The influence of uncouplers on facilitated diffusion of sorbose in Saccharomyces cerevisiae

Sorbose uptake in Saccharomyces cerevisiae, strain Delft 1, proceeds via mediated passive transport. In the cell sorbose is distributed in at least two compartments. Efflux studies showed that sorbose uptake in one of these compartments is not readily reversible. Uncouplers of oxidative phosphorylation inhibit both transport velocity and steady-state uptake level. It could be shown that these two effects are caused by different modes of action of the uncouplers. None of these two effects could be ascribed to changes of the electrochemical H⁺ gradient or of the intracellular pH. It is suggested that the inhibition of uptake velocity is caused by binding of the uncoupler to the sorbose translocator, thus lowering the transport activity. The uncoupler binding site is probably located at the intracellular fragment of the carrier. The second effect, reduction of the steady-state uptake level, is probably due to blocking of sorbose influx into the compartment that exhibits poor reversibility.     

Influence of rootstocks on growth,yield, fruit quality and leaf mineral element contents of pear cv. ‘Santa Maria’ in semi-arid conditions

Background

Rootstocks play an essential role to determining orchard performance of fruit trees. Pyrus communis and Cydonia oblonga are widely used rootstocks for European pear cultivars. The lack of rootstocks adapted to different soil conditions and different grafted cultivars is widely acknowledged in pear culture. Cydonia rootstocks (clonal) and Pyrus rootstocks (seedling or clonal) have their advantages and disadvantages. In each case, site-specific environmental characteristics, specific cultivar response and production objectives must be considered before choosing the best rootstock. In this study, the influence of three Quince (BA 29, Quince A = MA, Quince C = MC) and a local European pear seedling rootstocks on the scion yield, some fruit quality characteristics and leaf macro (N, P, K, Ca and Mg) and micro element (Fe, Zn, Cu, Mn and B) content of ‘Santa Maria’ pear (Pyrus communis L.) were investigated.

Results

Trees on seedling rootstock had the highest annual yield, highest cumulative yield (kg tree⁻¹), largest trunk cross-sectional area (TCSA), lowest yield efficiency and lowest cumulative yield (ton ha⁻¹) in the 10^th year after planting. The rootstocks had no significant effect on average fruit weight and fruit volume. Significantly higher fruit firmness was obtained on BA 29 and Quince A. The effect of rootstocks on the mineral element accumulation (N, K, Ca, Mg, Fe, Zn, Cu, Mn and B) was significant. Leaf analysis showed that rootstocks used had different mineral uptake efficiencies throughout the early season.

Conclusion

The results showed that the rootstocks strongly affected fruit yield, fruit quality and leaf mineral element uptake of ‘Santa Maria’ pear cultivar. Pear seedling and BA 29 rootstock found to be more prominent in terms of several characteristics for ‘Santa Maria’ pear cultivar that is grown in highly calcareous soil in semi-arid climate conditions. We determined the highest N, P (although insignificant), K, Ca, Mg, Fe and Cu mineral element concentrations on the pear seedling and BA 29 rootstocks. According to the results, we recommend the seedling rootstock for normal density plantings (400 trees ha⁻¹) and BA 29 rootstock for high-density plantings (800 trees ha⁻¹) for ‘Santa Maria’ pear cultivar in semi-arid conditions.     

The influence of uncouplers on proton-sugar symport in Saccharomyces fragilis

Uncouplers of oxidative phosphorylation inhibit proton-sugar symport in Saccharomyces fragilis. However, they do not induce efflux of accumulated sugar. It is shown that the effect cannot be explained by uncoupler-induced alterations in the transmembrane potential or transmembrane pH difference. It is also indicated that a decrease in intracellular pH is not involved in inhibition of sugar transport. It is argued that inhibition of transport by uncouplers is most likely caused by a direct interaction with the translocator.