Levans in excised leaves of Dactylis glomerata: Effects of light, sugars, temperature and senescence

Dactylis glomerata (orchardgrass) accumulates a single series of levans and the high DP polymers might be correlated with an increased stress resistance. A single levan series could be induced in excised orchardgrass leaves, without any 1-kestose accumulation, strongly suggesting that fructan synthesis occurs independently of 1-SST activity. This elegant excised leaf system was used to study fructan metabolism regulation as affected by environmental conditions and exogenous sugar treatments. In contrast to the well-studied barley excised leaf system, fructan biosynthesis could not be rapidly induced in the light without exogenous sugar and only a limited fructan synthesis was observed in the dark with sugar. it can be concluded that both light and sugar are needed to achieve an optimal fructan synthesis. To induce fructan biosynthesis, sucrose could be replaced by a combination of glucose and fructose. Fructans were found to be a surplus pool of sucrose when a threshold sucrose concentration is surpassed. A metabolic switch to fructan degradation was observed when induced orchardgrass leaves were incubated in the dark at 30 degrees C. Interestingly, fructans persisted during senescence of sugar-induced orchardgrass leaves. On the longer term, these fundamental regulatory insights might help to create superior grasses for future feed and/or biomass production.status: publishe