The Solanum lycopersicum AUXIN RESPONSE FACTOR 7 (SlARF7) mediates cross-talk between auxin and gibberellin signalling during tomato fruit set and development

Transgenic tomato plants (Solanum lycopersicum L.) with reduced mRNA levels of AUXIN RESPONSE FACTOR 7 (SlARF7) form parthenocarpic fruits with morphological characteristics that seem to be the result of both increased auxin and gibberellin (GA) responses during fruit growth. This paper presents a more detailed analysis of these transgenic lines. Gene expression analysis of auxin-responsive genes show that SlARF7 may regulate only part of the auxin signalling pathway involved in tomato fruit set and development. Also, part of the GA signalling pathway was affected by the reduced levels of SlARF7 mRNA, as morphological and molecular analyses display similarities between GA-induced fruits and fruits formed by the RNAi SlARF7 lines. Nevertheless, the levels of GAs were strongly reduced compared with that in seeded fruits. These findings indicate that SlARF7 acts as a modifier of both auxin and gibberellin responses during tomato fruit set and development.     

Induced parthenocarpy-a way of manipulating levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 2. Diffusible hormones

Indol-3-acetic acid (IAA), gibberellin-like substances (GAs), and abscisic acid (ABA) were measured throughout the first 35 days of fruit development in agar diffusates from seeded and parthenocarpic tomato fruits. Parthenocarpic fruit growth was induced with either an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃). IAA and GAs were at their highest levels in diffusates during the early stages of fruit growth, whereas diffusible ABA increased later. Most IAA was found in diffusates from auxin-induced and seeded fruits, whereas GAs were at their lowest levels in seeded fruits. There were only minor differences in ABA concentrations regardlesss of the treatments.Levels of diffusible hormones of tomato fruits may be easily manipulated by inducing parthenocarpic fruit growth. In spite of no obvious relationship between fruit growth and hormone levels in this study, induced parthenocarpy is considered a useful tool to further elucidate the role of hormones in fruit development and sink-source interactions.     

l-Ascorbic acid metabolism in parthenocarpic and seeded cherry tomatoes

The auxin treatment in tomato plants during anthesis has been extensively used for setting fruits in adverse climatic conditions (e.g., low temperatures and inadequate light), which is well known that reduces pollen availability and fertility. Since auxin application may affect fruit composition and quality, we examined l-ascorbic acid metabolism in seeded fruit (set by natural pollination) and parthenocarpic fruit (set by auxin) in cherry tomato cv. Conchita. Specifically, we studied the oxidized and total ascorbic acid contents, the expression of all characterized genes of l-ascorbic acid metabolism, the activity of ascorbate peroxidase and dehydroascorbate reductase and the immunolocalization of ascorbate peroxidase. Differences were detected between seeded and parthenocarpic fruits, in the expression of some of the genes of ascorbic acid metabolism. However, strong presence of l-ascorbic acid peroxidase protein was detected on the developing seeds. Our data indicate that induced parthenocarpy in auxin treated plants has a significant influence in ascorbic acid metabolism comparing to seeded tomato fruits.     

Changes in Endogenous Plant Hormones in Cherry Tomato Fruits during Development and Maturation

Hormonal extracts of cherry tomato fruits (Lycopersicon esculentum Mill.) cv. Small Fry at different stages of fruit development and maturation were bioassayed for their auxin, gibberellin, cytokinin and growth inhibitor activities. In general, the levels of endogenous growth promoters were much higher in the young developing fruits than in the more mature fruits. Free cytokinin levels were highest in the first two weeks of development then declined rapidly. However, cytokinin activity in the ribotide fraction, after treatment with alkaline phosphatase, decreased during thefirst three weeks of development then increased rapidly over the following four weeks. Auxin levels increased during early development to reach a maximum in three-week-old fruits after anthesis. Gibberellin levels during the first two weeks of development were much lower than those of auxins and cytokinins, but then increased to reach a peak in the fourth week after anthesis. A growth inhibiting substance with Rf similar to that of abscisic acid was found in the acidic fraction of the fruit extracts. This inhibitor increased gradually during fruit growth and development and reached a peak at the age of five weeks which coincides with the green mature stage.     

Induction of fruit set and development in pea ovary explants by gibberellic acid

The response of unpollinated ovary explants ofPisum sativum L. cv. Alaska No. 7 to several plant growth regulators and nutrients has been studied. Explants consisted of a segment of stem and an emasculated flower with or without the adjacent leaf. They were made on the day equivalent to anthesis and were cultured in a liquid medium. Growth regulators were applied either in the solution or directly to the ovaries. Giberellic acid (GA₃) in the presence of sucrose, but not indole-3-acetic acid or N⁶-(Δ²-isopentenyl)-adenine (2iP), induced fruit set and development of parthenocarpic fruits, the final length of these being a function of the intensity of the GA₃ treatment. The capacity of ovaries to respond fully to GA₃ was not lost after incubation of explants in water or 50 mM sucrose for 1 day and was similar in explants made between the day of anthesis and 3 days later. Limited growth was obtained with 100 mM sucrose alone but this effect was counteracted by 2′-isopropyl-4′-(trimethyl ammonium chloride)-5′-methylphenyl piperidine-1-carboxylate (AMO-1618). This inhibitor was ineffective when GA₃ was applied to the ovary. The development of the fruit was proportional to the length of the segment of stem up to 5 cm. The presence of the leaf in the explant enhanced the development of the fruit. These results indicate that a gibberellin is necessary for setting and development of fruits from cultured ovaries and that this effect depends on an appropriate source of nutrients. The course of development of parthenocarpic fruits on explants was similar to that of seeded fruits on the intact plant. The cultured pea ovary systemoffers convenient means to investigate the role of gibberellins and nutrients in fruit set and development.     

Vegetative Parthenocarpy in the Cactus Pear Opuntia ficus-indica (L.) Mill.

The dependence of fruit development on fertilization was studiedin two clones of Opuntia ficus-indica, Ofer and BSI. Fruitsof the clone Ofer bear fully developed seeds, whereas fruitsof the clone BSI contain only degenerated seeds and it was suspectedthat BSI is parthenocarpic. The two clones differed in theirpattern of fruit development. The increase in fruit fresh weightin Ofer was a result of both peel and pulp growth, whereas inBSI fruit growth was mainly due to pulp growth and the peelhad reached its final weight almost at anthesis. Pulp growthin BSI commenced earlier and was faster than in Ofer, but thefinal pulp weight in BSI was only 64% of that in Ofer. Seedgrowth in BSI was limited to the development of semilignifiedand lignified seed coats, whereas in Ofer 43·5% of theseeds were completely developed, the remainder being similarto those found in BSI. Fruits bearing well-developed seeds werealso found in a 'mutant' of BSI that, like Ofer, contained smallerovules at anthesis than flower of the regular BSI genotype.Germination in vivo and in vitro were similar in BSI and Ofer,but pollen tubes failed to reach the ovules in the regular BSIgenotype, while penetrating the ovules in Ofer and the small-ovuledgenotype of BSI. Good-quality fruits similar to Ofer fruitsin weight but with a higher peel to pulp ratio developed inBSI after flower-sterilization in the spring and in the autumn.In Ofer, sterilized flowers failed to develop fruits in springand partially set fruit in the autumn; the fruits consistedalmost exclusively of peel tissue. It was concluded that BSIis a vegetative parthenocarpic clone, i.e., that pollinationis not required for fruit set and development.Copyright 1993,1999 Academic Press Opuntia ficus-indica, cactus pear, fruit development, parthenocarpy, pollen-tube-growth, fluorescence microscopy     

Differential regulation of a fruit-specific 62 kDa protein in developing parthenocarpic (pat-2/pat-2) and seeded tomato fruits

The denatured protein profiles of developing tomato ( Lycopersicon esculentum Mill.) fruits, from the anthesis stage up to fruits at 30% of their final diameter, were examined in a pai-2l pat-2 parthenocarpic line and in its near isogenic non-partheno-carpic line. At anthesis no differences were detected between the protein patterns of ovaries developed on parthenocarpic and non-parthenocarpic plants. In subsequent stages the seeded and seedless fruits differed in the pattern of manifestation of several abundant proteins, none of which seem to be included in seeds The most prominent difference was found in an insoluble protein of 62 kDa; in developing seeded fruits of either the parthenocarpic or the non-parthenocarpic line, its rate of decline was much faster than in seedless fruits. In seeded fruits larger than 4-6 mm in diameter it was scarcely detected, whereas in parthenocarpic seedless 8–10 mm fruits it was still abundant. This protein is fruit specific; it is also enhanced in chemically (n-n-tolyl phthalamic acid) – induced parthenocarpic fruits of the non-parthenocarpic line. The prolonged manifestation in the parthenocarpic fruits results from de novo synthesis of this protein. There are indications that it is not a stress-related protein. This is the first demonstration of an association between the pattern of modulation of a protein and the phenotypic expression of genetically controlled parthenocarpy.     

Effects of Exogenous Growth Regulators on Fruit Development in Citrus unshiu

The effects of applied growth regulators on fruit developmenthave been determined in the parthenocarpic Satsuma mandarin(Citrus unshiu Marc.). The application of either gibberellicacid or benzyladenine at flower opening, caused a transientincrease in cell division in the ovary wall, but had no significanteffect on final fruit size. Late fruit growth and final fruitsize were increased by the application of the synthetic auxin2,4,5-trichlorophenoxyacetic acid, which had a specific effecton the enlargement of the juice vesicles. The three growth regulators enhanced vascularization in thepedicel, but the growth effects observed were unrelated to theirinfluence on the transport capacity of the phloem but causedby their direct effects on the fruit tissues. The sensitivityof the fruit tissues to the applied growth regulators changedmarkedly during early fruitlet development, and was characterizedculturing the fruit tissues in vitro.Copyright 1993, 1999 AcademicPress Citrus unshiu Marc., fruit growth, hormone treatment, in vitro culture, phloem formation, phloem transport, xylogenesis     

Induced parthenocarpy—a way of changing the levels of endogenous hormones in tomato fruits (Lycopersicon esculentum Mill.) 1. Extractable hormones

Ethylene, indol-3-acetic acid (IAA), gibberellin-like substances (GAs) and abscisic acid (ABA) were analysed in extracts from normal, seed-containing and parthenocarpic tomato fruits throughout fruit development. Parthenocarpic fruit growth was induced with an auxin (4-CPA), morphactin (CME) or gibberellic acid (GA₃) and compared with that of pollinated control fruits. Fruit growth was only affected by the treatment with GA₃, decreasing size and fresh weight by 60%. The peak sequence of hormones during fruit development was ethylene-GAs-IAA-ABA. Seeded fruits contained the highest levels of IAA and ABA but the lowest levels of GAs. Also, in seeded fruits, a high proportion of IAA and ABA was found in the seeds whereas this was not the case for GAs.Hormone levels of tomato fruits may be successfully, easily and reproducibly altered by inducing parthenocarpic fruit growth and thus eliminating development of seeds which are a major source of hormone synthesis. In spite of markedly changed hormone levels, there was no obvious relationship between fruit growth and extractable hormones per se. However, the results indicate that a high ratio of GAs: auxins is unfavourable for growth of tomato fruits.     

Induction of fruit set and development in pea ovary explants by gibberellic acid

The response of unpollinated ovary explants ofPisum sativum L. cv. Alaska No. 7 to several plant growth regulators and nutrients has been studied. Explants consisted of a segment of stem and an emasculated flower with or without the adjacent leaf. They were made on the day equivalent to anthesis and were cultured in a liquid medium. Growth regulators were applied either in the solution or directly to the ovaries. Giberellic acid (GA₃) in the presence of sucrose, but not indole-3-acetic acid or N⁶-(²-isopentenyl)-adenine (2iP), induced fruit set and development of parthenocarpic fruits, the final length of these being a function of the intensity of the GA₃ treatment. The capacity of ovaries to respond fully to GA₃ was not lost after incubation of explants in water or 50 mM sucrose for 1 day and was similar in explants made between the day of anthesis and 3 days later. Limited growth was obtained with 100 mM sucrose alone but this effect was counteracted by 2-isopropyl-4-(trimethyl ammonium chloride)-5-methylphenyl piperidine-1-carboxylate (AMO-1618). This inhibitor was ineffective when GA₃ was applied to the ovary. The development of the fruit was proportional to the length of the segment of stem up to 5 cm. The presence of the leaf in the explant enhanced the development of the fruit. These results indicate that a gibberellin is necessary for setting and development of fruits from cultured ovaries and that this effect depends on an appropriate source of nutrients. The course of development of parthenocarpic fruits on explants was similar to that of seeded fruits on the intact plant. The cultured pea ovary systemoffers convenient means to investigate the role of gibberellins and nutrients in fruit set and development.     

Induction of parthenocarpy in tomato via specific expression of the<Emphasis Type="Italic"> rolB</Emphasis> gene in the ovary

The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato ( Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis expressed under ovary- or ovule-specific promoters were shown earlier to enable parthenocarpic (i.e. seedless) fruit development. In the present study, we tested an alternative approach for the induction of parthenocarpy that is based on ovary-specific expression of the Agrobacterium rhizogenes-derived gene rolB. This gene was chosen because rolB transgenic plants manifest several syndromes characteristic of auxin treatment. Tomato plants transformed with a chimeric construct containing the rolB gene fused to the ovary- and young-fruit-specific promoter TPRP-F1 developed parthenocarpic fruits. Fruit size and morphology, including jelly fill in the locules of the seedless fruits, were comparable to those of seeded fruits of the parental line. Although it is not known whether ROLB signals for the same cassette of genes involved in fertilization-dependent fruit development, it clearly activates a battery of genes that enable successful completion of seedless fruit development in tomato.     

Identification and Expression Analysis of D-type Cyclin Genes in Early Developing Fruit of Cucumber (Cucumis sativus L.)

Plant D-type cyclin genes (CYCDs) are important regulators of cell division. However, little is known on their participation during the early developmental stage of cucumber fruit. In this study, cucumber CYCD genes were identified and characterized. The expression levels of these genes during early fruit development were assessed from 0 to 8 days after anthesis (DAA). The results revealed the presence of 13 different CYCD genes, which were named according to identity percentages of the corresponding orthologs in Arabidopsis thaliana and poplar. The genomic organization of each subgroup CYCD was similar to their orthologs in A. thaliana and poplar. The expression levels of CsCYCD genes were analyzed in cucumber fruits under different treatments including natural parthenocarpic fruit, pollinated fruit, and N-(2-chloro-4-pyidyl)-N′-phenyurea (CPPU)-induced parthenocarpic fruit. The highest expression levels of most CsCYCDs genes were at four DAA in natural parthenocarpic and pollinated fruits. Interestingly, the expression patterns of 8 of 13 CsCYCD genes in natural parthenocarpic fruit were similar to those in pollinated fruit, but different from those in CPPU-induced parthenocarpic fruit. Collectively, the results of this study provide insights on the CYCDs involved in cucumber parthenocarpic fruit development.     

Peroxidase and IAA oxidase activities and peroxidase isoenzymes in the pericarp of seeded and seedless “Redhaven” peach fruit

Parthenocarpic peach fruit (Prunus persica L. Batsch., cv. Redhaven) were induced with 1-(3-chlorophthalimide)-cyclohexane carboxamide (AC 94377). The activities of soluble, and ionically and covalently bound peroxidase and indole-3-acetic acid (IAA) oxidase in the pericarp of both seeded and parthenocarpic fruit were determined from 21–43 days after anthesis. Seedless fruit grew faster during early stage I and ceased growth earlier than seeded fruit. Total peroxidase and IAA oxidase activities increased with development on both types of fruit, but higher values were found in seedless fruit. The ionic fraction showed the greatest increase for both enzyme activities. Isoperoxidase profile showed new cationic isoenzymes and higher levels of the less anionic isoenzymes in the pericarp of seedless fruit, whereas the seeded fruit contained higher levels of the more acidic isoperoxidases.     

Xyloglucan endotransglycosylase activity during fruit development and ripening of apple and kiwifruit

Xyloglucan endotransglycosylase (XET) activity was measured in apple (Malus domestica Borkh. cv. Braeburn) pericarp and kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) outer pericarp and core tissues in order to establish whether a correlation exists between the activity of the enzyme and different stages of fruit development Whereas the growth rate of kiwifruit paralleled changes in XET activity throughout fruit growth, that of apple did not. Both fruits showed the highest XET activity, on a fresh weight basis, in the first two weeks after anthesis when cell division was at its highest. XET activity then decreased sharply, but as the fruit increased in size (4–8 weeks after anthesis) there was a concomitant increase in XET activity in both fruits. In the latter stage of fruit development (16–26 weeks after anthesis) XET activity increased to peak at harvest in apple fruit. During this time there was relatively little increase in fruit size and presumably therefore minimal cell expansion. XET activity then declined as fruit softened after harvest. In core tissue from kiwifruit, XET activity increased throughout the later stages of fruit growth to harvest maturity in a similar manner to apple, but continued to increase after harvest until fruit were ripe. In contrast, XET activity in the outer pericarp of kiwifruit did not increase until ripening after harvest. In apple tissue up to 30% of the XET activity was cell wall bound and could not be solubilised, even in buffer containing 2 M NaCl. The results implicate XET in cell wall assembly during cell division and expansion early in apple and kiwifruit growth. However, the disparity between apple and kiwifruit with respect to XET activity late in fruit development and ripening and the different affinities of the enzyme for the cell wall in each fruit, suggest that XET has several roles in plant development, not all of which are related to cell wall loosening during periods of accelerated growth.     

Genetic Analysis of Growth-Regulator-Induced Parthenocarpy in Arabidopsis

In Arabidopsis, seedless silique development or parthenocarpy can be induced by the application of various plant growth regulators (PGRs) to unfertilized pistils. Ecotype-specific responses were observed in the Arabidopsis ecotypes Columbia and Landsberg relative to the type of PGR and level applied. The parthenocarpic response was greatest in ecotype Landsberg, and comparisons of fruit growth and morphology were studied primarily in this ecotype. Gibberellic acid application (10 micromol pistil(-1)) caused development similar to that in pollinated pistils, while benzyladenine (1 micromol pistil(-1)) and naphthylacetic acid (10 micromol pistil(-1)) treatment produced shorter siliques. Naphthylacetic acid primarily modified mesocarp cell expansion. Arabidopsis mutants were employed to examine potential dependencies on gibberellin biosynthesis (ga1-3, ga4-1, and ga5-1) and perception (spy-4 and gai) during parthenocarpic silique development. Emasculated spy-4 pistils were neither obviously parthenocarpic nor deficient in PGR perception. By contrast, emasculated gai mutants did not produce parthenocarpic siliques following gibberellic acid application, but silique development occurred following pollination or application of auxin and cytokinin. Pollinated gai siliques had decreased cell numbers and morphologically resembled auxin-induced parthenocarpic siliques. This shows that a number of independent and possibly redundant pathways can direct hormone-induced parthenocarpy, and that endogenous gibberellins play a role in regulating cell expansion and promoting cell division in carpels.