Leaf water relations and gravimetric water loss as influenced by K rate (25, 75, 150, 300, 450 and 600 ppm) and moisture stress conditioning (MSC - exposing plants to 4 sub-lethal dry down cycles) were determined for salvia (Salvia splendens `Bonfire'). K rate and MSC had a synergistic effect on leaf osmotic potentials. Osmotic potentials at both full and zero turgor decreased with increasing K rate and MSC. Differences between MSC and no-MSC plant osmotic potentials increased as K rate increased. Active osmotic adjustment with increasing K rate and MSC resulted in increased cellular turgor potentials. Both high K rates and MSC reduced plant gravimetric water loss on a unit leaf area basis.
Abbreviations: EC, electrical conductivity; MSC, moisture stress conditioning; P L , leaf turgor potential; PV, pressure-volume; RWC, relative leaf water content; SWC, symplastic water content; ψ L , leaf water potential; π 100 , π 0 osmotic
The possibility of osmotic adjustment to salinity in Jojoba was studied in a sand culture system. After being stablished, 2 WKs old seedlings were exposed to 1/2 strength hoagland's solution plus NaCl salt to make up -0.7., -0.4, -0.6, -0.8, & -1 MPa. Shoot & leaf elongation, components of Ψleaf, proline accumulation, & inorganic salts were determined every 24 hour for 9 days. Shoot & leaf length were reduced at -0.8 and -0.4 MPa respectively. Osmotic adjustment occured only above -0.8 MPa at the rate of 0.21 If MPa/day. Total inorganic salts in whole plant increased with a decrease in solution Ψw. However, above -0.8 MPa excess Na & Cl ions were excluded from the leaves & accumulated within the roots, while K/Na ratio remained higher above -1 MPa. The selective uptake of K ions seems a possible mechanism for osmotic adjustment in Jojoba. Accumulation of Na & Cl ions under -1 MPa correlated with occasional pale green discoloration & tip-burn of leaves. Although the accumulation of proline was considerable at & below -0.8 MPa, but did not play a significant role in osmoregulation.
Osmotic adjustment in response to onset of winter dormancy was characterized in well-watered, potted sweetgum (Liquidambar styraciflua L.) and southern magnolia (Magnolia grandiflora L.) growing outdoors in Knoxville, Tenn. Analyses of water potential isotherms indicated that adjustment occurred in both species, with osmotic potential (ψπ) at full turgor decreasing 0.8 MPa in sweetgum (by the time of first color, 27 Oct.) and 1.0 MPa in magnolia (by 1 Dec.). Osmotic adjustment occurred despite the fact that plants did not suffer osmotic stress; morning and afternoon leaf relative water content (RWC) and leaf water potential (ψ) remained high throughout the fall. Leaf conductance was halved in sweetgum and doubled in magnolia as the autumn progressed. A correlation was found in magnolia between turgid : dry weight ratio and ψπ at full turgor. Tissue elasticity decreased somewhat, as the elastic modulus increased ≈2 to 3 MPa in each species through the autumn. Water potential isotherms changed most dramatically through the autumn in magnolia. Initially, ψ was −1 MPa at 82% RWC and, by December, leaves were able to withstand ψs of −3 MPa before RWC dropped to 82%. These changes are similar to those commonly reported as responses to drought or salinity.
A strategy of chemical crop load control has been to use chemical desiccants to prevent fertilization and cause fruitlet drop. However, little is known of the solution characteristics that reduce pollen viability, inhibit pollen germination and growth, and cause pistil damage. This project was established to determine the solution characteristics effecting those results. Apple pollen was dispersed on germination media mixed with PEG (MW 10,000) to attain osmotic tensions from 0 to -5.0 MPa to evaluate effect on pollen germination and growth. Similarly, apple pollen was dispersed on germination adjusted to a range of pH from 2.3 to 12.0 with acids and NaOH. Excised apple pistils were place on filter paper supports saturated with solutions with osmotic tension adjusted by PEG in the range of 0 to -5.0 M Pa, and pH from 3.0 to 12.0. Solutions of osmotic tension in the range of 0 to -5.0 M Pa were applied by brush to intact pistils on apple flowers in a greenhouse and under field conditions. Pollen germination decreased with increasing osmotic tension and no pollen germinated at tensions greater than 4.0. Pistils, either excised or intact, had significant desiccation and death when treated with solution osmotic tensions greater than 4.0. Fruit set of individual spurs of the cvs Jonagold, Gala, and Arkansas Black were highly related to pistil survival 48 h after treatment with PEG. When solution osmotic potential exceeded 4.0, fruit set was reduced by more than 80%. Pollen germination was reduced by more than 50% at solution pH below or equal to 4.0 and greater than 10.0 and completely inhibited at solution pH below or equal to 3.0 and greater than 11.0. Similar results were observed for excised pistil and intact viability.
Using psychrometric pressure-volume analysis, root water relations following drought were characterized in Rosa hybrida L. plants colonized by the vesicular-arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith. Measurements were also made on uncolonized plants of similar size and adequate phosphorus nutrition. Under well-watered conditions mycorrhizal colonization resulted in lower solute concentrations in root symplasm, and hence lower root turgors. Following drought, however, mycorrhizal roots maintained greater turgor across a range of tissue hydration. This effect was apparently not due to increased osmotic adjustment (full turgor osmotic potentials were similar in mycorrhizal and nonmycorrhizal roots after drought) or to altered elasticity but to an increased partitioning of water into the symplast. Symplast osmolality at full turgor was equivalent in mycorrhizal and nonmycorrhizal roots but because of higher symplastic water percentages mycorrhizal roots had greater absolute numbers of osmotic (symplastic) solutes. Drought-induced osmotic potential changes were observed only in mycorrhizal roots, where a 0.4 megapascal decrease (relative to well-watered controls) brought full turgor osmotic potential of mycorrhizae to the same level as nonmycorrhizal roots under either moisture treatment.
The effects of water deficits were examined on osmotic regulation of germinating seedlings of tomato (Lycopersicon esculentum Mill cv. Campbell 1327). Seed were germinated in aerated water and then grown for an additional 2 days in Petri dishes. The germinated seeds were then transferred to water potentials of 0 to −6 bars in 2-bar increments. Mannitol and water was used to obtain the desired water potential of the media. Water relations, growth rates and reducing sugars, non-reducing sugars, amino acids, proline, nitrates, phosphates, potassium, and electrical conductivity were determined for roots and shoots at different water stresses. As water stress increased, osmotic adjustment occurred in the roots which accounted for the maintenance of turgor and growth. During the same period, little adjustment occurred in the shoots and consequently growth decreased. Turgor potential was highly correlated with growth rates for both plant parts. All solutes measured, except proline, generally increased in the roots and decreased in the shoots as water stress increased. Proline increased in both plant parts during the same period. Thus, solute regulation occurred during water deficits. Osmotic regulation in germinating tomato seedlings appears to be an adaptive feature during periods of water stress.
The effect of water deficit on shoot growth and fruit development in jojoba was studied in 8-year-old jojoba [Simmondsia chinensis (Link) Schneider] plants. In both fruiting and defruited nonirrigated plants, shoot growth, which started at the beginning of April, stopped in June when the xylem water potential (ψx) measured at dawn fell to a value below the osmotic pressure at the point of turgor loss. Osmotic adjustment during the summer enabled some resumption of growth in the autumn at low ψx values. Irrigated plants grew throughout the warm season only if defruited: competition for assimilates evidently inhibits growth during the period of fruit filling. Fruit growth was not affected by water deficit, since fruit are apparently highly resistant to water loss.
Stomatal conductance, abscisic acid levels, and water potential components (water, osmotic, and rurgor potentials) were measured in irrigated and non-irrigated open pollinated seedlings of ‘Northern Spy’ apples (Malus domestica Borkh.). Although non-irrigated seedlings typically displayed water potentials of 0.2 to 0.6 MPa lower than those of irrigated seedlings, turgor potentials remained comparable in both groups, Because diurnal osmotic adjustment was also greater for non-irrigated seedlings. Abscisic acid (ABA) levels in the leaf increased linearly in response to changes in leaf turgor, rather than water potential. Stomatal conductance was independent of bulk leaf ABA levels and was poorly correlated with leaf turgor potential above a critical value of 0.7 MPa.
Accumulation of glycinebetaine occurs in Chenopodiaceae members and is thought to assist in osmotic adjustment and protect cytoplasm from sodium toxicity. Red beet has an ability to tolerate high tissue sodium levels, which may result in increased glycinebetaine production. To test this hypothesis, two cultivars of red beet ['Scarlet Supreme' (SS) and `Ruby Queen' (RQ)] were grown under nonsaline (4.75 mM Na) and saline (54.75 mM Na) conditions in a recirculating hydroponic system for 42 days at elevated CO2 (1200 μmol•mol-1) in a growth chamber. Leaf glycinebetaine level, relative water content, and osmotic potential were measured at weekly intervals. Leaf glycinebetaine levels increased with plant age and reached a maximum of 67 μmol•g-1 dw under nonsaline and 101 μmol•g-1 dry weight (dw) under saline conditions at 42 days in SS; in RQ, the glycinebetaine levels reached a maximum of 91 μmol•g-1 dw under nonsaline and 121 μmol•g-1 dw under saline conditions by 26 days. The mean glycinebetaine levels were increased over two-thirds under saline conditions in both the cultivars. RQ accumulated significantly higher (37% more under nonsaline, and 46% more under salinity) glycinebetaine than SS. The turgid leaf osmotic potential of RQ was consistently higher than SS under nonsaline (2.23 MPa in RQ vs. 1.82 MPa in SS) and saline (2.48 MPa in RQ vs. 2.02 MPa in SS) conditions. The results indicate that higher glycinebetaine levels in the leaf could result in better osmotic adjustment, and glycinebetaine accumulation in red beet can vary among cultivars and is strongly affected by external salinity.