Abstract

Experiment was performed in a pot to examined the effect of leaf locations on the concentrations of some plant toxins (cyanide, nitrate, soluble and total oxalates), and nutrients viz; beta-carotene (provitamin A), vitamin C and mineral elements (Fe, Mg, Cu, Zn, Ca Na and K) at market maturity (vegetative phase) of Corchorus olitorius grown in nitrogen and non – nitrogen treated soil. The leaves of Corchorus olitorius were harvested at three different leaf locations (basal, middle and upper positions) and they were subjected to chemical analysis. The result showed that there was no significant differences in the cyanine concentration between basal and middle leaves, however, the leaves obtained from upper leaf location was significantly (p < 0.05) lower in cyanide concentration than those leaves obtained each from basal and middle leaf regions in control and nitrogen treated Corchorus olitorius. The nitrate content in Corchorus olitorius was significantly (p < 0.05) highest in the basal leaves closely followed by middle leaves and least in the upper leaves in control, however, with the application of nitrogen fertilizer, no significant variation in the nitrate concentration was observed between leaves obtained from middle and upper leaf locations, but leaves obtained from each of these locations were significantly (p < 0.05) lower than those from basal leaf region. Both soluble and total oxalate concentrations increased with leaf age in Corchorus olitorius irrespective of soil nitrogen levels. The concentration of beta-carotene was significantly (p < 0.05) higher in middle leaves compared to basal and upper leaves each in nitrogen and non-nitrogen fertilized Corchorus olitorius. While the concentration of vitamin C was significantly highest in middle leaves followed by upper leaves and least in the basal leaves of Corchorus olitorius irrespective of soil nitrogen levels. The Fe, Cu and Ca contents were generally concentrated in basal and middle leaves of the vegetable. Leaf location had no significant enfluence on the accumulation of Na and Mg in Corchorus olitorius, except that the concentration of Mg in basal and middle leaves was significantly elevated than upper leaves with the application of nitrogen fertilizer. While the concentration of K in Corchorus olitorius was significantly (p < 0.05) elevated in upper and middle leaves compared basal leaves, the concentration of Zn was significantly (p < 0.05) higher in the middle leaves than those obtained each from basal and upper leaf locations. The result concludes that the concentrations of phytoxins (cyanide, nitrate, soluble and total oxalates) are elevated in older leaves than younger ones of Corchorus olitorius.Thus avoiding the consumption of older leaves of the vegetables will reduced the health problems associated with high intake of these plant toxins.

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