Effect of phosphon-D on photosynthetic light reactions and on reactions of the oxidative and reductive pentose phosphate cycle in a reconstituted spinach (Spinacia oleracea L.) chloroplast system |
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Authors: | K J Lendzian H Ziegler N Sankhla |
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Institution: | (1) Institut für Botanik und Mikrobiologie, Lehrstuhl für Botanik, Technische Universität, Arcisstr. 21, D-8000 München 2;(2) Botany Department, University of Jodhpur, 342001 Jodhpur, India |
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Abstract: | Phosphon-D (tributyl-2, 4-dichlorobenzylphosphonium chloride), known as an inhibitor of gibberellin biosynthesis, enhances photosynthetic electron transport by up to 200%, with Fe(CN)
6
3-
and NADP+ being the electron acceptors. Maximum stimulation is reached at phosphon-D concentrations around 2–5 M. At the same time photosynthetic ATP formation is gradually inhibited. Phosphon-D concentrations over 0.1 mM inhibit electron transport. The uncoupling activity of phosphon-D is manifested by inhibition of noncyclic ATP synthesis and by stimulation of light-induced electron flow. The inhibition of ATP synthesis drastically decreases photosynthetic carbon assimilation in a reconstituted spinach chloroplast system. The two ATP-dependent kinase reactions of the reductive pentose phosphate cycle become the rate-limiting steps. On the other hand a stimulated photoelectron transport increases the NADPH/NADP+ ratio, resulting in a drastic inhibition of chloroplast glucose-6-phosphate dehydrogenase (EC 1.1.1.49), the key enzyme of the oxidative pentose phosphate cycle. When light-induced electron flow is inhibited by high phosphon-D concentrations and the NADPH/NADP+ ratio is low, the light-dependent inhibition of glucose-6-phosphate dehydrogenase is gradually abolished.Abbreviations AMO-1618
2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride
- B-Nine
N-dimethylaminosuccinamic acid
- CCC
(2-chloroethyl)-trimethylammonium chloride
- DCMU
3-(3,4-dichlorophenyl)-1, 1-dimethyl urea
- DCPIP
dichlorophenolindophenol
- G-6-PDH
glucose-6-phosphate dehydrogenase
- FBP
fructose bisphosphate
- F-6-P
fructose-6-phosphate
- 3-PGA
3-phosphoglyceric acid
- Posphon-D
tributyl-2,4-dichlorobenzylphosphonium chloride
- PMP
pentose monophosphates
- PPC
pentose phosphate cycle
- RuBP
ribulose bisphosphate
- Ru-5-P
ribulose-5-phosphate
Dedicated to Prof. Dr. Drs.h.c. Adolf Butenandt on the occasion of his 75. birthday |
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Keywords: | Chloroplast Glucose-6-phosphate dehydrogenase Growth retardants NADPH/NADP+ ratio Phosphon-D Spinacia Uncoupler |
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