Development of Soluble and Insoluble Invertase Activity in Washed Storage Tissue Slices

Recently Palmer (7) published some observations on the development of invertase activity in washed beetroot disks, btut made no reference to previous work with this tissuie. The appearance of invertase in washed disks of storage tissue was first observed with beet (1). Further, the desirability of uising aseptic conditions has been stressed by Bacon et al. (2). The absence of any effect of ad(led penicillin and streptomycin, which was taken by Palmer as evidence that contaminating micro-organisms were not contributing to the metabolic changes he observed muist be viewed in the light of the observations of Leaver and Edelman (5) that these antibiotics were of little uise, permitting the growth of 5 X 106 organisms/g fresh weight in carrot disks washed for 24 hou rs. Palmer's measLurements of invertase activity rest on the assulmption (shown to be incorrect by the observations reported below) that the enzyme is locatedI only in the cell wall. As far as can be made out his assavs were made at 250 and pH 6.5, althou1gh the pH optimutm of this invertase lies in the range 4.5 to 5.0 (see below). Even when allowance is made for these differences, the activities he reports (0.1 mg sucrose hvdrolysed/g fr wt hr) are of a different ordler of magnitu(le from those previously reported [e.g. Bacon et al. (2) g ve 3.0 mg/g fr wt bri. Tt is the pirpose of this commulnication to show that anly study of invertase (levelopment in washed s;torage tissute mtust take account of the ex'stenc2 of a soluldlfe as xvell as ani insoluble (cell wall) invertase. Storage tissuie (lisks of carrot (Dautcts carot(a 1,.), potato (.So(oianm1 tuibcrosunio L.) and red beet (Bet(a vuldgris L.) were cuit and(I age(l (washel) aseptically. Invertase activity was mea-iured 1) incuibatinig 10 (lisks in 10 ml of 0.1 M citrate-phosphate bulffer, pH 5.0 containing 5 % stucrose, at 350 for 1 houir and estimating the reduicing suigars formed with a Technicon atitoanalyser. The pH optimuim for invertase activity in each of the 3 tissutes studied was fouind to be between 4.0 and 5.0 (fig 1) and there was nevidence of the 25