Leaf Elongation in Relation to Leaf Water Potential in Soybean

Abstract

Leaf water potential, turgor pressure, and leaf elongation rate were measured in soybeans grow ing in controlled environment chambers, greenhouses, and outdoors. Plants in chambers had the highest water potentials and turgor pressures, and plants outdoors the lowest. In all three environments there was a linear relationship between elongation rate and turgor pressure. Leaves of plants in drier environments required less turgor for elongation, and showed a greater increase in elongation rate per unit increase in turgor. Elongation rates over a 72 h period were equal in the three environments. Leaves reached the largest final size in the greenhouse (intermediate in water potential). Epidermal cells were larger in chamberand greenhouse grown leaves than in leaves of plants grown outdoors. The number of epidermal cells per leaf was greater in the greenhouse and outdoors than in the chamber. Leaf elongation characteristics of greenhouse plants were duplicated by mildly stressing chamber plants, and leaf elongation characteristics of field plants were duplicated by more severely stressing chamber plants. Leaves of mildly stressed chamber plants also reached a larger final size than leaves of more severely stressed chamber plants, or leaves of control plants in the chamber. Water stress in the chamber increased the number of epidermal cells per leaf. More severe water stress in the chamber re duced epidermal cell size. Based on the water stress experiments it is concluded that the differ ences in plant water status in the chamber, greenhouse, and field caused differences in elonga tion characteristics, and were responsible for the differences in leaf size.