Genotypic Variation for Glycinebetaine in Sorghum

Abstract

Glycinebetaine (GB) accumulation has been suggested to be an adaptive response to several abiotic environmental stresses. Genetic and metabolic studies of GB accumulation in maize ( Zea mays L.) indicate that recessive alleles of a single locus are responsible for the phenotype of GB nonaccumulation. The present study was undertaken to determine whether a similar genetically determined range of GB levels exists in the related C 4 species Sorghum bicolor (L.) Moench. In a preliminary analysis of 240 sorghum genotypes, sampled at the postflowering stage, total quaternary ammonium compound (QAC) levels in the betaine fraction of the flag leaves were found to range from as low as 0.1 μmol g −1 FW to as much as 33 μmol g −1 FW. Stable isotope dilution desorption chemical ionization mass spectrometry of six genotypes with high QAC levels and five genotypes with low QAC levels confirmed that this variation could be attributed almost exclusively to genetic variability for GB level. GB‐nonaccumulating sorghum genotypes were confirmed to be GB‐non‐accumulating in a second year of field‐testing, and in greenhouse studies under salinized and non‐salinized conditions. GB levels increased with seedling age and/or salinization in GB‐accumulating genotypes. Also, GB levels were highest in the youngest leaves of GB‐accumulating sorghum genotypes. This work shows that GB is the major QAC in sorghum, that genetic differences in GB accumulation exist in sorghum as they do in maize, and that the level of GB in GB‐accumulating lines is developmentally and environmentally regulated. A list of GB levels of publicly available lines of sorghum is also provided.