Young Tomato Fruit Research Articles

Transcriptome analysis of sugar and acid metabolism in young tomato fruits under high temperature and nitrogen fertilizer influence.

Environmental temperature and nitrogen (N) fertilizer are two important factors affecting the sugar and organic acid content of tomato fruit. N is an essential nutrient element for plant growth and development, and plays a key role in regulating plant growth, fruit quality and stress response. However, the comparative effect of different N fertilizer levels on the accumulation of soluble sugar and organic acid in tomato young fruit under high temperature stress and its mechanism are still unknown. Three N fertilizer levels (N1, N2, N3) combined with two temperatures (28/18°C, CK; 35/25°C, HT) were used to study the effects of N fertilizer, HT and their interaction on the soluble sugar and organic acid components, content, metabolic enzyme activity and the expression level of key genes in tomato young fruit, revealing how N fertilizer affects the sugar and organic acid metabolism of tomato young fruit under HT at physiological and molecular levels. The content of soluble sugar and organic acid in tomato young fruit under HT exposure was increased by appropriate N fertilizer (N1) treatment, which was due to the accumulation of glucose, fructose, citric acid and malic acid. High N (N3) and HT exposure had a negative impact on soluble sugar and reduce sugar accumulation. Further studies showed that due to the up-regulation of the expression of sucrose metabolizing enzyme genes (CWINV2, HK2, SPS, PK) and sucrose transporter (SUT1, SUT4, SWEETs) in tomato, N fertilizer increased the accumulation of soluble sugar by improving the sucrose metabolism, absorption intensity and sucrose transport of fruit under HT exposure. Due to the increase of PEPC gene expression, N fertilizer increased the accumulation of citric acid and malic acid by improving the TCA cycle of fruit under HT exposure. Nitrogen fertilizer can improve the heat tolerance of tomato young fruits by improving sugar metabolism under HT exposure. The results can provide theoretical support for the correct application of N fertilizer to improve the quality of tomato fruit under HT exposure.

Response of Tomato Sugar and Acid Metabolism and Fruit Quality under Different High Temperature and Relative Humidity Conditions

The combined stress of high temperature and high relative air humidity is one of the most serious agrometeorological disasters that restricts the production capacity of protected agriculture. However, there is little information about the precise interaction between them on tomato fruit quality. The objectives of this study were to explore the effects of the combined stress of high temperature and relative humidity on the sugar and acid metabolism and fruit quality of tomato fruits, and to determine the best relative air humidity for fruit quality under high temperature environments. Four temperature treatments (32°C, 35°C, 38°C, 41°C), three relative air humidity (50%, 70%, 90%) and four duration (3, 6, 9, 12 d) orthogonal experiments were conducted, with 28°C, 50% as control. The results showed that under high temperature and relative air humidity, the activity of sucrose metabolizing enzymes in young tomato fruits changed, which reduced fruits soluble sugar content; in addition, enzyme activities involved phosphopyruvate carboxylase (PEPC), mitochondria aconitase (MDH) and citrate synthetase (CS) increased which increased the content of organic acids (especially malic acid). Eventually, vitamin C, total sugar and sugar-acid ratio decreased significantly, while the titratable acid increased, resulting in a decrease in fruit flavor quality and nutritional quality in ripe fruit. Specifically, a temperature of 32°C and a relative air humidity of 70% were the best cultivation conditions for tomato reproductive growth period under high temperature. Our results indicating that fruit quality reduced under high temperature at the flowering stage, while increasing the relative air humidity to 70% could alleviate this negative effect. Our results are benefit to better understand the interaction between microclimate parameters under specific climatic conditions in the greenhouse environment and their impact on tomato flavor quality.

Effectiveness of Dunaliella salina Extracts against Bacillus subtilis and Bacterial Plant Pathogens.

Several bacteria pathogens are responsible for plant diseases causing significant economic losses. The antibacterial activity of Dunaliella salina microalgae extracts were investigated in vitro and in vivo. First, biomass composition was chemically characterized and subjected to extraction using polar/non-polar solvents. The highest extraction yield was obtained using chloroform:methanol (1:1 v/v) equal to 170 mg g−1 followed by ethanol (88 mg g−1) and hexane (61 mg g−1). In vitro examination of hexane extracts of Dunaliella salina demonstrated antibacterial activity against all tested bacteria. The hexane extract showed the highest amount of β-carotene with respect to the others, so it was selected for subsequent analyses. In vivo studies were also carried out using hexane extracts of D. salina against Pseudomonas syringae pv. tomato and Pectobacterium carotovorum subsp. carotovorum on young tomato plants and fruits of tomato and zucchini, respectively. The treated young tomato plants exhibited a reduction of 65.7% incidence and 77.0% severity of bacterial speck spot disease. Similarly, a reduction of soft rot symptoms was observed in treated tomato and zucchini fruits with a disease incidence of 5.3% and 12.6% with respect to 90.6% and 100%, respectively, for the positive control.

Monitoring infection of tomato fruit by Tomato yellow leaf curl virus

Fruit constitutes a strong sink organ and thus accumulates infecting viruses, but there is limited information about the infection process of viruses in fruit. Tomato yellow leaf curl virus (TYLCV, genus Begomovirus, family Geminiviridae) is one of the most important viruses affecting the production of tomato fruit. Using real‐time quantitative PCR, TYLCV was shown to accumulate with increasing titres in early developing tomato fruit tissues from anthesis until 21 days post‐anthesis. In situ hybridization demonstrated that TYLCV DNA and transcripts of the coat protein gene localized specifically to the phloem tissue of young fruit as well as sepals and petals. Embryos of developing seeds were also found to be infected. Expression of a host histone H4 gene was used as a marker for S‐phase and the gene was also found to be expressed in phloem cells of young tomato fruit. The results indicate that TYLCV is transported to developing tomato fruit, where the virus titre gradually increases because of movement and probably also due to virus replication. In this study, the accumulation and localization of TYLCV in early developing tomato fruit are monitored for the first time.

IMPLEMENTASI WEB CAMERA SEBAGAI VISUAL INSPECTION OTOMATIS UNTUK PROSES PEMUTUAN UKURAN DAN TINGKAT KEMATANGAN BUAH TOMAT

Quality and sorting is one method to classify an observed object and the end result of the inspection process. Quality and sorting can be done manually or automatically where quality and one manually sorting can be done by utilizing the human senses. Quality automatically requires certain tools such as the use of digital cameras to replace the sensory function of the human eye as a visual inspection. By using a digital camera, the camera capture object images obtained is processed via image processing, the processing system can be used as an automated visual inspection for the decision making process quality and sorting. The ability to recognize objects in the form of camera pixel component, can be used to determine the size and color, while the components can be used to determine the level of maturity. This system implemented as automatic visual inspection to determine quality tomato fruit size and maturity level. Results of testing this system is able to recognize 100% ripe tomatoes and 73% were able to recognize the young tomato fruit, the overall ability of the system to recognize the maturity level of the tomato fruit was 86.15%. While the tomatoes quality test based on class size with large, medium and small work 100%. Recognize the success rate of fruit maturity is greatly influenced by the current lighting objects tomatoes in camera capture. We hope this research can be used as input data for the next stage as the data input to the system pemutuan and automatically sorting tomatoes.

High invertase activity in tomato reproductive organs correlates with enhanced sucrose import into, and heat tolerance of, young fruit.

Heat stress can cause severe crop yield losses by impairing reproductive development. However, the underlying mechanisms are poorly understood. We examined patterns of carbon allocation and activities of sucrose cleavage enzymes in heat-tolerant (HT) and -sensitive (HS) tomato (Solanum lycopersicum L.) lines subjected to normal (control) and heat stress temperatures. At the control temperature of 25/20 °C (day/night) the HT line exhibited higher cell wall invertase (CWIN) activity in flowers and young fruits and partitioned more sucrose to fruits but less to vegetative tissues as compared to the HS line, independent of leaf photosynthetic capacity. Upon 2-, 4-, or 24-h exposure to day or night temperatures of 5 °C or more above 25/20 °C, cell wall (CWIN) and vacuolar invertases (VIN), but not sucrose synthase (SuSy), activities in young fruit of the HT line were significantly higher than those of the HS line. The HT line had a higher level of transcript of a CWIN gene, Lin7, in 5-day fruit than the HS line under control and heat stress temperatures. Interestingly, heat induced transcription of an invertase inhibitor gene, INVINH1, but reduced its protein abundance. Transcript levels of LePLDa1, encoding phospholipase D, which degrades cell membranes, was less in the HT line than in the HS line after exposure to heat stress. The data indicate that high invertase activity of, and increased sucrose import into, young tomato fruit could contribute to their heat tolerance through increasing sink strength and sugar signalling activities, possibly regulating a programmed cell death pathway.

Tomato fruit photosynthesis is seemingly unimportant in primary metabolism and ripening but plays a considerable role in seed development.

Fruit of tomato (Solanum lycopersicum), like those from many species, have been characterized to undergo a shift from partially photosynthetic to truly heterotrophic metabolism. While there is plentiful evidence for functional photosynthesis in young tomato fruit, the rates of carbon assimilation rarely exceed those of carbon dioxide release, raising the question of its role in this tissue. Here, we describe the generation and characterization of lines exhibiting a fruit-specific reduction in the expression of glutamate 1-semialdehyde aminotransferase (GSA). Despite the fact that these plants contained less GSA protein and lowered chlorophyll levels and photosynthetic activity, they were characterized by few other differences. Indeed, they displayed almost no differences in fruit size, weight, or ripening capacity and furthermore displayed few alterations in other primary or intermediary metabolites. Although GSA antisense lines were characterized by significant alterations in the expression of genes associated with photosynthesis, as well as with cell wall and amino acid metabolism, these changes were not manifested at the phenotypic level. One striking feature of the antisense plants was their seed phenotype: the transformants displayed a reduced seed set and altered morphology and metabolism at early stages of fruit development, although these differences did not affect the final seed number or fecundity. Taken together, these results suggest that fruit photosynthesis is, at least under ambient conditions, not necessary for fruit energy metabolism or development but is essential for properly timed seed development and therefore may confer an advantage under conditions of stress.

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.

Molecular characterization of the plant biopolyester cutin by AFM and spectroscopic techniques

Atomic force microscopy, FT-IR spectroscopy, and solid-state nuclear magnetic resonance have been used to improve our current knowledge on the molecular characteristics of the biopolyester cutin, the main component of the plant cuticle. After comparison of samples of cutin isolated from young and mature tomato fruit cuticles has been possible to establish different degrees of cross-linking in the biopolymer and that the polymer is mainly formed after esterification of secondary hydroxyl groups of the monomers that form this type of cutin. Atomic force microscopy gave useful structural information on the molecular topography of the outer surface of the isolated samples. The texture of these samples is a consequence of the cross-linking degree or chemical status of the polymer. Thus, the more dense and cross-linked cutin from ripe or mature tomato fruit is characterized by a flatter and more globular texture in addition to the development of elongated and orientated superstructures.

Phase transitions in the biopolyester cutin isolated from tomato fruit cuticles

The specific heat of isolated tomato fruit cuticles and their corresponding cutins have been measured by first time for the physiological temperature in the range of 0–55 °C. Variation of specific heat of the different isolates during fruit growth have been also measured. Isolated cuticles and cutin from young tomato fruits presented a clear glass transition temperature around 23 °C. Water sorption on cutin samples shifted the glass transition temperature to 16.3 °C indicating a clear plasticization of the biopolymer. The presence of these second-order transitions in these lipophilic plant material that act as a molecular barrier between the atmosphere and the plant cell, determine the mechanical and rheological properties of this biological barrier modulating the mass transfer between the environment ant the plant cell.

The tomato hexokinase LeHXK1 cloning, mapping, expression pattern and phylogenetic relationships

A tomato ( Lycopersicon esculentum L. Mill.) hexokinase, LeHXK1, was cloned from a tomato fruit cDNA library. Functional complementation of triple-mutant yeast cells ( hxk1 hxk2 glk1) that lack the ability to phosphorylate glucose and fructose confirmed the identity of LeHXK1 as a hexokinase. LeHXK1 was mapped to tomato chromosome 3-distinct from LeHXK2 which mapped to chromosome 6. Interestingly, expression of LeHXK1 was very low in leaves and very high in young tomato fruits. Two hexokinase isozymes, HXKl and HXK2, were chromatographically separated from young fruit extracts, Antisense StHXK1 the homologue of, LeHXK1, knocked out the HXKl isozyme, identifying HXKl as the gene product of LeHXK1. Phylogenetic analysis of eukaryotic and prokaryotic hexose phosphorylating enzymes indicates that tomato hexokinase genes, LeHXK1 and LeHXK2, and the known eukaryotic hexokinases and ‘glucokinases’ belong to the same hexokinase family whose members are unrelated to the glucose-specific glucokinases of bacteria. Hence, the data suggest that thus far no true eukaryotic glucokinases have been identified, neither from plants, nor from fungi or mammalian cells.

Water import in the young tomato fruit limited by pedicel resistance and calyx transpiration.

Approximately 3 weeks after pollination, the water import rate per unit tomato fruit area generally decreases linearly with fruit radius. In order to explain why, in the first 3 weeks, the water import rate of the fruit is lower than predicted by this regression, a model of water flow through the pedicel and a model of water import based on the potential of water entering the fruit and calyx transpiration were formulated. Using data sets available in the literature, these models predict a water potential drop along the pedicel that decreases sharply during the first 3 weeks, while the calculated hydraulic conductivity of the pedicel phloem, which is presumed to be the main pathway of the water imported in the tomato fruit, increases sharply in the lower range of values known for plant phloem conductivity. These models also predict an increase in water import into young fruit when calyx transpiration is decreased, which is consistent with data from the literature. In order to explain the increasing pedicel phloem conductivity, a model of water flow in the pedicel sieve tubes was formulated based on the literature data for the fruit stalk of Lupinus albus. It was suggested that the conductivity might increase because of the development of pores in the sieve plates. Using this hypothesis, the increase in pore radius values within an acceptable range was calculated. This study shows that, under a wide range of conditions, water import in young tomato fruit is limited by the low potential of the water entering the fruit due to pedicel resistance and calyx transpiration. It provides a model to predict young tomato fruit expansion and a testable hypothesis, which can be checked by measuring the size of the phloem component in the fruit pedicel.

A fruit-specific phospho enolpyruvate carboxylase is related to rapid growth of tomato fruit.

Malic and citric acids accumulate in cherry tomato (Lycopersicon esculentum Mill.) fruit during the period of rapid growth, from the end of cell division to the onset of ripening. The involvement of phospho enolpyruvate carboxylase (PEPCase, EC 4.1.1.31) in organic acid accumulation and tomato fruit development was investigated. Two PEPCases, named LYCes;Ppc1 and LYCes;Ppc2 and mapped to chromosomes 12 and 7, respectively, were shown to be differentially expressed during tomato fruit development. LYCes;Ppc1 mRNA was present in all fruit tissues and in all other plant organs examined. In contrast, LYCes;Ppc2 was strongly and specifically expressed in fruit from the end of cell division to ripening. No LYCes;Ppc2 expression was detected by northern blot in other plant tissues. In fruit, the increase in LYCes;Ppc2 mRNA was closely followed by an increase in fruit PEPCase protein and activity, and was coincident with the increased accumulation of malate and citrate during the initial period of rapid growth rate, from 8 to 20 days post anthesis. Localization of LYCes;Ppc2 mRNA in young tomato fruit by in situ hybridization revealed that LYCes;Ppc2 is preferentially expressed in large cells of the pericarp and in enlarging cells of the gel surrounding the seeds. Examination of the kinetic and regulatory properties of the PEPCases of growing and ripening fruit further showed that PEPCase in growing fruit is less sensitive to low pH and malate inhibition, indicating a high phosphorylation state and/or the presence of a PEPCase isoform with these characteristics. Taken together, these results indicate that in developing tomato fruit PEPCase is probably important in permitting the synthesis of organic acids to provide the turgor pressure necessary for cell expansion.

Cloning and characterization of a cDNA encoding hexokinase from tomato

Two different partial sequences encoding putative hexokinase (HXK, ATP: hexose-6-phosphotransferase, EC 2.7.1.1) were isolated from tomato ( Lycopersicon esculentum) by RT-PCR using degenerate primers. Southern blot analysis suggested the existence of two divergent HXK genes. A complete cDNA of one HXK was isolated by screening a cDNA library prepared from young cherry tomato fruit. The 1770 bp cDNA of LeHXK2 contained an open reading frame encoding a 496 amino acid protein that has 69% identity with the two Arabidopsis HXKs, 83 and 85% identity with potato StHXK1 and tobacco NtHXK, respectively. However, this clone had 97% amino acid identity with potato StHXK2 and, therefore, was named LeHXK2. LeHXK2 cDNA was expressed in a triple mutant yeast ( Saccharomyces cerevisiae) strain which lacked the ability to phosphorylate glucose and fructose and, therefore, was unable to grow on these sugars as carbon sources. Mutant cells expressing LeHXK2 grew on both glucose and fructose with shorter doubling time on glucose. The kinetic properties of LeHXK2 expressed in yeast were determined after the purification of LeHXK2 by HPLC-ion exchange chromatography, confirming the identity of LeHXK2 as hexokinase with higher affinity to glucose. LeHXK2 mRNA was detected by RT-PCR expression analysis in all organs and tissues and at all stages of fruit development. However, semi-quantitative RT-PCR analysis showed that LeHXK2 was most highly expressed in flowers.

Bird's Eye Lesions of Tomato Fruit Produced by Aerosol and Direct Application of Clavibacter michiganensis subsp. michiganensis.

Development of the bird's eye fruit lesion of tomato was studied by inoculating flowers and the surface of young tomato fruit with strains of Clavibacter michiganensis subsp. michiganensis. Flowers were sprayed once or twice with C. michiganensis subsp. michiganensis at 108 CFU/ml. The maximum incidence (80%) and severity (12 spots/fruit) of spotted fruit resulted when inoculum was sprayed twice, 3 days apart. Flowers were most susceptible to infection 2 days after anthesis. When a paintbrush was used to apply inoculum to the surface of small fruit, a large number of fruit spots (≤456 spots/fruit) resulted. Even strains determined to be avirulent based on a tomato stem inoculation assay and a hypersensitive response on four-o'clock leaves (Mirabilis jalapa) were able to produce fruit spots, although at a reduced level. The inoculation methods developed in this study can provide opportunities to observe subtle host-pathogen interactions between C. michiganensis subsp. michiganensis strains and tomato and to help formulate methods to quantify infection.

Isolation of three distinct CycD3 genes expressed during fruit development in tomato.

Tomato (Lycopersicon esculentum Mill.) is an important fruit crop world-wide and a model for studying fruit development. As determined using flow cytometry, fruit growth was characterized by high cell division activity in tomato during the first week after anthesis and followed by endoreduplications (DNA replication without cell divisions). D-type cyclins are considered to be important parts of the signal transduction for stimulation of DNA replication and cell division. To study the function of D cyclins in fruit development, full-length cDNA clones for three D cyclin genes were isolated from young tomato fruit. They were classified as D3 cyclins by sequence similarities and a phylogenetic analysis and named as LeCycD3;1, LeCycD3;2 and LeCycD3;3. The deduced amino acid sequences for LeCycD3;1-3 contained a retinoblastoma-binding motif and a PEST-destruction motif. Pollination and fertilization were followed by a high increase in the transcript levels of LeCycD3;1-3 in young fruit. Using in situ hybridization, high expression of LeCycD3;3 was detected in the vascular tissue of young fruit suggesting a role in vascular development. The D3 cyclins are probably involved in transducing the signals leading to fruit growth by cell divisions. Distinct differences were detected in their temporal and spatial expression patterns suggesting that they play different roles in fruit development as well as in the development of other plant organs.

Antisense inhibition of tomato fruit sucrose synthase decreases fruit setting and the sucrose unloading capacity of young fruit.

The role of sucrose synthase (SuSy) in tomato fruit was studied in transgenic tomato (Lycopersicon esculentum) plants expressing an antisense fragment of fruit-specific SuSy RNA (TOMSSF) under the control of the cauliflower mosaic virus 35S promoter. Constitutive expression of the antisense RNA markedly inhibited SuSy activity in flowers and fruit pericarp tissues. However, inhibition was only slight in the endosperm and was undetectable in the embryo, shoot, petiole, and leaf tissues. The activity of sucrose phosphate synthase decreased in parallel with that of SuSy, but acid invertase activity did not increase in response to the reduced SuSy activity. The only effect on the carbohydrate content of young fruit was a slight reduction in starch accumulation. The in vitro sucrose import capacity of fruits was not reduced by SuSy inhibition at 23 days after anthesis, and the rate of starch synthesized from the imported sucrose was not lessened even when SuSy activity was decreased by 98%. However, the sucrose unloading capacity of 7-day-old fruit was substantially decreased in lines with low SuSy activity. In addition, the SuSy antisense fruit from the first week of flowering had a slower growth rate. A reduced fruit set, leading to markedly less fruit per plant at maturity, was observed for the plants with the least SuSy activity. These results suggest that SuSy participates in the control of sucrose import capacity of young tomato fruit, which is a determinant for fruit set and development.

Reduction of G-box binding factor DNA binding activity, but not G-box binding factor abundance, causes the downregulation of RBCS2 expression during early tomato fruit development

The downregulation of RBCS2 promoter activity during tomato fruit development has been investigated by transient gene expression. A major drop in promoter activity occurs between 5 and 25 mm fruit diameter, corresponding to the late cell division to early cell enlargement phase. This drop is abolished by a mutation of the single G-box element necessary for high RBCS2 promoter activity in young tomato fruit. The G-box binding activity of fruit nuclear and total protein extracts drops concomitantly with the reduction of RBCS2 promoter activity while G-box binding factor expression is not affected. The data indicate that the developmental signal that downregulates the RBCS2 promoter acts on the regulation of DNA binding activity of constitutively expressed G-box binding factors.

Regulation of tomato HMG1 during cell proliferation and growth

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR, EC 1.1.1.34) is encoded by a small multigene family in tomato (Lycopersiconesculentum Mill.) and catalyzes the synthesis of mevalonic acid (MVA), a committed step in the biosynthesis of sterols and isoprenoids. A chimeric HMG1::GUS reporter gene fusion was used to analyze the regulation of HMG1 gene expression in detail. HMG1 promoter 5′ deletion mutants established the boundary of a fully inducible promoter. In HMG1::GUS transgenic tomato plants, histochemical staining with 5-bromo-3-indolyl-glucuronide demonstrated that HMG1 was primarily expressed in shoot and root meristems, and in young tomato fruit. This result was confirmed by both HMG1 in-situ hybridization and RNA gel blot analysis. Tomato suspension cell experiments showed that steady-state HMG1 mRNA accumulated during lag and exponential growth phases, but not during the stationary phase. Transient expression of the HMG1::GUS in tissue culture cells treated with mevinolin indicated that HMG1 expression was subject to feedback regulation by a biosynthetic product derived from MVA. These results suggest that a primary, although not exclusive, role of HMG1 is to supply the MVA demand associated with cell division and growth.

Purification of Tomato Sucrose Synthase Phosphorylated Isoforms by Fe(III)-Immobilized Metal Affinity Chromatography

The major phosphorylation site of maize sucrose synthase (SuSy) is well conserved among plant species but absent in the deduced peptide sequence of the tomato SuSy cDNA (TOMSSF). In this study, we report thein vitrophosphorylation of 25-day-old tomato fruits SuSy on seryl residue(s) by an endogenous Ca2+-dependent protein kinase activity. Two distinct32P-labeled peptides detected in the tryptic peptide map ofin vitro32P-radiolabeled tomato fruit SuSy were purified. Amino acid sequencing and phosphoamino acid analysis of the major32P-labeled peptide revealed the presence of a SuSy isozyme in young tomato fruit having the N-terminus phosphorylation site present in other plant species. By using Fe(III)-immobilized metal affinity chromatography [Fe(III)-IMAC] as a final purification step of tomato fruit SuSy, two32P-labeled tomato SuSy isoforms were separated from a nonradiolabeled SuSy fraction by using a pH gradient. The major32P-SuSy isoform was phosphorylated exclusively at the seryl residue related to the phosphorylation site of maize SuSy. The multiphosphorylated state of the second radiolabeled SuSy fraction was indicated by a higher retention during Fe(III)-IMAC and by tryptic peptide mapping analysis. Kinetic analyses of SuSy isoforms purified by Fe(III)-IMAC have revealed that phosphorylation of the major phosphorylation site of tomato fruit SuSy was not sufficient by itself to modulate tomato SuSy activity, whereas the affinity for UDP increased about threefold for the multiphosphorylated SuSy isoform.