Response of leaf photosynthetic characteristics and anatomical structure of Brassica rapa seedlings to drought stress

Abstract [Objective] The study aims to investigate the effects of drought stress on the photosynthetic characteristics and anatomical structure of turnip (Brassica rapa) leaves, and to provide a basis for the selection and breeding of drought-resistant germplasm and the development of cultivation measures. [Methods] Drought-resistant and drought-sensitive turnip seedlings were selected for normal water-supply and drought-stress potting experiments to analyze the changes in leaf photosynthetic characteristics and anatomical structures. [Results] Drought stress reduced chlorophyll a, chlorophyll b, and total chlorophyll contents, net photosynthetic rate, stomatal conductance, transpiration rate, stomatal limiting values, as well as maximal fluorescence, variable fluorescence, maximal photochemical efficiency, and photochemical potential activity of turnip leaves, while the inter-cellular CO2 concentration, water-use efficiency, and initial fluorescence were increased, with greater variations in drought-sensitive germplasm. Drought also reduced leaf stomatal length, width, openness, density, and tissue laxity, while leaf thickness was increased. Drought also caused swelling of chloroplasts, blurring of basal lamellae, the appearance of cavities, and an increase in osmiophilic and amylopectin granules, while mitochondria were swollen and their internal cristae blurring, while the drought-sensitive germplasm was severely damaged. [Conclusion] Drought stress reduces stomatal opening and tissue structure laxity, increases leaf thickness, impaires the morphological structure of chloroplasts and mitochondria, and reduces the chlorophyll content and photosynthetic efficiency. The drought-resistant germplasm has stronger adaptive regulation to drought stress.