Ears of wheat were exposed for up to 10 days during the grain-filling stage to high temperature (35�C) and activities of five enzymes in the sucrose to starch pathway were compared to those in ears maintained at lower temperature (21�C day/16�C night). Two cultivars of wheat known to differ in their post-anthesis tolerance of high temperature were compared. On a per grain basis, the activity of sucrose synthase and of ADPglucose pyrophosphorylase in ears maintained at 21/16�C throughout did not change greatly between days 16 and 32 after anthesis, whereas UDPglucose pyrophosphorylase and soluble starch synthase activities declined with advancing development. Soluble starch synthase activity in grains of heated ears was decreased within 1 day to about one- half of the value in unheated grains, and 3 days' additional heating did not reduce the activity much further. Insoluble starch synthase activity was not significantly reduced by heating. Compared to soluble starch synthase, ADPglucose pyrophosphorylase activity was more slowly affected and decreased to a lesser extent by heat. Sucrose synthase and UDPglucose pyrophosphorylase activities were either not affected or only slightly reduced; part of this reduction could be due to advanced development at the higher temperature. In recovery experiments ears were heated for brief periods and then returned to 21/16�C for a few days. ADPglucose pyrophosphorylase and soluble starch synthase activities recovered in the cooler conditions but the other two enzymes generally only maintained or lost further activity. From a comparison of the activities of these enzymes with the rate of starch deposition, and by taking into account the effects of heating, it is proposed that the influence of heating on final grain dry weight is attributable to the observed reductions of soluble starch synthase activity.

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Soluble ADPglucose-az-glucan 4-a-glucosvltransferase (starch synthetase), ADPglucose pyrophosphorylase, UDPglucose pyrophosphorylase and phosphorylase were assayed in extracts from developing kernels of maize (Zea mays). Normal, waxy and amylose-extender maize at stages of development ranging from 8 days to 28 days after pollination were studied. Shrunken-4 maize at the 22-day stage was also studied. There is adequate activity of both ADPglucose pyrophosphorylase and starch synthetase at all stages of development to account for the synthesis of starch. Thus all starch could be synthesized via the ADPglucose pathway. High levels of UDPglucose pyrophosphorylase and of phosphorylase activities were also found at all stages of development. The possible role of phosphorylase in starch synthesis could not be discounted. The levels of phosphorylase, ADPglucose pyrophosphorylase, starch svnthetase, and UDPglucose pyrophosphorylase activities in shrunken-4 kernels were about 20 to 40% of that found in normal maize kernels. It appears that the mutation in shrunken-4 affects the activities of more than one enzyme. The defective starch svnthesis seen in this mutant could be due to the low activities of ADPglucose pyrophosphorylase and starch synthetase rather than the low activity of phosphorylase.Biosynthesis of a-1 ,4-glucosidic linkages of starch in higher plants is generally considered to be catalyzed by ADPglucosea-,4-glucan 4-a-glucosyltransferase (starch synthetase) (13). It has recently been shown that some forms of this enzyme extracted from spinach, maize, and potato can synthesize a-1, 4-glucosidic linkages in the absence of added primer (7,11,12 Carbohydrate Determinations. To 0.5 g of frozen kernels were added 5 ml of 75% (v/v) ethanol. The kernels were thawed and ground in the ethanol and then heated for 20 min in a boiling H20 bath. After cooling, the suspension was centrifuged at 10,000g for 10 min. The supernatant fluid was decanted, and the starch precipitate was extracted a second time as above. The supernatant fluids were combined, evaporated to dryness, and dissolved in 1 ml of H20. This solution was used for analyses of reducing sugars (10), total soluble sugars (6), and sucrose (6).

The effects of ethylene gas, 2-chloroethylphosphonic acid, and the auxin, benzothiazole-2-oxyacetic acid, on the ripening of grapes (Vitis vinifera L.) was investigated. Ethylene hastened the start of ripening of Doradillo grapes when it was aplied for 10 days starting midway through the slow growth phase. 2-Chloroethylphosphonic acid applied to Shiraz grapes showed the same effect, but when it was applied earlier, during the second half of the first rapid growth phase or at the start of the slow growth phase of berry development, it delayed ripening. 2-Chloroethylphosphonic acid and benzothiazole-2-oxyacetic acid delayed the ripening of Doradillo grapes, and ethylene partially reversed the effect of benzothiazole-2-oxyacetic acid. The results demonstrate the importance of the slow growth stage in grape berry development and suggest that an auxin-ethylene relationship may be involved in the regulation of grape ripening.The ripening of fleshy fruits is preceded by a shift in metabolism which leads to characteristic changes in composition, texture, and color of the fruit (3). In grapes, which have a double sigmoid growth curve (9), this shift occurs at the end of the slow growth phase of berry development; the changes include berry softening, an increase in reducing sugar, a fall in acidity, a loss of green color and, in some cultivars, the appearance of anthocyanin pigments. Changes in enzyme complement also occur (15,16).Ethylene accelerates the ripening of all fruits on which it has been tested (5, 6), and there is strong evidence that it is a fruit-ripening hormone (6,13,21). The ripening of grapes is delayed by auxins (4,12,22,24) of Ethrell containing 0.05%/ (v/v) of a nonionic wetting agent.Bunches were dipped at 4, 5, 6, 7, 8, or 9 weeks after anthesis or six times at weekly intervals starting at 4 weeks after anthesis. In addition there were two untreated control treatments. There were 10 bunches of 150 to 200 berries in each treatment in a randomized block design.The start of ripening was assessed visually by noting the first appearance of anthocyanin pigments, and the progress of ripening was followed by counting the number of colored berries on the bunches at intervals during the early stages of ripening. The fruit of a particular treatment was harvested 2 weeks after the start of ripening, and the reducing sugar and titratable acid contents were determined. Reducing sugar was determined by the 3,5-dinitrosalicylic acid reagent (1) and titratable acid by titration with 0.05 N NaOH to the phenolphthalein end point. Titratable acid is expressed as grams of tartaric acid.Ethylene, Ethrel, and BTOA on cv. Doradillo. Mature vines of V. vinifera L. cv. Doradillo growing in the Waite Agricultural Research Institute orchard near Adelaide were used. This cultivar has large berries with a prolonged slow growth stage.Twelve bunches were selected in four replicate groups of three on two adjacent vines. Each bunch was trimmed to two laterals each of about 15 berries from which 5 berries of 14.0 ffi 0.4 mm d...

SummaryIn sugar-cane stems which contain large amounts of sucrose the concentration of sucrose in the volume external to the vacuoles was found to approach the concentration present in the vacuoles (20%). It was shown that this sucrose is situated mainly in the aqueous phase of the cell walls and intercellular spaces of the storage parenchyma cells.It is suggested that the high concentrations of sucrose in this compartment contribute to the maintenance of the high levels of sucrose present in the vacuoles of parenchyma of cane grown under conditions of high sugar storage.The presence of high concentrations of sucrose in the cell walls strongly favours the view that intercellular sugar transfer occurs mainly via the cell walls rather than via plasmodesmata.

Claussen, W., Loveys, B. R. and Hawker, J. S. 1985. Comparative investigations on the distribution of sucrose synthase activity and invertase activity within growing, mature and old leaves of some Q, and C, plant species. -Physiol-Plant. 65; 275-280.Sucrose synthase (EC 2.4.1.13) activity in young growing leaves was highest in the leaf base in eggplants (Sotanum melongena L.), cassava (Manihoi esculenta Crantz), grapevine {Vitis vinifera L.), and in the leaf sheath of sugar cane (Saccharum offwinarum L.) and maize {Zea mays L.). In addition, increasing sucrose synthase activity was meastu-cd towards the edge of growing eggplant leaves while the activity in mature leaves was highest in the midrib. The activity of acid and alkaline invertase was very low in the midrib but higher in the blade of fully expanded eggplant leaves. Highest invertase activities were found in younger growing leaves. It was concluded that in growing leaves a close relationship might exist between the activity of sucrose synthase and the import of sucrose from source leaves. Detachment of mature eggplant leaves led to a 2-to 3-foId increase of sucrose synthase activity in blade and midrib of these leaves. In contrast, invertase activity decreased after detachment in both leaf blade and midrib,. It was concluded that the rise in sucrose synthase activity might have been caused by the observed increase of sucrose concentration in detached leaves and that sucrose synthase might have an important role in the regulation of sucrose content of the conducting tissue.