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KMID : 0380219940270030205
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Journal of Biochemistry and Molecular Biology
1994 Volume.27 No. 3 p.205 ~ p.210
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Evidence Against the Involvement of Stromal Acidification in The Heat Induced Inhibition of Photosynthesis in Isolated Spinach Chloroplasts
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Abstract
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Abstract:
@EN The inhibitory effect of heat treatment on CO2 fixation in isolated chloroplasts was increased as the medium pH was lowered. At pH 8.1 heat treatment at 35℃ for 10 min produced a 50% inhibition while the same treatment caused a nearly 90%
inhibition at pH 6.0. As a result. Involvement of stromal acidification as an intermediate step in the heat-induced inhibition of CO2 fixation was suggested. Addition of alkalinizing agents (NH4Cl and KCl) to the medium prior to heat treatment of
chloroplasts did not prevent inhibition. Also addition of these agents to heated chloroplasts did not reverse or alleviate inhibition, suggesting stromal acidification is not involved. Consequently, direct measurement of stromal pH was attempted.
Heat
treatment did not lower the stromal pH either at pH 8.1 or at pH 6.0. Rather, it slightly raised the stromal pH. Thus, stromal acidification as an intermediate step for the heat induced inhibition of CO2 fixation in isolated chloroplasts can be
excluded. Reconstituted chloroplasts revealed thylakoidal damage after heat treatment at pH 6.0, which did not occur pH 8.1. It seems that this additional damage in thylakoids is the cause for the higher degree of inhibition at pH 6.0.
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