Abstract
Rice (Oryza sativa L.) plants are influenced by salinity, which is a global soil problem. Plants utilise different mechanisms to regulate solute homeostasis and to balance cellular water transport. The objective of the current study was to investigate the presence of any potential role of dopamine (D, a natural product synthesised in the catecholamine pathway from tyrosine) in enhancing salinity tolerance in two-month-old rice (Oryza sativa L.) plants through modulating the plasma membrane intrinsic proteins (PIPs). Using RT-PCR technique, the level of OsPIP 1-3 expression was up-regulated in response to mild salt treatment (0.15 M NaCl), but gene expression was considerably down regulated in response to dopamine, indicating the possible regulatory role of dopamine in water permeation. Relative water content in stressed rice plants was highly retrieved in response to 0.2 mu gml(-1) dopamine. The content of pigment and proline was regulated significantly when dopamine was administered to plants before their exposure to salt stress. Fluorescence emission spectra showed non-significant changes in 0.2 mu gml(-1)D plants and slight intensity increase in 0.4 mu gml(-1)D plants, whereas no change was detected in 0.6 mu gml(-1)D plants. Decreased sodium uptake in response to 0.4 mu gml(-1) D is explained by the low expression of PIP1-3 and, hence related to the possible block of aquaporins. A high detection of membrane stability index in stressed-rice plants pre-treated with dopamine was associated with low membrane leakage. We concluded two facts; (1) the participation of OsPIP1-3gene in water permeation in salinity-stressed rice and, (2) the role of exogenous dopamine in OsPIP1-3 gene expression regulation, which was shown to be concentration-dependent. Subsequently, dopamine applications in a few doses are recommended as cheap and potential material which ameliorates salt stress in rice plants through its effect on plasma membrane aquaporins.