When exposed to high light, plants produce reactive oxygen species (ROS). In Arabidopsis thaliana, local stress such as excess heat or light initiates a systemic ROS wave in phloem and xylem cells dependent on NADPH oxidase/respiratory burst oxidase homolog (RBOH) proteins. In the case of excess light, although the initial local accumulation of ROS preferentially takes place in bundle-sheath strands, little is known about how this response takes place. Using rice and the ROS probes diaminobenzidine and 2′,7′-dichlorodihydrofluorescein diacetate, we found that, after exposure to high light, ROS were produced more rapidly in bundle-sheath strands than mesophyll cells. This response was not affected either by CO₂ supply or photorespiration. Consistent with these findings, deep sequencing of messenger RNA (mRNA) isolated from mesophyll or bundle-sheath strands indicated balanced accumulation of transcripts encoding all major components of the photosynthetic apparatus. However, transcripts encoding several isoforms of the superoxide/H₂O₂-producing enzyme NADPH oxidase were more abundant in bundle-sheath strands than mesophyll cells. ROS production in bundle-sheath strands was decreased in mutant alleles of the bundle-sheath strand preferential isoform of OsRBOHA and increased when it was overexpressed. Despite the plethora of pathways able to generate ROS in response to excess light, NADPH oxidase–mediated accumulation of ROS in the rice bundle-sheath strand was detected in etiolated leaves lacking chlorophyll. We conclude that photosynthesis is not necessary for the local ROS response to high light but is in part mediated by NADPH oxidase activity.

当暴露在强光下时，植物会产生活性氧 (ROS)。在拟南芥中，局部压力如过热或光照会在韧皮部和木质部细胞中引发全身性 ROS 波，这依赖于 NADPH 氧化酶/呼吸爆发氧化酶同源物 (RBOH) 蛋白。在光线过剩的情况下，尽管 ROS 的初始局部积累优先发生在束鞘链中，但人们对这种反应如何发生知之甚少。使用水稻和 ROS 探针二氨基联苯胺和 2',7'-二氯二氢荧光素二乙酸酯，我们发现，在暴露于强光后，束鞘链中的 ROS 产生速度比叶肉细胞更快。该响应不受 CO _{2 的}影响供应或光呼吸。与这些发现一致，从叶肉或束鞘链中分离的信使 RNA (mRNA) 的深度测序表明编码光合装置所有主要成分的转录物的平衡积累。然而，编码超氧化物/H ₂ O _{2 产生}酶NADPH 氧化酶的几种同工型的转录物在束鞘链中比叶肉细胞更丰富。OsRBOHA束鞘链优先亚型的突变等位基因中束鞘链中 ROS 的产生减少并在过度表达时增加。尽管有多种途径能够响应过量光产生 ROS，但在缺乏叶绿素的黄化叶片中检测到 NADPH 氧化酶介导的 ROS 在水稻束鞘链中的积累。我们得出结论，光合作用对于局部 ROS 对高光的反应不是必需的，但部分由 NADPH 氧化酶活性介导。