Experiments on Sucrose Formation by Potato Tubers as Influenced by Temperature

Abstract

Methods STORAGEPotatoes of the Russet varietv w-ere obtainied froimi the market and were theii randomlv divided into groups. Each grouip was stored in the dark at controlled temperature (± 1°C). SUTGAR ANALYSISSamples of potato tissue were rapidly dried in a foreed draft oveni at 700 C. The dry samples were ground in a Wileyimill to 20 mesh and aliquots were theni weighed out and extracted with 80 per cent. ethanol according to HASSID (10). After the extracts were cleared with lead acetate, aliquots were used for determiniations of reducinig sugars by the ceric sulphate method. Sucrose was determined as the increase in reducing power after hydrolysis with inivertase. 'on-sug-ar reducing substainces were determined as the redueing power in aliquots of extracts which had been previously fermented with veast. Fruietose gives a characteristic color reaction with alcoholic resorcinol in strong acid solution (16) and was determined colorimetrically in a Klett-Summerson photoelectric colorimeter. Starch was analyzed in the residue of the alcohol extraction by hvdrolysis either with amylase or with acid and titrated as glucose. In reaction mixtures, starch synthesis by phosphorvlase was followed colorimiietrieally as follows: 1 ml. aliquots were removed from the digest to 1 ml. of 16 per cent. trichloroacetic acid in order to arrest the enzymatic activity. The samples were filtered and the precipitate washed several times. Onehalf ml. of iodinie-potassiumii iodide solution was added aind the sample wvas maIde up to 25 ml. final volume. The color developed was then measured in a Klett-SuLmnierson colorimeter and compared with a calibration cuirve made for potato stareh. This calibrationi is Inot an absolute one, anid can be ulsed only for the piurpose of comparisonis withini anl experiment. PHOSPHORYLATED INTER-MEDIATESA portion of dried tuber samiiple was extracted with successive portionis of 5 per cent. trichloroacetic acid in the cold by a slight modification of the method described by UMBREIT, BURRIs and STAUFFER (18)

Turnover Rates of Phosphate Esters in Fresh and Aged Slices of Potato Tuber Tissue

“…The value for total hexose-P given in this paper is only about 2 % of that found for potato in one study (2) The data also show that the tissue inorganic phosphate exists in at least 2 pools: a nonmetabolic pool containing 95 % and a metabolic pool containing 5 %. Phosphate accumulated into the tissue passes into the metabolic pool first, and from there into the nonmetabolic pool.…”

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues

“…Arreguin-Lozano and Bonner (1949) reported that an inhibitor of starch phosphorylase accumulated in potatoes at high temperatures, the inhibitor disappearing at low temperatures. This evidence may indicate that sweetening at low temperatures is due to phosphorylase action but Porter and Rees (1954) could not confirm tbe observation of Arreguin-Lozano and Bonner.…”

“…Potato extracts contain little, if any P-amylase activity (Whelan, 1963, personal communication) and Porter and Rees (1954) found no difference in content of short chain dextrins in extracts from potatoes sweetening rapidly at 0° C and from potatoes with stable sugar at 25° C; these observations may mean that amylases do not participate in sweetening. The changes in various phosphate esters during sweetening at low temperatures were determined by Arreguin-Lozano and Bonner (1949) and by Samotus (i960); the alteration of the key ester, glucose-1-phosphate was not, however, estimated by a reliable technique. …”

Studies on the Chemistry of the Living Bark of the Black Locust Tree in Relation to Frost. VI. Amylase and Phosphorylase Systems of the Bark Tissues

“…The observed variations in activity of an enzymi-e under different conditions of temperature and pH can represent the combined effects of inacti- 1 (22), the chromatographic detection of glucose after long incubation suggests that an a-amylase was also present. Thus, it is probable that; amylases of both the a and /3 types occur in the locust tree tissue.…”