Inibizione Da Saccarosio Della Demolizione Delle Riserve Lipidiche inCucurbita Maxima

Abstract

Inhibition by sucrose of ufilizatiom of storage lipids in germinating seeds of <( Cucurbita maxima D.-Previous work demonstrated that sugars inhibit almost completely the respiratory utilization of lipid in isolated cotyledons from germinating << Ricinus communiss seeds as well as in a yeast, <( Rhodotorula gracilis x This research was carried out with the aim to further characterize this phenomenon; the material used are the cotyledons and the embryonic axes of <( Cucurbita maxima >> var. Q mammouth n, where the lipid contents markedly decrease during the first 72 hours of germination. By incubating the embrional axes, isolated from 48 hours germinating seeds in O.lhI sucrose it was observed: a ) a rise of the R.Q. from 0,65 to 1 which is not due to alchoolic fermentation since no degradation of sucrose to ethanol was detected. b) a marked decrease or a complete inhibition of the utilization of fatty acids. On the contrary, no significant increase of R. Q. occurs, when the cotyledons are incubated in presence of 0.1M sucrose. The metabolic utilization of the fatty acids in <( Cucurbita maxima D has been studied by using acetate-2-C". Labelled acetate was fed after 30 and 90 minutes of incubation of the embryonic axes in water and, respectively in 0.1M sucrose. The radioactivity in the CO, and in total fatty acids fractions was measured 30 minutes after feeding the labelled acetate. It was found that: in the presence of sucrose: a) the incorporation of labelled acetate in fatty acids was increased by about 43% after 30' and by 10% after 90'. b) the dissimilation of acetate to CO, was decreased by about 50%. These results indicate that sucrose replaces lipids as respiratory material. Experiments with labelled acetate ale in agreement with the hypotesis that the inhibition of lipid catabolism by sugars (or some derivative) is due chiefly an enhancement of lipid synthesis. At the same time there is probable an inhibition of fatty acids oxidation. INTRODUZIONE I n un precedente lavoro (COCVCCI e RASI CALDOGNO, non pubbl.) abbiamo studiato l'andamento del Qo, del Q.R. e del contenuto in glucidi e in lipidi di seme di Cttcttrbita maxima var. manmouth durante le prime 72 ore di germinazione. Precedentemente era stato visto che la somministrazione di glucidi blocca 231 Downloaded by [Universite Laval] at 23:09 12 June 2016 quasi totalmente I'utilizzazione dei lipidi sia in cotiledoni isolati da semi di ricino (ALBERGHINA e MARRB 1965) che in Rhodotortila (COCUCCI 1966, COCUCCI e MARRB 1966) sostituendosi ai lipidi come principale substrato utilizzabile.Le ricerche riferite in questa nota riguardano l'effetto della somministrazione di saccarosio o glicerolo sul metabolismo dei cotiledoni e degli assi embrionali isolati da semi germinanti di Crmrrbita. MATERIAL1 E hlETODIDopo aver rimosso i tegumenti, i semi di Cuctirbifa niaxinia var. inarnti~oir~h venivan0 posti a germinare in piastre di Petri su due strati di carta da filtro imbevuta d'acqua o di una soluzione di saccarosio o di glicerolo alle concentrazioni indicate pe...