COLD-INDUCED CHANGES IN PROTEIN-PATTERNS AND ULTRASTRUCTURE OF ROOT-CELLS OF MAIZE SEEDLINGS

The effects of low temperature on the soluble and membrane-associated protein patterns and ultrastructure of primary root meristematic cells of two Zea mays L. genotypes, the tolerant Z7 and the sensitive Penja linan, were studied. The aim was to identify polypeptides and ultrastr uctural characteristics which might be specifically associated with th e development of chilling tolerance in maize. The exposure of the plan ts to low temperature (6 degrees C) caused changes predominantly in me mbrane-associated proteins. A group of up to 13 low molecular weight p roteins with an apparent size of 11 to 24 kDa was induced in both chil ling sensitive and chilling tolerant genotypes. By contrast, levels of polypeptides of 27, 29, 30 and 36,5 kDa increased specifically in the roots of chilling-sensitive plants. Most of the accumulated proteins were peripheral membrane proteins whereas the level of some integral m embrane proteins decreased somewhat. The changes in soluble proteins w ere less marked. Relatively high proteosynthetic ability of the root c ells during the chilling was also documented by the ultrastructure of the cell components responsible for protein synthesis. Nuclear chromat in was less condensed, cisternae of endoplasmic reticulum were more fr equent and elongated, numerous polyribosomes and dictyosomes with incr eased number of cisternae were present in cytoplasm of both genotypes. It can be concluded that the chilling temperatures did not damage the root cell organelles responsible for protein synthesis and intracellu lar transport in either genotypes. Qualitative and quantitative differ ences in the peripheral and integral membrane proteins demonstrate tha t cellular membranes of maize roots are in dynamic state, changing the ir surface activity together with their internal molecular organizatio n in response to environmental temperatures. Similarity of the changes in the roots of chilling-sensitive and chilling-tolerant genotypes in dicates that not all these changes may necessarily be responsible for the increase in chilling tolerance. Some might be involved in the adju stment of physical and functional properties of the membranes to low t emperatures and also in root growth retardation caused by such environ ment.