Cytokinin-Induced Parthenocarpic Fruit Development in Tomato Is Partly Dependent on Enhanced Gibberellin and Auxin Biosynthesis

Fruit set of plants largely depends on the biosynthesis and crosstalk of phytohormones. To date the role of cytokinins (CKs) in the fruit development is less understood. Here, we showed that parthenocarpic fruit could be induced by 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU, an active CK) in tomato ( Solanum lycopersicum cv. Micro-Tom). The fresh weight of CPPU-induced parthenocarpic fruits was comparable with that induced by GA₃. Importantly, CPPU-induced parthenocarpy was found to be compromised by simultaneous application of paclobutrazol (a GA biosynthesis inhibitor), and this effect could be restored by exogenous GA₃. Like pollination, CPPU-induced fruit showed enhanced accumulation of GA₁₊₃ and indole-3-acetic (IAA), which were accompanied by elevated expression of GA biosynthesis genes like SlGPS, SlGA20ox1, SlGA20ox2 and SlGA3ox1, and IAA biosynthesis gene ToFZY. Elevated GAs level in CPPU-induced fruits was also associated with down-regulation of GA inactivation genes, namely SlGA2ox1,2,3,4,5 in comparison with untreated control. These results suggested that CKs may induce parthenocarpy in tomato partially through modulation of GA and IAA metabolisms.     

Effect of Gibberellin and Auxin on Parthenocarpic Fruit Growth Induction in the cv Micro-Tom of Tomato

The effect of applied gibberellin (GA) and auxin on fruit-set and growth has been investigated in tomato (Solanum lycopersicum L.) cv Micro-Tom. It was found that to prevent competition between developing fruits only one fruit per truss should be left on the plant. Unpollinated ovaries responded to GA₃ and to different auxins [indol-3-acetic acid, naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid (2,4-D)], 2,4-D being the most efficient. GA₃- and 2,4-D-induced fruits had different internal morphology, with poor locular tissue development in the case of GA, and pseudoembryos development in the case of 2,4-D. Also, GA₃ produced larger cells in the internal region of the mesocarp (IM) associated with higher mean C values, whereas 2,4-D produced more cell layers in the pericarp than pollinated fruits. The smaller size of GA₃- compared with 2,4-D-induced fruits was due to them having fewer cells, only partially compensated by the larger size of IM cells. Simultaneous application of GA₃ and 2,4-D produced parthenocarpic fruits similar to pollinated fruits, but for the absence of seeds, suggesting that both kinds of hormones are involved in the induction of fruit development upon pollination. It is concluded that Micro-Tom constitutes a convenient model system, compared to tall cultivars, to investigate the hormonal regulation of fruit development in tomato.     

Early Fruit Development in the Watermelon: Anatomical Comparison of Pollinated, Auxin-induced Parthenocarpic and Unpollinated Fruits

The anatomy of pollinated, auxin-induced parthenocarpic andunpollinated watermelon fruits was observed for nine days afterflowering. Parthenocarpic fruits were larger and had higherfresh weight and percentage water than pollinated fruits atday 1 but the positions were reversed by day 9. Unpollinatedfruits did not increase in size after day 3. Pericarp cells were small, of regular shape and showed no obviouschange with either time or treatment. Cell number increasedin the pollinated and parthenocarpic but not in the unpollinatedfruits. Cells divided in the flesh of the parthenocarpic but not ofthe pollinated fruits which increased in size by cell enlargementonly. Starch, present in the cells of the flesh and placentaat day 0 was absent from the unpollinated fruits at day 6. Ovules grew in both pollinated and parthenocarpic fruits largelydue to cell division in the nucellus and integuments; the pollinatedovules were larger than the parthenocarpic throughout. Embryoand endosperm development occurred in the pollinated but notin the parthenocarpic ovules. Starch was present throughoutthe nine-day period in the integuments of the pollinated andparthenocarpic ovules but was lost from the integuments of theunpollinated ovules by day 6. Pollinated and parthenocarpicovules contributed increasingly to fruit dry weight over thenine-day period. It is suggested that the ovule tissues, in particular the nucellusand integument may exert control over early development in bothpollinated and parthenocarpic fruits.     

Correlation between Ornithine Decarboxylase and Putrescine in Tomato Plants Infected by Citrus Exocortis Viroid or Treated with Ethephon

We have investigated the arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) activities and the levels of conjugated polyamines to explain the decrease of free putrescine level caused by citrus exocortis viroid (CEVd) and ethephon treatment in tomato (Lycopersicon esculentum Mill. cv Rutgers) plants (J.M. Belles, J. Carbonell, V. Conejero [1991] Plant Physiol 96: 1053-1059). This decrease correlates with a decrease in ODC activity in CEVd-infected or ethephon-treated plants; ADC activity was not altered. CEVd infection had no effect on polyamine conjugates, and ethephon produced a decrease in putrescine conjugates. Interference with ethylene action by silver ions prevented the decrease in ODC activity and in free and conjugated putrescine. It is suggested that changes in putrescine level after CEVd infection and ethephon treatment are regulated via ODC activity and that conjugation is not involved.     

Expression of Ornithine Decarboxylase Is Transiently Increased by Pollination, 2,4-Dichlorophenoxyacetic Acid, and Gibberellic Acid in Tomato Ovaries

A cDNA encoding for a functional ornithine decarboxylase has been isolated from a cDNA library of carpels of tomato (Lycopersicon esculentum Mill.). Ornithine decarboxylase in tomato is represented by a single-copy gene that we show to be up-regulated during early fruit growth induced by 2,4-dichlorophenoxyacetic acid and gibberellic acid.     

Arginine Decarboxylase and Putrescine Oxidase in Ovaries of Pisum sativum L. (Changes during Ovary Senescence and Early Stages of Fruit Development)

Enzymatic activities involved in putrescine metabolism in ovaries of Pisum sativum L. during ovary senescence and fruit set were investigated. Accumulation of putrescine was observed during incubation of extracts from gibberellic acid-treated unpollinated ovaries (young developing fruits) but not in extracts from untreated ovaries (senescent ovaries). Extracts from pea ovaries showed arginine decarboxylase (ADC) activity, but ornithine decarboxylase and arginase activity were not detected. ADC activity decreased in presenescent ovaries and increased markedly after induction of fruit set with gibberellic acid. Increases in ADC activity were also observed with application of other plant growth substances (benzy-ladenine and 2,4-dichlorophenoxyacetic acid), after pollination, and in the slender (la crys) pea mutant. By contrast, putrescine oxidase activity increased in presenescent ovaries but did not increase during early fruit development. All of these results suggest that ADC and putrescine oxidase are involved in the control of putrescine metabolism. Ovary senescence is characterized by the absence of putrescine biosynthesis enzymes and increased levels of putrescine oxidase and fruit development by an increase in ADC and a constant level of putrescine oxidase.     

Polyamines, Ornithine Decarboxylase, and Diamine Oxidase in the Substantia Nigra and Striatum of the Male Rat After Hemitransection

Partial hemitransection at the mesodiencephalic junction in the rat increased striatal and nigral putrescine concentrations on the lesioned side for at least 168 h, with maximal increases between 24 and 48 h. Spermidine and spermine levels declined at 24 h in the striatum, rising above control values at 48 h and further at 168 h. In the substantia nigra, they remained unchanged for the first 48 h and then increased by 168 h. Cadaverine in the striatum also increased at 48 h. On the intact side putrescine increased but to a much lesser extent (at 48 h in the striatum and at 24 and 48 h in the substantia nigra). Ornithine decarboxylase and diamine oxidase activities showed maximal increases at 24 h in the striatum of the lesioned side, whereas in the substantia nigra ornithine decarboxylase attained a very high value as early as 4 h after the operation and diamine oxidase activity peaked at 48 h. The enzyme activities returned toward the basal values at 168 h. On the intact side, ornithine decarboxylase showed a small increase starting at 4 h and diamine oxidase was enhanced at 48 h. These results indicate that the stimulation of biosynthetic and degradative enzymes of polyamine metabolism accompanied by marked and prolonged increases in putrescine may be essential events in the early phases of neuronal response to mechanical injury in the CNS.     

S02对冷藏枇杷果实品质及活性氧和多胺代谢的影响

以"大红袍"枇杷果实为试材,研究了SO2处理对冷藏枇杷果实活性氧代谢和内源多胺含量变化的影响及与果实木质化败坏的关系。结果表明,SO2可提高超氧物歧化酶(SOD)和过氧化氢酶(CAT)活性,抑制过氧化物酶(POD)活性的上升,减少H2O2的积累。经SO2处理的果实,精胺(Spm)和亚精胺(Spd)含量的变化很小,基本维持在贮前水平上,腐胺(Put)的积累则受到极大抑制,贮藏5周后的果实不出现木质化败坏症状。这些结果表明,SO2可能通过维持活性氧代谢的平衡,抑制活性氧的积累,从而防止果实木质化的发生。     

SO_2对冷藏枇杷果实品质及活性氧和多胺代谢的影响

以“大红袍”枇杷果实为试材 ,研究了SO2 处理对冷藏枇杷果实活性氧代谢和内源多胺含量变化的影响及与果实木质化败坏的关系。结果表明 ,SO2 可提高超氧物歧化酶 (SOD)和过氧化氢酶 (CAT)活性 ,抑制过氧化物酶 (POD)活性的上升 ,减少H2 O2 的积累。经SO2 处理的果实 ,精胺 (Spm)和亚精胺 (Spd)含量的变化很小 ,基本维持在贮前水平上 ,腐胺 (Put)的积累则受到极大抑制 ,贮藏 5周后的果实不出现木质化败坏症状。这些结果表明 ,SO2 可能通过维持活性氧代谢的平衡 ,抑制活性氧的积累 ,从而防止果实木质化的发生     

聚乙二醇胁迫下的番茄幼苗内ABA、JA和多胺含量以及多胺氧化酶活性的变化

聚乙二醇模拟的干旱胁迫下,2个品种番茄幼苗根和叶中脱落酸(ABA)和茉莉酸(JA)含量均迅速积累,叶中ABA累积比根中滞后;游离态亚精胺(fSpd)、精胺(fspm)、腐胺(fPut)含量和多胺氧化酶(PAO)活性均先上升,12 h时达到峰值后下降,耐旱性强的品种'毛粉802'幼苗根和叶中积累ABA、JA和spd、Spm的能力明显强于耐旱性弱的品种'皇冠'.'皇冠'的PAO活性提高程度大于'毛粉802'.番茄根和叶中多胺含量和PAO活性呈显著正相关.内源多胺的积累诱导ABA和JA含量的升高,从而导致番茄幼苗的耐旱性增强.     

低温胁迫下褪黑激素对烟草悬浮细胞精氨酸脱羧酶活性的影响

研究了褪黑激素对烟草(Nicotiana tabacum)悬浮细胞在低温胁迫下精氨酸脱羧酶活性及细胞生存率的影响.发现褪黑激素可以明显提高低温胁迫下烟草悬浮细胞精氨酸脱羧酶的活性,并明显提高细胞的生存率.表明褪黑激素可能在低温条件下通过调节植物细胞内多胺的合成而提高抵御冷害的能力.     

A Comparative Study of the Changes in Root Growth, Induced by Coumarin, Auxin, Ethylene, Kinetin and Gibberellic Acid

The effect of coumarin, IAA, ethylene, kinetin and gibberellic acid on roots of maize and wheat was investigated. Sterile attached and detached roots and isolated elongation zones were used. In some experiments a semi-sterile procedure was followed. The effects of the different regulators separately or in various combinations together with coumarin were studied on the root growth with regard to division, elongation and swelling of the cells. The ethylene production in isolated elongation zones was measured after treatment with coumarin, IAA, PCIB, kinetin, colchicine and dinitrophenol. The results show the following: 1) Each substance produces a specific morphologic pattern. 2) Changes in polarity were demonstrated for auxin-induced swelling in cell divisions and cell expansion and for coumarin-induced swelling in cell divisions. Other cell expansion in swollen parts was due to cylindric cells increasing in width while retaining their cylindric form. 3) Coumarin-induced inhibition could not be counteracted by IAA, PCIB, carbon dioxide, kinetin, gibberellic acid or Cycocel. 4) The ethylene production in isolated elongation zones increases noticeably after kinetin treatment, less strongly after auxin treatment and least after coumarin treatment. The production of ethylene does not seem to be correlated with the morphogenetic effect of the different substances. 5) The isolated elongation zones reacted to a) IAA and kinetin with an increase in length in some cases and b) gibberellic acid with a reduction of their width. 6) The inhibitory effect of coumarin on the growth in length of the elongation zones was diminished by kinetin. The swelling produced by coumarin in these zones was reduced by gibberellic acid. The effects just mentioned of kinetin and gibberellic acid were considered as indirect ones. - From the present findings it was concluded that concomitant effects of auxin, ethylene, cytokinins and gibberellins are not obligatory for coumarin to exert its morphogenetic effects on root growth. In discussing the results some pitfalls in studies of growth reactions after application of hormones to roots containing meristem were emphasized.     

Changes in Tomato Leaves Induced by NaCl Stress: Leaf Organization and Cell Ultrastructure

The alterations of organization of leaf tissues and cell ultrastructure as a consequence of salt stress (75 and 150 mM NaCl) were studied in two tomato (Lycopersicum esculentum Mill.) cultivars showing different salinity tolerance. The salinity brought changes in cell shape, volume of intercellular spaces and chloroplast number, shape and size. These characteristics were specific in each cultivar. The ultrastructural changes were also different in the two tomato cultivars studied and the most important ones were in the number and size of starch granules in chloroplasts, the number of electron-dense corpuscules in the cytoplasm, the structure of mitochondria, and number of plastoglobuli. This revised version was published online in July 2006 with corrections to the Cover Date.     

Changes in the Level of Peptidase Activities in Pea Ovaries during Senescence and Fruit Set Induced by Gibberellic Acid

The activities and changes in the levels of exopeptidase and endopeptidase activities were characterized in unpollinated ovaries of Pisum sativum L. cv Alaska during senescence and early fruit development induced by gibberellic acid (GA₃). Two aminopeptidases and one iminopeptidase were electrophoretically separated. These peptidases were sensitive to inhibitors of sulfhydryl proteases. Carboxypeptidase activity was inhibited by phenylmethyl sulfonyl fluoride. An azocasein-degrading endopeptidase, sensitive to thiol protease inhibitors, was also found. An increase in the specific activity of aminopeptidase during both fruit development and ovary senescence was observed. In contrast, the specific activity of carboxypeptidase and endopeptidase increased only during senescence of the ovary. Changes in exopeptidase activity in senescing ovaries could be mainly the consequence of a greater stability to proteolysis while the rise in endopeptidase activity appeared to be due to new or increased synthesis of the enzyme. These results suggest that endopeptidase, and not amino or carboxypeptidase, plays a key role in the senescence of pea ovaries and that the changes in unpollinated ovaries leading to ovary senescence or fruit development can be controlled by gibberellins.     

Ornithine cycle in Nostoc PCC 73102. Arginase,OCT and arginine deiminase,and the effects of addition of external arginine,ornithine, or citrulline

Arginase, ornithine carbamoyl transferase (OCT) and arginine deiminase activities were found in cell-free extracts of Nostoc PCC 73102, a free-living cyanobacterium originally isolated from the cycad Macrozamia. Addition of either arginine, ornithine or citrulline to the growth medium induced significant changes in their in vitro activities. Moreover, growth in darkness, compared to in light, induced higher in vitro activities. The in vitro activities of arginase and arginine deiminase, two catabolic enzymes primarily involved in the breakdown of arginine, increased substantially by a combination of growth in darkness and addition of either arginine, or ornithine, to the growth medium. The most significant effects on the in vitro OCT activities where observed in cells grown with the addition of ornithine. Cells grown in darkness exhibited about 6% of the in vivo nitrogenase activity observed in cells grown in light. However, addition of external carbon (glucose and fructose) to cells grown in darkness resulted in in vivo nitrogenase activity levels similar to, or even higher than, cells grown in light. Growth with high in vivo nitrogenase activity or in darkness with the addition of external carbon, resulted in repressed levels of in vitro arginase and arginine deiminase activities. It is suggested that nitrogen starvation induces a mobilization of the stored nitrogen, internal release of the amino compound arginine, and an induction of two catabolic enzymes arginase and arginine deiminase. A similar and even more pronunced induction can be observed by addition of external arginine to the growth medium.     

Glutamic Acid Decarboxylase in Sea Lamprey (Petromyzon marinus): Characterization, Localization, and Developmental Changes

Abstract: We have carried out assays for glutamic acid decarboxylase (GAD) in homogenates of brain and spinal cord from larval and adult sea lamprey ( Petromyzon marinus ). The enzyme had similar characteristics in both stages. Optimal pH was 6.8; optimal temperature was 27–30° C; K _m at 27°C was 5 mM. GAD activity was distributed uniformly along the length of the spinal cord. Specific activities for the larval cord and brain were 26 and 63 nm CO₂/mg protein/h. respectively. The specific activities for the adult cord and brain were 29 and 236 nm CO₂/mg protein/h, respectively. Thus, the activity of cord homogenates did not change significantly between larval and adult stages, but that of the brain increased about fourfold.     

Changes in Assimilated C Distribution and Soluble Acid Invertase Activity of Zinnia elegans Induced by Uniconazol, an Inhibitor of Gibberellin Biosynthesis

The physiological aspects involved in the Uniconazol-induced morphological changes in Zinnia elegans Jacq. cv Red Sun were clarified biochemically by determining the distribution of assimilated ¹³C as well as the soluble acid invertase activity. The application of Uniconazol, (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-pentane-3-ol, reduced the growth of stems and leaves without affecting the roots. In addition, the translocation of assimilated ¹³C from leaf to other organs was inhibited, with the stem being more restricted than the root. These changes were matched by a corresponding decrease in the specific activity of soluble acid invertase. Subsequent treatment of GA₃ counteracted these effects of Uniconazol. Moreover, the total and reducing sugar content was closely correlated with the soluble acid invertase activity in the stem. It is concluded that the reduction in invertase activity of stem is a biochemical manifestation of the retardation of stem growth induced by Uniconazol.     

Amino Acid Utilization in Seeds of Loblolly Pine during Germination and Early Seedling Growth (I. Arginine and Arginase Activity)

The mobilization and utilization of the major storage proteins in loblolly pine (Pinus taeda L.) seeds following imbibition were investigated. Most of the seed protein reserves were contained within the megagametophyte. Breakdown of these proteins occurred primarily following radicle emergence and correlated with a substantial increase in the free amino acid pool in the seedling; the majority of this increase appeared to be the result of export from the megagametophyte. The megagametophyte was able to break down storage proteins and export free amino acids in the absence of the seedling. Arginine (Arg) was the most abundant amino acid among the principal storage proteins of the megagametophyte and was a major component of the free amino acid pools in both the seedling and the megagametophyte. The increase in free Arg coincided with a marked increase in arginase activity, mainly localized within the cotyledons and epicotyl of the seedling. Arginase activity was negligible in isolated seedlings. Experiments with phenylphosphorodiamidate, a urease inhibitor, supported the hypothesis that arginase participates in Arg metabolism in the seedling. The results of this study indicate that Arg could play an important role in the nutrition of loblolly pine during early seedling growth.