Changes in apoplastic carbohydrate concentrations and activities of carbohydrate-degrading enzymes were determined in crown tissues of oat (Avena sativa L., cv Wintok) during cold hardening. During second-phase hardening (؊3°C for 3 d) levels of fructan, sucrose, glucose, and fructose in the apoplast increased significantly above that in nonhardened and first-phase-hardened plants. The extent of the increase in apoplastic fructan during second-phase hardening varied with the degree of fructan

more »

... lymerization (DP) (e.g. DP3 and DP4 increased to a greater extent than DP7 and DP > 7). Activities of invertase and fructan exohydrolase in the crown apoplast increased approximately 4-fold over nonhardened and first-phase-hardened plants. Apoplastic fluid extracted from nonhardened, first-phase-hardened, and second-phase-hardened crown tissues had low levels, of symplastic contamination, as determined by malate dehydrogenase activity. The significance of these results in relation to increases in freezing tolerance from second-phase hardening is discussed. ; fax 1-919 -515-2305. Abbreviations: DP, degree of polymerization; FEH, fructan exohydrolase; LT 50 , temperature at which 50% of a population survives; MDH, malate dehydrogenase; NH, nonhardened; 1PH, first phase of cold hardening; 2PH, second phase of cold hardening.