Pairs of homozygous near-isogenic glycinebetaine-containing (Betl/Betl) and -deficient (betlhetl) F, lines of Zea mays L. (maize) were tested for differences in salt (1 50 mM NaCl or 127.25 mM NaCl plus 22.5 mM CaCI,) tolerance. The Betl/Betl lines exhibited less shoot growth inhibition (as measured by dry matter accumulation, leaf area expansion rate and/or, plant height extension rate) under salinized conditions in comparison to their nearisogenic betl/betl sister lines. These growth differences were associated with maintenance of a significantly higher leaf relative water content, a higher rate of carbon assimilation, and a greater turgor in Betl/Betl lines than in b e t l h e t l lines under salinized conditions. These results strongly suggest that a single gene conferring glycinebetaine accumulation (and/or a tightly linked locus) plays a key role in osmotic adjustment in maize. Yancey (1994) has recently discussed the roles of betaines and their sulfonio analogs as compatible solutes and in cell volume regulation. These solutes are excluded from the hydration sphere of proteins and tend to stabilize the tertiary structure of proteins (Yancey, 1994). They also prevent or reverse the disruption of the tertiary structure caused by noncompatible (perturbing) solutes such as urea (Bateman et al., 1992). It is probable that these compounds have similar functions in higher plants (Wyn Jones and Storey, 1981;Grumet and Hanson, 1986;Robinson and Jones, 1986; Rhodes and Hanson, 1993), but rigorous genetic experiments with higher plant mutants defective in betaine synthesis are needed to verify this point.Genetic tests for the role of glycinebetaine in osmotic stress resistance in Zea mays L. (maize) are now possible because of the development of a series of near-isogenic F, pairs of glycinebetaine-containing and glycinebetaine-deficient lines (Yang et al., 1995). Here we report the growth, water relations, gas-exchange characteristics, and solute compositions of these glycinebetaine-containing and gly-

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Two gramineae species, Panicum maximum and Eleusine coracana, were exposed to salinity stress and leaf water status, solute concentrations in cell sap, levels of betaine aldehyde dehydrogenase (BADH) and BADH mRNA were measured. Panicum maximum was able to maintain a high turgor and high relative water content at low leaf water potentials, and this was associated with the greater capacity for osmotic adjustment. Major osmotica in Panicum maximum leaves were Na+, Cl", sugar and glycinebetaine, and these solutes were increased by salinity. Na+ and glycinebetaine concentrations in Eleusine coracana leaves also were increased by salt stress, but these solutes were in significantly lower concentrations than those measured in Panicum maximum. BADH enzyme activity and BADH mRNA levels in Panicum maximum leaves were both increased by salt stress, and their expression coincided with the observed betaine accumulation. Although the addition of abscisic acid (ABA) to leaf disks of Panicum maximum plants also increased BADH mRNA levels, these were smaller than those observed in NaCI treated leaves.