Abstract
Starch degradation in barley endosperm provides carbon for early seedling growth, but the control of this process is poorly understood. We investigated whether endosperm cell wall degradation is an important determinant of the rate of starch degradation. We identified iminosugar inhibitors of enzymes that degrade the cell wall component arabinoxylan. The iminosugar 1,4-dideoxy-1, 4-imino-l-arabinitol (LAB) inhibits arabinoxylan arabinofuranohydrolase (AXAH) but does not inhibit the main starch-degrading enzymes α- and β-amylase and limit dextrinase. AXAH activity in the endosperm appears soon after the onset of germination and resides in dimers putatively containing two isoforms, AXAH1 and AXAH2. Upon grain imbibition, mobilisation of arabinoxylan and starch spreads across the endosperm from the aleurone towards the crease. The front of arabinoxylan degradation precedes that of starch degradation. Incubation of grains with LAB decreases the rate of loss of both arabinoxylan and starch, and retards the spread of both degradation processes across the endosperm. We propose that starch degradation in the endosperm is dependent on cell wall degradation, which permeabilises the walls and thus permits rapid diffusion of amylolytic enzymes. AXAH may be of particular importance in this respect. These results provide new insights into the mobilization of endosperm reserves to support early seedling growth.
Highlights
Chemical inhibitors that would retard degradation of endosperm cell wall components without directly affecting enzymes of starch degradation during grain germination and early seedling growth
We demonstrate that incubation of barley grains with an iminosugar that inhibits a specific AX-degrading enzyme reduced both cell wall degradation and starch mobilisation
In order to test the effect of endosperm cell wall integrity on starch loss during barley grain germination and early seedling growth, we looked for inhibitors of enzymes that degrade components of the wall
Summary
Chemical inhibitors that would retard degradation of endosperm cell wall components without directly affecting enzymes of starch degradation during grain germination and early seedling growth. We demonstrate that incubation of barley grains with an iminosugar that inhibits a specific AX-degrading enzyme reduced both cell wall degradation and starch mobilisation.
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