Foliar treatment of potassium nitrate modulates the fermentative and sucrose metabolizing pathways in contrasting maize genotypes under water logging stress

Abstract

The effect of potassium nitrate on the status of fermentative and sucrose metabolizing pathways was studied in two maize (Zea mays L.) genotypes, viz., LM 5 (relatively susceptible to flooding) and I 167 (relatively tolerant to flooding) under water logging stress. The higher increase in pyruvate decarboxylase, alcohol dehydrogenase and aldehyde dehydrogenase activities in the hypoxic roots of I 167 seedlings over LM 5 showed the former's efficient tolerance mechanism towards anaerobic conditions. Foliar application of KNO₃ reduced these enzymatic activities in the roots of both the genotypes. The shoots of I 167 seedlings also showed a parallel increase in alcohol dehydrogenase and pyruvate decarboxylase activities under water logging stress. These enzymatic activities, however, remained unaffected in shoots of water logged LM 5 seedlings. There was a higher decrease in acid and alkaline invertase activities in the hypoxic roots of I 167 seedlings. KNO₃ treatment led to higher acid invertase activity in roots of I 167 seedlings than those of LM 5. Sucrose synthase (synthesis) and sucrose phosphate synthase activities decreased, but sucrose synthase (breakdown) activity increased in the roots of both the genotypes, during water logging. KNO₃ increased sucrose synthesizing activities with a parallel increase in the sucrose content of the roots. Sucrose synthesis was comparatively unaffected in I 167 shoots under water logging stress while LM 5 shoots showed higher reduction in its sucrose synthase (synthesis) and sucrose phosphate synthase activities. It may thus be concluded that KNO₃ induced a network of reactions for improving water logging tolerance. The nitrate ions acted as an alternate electron acceptor and thus reduced the activities of fermentative enzymes. It promoted the funneling of sugars into the glycolytic pathway by inducing the activities of acid and alkaline invertases in the roots and shoots of maize genotypes. It also directed the hexoses towards biosynthetic pathway by increasing the activities of sucrose synthesizing enzymes.

Keywords: Fermentative pathway; Potassium nitrate; Sucrose metabolism; Water logging.

Fig. 1

Effect of KNO₃ on ADH, PDC and ALDH activity in the roots (a, c, e) and shoots (b, d, f) of LM-5 and I-167 seedlings respectively, under water logging conditions. Error bars represent standard deviations. Bars with different alphabets represent significant differences at p < 0.05

Fig. 2

Effect of KNO₃ on AI and AKI activity in the roots (a, c) and shoots (b, d) of LM-5 and I-167 seedlings respectively, under water logging conditions. Error bars represent standard deviations. Bars with different alphabets represent significant differences at p < 0.05

Fig. 3

Effect of KNO₃ on SS (synthesis), SPS and SS (breakdown) activity in the roots (a, c, e) and shoots (b, d, f) of LM-5 and I-167 seedlings respectively, under water logging conditions. Error bars represent standard deviations. Bars with different alphabets represent significant differences at p < 0.05

Fig. 4

Effect of KNO₃ on total soluble sugars, reducing sugars and sucrose content in the roots (a, c, e) and shoots (b, d, f) of LM-5 and I-167 seedlings respectively, under water logging conditions. Error bars represent standard deviations. Bars with different alphabets represent significant differences at p < 0.05