Cytokinin and Nitrate Mediated Expansion of Leucaena Leucocephala Cotyledons

Incubation of cotyledons from light or dark grown Leucaena seedlings in half strength Hoagland's solution for 24 h in light at 25 ± 2°C caused a significant increase in cotyledon area, which was further amplified by the addition of 50 µM kinetin or benzyladenine (BA) in the incubation medium. The kinetin mediated expansion of cotyledon was unaffected by the presence of nitrate in the incubation medium, while that mediated by BA was higher in the presence of 10m MNO⁻₃than in its absence. The cytokinin mediated cotyledon expansion was higher in the case of cotyledons from dark grown seedlings than those from light grown and hence dark grown cotyledons were used for further study. The pH of the medium in which these cotyledons were incubated increased slightly in the absence or presence of cytokiains, although the increase was higher in the presence of kinetin + NO⁻₃ and in the BA + NO⁻₃. The increase in cotyledon expansion and growth and total organic nitrogen by BA + NO⁻₃ were substantially inhibited when 0.1 mM sodium tungstate or serinol was included in the incubation medium. In each case, the change in the pH of the incubation medium was not correlated with the increase in cotyledon expansion. It is suggested that the mechanisms other than the pH changes might be involved in cytokinin mediated cotyledon expansion and that the assimilation of nitrate is prerequisite in nitrate induced cotyledon expansion.