Activity of Lactate Dehydrogenase and the Levels of Glucose and Starch in Vigna unguiculata Seedlings Exposed to Different Fractions of Crude Oil

Abstract

The study examined lactate dehydrogenase activity and the levels of glucose and starch in Vigna unguiculata seedlings exposed to Bonny Light whole crude oil (WC), its water soluble fraction (WSF) and water insoluble fraction (WIF). An in situ experiment was conducted with 500g sandy loam soil (0%) which served as control, and other bags of sandy loam soil which were mixed with different fractions of crude oil to give 2%, 5% and 10% contamination. Another sets of 500g filled bags of sandy loam soil were collected from a crude oil spill site at Ubeji community in Niger Delta. Three seeds of V. unguiculata were planted in each 500g soil bags and their roots recovered for analysis after 7, 14 and 21 days post germination. Lactate dehydrogenase (LDH) activity of the root had 46%, 57% and 60% increase in the 2%, 5% and 10% crude oil contaminated soil indicating a dose dependent increase when compared with the control. Glucose content also increased in the root of the contaminated soil from a range of 33% to 92% in the 2% contaminated soil and 33% to 94% in the 5% and 10% crude oil contaminated soil respectively. The WIF indicates the highest increase in both LDH activity and glucose content. However, starch content decreased significantly within the range of 13% to 67%. The WIF of 10% crude oil contamination having the highest decrease of 67% 21 days post germination (DPG) while the least decrease was observed in the root of 2% WC, 21 DPG. The result of the study suggests that the reduction in percentage germination and growth may be due to the decrease observed in starch content. The high LDH activity and high glucose content observed may indicate that high LDH activity is connected with increased energy demand to enable the seeds overcome the stress of germination and crude oil toxicity.