Interactive effects of temperature and heavy metals (Cd, Pb) on the elongation growth in maize coleoptiles

The effect of Cd and Pb on endogenous and IAA-induced elongation growth and medium pH of maize coleoptile segments incubated at 20, 25 and 30 °C was studied. It was found that the elongation of coleoptile segments and proton extrusion increased with the temperature and reached its maximum at 30 °C. For Cd, the maximal inhibition of endogenous and IAA-induced growth as well as medium acidification of coleoptile segments was observed at 25 °C. Meanwhile, Pb, irrespective of the temperature, diminished the growth of the segments by ca. 20%, increasing the acidification of the incubation medium. It was also found that in contrast to Cd, Pb accumulation in maize coleoptile segments did not correlate with temperature. The results suggest that the toxic effect of Cd on elongation growth of coleoptile segments is connected with the decrease of the PM H+-ATPase activity and probably with Cd-induced high acivity of IAA oxidase, whereas the effect of Pb did not depend on activity of any of the enzymes.