The Effect of Exogenous IAA and Kinetin on Nitrate Reductase, Nitrite Reductase and Glutamate Dehydrogenase Activities in Excised Pea Roots

Nitrate reductase (NO 3 R) activity, nitrite reductase (NO 2 R) activity and NADH 2 dependent glutamate dehydrogenase (GDH) activity were followed in extracts from excised pea roots incubated under aseptic conditions for 9 and 24 h in nitrate containing nutrient medium to which IAA was added in concentrations promoting lateral root formation (1 × 10 −5 ; 3 × 10 −5 ; 5 × 10 −5 M) and kinetin in concentrations which reduce lateral root formation (0.1; 1; 5 mg 1 −1 , that is 4.65 × 10 −7 ;4.65 × 10 −6 and 2.3 × 10 −5 M). NO 3 R activity was not influenced by IAA, NO 2 R activity was slightly depressed by IAA after 24 h incubation and GDH activity was slightly increased after 24 h incubation in the presence of IAA. Kinetin decreased NO 3 R activity significantly both after 9 h and 24 h incubation, slightly increased NO 2 R activity after 9 h incubation but slightly decreased it after 24 h incubation, and did not affect GDH activity after 24 h incubation. However, when applied together with IAA, kinetin abolished the promoting effect of IAA on GDH activity. IAA neither reversed nor accentuated the effect of kinetin on NO 2 R activity. Nevertheless the depressing effect of kinetin on NO 3 R activity was emphasized by the presence of IAA after 9 h incubation. The results obtained indicate that reduced nitrate assimilation due to the depression of nitrate reductase activity caused by kinetin probably contributes to the negative growth effect of kinetin in pea root segments grown in nitrate medium.