Role of Changes in Solute Concentration in Maintaining Favorable Water Balance in Field‐Grown Cotton¹

Abstract

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.

Osmoregulation in Cotton in Response to Water Stress

“…Alternatively, solutes in adapted leaves may be concentrated to a greater extent if adapted leaves have larger nonosmotic cell volumes, as compared with control leaves. This is typical in drought-adapted cotton (11). Electron micrographs of fully turgid control and adapted leaves (node 5) indicate that starch accumulated in adapted leaves (Fig.…”

Osmoregulation in the Avena Coleoptile in Relation to Auxin and Growth

“…In contrast, the auxin-induced growth rate and the OC are maintained at a constant level for over 20 h if 2% sucrose is included in the medium. The importance of osmoregulation in maintaining rapid cell enlargement has also been demonstrated for stem (21,22) and leaf tissues (9,10).…”

Relations hydriques et formation des racines adventives caulinaires chez des semis d'épinette noire (Picea mariana (Mill.) B.S.P.) /

“…Le stress hydrique peut induire des changements dans les paramètres des relations hydriques (Abrams 1988). Des changements périodiques dans ces mêmes paramètres associées à des changements dans la concentration de solutés osmotiquement actifs dans les cellules sont aussi détectables durant la saison de croissance (Cutler et al 1977, Tyree et al 1978, Morgan 1984, Ritchie et Shula 1984, Abrams 1988, Kozlowski 1992 (Hsiao et al 1976).…”

“…Ces derniers sont causés par les variations des conditions environnementales, en particulier la température et la photopériode (Zur et al 1981, Calkin et Pearcy 1984, Andersen et McLaughlin 1991, Zine El Abidine étal. 1993, avec la concentration de solutés osmotiquement actif (Cutler et al 1977, Tyree et al 1978, Morgan 1984, Ritchie et Shula 1984, Abrams 1988, Kozlowski 1992, Zine El Abidine et al 1993) et avec l'ontogénie des nouvelles expansions foliaires (Tyree et al 1978, Roberts et al 1981, Parker et al 1982, Zine El Abidine et al 1993 La diminution de \|/ nFT à la deuxième date d'échantillonnage n'est pas nécessairement liée à un déficit hydrique du sol. Une diminution significative du potentiel osmotique a été observée chez des semis saturés en eau malgré une grande humidité du sol et un faible déficit de pression de vapeur (Abrams 1988).…”