Genes encoding chitinase-antifreeze proteins are regulated by cold and expressed by all cell types in winter rye shoots.
ABSTRACT 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 nonacclimated and cold-acclimated rye leaves by immunoelectron microscopy with an antiserum produced against the purified winter rye 35-kDa chitinase-AFP. In cold-acclimated winter rye leaves, labelled chitinase-AFPs were abundant in the walls of epidermal, parenchymal sheath and mesophyll cells and xylem vessels, while less label was present in walls of vascular parenchyma cells. In contrast, chitinase labelling was essentially absent in the nonacclimated cells except in xylem vessels. As shown by RNA blotting, the transcripts of chitinase-AFPs accumulated to a high level in rye leaves during cold acclimation, to a lesser extent in crowns and were not detectable in roots. mRNA transcripts of the 28-kDa chitinase-AFP were localized in rye leaves by in situ hybridization. The chitinase-AFP transcripts were 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 synthesize chitinase-AFPs and secrete them into adjacent cell walls, where they may interact with ice to delay its propagation through the plant and modify its growth.
Article: A novel plant defensin-like gene of winter wheat is specifically induced during cold acclimation.[show abstract] [hide abstract]
ABSTRACT: A novel cDNA clone, Tad1, was isolated from crown tissue of winter wheat after differential screening of cold acclimation-induced genes. The Tad1 cDNA encoded a 23kDa polypeptide with a potential N-terminal signal sequence. The putative mature sequence showed striking similarity to plant defensins or gamma-thionins, representing low molecular size antipathogenic polypeptides. High levels of Tad1 mRNA accumulation occurred within one day of cold acclimation in crown tissue and the level was maintained throughout 14 days of cold acclimation. Similar rapid induction was observed in young seedlings treated with low temperature but not with exogenous abscisic acid. In contrast to defensins from other plant species, neither salicylic acid nor methyl jasmonate induced expression of Tad1. The recombinant mature form of TAD1 polypeptide inhibited the growth of the phytopathogenic bacteria, Pseudomonas cichorii; however, no antifreeze activity was detected. Collectively, these data suggested that Tad1 is induced in cold-acclimated winter wheat independent of major defense signaling(s) and is involved in low temperature-induced resistance to pathogens during winter hardening.Biochemical and Biophysical Research Communications 11/2002; 298(1):46-53. · 2.48 Impact Factor