Effects of high light exposure on leaf gas exchange parameters and xanthophyll cycle pigments in rice seedlings

Abstract

The rice seedlings of Aathira and Swarnaprabha varieties were exposed to 8 h of high light (2000 μmolm-2s-1) and the effects on leaf gas exchange parameters and interconversions of xanthophyll cycle pigments were analyzed. High light exposure resulted in decrease of net photosynthetic rate (Pn ), stomatal conductance (gs ) and transpiration rate (E) both in Aathira and Swarnaprabha leaves. However, the rate of reduction of Pn , gs and E was more prominent in Swarnaprabha than Aathira seedlings upon treatment with high light stress. The xanthophyll pigment profile analyzed by HPLC showed significant difference between Aathira and Swarnaprabha leaves after exposure to 8 h of high light irradiation. HL exposure in rice leaves led to the reduction of violaxanthin and concomitant accumulation of antheraxanthin and zeaxanthin in both Aathira and Swarnaprabha seedlings. However, conversion of violaxanthin to zeaxanthin was maximum in Aathira than Swarnaprabha leaves upon exposure to high light irradiation. Moreover, the de-epoxidation state of xanthophyll cycle pigments was enhanced while the epoxidation state of xanthophyll cycle pigments was decreased upon exposure to 8 h of high light irradiation in rice leaves. The proportion of the xanthophyll cycle pool to total chlorophyll was tremendously increased in Aathira than Swarnaprabha upon high light exposure, revealing the superior nature of Aathira variety in terms of tolerance potential towards high light exposure.