Inactivation of a plastid evolutionary conserved gene affects PSII electron transport, life span and fitness of tobacco plants

Abstract

• Chloroplasts contain a plastoquinone-NADH-oxidoreductase (Ndh) complex involved in protection against stress and the maintenance of cyclic electron flow. Inactivation of the Ndh complex delays the development of leaf senescence symptoms. • Chlorophyll a fluorescence measurements, blue native gel electrophoresis, immunodetection and other techniques were employed to study tobacco (Nicotiana tabacum) Ndh-defective mutants (ΔndhF). • The ΔndhF mutants compared with wild-type plants presented: (i) higher photosystem II : photosystem I (PSII : PSI) ratios; (ii) similar or higher levels of ascorbate, carotenoids, thylakoid peroxidase and superoxide dismutase, yield (ΦPSII) and maximal photochemical efficiency of PSII levels (Fv/Fm) than wild-type plant leaves of the same age; (iii) lower values of nonphotochemical quenching yield (Φ NPQ), but not at very high light intensities or during induced leaf senescence; (iv) a similar decrease of antioxidants during senescence; (v) no significant differences in the total foliar area and apical growth rate; and (vi) a production of viable seeds significantly higher than wild-type plants. • These results suggest that the Ndh complex is involved in one of the redundant mechanisms that play a safety role in photosynthesis under stress, which has been conserved during evolution, but that its deletion increases fitness when plants are grown under favourable controlled conditions. © The Authors (2007).