Role of Changes in Solute Concentration in Maintaining Favorable Water Balance in Field-Grown Cotton1
- J. M. Cutler,
- D. W. Rains and
- R. S. Loomis2
Cotton (Gossypium hirsutum L.) shows various adaptive responses to water deficits, including alterations in cellular osmotic concentrations. The role of changes in solute concentration in maintaining favorable water balance in field-grown cotton was evaluated under wet and dry irrigation treatments. The experiments were conducted with a fine loamy mixed, calcareous thermic-Typic Torriorthents soil in a semi-arid environment. Leaf diffusive resistance, measured by a resistance porometer, was unaffected by leaf water potential (down to −29 bars in adapted leaves of the dry treatment) while the typical response to light was maintained. Leaf blade elongation rate was less in plants with low leaf water potential. The rate was maximal in the early evening and depressed during the midday water potential minimum and at night. Some blade enlargement occurred during time intervals when leaf water potentials were as low as −19 to −23 bars. The osmotica of primary importance in cotton leaves were K, nitrate, citrate, malate, and sugars; K and other soluble inorganic leaf constituents did not vary diurnally or with plant status. In contrast, sugar and malate concentrations (expressed on a dry weight basis) were 20 to 60% greater in leaves from the dry treatment than in leaves from the frequently irrigated treatment. In addition, diurnal variations in sugars and malate followed the variation in leaf water potential, with a slight lag, and a simple model of leaf osmotic relations suggested that these accounted for 10 to 40% of the diurnal changes in the calculated osmotic potential. A diurnal hysteresis of as much as 7 bars was observed in the .relation between water potential and relative water content due largely to changes in the elasticity of cell walls. We conclude that the maintenance of low leaf diffusive resistance and continued leaf elongation despite reductions in leaf water potential indicates that turgor is also maintained. This was due partly to the accumulation of sugars and malate and partly to high cell wall elasticity.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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