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During cold acclimation, winter rye (Secale cerealeL.) plants develop the ability to tolerate freezing temperatures by forming ice in intercellular spaces and xylem vessels. In this study, proteins were extracted from the apoplast of rye leaves to determine their role in controlling extracellular ice formation. Several polypeptides in the 15 to 32 kDa range accumulated in the leaf apoplast during cold acclimation at 5°C and decreased during deacclimation at 20°C. A second group of polypeptides (63, 65 and 68 kDa) appeared only when the leaves were maximally frost tolerant. Ice nucleation activity, as well as the previously reported antifreeze activity, was higher in apoplastic extracts from cold‐acclimated than from nonacclimated rye leaves. These results indicate that apoplastic proteins exert a direct influence on the growth of ice. In addition, freezing injury was greater in extracted cold‐acclimated leaves than in unextracted cold‐acclimated leaves, which suggests that the proteins present in the apoplast are an important component of the mechanism by which winter rye leaves tolerate ice formation

Link to this article: http://journals.cambridge.org/abstract_S0960258500004293How to cite this article: Eduardo Marentes and Michael A. Grusak (1998). Iron transport and storage within the seed coat and embryo of developing seeds of pea ( Pisum sativum L.). AbstractTo understand the cellular processes related to iron transport and sequestration within the developing pea seed (Pisum sativum), total iron and ferntin iron were analysed in seed coat and embryo tissues of the ironhyperaccumulatmg pea mutant, Sparkle [dgl, dgl\, and its wild-type parent, cv Sparkle For plants grown hydroponically with 2 UM Fe, embryo Fe concentrations averaged 65 ug g~1 dry weight in mature wild-type seeds and 163 ug g~1 dry weight in mature dgl seeds, iron concentrations were also higher in dgl seed coats Extracted and electrophoretically separated seed proteins were probed with a polyclonal antibody raised against pea seed ferntin In both genotypes, ferntin was detected in the embryo, but not in the seed coat Ferntin iron accounted for 92% of the total iron in mature wildtype embryos, but only 42% of the total iron in mature dgl embryos Radiotracer studies using 59 Fe were used to characterize the movement of iron within the seed coat Unequal distribution of 59 Fe in opposing sections taken from the two hemispheres of the seed coat demonstrated that iron was symplastically phloem unloaded These results suggest that iron resides transiently within the nonvascular seed coat cells and that all cells at the inner surface of the seed coat may be involved in the release of iron to the embryo apoplast However, the form of iron resident within the seed coat and/or taken up by the embryo is presently unknown Abbreviations EDDHA = N,N'-ethylenebis [2-(2-hydroxyphenyD-glycine], EDTA = Ethylenediammetetraacetic acid, HSF = horse spleen ferntin, PAGE = polyacrylamide gel electrophoresis, PMSF = phenylmethylsulfonyl fluoride, PVP = polyvinylpyrrohdone, WT = wild-type

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