Sulfhydryls—a new factor in frost resistance. I. Changes in SH content during frost hardening

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Abstract
In the 4 hardy species of plants tested, SH increases always accompanied increases in hardiness during the 1st stage of hardening. In 2 species, the 2d stage of hardening was accompanied by a drop in SH but when -ever a further hardening occurred beyond this stage, SH again increased. In the other 2 species the correlation was consistent. When hardiness decreased, SH decreased also, and when hardiness failed to develop at hardening temperatures, SH failed to increase. Tender plants (incapable of hardening at low temperatures) also showed a marked increase in SH at hardening temperatures, but only if permitted to wilt. If wilting was kept to a minimum, no appreciable increase in SH occurred. These results are in agreement with the hypothesis that hardening in -volves an increase in protein SH, and that other increases in SH may occur without hardening.