Abstract
Citric acid may be involved in plant response to high temperature. The objective of this study was to investigate whether exogenous citric acid could improve heat tolerance in a cool-season turfgrass species, tall fescue (Lolium arundinaceum), and to determine the physiological mechanisms of citric acid effects on heat stress tolerance. The grasses were subjected to four citric acid levels (0, 0.2, 2, and 20 mM) and two temperature levels (25/20 and 35/30 ± 0.5°C, day/night) treatments in growth chambers. Heat stress increased an electrolyte leakage (EL) and malonaldehyde (MDA) content, while reduced plant growth, chlorophyll (Chl) content, photochemical efficiency (Fv/Fm), root activity and antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD). External citric acid alleviated the detrimental effects of heat stress on tall fescue, which was evidenced by decreased EL and MDA content, and improved plant growth under stress conditions. Additionally, the reduction in Chl content, Fv/Fm, SOD, POD, CAT and root activity were ameliorated in citric acid treated plants under heat stressed conditions. High temperature induced the expression of heat shock protein (HSP) genes, which exhibited greater expression levels after citric acid treatment under heat stress. These results suggest that exogenous citric acid application may alleviate growth and physiological damage caused by high temperature. In addition, the exogenously applied citric acid might be responsible for maintaining membrane stability, root activity, and activation of antioxidant response and HSP genes which could contribute to the protective roles of citric acid in tall fescue responses to heat stress.
Highlights
High temperature is becoming one of the major factors limiting the growth and development of cool-season turfgrass (Larkindale and Huang, 2004)
To investigate the relationship between heat stress and citric acid content, the endogenous citric acid levels in leaves of tall fescue were quantified after treatments with high temperature (35/30 ± 0.5◦C, day/night) for 15 days
Leaf electrolyte leakage (EL) and MDA in tall fescue increased under heat stress, but exogenous application of citric acid reduced lipid peroxidation, as indicated by the less accumulation of MDA and lower EL when compared to the untreated plants (Figure 3).These results suggested that application of citric acid would reduce loss of grasses under high temperature environments by mitigating oxidative stress
Summary
High temperature is becoming one of the major factors limiting the growth and development of cool-season turfgrass (Larkindale and Huang, 2004). The optimal temperatures for the growth and development of cool-season turfgrass species range from 15 to 24◦C for shoots and 10 to 18◦C for the roots (Paulsen, 1994); in transitional and warm climatic regions, Abbreviations: CAT, catalase; Chl, chlorophyll; EDTA, ethylene diaminetetra acetic acid; EL, electrolyte leakage; Fv/Fm, photochemical efficiency; HSP, heat shock protein; HMW-HSP, high molecular weight-HSP; HSP74.8, heat shock protein 74.8; HSC70, heat shock protein cognate 70; LMW-HSP, low molecular weight-HSP; MDA, malondialdehyde; NBT, nitro blue tetrazolium; PAR, photosynthetically active radiation; POD, peroxidase; ROS, reactive oxygen species; SOD, superoxide dismutase; TBA, thiobarbituric acid; TTC, triphenyl tetrazolium chloride. The enzymatic scavenging system includes SOD, which convert the superoxide radicals to hydrogen POD, and the CAT and PODs (POD), which trigger the conversion of H2O2 to water and oxygen (Mittler, 2002)
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