Effects of timing of defoliation on nitrogen assimilation and associated changes in ethylene biosynthesis in mustard (Brassica juncea)

Mustard (Brassica juncea L.) is characterized by oblong-shaped leaves on the lower layers of axis. These leaves are poorly illuminated, remain below light photosynthetic compensation point and abscise at maturity. Earlier research has shown that the removal of these shaded leaves improves photosynthetic potential of the rest of the leaves, the overall growth and yield of the crop. Now we show that 50% removal of these leaves at pre-flowering stage, i.e. 40 days after sowing (DAS) enhances nitrogen assimilation in the leaves more substantially than defoliation at post-flowering stage, i.e. 60 DAS. Further, the changes in N assimilation were concurrent with the ethylene evolution. It is suggested that strategies that lead to the abscission of lower leaves at early stage of growth may be adopted for efficient N utilization, and ethylene may be considered as an important physiological tool.