SUGAR ACCUMULATION IN TOMATO AND PARTIAL-PURIFICATION OF BUFFER-INSOLUBLE INVERTASE

Sugar accumulation and invertase activity were studied during fruit de velopment in tomatoes (Lycopersicon esculentum) of two breeding lines. Tomatoes of breeding line A had substantially larger amounts of reduc ing sugars (38%), glucose (33%) and fructose (23%) at the ripe stage c ompared to breeding line B. Differences in sugar content between the t wo breeding lines were significant at all stages of maturation, and hi gher amounts of sugars were consistently linked to higher invertase ac tivities. Buffer-insoluble acid invertase from pericarp was partially purified (12-fold) and consisted, under denaturing conditions (SDS-PAG E), of four distinct bands with estimated M(r), of 56, 32, 21 and 19 k , respectively. Gel filtration chromatography on Sephacryl S-200 and o n FPLC Superose 12 indicated a M(r), of 50 k for the active invertase enzyme. Western blot analysis with an antibody to carrot cell wall inv ertase suggested that the two bands with M(r), of 56 and 21 k correspo nd to the invertase enzyme. IEF of purified invertase enzyme gave thre e major bands with estimated isoelectric points between 5.65 and 5.80. The pH optimum of invertase activity was 5.0, and the activity was st able from pH 3.5 to 7.0.