Bound water and electrical conductivity as measures of cold resistance in winter wheat

Relation of free water, the amount at -20 degrees C, and of bound water, the amount unfrozen at -20 degrees C, to cold resistance of winter wheat was studied. Specific conductivity of water extracts of frozen and subsequently thawed tissue was used as a measure of the soluble minerals released from the cells as a result of injury due to freezing. Low total water, low free water, and high bound water of leaves of field grown winter wheat varieties were not consistently related to their known resistance to low temperatures. However, two varieties which differ widely in known resistance showed consistent differences in total and free water content. Leaves from Minhardi, a hardy variety, contained less total and less free water than leaves from Blackhull, a less hardy variety. No consistent differences in bound water were found even in leaves of Minhardi and Blackhull. Total water in leaves from Minhardi and Blackhull winter wheat varieties grown in the greenhouse in soils of low and of high levels of fertility was greater in plants grown in the soil of high level of fertility. Differences between the amounts of free and bound water were not consistent. Crown tissue of winter wheat varieties should receive more consideration than leaf tissue in testing cold resistance of winter wheat varieties. Soluble minerals measured by electrical conductivity in water extracts of frozen leaves from Minhardi and Blackhull winter wheat varieties were greater than in water extracts from frozen crowns. This indicates greater injury to leaves from freezing at -20 degrees C. The amount of total and free water in both varieties was also greater in the crowns than in the leaves. The amount of bound water was more than twice as much in the crowns as in the leaves of Minhardi. The reverse relation was found in Blackhull, although the difference was not significant. Greater cold injury to both leaf and crown tissue when exposed at -20 degrees C was found in Blackhull than in Minhardi. Total and free water content both of Minhardi and Blackhull leaves were increased by washing. Bound water content of Minhardi was increased slightly more than the bound water content of Blackhull through increased hydration of tissues from washing.