The Sweet Taste of Adapting to the Desert: Fructan Metabolism in Agave Species

Abstract

Over 70% of Agave species, (159 of 206) are found in Mexico and are well adapted to survive under hot, arid conditions, often in marginal terrain, due to a unique combination of morphological and physiological attributes. In the pre-Columbian era agaves were also key to human adaptation to desert terrain. In contrast to other species such as cacti or resurrection plants, Agaves store carbohydrates in the form of fructan polymers rather than starch or sucrose, however, properties specific to fructans such as a strong hydration shell, the ability to be transported through phloem, variable composition throughout the Agave life-cycle and accumulation in succulent tissues and flowers suggest a potential for multiple functional roles. This mini-review summarizes current knowledge of molecular and biochemical aspects of fructan metabolism in Agave species.

Agave Fructans in Oaxaca’s Emblematic Specimens: Agave angustifolia Haw. and Agave potatorum Zucc.

“…It is possible that the heterogeneity in sugar levels was due to the sucrose produced by photosynthesis being metabolized by vacuolar invertases. This theory is supported by the high amounts of glucose and fructose present in A. potatorum , while the large amounts of sucrose in A. angustifolia might be related to the fact that the plant must accumulate this sugar for “hijuelo” formation and development during its asexual reproduction [ 34 ], unlike A. potatorum , which is an Agave species with only sexual reproduction. On the other hand, there was not a large difference in the accumulation of FOS-type carbohydrates among species; however, in both cases the amounts of FOS also decreased with age.…”

Agave Syrup: Chemical Analysis and Nutritional Profile, Applications in the Food Industry and Health Impacts

“…Such plants prevail in Central and Northern America, but a large proportion of the species (about 55%) are located in Mexico, believed to be the centre of agave’s diversity and origin [ 4 ]. Both the consumption and socio-economic impacts of agave originate from pre-Columbian times, given its high sugar content [ 5 ].…”

Localization and Composition of Fructans in Stem and Rhizome of Agave tequilana Weber var. azul

“…Fructans are branched or linear polyfructose molecules that accumulate in 15% of angiosperms ( Hendry, 1993 ) in families of both dicotyledons and monocotyledons ( Van den Ende, 2013 ; Versluys et al, 2018 ; Pérez-López and Simpson, 2020 ). They can be defined as compounds where one or more fructosyl-fructose linkage constitutes the majority of linkages and they may or may not contain a D-glucosyl ( Lewis, 1993 ).…”

“…To date, these complex and highly branched fructans have only been found and described in agaves and closely related species and they are commonly referred to as agavins. The presence of complex fructan polymers in A. tequilana suggests that up to four different fructosyltransferase activities are involved in their biosynthesis and fructan exo-hydrolases specific for different terminal bonds are responsible for fructan degradation ( Cimini et al, 2015 ; Versluys et al, 2018 ; Morales-Hernández et al, 2019 ; Tarkowski et al, 2019 ; Pérez-López and Simpson, 2020 ).…”

“…In contrast, fructans are found in all agave tissues including roots, rhizomes and flowers although they accumulate to the highest levels in the oversized stem. More recently, based on specific properties, the importance of fructan metabolism in many adaptive traits of Agave species is beginning to be recognized ( Avila de Dios et al, 2015 ; Pérez-López and Simpson, 2020 ). Fructans are highly soluble ( Morales-Hernández et al, 2019 ) and strongly associated with succulence, can be transported through the phloem and can associate with plant membranes.…”