GLYOXYLATE CYCLE ENZYMES IN SEEDLINGS AND IN MATURE PLANTS OF TOMATO (LYCOPERSICON-ESCULENTUM MILL.)

The presence of the two glyoxylate cycle marker enzymes, isocitrate ly ase (ICL, EC 4.1.3.1) and malate synthase (MS, EC 4.1.3.2), was invest igated in cotyledons during the post-germinative growth of tomato (Lyc opersicon esculentum Mill., cv Chico III) seedlings. Both ICL and MS i ncreased in the dark and declined after illumination. Cotyledons from seedlings grown in the dark for 7 days were employed for sucrose densi ty gradient fractionation of cell organelles. It was shown that ICL an d MS are localized in glyoxysomal fractions. The presence of the two k ey enzymes of the glyoxylate cycle in tomato cotyledons was confirmed by immunoblotting both in crude extracts and in glyoxysomal fractions. The occurrence of such enzymes was also investigated in different tis sues of tomato plants (leaves, fruits, roots and flowers). Although it was difficult to detect ICL and MS activities by spectrophotometric a ssays, immunoblot analysis showed the presence of both enzymes in sene scent leaves and, surprisingly, in young expanding leaves, but not in mature leaves. The role of glyoxylate cycle enzymes in leaves and the value of further studies with tomato are discussed. (C) 1997 Elsevier Science Ireland Ltd.