Structure and histochemical details of style and stigma

Pollen Pistil Interaction:-

> Pollination→Pollen adhesion→ Pollen hydration→ Pollen germination→ Pollen tube entry into stigma→ Pollen tube growth to the style→ Pollen tube entry into the ovule and embryo sac → Double fertilization. 

> All the events leading from pollination to release of gametes in the embryo sac form a part of pollen pistil interaction is called Programic phase.

Structure of Pistil:- The female reproductive organ of the flower is called Gynoecium and the individual member is called pistil.Pistil is divisible into lower bulbous portion- Ovary, the long filamentous structure -style and the upper part of the style called stigma. All the three part of the pistil enjoy a wide degree of diversity as far as taxonomic point of view.But whatever may be the diversity, it is adapted to receive the pollen, aid its germination and subsequently entry of the pollen tube into the ovary, ovule and finally into the embryo sac for fertilization.The ultimate aim to acomplish the biological actvities as designed for do that.

Structure of Stigma:-

> Stigma-the specialized part where pollen grains are trapped during pollination.The features of the srtigma has wide diversity as far as structural composition is cencerned. 

> Stigma based on amount of secretion present during receptive period, decoration of the reseptive surface with glandular cells or papillae-Wet or Dry, 

> The composition of secretion produced by the subepidermal cells of the stigma highly heterogenous having lipids, proteins, glycoproteins, amino acids, arbionogalactans, Ca++,Phenols. 

> Stigma of four types-I, II, III, IV(J. Heslop-Harrison, 1976;Y.Heslop-Harrison & Shivanna, 1977). 

> Enzymes are diverse types-non-specific esterases on the receptive surface, Stigmatic epidermis is covered with cuticle and some extracelluar protineaceous lipoidal layer called Pellicle present. 

> The layer capture pollen grains and hydration of pollen grains.

Different Types of Stigma:-

Structure of Wet Stigma:-

Peroxidase Activity of Stigma:-

Structure of Dry Stigma:-

> In dry stigma, no exudates are released. 

> The cuticle is discontinuous.

> Behind the Pellicle & cuticle, thin mucilagenous layer opresent and the pectocellulosic layer id differentiated into several layers that form parammural bodies associated with secrtion of surface components, protein, Polysacchrides, Constituents of pectocellulosic wall and intercellular matrix. 

> In some cases, the pellicle shows ATPase and carbonic anhydrase activity. 

> The pellicle also binds to the lectins and contains arbinogalactans, a group of carbohydrates with adhesive properities.

Functions of Stigma:-

i.Pollen-Pistil interaction. 

ii. Lipoidal components secreted by the stigma to prevent evaporation and wetting by acting as liquid cuticle. 

iii.Pheolics & Protease inhibitors of stigma give protection againest insects & pathogens. 

iv.Stigmatic exudates serve as a nutrient sources for pollinating insects. 

v. Ther pellicle components originate from the epidermal cells of the stigma or stigmatic papillae shows ATPase and carbonic anahydrase activity. 

vi. The pellicle binds with lactins and arbinogalactans as adhesive properities.

After Pollen-Pistil Interaction:-

Structure of Style:-

> Style is a tubular structure having the connections between stima and ovary. 

> Mainly of two types-Solid (closed) & Hollow (Open). 

> The solid style has a central stand of transmitting tissues of elongated cells interconnected by plasmodesmata. Intercellular substances of protinaceous nature surrounded the cells of the transmitting tissue. It also contains Proteins, glycoproteins and lipid. A number of transmitting proline rich proteins have been localized in intercellular matrix. The cells of the transmitting tissue exhibit normal ultrastructural profiles with numerous mitochondria,active dictyosomes, roughER,plastids and ribosomes.Pollen tube grow down the style throgh the intercellular matrix of the transmitting tissue.

Hollow Style:-

> In the hollow style, the central core has one or more canals which normally correspond to the number of carpels.The stylar canal is bordered by one or few layers of glandular cells, canal cells. A layer of cuticle lines the canal cells in the young bud and the secretion product from the canal cells accumulate below the cuticle.The canal cells aree glandular and may be filled with secretion fluid. 

> whatever may be, the pollen grains after getting attachment with the stigma followed by the recognition of the pollen grains as compatible for germination, either by the sol;id satyle or the hollow style, a passage is made for the easy transportation of the pollen grains after germination in the form of pollen tube until the entire process of the biological dramas of fertil;iozartuion cme to an end.

Path of Pollen Tube:-

> The pollen tube pathway depends on the nature of the stigma.In the species with wet stigma and soild style differs with that of wet stigma and hollow style. 

> In wet stigma and solid style, the cuticle of the stgma or papillae is disrupted during the secretion of exedutes, thus there is no physical barrier for the pollen tube entry into the intcellular spaces before the transmitting tissue of the stigma. 

> In the wet stigma with hollow style, pollen tube grows on the surface of the stigma and enter the stylar canal. 

> In the species of the dry stigma and solid style, the cuticle provides the physical barrier for the pollen tube entry.The cuticle is eroded at the point of contact by the activity of the cutineses released by the pollen.After the digestion of the cuticle, the tube enters the pectocellulosic wall of the papillae and finally grows throgh the intercellular substances of the

Pollen tube guidance of the stigma and the style:-

> In most of the tissues, pollen tube makes their way to the ovary though the intercellular matrix of the transmitting tissues or throgh the mucilagenous matrix of ther hollow style. Different types of glycoproteins, sugar, proteins plauyed an important role in this regard. 

> The pollen tube finally pushes throgh the ovule and reaches the embryo sac.The guidance in the ovule is in terms of essential signal originating from the male and female tissue.In Arabidopsis, bel1 and sin1-the two genes activate in the female gametophyte play a crucial role in the signalling process that guides in the pollen tubes into the ovule.In fact, pollen tube are always attracted to the ovules with a functional embryo sac that confirms a female gametophyte control of pollen tube guidance.