Alleviation of heavy metal stress by arbuscular mycorrhizal fungi and jasmonic acid in maize plants

Abstract

The responses of maize plants grown in sterilized sand loamy soil to addition of different concentrations of zinc or chromium (0, 1, 2 and 4 mM) in presence or absence of arbuscular mycorrhizal (AM) fungi (Glomus fasciculatum) and / or jasmonic acid (JA) [the hormonal regulator involved in plant responses to abiotic and biotic stress] were investigated in pot experiments . In general, addition of zinc or chromium especially at high levels to the growth medium of maize plants reduced all growth parameters (plant height, number of leaves, leaf area, stem thickness, fresh and dry matter and photosynthetic pigments). However, the presence of AM fungi and JA individually or in combination statistically increased value of all the previous parameters. In presence of AM fungi and JA a marked increase in N, P, K and Mg contents in roots and leaves of maize plants occurred, but Zn or Cr accumulation decreased and their accumulation was higher in roots than in shoots. The accumulation of total soluble sugars, proline and total free amino acids in maize plants in presence of AM plus JA, indicate increased tolerance in plant to zinc and chromium stress. Mycorrhizal colonization was adversely affected by zinc or chromium; however, high levels of colonization still occurred at even the most toxic levels. The increase in mycorrhizal inoculation effect (MIE) with increasing Zn or Cr concentrations, indicate that the plants became highly mycorrhizal dependant.