Effects of Temperature and Photoperiod on Metabolic Changes in Alfalfa in Relation to Cold Hardiness¹

Abstract

Investigations were conducted to evaluate the effects of temperature and photoperiod on metabolic changes during development and maintenance of cold hardiness of two alfalfa ( Medicago sativa L.) varieties varying widely in inherent cold hardiness. Cold temperatures appeared to be of primary importance for development and maintenance of cold hardiness, whereas both temperature and pbotoperiod played important roles in the metabolic processes. The content of protein, RNA, or DNA was positively associated with development and maintenance of cold hardiness. The content of protein or RNA located in microsomes was more closely associated with cold hardiness than was the content of these constituents located in other subcellular fractions. Tissue pH was higher at the peaks of cold hardiness than at other times. The hardy ‘Vernal’ variety contained more protein, RNA, or DNA than the nonhardy ‘Arizona Common’ variety during development and maintenance of cold hardiness.