Effects of light intensity and temperature on chlorophyll fluorescence in leaves of basil seedlings

In this paper, taking Ocimum basilicum ‘purple ruffles’ and O.cimun gratissimum seedlings at different anthocyanin contents in leaves of two varieties as test material, effects of anthocyanin in leaves on chlorophyll fluorescence and light energy distribution in leaves of O.basilicum seedlings exposed to low (200 μmol·m-2·s-1) and high (1 000 μmol·m-2·s-1) light intensity after low temperature at 4 ℃ in dark for 3 hours were studied. The results showed that fluorescence parameters in leaves of O.gratissimum seedlings at low temperature were essentially unchanged under low light. The quantum yield of photochemistry (YPSⅡ) in leaves of O.basilicum ‘purple ruffles’ seedlings under low light after low temperature was lower than that under high light. However, the quantum yield of trans-thylakoid pH gradient and xanthophyll-regulated thermal energy dissipation (YNPQ) was higher than that of high light. It indicated that responses of O.basilicum ‘purple ruffles’ and O.gratissimum seedlings to low light were different. The low light was beneficial to promote recovery in leaves of O.gratissimum seedlings after releasing low temperature stress, and low light led to O.basilicum ‘purple ruffles’ seedlings to extend recovery time from low temperature. The Fv/Fm in leaves of O.gratissimum seedlings was decreased under high light after low temperature, and photoinhibition in leaves of O. gratissimum seedlings was occurred. Photoinhibition in leaves of O.basilicum ‘purple ruffles’ seedlings was not occurred under high light because of the high content of anthocyanins in leaves, which played the role of the light attenuation and filtration. The high light decreased of YPSⅡ and increased quantum yield of thermal dissipation associated with the presence of non-functional PSⅡ (YNF) in leaves of O.gratissimum seedlings after low temperature, while high light resulted in the increase of YPSⅡ and the decrease of YNPQ in leaves of O.basilicum ‘purple ruffles’ seedlings after low temperature pretreatment. It concluded that anthocyanin in leaves of O.basilicum ‘purple ruffles’ played a role in plant photoprotective mechanisms.