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Regulation of cyclic electron flow in C 3 plants: differential effects of limiting photosynthesis at ribulose‐1,5‐bisphosphate carboxylase/oxygenase and glyceraldehyde‐3‐phosphate dehydrogenase
Ist Teil von
Plant, cell and environment, 2010-11, Vol.33 (11), p.1779-1788
Erscheinungsjahr
2010
Quelle
Wiley Online Library
Beschreibungen/Notizen
ABSTRACT
Cyclic electron flow around photosystem I (CEF1) is thought to augment chloroplast ATP production to meet metabolic needs. Very little is known about the induction and regulation of CEF1. We investigated the effects on CEF1 of antisense suppression of the Calvin–Benson enzymes glyceraldehyde‐3‐phosphate dehydrogenase (gapR), and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU), in tobacco (
Nicotiana tabacum
cv. Wisconsin 38). The gapR, but not ssuR, mutants showed substantial increases in CEF1, demonstrating that specific intermediates, rather than slowing of assimilation, induce CEF1. Both types of mutant showed increases in steady‐state transthylakoid proton motive force (
pmf
) and subsequent activation of the photoprotective
q
E
response. With gapR, the increased
pmf
was caused both by up‐regulation of CEF1 and down‐regulation of the ATP synthase. In ssuR, the increased
pmf
was attributed entirely to a decrease in ATP synthase activity, as previously seen in wild‐type plants when CO
2
levels were decreased. Comparison of major stromal metabolites in gapR, ssuR and
hcef1
, a mutant with decreased fructose 1,6‐bisphosphatase activity, showed that neither the ATP/ADP ratio, nor major Calvin–Benson cycle intermediates can directly account for the activation of CEF1, suggesting that chloroplast redox status or reactive oxygen species regulate CEF1.