Hidema J, Makino A, Mae T, Ojima K
Department of Agricultural Chemistry, Faculty of Agriculture, Tohoku University, Tsutsumidori-Amamiyamachi, Sendai 981, Japan.
Plant Physiol. 1991 Dec;97(4):1287-93. doi: 10.1104/pp.97.4.1287.
Effects of irradiance on photosynthetic characteristics were examined in senescent leaves of rice (Oryza sativa L.). Two irradiance treatments (100 and 20% natural sunlight) were imposed after the full expansion of the 13th leaf through senescence. The photosynthetic rate was measured as a function of intercellular CO(2) pressure with a gas-exchange system. The amounts of cytochrome f, coupling factor 1, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and chlorophyll were determined. The coupling factor 1 and cytochrome f contents decreased rapidly during senescence, and their rates of decrease were much faster from the 20% sunlight treatment than from the full sunlight treatment. These changes were well correlated with those in the photosynthetic rate at CO(2) pressure = 600 microbars, but not with those under the ambient air condition (350 microbars CO(2)) and 200 microbars CO(2). This suggested that the amounts of coupling factor 1 and cytochrome f from the full sunlight treatment cannot be limiting factors for the photosynthetic rate at ambient air conditions. The Rubisco content also decreased during senescence, but its decrease from the 20% sunlight treatment was appreciably retarded. However, this difference was not reflected in the photosynthetic rates at the ambient and 200 microbars CO(2). This implied that in vivo Rubisco activity may be regulated in the senescent leaves from the 20% sunlight treatment. The chlorophyll content decreased most slowly. In the 20% sunlight treatment, it remained apparently constant with a decline in chlorophyll a/b ratio. These photosynthetic characteristics of the senescent rice leaves under low irradiance were discussed in relation to acclimation of shade plants.
研究了光照强度对水稻（Oryza sativa L.）衰老叶片光合特性的影响。在第13片叶完全展开至衰老后，设置了两种光照处理（100%和20%自然阳光）。使用气体交换系统测定光合速率与细胞间CO₂压力的函数关系。测定了细胞色素f、偶联因子1、核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）和叶绿素的含量。在衰老过程中，偶联因子1和细胞色素f的含量迅速下降，且20%阳光处理下它们的下降速率比全光照处理快得多。这些变化与CO₂压力为600微巴时的光合速率变化密切相关，但与环境空气条件（350微巴CO₂）和200微巴CO₂下的光合速率变化无关。这表明全光照处理下偶联因子1和细胞色素f的含量在环境空气条件下不是光合速率的限制因素。衰老过程中Rubisco含量也下降，但20%阳光处理下其下降明显延迟。然而，这种差异并未反映在环境和200微巴CO₂条件下的光合速率上。这意味着在20%阳光处理的衰老叶片中，体内Rubisco活性可能受到调控。叶绿素含量下降最慢。在20%阳光处理下，叶绿素a/b比值下降时，叶绿素含量明显保持恒定。结合阴生植物的适应性，讨论了低光照下衰老水稻叶片的这些光合特性。
