Photoregulation of the Cytoplasmic PGA Dehydrogenase Complex in Wheat Leaves

Abstract

Experiments were performed with 10-day-old seedlings of wheat (Triticum aestivum L.) grown on sand saturated with Knop’s solution at a temperature of 22/18°С by natural light (16 h, 200 µmole quanta/(m² s). Phytochrome was activated by means of an array of light diodes emitting light in the red spectral region (RL, λ = 656 nm, λ_1/2 = 26 nm), inactivation was induced with an array of light diodes emitting far red light (FRL, λ = 737 nm, λ_1/2 = 30 nm). At the end of the night period (8 h), activity of the NAD-dependent PGA-dehydrogenase complex (3-phosphoglycerate: ATP phosphotransferase and D-glyceraldehyde-3-phosphate:NAD⁺ oxidoreductase) in the direction of 3-PGA → 1,3-BPG → G3P was 6.0–7.0 µmoles of oxidized NADH/(min g fr wt). At the highest dose of RL radiation (20 min, 17.6 kJ/m²) incident on intact plant leaves, enzyme activity decreased by 35–40%. Longer exposure to RL (30 and 40 min) did not cause additional changes in enzyme activity. When exposure to RL was followed by FRL (20 min, 3.00 kJ/m²), the inactivating effect of RL on the enzyme complex was negated. It was shown that 5-min-long exposure to RL already caused a decrease in the rate of NADH oxidation by 10–15%, and enzyme activity decreased linearly when the dose rose. When plants exposed to RL were accommodated in the dark for up to 120 min, the half-life of the RL-inactivated state of the NAD-PGA dehydrogenase complex was 30–45 min. Thus, a dynamic regulation of the energy-transforming phase of glycolysis in wheat leaves mediated by the phytochrome system was shown and investigated. Such a photocompetent low-energy system can operate as a regulator of total oxidative processes (glycolysis + the Krebs cycle) in the course of daily transition from dark to light and back.