Improvement of plant heat tolerance by modification of xanthophyll cycle activity

Plants are sessile organisms hence environmental factors such as excessive light and high air temperature lead to significant reductions of their productivity and quality of gained yield. In fact, scientific and agriculture hubs make lots of efforts to improve crop tolerance to elevated temperature, selecting more tolerant varieties. We analyzed less expensive and highly efficient method to improve resistance of well-known cultivars of crop plant by reversible modification of xanthophyll cycle. It functions as a safety valve to adjust energy transfer and protects fragile structures of photosynthetic machinery from excessive light, especially accompanied by heat or water stress. Efficiency of modified xanthophyll cycle activity was measured after pre-treatment with four, chemically different regulators, with or without light illumination. Analyses were carried out on barley (Hordeum vulgare L.) cv. Zenek treated with ascorbic acid (AsA), dithiothreitol (DTT), putrescine (Put) and calcium ions (Ca2+). To measure the scale of thermal energy dissipation we traced energy transfer absorbed by PSII with PAM chlorophyll fluorescence technique. Results showed clear correlation between AsA (activator of violaxanthin de-epoxidase) treatment and stimulation of the Φ(NPQ) at increased temperature. DTT (inhibitor of violaxanthin de-epoxidase) decreased the cycle activity at 45 °C at the same time increasing its value at 35°C, caused by interaction with other enzymes. Action of Put (hydrogen ions buffer) concerned mainly a non regulated Φ(NO) energy quenching. We noticed that application of Ca(NO3)2 (Ca2+ source for enzyme activity) reduced the Φ(NPQ) at 45 °C and stimulated it at 25 °C. Obtained results confirmed postulated possibility of creating new type of plant protection products (PPPs) able to precisely manage natural mechanisms of heat resistance.