Modulation of light spectrum affects the physiology of beet (Beta vulgaris L.) plants irradiated with heavy ions

Manipulation of the light spectrum during growth can induce changes in photosynthesis, biomass production and in the synthesis of metabolites that defend plants against abiotic stress. In this study, beet (Beta vulgaris L.) plants were grown from seeds irradiated with 10 Gy Carbon (C) or Titanium (Ti) and from non-irradiated control seeds under three different light quality regimes: RGB (33:33:33 Red-Green-Blue), RB (66:33 Red-Blue) and white light (WL). The impact of light quality and ionising radiation on plant growth and photosynthetic and antioxidant metabolism was monitored across plant development and until harvesting. Under WL, both plants from ions irradiated seeds (IS plants) showed a significant reduction of photosynthesis and stomatal conductance compared to non-irradiated controls. However, under RGB and RB light, photosynthesis of IS and control plants was similar. In IS plants, growth under RB stimulated total biomass, shoot and root elongation and anthocyanins production, compared to controls, while no difference was observed under RGB and WL. The RGB treatment induced higher levels of antioxidant and protein content in IS plants compared to control. A significant reduction of these parameters was observed under the other light regimes. In plants from C-irradiated seeds growth under RGB and RB determined a higher sugar production compared to WL, whereas in plants from Ti- irradiated seeds sugars decreased under RGB light. In conclusion, our study indicates that growth under light enriched with red and blue components of the spectrum can promote biosynthesis of valuable traits, such as antioxidants, proteins and sugars, that may help plants tolerate ionising radiations.