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
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.