J Plant Growth Regul (1995) 14:211-218 Journad of 'Plant G 'owth gulation 9 1995 Springer-Verlag NewYorkInc. Involvement of Abscisic Acid in Photosynthetic Process in Hordeum vulgare L. during Salinity Stress Losanka P. Popova,* Zhivka G. Stoinova, and Liliana T. Maslenkova Institute of Plant Physiology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria Received June 28, 1995; accepted November 9, 1995 Abstract. In Hordeum vulgare L. plants, NaCI stress imposed through the root medium for a pe- riod of 8 days decreased the rate of CO2 assimila- tion, the chlorophyll and protein leaf content, and the activity of ribulose-l,5-bisphosphate carboxyl- ase. The activity of phosphoenolpyruvate carbox- ylase was twofold over the control. Pretreatment with abscisic acid (ABA) for 3 days before saliniza- tion diminished the inhibitory effect of NaCI on the rate of CO2 fixation. The leaf Na § and C1- content decreased in ABA-pretreated plants. Both ABA and NaC1 treatments led to an increase in the en- dogenous level of ABA in the plant leaves. Patterns of total proteins extracted from the leaves of control or ABA- and salt-treated plants were compared. Both ABA and NaCI induced marked quantitative and qualitative changes in the polypeptide profiles concerning mainly the proteins with approximately equal mobility. The results are discussed in terms of a possible role of ABA in increasing the salt toler- ance when ABA is applied to the plants for a short period before exposure to salinity stress, thus im- proving the invulnerability to unfavorable condi- tions. Among environmental stresses NaCI salinity is one of the main limitations to the growth and photosyn- thesis of nonhalophytic plants. The extent of this Abbreviations: RuBPC, ribulose-l,5-bisphosphate carboxylase; PSII, photosystem It; ABA, abscisic acid; PEPC, phosphoe- nolpyruvate carboxylase; DTTr, dithiothreitol; BSA, bovine se- rum albumin; ELISA, enzyme-linked immunosorbent assay; SDS, sodium dodecyl sulfate; PAGEr, polyacrylamide gel elec- trophoresis. *Author for correspondence: Institute of Plant Physiology, Bul- garian Academy of Sciences, Acad. G. Bonchev Str., Bldg. 21, 1113 Sofia, Bulgaria. inhibition is correlated to the extent of NaCI salin- ity, the plant species sensitivity, and the environment. Physiologic and biochemical responses to NaCI salinity include lowered leaf water potentials, in- creased stomatal resistance, altered ion relations, and slower net CO2 assimilation rates (Bethke and Drew 1992, Greenway and Munns 1980, Poljakoff- Mayber and Gale 1975). Much of the reported re- duction of CO2 assimilation can be attributed to the direct effect of salinity on the biochemical reactions of photosynthesis, e.g. reduced activity of ribulose- 1,5-bisphosphate carboxylase (RuBPC) (Miteva and Vaklinova 1991, Seemann and Sharkey 1986), inhi- bition of photosynthetic electron transport and PSII activity (Maslenkova et al. 1991, Mohanty and Sa- radhi 1992), deleterious effects on structural and functional integrity of cell walls, cellular and inter- cellular membranes (Kurth et al. 1986, Leopold and Willing 1984), alterations in polypeptide profiles (Hurkman et al. 1989; Miteva et al. 1992, Rani and Reddy 1994), and also in gene expression (Claes et al. 1990). Moreover, unavoidable uptake of specific ions by the plants and accumulation of these in the leaves are widely assumed to result in inhibition of photo- synthesis (Seemann and Critchley 1985). There are reports of a decline in photosynthesis in glyco- phytes caused by increased Na § and C1- ion con- centration in leaves (Robinson et al. 1983). To improve salt tolerance nonhalophytic species have developed different strategies that allow plants to withstand salinity stress (see Greenway and Munns 1980 for review). The tolerance of certain plants to conditions of stress, particularly osmotic stress, appears to be re- lated to their capacity to produce a high level of abscisic acid (ABA). Elevated levels of ABA have been reported as a result of water stress (Henson and Quarrie 1981) and salt stress (Downton and Loveys 1981, Walker and Dumbroff 1981).