Rapid Response of Photosynthetic Apparatus of Triticum aestivum L. and Beta vulgaris L. to He–Ne Laser Irradiation

A comprehensive analysis of the rapid response of the photosynthetic apparatus of two botanical species, Triticum aestivum L. and Beta vulgaris L., to treatment with a low-intensity He–Ne laser (He–Ne LILR) was made for the first time. The effect of irradiation on the light phase of photosynthesis was proved to be both stressful and stimulating. Thus, the impact of He–Ne LILR on wheat and beet leaves resulted in a decrease in Fv/Fm (14 and 10%, respectively), PI_ABS (50 and 47%, respectively), and Fv/F₀ (39 and 34%, respectively), accompanied by an increase in φD₀ (30 and 42%, respectively), which suggests a reduced efficiency of photosynthesis. It was found that He–Ne LILR at the indicated doses had a less pronounced reduction in photosynthetic efficiency in beet leaves when compared to wheat leaves. The stimulating effect of He–Ne LILR on the pigments of the photosynthetic apparatus (PSA) of the studied plants was most notably manifested in the increase in the rate of carbon dioxide assimilation. It was shown that within the first hour after exposure, there was an increase in the content of pigments, specifically chlorophylls (35% for wheat and 28% for beet) and carotenoids (50% for wheat and 10% for beet), in the leaves of the plants under study. Concomitantly, the concentration ratios of these pigments decreased, which is a clear sign of the PSA returning to normal operation. The true rate of photosynthesis in laser-irradiated wheat and beet leaves increased approximately twofold 15 min after laser treatment. The results suggest that He–Ne LILR induces a stress-like reaction in the PSA of the exposed plants.