Effect of Dehydration on Leakage and Membrane Structure in Lotus corniculatus L. Seeds

Abstract

Membrane damage as a result of dehydration was studied in Lotus corniculatus L. cv. Carrol seeds which had been pregerminated for 0, 12, and 24 hours prior to dehydration. During reimbibition, desiccation-tolerant (0-and 12-hour) seeds leaked relatively low quantities of all solutes (total electrolytes, potassium, phosphate, sugar, amino acid, and protein). Desiccation-sensitive (24-hour) seeds leaked higher levels, but evidence of selective permeability remained. Membrane damage was not manifested as a complete removal of the diffusion barrier, although its permeability properties were dramatically altered. Consequently, the plasmalemma was not ruptured or torn by the dehydration treatment, but a more subtle structural alteration occurred.The possibility that seed membranes form a hexagonal rather than a lamellar phase at moisture contents below 20% was investigated by x-ray diffraction. Phospholipids were extracted from desiccation-tolerant (0-hour) and desiccation-sensitive (24-hour) seeds and hydrated to 5, 10, 20, and 40% water. This phospholipid-water system was examined using lowand wide-angle x-ray diffraction and was found to be exclusively lamellar, even at 5% water. Consequently, membrane damage and the leakage of cytoplasmic solutes from seeds cannot be explained by the formation of a hexagonal phase by membrane phospholipids.lapse to form large discontinuities in the lipid bilayer. This possibility is supported by the observation that the transition from desiccation-tolerant to desiccation-sensitive occurs coincidently with the initiation of radicle elongation (9). Since elongation is facilitated by the uptake of water into the vacuole (5), it is conceivable that the rapid loss of this water collapses the cell and, in so doing, breaks the continuity of the plasmalemma and/or the tonoplast. However, this model does not explain why dehydration damage is induced only when seeds are dehydrated below 20% water (9). An alternative model is that dehydration induces an alteration in the hydrophobic-hydrophilic interaction within the membrane so that the structure of the cellular membranes below 20% hydration is different than that above 20% hydration. Water uptake by desiccation-tolerant seeds reinstates the original structure of the cellular membranes, whereas the membranes of desiccation-sensitive seeds are unable to reform completely. A structural rearrangement of membrane phospholipids by dehydration has been proposed by Simon (13), who suggested that membrane lipids in seeds form a hexagonal phase below 20% moisture. However, his proposal has not been experimentally verified using seed phospholipids.This study was intended to investigate these two models of induced damage. The results indicate that dehydration induces a reorganization of the cellular membranes in dehydration-sensitive seeds; however, this reorganization does not involve a lipid phase change.Dehydration treatments of seeds have also been shown to influence seed viability adversely and to increase electrolyte leakage (1, 5, 9). S...

Characterization of Solute Efflux from Dehydration Injured Soybean (Glycine max L. Merr) Seeds

“…The ability of plant tissues to tolerate dehydration is thought to reflect the inherent protoplasmic properties of these tissues (2) and in seeds, the protoplasmic properties which impart tolerance are presumably lost as the seed germinates. The loss of tolerance has been asso- ' ciated with the initiation of cell elongation and hydration of vacuoles (11), onset of DNA replication and RNA transcription (4), and changes in cellular membranes (14). Although the loss of dehydration tolerance is coincident with the initiation of cell elongation in many systems (1 1), the relationship does not appear to be causal.…”

“…The maintenance of the lipoprotein associations in membranes requires 20 to 30o hydration (10). Low angle x-ray diffraction has not confirmed Simon's (18) proposal that seed phospholipids are involved in a lamellar-hexagonal phase transition at 20o hydration (14). It remains unclear how the seed membranes change in structure during drying and also how the seed tolerates this stress at one stage in germination but is sensitive to it at another.…”

“…It remains unclear how the seed membranes change in structure during drying and also how the seed tolerates this stress at one stage in germination but is sensitive to it at another. A typical symptom of dehydration injury in seeds is an increase in the quantity of electrolytes and other cytoplasmic solutes that can be leached from the tissue during rehydration (14,17). Solutes may leak from injured tissue more rapidly because the plasmalemma and/or tonoplast has been mechanically ruptured by the dehydration treatment or because the permeability of an intact membrane has been altered.…”

Differential Leakage of Intracellular Substances from Imbibing Soybean Seeds

“…The most common measurements of seed leakage in steep water are conductivity of electrolytes (1,3,7,14,16,19,22,24,25,27,30) and UV light absorbance at various wavelengths (5,7,17,19).…”

Efeito dos períodos de envelhecimento na lixiviação de íons e de proteínas solúveis em sementes de milho

“…Conforme trabalhos realizados por Halloin (1975), McKersie & Stinson (1980) e Woodstock et al (1985, a quantidade de K liberado por sementes embebidas tem sido utilizada como indicador da integridade do sistema de membranas celulares.…”