Light regulation of NADP-isocitrate dehydrogenase isoforms functioning in maize leaves

Abstract

Light is the most important regulator of the process of photosynthesis, and the Krebs cycle closely related to it. Light regulation has been established for many enzymes, including the enzymes of the tricar-boxylic acid cycle, the phytochrome system also can be involved in the process of light regulation. NADP-isocitrate dehydrogenases of higher plants (NADP-IСDH, EC 1.1.1.42) are a complex of enzymes localized in the cytosol, mitochondria, chloroplasts, and peroxisomes, which can be involved in the adaptation of plants to a change in light regime. This study is devoted to the investigation of the isocitrate dehydrogenase system under conditions of changing light regime in maize leaves. The enzyme activity was measured spec-trophotometrically; differential centrifugation was used for the investigation of subcellular localization. The isozyme composition was determined by PAGE. The effect of the phytochrome system on the activity of the cytosolic, chloroplast, and mitochondrial isoforms of NADP-IDH was studied by modelling the effect of light of different wavelengths on maize plants. The dependence of the activity of NADP-IСDH from maize leaves during the germination stage was established. The peak of activity of the cytosolic form was observed on the fifth day of germination, while the peak of activity of the mitochondrial form was observed on the fourth day, and the chloroplast isoform had maximal activity on the eighth day of germination of maize seeds. It was shown the differential activity of NADP-IСDH isoforms in maize leaves during development was due to their different functions in the plant cell. Subcellular localization of NADP-IDH was demonstrat-ed and the activity in subcellular fractions was determined. It was revealed that the dominant activity is pre-sent in the cytosol, accounting for 72% of the total activity. The light regulation of NADP-ICDH isoforms was investigated. An increase in the activity of the cytosolic and chloroplast isoforms in maize leaves was revealed under red light with a wavelength of 660 nm (RL), while for the mitochondrial isoform, a decrease in activity was observed under RL. Irradiation with far red light, 730 nm (FRL), removed this effect for both isoforms. The obtained results indicate the involvement of the phytochrome system in the regulation of the activity of the cytosolic, chloroplast, and mitochondrial isoforms of NADP-ICDH in maize leaves under the changed light pattern.