The Role of Carbohydrates in Active Osmotic Adjustment in Apple under Water Stress

Abstract

<jats:p>Greenhouse grown 2-year-old potted `Jonathan' apple trees <jats:italic>(Malus domestica</jats:italic> Borkh.) were subjected to various levels of water stress in February. Midday leaf water potential (ψ<jats:sub>W</jats:sub>), leaf osmotic potential (ψ<jats:sub>S</jats:sub>), soluble sugars, and starch contents of mature leaves were measured throughout the development of water stress to determine whether active osmotic adjustment could be detected and whether carbohydrates were involved. Active adjustments of 0.6 MPa were observed 3 and 5 days, respectively, after water stress was initiated. Leaf turgor potential (ψ<jats:sub>P</jats:sub>) could not be maintained through the osmotic adjustment when ψ<jats:sub>W</jats:sub> dropped below -1.6 MPa. Sorbitol, glucose, and fructose concentrations increased while sucrose and starch levels decreased significantly as water stress developed, strongly suggesting that sugar alcohol and monosaccharide are the most important osmotica for adjustment. Sorbitol was a primary carbohydrate in the cell sap and accounted for &gt; 50% of total osmotic adjustment. The partitioning of newly fixed W-labeled photosynthates in mature leaves was not affected by water stress immediately after the 30-min <jats:sup>14</jats:sup>CO<jats:sub>2</jats:sub> treatment. All the W-labeled carbohydrates decreased in the labeled leaves very rapidly after <jats:sup>14</jats:sup>CO<jats:sub>2</jats:sub> labeling. The decrease in <jats:sup>14</jats:sup>C-sorbitol was greater than the decrease in other carbohydrates under both well-watered and stressed conditions. After 24 hours of water stress, however, the percentage of <jats:sup>14</jats:sup>C-sorbitol increased while the percentages of sucrose, starch, glucose, and fructose decreased significantly with increasing levels of stress. The ratio of <jats:sup>14</jats:sup>C-sorbitol in leaves with ψ<jats:sub>W</jats:sub> = -3.5 MPa to leaves with ψ<jats:sub>W</jats:sub> = -0.5 MPa was significantly higher than that of <jats:sup>14</jats:sup>C-sucrose, <jats:sup>14</jats:sup>C-glucose, W-fructose, or <jats:sup>14</jats:sup>C-starch.</jats:p>

Characterization of Three Sorbitol Transporter Genes in Micropropagated Apple Plants Grown under Drought Stress

“…2), and these observations were in agreement with previous studies (Wang and Stutte 1992;Escobar-Gutiérrez et al 1998;Li and Li 2005;Meyer et al 2004). The stress-induced changes in sorbitol content were related to the intensity and duration of the experimental drought stress.…”

Changes in water status and osmolyte contents in leaves and roots of olive plants (Olea europaea L.) subjected to water deficit

“…Inorganic cations were extracted by an acid digestion, according to Walinga et al (1995). A weighed amount (approximately 400 mg) of lyophilized tissue was added to 10 mL of 95% H 2 SO 4 and 4 mL of HNO 3 concentrated.…”

Antisense inhibition of sorbitol synthesis leads to up-regulation of starch synthesis without altering CO2 assimilation in apple leaves

“…A 50 ll sample was injected into a Shimadzu HPLC equipped with an RID-10A refractive index detector (Shimadzu, Kyoto, Japan). The 14 C-soluble sugars were separated on a Bio-Rad HPX-87C (BioRad, Richmond, Calif.) carbohydrate column (300·7.8 mm) as described by Wang and Stutte (1992). Fractions containing sucrose, glucose, fructose and sorbitol were collected separately and counted for radioactivity.…”

“…When sorbitol is transported to sink tissues, it is converted to fructose by sorbitol dehydrogenase for further metabolism (Loescher et al 1982). In addition, sorbitol is implicated in responses of sorbitol-synthesizing plants to abiotic and biotic stresses, such as osmotic adjustment under water stress (Lo Bianco et al 2000;Ranney et al 1991;Wang and Stutte 1992), cold hardiness (Raese et al 1978), mobility of boron in the phloem and tolerance of boron deficiency (Brown et al 1999;Hu et al 1997), and disease resistance (Suleman and Steiner 1994).…”