Physiological mechanism of mitigation of high temperature stress by peptide-chelated iron application in cherry radish seedling

Objectives Cherry radish (Raphanus sativus L.var. radculus Pers.) is vulnerable to high temperature induced damages. Peptide-chelated iron (T-Fe) is effective in improving the crop’s resistance and alleviating damages caused by high temperature stress as an exogenous biostimulant.The effect of different T-Fe treatment concentrations on the high temperature stress related physiological regulators was studied, which would provide support for the effective application of T-Fe in reducing the hot damage to crop.

Methods The seed soaking and irrigation experiment was conducted using cherry radish as the test crop. For the experiments, 25℃ and 30℃ without any biostimulants were used as the controls (CK0, CK), the brassin-heteroauxin-gibberellic acid treatment with concentration of 66.7 mg/L (BHG), the peptide-chelated iron treatments with 21.0, 32.0 and 48.0 mg/L (T-Fe-1, T-Fe-2, T-Fe-3) at 30℃ were set up. The plant biomass were weighed, and the content of auxin (IAA), abscisic acid (ABA) and proline (Pro), and the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), net photosynthetic rate (P_n) and transpiration rate (T_r) were measured after the cherry radish seedling grown for 28 days.

Results Comparing with CK, the IAA level of cherry radish in T-Fe-1 treatment was significantly increased by 144.2%, the biomass was increased by 26.0% and root length increased by 35.8%. The content of Pro was significantly increased by 229.9%. Meanwhile, APX activity was significantly increased by 21.7% in the antioxidant system, GR activity was significantly increased by 11.7%. There was no significant difference in superoxide anion (\rmO_\small 2^\overline \,\cdot\, ) activity, malondialdehyde (MDA) content and P_n. Compared with BHG treatment, the content of IAA was significantly increased by 141%, Pro content increased by 11.4%, the peroxidase (CAT), APX and GR activities were significantly increased by 262%, 44.7% and 19.4%, respectively, the \rmO_\small 2^\overline \,\cdot\, content was significantly reduced by18.6%. In the T-Fe-2 treatment, comparing with CK, the Pro content was significantly increased by 184%, SOD activity and GR activity were significantly increased by 366% and 19.8%, respectively, thus significantly reducing hydrogen peroxide (H₂O₂), \rmO_\small 2^\overline \,\cdot\, activity, MDA content by 41.5%, 24.2% and 76.5%, respectively, but the biomass was significantly reduced by 36.5%. In the T-Fe-3 treatment, comparing with CK, the IAA and Pro contents were significantly increased by 26.1% and 132.6%, the SOD and GR activities were significantly increased by 633.4%and 19.4%, respectively, the H₂O₂ and \rmO_\small 2^\overline \,\cdot\, activity were significantly reduced by 29.9% and 26.2%, respectively, there was no significant difference in total biomass, and the growth-promoting effect was not obvious.

Conclusions Under the experimental conditions, applying peptide-chelated iron in concentration of 21 mg/L is satisfactory in the promotion effect of plant endogenous hormone levels and proline and activity of the antioxidant system of cherry radish, which consequently alleviate the damage caused by high temperature stress significantly. The concentration higher than 21 mg/L might cause inhibition of crop growth.