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The influence of phenolic and humic acids on the activity of glucose-6-phosphate-dehydrogenase in the roots of pea under aseptic conditions has been investigated. It seems clear that vanillic and protocatechuic acids inhibit the enzyme activity in the excised roots of pea, but their dry weight increases in relation to the control. Gallic acid stimulates the G-6-PD activity in the roots of whole plants. The humic acids influence neither the enzyme activity nor the dry weight of pea seedlings after short-term treatment.

The oxidation of gallic acid by an enzyme preparation isolated from the culture medium ofNicotiana tabacumcell suspension could be followed by means of fast scan differential pulse polarography (DPP). A product was formed which could be reduced by means of DPP at- 0.47 V (MSE). The nature of the oxidation products is discussed.

The dynamics of changes in the content of four groups of phenolic substances was investigated during the growth cycle of the cell suspension culture ofNicotiana tábacumby means of fractionation. The relative contents of free phenolic acids, their esters, phenolic glycosides, and phenole acids non-extractable with methanol changed in dependence on the growth phase of the culture. A sharp increase, especially in the content of ester- and glycoside-bound phenolics and to a lesser extent also of phenolics belonging to the other two groups, occurred at the end of the lag phase. Then, after a temporary decrease at the early linear phase, the level of phenolics in the three fractions representing bound forms considerably increased again at the late linear and early stationary phases. The synthesized phenolic substances were partially released from the cells into the cultivation medium, which contained 15 to 30 % of the total content of the phenolics in the culture at different phases of the growth cycle. Likely causes of these changes are discussed.

Anodic oxidation of coumaric acid led to the inhibition of the process at the electrode due to a film which was formed after one-electron oxidation of the acid to phenoxy radical.By contrast, caffeic acid is oxidized in two steps-the phenoxy radical is formed in the first step, quinone in the second step. The inhibition of nitrate uptake by coumaric and caffeic acids is dependent on their concentration. 10-4M eaffeic acid totally inhibited nitrate uptake and the growth ofNicotiana tabacumcell suspension. 10-6M caffeic acid markedly inhibited nitrate uptake especially in the first three days after inoculation. 10-6M coumaric acid did not affect nitrate uptake and nitrate reductase activity, 10-4M coumaric acid inhibited nitrate uptake by day two after inoculation. Nitrate reductase synthesis correlated with the inhibition of nitrate uptake. Differential effects of coumaric and caffeic acids are explained on the basis of different products of their electrochemical oxidation.

Exposure of isolated pea roots to 0.5 and 2.0 mM nitrite resulted in a temporary decrease in glutamine synthetase (GS) level. The GS level decrease was preceded by a temporary increase in NO2- content: nitrite content maximum was observed after 6 h exposure, GS level was depressed most after 12 h. At this time, GS level also significantly decreased by 0.3 and 0.4 mM NO2-, but the effect of these concentrations was only slight and not significant after 18 h exposure. By contrast, GS level in roots precultivated for 24 h in solutions containing 2 mM NO2- did not fully recover even after further 24 h cultivation in nutrient solutions lacking NO2-. The inhibitory effect of NO2-on GS level was stressed by lack of sugar in nutrient solutions. Nitrite did not affect GS activity (transferase reaction)in vitro. The decrease in GS level due to exposure to No2- was accompanied by KH3excretion to nutrient solution.

The optimum conditions for cell suspension culture experiments have been characterized by respiration,p-Phenylenediamine oxidase and growth of cell suspension ofNicotiana tabacumfor 15 days in stationary culture. Change of 3,4-Dihydroxybenzoic and 4-Hydroxybenzoic acids both present at 10−4M in culture medium were studied in short term experiments. An oxidation product of 3,4-Dihydroxybenzoic acid characterized by an absorption maximum at 280 nm was isolated after 1 h of incubation. The 4-Hydroxybenzoic acid did not change when incubated for 4 h under the same conditions.