背景回顾：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. 

提出问题：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.

结果1-ROS染色：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. 

结果2-基因表达：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. 

结果3-基因敲除及过表达：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. 

结果4-黄化叶片：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.

结论：We conclude that photosynthesis is not necessary for the local ROS response to high light but is in part mediated by NADPH oxidase activity.

 摘 要 

当植物暴露在高光强下是，植物组织会产生活性氧物质（ROS）。在拟南芥中，局部过剩的热或者光照胁迫会起始一个在韧皮部和木质部中传播的系统性ROS波动，并且该过程依赖于呼吸爆发氧化酶同系物蛋白RBOH。在存在过剩光能的情况下，尽管目前已经知道ROS的局部积累优先发生在束鞘细胞中，但是具体的分子调控机制还不清楚。本文中，作者以水稻为材料，利用ROS探针二氨基联苯胺（DAB）和二氯荧光素二乙酸酯，发现水稻在高光强处理后，束鞘细胞中产生ROS要比叶肉细胞中更快。该现象不受二氧化碳供应或光呼吸的影响。与此一致，通过对叶肉或束鞘细胞中分离的mRNA深度测序表明，编码光合器所有主要成分的转录本平稳积累。但是，编码超氧化物/过氧化氢生成酶NADPH氧化酶的几种转录本在束鞘细胞中比叶肉细胞中丰度更高。OsRBOHA异构体在束鞘细胞存在优势表达，如果突变掉该基因会导致束鞘细胞中ROS产量降低；相反，过表达该基因会促进束鞘细胞中ROS的产生。尽管在过量光照下，有很多途径都能够产生活性氧，但在缺乏叶绿素的水稻黄化叶片中，作者发现NADPH氧化酶介导的活性氧在束鞘细胞中积累。因此，作者认为植物对强光的局部ROS响应并不一定需要光合作用，但确实部分依赖于NADPH氧化酶的活性来介导该响应。