The Use of14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves ofOryza sativaL.

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Abstract
Yeo, A. R., Yeo, M. E., Caporn, S. J. M., Lachno, D. R. and Flowers, T. J. 1985. The use of 14C-ethane diol as a quantitative tracer for the transpirational volume flow of water and an investigation of the effects of salinity upon transpiration, net sodium accumulation and endogenous ABA in individual leaves of Oryza sativa L.—J. exp. Bot. 36: 1099–1109. Oryza sativa L. (rice) seedlings growing in saline conditions exhibit pronounced gradients in leaf sodium concentration which is always higher in the older leaves than the younger ones. Individual leaf transpiration rates have been investigated to discover whether movement of sodium in the transpiration stream is able to explain these profiles from leaf to leaf. The use of 14C labelled ethane diol to estimate transpiration was evaluated by direct comparison with values obtained by gas exchange measurements. Ethane diol uptake was linearly related to the transpirational volume flow and accurately predicted leaf to leaf gradients in transpiration rate in saline and non-saline conditions. 14C-ethane diol and 22NaCl were used to compare the fluxes of water and sodium into different leaves. The youngest leaf showed the highest transpiration rate but the lowest Na accumulation in saline conditions; conversely, the older leaves showed the lower transpiration rates but the greater accumulation of Na. The apparent concentration of Na in the xylem stream was 44 times lower into the younger leaf 4 than into the older leaf 1. Exposure to NaCl (50 mol m−3) for 24 h elicited an increase in endogenous ABA in the oldest leaf only, but no significant changes occurred in the younger leaves.