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The structure of the starch granule affects cereal grain germination
A. BLENNOW (1), S. S. Shaik (1), M. Carciofi (1), K. H. Hebelstrup (2), H. J. Martens (1). (1) University of Copenhagen, Frederiksberg C, Denmark; (2) Aarhus University, Flakkebjerg, Denmark
Cereal grain germination is central for plant early development and efficient germination has a major role in crop propagation and malting. Endosperm starch is the prime energy reserve in germination and in this study we hypothesized that optimized starch granule structure, not only the endosperm starch content <i>per se</i>, is important for germination and seedling establishment. For that purpose we used barley wild-type (WT) and specifically engineered degradable hyper-phosphorylated (HP) starch and more resistant amylose-only (AO) starch barley lines. None of the engineered lines showed severe phenotypic effects on germination and the WT and HP lines degraded the starch similarly having 30% residual starch after 12 days of germination. However, the AO showed significant degradative resistance having almost twice as much of residual starch. Interestingly, protein degradation was stimulated for both HP and AO lines as compared to WT and BG (BG) degradation was moderately stimulated. AT later germination stages, specific sugars were rapidly consumed in the AO line due to carbon starvation. α-Amylase activity was distinctly suppressed in both the HP and the AO lines. Pre-germination β-amylase deposition was low in the AO grains and was generally suppressed in both HP and AO lines over germination. Scanning electron microscopy of grain sections demonstrated differential patterns of degradation. The data conclude that correctly structured endosperm starch granules are vital for establishing correct initiation and maintenance of metabolic dynamics during grain germination and sub-optimal granule structure leads to temporal and compensating re-directions of starch, sugar and protein catabolism.
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