Biochemical and Genetic Analysis of Carbohydrate Accumulation in Allium cepa L

Abstract

Onion and shallot (Allium cepa L.) exhibit wide variation in bulb fructan content, and the Frc locus on chromosome 8 conditions much of this variation. To understand the biochemical basis of Frc, we conducted biochemical and genetic analyses of Allium fistulosum (FF)-shallot (A. cepa Aggregatum group) alien monosomic addition lines (AALs; FF+1A-FF+8A) and onion mapping populations. Sucrose and fructan levels in leaves of FF+2A were significantly lower than in FF throughout the year, and the springtime activity of acid invertase was also lower. FF+8A showed significantly higher winter sucrose accumulation and sucrose phosphate synthase (SPS) activity. Inbred high fructan (Frc_) lines from the 'W202Ax Texas Grano 438' onion population exhibited significantly higher sucrose levels prior to bulbing than low fructan (frcfrc) lines. Sucrose synthase (SuSy) activity in these lines was correlated with leaf hexose content but not with Frc phenotype. Markers for additional candidate genes for sucrose metabolism were obtained by cloning a major SPS expressed in onion leaf and exhaustively mining onion expressed sequence tag resources. SPS and SuSy loci were assigned to chromosome 8 and 6, respectively, using AALs and linkage mapping. Further loci were assigned, using AALs, to chromosomes 1 (sucrose phosphate phosphatase), 2 (SuSy and three invertases) and 8 (neutral invertase). The concordance between chromosome 8 localization of SPS and elevated leaf sucrose levels conditioned by high fructan alleles at the Frc locus in bulb onion or alien monosomic additions of chromosome 8 in A. fistulosum suggest that the Frc locus may condition variation in SPS activity.

Single Alien Chromosome Additions from Shallot (Allium cepa L. Aggregatum group) Increase Endogenous Polyphenol Contents in Japanese Bunching Onion

“…Previous studies of the seasonal change of sugar accumulation in the monosomic addition lines revealed that the sugar content in the green leaf tissues of monosomic addition lines decreased from spring to summer and then increased from autumn to winter (Hang et al, 2004;Yaguchi et al, 2008b). Bolting and flowering were observed in all plant materials between March and May during the term of this study.…”

“…The production of Lascorbic acid (vitamin C) in three monosomic additions (FF + 1A, FF + 2A, and FF + 8A) showed a significant increase than in A. fistulosum and the remaining five monosomic additions showed the same tendency as A. fistulosum (Yaguchi et al, 2008a). In the production of non-reducing sugar, including sucrose and fructan, FF + 8A showed significantly higher sucrose accumulation but FF + 2A hardly accumulated non-reducing sugar (Hang et al, 2004;Yaguchi et al, 2008b). Almost all monosomic addition lines showed a decrease of the content of S-alk(en)yl-L-cystein sulfoxides, which is known as a flavor precursor of Allium crops, compared with A. fistulosum (Yaguchi et al, unpublished data).…”

Biochemical Analyses of the Antioxidative Activity and Chemical Ingredients in Eight DifferentAlliumAlien Monosomic Addition Lines

“…12,13) Polyphenol seemed to be the major contributor to the antioxidative activity of MALs and A. fistulosum. In previous studies, a small decrease in several chemical compounds, including polyphenol, has been reported in August 7,8,14,15) as well as the ORAC values found in this study. Shigyo et al have described that the growth rate of MALs and A. fistulosum, including the leaf extension speed, gradually decreased from the summer (August) to winter.…”

“…Different effects of a single alien chromosome addition have been apparent in the production of several chemicals in previous studies. 7,14,15,19) In the present and previous studies, 8) three MALs (FF+2A, FF+6A, and FF+8A) showed a higher polyphenol content than A. fistulosum; it therefore could be expected that the increased polyphenol content in A. fistulosum could be accomplished by alien chromosome addition from shallot. As a result, high ORAC values for FF+2A and FF+6A could be detected.…”

Characterization of Amino Acid and S-alk(en)yl-L-cysteine Sulfoxide Production in Japanese Bunching Onion Carrying an Extra Chromosome of Shallot

“…Studies using these lines have revealed that several lines with alien chromosomes showed different compositions of flavonoids (Masuzaki et al, 2006a, b;Shigyo et al, 1997b), ascorbic acid (Yaguchi et al, 2008a), polyphenols (Yaguchi et al, 2009), and carbohydrates (Hang et al, 2004;Yaguchi et al, 2008b). The results of these studies indicate that the biochemical analyses of eight MALs can define the chromosomal locations of genes or QTLs affecting biochemical component production in A. cepa.…”