RESUMEN
Bud burst is a decisive process in plant architecture that requires light in Rosa sp. This light effect was correlated with stimulation of sugar transport and metabolism in favor of bud outgrowth. We investigated whether sugars could act as signaling entities in the light-mediated regulation of vacuolar invertases and bud burst. Full-length cDNAs encoding two vacuolar invertases (RhVI1 and RhVI2) were isolated from buds. Unlike RhVI2, RhVI1 was preferentially expressed in bursting buds, and was up-regulated in buds of beheaded plants exposed to light. To assess the importance of sugars in this process, the expression of RhVI1 and RhVI2 and the total vacuolar invertase activity were further characterized in buds cultured in vitro on 100 mM sucrose or mannitol under light or in darkness for 48 h. Unlike mannitol, sucrose promoted the stimulatory effect of light on both RhVI1 expression and vacuolar invertase activity. This up-regulation of RhVI1 was rapid (after 6 h incubation) and was induced by as little as 10 mM sucrose or fructose. No effect of glucose was found. Interestingly, both 30 mM palatinose (a non-metabolizable sucrose analog) and 5 mM psicose (a non-metabolizable fructose analog) promoted the light-induced expression of RhVI1 and total vacuolar invertase activity. Sucrose, fructose, palatinose and psicose all promoted bursting of in vitro cultured buds under light. These findings indicate that soluble sugars contribute to the light effect on bud burst and vacuolar invertases, and can function as signaling entities.
Asunto(s)
Flores/efectos de la radiación , Luz , Rosa/efectos de la radiación , beta-Fructofuranosidasa/metabolismo , Secuencia de Aminoácidos , Transporte Biológico , Clonación Molecular , Técnicas de Cultivo/métodos , ADN Complementario/genética , ADN Complementario/metabolismo , Oscuridad , Activación Enzimática , Flores/genética , Flores/metabolismo , Fructosa/farmacología , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Glucosa/farmacología , Isomaltosa/análogos & derivados , Isomaltosa/farmacología , Manitol/farmacología , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Rosa/enzimología , Rosa/genética , Transducción de Señal , Sacarosa/farmacología , Factores de Tiempo , Transcripción Genética , Vacuolas/enzimología , Vacuolas/metabolismo , beta-Fructofuranosidasa/genéticaRESUMEN
In temperate woody species, the vegetative growth period is characterized by active physiological events (e.g., bud break), which require an adequate supply of soluble sugars imported in the xylem sap stream. One-year-old shoots of walnut (Juglans regia L. cv. 'Franquette') trees, which have an acrotonic branching pattern (only apical and distal vegetative buds burst), were used to study the regulation of xylem sugar transporters in relation to bud break. At the end of April (beginning of bud break), a higher xylem sap sucrose concentration and a higher active sucrose uptake by xylem parenchyma cells were found in the apical portion (bearing buds able to burst) than in the basal portion (bearing buds unable to burst) of the sample shoots. At the same time, xylem parenchyma cells of the apical portion of the shoots exhibited greater amounts of both transcripts and proteins of JrSUT1 (Juglans regia putative sucrose transporter 1) than those of the basal stem segment. Conversely, no pronounced difference was found for putative hexose transporters JrHT1 and JrHT2 (Juglans regia hexose transporters 1 and 2). These findings demonstrate the high capacity of bursting vegetative buds to import sucrose. Immunological analysis revealed that sucrose transporters were localized in all parenchyma cells of the xylem, including vessel-associated cells, which are highly specialized in nutrient exchange. Taken together, our results indicate that xylem parenchyma sucrose transporters make a greater contribution than hexose transporters to the imported carbon supply of bursting vegetative buds.