Königer Martina, Delamaide Joy A, Marlow Elizabeth D, Harris Gary C
Department of Biological Sciences, Wellesley College, Wellesley, MA 02481, USA.
J Exp Bot. 2008;59(9):2285-97. doi: 10.1093/jxb/ern099. Epub 2008 May 8.
The effects of chloroplast number and size on the capacity for blue light-dependent chloroplast movement, the ability to increase light absorption under low light, and the susceptibility to photoinhibition were investigated in Arabidopsis thaliana. Leaves of wild-type and chloroplast number mutants with mean chloroplast numbers ranging from 120 to two per mesophyll cell were analysed. Chloroplast movement was monitored as changes in light transmission through the leaves. Light transmission was used as an indicator of the ability of leaves to optimize light absorption. The ability of leaves to deal with 3 h of high light stress at 10 degrees C and their capacity to recover in low light was determined by measuring photochemical efficiencies of PSII using chlorophyll a fluorescence. Chloroplast movement was comparable in leaves ranging in chloroplast numbers from 120 to 30 per mesophyll cell: the final light transmission levels after exposure to 0.1 (accumulation response) and 100 micromol photons m(-2) s(-1) (avoidance response) were indistinguishable, the chloroplasts responded quickly to small increases in light intensity and the kinetics of movement were similar. However, when chloroplast numbers per mesophyll cell decreased to 18 or below, the accumulation response was significantly reduced. The avoidance response was only impaired in mutants with nine or fewer chloroplasts, both in terms of final transmission levels and the speed of movement. Only mutants lacking both blue light receptors (phot1/phot2) or those with drastically reduced chloroplast numbers and severely impacted avoidance responses showed a reduced ability to recover from high light stress.
在拟南芥中研究了叶绿体数量和大小对蓝光依赖型叶绿体运动能力、弱光下增加光吸收的能力以及对光抑制敏感性的影响。分析了野生型和叶绿体数量突变体的叶片，其每个叶肉细胞的平均叶绿体数量范围从120个到2个。通过监测叶片透光率的变化来监测叶绿体运动。透光率被用作叶片优化光吸收能力的指标。通过使用叶绿素a荧光测量PSII的光化学效率，来确定叶片在10摄氏度下应对3小时高光胁迫的能力及其在弱光下恢复的能力。叶绿体数量从每个叶肉细胞120个到30个的叶片中，叶绿体运动情况相当：暴露于0.1（积累反应）和100微摩尔光子·米⁻²·秒⁻¹（回避反应）后最终的透光水平没有区别，叶绿体对光强的小幅增加反应迅速，且运动动力学相似。然而，当每个叶肉细胞的叶绿体数量减少到18个或更低时，积累反应显著降低。回避反应仅在叶绿体数量为9个或更少的突变体中受到损害，无论是最终透光水平还是运动速度方面。只有缺乏两种蓝光受体（phot1/phot2）的突变体，或者叶绿体数量大幅减少且回避反应严重受损的突变体，从高光胁迫中恢复的能力才会降低。
