Genes encoding chitinase-antifreeze proteins are regulated by cold and expressed by all cell types in winter rye shoots

One group of antifreeze proteins (AFPs) is composed of two chitinases that accumulate in the apoplast of winter rye leaves during cold acclimation. In this study, the 28- and 35-kDa chitinase-AFPs were localized in nonacclima ted and cold-acclimated rye leaves by immunoelectron microscopy with an ant iserum produced against the purified winter rye 35-kDa chitinase-AFP. In co ld-acclimated winter rye leaves, labelled chitinase-AFPs were abundant in t he walls of epidermal, parenchymal sheath and mesophyll cells and xylem ves sels, while less label was present in malls of vascular parenchyma cells, I n contrast, chitinase labelling was essentially absent in the nonacclimated cells except in xylem vessels, As shown by RNA blotting, the transcripts o f chitinase-AFPs accumulated to a high level in rye leaves during cold accl imation, to a lesser extent in crowns and mere not detectable in roots. mRN A transcripts of the 28-kDa chitinase-AFP mere localized in rye leaves by i n situ hybridization, The chitinase-AFP transcripts mere found in the same cell types as the protein itself. We conclude that all metabolically active cell types in cold-acclimated winter rye leaves and crowns are able to syn thesize chitinase-AFPs and secrete them into adjacent cell walls, where the y may interact with ice to delay its propagation through the plant and modi fy its growth.