Photochemical functioning of Dracocephalum kotschyi ecotypes under UVB

The objective of the present study was to determine the efficacy of chlorophyll fluorescence analysis and to understand the specific photosynthetic parameters for detection of UVB radiation and high light (HL)-induced stress in Dracocephalum kotschyi plants under low and high altitudes. Seeds of high (3,300 m) and low (2,600 m) altitude ecotypes of D. kotschyi were sown in a growth chamber. Following a 3-month acclimation period, independent pots were chosen and exposed to light intensities including 400 and HL (800 µmol m -2 s -1 ) as well as with two levels of UVB (15 and 30 kJ m -2 d -1 ) for further 10 days. High altitude plants displayed more protection to photoinhibition in comparison to low-altitude plants. Under combined stress, only in high altitude plants, the levels of carotenoids correlated well with the maximal quantum yield of photosystem II (F v /F m ), suggesting that the accumulation of antioxidant metabolites including carotenoids play a key role in enhancing resistance to stresses. Under combined stress condition, low-altitude plants exhibited the occurrence of photoinhibition, which was assessed by the analysis of F v /F m . Additionally, in low-altitude plants, under combined stress, IP-phases from the OJIP curve decreased due to a decrease in electron transport towards PSI. To sum up, this study explored the key OJIP parameters that can be used for distinguishing primary mode of action of HL and UVB on photosystem II in different D. kotschyi populations.