Date of Publication


Document Type

Master's Thesis

Degree Name

Master of Science in Biology

Subject Categories



College of Science




The study determined the tolerance of pole bean (Vigna sesquipedalis [L] Verdec subspecies sesquipedalis) and cowpea (Vigna unguiculata [L} Walp. subspecies unguiculata) to lead (Pb). Pb is a common soil contaminant that is toxic and causes oxidative stress in many plants. Under laboratory conditions, seeds were germinated and grown in paper towels with Pb at 2 ppm, 20 ppm, 200 ppm, 2000 ppm, and tap water as the control. Two days after sowing, the lengths of primary root and hypocotyl were measured. Seven day-old seedlings were harvested and growth measurements included primary root length, number and length of lateral root, hypocotyl length, shoot length, wet and dry weights. Pb uptake was determined using Atomic Absorption Spectrophotometry (AAS) of nitric acid-digested samples. Protein content was estimated using the Bradford method, while peroxidase activity was detected through spectrophotometry. Comparison of the two species of seedlings was based on root-to-shoot ratio, tolerance index and growth increments. Results indicated that high Pb concentration affected the growth of pole bean and cowpea seedlings. However, Pb neither enhanced nor hindered the seed germination. Inhibition of root growth, but not the hypocotyl elongation was evident in 2-day-old Pb- treated seedlings. In 7-day-old seedlings, the primary root, lateral root, hypocotyl, and shoots were shorter in the Pb-treated compared to those grown in tap water. The number of lateral roots in both species was reduced with Pb treatment. Root cortical cells increased in size with increasing Pb concentrations. Pb uptake in seedlings ranged from 33 to 38 Ag/g dry weight when exposed to Pb concentrations lower than 2000 ppm, and the uptake was not significantly different (pC0.05) between the two species. Seedlings grown in lower concentrations of Pb did not desorb the Pb, even after soaking the roots for 24 hours in deionized water. Protein content and peroxidase activity in seedlings increased with increasing Pb uptake. Root–to-shoot ratio in pole bean seedlings significantly decreased when grown in high concentration of Pb, which did not occur in cowpea. Tolerance index did not significantly differ among Pb-treated seedlings of both species. Although growth was stunted, both pole bean and cowpea seedlings survived and tolerated Pb concentration as high as 200 ppm. At 2000 ppm, the growth of both seedling species was significantly reduced.

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x, 108 leaves


Cowpea; Beans; Soil pollution

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