1978 Volume 47 Issue 2 Pages 344-353
In this study, three experiments were conducted to clarify the effect of subambient oxygen concentration during light or darkness on the growth, especially the leaf expansion of rice plant (Oryza sativa L. cv. Norin No. 18) in C3-plant and barnyard millet (Echinochloa crus-galli Beauv. var kasaharae Ohwi) in C4-plant. Exp. I. Seedlings of rice plant and barnyard millet were grown for 7 days under four experimental conditions, that is, 21% O2 during both light and darkness, 21% O2 during light and 2.5% O2 during darkness, 2.5% O2 during light and 21% O2 during darkness, and 2.5% O2 during both light and darkness. The growth parameters of both plants were investigated at the start and the end of each experiment. Exp. II. The leaf elongation rate during light or darkness of both plants was measured in the phytotron (constantly 20, 25 and 30°C) and outdoors under normal air condition. Exp. III. Seedlings of rice plant were grown for 7 days under two experimental conditions, that is, 21% O2 during both light and darkness, and 2.5% O2 during light and 21% O2 during darkness. The leaf elongation rate during light or darkness was measured. The results obtained are summarized as follows: 1. The dry matter production (ΔW) and relative growth rate (RGR) of rice plant were enhanced with 2.5% O2 during light, but not during darkness. Those of barnyard millet were little affected by 2.5% O2 during both light and darkness. This increased growth occuring only in light is related to a reduction in photorespiration. 2. The partitioning of assimilates in both plants was controlled by 2.5% O2 during light, but not during darkness, that is, unloading of assimilates to the leaf blades decreased and that to the roots increased. 3. Increase of leaf area, and relative growth rate of leaf area (RLGR) of both plants were unaffected by 2.5% O2 during both light and darkness. However, plant height, and the area of the leaf blade which emerged and fully expanded in both plants during experimental period decreased by 2.5% O2 during light similar to that previously observed for continuous exposure, but were unaffected during darkness. The number of tillers in both plants increased by 2.5% O2 during light, but not during darkness. 4. The leaf expansion of rice plant during both light and darkness was suppressed by 2.5% O2 during light. These results suggest that this O2 process which controls the leaf expansion and the partitioning of assimilates is directly or indirectly related to a light reaction.
