Osmoregulation in Cotton in Response to Water Stress

Abstract

ABSTRACrCotton (Gossypium hirsutum) (L.) was grown in a sand and nutrient solution system at two levels of phosphorus (0.5 and 5.0 millimolar). Within each phosphorus treatment, plants were either watered daily or acclimated to water stress by subjection to several water stress cycles.Stress acclimation increased leaf starch at the low phosphorus level, but not at the high phosphorus level. High phosphorus increased leaf sucrose and glucose concentration in both acclimated and nonacclimated plants, but had little effect on osmotic adjustment or the relationship between turgor and water potential.In nonacclimated plants, high phosphorus increased both leaf conductance and photosynthesis at high water potentials. In acclimated plants, high phosphorus increased photosynthesis but decreased conductance, thus increasing water use efficiency at the single leaf level.Recent evidence suggests that the partitioning of photosynthetically fixed carbon between sucrose and starch may be regulated by cellular Pi levels (6, 8, 9, 1 1). Cotton leaves accumulate starch as a consequence of water stress acclimation (2, 3). Moreover, water stress significantly depresses phosphorus uptake (5, 7, 16) and low cellular Pi levels lead to starch accumulation in isolated chloroplasts and leaves (6, 8, 9, 11). Consequently, phosphorus fertility may play a role in altering the response of plants to water stress by changing the ratio of starch to soluble sugars in leaf cells.The influence of phosphorus fertility on internal water relations, leaf conductance, photosynthesis, and cellular carbohydrates in cotton is reported in this study. MATERIALS AND METHODSPlant Culture. Cotton (Gossypium hirsutum L. Tamcot SP37) was grown in 2 1-cm diameter plastic pots containing sand. Plants were thinned to two per pot after emergence. Conditions in the controlled environment chamber used for plant growth were as previously described (2, Five days after the last stress cycle, all plants were subjected to dehydration. During this dehydration period, data were obtained from leaves at nodes 6 and 7.Water Potential Leaf Conductance, Photosynthesis, and Leaf Carbohydrates. Water potentials and osmotic potentials were determined with isopiestic thermocouple psychrometers (4) as previously described (1-3). Procedures for diffusion porometry and for measurement of photosynthesis, and determination of glucose, sucrose, and starch levels in the leaves were described earlier (1-3).The data reported represent the combined results of three experiments. Based on plant height measurements, the two phosphorus fertility regimes did not differentially affect growth. Acclimated plants were shorter than the appropriate controls following cessation of the stress cycles as previously noted (3). RESULTS Phosphorus (P) fertility level did not significantly alter the relationship between leaf turgor and leaf water potential (Fig. 1). At any given water potential, plants grown on 5.0 mM P maintained leaf pressure potentials 0.5 to 1.0 bars higher than plants grown on 0.5 mM P. A...

Growth, phosphorus uptake, and water relations of safflower and wheat infected with an arbuscular mycorrhizal fungus

“…For instance, enhanced P fungi can dramatically increase a host plant's nutrition can increase stomatal conductance and absorption of mineral nutrients from the soil, transpiration (Radin, 1984;Ackerson 1985; particularly immobile nutrients such as phosphate Auge, 1992), and several investigators concluded (Marschner & Dell, 1994). Safir, Boyer & Gerdemann that increases in stomatal conductance and transpir- (1971) were the first to report that mycorrhizal ation of plants infected by mycorrhizal fungi were infection also alters plant water relations.…”

Carbon Partitioning and Export from Mature Cotton Leaves

“…The level of cotton leaf starch required to continue nocturnal carbon export at daytime rates is less than that normally found in nonstressed field-grown cotton (20) but water stress decreases starch levels in cotton leaves (4,20) provided other stress factors do not interfere (1,2). Severe water stress depresses the starch content of cotton leaves (4) to such an extent that carbon export from them should be largely limited to daylight hours.…”

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

“…Increased P supply appears to have an inconsistent effect on the stomatal conductance and growth in various plant species. For example, Atkinson & Davison (1972), Ackerson (1985) and Dosskey et al (1993), reported that increased P supply decreased stomatal conductance in Douglas fir seedlings (Pseudotsuga menziesii), cotton plants (Gossypium hirsutum) and Arctium minus, respectively, whereas transpiration rates increased in tea (Camellia sinesis) and cotton plants (Nagarajah & Ratnasuriya, 1978 ;Radin, 1984). Auge!…”

“…Although a lower rate of CO # assimilation and growth can generally be attributed to decreased stomatal conductance, Ackerson (1985), Dosskey et al (1993) and Auge! et al (1994) could demonstrate no differences in the growth of their respective plants between low and high P treatments.…”