Tomato Fruit Tissue Research Articles

LeMAN4 endo-β-mannanase from ripe tomato fruit can act as a mannan transglycosylase or hydrolase

Mannan transglycosylases are cell wall enzymes able to transfer part of the mannan polysaccharide backbone to mannan-derived oligosaccharides (Schröder et al. in Planta 219:590-600, 2004). Mannan transglycosylase activity was purified to near homogeneity from ripe tomato fruit. N-terminal sequencing showed that the dominant band seen on SDS-PAGE was identical to LeMAN4a, a hydrolytic endo-beta-mannanase found in ripe tomato fruit (Bewley et al. in J Exp Bot 51:529-538, 2000). Recombinant LeMAN4a protein expressed in Escherichia coli exhibited both mannan hydrolase and mannan transglycosylase activity. Western analysis of ripe tomato fruit tissue using an antibody raised against tomato seed endo-beta-mannanase revealed four isoforms present after 2D-gel electrophoresis in the pH range 6-11. On separation by preparative liquid isoelectric focussing, these native isoforms exhibited different preferences for transglycosylation and hydrolysis. These results demonstrate that endo-beta-mannanase has two activities: it can either hydrolyse mannan polysaccharides, or in the presence of mannan-derived oligosaccharides, carry out a transglycosylation reaction. We therefore propose that endo-beta-mannanase should be renamed mannan transglycosylase/hydrolase, in accordance with the nomenclature established for xyloglucan endotransglucosylase/hydrolase. The role of endo-acting mannanases in modifying the structure of plant cell walls during cell expansion, seed germination and fruit ripening may need to be reinterpreted in light of their potential action as transglycosylating or hydrolysing enzymes.

Cyclin-dependent Kinase (CDK) Inhibitors Regulate the CDK-Cyclin Complex Activities in Endoreduplicating Cells of Developing Tomato Fruit

The jelly-like locular (gel) tissue of tomato fruit is made up of large thin-walled and highly vacuolized cells. The development of the gel tissue is characterized by the arrest of mitotic activities, the inhibition of cyclin-dependent kinase A (CDKA) activity, and numerous rounds of nuclear DNA endoreduplication. To decipher the molecular determinants controlling these developmental events, we investigated the putative involvement of CDK inhibitors (p27(Kip)-related proteins, or KRPs) during the endoreduplication process. Two cDNAs, LeKRP1 and LeKRP2, encoding tomato CDK inhibitors were isolated. The LeKRP1 and LeKRP2 transcript expression was shown to be enhanced in the differentiating cells of the gel undergoing endoreduplication. At the translational level, LeKRP1 was shown to accumulate in the gel tissue and to participate in the inhibition of the CDK-cyclin kinase activities occurring in endoreduplicating cells of the gel tissue. We here propose that LeKRP1 participates in the control of both the cell cycle and the endoreduplication cycle.

CHARACTERIZATION OF DFD (DELAYED FRUIT DETERIORATION): A NEW TOMATO MUTANT

Fruit softening is a complex physiological event and a major determinant of postharvest fruit quality. Attempts to understand the molecular basis of softening have focused on cell wall metabolism and it is now generally believed that fleshy fruits soften as a consequence of polysaccharide degradation in the primary cell wall and middle lamella. Tomato has provided the principal model system for these studies and yet efforts over the last ten years to substantially reduce softening in transgenic tomato lines by suppressing the expression of genes encoding cell wall degrading proteins, such as polygalacturonase (PG), pectin methylesterase (PME) and expansin, have been largely unsuccessful. We have recently identified a tomato line that we named the DFD (delayed fruit deterioration) mutant, which promises to provide a new perspective of the key molecular determinants of softening and other postharvest quality traits. The two major characteristics of DFD are substantially reduced fruit softening and complete resistance to postharvest disease, which collectively result in a remarkable shelf life. Unlike other well known ripening-related tomato mutants such as rin (ripening inhibitor) and nor (non-ripening), DFD fruits undergo essentially normal climacteric ripening while attached to the plant, with all the organoleptic characteristics and quality properties that are essential for commercialization, such as color, aroma and accumulation of sugars. However, the DFD fruits also maintain a firm texture for a dramatically extended period of time after harvesting and can be stored with no further treatment at room temperature for more than seven months with any signs off deterioration. Moreover, after more than one year, intact and untreated DFD tomatoes show no signs of microbial infection. These data suggest the need for a new model to understand the key features that underlay tomato fruit softening and tissue disintegration.

MACRO- AND MICROSCOPIC ASPECTS OF FRUIT WATER RELATIONS INFLUENCING GROWTH AND QUALITY IN TOMATO

Quality of fresh tomato fruits is basically determined during growth of the fruits on the plant. Import of water, nutrients and assimilates from other parts of the plant largely determine fruit growth. Previous research has shown that during fruit development 90% of all water entering the fruit is transported via the phloem. Water import via the xylem seems to cease after maximal growth rate of the fruit has be reached. It seems therefore logical to assume that somewhere along the xylem transport path between shoot and fruits a large hydraulic resistance exists, which besides water also restricts Ca 2+ import. Though, previous research has shown that the xylem hydraulic resistance between stem and tomato fruits is not high enough to significantly restrict water flow via the xylem. Other explanations for the restricted water exchange between stem and tomato fruit should be investigated. In present research we examined macro- and microscopic aspects of water relations of tomato fruits, including changes in apo- and symplastic osmotic pressures and cell pressure (turgor, measured by cell pressure probe) in pericarp tissue of tomato fruit during development and due to water stress aiming to investigate the driving force for water exchange between apo- and symplast at cell level. Turgor pressure in tomato fruit cells was extremely low (< 0.1 MPa), almost constant during fruit development and not influenced by water stress during growth that actually reduced fruit size by 30%. Symplastic osmotic pressures in pericarp tissue slightly increased during fruit development (15 to 50 Days After Anthesis) and increased due to low water availability in the root environment. Apoplastic osmotic pressures in pericarp tissue also increased with fruit development and due to low water availability during growth. A possible role for apoplastic solutes, regulating the water exchange of fruit pericarp cells during growth is proposed.

Determination of pathogen-related enzyme action by mass spectrometry analysis of pectin breakdown products of plant cell walls

An analytical approach using matrix-assisted laser desorption/ionization mass spectrometry for the structural characterization and assessment of the degree of polymerization of cell wall pectin-derived oligosaccharides (PDOs) in three regions of Botrytis cinerea-infected tomato fruit tissue is described. The PDOs were isolated from lesion centers (extensively macerated tissue), the area just beyond visible lesion margins, and healthy and intact tissue of an inoculated fruit, sampled at a distance from developing lesions. PDO mixtures were directly analyzed by mass spectrometry without chromatographic separation, after minimum cleanup by membrane drop dialysis. The structures identified implied the action of three different pathogen pectin-modifying enzymes. Modifications such as methyl esterification were identified by determination of exact PDO molecular masses and tandem mass spectrometry via collision-induced dissociation. We have identified four PDO series that were generated through the breakdown of homogalacturonan pectins. The decayed and lesion edge areas had fewer and less diverse PDOs than healthy tissues, possibly due to metabolic by-products of the pathogen. This analytical technique provides a simple and rapid method to characterize the pectin-derived oligosaccharides produced by in vivo digestion during pathogen infection.

Molecular characterization of a WEE1 gene homologue in tomato (Lycopersicon esculentum Mill.)

Early fruit development in tomato (Lycopersicon esculentum Mill.) proceeds in two distinct phases of growth that comprise cell division and cell expansion, respectively. In pericarp and the jelly like locular tissue of tomato fruit, the transition between cell division to cell expansion is characterized by the arrest of mitotic activity, numerous rounds of nuclear DNA endoreduplication and the inhibition of Cyclin-Dependent Kinase A (CDKA) activity. To investigate whether the WEE1 kinase may play a role during the endoreduplication process, we isolated and characterized the tomato homologue for WEE1. The LeWEE1 gene consisted of 10 exons with a predicted 510 amino acid-long protein. The accumulation of the corresponding transcripts was associated with mitotically active organs: developing fruits, seeds and roots. Interestingly, LeWEE1was expressed in the jelly like locular tissue concomitant with endoreduplication during fruit development. Using tobacco BY-2 synchronized cells, we showed that the WEE1 gene expression is cell-cycle regulated with a maximum transcript accumulation at S phase. Our data indicate the putative dual contribution of LeWEE1 in the classical cell cycle and the endocycle.

Aminoethoxyvinylglycine (AVG) reduces ethylene and protein biosynthesis in excised discs of mature-green tomato pericarp tissue

Application of an aqueous solution of aminoethoxyvinylglycine (AVG) ([S]-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride) to the locular surface of excised 1 cm diameter × 4 mm thick pericarp discs of pre-climacteric, mature-green tomato (Lycopersicon esculentum Mill., cv. Castlemart) fruit significantly reduced both ethylene and protein biosynthesis in a log-linear fashion. Exposure to 1.0 μL L−1 1-MCP (SmartFresh™) increased ethylene production by about 30% at each AVG concentration. Incorporation of H3-leucine into protein in tomato pericarp discs was reduced 65%, 76%, and 93% by the application of 20 μL of 0.1, 3.0, and 10 mM AVG, respectively. In comparison, ethylene production was reduced 57%, 73%, and 89% by 20 μL 0.1, 3.0, and 10 mM AVG, respectively. Application of similar AVG concentrations had no significant effect on CO2 production by the tissue. A tissue concentration of 6 μM AVG (16-fold dilution of the 0.1 mM applied concentration: 20 μL in 0.3 g of tissue) significantly reduced both ethylene and protein biosynthesis. The ability of AVG to reduce ethylene production was highly correlated (R2 = 0.98) to its ability to reduce protein synthesis in both air and 1-MCP treated pre-climacteric tomato fruit tissue. Some of the physiological effect of AVG may be dependent on it ability to alter protein synthesis.

Class V chitin synthase determines pathogenesis in the vascular wilt fungus Fusarium oxysporum and mediates resistance to plant defence compounds.

Chitin, a beta-1,4-linked polysaccharide of N-acetylglucosamine, is a major structural component of fungal cell walls. Fungi have multiple classes of chitin synthases that catalyse N-acetylglucosamine polymerization. Here, we demonstrate the requirement for a class V chitin synthase during host infection by the vascular wilt pathogen Fusarium oxysporum. The chsV gene was identified in an insertional mutagenesis screen for pathogenicity mutants. ChsV has a putative myosin motor and a chitin synthase domain characteristic of class V chitin synthases. The chsV insertional mutant and a gene replacement mutant of F. oxysporum display morphological abnormalities such as hyphal swellings that are indicative of alterations in cell wall structure and can be partially restored by osmotic stabilizer. The mutants are unable to infect and colonize tomato plants or to grow invasively on tomato fruit tissue. They are also hypersensitive to plant antimicrobial defence compounds such as the tomato phytoanticipin alpha-tomatine or H2O2. Reintroduction of a functional chsV copy into the mutant restored the growth phenotype of the wild-type strain. These data suggest that F. oxysporum requires a specific class V chitin synthase for pathogenesis, most probably to protect itself against plant defence mechanisms.

Distinct physiological roles of fructokinase isozymes revealed by gene-specific suppression of Frk1 and Frk2 expression in tomato.

There are two divergent fructokinase isozymes, Frk1 and Frk2 in tomato (Lycopersicon esculentum Mill.) plants. To investigate the physiological functions of each isozyme, the expression of each fructokinase mRNA was independently suppressed in transgenic tomato plants, and the respective phenotypes were evaluated. Suppression of Frk1 expression resulted in delayed flowering at the first inflorescence. Suppression of Frk2 did not effect flowering time but resulted in growth inhibition of stems and roots, reduction of flower and fruit number, and reduction of seed number per fruit. Localization of Frk1 and Frk2 mRNA accumulation by in situ hybridization in wild-type tomato fruit tissue indicated that Frk2 is expressed specifically in early tomato seed development. Fruit hexose and starch content were not effected by the suppression of either Frk gene alone. The results collectively indicate that flowering time is specifically promoted by Frk1 and that Frk2 plays specific roles in contributing to stem and root growth and to seed development. Because Frk1 and Frk2 gene expression was suppressed individually in transgenic plants, other significant metabolic roles of fructokinases may not have been observed if Frk1 and Frk2 play, at least partially, redundant metabolic roles.

A rapid and inexpensive microplate assay for the enzymatic determination of glucose, fructose, sucrose, L-malate and citrate in tomato (Lycopersicon esculentum) extracts and in orange juice.

Sugars and organic acids are important determinants of taste in fruits and vegetables. Based on the enzymatic analyses originally developed by Boehringer-Mannheim, rapid and reliable microplate-based assays were devised for glucose, fructose and sucrose in tomato and orange juice, and citrate and L-malate in tomato. These microplate assays were used to compare some commercially available tomato types, and to study the compartmentation of sugars and acids between pericarp and locular tissue of tomato fruit. The microplate format allows analysis of many samples per day and the only apparatus required is a microplate reader.

A MAP kinase of the vascular wilt fungus Fusarium oxysporum is essential for root penetration and pathogenesis

The soil-borne vascular wilt fungus Fusarium oxysporum infects a wide variety of plant species by directly penetrating roots, invading the cortex and colonizing the vascular tissue. We have identified fmk1, encoding a mitogen-activated protein kinase (MAPK) of F. oxysporum that belongs to the yeast and fungal extracellular signal-regulated kinase (YERK1) subfamily. Targeted mutants of F. oxysporum f. sp. lycopersici carrying an inactivated copy of fmk1 have lost pathogenicity on tomato plants but show normal vegetative growth and conidiation in culture. Colonies of the fmk1 mutants are easily wettable, and hyphae are impaired in breaching the liquid-air interface, suggesting defects in surface hydrophobicity. Fmk1 mutants also show reduced invasive growth on tomato fruit tissue and drastically reduced transcript levels of pl1 encoding the cell wall-degrading enzyme pectate lyase. Conidia of the mutants germinating in the tomato rhizosphere fail to differentiate penetration hyphae, resulting in greatly impaired root attachment. The orthologous MAPK gene Pmk1 from the rice leaf pathogen Magnaporthe grisea complements invasive growth and partially restores surface hydrophobicity, root attachment and pathogenicity in an fmk1 mutant. These results demonstrate that FMK1 controls several key steps in the pathogenesis of F. oxysporum and suggest a fundamentally conserved role for the corresponding MAPK pathway in soil-borne and foliar plant pathogens.

Ethylene feedback mechanisms in tomato and strawberry fruit tissues in relation to fruit ripening and climacteric patterns

Exposing pericarp tissue excised from immature tomato fruit to 4.5 mmol l 1 C2H4 revealed a negative C2H4 feedback mechanism in relation to its biosynthesis since ACC concentration and C2H4 production by the tissue were reduced. An opposite trend (positive C2H4 feedback mechanism) was observed in pericarp tissue excised from fruit at the pink stage. At the mature-green stage however, tissue showed a transition from negative to positive C2H4 feedback mechanism with the onset of tissue ripening. In strawberry tissues excised from green, white and half-coloured fruits however, C2H4 application caused a short-term increase in C2H4 production followed by a sharp reduction to the control level along with a marked reduction in ACC levels. In both tomato and strawberry fruit tissues, C2H4 application significantly induced ACC oxidase (ACO) activity at all ripening stages, as measured by in vivo ACC conversion to C2H4. This strongly suggests that ACC synthesis is the limiting step in C2H4 autocatalysis and the only limiting step in C2H4 autoinhibition. In tomato pericarp tissues, C2H4 autoinhibition and autocatalysis caused by C2H4 application in immature and pink fruits, respectively, were eliminated when tissues were transferred to air and re-occurred when tissues were returned back to C2H4. These responses did not occur in all strawberry tissues due to the sharp reduction in C2H4 production with the time course of C2H4 application. Inhibiting C2H4 action with STS pretreatment inhibited both negative and positive C2H4 feedback mechanisms in both tomato and strawberry tissues indicating that C2H4 feedback mechanism is one sort of C2H4 action. In addition, only tomato fruit tissue showed significant increases in CO2 production with C2H4 application. In contrast to the nonclimacteric behaviour of strawberry fruit which exhibits only a negative C2H4 feedback mechanism, these data strongly suggest that the transition of the C2H4 feedback mechanism from negative to positive, which occurs in tomato fruit only with ripening initiation and progress, may be the reason behind the climacteric behaviour of tomato fruit. © 2000 Elsevier Science B.V. All rights reserved.

Impact of UV-C irradiation on the cell wall-degrading enzymes during ripening of tomato (Lycopersicon esculentum L.) fruit.

The effect of a hormic dose of UV-C (254 nm) on changes in fruit firmness and cell wall-degrading enzyme (CWDE) activity was determined using tomato fruit. Throughout the storage period, a decrease in firmness was jointly observed with an increase of the CWDE (polygalacturonase, pectin methyl esterase, cellulase, xylanase, beta-D-galactosidase, and protease) activity for all treatments, suggesting the involvement of these enzymes in the ripening process. However, the enhancement in the activity of the CWDE was significantly less in fruit subjected to the hormic dose of UV-C. This reduction may explain why irradiated fruit were firmer than control and consequently may explain how UV-C could delay the ripening and senescence process. We suggest that the CWDE are one of the targets of the UV-C, and by this action, irradiation contributed to a delay of the cell wall degradation and consequently retarded softening of the tomato fruit tissues.

Studies on lipoxygenase and the formation of ethylene in tomato

SummaryLipoxygenase (LOX) activity was assayed in various parts of tomato (Lycopersicon esculentum cv. Caruso) fruits, after harvest and at different stages of ripening. Lipoxygenase activity reached a peak at the turning stage of ripeness in the pericarp and radical pericarp tissue. The changing pattern of C2H4 production in different tomato fruit tissues at different stages of ripeness closely followed that of LOX activity. Application of linoleic acid and linolenic acid to tissue slices of tomato fruit promoted ethylene production. This effect was speci®c to unsaturated fatty acids which serve as substrates for lipoxygenase action, and did not occur following similartreatments with saturated fatty acids (palmitic acid and stearic acid). Two major lipoxygenase pathway metabolites, including jasmonic acid and traumatic acid, also promoted ethylene production by tomato fruits. Treating fruits with lipoxygenase inhibitors (n-propyl gallate, nordihydroguariaretic acid), inhibited ethylene production. These results suggest that lipoxygenase activity and jasmonates were involved in the ripening of tomato fruits. The possible way in which LOX is involved in ethylene biosynthesis is discussed.

Regulation of Glutamate-l-semialdehyde Aminotransferase Expression during Tomato ( Lycopersicon esculentum Mill.) Fruit Development

Summary A full-length clone that encodes tomato fruit tissue ( Lycopersicon esculentum Mill. ‘Rutgers’) glutamate-1-semialdehyde aminotransferase (GSAT; EC 5.4.3.8) was isolated and characterized. Amino acid sequence analysis showed that the tomato GSAT clone exhibited a high level of homology to the amino acid sequences of corresponding GSAT proteins from other plant species. The primary structure of GSAT consists of a 481-amino acid precursor that includes a 46.7 kilounit (kU), 437-amino acid mature protein and a transit peptide of 44 amino acids. Southern analysis showed that a single copy of the GSAT gene was present in the tomato genome. Northern analysis showed that the abundance of GSAT transcripts declined throughout tomato fruit development and ripening. GSAT protein content decreased dramatically by 25 days postanthesis, and GSAT protein was undetectable by day 45, the approximate beginning of chlorophyll loss and carotenoid synthesis. These results show that GSAT is regulated developmentally at the level of transcript accumulation. In addition, posttranscriptional regulation may occur through decreased translation or increased degradation of GSAT protein.

α-d-Mannosidase from Lycopersicon esculentum ii

Abstract Tomato ( Lycopersicon esculentum Mill) fruit tissue was found to contain two isoforms of a- d -mannosidase (EC. 3.2.1.24), which were purified by ion-exchange chromatography on DEAE sephadex A-50 followed by gel filtration on sephadex G-100. The two isoforms were named isoform I and II (minor and major forms, respectively) which differed in their abundance, their elution profile on both ion-exchange and gel filtration column chromatography. Isoforms I and II showed 6 and 24% of the total activity, respectively. Both the isoforms had an acid pH optimum (4.5) and were thermally stable at 65° for up to 15 min. Isoform I showed a broad temp optimum between 55 and 65° whereas isoform II had an optimal activity at 65°. The K m values of isoforms I and II for p -nitrophenyl-a- d -mannopyranoside were 1.11 and 1.05 mM, respectively. The activity of isoform I was inhibited by Hg 2 (1 mM) whereas isoform II was inhibited by Cu 2 (0.1 mM) and Hg 2 (1 mM). Both the isoforms were free of other glycosidases. Purified isoform II had a SDS M r of ca. 38,000.

Sugar uptake by protoplasts isolated from tomato fruit tissues during various stages of fruit growth

The uptake of radioactive glucose and sucrose by protoplasts isolated from pericarp and placenta tissues of tomato (Lycopersicon esculentum cv. Counter) fruit was investigated in relation to the dry matter accumulation rates of these tissues. Uptake of glucose by protoplasts isolated from pericarp tissue was highest in fruit of around 20 g fresh weight or 25 days after anthesis. Sucrose uptake by pericarp protoplasts was lower than that of glucose and did not show a peak of uptake. The maximum rate of glucose uptake by protoplasts from the pericarp was at the time when the tomato fruit was accumulating dry matter at the highest rate. Glucose uptake by placenta protoplasts was lower and at a similar level as sucrose.Protoplast uptake of glucose, but not of sucrose, was partially inhibited by (1) p‐chloromercuribenzene sulphonic acid, a sulphydryl group modifier; (2) erythrosin B, an H+‐ATPase inhibitor; and (3) valinomycin, a K+‐ionophore, suggesting that membrane transport of glucose by tomato fruit sink cells may be a carrier‐mediated, energy‐dependent process.The main route of carbohydrate accumulation by tomato fruit during the period of rapid fruit growth may be by cleavage of sucrose by apoplastic acid invertase prior to hexose transport across the plasma membrane.

Sugar uptake by protoplasts isolated from tomato fruit tissues during various stages of fruit growth

Sugar uptake by protoplasts isolated from tomato fruit tissues during various stages of fruit growth

TOMATO PERICARP TISSUE RESONANCE AND ITS USE IN TEXTURE EVALUATION

ABSTRACTThe use of resonance properties, measured by dynamic oscillation using a constant stress rheometer, as textural parameters for excised pericarp tissue of tomato (Lycopersicon esculentum Mill cv Trust) fruit during 21 days of ambient temperature ripening was assessed relative to the large‐deformation behavior measured by flat‐plate compression. The resonance frequency (fr) of excised tissue discs decreased significantly (P &lt; 0.05) over the first 9–12 days, and then approached a relatively low and constant value with subsequent ripening. A significant (P &lt; 0.05) increase in associated resonance strain amplitude (ymax) became apparent after the first 9–12 days of tomato fruit ripening. Ripening‐associated changes in bioyield and failure strengths, toughness, and apparent elastic and failure deformability moduli derived from flat‐plate compression tests were similar to those observed for tissue fr. Results were consistent with a change in the dominant mode of tissue failure from cell relaxation and rupture to debonding after 9–12 days of fruit ripening. A significant (P &lt; 0.05) semilogarithmic relationship was observed between fr, but not ymax, and compression parameters, allowing for reasonable prediction of large‐deformation behavior on the basis of measurement of only fr. The results demonstrate that resonance frequency may provide a useful parameter in the evaluation of tomato pericarp tissue texture.

Glutamic Acid and 5-Aminolevulinic Acid May Function as Precursors of System II Ethylene in Ripening Tomato Fruit

The ethylene biosynthetic pathway has been established as methionine (MET) to S-adenosylmethionine to 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, and this pathway has been labeled System I. Another pathway to ethylene may exist during synthesis of massive amounts of ethylene, and this system has been labeled System II. Our objective was to evaluate the efficacy of several compounds as possible precursors of System II ethylene in ripening tomato fruit tissue. Discs of `Rutgers' tomato pericarp tissue at the mature green, pink, and red ripe stages were incubated continuously in 10, 25, or 40 mm solutions of MET, ACC, 5-aminolevulinic acid (ALA), homocysteine, glutamic acid (GLU), alpha-ketoglutarate, or citrate buffer (control). The ethylene production rate at 8-hour intervals during a 32-hour incubation period and free and conjugated ACC content at the end of the incubation period were quantified. Fruit discs at the mature green stage treated with MET and ACC exhibited increased ethylene production and increased free ACC content. These results confirmed the role of MET and ACC as the predominant precursors of ethylene during the early stages of fruit development in tomato (System I). At the pink stage (System II); however, ALA increased ethylene production by 75% and free ACC content by 46% over the control, and MET increased ethylene by 27% and free ACC content by 57% over the control. At the red ripe stage, ALA caused a 35% increase and GLU caused a 31% increase in ethylene production over the control. These results suggest that ALA and GLU may be metabolized to ethylene via an unknown pathway during tomato fruit ripening (System II).