Biochemical and physiological response of borage to seed priming and water deficit: antioxidant enzymes, osmolytes, photosynthetic pigments, and fluorescence parameters

Aim of study: To investigate the general response patterns of the borage plant to water fluctuations from a biochemical and physiological perspective. Area of study: East Azerbaijan Province of Iran during the period 2012 and 2013. Material and methods: The study investigated the effects of irrigation (after 60, 90, 120 and 150 mm evaporation) and priming (unprimed, and primed seeds with water, 1% KNO3 and 1% KH2PO4) on the antioxidant enzymes, osmolytes, photosynthetic pigments, and fluorescence parameters of borage using a Split-plot experimental design. Main results: The statistical analyses showed no effect of seed priming on all evaluated traits other than mitochondrial superoxide dismutase 3 (SOD3) activity where it was significantly enhanced by seed pretreatment with 1% KNO3 and 1% KH2PO4. However, irrigations after 120 and 150 mm evaporation increased SOD1, SOD2, and SOD3, soluble sugars, and initial fluorescence (F0). The mean contents of Ch a, Ch b, and Ch a+Ch b under mild, moderate and severe water deficit were significantly higher than those under normal irrigation. Severe drought stress gave the highest carotenoids content and quantum yield baseline parameter (F0/Fm) of borage leaves. However, water limitation decreased Chl a/Chl b ratio, maximum primary yield of photosystem II (Fv/F0), and maximum quantum yield of photosystem II (Fv/Fm). Research highlights: Based on these findings, it is postulated that the increase in soluble sugars and SOD activity under stress, and the accumulation of carotenoids under severe water limitation indirectly enhance the tolerance of borage plants to drought stress.