Seasonal Trends of Nitrate Reductase, Carboxylating Enzymes, and Water-soluble Proteins in Two Field-grown Cultivars of Triticum

Nitrate reductase, RuDP¹ carboxylase, PEP carboxylase, and water-solubleproteins have been studied during the vegetative cycles of onesoft and one hard wheat cultivar. Nitrate reductase was similarin amount and in pattern of variation in both varieties, thevariations being related to the phenological state of the plant,because the seasonal trend was not in phase in the two varieties.The pattern of change in water-soluble proteins was significantlydifferent in the two cultivars, namely in the consistent declineshown by the upper leaves of soft wheat. RuDP carboxylase was almost identical in amount and absolutelyin phase between the two varieties, showing a dependence onseasonal factors, possibly through a photoperiodic effect. Thechanges in PEP carboxylase were similar in the two wheats andgenerally synchronous. The fluctuation in the RuDP carboxylase/PEPcarboxylase ratio was due primarily to the increase in RuDPcarboxvlase activity.