Effects of gibberellic acid on photosynthesis and endogenous hormones of Camellia oleifera Abel. in 1st and 6th leaves

Abstract

ABSTRACTTo investigate the effects of gibberellic acid (GA) on photosynthesis, nutrient partitioning and endogenous hormones at different leaf locations (1 and 6), Camellia oleifera was treated with four levels of GA (0, 100, 200 and 300 mg L−1) during the flower bud physiological differentiation stage. GA increased the net photosynthetic rate (Pn), chlorophyll content and chlorophyll fluorescence parameters of 1st and 6th leaves. The 100 mg L−1 dose was most effective for increasing the total chlorophyll content and Pn, which increased by 100.00% and 59.55%, respectively, in the 1st leaf, and 110.18% and 44.90%, respectively, in the 6th leaf compared with the control. The 100 and 200 mg L−1 GA solutions decreased the starch and soluble sugar levels in both 1st and 6th leaves, but increased those of the 1st and 6th buds which suggested that exogenous GA promotes the transportation of photosynthetic products from leaves to buds with the regulation of a sink–source relationship. Endogenous levels of gibberellin and auxin increased, but abscisic acid decreased in the 1st and 6th leaves after GA applications. The Pn was positively correlated with the total chlorophyll content (0.922 for 1st leaf and 0.944 for 6th leaf) and fluorescence parameters, but negatively correlated with soluble sugar and starch contents in 1st (−0.940 and −0.875, respectively) and 6th (−0.866 and −0.854, respectively) leaves. The difference in responses of leaves at different positions to exogenous GA due to the physiological differences of the leaves themselves.