The role of photorespiration in redox and energy balance of photosyntheticplant cells: A study with a barley mutant deficient in glycine decarboxylase

Citation
Au. Igamberdiev et al., The role of photorespiration in redox and energy balance of photosyntheticplant cells: A study with a barley mutant deficient in glycine decarboxylase, PHYSL PLANT, 111(4), 2001, pp. 427-438
Citations number
57
Categorie Soggetti
Plant Sciences","Animal & Plant Sciences
Journal title
PHYSIOLOGIA PLANTARUM
ISSN journal
00319317 → ACNP
Volume
111
Issue
4
Year of publication
2001
Pages
427 - 438
Database
ISI
SICI code
0031-9317(200104)111:4<427:TROPIR>2.0.ZU;2-5
Abstract
Protoplasts and mitochondria were isolated from leaves of homozygous barley (Hordeum vulgare L,) mutant deficient in glycine decarboxylase complex (GD C, EC 2.1.2.10) and wild-type plants. The photosynthetic rates of isolated protoplasts from the mutant and wild-type plants under saturating CO, were similar, but the respiratory rate of the mutant was two-fold higher. Respir ation in the mutant plants was much more strongly inhibited by antimycin A than in wild-type plants and a low level of the alternative oxidase protein was found in mitochondria, The activities of NADP- and NAD-dependent malat e dehydrogenases were also increased in mutant plants, suggesting an activa tion of the malate-oxaloacetate exchange for redox transfer between organel les. Mutant plants had elevated activities of NADH- and NADPH-dependent gly oxylate/hydroxypruvate reductases, which may be involved in oxidizing exces s NAD(P)H and the scavenging of glyoxylate. We estimated distribution of po ols of adenylates, NAD(H) and NADP(H) between chloroplasts, cytosol and mit ochondria. Under photorespiratory conditions, ATP/ADP and NADPH/NADP ratios in the mutant were higher in chloroplasts as compared to wild-type plants. The cytosolic NADH/NAD ratio was increased, whereas the ratio in mitochond ria decreased. It is concluded that photorespiration serves as an effective redox transfer mechanism from the chloroplast, Plants with a lowered GDC c ontent are deficient in this mechanism, which leads to over-reduction and o ver-energization of the chloroplasts.