Photoregulation of the Cytoplasmic PGA Dehydrogenase Complex in Wheat Leaves
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Photoregulation of the Cytoplasmic PGA Dehydrogenase Complex in Wheat Leaves V. Yu. Lyubimova, *, V. D. Kreslavskia, and A. N. Shmareva a
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, 142290 Russia *e-mail: [email protected] Received March 3, 2020; revised March 19, 2020; accepted March 19, 2020
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, λ1/2 = 26 nm), inactivation was induced with an array of light diodes emitting far red light (FRL, λ = 737 nm, λ1/2 = 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. Keywords: Triticum aestivum, far red light, red light, NAD-phosphoglyceraldehyde dehydrogenase, phytochrome, photoregulation DOI: 10.1134/S102144372005009X
INTRODUCTION During the day, plants growing under natural conditions are exposed to different light conditions with varying energy of incident radiation and different spectral composition [1, 2]. In the morning, the I660/I730 ratio is approximately 1.5, while it is ≤1.0 in the afternoon. This circumstance probably ensures a more pronounced activation of the phytochrome system during early daylight hours. The conversion of phytochrome from PRL to PFRL form under the effect of light with a wavelength of 660 nm acts as a regulatory trigger for some intricate physiological processes, such as seed germination, flowering, and fruit bearing [3, 4]. Phytochrome control also operates in respect to some stress factors: low and high temperatures, drought, UV radiation, salinization and associated
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