Genetic variation in the photosynthetic induction response in rice (<i>Oryza sativa</i> L.)

Crop leaves growing under field conditions experience fluctuating light intensities. The photosynthetic response to a sudden increase in light intensity, which is termed the photosynthetic induction response, can potentially affect crop productivity. In the present study, the genetic variation in the photosynthetic induction response and the related gas exchange parameters in the rice diversity research set of germplasm (RDRS) were evaluated using two reference genotypes: Koshihikari and Takanari. Takanari is known to show superior induction response than Koshihikari. The photosynthetic induction response was found to be highly diverse in 59 rice genotypes. The cumulative CO₂ fixation during the first 10 minutes after a transition from low to high light intensity (CCF₁₀) differed by a factor of four between genotypes. The variation of CCF₁₀ showed no relationship with light saturated photosynthetic rate (R = 0.21), but was significantly correlated with photosynthetic rate (A) under low light conditions (R = 0.88). Several genotypes showed even more rapid induction responses than that of Takanari. In particular, A of ARC 11094 and Rexmont both increased rapidly during the first two minutes of the induction response. The CCF₁₀ of these two genotypes was approximately four times greater than that of Koshihikari. The rapid induction responses of Rexmont and ARC 11094 most likely resulted from the activation of CO₂ fixation in mesophyll cells and CO₂ diffusion from the air to the leaves, respectively. This study demonstrates that there is a large genetic variation in and, therefore, much potential for genetic improvement of, the photosynthetic induction response in rice.田间生长的作物叶片会经历不断波动的光照强度。作物对光照强度骤然升高的光合响应，即光合诱导响应（photosynthetic induction response），可对作物生产力产生潜在影响。本研究以Koshihikari和Takanari两个参照基因型为材料，对水稻种质资源多样性研究群体（Rice Diversity Research Set of Germplasm, RDRS）中各基因型的光合诱导响应及相关气体交换参数的遗传变异进行了评估。已知Takanari的光合诱导响应优于Koshihikari。 研究发现，59份水稻基因型的光合诱导响应存在高度多样性。低光转高光后前10分钟的累积CO₂固定量（cumulative CO₂ fixation within the first 10 minutes, CCF₁₀）在不同基因型间相差可达4倍。CCF₁₀的变异与光饱和光合速率无显著相关性（相关系数R=0.21），但与低光条件下的光合速率（A）呈显著正相关（相关系数R=0.88）。 部分基因型的光合诱导响应速度甚至快于Takanari。具体而言，ARC 11094与Rexmont的光合速率（A）在诱导响应初始的2分钟内便快速上升。这两份基因型的CCF₁₀约为Koshihikari的4倍。Rexmont和ARC 11094的快速光合诱导响应，分别大概率源于叶肉细胞的CO₂固定激活与空气向叶片的CO₂扩散过程。 本研究证实，水稻的光合诱导响应存在丰富的遗传变异，因此具备通过遗传改良优化该性状的巨大潜力。