Sucrose metabolism in spring and winter wheat in response to high irradiance, cold stress and cold acclimation

Effects of low-temperature stress, cold acclimation and growth at high irra diance in a spring (Triticum aestivum L, cv, Katepwa) and a winter wheat (T riticum aestivum L, cv. Monopol) were examined in leaves and crowns with re spect to the sucrose utilisation and carbon allocation. Light-saturated and carbon dioxide (CO2)-saturated rates of CO2 assimilation were decreased by 50% in cold-stressed spring and winter wheat cultivars, Cold- or high ligh t-acclimated Katepwa spring wheat maintained light-saturated rates of CO2 a ssimilation comparable to those of control spring wheat. In contrast, cold- or high light-acclimated winter wheat maintained higher light and CO2-satu rated rates of CO2 assimilation than non-acclimated controls, In leaves, du ring either cold stress, cold acclimation or acclimation to high irradiance , the sucrose/starch ratio increased by 5- to 10-fold and neutral invertase activity increased by 2- to 2.5-fold in both the spring and the winter whe at. In contrast, Monopol winter wheat, but not Katepwa spring wheat, exhibi ted a 3-fold increase in leaf sucrose phosphate synthase (SPS) activity, a 4-fold increase in sucrose:sucrose fructosal transferase activity and a 6.6 -fold increase in acid invertase upon cold acclimation. Although leaves of cold-stressed and high light-grown spring and winter wheat showed 2.3- to 7 -fold higher sucrose levels than controls, these plants exhibited a limited capacity to adjust either sucrose phosphate synthase or sucrose synthase a ctivity (SS[s]), In addition, the acclimation to high light resulted in a 2 3-31% lon er starch abundance and no changes at the level of fructan accumu lation in leaves of either winter or spring wheat when compared with contro ls. However, high light-acclimated winter wheat exhibited a 1.8-fold higher neutral invertase activity and high light-acclimated spring wheat exhibite d an induction of SS(d) activity when compared with controls, Crowns of Mon opol showed higher fructan accumulation than Katepwa upon cold and high lig ht acclimation, We suggest that the differential adjustment of CO2-saturate d rates of CO2 assimilation upon cold acclimation in Monopol winter wheat, as compared with Katepwa spring wheat, is associated with the increased cap acity of Monopol for sucrose utilisation through the biosynthesis of fructa ns in the leaves and subsequent export to the crowns. In contrast, the diff erential adjustment of CO2-saturated rates of CO2 assimilation upon high li ght acclimation of Monopol appears to be associated with both increased fru ctan and starch accumulation in the crowns.