Different Mechanisms for Photosystem 2 Reversible Down-Regulation in Pumpkin and Soybean Leaves Under Saturating Irradiance |
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Authors: | Zhang Hai-Bo Xu Da-Quan |
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Institution: | (1) Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, China |
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Abstract: | After saturating irradiation for 3 h (SI), the original fluorescence F0 increased while the photosystem 2 (PS2) photochemical efficiency (Fv/Fm) declined significantly. These parameters could largely recover to the levels of dark-adapted leaves after 3 h of subsequent
dark recovery. No net loss of the D1 proteins occurred after SI. Soybean and pumpkin leaves had different responses to SI.
Low temperature fluorescence parameters, F685 and F685/F735, decreased significantly in soybean leaves but not in pumpkin leaves. Part of the light-harvesting complex LHC2 dissociated
from PS2 complexes in soybean leaves but not in pumpkin leaves, as shown by sucrose density gradient centrifugation and SDS-PAGE.
The photon-saturated PS2 electron transport activity declined significantly in pumpkin thylakoids but not in soybean thylakoids.
In addition, a large amount of phosphorylated D1 proteins was found in dark-adapted soybean leaves but not in dark-adapted
pumpkin leaves. Hence at excessive irradiance soybean and pumpkin have the same protective strategy against photo-damage,
reversible down-regulation of PS2, but two different mechanisms, namely the reversible down-regulation is related to the dissociation
of LHC2 in soybean leaves but not in pumpkin leaves.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | chlorophyll fluorescence Cucurbita D1 protein dissociation Glycine light-harvesting complex 2 (LHC2) polyacrylamide gel electrophoresis species differences sucrose density gradient centrifugation |
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