Protein content in cassava storage root is associated with total abundance of carotenoids

Protein content in Cassava (Manihot esculenta Crantz) Storage Root (CSR) is low but variable. Detailed characterization of this variability is missing due to past inappropriate protein quantification procedures. Here we used conventional protein analytical procedures to access variation in Total Buffer Extractable Proteins (TBEPs) associated with Cassava Storage Root (CSR) color in landraces from the Amazon (Brazil). TBEPs values varied according to storage root color from 7.5 (mg/g DWt) in intense yellow landraces to less than 2 (mg/g DWt) in white CSR, an enhancement of up to 4x were detected in intense yellow compared to white CSR, represent up to 55% more protein in the bulk of CSR. Correlations of total buffer extractable proteins and total carotenoid content produced R2 values of 0.4757, 0.6849 and 0.8958 depending on the extraction procedure. Protein polymorphisms were accessed by buffer fraction, carotenoid-protein complex separation in size exclusion chromatography, and protein size separation in SDS-PAGE profile analysis. Total buffer extractable protein molecular weight varied from 10 to 260 Kda in chromoplast enriched suspensions, while purified chromoplast carotenoid-protein complex had specific protein molecular weights of 18 kDa in white CSR, 38 and 43 kDa for yellow CSR, and 23 and 58 kDa in pink CSR phenotypes. Furthermore, of the 143 protein spots observed from purified chromoplasts using 2DE, up to 30 protein spot variations were identified among the four CSR color categories. Furthermore, -carotene and lycopene were the major carotenoid types present in the carotenoid-protein complexes, which was dependent on the CSR color phenotype.