger (1879). The embryo sac is formed by the chalazal megaspore of the tetrad and is eight nucleate. The mature embryo sac comprises a 3- celled egg apparatus, three antipodal cells, and a binucleate central cell.
ii. Oneothera Type:- This type of embryo sac is derived from the micropylar megaspore of the tetrad and is four nucleate. The organization of the mature embryo sac is_ an egg apparatus and a uninucleate central cell. It does not have antipodals. This type of embryo sac is characteristic of the family Onagraceae. Schisandra chinensis, however, is the only example outside this family where such a type of embryo sac occurs.
2. Bisporic embryo sac:- In plants bearing bisporic embryo sacs the first meiotic division is accomplished by wall formation, so that a dyad is formed. Only one of the dyad cells undergoes the second meiotic division whereas the other one degenerates. In the functional dyad cell wall formation does not occur after the second division, and both the megaspore nuclei contribute to the formation of the embryo sac. Each megaspore nucleus undergoes two mitotic divisions forming eight nuclei.
On the basis of the position of functional dyad bisporic embryo sacs are of two types:
i. Allium Type:- The embryo sac is derived from the chalazal dyad cell.
ii. Endymion Type:- The embryo sac is formed by the micropylar dyad cell.
3. Tetrasporic embryo sac:- In this type of embryo sac, meiotic division of the megaspore mother cell is not accompanied by cytokinesis and hence all the four haploid nuclei lie in a single cell called Coenomegaspore. All four nuclei of coenomegaspore participate in the formation of embryo sac. Genetically, it is more heterogeneous than bisporic type of embryo sac because the four products of meiosis involved in its formation are genetically different. The tetrasporic embryo sacs are further divided into many types:
i. Adoxa Type:- It has 8 nuclei which are formed by the mitotic division of the four haploid nuclei of the coenomegaspore. The arrangement of the 8 nuclei in the embryo sac is the same as in Polygonum type. Example –Adoxa, Sambucus, Ulmus, Tulipa, Erythronium etc.
ii. Plumbago Type:- This type of embryo sac is characterized by the absence of synergids and antipodals. Out of four haploid coenomegaspore one migrates to the micropylar end, one at chalazal end and two at the lateral sides. Each nuclei divides again and formed four groups of two nuclei. One of the nucleus from each group moves to the center of the cell and form four polar nuclei. The remaining nucleus at the micropylar is cut off by a membrane and form the egg. There are no synergids. The other three nuclei usually disappear but occasionally they too may be cut off by membranes and appear as accessory egg cells. Example –Plumbaginaceae family.
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iii. Penaea Type:- The four haploid nuclei of the coenomegaspore undergo two successive mitotic divisions forming 16 nuclei. These nuclei arrange themselves in four groups of four each, one at the micropylar end, one at chalazal end and one each on the two lateral sides. Now one nucleus from each groups migrates to the centre, and these four nuclei in the centre form polar nuclei. The three nuclei at the micropylar end are cut off by membranes and form the egg apparatus. The remaining three groups of nuclei (one chalazal and two lateral) degenerate at maturity. Example –Family Penaeaceae, Malpighiaceae and Euphorbiaceae.
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iv. Peperomia Type:- The egg apparatus of Peperomia type is characterized by a single synergid. The four haploid nuclei of coenomegaspore undergo two successive mitotic divisions forming 16 nuclei. Two nuclei at the micropylar end form egg and a synergid, eight fuse in the centre of the cell to form a polar nucleus and the remaining six at the chalazal end formed antipodals. Example-Peperomia and Gunnera.
v. Drusa Type:- 16 nucleate embryosac. This type of embryo sac is characterized by large number of antipodals. In the mature embryo sac three nuclei form egg apparatus. Two act as polar nuclei and the remaining 11 nuclei are cut off by membrane and form antipodal cells. The number and organization of nuclei may vary due to irregularity in the divisions. Example– Drusa, Rubia, Chrysanthemum,Ulmus etc.
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Pollen grain:- A pollen grain is the male gametophyte of flowering plants (angiosperms) and gymnosperms. It is produced in the anther of the stamen and carries the male reproductive cells needed for fertilization.
Structure of a pollen grain:-
Exine:- The outer, thick, tough wall made of sporopollenin, one of the most resistant biological substances.
Intine:- The inner, thin wall made of cellulose and pectin.
Germ pore:- A thin region in the exine through which the pollen tube emerges during germination.
Vegetative (tube) cell:- Forms the pollen tube.
Generative cell:- Divides to produce two male gametes (sperm cells).
Functions:-
> Transfers male gametes from the anther to the stigma during pollination.
> Germinates on the stigma to form a pollen tube.
> Enables fertilization by delivering sperm cells to the ovule.
Key facts:-
> Pollen grains vary in size, shape, and surface patterns depending on the plant species.
> They are dispersed by wind, insects, water, birds, or other animals.
> Their durable exine allows pollen grains to survive for long periods and makes them useful in forensic science and studies of ancient climates (palynology).
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).
Importance of Polyembryony:-
i. Plant breeding and horticulture:- The embryos in fruit trees, such as citrus and mango, are often free from genetic variation, making them valuable for maintaining desirable traits in new generations of plants.
ii. Nucellar disease:- Polyembryony plays a role in the propagation of fruit trees, as the embryos produced are genetically uniform, helping to ensure consistent quality and characteristics in seedlings.
iii. Propagation:- Polyembryony offers a method for developing homozygous diploid plants, which can be advantageous in breeding programmes aimed at fixing desirable traits.
iv. Artificial production:- Polyembryony can be artificially induced to produce genetically uniform plant material from eggs or synergids, ensuring the quality and productivity of fruit tree crops.
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