Reorientation of shoots to the horizontal position influences the sugar metabolism of lateral buds and shoot internodes in Japanese pear (Pyrus pyrifolia (Burm.) Nak.)

摘要

We investigated the effects of reorienting shoots 60?from the vertical to horizontal on carbohydrate concentrations and the related enzyme activities in the lateral bud and the shoot internode of 'Kosui' Japanese pear, to clarify the change of sugar m etabolism in response to shoot reorientation which is known to accelerate flower-bud formation. The carbohydrates included: fructose, glucose, sorbitol, sucrose and starch, where the related enzymes included: NAD-dependent sorbitol dehydrogenase (NAD-SDH ), NADP-dependent SDH (NADP-SDH), sorbitol oxidase (SOX), sucrose synthase (SS) and acid invertase (AI). Concentrations of sorbitol and sucrose in the lateral buds of a horizontal shoot temporarily decreased on 3 d after shoot reorientation (DAR) but did not differ significantly from those of the controls on 7 DAR and thereafter. On the other hand, sorbitol and sucrose concentrations of the central internode of horizontal shoots were higher on 30 DAR than those of untreated shoots. Glucose and fructose levels were not influenced by shoot reorientation. Activities of NAD-SDH, NADP-SDH and soluble AI, that degrade translocated sugars, in lateral buds increased on 20 and 30 DAR, whereas NAD-SDH in the internode of the shoot center decreased on 30 DAR. No other enzymes measured were influenced by the reorientation. Consequently, these changes may increase the sink capacity of the bud relative to shoot tissue, thereby stimulating bud growth.