The effect of Phytate reduction on Sorghum (Sorghum bicolor L. Moench) grain germination

Abstract

Sorghum quality is improved by reducing anti-nutritional components, including phytates that sequester cations such as iron, zinc and calcium, to make nutrients more bioavailable for absorption. The current study investigated the quality and germination of a transgenic variety developed by the Africa Biofortified Sorghum project, aimed at developing sorghum varieties with reduced phytate content. However, results showed a significantly higher phytate content in transgenic grains (p<0.05) when compared with the wild type (WT). Furthermore, phytate in transgenic grains was less susceptible to degradation over 96 hrs of germination when compared with WT. Further study focused exclusively on WT grain where starch degradation was limited in the first 72 hrs but significantly increased by 96 hrs. This decrease in starch content strongly correlated (r²=0.93) with α-amylase activity that peaked at 115 CU/g at 96 hrs. (1,3;1,4)-β- glucan levels changed a little during germination, remaining at approximately 0.5% (w/w) even in the presence of increased beta-glucanase activity. Fluorescent microscopy showed that (1,3;1,4)-β- glucan and arabinoxylan around the pericarp, aleurone layer and embryo changed marginally over 96 hrs of germination. While treatment with GA repressed α-amylase activity, starch degradation patterns resembled untreated samples. GA induced lower, but same secretion patterns of endo-(1,3;1,4)-β-glucanase as untreated samples but delayed degradation pattern of (1,3;1,4)-β-glucan. These results suggest that the germination process in sorghum grain may be more similar to events in barley than previously reported.