Nitrate Reductase Activity During Ontogeny of the Fruit of Cashew (Anacardium occidentale L.)

Abstract

The in vivo nitrate reductase (NR) activity was assayed in the pedicel (apple), the fruit wall (shell) and the ovule (kernel) of cashew at 5-day intervals after fertilization. The pericarp showed high rates of enzyme activity during fresh weight accumulation, but activity remained low in the pedicel during its development. Estimation, using a graphical integration method, of total nitrate reduced by individual parts of the fruit showed that the pericarp contributed the maximum (67.5%) and the pedicel the least (7.8%) to the total nitrate assimilated in the fruit.

The rate of NR activity varied with tissue nitrate content in any fruit part but was not related to the pattern of organic nitrogen accumulation except in the case of the ovule. However, NR activity of the true fruit (the nut) was accountable for about 3-4% of the total organic nitrogen present at maturity. Besides its major role in nitrate assimilation, there was evidence that the pericarp exports about 60% of its nitrogen to the seed.