Control of water movement in reproductive organs of tobacco

This thesis describes experiments performed to investigate the role that two different protein families play during reproduction in tobacco. As plants cannot move, reproduction is difficult: it is for example not possible to go and find a suitable mate. Instead, sperm cells are transported to the female reproductive organs in pollen grains, which develop in the anther. During the period of transfer to the stigma, pollen grains of most angiosperm species are dehydrated and only contain 30% water. When a pollen grain has reached a compatible stigma, hydration occurs by uptake of stigmatic water. When pollen grains are completely hydrated, a pollen tube can be formed that will deliver the sperm cells to the ovary, where fertilization occurs. Water is required for the hydration of pollen grains, and it is reasonable to assume that it is required also during pollen tube growth in the pistil. However, transport of water is also important during development of the pollen grains in the anther. Mature pollen grains contain little water during transfer because they dehydrate in the last phase of development. Concurrently with the pollen grains, the anther itself also dehydrates. This may generate a force on the anther walls, causing it to open at dehiscence, releasing the pollen grains, so that pollination can take place. Recently, a class of proteins called aquaporins has been found that forms water channels in cellular membranes. As the transport of water appears important for successful reproduction, and because reproduction is crucial for the existence of a species, we have analyzed the role of aquaporins in tobacco reproductive processes. The results indicate that various aquaporins are present in reproductive organs of tobacco. A role of the PIP2 class of aquaporins in anther dehydrations prior to dehiscence could be shown