Sugars and Desiccation Tolerance in Seeds

Abstract

Soluble sugars have been shown to protect liposomes and lobster microsomes from desiccation damage, and a protective role has been proposed for them in several anhydrous systems. We have studied the relationship between soluble sugar content and the loss of desiccation tolerance in the axes of germinating soybean (Glycine max L. Merr. cv Williams), pea (Pisum sativum L. cv Alaska), and corn (Zea mays L. cv Merit) axes. The loss of desiccation tolerance during imbibition was monitored by following the ability of seeds to germinate after desiccation following various periods of preimbibition and by following the rates of electrolyte leakage from dried, then rehydrated axes. Finally, we analyzed the soluble sugar contents of the axes throughout the transition from desiccation tolerance to intolerance. These analyses show that sucrose and larger oligosaccharides were consistently present during the tolerant stage, and that desiccation tolerance disappeared as the oligosaccharides were lost. The results support the idea that sucrose may serve as the principal agent of desiccation tolerance in these seeds, with the larger oligosaccharides serving to keep the sucrose from crystallizing.Most angiosperm seeds can survive desiccation but only at a discrete developmental stage. If they are dried before reaching the desiccation tolerant stage of maturity, they will not germinate (2,26). Similarly, if they are dried after germination has progressed too far, they will not continue to germinate upon rehydration (4,18,26). The emergence of the radicle from the seed coat is generally considered to be the stage at which desiccation tolerance is lost during germination (26).Water is important to organisms not only as a solvent for biochemical reactions, but as a stabilizer of structure. Hydrophilic and hydrophobic interactions impart structure to macromolecules and organelles within cells. Membrane structure, in particular, depends on these complex interactions, and is often regarded as a primary site of desiccation damage (6, 26). The water replacement hypothesis suggests that polyhydroxy compounds can substitute for water in stabilizing membrane structure in the dry state (7,23,30 Leakage of Electrolytes. Seeds were imbibed for periods up to and beyond radicle emergence, then transferred to a chamber containing saturated LiCl, which equilibrates to 11% RH (21). Here the seeds dried to approximately 8% moisture content (dry weight basis). This low moisture content is lethal to desiccationintolerant tissues. After drying, the seeds were transferred to 100% relative humidity for 24 h for slow rehydration in order to minimize damage to cells from hydrational forces (15). Thus, leakage from cells damaged by desiccation should be the main source of the electrolytes measured. Groups of 10 axes were isolated and submerged in 15 mL of deionized water. Conductivity was monitored continuously with an ElectroMark Conductivity Meter (Markson Science, Inc., Del Mar, CA). The rate of leakage was measured after 15 min, by which time it ...

Acetaldehyde Stimulation of Net Gluconeogenic Carbon Movement from Applied Malic Acid in Tomato Fruit Pericarp Tissue

“…Stress conditions in plants are associated with the synthesis of sugars presumably because sugars are protectants of biopolymers (15). From this perspective the AA inducement of sugar accumulation may add to the survivability of tissues, suggesting that the view of the volatile as stress agent (25) may be reevaluated and AA and perhaps related volatiles may be regarded as a stress antagonist.…”

The Glassy State in Corn Embryos

“…Sucrose, whose thermal behavior closely resembles the corn embryo data in Figure 7, is present in the corn embryo at levels of 17%. Raffinose is present at 3% (6). Thus, 20% of the embryo dry weight is comprised of solutes with strong tendencies to form glasses at low water contents and in the relevant temperature range.…”

Degradation of α-galactosides during the germination of grain legume seeds

“…The degradation of α-galactosides during the germination of leguminous seeds commences with inhibition, and continues intensively during the embryonic stage. In the case of soy, peas, and lupine seeds, α-galactoside levels have been shown to decrease during the first two days of imbibition, with hydrolysis of the α-galactosides in cells taking from 4-6 days, the enzyme α-d-galactosidase catalysing the hydrolysis of the bond between α-galactosides, the cell polysaccharide barrier, and the stored glycoprotein (Koster & Leopold 1988;Górecki et al 1997a). Mature seeds usually contain isoforms of this enzyme, differing in activity and molecular weight (Pridham & Dey 1974).…”