Mutation of the maize sbela and ae genes alters morphology and physical behavior of wx-type endosperm starch granules

摘要

In maize,three isoforms of starch-branching enzyme,SBEI,SBEIIa,and SBEIIb,are encoded by the Sbela,Sbe2a,and Amylose extender}Ae)genes,respectively.The objective of this research was to explore the effects of null mutations in the Sbela and Ae genes alone and in combination in wx background on kernel characteristics and on the morphology and physical behavior of endosperm starch granules.Differences in kernel morphology and weight,starch accumulation,starch granule size and size distribution,starch microstructure,and thermal properties were observed between the ae wx and sbela ae wx plants but not between the sbela wx mutants when compared to wx.Starch from sbela ae wx plants exhibited a larger granule size with a wider gelatinization temperature range and a lower endotherm enthalpy than ae wx.Microscopy shows weaker iodine staining in sbela ae wx starch granules.X-ray diffraction revealed A-type crystallinity in wx and sbela wx starches and B-type in sbela ae wx and ae wx.This study suggests that,while the SBEIIb isoform plays a dominant role in maize endosperm starch synthesis,SBEI also plays a role,which is only observable in the presence of the ae mutation.