Agronomie II

SUMMARY: Fertilisation is the fusion of the male gamete with the female gamete to form a zygote. In flowering plants, the male gametes are found in pollen grains, produced in the anthers, while the female gametes are found in the ovules. Pollen must first travel from an anther to the stigma in a process called pollination. When a pollen grain lands on the stigma, it forms a pollen tube down the style of the flower. The pollen grain’s nucleus travels down the pollen tube as it grows towards the ovary and the ovule. The pollen tube reaches a tiny opening in the ovule, and then the tip of the pollen tube dissolves allowing the pollen nucleus to enter the ovule. Here, the pollen nucleus fuses with the egg cell nucleus. This fusion of the two nuclei is fertilisation. Fertilisation creates a new cell, called a zygote. The single zygote cell divides and develops to become a plant embryo which has a plumule and a radicle. The plumule will go on to become the first shoot of the plant while the radicle will become the first root. The remaining contents of the ovule develop into cotyledons which act as a food store for the new plant. Seeds need their own food store for the earliest stage of growth because no food is produced by photosynthesis until leaves develop. Surrounding the seed is a seed coat, a protective layer which forms from the ovary wall.