Jajoo A, Bharti S
School of Life Sciences, Vigyan Bhavan, Khandwa Road Devi Ahilya University, Indore, India.
FEBS Lett. 1998 Aug 28;434(1-2):193-6. doi: 10.1016/s0014-5793(98)00978-8.
The role of cations in excitation energy distribution between the two photosystems of photosynthesis is well established. This paper provides evidence, for the first time, for an important role of anions in the regulation of distribution of absorbed light energy between the two photosystems. Inorganic anions caused redistribution of energy more in favour of photosystem I, as judged from measurements of chlorophyll a fluorescence transients, rates of electron transport in low light and 77 K fluorescence emission spectra: the Fv/Fm ratio was decreased by inorganic anions even in the presence of DCMU, the PS II electron transport was decreased whereas PS I electron transport was increased and the F735 (77 K emission from PS I)/F685 (77 K emission from PS II) ratio was increased. Such changes were observed with inorganic anions having different valencies (Cl- , SO4(2-), PO4(3-)): the higher the valency of the inorganic anion, the more the energy transferred towards PS I. Change in the valency of the inorganic anions thus regulates distribution of absorbed light energy between the two photosystems. However, organic anions like acetate, succinate, and citrate caused no significant changes in the Fv/Fm ratio, and in rates of PS I and PS II electron transport, showing their ineffectiveness in regulating light energy distribution.
阳离子在光合作用两个光系统之间的激发能分布中的作用已得到充分证实。本文首次提供证据表明，阴离子在调节两个光系统之间吸收光能的分布中起重要作用。从叶绿素a荧光瞬变、低光下的电子传递速率和77K荧光发射光谱的测量结果判断，无机阴离子导致能量重新分布，更有利于光系统I：即使在存在二氯苯基二甲基脲（DCMU）的情况下，无机阴离子也会使Fv/Fm比值降低，光系统II的电子传递速率降低，而光系统I的电子传递速率增加，并且F735（光系统I的77K发射）/F685（光系统II的77K发射）比值增加。对于具有不同化合价的无机阴离子（Cl-、SO4(2-)、PO4(3-)）都观察到了这种变化：无机阴离子的化合价越高，向光系统I转移的能量就越多。因此，无机阴离子化合价的变化调节了两个光系统之间吸收光能的分布。然而，像乙酸盐、琥珀酸盐和柠檬酸盐这样的有机阴离子在Fv/Fm比值以及光系统I和光系统II的电子传递速率方面没有引起显著变化，表明它们在调节光能分布方面无效。
