Greene R M, Geider R J, Kolber Z, Falkowski P G
Oceanographic and Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, New York 11973.
Plant Physiol. 1992 Oct;100(2):565-75. doi: 10.1104/pp.100.2.565.
The role of iron in regulating light harvesting and photochemical energy conversion processes was examined in the marine unicellular chlorophyte Dunaliella tertiolecta and the marine diatom Phaeodactylum tricornutum. In both species, iron limitation led to a reduction in cellular chlorophyll concentrations, but an increase in the in vivo, chlorophyll-specific, optical absorption cross-sections. Moreover, the absorption cross-section of photosystem II, a measure of the photon target area of the traps, was higher in iron-limited cells and decreased rapidly following iron addition. Iron-limited cells exhibited reduced variable/maximum fluorescence ratios and a reduced fluorescence per unit absorption at all wave-lengths between 400 and 575 nm. Following iron addition, variable/maximum fluorescence ratios increased rapidly, reaching 90% of the maximum within 18 to 25 h. Thus, although more light was absorbed per unit of chlorophyll, iron limitation reduced the transfer efficiency of excitation energy in photosystem II. The half-time for the oxidation of primary electron acceptor of photosystem II, calculated from the kinetics of decay of variable maximum fluorescence, increased 2-fold under iron limitation. Quantitative analysis of western blots revealed that cytochrome f and subunit IV (the plastoquinone-docking protein) of the cytochrome b(6)/f complex were also significantly reduced by lack of iron; recovery from iron limitation was completely inhibited by either cycloheximide or chloramphenicol. The recovery of maximum photosynthetic energy conversion efficiency occurs in three stages: (a) a rapid (3-5 h) increase in electron transfer rates on the acceptor side of photosystem II correlated with de novo synthesis of the cytochrome b(6)/f complex; (b) an increase (10-15 h) in the quantum efficiency correlated with an increase in D1 accumulation; and (c) a slow (>18 h) increase in chlorophyll levels accompanied by an increase in the efficiency of energy transfer from the light-harvesting chlorophyll proteins to the reaction centers.
在海洋单细胞绿藻三角褐指藻（Dunaliella tertiolecta）和海洋硅藻三角褐指藻（Phaeodactylum tricornutum）中研究了铁在调节光捕获和光化学能量转换过程中的作用。在这两个物种中，铁限制导致细胞叶绿素浓度降低，但体内叶绿素特异性光吸收截面增加。此外，光系统II的吸收截面（陷阱的光子靶面积的量度）在铁限制细胞中更高，并且在添加铁后迅速降低。铁限制细胞在400至575nm之间的所有波长下表现出降低的可变/最大荧光比和每单位吸收的荧光降低。添加铁后，可变/最大荧光比迅速增加，在18至25小时内达到最大值的90％。因此，尽管每单位叶绿素吸收更多的光，但铁限制降低了光系统II中激发能量的转移效率。根据可变最大荧光的衰减动力学计算，光系统II初级电子受体氧化的半衰期在铁限制下增加了2倍。蛋白质免疫印迹的定量分析表明，细胞色素b（6）/ f复合物的细胞色素f和亚基IV（质体醌对接蛋白）也因缺铁而显著减少；用环己酰亚胺或氯霉素完全抑制了从铁限制中的恢复。最大光合能量转换效率的恢复分三个阶段发生：（a）光系统II受体侧电子转移速率迅速（3-5小时）增加，与细胞色素b（6）/ f复合物的从头合成相关；（b）量子效率增加（10-15小时），与D1积累增加相关；（c）叶绿素水平缓慢增加（> 18小时），同时伴随着从光捕获叶绿素蛋白到反应中心的能量转移效率增加。
