Cold‐Hardiness Response of Sequential Winter Wheat Tissue Segments to Differing Temperature Regimes1

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Abstract
This experiment was initiated to determine if low‐temperature acclimation in one part of a winter wheat plant (Triticum aestivum L.) can influence cold tolerance levels in other plant parts not exposed to cold‐acclimating temperatures. Whole plants and sequential plant segments were exposed to differing temperature regimes in a controlled environment chamber. The level of cold hardiness was determined in whole plant crowns by the regrowth method and in each tissue segment by the leachate conductivity method. Cold hardening of plant parts occurred in dependent of hardiness levels in other parts of the plant. The results indicated that plant response to temperature was the ultimate factor inducing cold hardiness. Reduced tissue moisture content enhanced the cold‐hardening ability of plant tissues, although it also was a plant response to cold acclimating temperatures. The moisture content of upper plant parts was controlled largely by root temperature rather than leaf or crown temperature, although low leaf temperature had some effect on water conductance through the leaves. Tissue segments with low moisture content were more cold hardy than comparable segments with higher moisture content under similar acclimation temperatures. However, tissue segments subjected to cold‐acclimating temperatures achieved greater levels of cold hardiness than comparable tissues of similar moisture content subjected to nonhardening conditions. Exposure temperature was most highly correlated with cold hardiness. Regression analysis indicated that acclimation temperature and tissue moisture content explained a large part of the variation in LT50 (temperature at which 50% of the plants were killed). There was little evidence of any translocatable substance in cold acclimated segments that was able to induce cold hardiness in nonacclimated segments of the plant.