Abstract
Rice seedlings were grown on a medium containing polyethylene glycol (PEG), which lowers the osmotic potential of the medium under high humidity, or on a medium containing no PEG under a low humidity, and their growth and partition of dry matter were compared with those of plants grown on a medium without PEG under high humidity. The growth of plant tops showed a similar tendency under both water stresses induced by a low osmotic potential and low humidity : leaf blade length, leaf area and dry weight decreased and specific leaf weight increased. In the growth of plant roots, the water stress induced by a low osmotic potential increased the total length, diameter of main roots and dry weight, while the water stress induced by a low humidity decreased these parameters. The partition of dry matter also changed in response to water stress conditions. The stress caused by low humidity increased the partition of dry matter to the top. However, the stress caused by a low osmotic potential of the medium increased the partition to the root, resulting in the decrease of the top-root ratio. These results show that the effect of water stress induced by a low osmotic potential in a medium containing PEG on the growth of rice seedlings considerably differs from that of water stress induced by low humidity.
