Tag: male & female gametophytes: structure and development

The male gametes of angiosperms consist of two sperm cells within a pollen grain or a pollen tube. They are derived from a single generative cell, which is formed as the smaller cell by unequal cell division in the microspore after meiosis. The gametes formed will be non-motile as there is no flagellated stage in the life cycle of angiosperms.

Sporopollenin is major component of the tough outer walls called as exine of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from lake sediments to provide useful information to palynologists about plant and fungal populations in the past. The chemical composition of sporopollenin is not exactly known, due to its unusual chemical stability and resistance to degradation by enzymes and strong chemical reagents.

Ubisch bodies have been largely observed in plants, after they were first recorded around the aggregates of mimosoid pollen by Rosanoff. The tapetum may be secretory (glandular) or amoeboid (periplasmodial). The cells of tapetum form pro-ubisch bodies which get surrounded by sporopollenin and now called ubisch bodies. They participate in the formation of pollen exine. 

Gymnosperms are having a haploid endosperm. But, angiosperms have a triploid endosperm due to the double fertilization. The pollen grain is the haploid in nature. Therefore, in gymnosperms, the pollen grains and the megaspores are the haploids. The functional megaspores from the embryo sac. The endosperm is formed prior to the fertilization and hence it is haploid.

Germ pore is the pore in the outer wall of a pollen grain through which the germ tube or pollen tube makes its exit on germination. When this fusion happens, the zygote is produced. The germ pore also releases the extra nucleus which results in the formation of triploid endosperm.

Intine - cellulose
Pollen - microspore mother cell
Pin-eyed - Long styled
Thrum-eyed - Short styled
The pollen grain has an inner and outer layer. The inner layer is called as intine and the outer one is called as exine. Intine is composed of cellulose.
A diploid cell in plants that divides by  meiosis to give rise to four haploid microspores. In flowering plants microspore mother cells are formed within the pollen sacs of the anthers by mitosis; the microspores they produce develop into pollen grains.
Pin-eyed : Having the stigma in the mouth of the corolla, on one end of a long style with the stamens lower in the tube
Thrum-eyed: Having on a short style below the anthers, which like in the mouth of the corolla on big stamens.

Sporopollenin is a major component of the tough outer walls called as exine walls of plant spores and pollen grains. It is chemically very stable and usually well preserved in soils and sediments. The chemical composition of sporopollenin is not exactly known due to its unusual chemical stability and resistance to degradation by enzymes and string chemical reagents.

Pollen grains are haploid microspores produced in higher plants like gymnosperms and angiosperms. In higher plants the pollen grains produce male gametes by the process of mitosis. The study of pollen grains is called palynology. It is useful in forensics, evolutionary studies etc. The important pollen characters that are studied are number, position and character of aperture, encrustations of exine, viability, longevity etc.

Pollen sacs are located in the anther. It is the structure where pollen are produced. Angiosperms have 4 pollen sac in anther. 

Sporopollenin is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from (for example) lake sediments to provide useful information to palynologists about plant and fungal populations in the past. The chemical composition of sporopollenin is not exactly known, due to its unusual chemical stability and resistance to degradation by enzymes and strong chemical reagents. Analyses have revealed a mixture of biopolymers, containing mainly long chain fatty acids, phenylpropanoids, phenolics and traces of carotenoids. Tracer experiments have shown that phenylalanine is a major precursor, but other carbon sources also contribute. It is likely that sporopollenin derives from several precursors that are chemically cross-linked to form a rigid structure.