Changes in gene‐expression in response to sucrose accumulation in leaf tissue of Lolium temulentum L.

Sucrose accumulation and subsequent fructan synthesis was initiated in detached, mature leaves of Lolium temulentum by incubating them either in the light or with 200 mm sucrose in the dark. Fructan synthesis was also induced in intact seedlings by lowering root and shoot meristem temperature to 5 ?C while maintaining aerial parts of the plant at 20 ?C in the light. In this system, subsequent breakdown of fructans was induced by raising root and meristem temperature to 20 ?C in the dark. Products of in vitro translations showed that transcripts encoding polypeptides of 17 and 35 kDa increased in sucrose accumulating-tissue. Transcripts encoding 28 and 32 kDa polypeptide products appeared to be associated with leaf tissue actively exporting carbohydrate. Labelling studies in vivo in mature leaf tissue showed transient increases in the synthesis of polypeptides with MR 59, 60 and 70 kDa during the first 6 h of sucrose accumulation. Polypeptides with an MR of 74 and 27 kDa showed increased amounts later in induction.
Cordycepin and cycloheximide were fed to mature leaf tissue at different stages during induction of sucrose accumulation in the light. Both control and cordycepin-treated tissue showed higher levels of monosaccharide
accumulation compared with cycloheximide-treated tissue. Cordycepin applied during the first 2 h after excision blocked subsequent synthesis of all fructans. When applied at two-hour-stages between 2 and 8 h, subsequent accumulation of 1-kestose occurred without accumulation of higher fructans. Application after 8 h had no effect upon the pattern of fructan accumulation when compared to untreated controls. Application of cycloheximide during the first 8 h following excision blocked all fructan accumulation. Subsequent administration had no effect on the pattern of fructan accumulation. The results are discussed in relation to the changes in gene expression associated with induction of fructan synthesis.