Under dark incubation, the presence of the photosystem II-specific inhibitor 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea and KCN, led to an ~50% reduction of Pi uptake. Moreover, uptake was significantly decreased in the presence of ion-gradient dissipating agents such as, gramicidin, the sodium ionophore, amiloride and valinomycin. Strong inhibition was also caused by carbonyl cyanide m-chlorophenylhydrazone
with the remaining activity ~ 25%. The Pi uptake was also diminished by N-ethylmaleimide. Altogether, these results indicated that the uptake of Pi by Synechocystis 6803 is energy-dependent and that an ion gradient is necessary for the uptake. Table 2 Effect of metabolic inhibitors, phosphate analogs, and incubation in the dark on phosphate uptake Selleck SBI-0206965 in Synechocystis BTSA1 sp. PCC 6803a Treatment Phosphate uptake (%) Control 100 ± 2 NaF 1 mM 93 ± 5 N, N-dicyclohexylcarbodiimide 40 μMb 91 ± 6 Na+ ionophore 10 μM 91 ± 4 Gramicidin10 μM 80 ± 3 Amiloride 20 μM 77 ± 5 Valinomycin 20 μM 77 ± 4 Monensin 20 μM 69 ± 4 KCN 5 mM 54 ± 3 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea 20 μMb 51 ± 6 Dark 48 ± 5 N-ethylmaleimide 1 mM 31 ± 6 Carbonyl cyanide m-chlorophenylhydrazone 40 μMb 23 ± 6 aCells were preincubated with inhibitors for 30 min before the addition of K2HPO4 to initiate uptake. Data are the mean of three experiments ± SD. bCells were preincubated with inhibitors for 2 min before assays. Effect of external pH on phosphate
uptake The Pi
uptake ability of wild-type Palbociclib clinical trial cells was tested at different pH buy Ulixertinib ranging from pH 5 to 11 using 25 mM of either MES/KOH (pH 5.0-6.0) or HEPES/KOH (pH 7.0-8.5) or ethanolamine/KOH (pH 10.0-11.0). The Synechocystis 6803 cells exhibited similar Pi uptake activity under broad alkaline conditions ranging from pH 7 to 10 (Figure 4). Figure 4 Effect of external pH on the initial rates of phosphate uptake in Synechocystis sp. PCC 6803. The 24 h cells grown in Pi-limiting medium were washed and resuspended in 25 mM each of MES/KOH (pH 5.0-6.0), HEPES/KOH (pH 7.0-8.5), and ethanolamine/KOH (pH 10.0-11.0) After 2 h incubation, aliquots were taken for assays of Pi uptake. Effect of osmolality on phosphate uptake The Pi uptake in many cyanobacteria was shown to be strongly activated by the addition of Na+ . The presence of NaCl could generate ionic stress and osmotic stress. To test whether ionic stress or osmotic stress affected Pi uptake, experiments were carried out in the presence of various concentrations of NaCl and sorbitol or a combination of both with a fixed osmolality equivalent to 100 mOsmol • kg-1. Figure 5 shows that NaCl stimulated Pi uptake whereas sorbitol reduced Pi uptake. The osmolality of 100 mOsmol • kg-1 contributed solely by sorbitol caused about 50% reduction in Pi uptake. However, increasing the concentration of NaCl while keeping the osmolality at 100 mOsmol • kg-1 led to a progressive increase of Pi uptake.