Physicochemical, Structural, and Proteomic Analysis of Starch Granules from Maize Landraces of Northwest Mexico

The variability in grain and starch characteristics and their relationship with the accumulation of starch granule associated proteins were investigated in five maize landraces of Northwest Mexico (Blando de Sonora, Chapalote, Elotero de Sinaloa, Reventador, and Tabloncillo). Significant differences were observed in grain hardness related traits, starch physicochemical properties, and structural properties. Blando de Sonora showed very soft grains, whereas the hardest grains were observed for Chapalote and Reventador. Starch granules isolated from landraces with hard grains contained more amylose and showed polygonal shapes, lower crystallinity and enthalpy of gelatinization, and greater retrogradation and proportion of long amylopectin chains. Proteomic analysis identified the enzymes granule-bound starch synthase I (GBSSI), starch synthase I and IIa, starch branching enzyme IIb, sucrose synthase 1, and pyruvate phosphate dikinase 2 as granule-associated proteins. The abundance of GBSSI correlated significantly with amylose content, consistent with the positive correlation observed between amylose and grain hardness. These results showed that the variability in the characteristics evaluated was mainly related to changes in the proportion of amylose in the starch granules, which were associated with differences in the expression of GBSSI. This information may be useful to define strategies for the exploitation and conservation of the landraces.