Metabolism of Sugars and Organic Acids in Immature Grape Berries

Abstract

A bstract. Individual intact excised immature Sultana berries were supplied through the cut pedicel with "-4C-sugars and organic acids. When 14C-hexoses were supplied malic and tartaric acids accounted for 25 %v and 10 % of the total activity extracted after 24 hours, and sucrose was synthesized. It is proposed that the changes in the levels of organic acids during ripening are related to changes in the ability of the berry to synthesize them. Although administration of uniformly labeled sucrose resulted in the unequal labeling of glucose and fructose, the results indicate breakdown of sucrose by invertase. It is suggested that the route of entry of the pedicel-fed sugars into the berry may be different from the route taken by sugar transloceated from the leaf.Sucrose is the major tranglocalted sugar in grapevines (12) but glucose and fructose make up the bulk of the sugar in the grape berry at all stages of development (9). During the early stages of berry development the total sugar concentraition is low and glucose exceeds fructose by uip to 5 times. At the onset of ripening the concentrations o,f glucose and fructose increase rapidly and soon become equal (9). Malic and tartaric acids increase in concentration in the imnmature berry but decline during ripen,ing (8).Bcoth acids can be synthesizetd in the imimature berry (4). Ra.dioac,tive malic and tartaric acids have been isoolated from graipe berries following administration of ",CO, to thie leaves, ma:lic adid being form,,ed more rapidly than tartaric (4, 6, 7).The labeling of organic aci,ds in the berry is greater where '4CO., is supplied to leaves lof vines hearing imnmature fru,it than nearly ripe fruxit (6) and the labeling of organic acoids is also influenced by temperature (6) and Ilight intensity (7). In these experiments iit is unclear whether the coml)outnds becoming labeled in -the berry are trauslocated fromn the leaves or are formed from sucrose in the berry. Thuis the changes in the reltative amouints of su,,gars and organic acids at different stages of herry deelopment may be (Itie either to chaniges ill the composlition of the translocated material or to changes in the metabolism of translocated suicroise in the berry. The uise o-f indivi-\idutal excise(d intact grape berries permits the sttudy of the utilization oif various 14C-metabollites over short time intervals. W\lhen "4C-suicrose, glucose or fructose were supplied to excised ripening b-err,ies, sma:ll amounts of radioactivity appeared in mallic acid but none in tartaric acid (5).The presence of invertase (1, 2) and eutial amouints of glucose and fructose in mature berries 224 (9) suggests that the tran,slocated sucrose may be inverted. When 14C-sucrose was presented to ri,pening berries however, fructose became more heav-ily labeled than glucose (5), whiioh seemed inconsiistent with inversion, and evidenc,e for suicro,se synthesizling enzymes was obtained (5). Thus it is clonceivable that sucrose is broken downl by a reversal of the stucrose syntheta,se reactioon, resuflting in the p...

Inheritance of sugars and acids in berries of grape (Vitis vinifera L.)

“…Inheritance of soluble sugars and organic acids, especially for acids, is more complex than that of total soluble solids content and titratable acidity of grape berries. Although the inheritance of total acid is certainly influenced by both malic and tartaric acid, malic acid and tartaric acid biosynthesis in grape berries are not closely related biochemically (Hardy 1968;DeBolt et al 2006). So that inheritance of titratable acidity may not reveal the essence of organic acid heritability in grape berries.…”

Movement of 14C-labeled Sugars into Kernels of Wheat (Triticum aestivum L.)

“…The high fructose to glucose ratio in the pericarp tissue does not support a mechanism involving a simple inversion of sucrose. Sucrose synthetase can catalyze the formation of fructose and UDP-glucose (9,21). The UDPglucose so produced could be used for polysaccharide synthesis and the fructose could accumulate (18).…”

Relationships between different berry components in Tempranillo (Vitis viniferaL) grapes from irrigated and non‐irrigated vines during ripening

“…8 Irrigation has a variable effect on sugar accumulation in the berries, and an increase, a decrease and no change in sugar concentration have all been observed. 6,9 The sugar/acidity ratio is ordinarily useful in evaluating the ripening period. 10 Both titratable acidity and pH are of great importance for grape juice stability and are parameters commonly used as an indicator of quality.…”