Sugars are under light control during bud burst in Rosa sp.

Abstract

Bud burst in certain species is conditioned by the luminous environment. With roses, the requirement for light is absolute, and darkness totally inhibits bud burst. Few studies have looked into understanding the action of light on the physiological bud burst processes. Here, we show the impact of light on certain components of glucidic metabolism during bud burst. Measurements were taken on decapitated plants of Rosa hybrida L. 'Radrazz' exposed either to darkness, white, blue or R light. Results show that a mobilization of bud and the carrying stem sucrose reserves only takes place in light and accompanies the bud burst. Furthermore, the activity of the RhVI vacuolar acid invertase which contributes to the breakdown of sucrose in the buds, as well as the transcription of the RhVI gene, is reduced in darkness, although it is strongly stimulated by light. The same analysis concerning the RhNAD-SDH gene, coding an NADdependent sorbitol dehydrogenase, shows, on the contrary, a strong induction of its transcription in darkness that could reflect the use of survival mechanisms in this condition.

Cytokinins Are Initial Targets of Light in the Control of Bud Outgrowth

“…An exogenous supply of sugars in darkness had little effect on the dark inhibition of bud outgrowth, as observed previously in vitro (Henry et al, 2011;Rabot et al, 2012). This confirms that the sugar level in the vicinity of the bud is not the initial limiting factor for bud outgrowth in the dark (Girault et al, 2010). Rather, light control of the vacuolar Suc invertase RhVI, the Suc synthase RhSUSY, and the two Suc transporters RhSUC2 and RhSWEET10, as shown here (Fig.…”

“…Norflurazon and masking experiments in this study confirm our previous evidence that a bud relies on sugar already present in the plant rather than on instant sugar assimilation through photosynthesis to achieve outgrowth (Girault et al, 2010;Henry et al, 2011). An exogenous supply of sugars in darkness had little effect on the dark inhibition of bud outgrowth, as observed previously in vitro (Henry et al, 2011;Rabot et al, 2012).…”

“…10A, red color code). As observed previously (Girault et al, 2010), the NAD-DEPENDENT SOR-BITOL DEHYDROGENASE gene (NAD-SDH) also was strongly induced in buds by dark treatment.…”

“…In the bud, strong up-regulation of RhVI at 6 h by light would contribute to rapid sugar degradation required for the initiation of bud outgrowth ( Fig. 10A; Girault et al, 2010;Mason et al, 2014;Barbier et al, 2015a). RhSUSY that is stimulated by WL at 24 h in the bud also would contribute to outgrowth, but in a later phase (Fig.…”

“…Recently, sugars were shown to act as an initial trigger of bud release in pea (Mason et al, 2014) and as an early modulator of the key hormonal mechanisms controlling bud outgrowth in rose (Barbier et al, 2015a) under a favorable light environment. In rose, the transcription and enzymatic activity of vacuolar invertase (RhVI) as well as transcription of the Suc transporter gene RhSUC2 are under light control, and darkness leads to their repression concomitant with the inhibition of bud outgrowth (Girault et al, 2010;Henry et al, 2011;Rabot et al, 2012Rabot et al, , 2014. However, in vitro culture of excised rose buds in the presence of sugars does not rescue dark inhibition (Henry et al, 2011;Rabot et al, 2012), suggesting that sugars are not the initial target of the light signal that controls outgrowth.…”