THE EFFECT OF CHILLING TEMPERATURE ON THE PERMEABILITY OF MEMBRANES TO K-POTENTIAL OF LEAVES IN THE SEEDLINGS OF MAIZE (ZEA-MAYS L)(, MG2+,CA2+ IONS AND ON THE ELECTRIC)

The relations between the extent of injuries in seedlings caused by a few day-long exposures to chill (5 degrees C) and the leakage of K+, M g2+ and Ca2+ ions from the leaves as well as the electric potential in seven maize hybrids, were investigated. The permeability of cells to ions was defined based on their absolute concentration in a water diff usate (C-t) and concentration expressed in relation to the total ion c ontent in the leaves (IL index). At lowered temperature the hybrids of higher resistance to chilling temperature were characterized by a low er value of the IL index for K+ and Mg2+ ions than the chill sensitive hybrids. On the other hand, absolute concentration of the ions (C-t) Mg2+ and Ca2+ leaking from the leaves before chill exposure of the see dlings was positively and highly correlated with the extent of injurie s in hybrids caused by 4 day-long exposures to chill. This-observation is evidence that the chill injuries were predetermined through increa sed cell permeability to the mentioned ions at room temperature. Chang es in the electric potential of leaves in conditions of lowered temper ature preceded the injuries of leaves, which became apparent after a l onger period of exposure to chill. Thus, as the leakage of Mg2+ and Ca 2+ ions occurs, changes in the electric potential may supply early inf ormation about the predisposition of the particular maize hybrids to c hilling injuries. Leakage measurements of Mg2+ and Ca2+ ions from the leaves at room temperature may find application in the selection of ch ill-tolerant maize genotypes.