Genotypic Variation of Rubisco Expression, Photosynthetic Electron Flow and Antioxidant Metabolism in the Chloroplasts of Chill-exposed Cucumber Plants
2006
Zhou, Yan-Hong | Mao, Wei-Hua | Huang, Lifeng | Song, Xing-Shun | Nogues, Salvador
Genetic improvement of agronomic crops is necessary to cope with chilling stress. To identify the physiological factors responsible for this genotypic difference in chill-induced inhibition of photosynthesis, leaf CO₂ assimilation, the electron flux in the chloroplast and the antioxidant metabolism in isolated chloroplasts were examined in two genotypes of cucumber (Cucumis sativus) plants with distinct chilling tolerance. Cucumber plants were exposed to 100 [micro]mol m⁻² s⁻¹ at 9/7°C (day/night) for 10 d and were then returned to optimal conditions for 2 d. Chilling resulted in more significant reductions in rbcL and rbcS transcripts, ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) content and initial Rubisco activity, leading to higher electron flux to O₂ in the chilling-sensitive genotype than in the chilling-tolerant genotype. The chilling-tolerant genotype showed lower H₂O₂ contents in the chloroplasts by maintaining higher H₂O₂-scavenging activity in the chloroplasts than in the chilling-sensitive genotype. H₂O₂ accumulation in chloroplast was negatively correlated with the initial Rubisco activity and photosynthetic rate.
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