Application of Exogenous Glycinebetaine Alleviates Lead Toxicity in Pakchoi ( Brassica Chinensis L.) by Promoting Antioxidant Enzymes and Suppressing Pb Accumulation

Lead (Pb) poses an adverse effect on plant growth and development. Glycinebetaine (GB) plays an important role in plants response to stress environment. The study was performed to examine the potential of exogenous GB (0.5, 1, 2, and 5 mM) in alleviating Pb toxicity, the physiological and biochemical responses in pakchoi under 100 μM Pb stress by hydroponic experiment. Pb stress significantly decreased the growth, contents of pigment and mineral nutrient, and activities of antioxidative enzymes (CAT, SOD, and APX) in roots and shoots of pakchoi, while it caused a significant increase in Pb and ROS accumulation both in roots and shoots of pakchoi in comparison to the control. Exogenous application of GB improved leaf and root length, fresh and dry weight, mineral nutrient, and pigment contents of pakchoi under Pb stress. GB also effectively enhanced antioxidative enzyme activities and the accumulation of proline, soluble sugar, and GB and reduced the oxidative stress and Pb contents in shoots and roots of pakchoi. Principle component analysis (PCA) provided useful information on the classification of Pb tolerance according to the response to GB. Overall, the 1 mM GB was more effective to ameliorate the detrimental impacts of Pb stress. These findings suggested that GB application might be considered an effective strategy for alleviating Pb toxicity and enhancing the tolerance of pakchoi plants under Pb stress.