Title : Physiological and Biochemical characterization of GABA shunt pathway in pea Pisum sativum L. seedlings under drought stress
The physiological and biochemical role of γ-aminobutyric acid (GABA) shunt pathway in green pea seedlings (Pisum sativum L.) was studied in response to soil water holding capacity levels: 80%, 60%, 40%, 20% and 10% grown under continuous light at 25ºC for 7 days and 14 days, separately. Characterization of seeds germination pattern, seedlings growth (plant height, fresh weight, dry mass and chlorophyll contents), GABA shunt metabolite levels (GABA, glutamate and alanine), total proteins and total carbohydrates level and oxidative damage (MDA level) were examined. Data showed significant effect of drought stress on seed germination, plant growth, GABA shunt metabolite level, total proteins and carbohydrates contents and MDA level. A significant decline in seed germination percentage was recorded at 20% drought level, which indicated that 20% of soil water holding capacity is the threshold value of water availability for normal germination after 14 days. Seedling fresh weight, dry mass and plant height were significantly reduced with positive correlation as water availability was decreased. There was a significant decrease with positive correlation in Chl a and Chl b content in response to 7 days and 14 days of drought. GABA shunt metabolites were significantly increased with negative correlation as water stress increased. Pea seedlings showed significant increase in protein content as drought stress was increased. Total carbohydrates level increased significantly when amount of water availability decreased. MDA content increased slightly but significant after 7 days and sharply after 14 days under all water stress levels. The maximum increase in MDA content was observed at 20% and 10% water levels. Results presented in this study indicated that pea seedlings suffered minor damage under mild drought stress but severe lipid peroxidation and oxidative damage occurred as water deficit increased. The elevated level of GABA metabolites, soluble sugars and total proteins under water stress might be involve in cellular osmotic adjustment, protecting plants from oxidative stress, balancing of Carbon and Nitrogen (C:N) metabolism and maintaining cell metabolic homeostasis and cell turgor.