Uptake, Transport, Re-translocation and Chelation of Ni in One Tolerant and One Susceptible Graminaceous Species

Abstract

From flora of Northwest Iran, two Graminaceous species including Secale montanum and Dactylis glomerata with different distribution and coverage on Ni-rich soils were selected for study of tolerance mechanisms to Ni concentrations up to 100 microM in hydroponic culture medium. Shoot and root growth of D. glomerata was inhibited up to 42 and 69% in response to 100 microM Ni, respectively, while growth reduction of S. montanum was as low as 20% in shoot and no growth inhibition of root was observed. Different growth response was not the result of different Ni accumulation, two studied species demonstrated a similar accumulation potential for Ni. A higher endogenous and Ni-induced malate accumulation did not cause a higher tolerance to Ni in D. glomerata. In contrast, high endogenous and Ni-induced accumulation of cysteine particularly in shoot was observed in Ni tolerant S. montanum. Distribution of Ni among various fractions of plant tissues studied by gel filtration chromatography suggested also an efficient chelation of excess Ni by low molecular weight fraction in S. montanum but not in D. glomerata. A higher re-translocation of Ni from mature into growing young leaves was one of the other causes of higher susceptibility of D. glomerata to excess Ni. Activity ofperoxidase and catalase was much stronger inhibited in D. glomerata than S. montanum and activity of polyphenol oxidase was induced in response to Ni toxicity in roots of S. montanum. A possible role of this enzyme, involving in lignification, for higher Ni tolerance ofS. montanum was discussed.