The effect of 2, 4-dichlorophenoxyacetic acid on the activity of phosphofructokinase in Vigna unguicula (L.) Walp. leaf tissue

Abstract

Phosphofructokinase (PFK) activity was found in all cowpea leaf tissue preparations. Phosphofructokinase activity in non-treated plant tissue preparations harvested during the light period was competitively inhibited. Preparations collected during the dark period from non-treated leaf tissue contained approximately 70% higher activity than non-treated leaf tissue preparations harvested in the light. Treatment of cowpea plants with a 4.5 x 10⁻⁴M sodium salt of 2,4-D solution resulted in equalization of PFK activity in both the light and dark harvested leaf tissue. It was suggested that PFK activity in the leaves of cowpea plants was controlled by a photoresponse or by a metabolic product which is under the influence of light. The data reported supports the energy concept of 2,4-D action. Monophosphorylated sugar concentration was inversely correlated with PFK activity at the 5% level of probability. Herbicide treatment resulted in a shift to a higher concentration of monophosphorylated sugars from the light to the dark period. The shift to a higher concentration may have resulted from a shift on the type of carbohydrate metabolism. The concentration of diphosphorylated sugar was directly correlated with PFK activity. For 10 to 14 hours after herbicide application diphosphorylated sugar occurred at a low level. This low level could be attributed to an increased rate of respiration. Free sugar concentration fluctuated erratically throughout the experimental period. However, the free sugar concentration in 2,4-D treated tissue was equal to or higher than the concentrations in the extracts form non-treated tissue. This could indicate a stimulation of photosynthesis or a stimulation of starch and sucrose hydrolysis as a result of sub-lethal treatment with 2,4-D.