Question

1) Compare and contrast embryo development in from fertilization to mature seed.

2) Fabian performed a mutant screen and found a plant the was extra droopy when compared to wildtype.  Upon further analysis, he found that the plant’s stomata didn’t open very well.  What kind of gene/protein might have been mutated in this plant?

3) How does plant biotechnology enable one to overcome genetic barriers between distant species (different genera or even families)

Answer 1

1. In flowers, androecium consisting of stamens represents the male reproductive organs and gynoecium consisting of pistils represents the female reproductive organs. A typical anther is bilobed, dithecous, and tetrasporangiate. Pollen grains develop inside the microsporangia   Four wall layers, the epidermis, endothecium, middle layers, and the tapetum sorround the microsporangium, undergo meiosis to form tetrads of microspores. Individual microspores mature into pollen grains. Pollen grains represents the male gametophytic generation. The pollen grains have a two-layered wall, the outer exine and inner intine. Pollen grains may have two cells or three cells at the time of shedding. The pistil has three parts--the stigma, style, and the ovary. Ovules are present in the ovary. The ovules have a stalk called, funicle, protective integument, and an opening called micropyle. The central tissue is the nucellus in which the archesporium differentiates. A cell of the archesporium, the megaspore mother cell divides meiotically and one of the megasopers forms the embryo sac. The mature embryo sac is 7-celled and 8-nucleate. At the micropylar end is the egg apparatus consisting of two synergids and egg cell. At the chalazal end are three antipodals. At the center is a large central cell with two polar nuclei. Pollination is the mechanism to transfer pollen grains from the anther to the stigma. Pollination agents are either abiotic or biotic.

Pollen-pistil interaction involves all events from the landing of pollen grains on the stigma until the pollen tube enters the embryo sac or pollen inhibition. Following compatible pollination, pollen grain germinates on the stigma and the resulting pollen tube grow through the style, enter the ovules and finally discharges two male gametes in one of the synergids. Angiosperms exhibit double fertilisation because two fusion events occur in each embryo sac, namely syngamy and triple fusion. The products of these fusions are the diploid zygote and the triploid primary endosperm nucleus. Zygote develops into the embryo and the primary endosperm cell forms the endosperm tissue. Formation of endosperm always precedes development of the embryo. The developing embryo passes through different stages such as the proembryo, globular, and heart-shaped stages before maturation. Mature dicotyledonous embryo has two cotyledons and an embryonal axis with epicotyl and hypocotyl. Embryos of monocotyledons have a single cotyledon. After fertilisation ovary develops into fruit and ovules develop into seeds.