Physiological response to salinity in rice [Oryza sativa] plant, 4: Ion exclusion in the excised root exposed to NaC1 stress with hydraulic pressure
1995
Tsuchiya, M. (Okayama Univ. (Japan). Faculty of Agriculture) | Miyake, M. | Boilla, P. | Kumano, S.
Ion exclusion in excised nodal root of rice (Oryza sativa L. cv. Kala-Rata 1-24) exposed to NaCl stress with hydraulic pressure was studied. The effects of collecting the exudate from the stele instead of the whole cut-surface of the root, making holes to penetrate the cell layers of the epidermis, exodermis and cortical sclerenchyma, and partial coating of root surface with epoxy resin on the ion exclusion rate were investigated under 20 mmol l(-1) NaCl at 490 kPa. Na+ and Cl- concentrations of the exudate from the stele and whole cut-surface of excised sorghum and corn roots were also measured and their ion exclusion capacities were compared with rice roots. Moreover, the effects of hydraulic pressure, temperature, pH, dissolved air content and ion constituent in the solution surrounding the root, and metabolic inhibitors on the ion exclusion rate were investigated. The exclusion rate was the highest in corn, followed by sorghum then rice. It increased when exudate was collected from the stele and decreased when cell layers from the epidermis to cortical sclerenchyma were holed. It was higher in the older tissues of the root compared with the tip. Though high pressure led to a higher exclusion rate, high temperature and high pH degraded the roots and lowered the rate. Deaerated solution also decreased the rate. The exclusion rate of different ions was in the same order as the radius of the hydrated ion, i.e. Mg(2+) Ca(2+) Na(+) Cl(-) K(+). The roots treated with 0.5 mmol l(-1) 2,4-dinitrophenol or sodium azide showed a negative linear correlation between the flow rate of the exudate and the Na+ exclusion rate. This suggests that the barrier against the inflow of ions broke down, consequently, that the ion selectivity of roots was lost
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