The male gametophyte in plants, also known as the pollen grain, does not become a specific structure. Instead, it develops into the male gametes (sperm cells) which are involved in fertilization.

Here's a breakdown of the process:

1. Pollen Grain: The pollen grain is a multicellular structure that contains the male gametophyte.

2. Germination: When the pollen grain lands on the stigma of a flower, it germinates, growing a pollen tube.

3. Pollen Tube Growth: The pollen tube grows down through the style of the flower towards the ovary.

4. Sperm Cell Development: Inside the pollen tube, the male gametophyte develops into two sperm cells.

5. Fertilization: When the pollen tube reaches the ovule, one sperm cell fertilizes the egg cell, forming the zygote (which will develop into the embryo). The other sperm cell fuses with the central cell, forming the endosperm, which nourishes the developing embryo.

Therefore, the male gametophyte itself doesn't transform into a specific structure, but rather serves as a vehicle to deliver the sperm cells for fertilization.