EFFECTS OF CHROMIUM(VI) AND HUMIC SUBSTANCES ON SELECTED PHYSIOLOGICAL-RESPONSES OF AZOLLA-CAROLINIANA

The independent and interactive effects of Cr(VI) and humic substances were investigated on several physiological and biochemical responses of Azolla caroliniana. Cr(VI) concentrations of 1 and 2 mg l(-1) were found to cause a reduction in growth and chlorophyll a and b concentra tions of Azolla with and without the coexistence of humic substances. The Cr(VI) toxicity on these parameters was less pronounced in the pre sence of humic substances. Carotenoid concentrations were not signific antly affected by Cr(VI) treatments while humic substances, in the abs ence of Cr(VI), influenced an increase in carotenoid concentration. An thocyanins were increased in treatments receiving Cr(VI) and humic sub stances, both individually and together. Increases in anthocyanins wer e less pronounced in treatments receiving humic substances with Cr(VI) in comparison to treatments receiving Cr(Vf) in the absence of humic substances. Cr(VI) and humic substances influenced an increase in sucr ose, starch, and total nonstructural carbohydrate (TNC) accumulation. In the coexistence of Cr(VI) and humic substances, accumulation of car bohydrates was reduced in comparison to those receiving Cr(VI) in the absence of humic substances. Humic substances in the absence of Cr(VI) influenced a significant decrease in the activities of sucrose phosph ate synthase (SPS) and invertase and a significant increase in the act ivity of sucrose synthase (SS). Cr(VI)was insignificantly influenced S PS activity at 1 mg l(-1) and at 2 mg l(-1). Invertase activity was si gnificantly increased at both Cr(VI) treatments. Humic substances and Cr(VI) interactively resulted in increased SS activity insignificantly above those treatments receiving Cr(VI) in the absence of humic subst ances. Phosphate synthase activity was reduced at both Cr(VI) treatmen ts when humic substances were coexistent in comparison to treatments r eceiving Cr(VI) in the absence of humic substances. Invertase activiti es were reduced in treatments receiving Cr(VI) and humic substances to gether in comparison to those receiving Cr(VI) in the absence of humic substances.