ABSTRACT
This chapter presents an aspect of cold acclimation of the photosynthetic apparatus in overwintering herbaceous plants. It investigates material from two chilling-insensitive species namely, spinach and field lettuce. If these plants are acclimated to low temperatures, several general responses can be distinguished that lead to an acclimated state suited to cope with low temperature stress. The chapter discusses the catalytic properties of the ribulose-1, 5-bisphosphate (RuBP) carboxylase in relation to cold acclimation and freezing stress. It shows that both the stability of the enzyme during the freezing/thawing cycles is increased and the kinetics of the enzymatic reaction is altered, favoring metabolism at chilling temperatures. Freezing/thawing pretreatment of hardened leaves resulted in much less inactivation of RuBP carboxylase. Inhibition of CO2 assimilation by freezing stress seems partly to be caused by impairment of light activation of the Calvin cycle. The changes in freezing tolerance of the RuBP carboxylase are accompanied by alterations in catalytic properties.
