What occurs when a pollen grain lands on the stigma of a plant?

When a pollen grain lands on the stigma of a plant, pollen tube growth is initiated. This process is critical for fertilization in flowering plants, or angiosperms. The pollen grain, which contains male gametes, adheres to the sticky stigma, which is part of the female reproductive structure, the pistil. Once settled, the pollen grain absorbs moisture and nutrients from the stigma and undergoes mitosis to form a pollen tube. This tube then grows down through the style toward the ovule, allowing the sperm cells to travel and reach the egg for fertilization.

The other options do not describe the immediate events following the landing of pollen on the stigma. Photosynthesis is the process plants use to convert light energy into chemical energy, and it does not occur as a direct consequence of pollination. Seed germination refers to the process by which a seed emerges and starts growing into a new plant, which happens only after fertilization and subsequent seed development. Pollination itself is the overall transfer of pollen from an anther to a stigma, but the specific event that occurs immediately after the pollen settles on the stigma is the growth of the pollen tube. This distinction is essential in understanding the stages of plant reproduction.