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Abstract Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψw) and osmotic potential (Ψs)decreased in response to NaCl levels. Although Ψwand Ψs decreased during salt stress, pressure potential Ψp remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m−3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na+ and Cl−. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca2+ and Mg2+ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na+ and Cl− accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars. ACKNOWLEDGMENTS This work is part of a M.S. Thesis by D.A.M., Federal University of Viçosa, Brazil 1998. D.A.M. was supported by a scholarship from CICyT-U.N.S.E., Argentina, and partially by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brasil). The authors gratefully acknowledge the contributions of Dr. Moacyr Maestri for critical reading of the manuscript.
Meloni et al. (Wed,) studied this question.