Carbohydrate Metabolism of Avocado. II. Formation of Sugars during Short Periods of Photosynthesis

M\ithough inannolheptulose andI perseitol have i)een known as major constituents of avocadlo sugars for matin years (14) no mlechanismi ftor the synthesis or accumulation of these seven carbon sugars has been dlemonstrate(l. Recently miianniolheptulose has been foun(l to be miiore wi(lely distributed than previously b)elievel, having been found in leaves of figs (4) andi alfalfa (15)). Olther lheptoses andl heptuloses (5, 7. 8. 10. 18) as Nvell as octuloses, octitols. an(l a nonulose (5, 16, 17) have also been isolated froml biological miiaterials. Thus, the syntlhesis of these less commoilnoi sugars has beconie of somilex-lhat wvider interest in mletabolic investigatioins. lFracer elxperimnents by 1 Nordal aan(l lBeiison (14) with photosynthesizing avocadlo leaves estai)lished that a phosphate ester of mannol)eptulose x-as formed (luring early photosynthesis. This was confirmed in this laboratorv` (3 ) vith the additional (lemonstration tllat mannolheptulose appears concurrenitly wN-ith sucrose (duriing photosynthesis in avocado lea-es. l'erseitol. in these experimiients. seemiie(l to he a seconi(larv plroduct, (lerive(l fromii mannolheptulose. ReId(lig and(t MAlcComb (13. 15 ) fe(l various sugars to alfalfa in attempts to eluci(late tlle miiechanisilm of Iimantiloheptuilose synthesis. Thex apparently didlnot find(l significant increases in mlaninolheptulose but sonme sugars gave rise to new lhepttuloses, prestumably by traanisketolase aIlCI transaldolase r-eactions. Since mannolheptulose appears to be a nmajor photosynthetic l)rodluct in avoca(lo leaves, a kinetic study of the lablele(d intermie(liates in short period photosynthesis w-ith C' 40. miiighlt aid in eluicidlating the mechanism of synthesis. This paper reports the results of studies in avocadlo leaves u.sinig photosynthetic exposure I)eriodls of 10 seconds to 16 nlinutes.