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

Abstract

It has been known for some time (6), that there are at least two distinct factors in frost hardinessA: cell sap concentration or sugar content, and B: physicochemical properties of protoplasm. The first must be in some way associated with enzyme activity, since it results from either a starch-sugar conversion or an accumulation of photosynthate in the form of sugar. The second seems to be dependent on protein hydration. Enzyme activation is in many cases associated with SH, and protein hydration depends on the number of polar groups and therefore perhaps on SH. These facts led to the hypothesis that SH might be quantitatively related to frost hardiness, and to the following investigation of that hypothesis. Although there is no record in the literature of an investigation of the relation of SH to frost hardiness there is one report of a relation to drought resistance (4). Since frost hardiness is usually correlated witlh drought hardiness (6), this might be considered as evidence in favor of a relationship between SH and frost hardiness. Unfortunately, no attempt was inade to measure the drought resistance of the several strains of loblolly pine used other than to accept the order well established by field experiment. The only attempt to measure desiccation resistance in the laboratory failed to yield any relationship to the field determined resistance. This agrees with Parker (7), who could not detect any better ability of the more drought resistance coniferous species to recover from a low leaf moisture than in the case of the less drought resistant species. There was, however, a greater ability to retain a high moisture content. In other words, the available evidence indicates that the drought resistance involved in the above investigation was avoidance rather than tolerance and therefore unrelated to frost resistance.