Characterized right here. Nevertheless, our calculations suggest that the estimated vacuolar ABA-GE
Characterized right here. Nevertheless, our calculations recommend that the estimated vacuolar ABA-GE accumulation could be reached within two h at the assumed continuous cytosolic ABA-GE concentration. In addition, ABA-GE levels in leaves have been shown to become fairly continual and only to substantially increase during repeated drought strain cycles (Boyer and Zeevaart, 1982). Hence, regardless of the low affinity for ABA-GE, the identified vacuolar ABA-GE import mechanisms are possiblyPlant Physiol. Vol. 163,Vacuolar Abscisic Acid Glucosyl Ester Import Mechanismsadequate for the upkeep of vacuolar ABA-GE levels in vivo under standard conditions and presumably also can accommodate escalating cytosolic ABA-GE levels that happen (e.g. during drought stress situations). The energized transport of glucosides of secondary metabolites and xenobiotics into plant vacuoles is well documented. The anthocyanin malvidin-3-O-glucoside is transported into vacuoles of grape (Vitis vinifera) berries by the ABCC transporter ABCC1 from grape (Francisco et al., 2013). Proton gradient-dependent vacuolar transport mechanisms were reported for diverse flavonoid glucosides (Klein et al., 1996; Frangne et al., 2002; Zhao and Dixon, 2009; Zhao et al., 2011). Furthermore, the vacuolar import mechanism of particular Glc conjugates was located to become species or tissue precise. Salicylic acid glucoside is transported into vacuoles from tobacco (Nicotiana tabacum) culture cells by protondependent transport mechanisms and into vacuoles from soybean (Glycine max) hypocotyls by ABC-type transport mechanisms (Dean and Mills, 2004; Dean et al., 2005). The glucoside of coniferyl alcohol was shown to become transported into endomembrane-enriched vesicles isolated from differentiating xylem of poplar (Populus spp.) via proton antiporters and into Arabidopsis leaf mesophyll vacuoles by way of ABC BRDT Storage & Stability transporters (Miao and Liu, 2010; Tsuyama et al., 2013). In addition, concurrent ABC-type and proton-dependent vacuolar transport mechanisms have been shown for the flavone diglucoside saponarin (Frangne et al., 2002). Hence, our findings around the simultaneous transport of ABA-GE by proton-dependent and ABC-type mechanisms are in agreement with earlier reports around the vacuolar import of glucosides. The reported Km values of those vacuolar transports have been in array of 10 to one hundred mM, that is 10- to 100-fold lower than the BRD2 supplier apparent Km with the ABA-GE import. Alternatively, the Vmax from the ABA-GE uptake was larger compared with some reported glucoside transports, which include that of saponarin (Frangne et al., 2002). The vacuolar membrane localization of Arabidopsis ABCC-type transporters and the recent demonstration that grape ABCC1 mediates the vacuolar transport of anthocyanidin glucosides (Kang et al., 2011; Francisco et al., 2013) recommended the participation of ABCC-type transporters in vacuolar ABA-GE accumulation. The Arabidopsis AtABCC1 and in particular AtABCC2 mediate the transport of structurally diverse metabolites, including phytochelatins, folates, and conjugates of chlorophyll catabolite and xenobiotics (Liu et al., 2001; Frelet-Barrand et al., 2008; Raichaudhuri et al., 2009; Song et al., 2010). We expressed AtABCC2 in yeast and observed a distinct MgATP-dependent ABA-GE transport activity of isolated membrane vesicles (Fig. 6). This transport was nearly fully abolished within the presence of ABC transporter inhibitors (Table II). We additionally tested AtABCC1, the closest paralog of AtABCC2. Additionally, it mediated MgATP-dependent.
