9507385 Berg Light-avoiding leaf movement (paraheliotropism) is an important stress response that allows some plants to reduce water loss, lower leaf temperature and decreases photodamage to leaves under hot, dry, bright condition. The capacity to reduce light interception is one of the properties that confers drought resistance on some legumes. While the factors known to stimulate paraheliotropism are well described (high temperature, drought, high light intensity), almost nothing is known about the cellular mechanisms underlying the movement of leaves. The movement involves the swelling and shrinking of cells of the motor organ at the base of leaves, requiring a consideration of ion channels, osmotic properties, cell size change, and physical forces. The proposed project has three principal objectives: 1) to compare how the stimuli known to cause paraheliotropism act differently upon excised tissue, isolated cells and protoplaqts from the motor organ; 2) to determine the fate of the cytoskeleton when motor cells change size; and 3) to determine which ion channels are are involved in cell size change associated with paraheliotropism. This project will advance scientific knowledge by establishing the functional relationships between the two major groups of reversibly expandable plant cells, one well studied, the other barely examined at this time. It will determine the mechanisms that underlie paraheliotropism, a stress response important for the survival and projectivity of native species and agronomically important plants.
