PHYSIOLOGIA PLANTARUM 101: 17-22. 1997 Printed in Denmark - all rights reserved Copyright © Physiologia Plantarum 1997 ISSN 0031-9317 Endogenous abscisic acid levels are linked to decreased growth of bush bean plants treated with NaCl Elena Montero, Catalina Cabot, Juan Barcelo and Charlotte Poschenrieder Montero, E., Cabot, C, Barcelo, J. and Poschenrieder, C. 1997. Endogenous abscisic acid levels are linked to decreased growth of bush bean plants treated with NaCl. - Physiol. Plant. 101: 17-22. This paper studies the relative importance of endogenous ABA and ion toxicity in the leaf growth inhibition caused by NaCl in salt-adapted and unadapted bush beans. Ad- aptation to salt-stress was achieved by germination of seeds in 75 mM NaCl, while un- adapted plants were germinated in tap water. The adaptation process caused a transi- tory increase in leaf ABA, Na* and C\~ concentrations, while leaf expansion was in- hibited. However, when grown for 8 or 13 days in 75 mM NaCl-containing nutdent solution, primary and first trifoliolate leaves of salt-adapted plants had greater areas than those of unadapted plants. Concentrations of ABA, Na* and Cl" in these leaves were lower in adapted plants, and a strong negative correlation between leaf expan- sion growth and either leaf Na*, Cr or ABA concentrations could be established. However, in the second trifoliolate leaves only the ABA, but not the Na* or Cr, con- centrations were significantly correlated with leaf expansion. Our results suggest that salt-induced inhibition of leaf expansion growth in bush beans is mediated by ABA rather than Na* or Cr toxicity. Moreover, the increase of ABA, induced by the salt-pretreatment, seems to play an important role in limiting the accumulation of Na* and c r in the leaves, leading to adaptation of bush beans to salt-stress. Key words - Abscisic acid, bush beans, NaCl-pretreatment, Phaseolus vulgaris, salt-adapted, salt-stress. E. Montero and C. Cabot (corresponding author, fax 34-71-173184), Dept Biologia Ambiental, Univ. de les Illes Balears, Car Vallemossa, km 7.5, E-07071 Palma de Mallorca, Spain; J. Barcelo and C. Poschenrieder, Lab. Fisiologia Vegetal, Univ. Au- tonoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain. Introduction Irrigated agricultural soils, especially those of arid and semiarid regions, often have high salt concentrations, which can limit the growth of most crop plants. Wa- ter-stress, specific ion toxicity and salt-induced nutrient deficiency have been reported to be the main problems plants face in salinized soils. During the last decade many studies have been con- ducted to establish the dynamic changes in plant physio- logical parameters that occur during salinization and their correlation with growth. In short-term studies, salt-induced inhibition of shoot growth is due neither to reduced leaf turgor (Thiel et al. 1988, Yeo et al. 1991) nor to ion toxicity caused by Na"^ or Cl accumulation in the expanding tissues (Munns et al. 1988). Munns and Termaat (1986) suggest that salinity rapidly limits shoot growth by the transmission of a metabolically-derived signal from the roots. At present, there is no conclusive evidence that ABA is this signal. However, there is now considerable experimental support for the hypothesis that increased ABA levels inhibit shoot growth in salt-stressed plants (Munns and Sharp 1993). Inhibition of cell expansion growth by ABA has been related to ABA-induced inhibition of the synthesis of some cell wall components, to decreased cell wall extensibility, and to effects on enzymes involved in cell wall-loosen- ing and cell elongation (Van Volkenburg and Davies Received 7 March, 1997 Physiol. Plant. 101, 1997 17