SUGAR METABOLISM IN COLD-HARDENED LOLIUM-PERENNE VARIETIES

Seven varieties of Lolium perenne L., representing a wide range of win ter hardiness, were used to investigate relationships between freezing tolerance of leaves and levels of non-structural carbohydrates and ke y enzymes of sugar metabolism in leaves. Relatively small differences were observed in freezing tolerance assessed by the electrolyte leakag e method among six of the seven varieties; only the variety Yatsyn I w as significantly less tolerant than the others. The differences in con tents of sugars and the related enzymes phosphofructokinase (PFK), glu cose 6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogena se (6PGDH) and fructose-3,6-biphosphatase (FBPase) among the six varie ties were also small and non-significant. in ca. Yatsyn I, the lower d egree of freezing tolerance was associated with significantly lower le vels of sugars, enzymes, and total protein. The lower activity of PFK was mainly due to reduced activity of the high molecular weight cytoso lic form of the enzyme. A similar phenomenon was observed in cv. Barol di of the frost sensitive species Westerwolds ryegrass (Lolium multifl orum Lam.). These results support the view that high levels of sugars promote the development of maximum hardiness only when associated with high metabolic activity. The consequence of the latter for the useful ness of the characters investigated for screening purposes is discusse d.