Role of kinetin in alleviation of copper and zinc toxicity in Lupinus termis plants

The effect of exogenous kinetin application on the growth and some physiological processes of Lupinus termis plants growing in metal containing solutions with excess concentrations of Cu and Zn ion were studied. Generally, plants growing in these solutions had a lower chlorophyll (Chl.) content, leaf relative water content (RWC) and produced less biomass than the control plants. Proline content was higher in metal-treated plants than in untreated controls. Chromatography of cell-free-extracts of roots and shoots indicated three main protein peaks with molecular weights about 170, 75--70 and 5--45 kDa. These peaks were coincident with Cu or Zn maxima. Addition of kinetin reduced the decline in Chl. content in metal-treated plants, improved water status of the plants and enhanced growth of the shoots and roots. The Cu or Zn content expressed on a per mg protein basis was raised when kinetin was applied to the growing shoots. Kinetin (Kin), Cu and Zn, singly and in the presence of kinetin (Cu x Kin and Zn x Kin), significantly affected the parameters tested. Only the effects of Cu x Kin and Zn x Kin interactions on shoot fresh weight and Cu x Kin on root length were statistically insignificant. Based on the calculated coefficient of determination (eta(2)) the roles of Cu and Zn in affecting Chl. content and growth were dominant in comparison to kinetin. Kinetin effect was dominant for root length and proline content, but the role of the interaction was subdominant. The results of this study indicate that kinetin can alleviate the harmful effects of Cu and Zn on the growth of lupin plants through stimulation of Cu and Zn incorporation into metal-binding proteins.