The capacity of the isolated barley aleurone layer for endosperm acidification has been demonstrated (J Mikola, M Virtanen 1980 Plant Physiol 66: S-142). The kinetics of this acidification by ...isolated wheat aleurone layer and its effect on starchy endosperm solubilization are reported.
Acidification of the starchy endosperm by the aleurone layer following germination has been established; however, the physiological and metabolic responses of this tissue to external pH have been ...incompletely investigated. In this investigation, isolated wheat (Triticum aestivum) aleurone layers were incubated in different solutions at initial pH values of 3, 4 and 6 in the absence of phytohormones. After 24h of incubation, the initial pH of all malate and succinate buffers shifted towards a value close to 4.2. These results suggest the existence of a pH-stating mechanism, instead of the simple acidification process reported previously. The rise of initial pH 3 by aleurone layers was accompanied by a high net uptake of external malic- or succinic acid. In contrast, incubation in glycyl-glycine buffer (a supposedly non-permeating cation at pH 3) partially prevented that pH rise in a pH-3 solution. The 14C-malate taken up from media at pH 3 was mostly broken down to CO2, indicating that an effective metabolic control of the intracellular malate level was operating. At pH 6, an uptake of 14C-malate and 14CO2 production occurred as well, but at slower rates than at pH 3. When buffer concentration was increased, at initial pH values of 3 or 6, a higher uptake or secretion of malic acid, respectively, was carried out by the aleurone layers. The pH of these buffers varied less than that of dilute ones, but always showed a tendency toward a pH near 4. These results suggest that a balance between secretion and uptake of malic acid, accompanied by the corresponding biosynthesis or degradation, is the basis of this pH-stating mechanism.
With the aim of determining the level at which ageing exerts its effect on the expression of α-amylase, GA3 regulation of α-amylase production was studied in isolated aleurone layers from aged wheat ...seeds. GA3-induced α-amylase activity was lower in the tissue from aged seeds than in controls. However, the proportion of 35S-methionine incorporated into α-amylase was higher in the aged than in control tissue. The pattern of α-amylase isoforms was resolved by isoelectric focusing and showed that two isogroups were present with the activity of the high-pl isogroup being higher in the control than in the aged lot. These apparently contradictory results may be explained in terms of differences in isozyme expression. Studies on the expression of α-amylase genes indicated a reduction in the level of high-pl mRNA in aged tissue. Doseresponse curves showed lower GA3-responsiveness of aleurone layers from aged seeds as compared to the controls. From these results, it is proposed that the diminished capacity of α-amylase production in aleurone from aged seeds is apparently due to a decrease in the expression of the high-pl α-amylase genes, and this reduction is associated with a decrease in the response to GA3.
With the aim of determining the level at which ageing exerts its effect on the expression of alpha-amylase, GA3 regulation of alpha-amylase production was studied in isolated aleurone layers from ...aged wheat seeds. GA3-induced a-amylase activity was lower in the tissue from aged seeds than in controls. However, the proportion of 35S-methionine incorporated into alpha-amylase was higher in the aged than in control tissue. The pattern of alpha-amylase isoforms was resolved by isoelectric focusing and showed that two isogroups were present with the activity of the high-pl isogroup being higher in the control than in the aged lot. These apparently contradictory results may be explained in terms of differences in isozyme expression. Studies on the expression of alpha-amylase genes indicated a reduction in the level of high-Pl mRNA in aged tissue. Dose-response curves showed lower GA3-responsiveness of aleurone layers from aged seeds as compared to the controls. From these results, it is proposed that the diminished capacity of alpha-amylase production in aleurone from aged seeds is apparently due to a decrease in the expression of the high-pl alpha-amylase genes, and this reduction is associated with a decrease in the response to GA3.
Isolated wheat (
Triticum aestivum var. Potam) aleurone layers have a high capacity to acidify their environment, and secrete hydrolytic enzymes (endoxylanase, glucanase, α-amylase, proteases, etc.) ...under the control of GA
3. Acidic pH and xylanases are found to be essential for cell wall relaxation in growing tissues, but aleurone is a non-growing, non-dividing tissue. In this tissue, we studied the effect of these loosening factors on aleurone cell walls.Exposure to pH 3.0 caused the release of carbohydrates and calcium ions from the pericarp, and a small amount of carbohydrates, mainly polysaccharides, from aleurone layers from which pericarp tissue had been removed. 50 percnt; of the total sugars released into the incubation medium by these isolated aleurone tissue was arabinose, but no xylose, calcium ions, or phenolic compounds were found. Acid preincubation decreased by 30 percnt; the susceptibility of aleurone cell walls to degradation by exogenously-applied endoxylanase, and also modified the architecture of cell wall as observed by autofluorescence of phenolic groups. These findings suggest that acid treatment and endoxylanase action, rather than having a loosening effect on aleurone cell wall, can have an opposite effect, increasing the resistance of aleurone cell walls to loosening.
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