Analysis and characterisation of Fructan oligosaccharides and enzymatic activities in the leaves of Agave tequilana (Weber) var. Azul

The ability of Agave species to synthesize fructans has been poorly investigated in the past. Agave tequilana, a CAM plant of Mexican origin, accumulates fructans in their false stem or pia that are harvested and used as a source of sugars for the production of tequila. Synthesis of fructans occurs in the agave leaf and in the past it has been suggested that they are transported through the phloem to the storage organ. In this work the structural characteristics of oligosaccharides present in plant leaves are examined by different methods such as TLC, MALDI-TOF and HPAEC-PAD. Also, leaf protein extracts were tested for enzyme activities by incubation with different sugars to identify the machinery responsible for agave fructan structures. Results showed that sucrose represents the largest contributor (67%) followed by fructans (20%) up to DP 12 and monosaccharides (13%), respectively. Leaf oligofructan structures are comprised of a mixture of inulin, neoseries and branched fructans. All DP3 and DP4 fructans were linear molecules of the inulin and neoseries type, with the notable absence of 6-kestose or bifurcose, which is considered to be the primer oligosaccharide in grasses. Enzymatic assays confirmed the presence of the synthetic activities 1-SST, 1-FFT and 6G-FFT, but could not detect any 6-SFT activity, generally considered responsible of the branching fructans and synthesizer of 6-kestose or bifurcose that could not be found. From this study we conclude that the branching activity in Agave spp. is of different nature than 6-SFT already characterized in grasses. We propose that an unknown 6- FFT activity may be responsible for the branched structure in Agave fructan