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Carbohydrate composition and key enzymes involved in carbohydrate metabolism were assayed throughout development of Lycopersicon esculentum and L. chmielewskll fruit. Translocation and assimilation of asymmetric sucrose and total soluble solids content was also determined in both species. The data showed that L. chmielewskii accumulated less starch than L. esculentum, and this was related to a lower level of ADPglucose pyrophosphorylase and a higher level of phosphorylase in L. chmielewskii. L. chmielewskii accumulated sucrose throughout fruit development rather than glucose and fructose which were accumulated by L. esculentum. A low level of invertase and nondetectable levels of sucrose synthase were associated with the high level of sucrose in L. chmielewskii. Translocation and assimilation of asymmetrically labeled sucrose indicated that sucrose accumulated in L. chmielewskii fruit was imported and stored directly in the fruit without intervening metabolism along the translocation path. In contrast, the relatively low level of radioactive sucrose found in L. esculentum fruit appeared to arise from hydrolysis and resynthesis of sucrose. The possible relationship between the level of soluble solids and differences in carbohydrate metabolism in sink tissue of the two species is discussed.The harvestable yield of tomato appears to be regulated by the net assimilation rate ofthe crop, the rate ofimport into individual fruit, and sink activity (9). High sink demand can significantly increase the quality of the tomato fruit by high accumulation of soluble solids, an important factor for processing tomatoes. Sugars are the major components of the soluble solids content in tomato comprising approximately 65% of the soluble solids.As reported by Gifford and Evans (6), the processes localized in sink tissue largely determine the distribution of photoassimilate between competing sinks. According to Walker and Ho (16), sink strength of a tomato fruit is principally affected by the sink activity of the fruit. The major mechanisms involved in sink activity are: (a) unloading ofsucrose by the phloem, (b) hydrolysis and uptake ofsugars, (c) biosynthesis and storage ofcarbohydrate (10). It has been suggested (16) that invertase activity may play a major role in regulating the rate of carbon translocation in tomato fruit.

In developing tomato (Lycopersicon esculentum Mill.) fruit, starch levels reach a peak early in development with soluble sugars (hexoses) gradually increasing in concert with starch degradation. To determine the enzymic basis of this transient partitioning of carbon to starch, the activities of key carbohydrate-metabolizing enzymes were investigated in extracts from developing fruits of three varieties (cv VF145-7879, cv LA1563, and cv UC82B), differing in final soluble sugar accumulation. Of the enzymes analyzed, ADPglucose pyrophosphorylase and sucrose synthase levels were temporally correlated with the transient accumulation of starch, having highest activities in cv LA1563, the high soluble sugar accumulator. Of the starch-degrading enzymes, phosphorylase levels were fivefold higher than those of amylase, and these activities did not increase during the period of starch degradation. , and cv UC82B (UC82) were sown in growing trays (Growing Systems, Inc.) and transplanted to the field approximately 6 weeks later. The plants were accorded normal cultural practices used for processing tomatoes in California.

ABSTRACIThe lliztion of enzymes involved in the flow of carbon into and out of starch was determined in guard cells of Commelina communis. The guard cell chloroplasts were separated from the rest of the cellular components by a modification of published microfuge methods. The enzymes of interest were then assayed in the supernatant and chloroplast fractions. The chloroplast yield averaged 75% with 10% cytoplasmic contamination. The enzymes involved in starch biosynthesis, ADPglucose pyrophosphorylase, starch synthase, and branching enzyme, are located exclusively in the chloroplast fraction. The enzymes involved in starch degradation show a more complex distribution. Phosphorylase is located in both the supernatant and chloroplast fraction, 50% in each fraction.Most of the amylase and debranching enzyme activity is present in the supernatant (70%) fraction. The majority of the rest of the enzymes involved in the degradation of starch to malate and synthesis of starch from a hexose precursor were also investigated. All of the enzymes were present in the chloroplast except for hexokinase and phosphofructokinase. The inability to assay these enzymes could possibly have been due to the lack of or low activity of the enzymes or to nonoptimal assay conditions. leaves. The sucrose is either degraded in the apoplast or in the cytoplasm of the storage cell. Sucrose, or its degradation products, can be further metabolized to the triose-P or 3-PGA level. These compounds may then move into the amyloplast via the triose-P/Pi translocator and are converted into starch. However, at present, the presence of the triose-P/Pi translocator in amyloplasts has not been demonstrated. Assuming that the triose-P/ Pi translocator is present, the movement of carbon into starch would be a reversal of the enzymic steps occurring in the cytoplasm with the last several steps resulting in the direct incorporation of carbon into starch. The above process will be reversed with starch degradation occurring and the products moving into the cytoplasm presumably via the triose-P/Pi translocator. Triose-P and 3-PGA are then further metabolized, as needed, in the cytoplasm.Using the amyloplast system as a model for guard cells, it was of interest to determine the enzyme activity of the starch biosynthetic and degradative pathways and their localization. A chloroplast and cytoplasmic (supernatant) fraction were obtained from guard cell protoplasts using a microfuge technique. Enzymes involved in the flow of carbon into and out of starch were then assayed in the two fractions.One ofthe consequences ofstomatal opening is the breakdown of starch during the day into malate and citrate, for use as an osmoticum. In the late afternoon or evening starch is resynthesized. This is the reverse of the situation in mesophyll cells. At the present time there is no evidence as to the source of carbon for the resynthesis of starch due to the lack of Rubisco4 activity (22) 4Abbreviations: Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase; ADPGlc, ADPglucose; Ru...

The subcellular localization of ADPglucose pyrophosphorylase, a key regulatory enzyme in starch biosynthesis, was determined in developing potato tuber cells by immunocytochemical localization techniques at the light microscopy level. Specific labeling of ADPglucose pyrophosphorylase by either immunofluorescence or immunogold followed by silver enhancement was detected only in the amyloplasts and indicates that this enzyme is located exclusively in the amyloplasts in developing potato tuber cells. Labeling occurred on the starch grains and, in some instances, specific labeling patterns were evident which may be related to sites active in starch deposition.