Saccharide and fructooligosaccharide accumulation across leaf-bases during growth and bulb development of onion ( Allium cepa L.)

Abstract

The accumulation of saccharides and fructooligosaccharides (FOS) in the individual leaf-bases of onion ( Allium cepa L.) was investigated during growth and bulb development. Saccharides and FOS were analysed by means of high performance anion exchange chromatography-pulsed amperometric detection (HPAEC-PAD). The glucose content was the highest, while the content of saccharides (glucose, fructose and sucrose) increased during June, July and August and decreased slightly during September. The trisaccharides all accumulated to a similar extent, although the neokestose [ 3b , 6 G - β -D fructofuranosylsucrose] content was higher than that of 1-kestose [ 3a , 1 F - β -D-fructofuranosylsucrose]. Tetra-, penta- and high-DP (degree of polymerization) FOS also showed a similar pattern, though the contents of 4b [6 G (1- β -D-fructofuranosyl) 2 sucrose] and 5b [6 G (1- β -D-fructofuranosyl) 3 sucrose] were higher compared with that of other tetra-[ 4a , 1 F (1- β -D-fructofuranosyl) 2 sucrose and 4c , 1 F , 6 G -di- β -D-fructofuranosyl sucrose] and penta-saccharides [ 5a , 1 F (1- β -D-fructofuranosyl) 3 sucrose]. Total FOS accumulated to a greater extent in the inner (youngest) leaf-bases than in the outer (oldest) leaf-bases, and their content was high during August. The total carbohydrates content was 6.71, 7.25, 8.10 and 6.30 g 100 g −1 FW during June, July, August and September, respectively. During bulb formation, a balance was observed between the glucose, fructose, sucrose and FOS contents, with an average ratio of 20:10:10:60 of total carbohydrates, respectively.