Section 6
Chapter 5,686

Influence of growth temperature and nitrogen nutrition on photosynthesis and nitrogen metabolism in the rice plant oryza sativa l

Shieh Y J.; Liao W Y.

Botanical Bulletin of Academia Sinica 28(2): 151-168


Accession: 005685544

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The four-leaf-stage seedlings of two rice varieties were grown in the combinations of 5 levels of nitrogen (N) (from 5 to 80 ppm N) and three temperature regimes (day/night temperature of 22/17, 27/22 and 32/27.degree. C). It was found that the photosynthetic rate was expressed as leaf area basis. With this unit the photosynthetic rate of single leaves was closely related with chlorophyll content. There was linear relation between total N content (and protein) and chlorophyll content, indicating that photosynthesis per unit leaf area was closely correlated with nitrogen assimilation in leaves of the rice plants. Temperature and N level both affected photosynthesis of the rice leaves. In a tiller, the photosynthetic rate of leaves at different node positions was influenced by temperature and N level. At low temperature (22/17.degree. C) there was no significant difference of photosynthesis among leaves at different node positions under different N treatments. However, when plants grew at higher tmeperatures, lower photosynthetic rate was found at lower- positioned leaves under low level of N, but not under higher levels of N. The results indicate that photosynthesis is under the control of N uptake and metabolism in rice plants. Total soluble protein and amino-N increased with the increase in N concentration. There was higher N content (both soluble protein and total amino-N) in plants grown at lower temperature as compared with those of higher temperature growth plants, particularly with plants grown at higher levels of N, indicating the dilution effect of N by plant growth. Ribulose bisphosphate carboxylase (RuBPCase) and cytochrome C oxidase activities increased with the increase in the N level. However, these enzyme activities were low under all N treatments of plants grown at low temperature. Nitrate and nitrite reductase activities were enhanced by N concentration. No detectable activity of nitrate reductase was found in rice roots grown at N levels below 20 ppm N. The increment of above-ground dry weight was closely correlated with N level and growth temperature. There was 2.7 fold increase in total dry weight in japonica rice and 3.3 fold in indica rice grown under high N level and at higher temperatures, as compared with those plants grown under low N and low temperature. However, leaf photosythesis increased only 18% and 30% for japonica and indica rice, respectively. Growth analysis revealed that the effects of temperature and N treatment. The growth of the rice plant was regulated by the uptake of N and subsequently the expansion of leaf growth which was governed by temperature under high N level. Thus, this study conformed our previous conclusion that the growth of the rice plant was regulated by the rate of nitrogen metabolisms and subsequently by leaf growth.

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