bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of auxin‐regulated genes
Authors: Sitbon Folke , Perrot‐Rechenmann Catherine
Published: May 2006

Auxins constitute a small class of plant hormones having profound effects on plant development. Among the fastest cellular responses to auxin addition is an alteration of gene expression, and the abundance of several mRNA species has been shown to increase, or decrease, within minutes to hours after auxin treatment. The regulation of this process appears, at least partly, to be at the transcriptional level. Using differential screening approaches, a number of auxin‐regulated cDNAs and genes have been isolated, mainly from elongating tissues and dividing cells. In addition, an influence of auxin on the regulation of genes isolated for other purposes has also been revealed. With respect to kinetic and dose‐response characteristics, as well as to cellular expression and hormonal specificity, individual auxin‐regulated genes seem to be regulated very differently. possibly reflecting different modes of auxin action. The present article gives an overview of the expression and function of genes whose mRNA levels have been demonstrated to be altered after auxin treatment, and relates altered gene expression patterns to known auxin responses at the cellular or whole plant level.
ABA metabolites induce group 3 LEA mRNA and inhibit germination in wheat
Authors: Walker‐Simmons M. K. , Holappa Lynn D. , Abrams Garth D. , Abrams Suzanne R.
Published: May 2006

In plants, metabolism of the plant hormone (+)‐S‐abscisic acid (ABA) occurs by oxidation at the 8′‐carbon on the ABA ring, producing (+)‐8′‐hydroxy‐ABA (8′OH‐ABA), which undergoes ring closure to phaseic acid (PA), or at the 7′‐carbon producing 7′‐hydroxy‐ABA (7′OH‐ABA). New methods for synthesixing and stabilizing 8′OH‐ABA have enabled us for the first time to compare the biological activities of the ABA metabolites. 8′OH‐ABA. PA and 7′OH‐ABA. Activities were determined in wheat (Triticum aestivum, cvs Brevor and Clarks Cream) using optically pure natural enantiomers of ABA. 8′OH‐ABA, PA, and 7′OH‐ABA. Comparison of wheat embryo germination inhibitory activity showed that only the metabolite 7′OH‐ABA had significant activity (10 to 40% of effective ABA activity) as a germination inhibitor of wheat embryos. The metabolites had differential effects on ABA‐responsive gene expression. Both 8′OH‐ABA and PA were effective inducers of an ABA‐responsive LEA (late embryogenesis abundant) gene, wheat group 3 LEA, in seedling roots, suggesting that ABA metabolites can maintain and prolong LEA gene expression. The metabolites had only a slight effect on accumulation of an ABA‐responsive protein kinase (PKABA1) mRNA or pMA1951. These results are consistent with the idea that there are several control points in the ABA metabolic pathway and indicate that assessment of ABA signalling responses should include consideration of the biological activities of ABA metabolites.
Stress‐induced abscisic acid transients and stimulus‐response‐coupling
Authors: Cowan A. K. , Richardson G. R. , Maurel J. C. G.
Published: May 2006

Loss of cell turgor and distortion of the plasma membrane occur as a result of dehydration and precede the stress‐induced bulk increase in concentration of tissue abscisic acid. The latter has been correlated with induction of stress‐related gene expression. However, several different stresses may trigger the same coupling mechanism. Thus, at least three signalling pathways have been proposed: abscisic acid‐requiring, abscisic acid‐responsive, and mechanosensory. In this paper, the role and contribution of stress‐induced abscisic acid transients is examined in an attempt to explain apparent abscisic acid‐dependent and ‐independent stimulus‐response‐coupling. Early, intermediate, and late response stages are defined within the stress‐induced abscisic acid transient and at least four signalling mechanisms are identified. These include, early and late intracellular modulation of gene expression through depression and/or negative regulation, rapid membrane‐initiated calcium release and ion channel activation, and late (slow) hormone‐receptor induction of gene expression. An assessment of these proposed ABA signalling mechanisms in terms of AABA‐dependent and ‐independent stimulus‐response‐coupling strongly suggests that rapid responses may not be a prerequisite for slow responses and that the receptor proteins involved have different steric requirements, i.e., they are tissue‐ and/or cell‐specific.
Endogenous abscisic acid during the germination of chick‐pea seeds
Authors: Iglesias Roberto G. , Babiano Maria J.
Published: May 2006

Over the past twenty years many studies have been undertaken to elucidate the regulation of seed germination. Abscisic acid (ABA) and the gibberellins (GAs) are the hormones proposed to control this process, the first by inhibiting and the second by inducing germination. It has been proposed that a high water potential increases the growth potential of the embryo, presumably permitting the production or activation by GA of the cell wall hydrolases and thus decreasing the yield threshold of the endosperm close to the radicle tip. A low water potential, e.g., imbibition in an osmoticum. imposes a stress on cell metabolism, by reducing the turgor of the radicle cells, and there is a decrease in growth potential. Exogenous ABA also causes a decline in growth potential of the radicle: however, the actions of low water potential in preventing germination are not mediated through an increase in ABA in the seeds. In the present paper an attempt is made to asses the role of ABA and polyethylene glycol (PEG) in the germination of chick‐pea (Cicer arietinum L.) seeds. The endogenous ABA of chick‐pea seeds was purified by reversed‐phase HPLC and quantified by GC‐ECD. The variations in the ABA levels in the embryonic axes and the cotyledons were studied during 120 h. of imbibition. The highest ABA level in the embryome axes was found at 18 h. coinciding with an increase in fresh weight and a high germination percentage. ABA was not detected in the cotyledons during incubation which probably indicates that the hormone is more involved in the active growth of the embryonic axes itself than in the mobilization process of the reserves. When seeds were treated with different PEG‐cycles. PEG delayed germination, reduced the fresh weight of embryonic axes, and retarded the onset of ABA synthesis. It is concluded that endogenous ABA is related to the onset of germination and the growth of the embryonic axis. In addition, there is no correlation among the different PEG‐cycles and the level of ABA and germination. Germination was related more to the water conditions inside the embryo's cells than to ABA levels.
Cytokinin‐binding proteins
Authors: Brault M. , Maldiney R. , Miginiac E.
Published: May 2006

This article is focused on the modalities of reception of cytokinins which remain largely unknown. It summarizes the main steps of the different protocols used to study cytokinin‐binding proteins (CBPs). We place emphasis on the significance and specificity of the detection according to the properties of the probes used: radioactive or photoreactive cytokinins, fluorescent anticytokinins, anti‐idiotype antibodies. The purification procedures are also examined. The cellular localisation and the putative physiological roles of the numerous and different CBPs found are considered. The interest of genetic and molecular studies is discussed.
Plant mutants with altered responses to cytokinins
Authors: Miklashevichs E. , Walden R.
Published: May 2006

Compared with other phytohormones, relatively little is known about the biosynthesis and the molecular action of cytokinins. A number of plant mutants with changed response to, or requirement for cytokinins are now available. It is likely that the biochemical and molecular genetic analysis of these mutants will contribute considerably to our understanding of the nature of cytokinin action.
Molecular characterisation of gibberellin 20‐oxidases. Structure‐function studies on recombinant enzymes and chimaeric proteins
Authors: Lange Theo , Kegler Carsten , Hedden Peter , Phillips Andy L. , Graebe Jan E.
Published: May 2006

Gibberellin (GA) 20‐oxidases are multifunctional enzymes that catalyse reactions at an important branch point in the GA biosynthetic pathway. These enzymes oxidise the C‐20 methyl group of a diterpene carboxylic acid precursor (e.g. GA12) to form an alcohol (in our case GA15‐open lactone) and an aldehyde (GA24). The aldehyde is either oxidised to a tricarboxylic acid (GA25) or, with loss of carbon‐20 and lactonisation, to a C19‐GA (GA9). This branching is interesting to study, because C19‐GA derivatives function as plant hormones in different tissues, whereas the C20‐GA tricarboxylic acids have no known function. We have constructed chimaeric proteins by combining a GA 20‐oxidase from immature seeds of Cucurbita maxima L., which produces mainly C‐20 carboxylic acids, with a 20‐oxidase from Marah macrocarpus immature seeds, which forms predominantly CC19‐GAs. The cDNAs encoding these two very similar 20‐oxidases were digested with restriction endonucleases Van 911. Bcl 1, and Bsa WI, and six chimaeric sequences were produced by recombination of the DNA fragments. The pCM1 ‐construct was obtained by exchanging nt 303–809 of the Cucurbita cDNA with the homologous DNA from the March 20‐oxidase. In pCM2, pCM3, pCM4, pCM5 and pCM6, nt 810–992, nt 993–end, nt 303–992, nt 810–end, and nt 311–end were exchanged, respectively. All constructs were cloned in a pUC18 vector and functionally expressed in E. coli NM522 cells. GA 20‐oxidase activity was detectable in cell‐lysates from the transformed E. coli, but the extent and kind of conversion depended on the construct. Highest conversion of GA12was found with pCM1 and pCM3, one‐tenth of this conversion was observed with pCM5 and pCM6, and one‐hundredth was obtained with the hybrid proteins from pCM2 and pCM4. With pCM2 and pCM4, neither the C19‐end product, GA9, nor the C20‐end product, GA25‐was formed. However, after transformation with constructs pCM1, pCM3, pCM5 or pCM6. GA9accounted for 30, 40, 60 and 90%, respectively, of the end products formed. Thus, the segments originating from M. macrocarpus conferred upon the chimaeric proteins an increasing ability to direct the biosynthetic flow into C19‐GAs in this order. Although GA24is the immediate precursor, much less end products were formed by using this substrate.
Ethylene and abscission
Authors: Brown Kathleen M.
Published: May 2006

A substantial body of literature supports the involvement of ethylene in abscission of leaves, flowers and flower parts, and fruit. Exogenous ethylene accelerates abscission in many, but not all, abscising plant systems. In some cases, endogenous ethylene production increases before abscission, while in others a change in ethylene sensitivity can be demonstrated. Ethylene interacts with auxin in regulating abscission, particularly in leaves and fruit. Ethylene has been shown to regulate expression of genes involved in cell separation, including cellulases and pectinases. Such regulation has been demonstrated at the level of mRNA abundance, but post‐transcriptional regulation may also be important.
Inhibitors of ethylene responses in plants at the receptor level: Recent developments
Authors: Sisler E. C. , Serek M.
Published: May 2006

A number of organic molecules that appear to block the ethylene receptor have been discovered recently. For example, on irradiation with visible light, diazocyclopentadiene (DACP), gives rise to some potent but as yet unidentified inhibitor compounds. Some synthetic cyclopropenes have been shown to bind to the ethylene receptor and prevent the physiological action of ethylene for extended periods. Cyclopropene (CP). 1‐methylcyclopropene (1‐MCP) and 3,3‐dimethylcyclopropene (3,3‐DMCP) have been shown to prevent ethylene effects in a number of plants. As low a concentration as 0.5 nl l−1 of 1‐MCP is sufficient to protect carnation (Dianthus caryophyllus) flowers for several days against ethylene, and 0.7 nl l−1 1‐MCP or CP will prevent the ripening of banana (Musa sapientum) for 12 days at 24°C. Some plant organs require higher concentrations of these inhibitors. Complete inhibition of ethylene effects in pea seedlings requires treatment with 40 n1 1−1 of 1‐MCP. These novel inhibitors appear to be suitable for many commercial applications including extending the vase life of cut flowers and the display life of potted plants. Since 1‐MCP apparently is non‐toxic at concentrations that are active, it may in future be available for regulating the ripening of fruits and preventing the deleterious effects of ethylene in vegetables.
Ethylene biosynthesis: The role of 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase, and its possible evolutionary origin
Authors: John Philip
Published: May 2006

Recent developments in our knowledge of the biochemistry of 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase, the enzyme responsible for the final stage in the biosynthesis of ethylene, are reviewed. Particular reference is made to the role of carbon dioxide as an essential cofactor, the activity of ACC oxidase in the plant cell, the enzyme catalytic centre, and the role of ACC oxidase in the evolutionary development of ethylene biosynthesis in plants. Evidence is marshalled to support a proposal that the membrane requirement for ACC oxidase that is observed in vivo is attributable to a need for a charged plasma membrane to maintain ascorbate in the reduced state for an ACC oxidase located in the apoplast. It is argued on biochemical grounds that the acquisition of the ACC oxidase was the crucial evolutionary step in the development by seed plants of an ethylene biosynthesis pathway that could easily be regulated, and that signalled the plant's response to stress and pathogen attack.
Ethylene and vegetative development
Authors: Smalle Jan , Van Der Straeten Dominique
Published: May 2006

The past decade has witnessed a tremendous increase in our understanding of the role of ethylene in plant development. Genes encoding enzymes of the ethylene biosynthesis pathway have been isolated, allowing the manipulation of endogenous ethylene levels in intact plants. In parallel, a collection of ethylene mutants was obtained by using a simple response assay. This resulted in the identification of several genes involved in ethylene signal transduction. The data obtained using these new tools have allowed long‐standing hypotheses to be tested, while gaining novel insight into the function of ethylene in development. Recent molecular evidence supported the existence of an intense hormonal cross‐talk during plant growth. Numerous processes are controlled by ethylene in a close interaction with auxin, and often it was impossible to differentiate between auxin and ethylene effects. Molecular‐genetic tools are now allowing the dissection of these interactions. Ethylene does not seem essential for many developmental processes. Nevertheless, it is of crucial importance for survival in most species as it occupies a key position in the developmental response mechanisms of plants under mechanical stress.
Ethylene and flower petal senescence: Interrelationship with membrane lipid catabolism
Authors: Borochoy Amihud , Spiegelstein Hanna , Philosoph‐Hadas Sonia
Published: May 2006

Accumulated experimental evidence suggests that the decline in the content of membrane components such as phospholipids (PL), is a key event in flower senescence. This loss of membrane integrity can be modulated by ethylene. The aim of this work was to examine the interrelationship between ethylene and one of the products of PL metabolism, diacylglycerol (DAG), during petunia (Petunia hybrida) flower senescence. DAG's role was studied using phorbol 12‐myristate 13‐acetate (PMA), which acts similarly in kinase activation. Our results demonstrate for the first time a senescence‐related transient increase in the content of DAG in petunia plasma membranes. The climacteric‐like ethylene rise associated with petal wilting appeared in petunia flowers well after PL degradation and DAG increase had commenced. The appearance and peak magnitude of the ethylene rise was enhanced or increased, respectively, by PMA treatment, thereby accelerating appearance and magnitude of all senescence parameters assayed. Conversely, suppression of ethylene action by silver thiosulfate (STS) resulted in retardation of flower wilting, as well as in abolishment of the PMA‐enhancing effects on senescence. The results suggest an active role for lipid metabolites like DAG in enhancing flower senescence, through regulation of ethylene production and action, or possible activation of kinases. This sequence of events implies that ethylene is a mediator of flower senescence, rather than a trigger of the process.
Ethylene and plant responses to nutritional stress
Authors: Lynch Jonathan , Brown Kathleen M.
Published: May 2006

Although ethylene is known to be involved in plant response to a number of biotic and abiotic stresses, relatively little is known concerning its role in nutritional stress arising from nutrient deficiency or mineral toxicity. There is clear evidence for involvement of ethylene in the symbiosis betweenRhizobiumand legumes, and in the ‘Strategy 1’ response to Fe deficiency. Ethylene may also be generated during tissue necrosis induced by severe toxicities and deficiencies. Metal toxicity may generate ethylene through oxidative stress. Evidence for a more general role for ethylene in regulating plant responses to macronutrient deficiency is suggestive but incomplete. Few studies have addressed this interaction, and most published reports are difficult to interpret because of the unrealistic way that nutrient treatments were imposed. Deficiency of N and P appear to interact with ethylene production and sensitivity. A role for ethylene in mediating adaptive responses to P stress is suggested by the fact that P stress can induce a variety of morphological changes in root systems that are also affected by ethylene, such as gravitropism, aerenchyma formation, and root hair development. Other adaptive responses include senescence or abscission of plant parts which cannot be supported by the plant. Ethylene and other plant hormones may be involved in mediating the stress signal to generate these responses. Although existing literature is inconclusive, we speculate that ethylene may play an important role in mediating the morphological and physiological plasticity of plant responses to nutrient patches in time and space, and especially root responses to P stress.
Ethylene and plant responses to stress
Authors: Morgan Page W. , Drew Malcolm C.
Published: May 2006

When plants are subject to a variety of stresses they often exhibit symptoms of exposure to ethylene. Although this relationship usually results from induction of ACC synthase thus raising the concentration of the precursor of ethylene, it is now apparent that there are numerous other ways that stresses produce ethylene‐like symptoms. This complex relationship between stress and ethylene‐like symptoms is here termed the stress ethylene syndrome. ACC synthase exists as a multi‐gene family whose individual members are differentially regulated, many by various stresses. In addition, ACC oxidase. AdoMet synthetase, enzymes in the Yang methionine cycle, and enzymes that conjugate ACC are regulated by stress. In more unusual cases, ethylene production is not increased by stress or may be reduced. There is evidence for stress effects on perception of ethylene and the potential exists that some steps of the ethylene signal transduction pathway may be influenced by stress. Because of the variability possible in the stress ethylene syndrome, it continues to be studied for a number of stresses and species. In particular, attention is being given to wounding, mechanical stress, drought, heat and water deficit stress, chilling, air pollution, chemical and salt stress, and low O2stress. It is becoming more apparent that a number of stress responses involve interactions with other hormones.
Update on the possible mode of action of the jasmonates: Focus on the metabolism of cell wall polysaccharides in relation to growth and development
Authors: Miyamoto Kensuke , Oka Mariko , Ueda Junichi
Published: May 2006

Jasmonic acid (JA) and its related compounds (jasmonates) applied to plant tissues exert either inhibitory or promotive effects in growth and developmental processes, which in some ways are similar to abscisic acid. However, little is known about the mode of action of the jamonates at the tissue or organ levels. Here, we review partial evidence for the physiological action of the jasmonates on cell elongation and abscission.

Jasmonates inhibit the IAA‐induced cell elongation of oat coleoptile segments not by affecting energy production, osmoregulation and cell wall loosening, but by inhibiting the synthesis of cell wall polysaccharides. The inhibition is partially reversed by simultaneous application of sucrose. Inhibition of IAA‐induced elongation by JA is only observed in monocotyledons, not in dicotyledons. These effects suggest that jasmonates exert their inhibitory effect on cell elongation by affecting the metabolism of the cell wall polysaccharides in monocotyledons.

Jasmonates promote the abscission of bean petiole explants without enhancing ethylene production. Cells in the petiole adjacent to the abscission zone expand during abscission. In the abscission zone, jasmonates decrease the amount of cellulosic but not that of noncellulosic polysaccharides. Jasmonates increase the activities of cellulase and decrease the levels of UDP‐sugars, which are important intermediates for the synthesis of cell wall polysaccharides in the abscission zone, probably resulting in the decreased level of cellulose and the mechanical weakness of cell walls.

Thus, it is suggested that jasmonates exert their multiple physiological effects by affecting the metabolic processes of cell wall polysaccharides.
Possible involvement of jasmonates in various morphogenic events
Authors: Koda Yasunori
Published: May 2006

Jasmonates (jasmonic acid and related compounds) seem to be involved in various morphogenic events of plants, such as tuberization (potato, yam and Jerusalem artichoke), tuberous root formation (sweet potato), bulb formation (onion and garlic), determination of plant structure (soybean) and thigmomorphogenesis (coiling of tendrils of Bryonia dioica). The involvement of jasmonates in tuberization in these plants was inferred from their ability to induce tubers in vitro, and from changes in the levels of endogenous jasmonates during the growth of the plants, which can account for the initiation of tuberization. As to potato tuberization, jasmonic acid (JA) and its methyl ester (JA‐Me) have strong tuber‐inducing activity. These compounds seem to exert their tuber‐inducing effects by elicting the expansion of cells, because JA and JA‐Me are capable of causing the expansion of cells in potato tubers. The JA‐induced expansion of cells is attributable to both an increase in osmotic pressure due to the accumulation of sucrose and changes in cell wall architecture that appear to affect the extensibility of the wall. And, moreover, the synthesis of cellulose might be indispensable for the JA‐induced expansion. The tuberization and the expansion of cells induced by JA always involve the reorientation of cortical microtubules (MTs), suggesting that JA controls the direction of cell expansion by changing the arrangement of MTs. However, the reorientation of MTs itself seems to be insufficient for the induction of expansion of cells.

Involvement of jasmonates in bulb formation and tuberous root formation is presumed from the fact that JA is able to induce these in vitro. The exact nature of the control that the jasmonates exert on morphogenesis remains to be elucidated.
Distinct pathways for jasmonate‐ and elicitor‐induced expressions of a cytochrome P450 gene in soybean suspension‐cultured cells
Authors: Ohta Hiroyuki , Suzuki Genki , Awai Koichiro , Masuda Tatsuru , Kato Tomohiko , Shibata Daisuke , Takamiya Ken‐ichiro
Published: May 2006

The mechanisms of the jasmonate‐induced expression of genes encoding the cytochrome P450 CYP93A1 and lipoxygenase L‐4 were analyzed in a soybean photomixotrophic cultured cell line, SB‐P. The induction of the cytochrome P450 gene caused by methyl jasmonate (MeJA) was specifically suppressed by trifluoperazine and DCMU, inhibitors of chloroplast electron transport. Additionally, induction of the cytochrome P450 gene required irradiation. In contrast, induction of the lipoxygenase L‐4 gene by the MeJA treatment occurred in both dark and light. Based on the results, the presence of two distinct signalling pathways for jasmonate‐inducible gene expression, light‐dependent and light‐independent, is proposed. The jasmonate‐inducible cytochrome P450 was also specifically induced by a fungal elicitor from a cell wall fraction of Phytophthora megasperma, a fungal pathogen, suggesting a role for P450 in the defense response to fungus in soybean cells. However, trifluoperazine did not block the elicitor‐induced expression of cytochrome P450.
Conjugated polyamines and reproductive development: Biochemical, molecular and physiological approaches
Authors: Martin‐Tanguy Josette
Published: May 2006

Whole tobacco plants containing the root‐inducing, left‐hand transferred DNA (Ri TL‐DNA) display a transformed phenotype, that includes alterations in a number of developmental processes, such as floral induction, flowering and reproduction. We show that the entire Ri TL‐DNA is responsible for repression of ornithine and tyrosine decarboxylases while it exerts no effect on transferase and the methyl transferase activities. Evidence is provided that two genes from the Ri TL‐DNA, rolA and rolC, alter polyamine metabolism as well as floral induction and flowering. Thus, plants transformed by the rolC gene (under the control of the 35S promoter from cauliflower mosaic virus) were male‐sterile (non‐viable pollen) and female fertility was reduced by approximatively 80%. A constitutive overexpression of the rolC gene may directly or indirectly cause inhibition of the accumulation of water‐insoluble amine conjugates located in the anthers and all the methyl transferases, leading to increases of ornithine decarboxylase, phenylalanine ammonia lyase and putrescine caffeoyl‐CoA transferase. The results suggest that male sterility is associated with catabolic processes exerted at the level of water‐insoluble amine conjugates and support the view that diamine oxidase may be involved in the regulation of the amine concentration during sexual differentiation, a factor that should be considered when attempting to decipher the mechanisms of control of sexual differentiation. The rolC gene could be useful in determining the role of diamine oxidase in the physiology of flowering. These results suggest that elevated free polyamine and water‐soluble polyamine levels (located in the ovaries) contribute to abnormal floral development. The transformed phenotype due to P35S‐rolA(the rolA gene fused to the 35S promoter) consisted of inhibited or delaved flowering, and altered floral morphology in the form of flower abortion. The effects of P35S‐rolA on flowering and fertility are closely correlated with limitations in the accumulation of the water‐soluble and ‐insoluble amine conjugates and increase in accumulation of free amines, indicating that amine conjugates (via transferases) have important functions in floral induction, floral evocation and reproduction. Spermidine availability as well as tyramine availability (in conjugated forms) could be limiting factor(s) in sexual development in tobacco.
Control of plant disease by perturbation of fungal polyamine metabolism
Authors: Walters D. R. , Mackintosh C. A.
Published: May 2006

The diamine putrescine and the polyamines spermidine and spermine are ubiquitous in nature and are essential for cell proliferation. Since polyamine biosynthesis in plants can start from either ornithine or arginine, while fungal polyamine biosynthesis appears to utilise only the ornithine route, it was suggested that specific inhibition of fungal polyamine biosynthesis should be lethal. Indeed, inhibitors of polyamine biosynthesis, e.g. the ornithine decarboxylase inhibitor α‐difluoromethylornithine, have been shown to inhibit fungal growth in vitro and to control fungal infections on a variety of plants under glasshouse and field conditions. It is now known that polyamine analogues can perturb polyamine metabolism leading to powerful antiproliferative effects in cancer cells. This paper reviews the results of a research programme focused on the synthesis and evaluation of putrescine analogues as novel fungicides. A number of aliphatic, alicyclic and cyclic diamines have been shown to possess considerable fungicidal activity, but although many of these compounds perturb polyamine metabolism in fungal cells, such changes are not considered sufficient to account for the observed antifungal effects. More recent work on spermidine analogues is also described.
Molecular genetic analysis of brassinosteroid action
Authors: Clouse Steven D.
Published: May 2006

Recent applications of molecular techniques to the study of brassinosteroid action have enhanced our understanding of these unique plant growth regulators. The cloning of genes regulated by brassinosteroids has revealed novel information on the control of gene expression by plant steroids and has extended our knowledge of brassinosteroid‐promoted cell expansion. The analysis of brassinosteroid‐deficient and brassinosteroid‐insensitive mutants has implicated these growth regulators in a number of essential developmental programs including organ elongation, leaf development, photomorphogenesis, fertility, apical dominance and vascular differentiation.
Biosynthesis and metabolism of brassinosteroids
Authors: Fujioka Shozo , Sakurai Akira
Published: May 2006

Natural brassinosteroids so far identified from various plant species include biosynthetic congeners of brassinolide, such as cathasterone, teasterone, 3‐dehydroteasterone, typhasterol and castasterone as well as another series of 6‐deoxoteasterone, 3‐dehydro‐6‐deoxoteasterone, 6‐deoxotyphasterol and 6‐deoxocastasterone. Using cell culture system of Catharanthus roseus, the outlines of biosynthetic pathways of brassinolide, via plant sterol of campesterol, have now been demonstrated. There are two pathways, named early C6‐oxidation pathway and late C6‐oxidation pathway, both of which would be operating in wide varieties of plants. Metabolic studies with various plant systems revealed multiple paths of metabolism such as hydroxylation, epimerization, side chain cleavage, reduction and conjugation with glucose and fatty acids. Recent progress of biosynthesis and metabolism of brassinosteroids is described.
Cellular ‘elementary organisms’ in vitro. The early vision of Gottlieb Haberlandt and its realization
Authors: Höxtermann Ekkehard
Published: May 2006

The botanist Gottlieb Haberlandt was the first who in 1898 (published in 1902) tried the systematic culture in vitro of single cells. His purpose was to study the mutual influences of cells as the last ‘living units’ within the multicellular body. Haberlandt visualized the theoretical potential of the culture approach in experimental plant morphology and physiology and nearly half a century was to elapse before his far‐reaching ideas were realized. The history of cell and tissue culture is traced from the first concepts and origins in experimental embryology (1858/59) to its final verification almost 100 years later. The paper reminds of essential steps, theoretical backgrounds, accidental and planned discoveries and methodological approaches, and attempts to present all sources. The more or less known reviews of White (1931, 1936 and 1946), Fiedler (1938/39), Stapp (1947), Kandler (1948) and Street (1959) are summarized, and the mutual influence of plant and animal tissue culture on each other is discussed. Previous retrospective articles on the particular role of Haberlandt, namely those of Gautheret (1942) and Krikorian and Berquam (1969), are included in a general assessment of physiological anatomy in memory of the 50th anniversary of this great botanist's death.
Respiration of barley protoplasts before and after illumination
Authors: Igamberdiev Abir U. , Zhou Guoquing , Malmberg Gunilla , Gardeström Per
Published: May 2006

Respiratory O2 consumption was investigated in dark‐adapted barley (Hordeum vulgare L. cv. Gunilla) protoplasts and after illumination for 10 min at high and very low CO2 in the presence of respiratory and photorespiratory inhibitors. In dark‐adapted protoplasts no difference was observed between inhibitor treatments in high and very low CO2. The respiratory rate increased somewhat after illumination and a difference in responce to inhibitors was in some cases observed between high and very low CO2. Thus, the operation of the mitochondrial electron transport chain is affected following a period of active photosynthesis. In all situations tested, oligomycin inhibited respiratiory O2 uptake indicating that respiration of mitochondria in protoplasts is not strictly ADP limited. Antimycin A inhibited respiration more in dark‐adapted protoplasts than after illumination whereas SHAM gave the opposite response. Rotenone inhibited respiration both in dark‐adapted protoplasts (about 30%) and after illumination where the inhibition was much greater in very low CO2 (50%) than in high CO2 (10%). After illumination in very low CO2. SHAM + rotenone inhibited respiration almost completely (70%). Photorespiratory inhibitors had very small effect on O2 consumption in darkness. After illumination the effect of aminoacetonitrile (AAN) was also very low whereas α‐hydroxypyridine‐2‐methane sulphonate (HPMS) in photorespiratory conditions inhibited O2 uptake much stronger (35%). The addition of glyoxylate enhanced respiration in the presence of HPMS up to the control level suggesting that alternative pathways of glyoxylate conversion might be operating.

The differences in inhibitor responses may reflect fine mechanisms for the regulation of energetic balance in the plant cell which consists of switching from electron transport coupled to ATP production to non‐coupled transport. Photorespiratory flux is also very flexible, and the suppression of glycine decarboxylation can induce bypass reactions of glyoxylate metabolism.
Metabolism of 14C‐aspartate during shoot bud formation in cultured cotyledon explants of radiata pine
Authors: Konschuh Michele N. , Thorpe Trevor A.
Published: May 2006

Aspartate metabolism was investigated in excised cotyledons of radiata pine (Pinus radiata D. Don). These cotyledons were cultured under shoot‐forming (plus N6‐benzyladenine, SF), non‐shoot‐forming (minus N6‐benzyladenine, NSF) and unresponsive (plus N6‐benzyladenine, OLD) conditions, then incubated with [14C]‐aspartate for 3‐h pulse treatments followed by 3‐h chase treatments with cold aspartate. The majority of label was recovered in the CO2, amino acid, organic acid and pellet fractions. Uptake was greatest in all tissue types early in culture. Most (over 80%) of the [14C]‐aspartate taken up by the tissues was converted to CO2 at day 0 in SF and NSF tissues, CO2 accounted for less than 50% of the total radioactivity in other tissues. Greater incorporation into fractions was observed in SF tissues during promeristemoid formation, while in NSF tissues the greatest incorporation was observed during a period of rapid elongation. Generally, less incorporation was observed in OLD cotyledons than in SF and NSF cotyledons. Analysis of the amino acid fraction showed that labelled aspartate was converted to other amino acids, mainly glutamate, glutamine, asparagine and 4‐aminobutyric acid.
White light promotes the formation of diferulic acid in maize coleoptile cell walls by enhancing PAL activity
Authors: Parvez Mohammad Masud , Wakabayashi Kazuyuki , Hoson Takayuki , Kamisaka Seiichiro
Published: May 2006

To elucidate the mechanism by which white fluorescent light (5 W m‐2) stimulates the formation of diferulic acid (DFA) in cell walls, the effect of light on phenylalanine‐and tyrosine‐ammonia‐lyase (PAL, EC 4.3.1.5 and TAL, EC 4.3.1.5) and peroxidase activities was studied using coleoptiles of maize (Zea mays L. cv. Cross Bantam T51). Growth rate of dark‐grown coleoptiles was highest at the basal zone and decreased towards the tip, while continuous irradiation caused an inhibition of growth, especially at the basal zone. Light decreased the cell wall extensibility in all zones of the coleoptile. The amounts of DFA, ferulic acid (FA) and p‐coumaric acid (p‐CA) increased by severalfold in cell walls of light‐grown maize coleoptiles as compared with those grown in the dark. Strong correlations were observed between the increase in the contents of either DFA, FA or p‐CA and the decrease in cell wall extensibility. Light decreased the wall‐bound peroxidase activity. No correlation was found between DFA content and peroxidase activity. The activities of PAL and TAL were enhanced upon white light irradiation. The increment in either DFA, FA or p‐CA content was correlated with an increase in PAL activity, but not with that in TAL activity. White light may promote DFA formation in the cell walls of maize coleoptiles by enhancing PAL activity.
Does availability of potassium affect cold hardening of Scots pine through polyamine metabolism?
Authors: Sarjala Tytti , Taulavuori Kari , Savonen Eira‐Maija , Edfast Ann‐Britt
Published: May 2006

The effect of different potassium availability on the polyamines and frost resistance of Scots pine seedlings (Pinus sylvestris L.) during cold hardening was studied. Scots pine seedlings were grown applying different rates of potassium by using the relative addition rate technique followed by a 2‐ or 9‐week hardening period with decreased light intensity, day length and temperature. After 2 weeks of treatment the seedlings were not hardened (LT50, =−11°C) and showed no differences in frost resistance, although differences in the polyamine levels between the K levels were observed. After 9 weeks of hardening the seedlings at the low, medium and high K levels showed a mean frost resistance (LTs.50) of −81, −63, and −47°C, respectively. A negative effect of K on the frost resistance of the needles was also found in adult trees in September. The results indicate that at the early stage of cold hardening, potassium or free polyamine levels do not affect the frost resistance of Scots pine needles. However, in hardened seedlings and adult trees potassium displays a negative and putrescine a positive correlation with frost resistance, whereas spermidine and spermine show no correlation.
Growth‐promoting activity of gibberellins on shoot elongation in Salix pentandra is reduced by 16,17‐dihydro derivatisation
Authors: Olsen J. E. , Junttila O.
Published: May 2006

The metabolism of GA10 is thought to be under photoperiodic control in the woody plant Salix pentandra. However, in a recent study using 16,17‐[3H2]GA19 as a mimic of Ga10, no effect of photoperiod was found on its metabolism to 16,17‐dihydro‐GA20 and 16,17‐dihydro‐GA1. To investigate if this was due to differential action of exogenous 16,17‐dihydro‐GAs and GAs, the effects of the 16,17‐dihydro‐derivatives of the gibberellins GA19, GA1, and GA1 as compared with their parent GAs, on shoot elongation in seedlings of S. pentandra were studied. 16,17‐Dihydro‐GA19, and ‐GA20 were both almost inactive, while 16,17‐dihydro‐GA1 induced some shoot elongation in seedlings treated with ancymidol as well as under short days. GA19, GA20 and GA1 were all able to counteract the inhibitory effect of ancymidol under continuous light, while inhibition induced by a 12‐h photoperiod was antagonised only by GA20 and GA1. Thus, the growth‐stimulating activity of the tested GAs is significantly reduced by 16,17‐dihydro derivatisation, but the derivatives do not inhibit stem elongation in S, pentandra, as has been found in monocotyledons.
Regulation of cytokinin oxidase activity in tobacco callus expressing the T‐DNA ipt gene
Authors: Redig Pascale , Motyka Václav , Van Onckelen Henri A. , Kamínek Miroslav
Published: May 2006

There are indications that the cytokinin content in transgenic tissues expressing the cytokinin biosynthetic ipt gene is under metabolic control, which prevents the accumulation of cytokinins to lethal levels. The objective of this study was to investigate the relationships between the content of endogenous cytokinins and the activity of cytokinin oxidase (which is believed to be a copper‐containing amine oxidase, EC 1.4.3.6.) in ipt transgenic tobacco callus. In addition, the effect of exogenously applied N‐benzyladenine (BA) on this relationship was examined. Endogenous cytokinin concentrations were measured in callus of Nicotiana tabacum L. cv. Petit Havana SRI transformed with the ipt of Agrobacterium tumefaciens under the control of a light‐inducible promoter and in non‐transformed tissue using LC‐tandem mass spectrometry. The activity of cytokinin oxidase was estimated by measuring the conversion of [2,8‐3H]N6‐(Δ2‐isopentenyl)adenine to [3H]adenine by enzyme preparations in vitro.

The 14‐day‐old ipt‐transformed callus contained a 25‐fold higher amount of cytokinins as compared to the non‐transformed tissue. Mainly zeatin‐ and dihydrozeatin‐types of cytokinins (free bases, ribosides, nucleotides and O‐glucosides) accumulated in the ipt transgenic tissue. The cytokinin pool of both ipt‐transformed and non‐transformed tissues consisted predominantly of cytokinins that are either resistant to cytokinin oxidase attack (nucleotides and O‐glucosides of cytokinins and cytokinins bearing N6‐saturated side chain) or have a low affinity for the enzyme (zeatin and its riboside). The former represented 71.6 and 74.8% and the latter 27.7 and 24.4% of the pool of endogenous cytokinins in ipt‐transformed and non‐transformed tissues, respectively. Enzyme preparations from ipt‐transformed tissue exhibited 1.5‐fold higher cytokinin oxidase activity compared with that observed in control tissues.

Application of exogenous BA affected the total levels of cytokinins of the two tissue lines in different ways. The cytokinin content increased by 1.7‐ and 1.5‐fold in ipt‐transformed tissues 6 and 12 h after BA application, respectively, while it declined in the non‐transformed control by 1.6‐ to 2.0‐fold between 3 and 12 h after BA application. The increase in cytokinin content in the ipt callus is due to an increase of zeatin‐ and dihydrozeatin‐type cytokinins (nucleotides, ribosides and free bases) leading to an enhanced accumulation of O‐glucosides after 12 h. Following BA treatment, the cytokinin oxidase activity increased up to 1.8‐fold in ipt‐transformed and 1.6‐fold in non‐transformed tissues. The levels of isopentenyl‐type cytokinins were near the detection limit; however, the enhancement of cytokinin oxidase activity after BA treatment in both tissue lines was correlated with the content of preferred substrate of the enzyme, N6‐(Δ2‐isopentenyl)adenosine.
Detoxification of chlorotoluron in a chlorotoluron‐resistant biotype of Alopecurus myosuroides. Comparison between cell cultures and whole plants
Authors: Menendez Julio , De Prado Rafael
Published: May 2006

The metabolism of chlorotoluron in whole plants and cell suspensions was investigated in a previously characterized chlorotoluron‐resistant biotype of Alopecurus myosuroides Huds. Both resistant plants and cell suspensions showed a greater capability to metabolize chlorotoluron to non‐phytotoxic compounds than the respective susceptible counterparts. Data revealed that although both biotypes degraded chlorotoluron by N‐dealkylation and ring‐methyl hydroxylation, the resistant biotype showed an enhanced capacity to hydroxylate the parent herbicide. The cytochrome (Cyt) P450 inhibitor 1‐aminobenzotriazole (ABT) inhibited the metabolism of chlorotoluron in both resistant and susceptible plants by reducing the formation of non‐toxic aryl‐hydroxylated derivatives and polar conjugates. N‐demethylations were less susceptible to ABT than the other oxidative reactions, but this does not necessarily imply that the second detoxification activity is not Cyt P450, as some P450 activities are more susceptible to ABT than others. Ring‐methyl hydroxylation inhibition affected the ability of resistant plants to recover photosynthetic activity after incubation in chlorotoluron, showing a similar fluorescence pattern to susceptible plants in the same conditions without ABT. Fluorescence and metabolism data strongly support the thesis of Cyt P450‐mediated 4‐methylphenyl hydroxylation as the main route of detoxification of chlorotoluron in the resistant biotype.
Starch determination in plant tissues using a computerized image analysis system
Authors: Rodrigo Javier , Rivas Eliseo , Herrero Maria
Published: May 2006

Starch is the main reserve compound in woody plant species. Changes in starch content are clear indicators of a variety of plant developmental processes. Thus, carbohydrate extraction and other analytical methods have been widely used to measure changes in starch content. However, the use of these methods can be limited by the fact that starch is often compartmentalized in very small portions of tissue. While changes in these small structures can be histochemically characterized and localized under the microscope, they cannot be quantified. As an alternative, an image analysis system attached to a microscope has been developed to detect quantitative variations in starch in particular tissues or cells. The system has been successfully used to study the differences in starch content of sections from pistillar structures in apricot (Prunus armeniaca L.). The procedure is based on the measurement of the optical density of black and white images obtained from the microscope. Two staining methods, I2KI (potassium iodide‐iodine) and PAS (periodic acid Schiff's reagent), and two embedding techniques, paraffin and JB4 plastic resin, were compared. The best results were obtained using I2KI‐stained sections of paraffin‐embedded material. Since the procedures used are non‐destructive for the tissues studied, additional information can be obtained, on the same section, by the subsequent use of additional stains. The method described here can be used to detect quantitative variations in starch content under the microscope in different plant tissues and thus to follow changes in starch reserves in small structures.
Cloning and characterization of a cDNA encoding gibberellin 20‐oxidase from rice (Oryza sativa) seedlings
Authors: Toyomasu T. , Kawaide H. , Sekimoto H. , von Numers C. , Phillips A. L. , Hedden P. , Kamiya Y.
Published: May 2006

Degenerate oligonucleotide primers based on the amino acid sequences of gibberellin (GA) 20‐oxidases from pumpkin and Arabidopsis were used in nested polymerase chain reactions to generate an internal cDNA fragment from rice (Oryza satiya L.) seedlings. Using this fragment as a probe, a full‐length cDNA (pOs20ox) was isolated from a cDNA library constructed from rice seedlings. The deduced amino acid sequence of Os20ox showed good identity (42–55%) with the GA 20‐oxidases from pumpkin and Arabidopsis. Recombinant Os20ox protein, produced in Escherichia coli, catalyzed the conversion of GA12 and GA53 to GA9 and GA20, respectively. In contrast to the enzyme from immature pumpkin seeds, the recombinant rice GA 20‐oxidase did not produce the tricarboxylic acids GA25 and GA17 from GA12 and GA53, respectively. The conversion rate of GA53 was higher than that of GA12. which is consistent with the relatively high abundance of 13‐hydroxylated GAs in rice seedlings. Os20ox mRNA accumulated at higher levels in seedlings of two GA‐deficient dwarf mutants than in normal plants. Treatment with uniconazole‐P. an inhibitor of GA biosynthesis, increased abundance of the mRNA, while exogenously applied GA3 decreased it. These results suggest that the expression of the Os20ox gene is regulated by the level of physiologically active GA.