Effects of exogenous proline and trehalose on physiological responses in rice seedlings during salt-stress and after recovery

Abstract

Two osmoprotectants (proline – Pro; trehalose – Tre) were exogenously supplied to seedlings of rice cvs. Pokkali (PK – salt-tolerant) and Khao Dawk Mali 105 (KDML105 – salt-sensitive) to investigate their effects on plants exposed to 200 mmol/L NaCl for 6 days and 5 days after recovery from stress. The reduction of growth, increase in Na<sup>+</sup> to K<sup>+</sup> ratio, high level of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) content, enhanced activity of antioxidant enzymes (superoxide dismutase – SOD, peroxidase – POX, catalase – CAT and ascorbate peroxidase – APX) were observed in both rice cultivars under NaCl treatments. Exogenous Pro and Tre supplement to NaCl-stressed plants did not mitigate the reduction of growth during salt-stress. Nevertheless, during recovery plants previously supplied with Tre showed markedly higher percentage of growth recovery than those treated with NaCl alone or supplied with Pro. The beneficial effect of Tre on growth recovery was clearly demonstrated in KDML105 in which growth enhancement was related to reduction in Na<sup>+</sup> to K<sup>+</sup> ratio. Exogenous Pro was able to reduce H<sub>2</sub>O<sub>2</sub> in both cultivars during salt stress whereas Tre could reduce it only in KDML105. Exogenous Tre did not enhance any antioxidant enzymes during stress but enhanced APX activity in KDML105 during recovery. Exogenous Pro enhanced the activity of APX in PK, and POX, CAT and APX in KDML105 during both stress and recovery period.