Abstract
A water culture experiment was conducted to evaluate the effects of mater stress on the movement and distribution of water through the plants of Rhodesgrass (Chloris gayana KUNTH.) and Job's tears (Coix lacryma-jobi L.) with tritiated water (^3H_2O) in the nutrient solution as a tracer. Water potential of the nutrient solution was adjusted to -0.97 MPa with mannitol in the water-stress treatment. Water potential of the non-stress control was -0.03 MPa. Under non-stressed conditions, relative ^3H radioactivity increased rapidly in the root and stem tissues followed by leaf tissues in the drought-tolerant species, Rhodesgrass, a few hours after the addition of ^3H_2O. In the drought-tolerant species, Job's tears, relative radioactivity increased rapidly in the root tissues but increased slowly in the stem and leaf tissues. Twenty-four hours after the addition of ^3H_2O, relative ^3H radioactivity in roots, stems, expanded and expanding leaves of Rhodesgrass reached about 20, 70, 51, and 58% of that in the nutrient solution. The respective values in Job's tears were 70, 42, 30, and 28%, indicating that the movement of water through plants of Rhodesgrass was faster than in Job's tears. The movement of ^3H_2O through plant's bodies were remarkably reduced in both species under water-stressed conditions. Twenty-four hours after the addition of ^3H_2O, relative ^3H radioactivity in roots, stems, expanded and expanding leaves of Rhodesgrass reached 5, 45, 9, and 8% of that in the nutrient solution. The respective values in Job's tears were 48, 18, 5.5, and 4%. The movement of ^3H_2O from roots to stem and leaves, especially to expanding leaves, was strongly restricted in Job's tears compared to Rhodesgrass. These results suggest that water movement through plants depends on plant species and that a series of resistance exists along the pathway of water movement from roots to leaves through the plants. It is concluded that resistance to water flow was higher in drought-sensitive species, Job's tears, than in drought-tolerant s species, Rhodesgrass.
