Effects Of Exogenous Glycinebetaine And5-Aminolevulinic Acid On Drought Tolerance In Tall Fescue

Two tall fescue cultivars’Zhengyi’and’Lingzhi’were used as materials to study effects of exogenous glycinebetaine (GB) and5-aminolevulinic acid (ALA) on improving turf quality under well-watered and drought conditions.Foliar treatments of GB and ALA were applied to plants at3d and1d before exposure to different water treatments, respectively.Here we measured the physiological indexs and biochemical indicators to examine the underlying mechanisms for the improved turf quality. Results were as follows:1) Drought stress gradually reduced the turf quality (TQ) of two cultivars. Exogenous GB and ALA, to some extent, alleviated drought-induced decline of two cultivars in TQ. Also,’Zhegnyi’with GB had higher TQ than ALA,while’Lingzhi’with ALA had higher TQ than GB.Under well-watered conditions, both GB and ALA had some active effects on TQ.2) Under drought stress, relative water content (RWC) of two cultivars decreased with treatment time. Foliar application of GB inhibited the downward trend of RWC, with better significance on ’Zhengyi’. Wherase, exogenous ALA did not affect RWC of two cultivars. Under well-watered conditions, both GB and ALA had no effect on RWC in two cultivars.3) Electrolyte leakage (EL) of two cultivars increased along with time. And application of GB and ALA alleviated this rising trend. GB had a good effect on both varieties with a significant difference with the control under drought stress,indicating GB had a better effect on maintaining the stability of cell membrane.4) Drought induced the decline of photosynthetic pigment content. Under drought stress, the foliar treatments of GB and ALA could increase the pigment content, of which GB had better improvement of the pigment content in ’Zhengyi’, while the effect of ALA was better on ’Lingzhi’. Under well-watered conditions, both GB and ALA helped increase the content of photosynthetic pigment, but ALA was more obvious than GB.5) Drought stress reduced the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as the content of ascorbate (AsA) and glutathione (GSH). Also drought stress caused lipid peroxidation in cell membrane with higher content of oxidative product malondialdehyde (MDA).6) Under drought stress, foliar applications of GB and ALA had a positive role of improving the activities of SOD,CAT and APX and increasing the content of AsA and GSH, resulting in less reactive oxygen species (ROS) and MDA. Thus, exogenous GB and ALA enhanced the drought tolerance by increasing the activity of antioxidant system. However, under well-watered condition, both GB and ALA had no influence on antioxidant system of two varieties.7) GB had better effect on the activity of antioxidant system in variety’Zhengyi’but ALA improved the antioxidant system activity of ’Lingzhi’ highly, suggesting different varieties with different response to the same hormone.