Sulfite inhibition of sucrose transport into vacuoles of cottonwood leaves

The mechanism of sucrose transport and the influence of various concentrations of sulfite on its activity was studied in the mesophyll vacuoles isolated from cottonwood (Populus deltoides Bartr. ex Marsh) leaves. Kinetic analysis of [14C] sucrose uptake by isolated vacuoles revealed the presence of a saturable component with Km for sucrose uptake = 23 mM and Vmax = 21.2 nmol sucrose 10-6 vacuoles min-1. The saturable component was inhibited by SH-blocker, p-chloromercuribenzenesulfonic acid (PCMBS) and was substrate specific. The transport of sucrose was not changed by ATP with or without Mg2+, by the ionophore, valinomycin and by protonophores, carbonylcyanide m-chlorophenyl hydrazone (CCCP) or dinitrophenol (DNP). Sulfite at concentrations of 0.01-2.5 mM inhibited the uptake of [14C] sucrose by isolated vacuoles. Inhibition was of the noncompetitive type with K; = 2.48 mM of sulfite (22oC)

Aluminium effects on pyridine nucleotide redox state in roots of Scots pine

After prolonged (3-9 weeks) hydroponic treatment of Scots pine seedlings with different concentrations (0.5-4.0 mM) of Al (AI(N03)3), the levels of pyridine nucleotides were determined in root homogenates. After 3 weeks of Al stress, a significant decrease of the anabolic reduction charge (ARC: NADPH/(NADP+ + NADPH)) and an increase of the redox status (NAD(P)H/NAD(P)+), catabolic reduction charge (CRC: NADH/(NAD+ + NADH)) and phosphorylation capacity expressed as NADP+/NAD+ ratio was found in the 4.0 mM Al treatment. After 6 weeks, Al at concentrations of 0.5 and 1.0 mM induced an enhancement of the NADH level and a reduction of NADPH level, but the redox ratios were not changed significantly. After 9 weeks treatment with Al concentrations ranging from 0.5 to 4.0 mM, decreases of the relative level of NADP+, NADPH and NADH and increases of NAD+ were found. Consequently, the CRC, NAD(P)H/NAD(P)+ and NADP+/NAD+ ratios reached a minimum and ARC a maximum as compared to previous measurements