Photosynthetic activity is affected by exogenous and endogenous inputs, including source-sink balance. Reducing the source to sink ratio by partial defoliation or heavy shading resulted in significant elevation of the photosynthetic rate in the remaining leaf of tomato plants within 3 d. The remaining leaf turned deep green, and its area increased by almost 3-fold within 7 d. Analyses of photosynthetic activity established up-regulation due to increased carbon fixation activity in the remaining leaf, rather than due to altered water balance. Moreover, senescence of the remaining leaf was significantly inhibited. As expected, carbohydrate concentration was lower in the remaining leaf than in the control leaves; however, expression of genes involved in sucrose export was significantly lower. These results suggest that the accumulated fixed carbohydrates were primarily devoted to increasing the size of the remaining leaf. Detailed analyses of the cytokinin content indicated that partial defoliation alters cytokinin biosynthesis in the roots, resulting in a higher concentration of trans-zeatin riboside, the major xylem-translocated molecule, and a higher concentration of total cytokinin in the remaining leaf. Together, our findings suggest that trans-zeatin riboside acts as a signal molecule that traffics from the root to the remaining leaf to alter gene expression and elevate photosynthetic activity.

• Keywords
• Solanum lycopersicum, Cytokinin, leaf development, photosynthesis, source–sink relationship, tomato, xylem,
• MeSH
• Cytokinins physiology   MeSH
• Photosynthesis * MeSH
• Plant Roots physiology   MeSH
• Plant Leaves metabolism   MeSH
• Signal Transduction * MeSH
• Solanum lycopersicum physiology   MeSH
• Plant Shoots physiology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytokinins MeSH

Seed-processing technologies such as polishing and washing enhance crop seed quality by limited removal of the outer layers and by leaching. Combined, this removes chemical compounds that inhibit germination. Industrial processing to deliver high-quality commercial seed includes removing chemical inhibitors of germination, and is essential to produce fresh sprouts, achieve vigorous crop establishment, and high yield potential in the field. Sugar beet (Beta vulgaris subsp. vulgaris var. altissima Doell.), the main sugar source of the temperate agricultural zone, routinely undergoes several processing steps during seed production to improve germination performance and seedling growth. Germination assays and seedling phenotyping was carried out on unprocessed, and processed (polished and washed) sugar beet fruits. Pericarp-derived solutes, known to inhibit germination, were tested in germination assays and their osmolality and conductivity assessed (ions). Abscisic acid (ABA) and ABA metabolites were quantified in both the true seed and pericarp tissue using UPLC-ESI(+)-MS/MS. Physical changes in the pericarp structures were assessed using scanning electron microscopy (SEM). We found that polishing and washing of the sugar beet fruits both had a positive effect on germination performance and seedling phenotype, and when combined, this positive effect was stronger. The mechanical action of polishing removed the outer pericarp (fruit coat) tissue (parenchyma), leaving the inner tissue (sclerenchyma) unaltered, as revealed by SEM. Polishing as well as washing removed germination inhibitors from the pericarp, specifically, ABA, ABA metabolites, and ions. Understanding the biochemistry underpinning the effectiveness of these processing treatments is key to driving further innovations in commercial seed quality.

• Keywords
• Abscisic acid (ABA), Germination inhibitors, Pericarp (fruit coat), Polishing and washing, Seed processing, Seed technology, Sugar beet (Beta vulgaris subsp. vulgaris),
• MeSH
• Beta vulgaris growth & development   physiology   MeSH
• Biochemistry MeSH
• Germination MeSH
• Abscisic Acid metabolism   MeSH
• Plant Growth Regulators metabolism   MeSH
• Seeds growth & development   physiology   MeSH
• Tandem Mass Spectrometry MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Abscisic Acid MeSH
• Plant Growth Regulators MeSH

The timing of seed germination is crucial for seed plants and is coordinated by internal and external cues, reflecting adaptations to different habitats. Physiological and molecular studies with lettuce and Arabidopsis thaliana have documented a strict requirement for light to initiate germination and identified many receptors, signaling cascades, and hormonal control elements. In contrast, seed germination in several other plants is inhibited by light, but the molecular basis of this alternative response is unknown. We describe Aethionema arabicum (Brassicaceae) as a suitable model plant to investigate the mechanism of germination inhibition by light, as this species has accessions with natural variation between light-sensitive and light-neutral responses. Inhibition of germination occurs in red, blue, or far-red light and increases with light intensity and duration. Gibberellins and abscisic acid are involved in the control of germination, as in Arabidopsis, but transcriptome comparisons of light- and dark-exposed A. arabicum seeds revealed that, upon light exposure, the expression of genes for key regulators undergo converse changes, resulting in antipodal hormone regulation. These findings illustrate that similar modular components of a pathway in light-inhibited, light-neutral, and light-requiring germination among the Brassicaceae have been assembled in the course of evolution to produce divergent pathways, likely as adaptive traits.

• Keywords
• Aethionema arabicum, light inhibition, model plant, natural variation, seed germination, transcriptional regulation,
• MeSH
• Brassicaceae physiology   radiation effects   MeSH
• Gene Expression radiation effects   MeSH
• Gibberellins metabolism   MeSH
• Germination radiation effects   MeSH
• Abscisic Acid metabolism   MeSH
• Genes, Plant * MeSH
• Sunlight * MeSH
• Transcriptome drug effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Gibberellins MeSH
• Abscisic Acid MeSH

Plant hormones have become appropriate candidates for driving functional plant mycorrhization programs, including the processes that regulate the formation of arbuscules in arbuscular mycorrhizal (AM) symbiosis. Here, we examine the role played by ABA/GA interactions regulating the formation of AM in tomato. We report differences in ABA and GA metabolism between control and mycorrhizal roots. Active synthesis and catabolism of ABA occur in AM roots. GAs level increases as a consequence of a symbiosis-induced mechanism that requires functional arbuscules which in turn is dependent on a functional ABA pathway. A negative interaction in their metabolism has been demonstrated. ABA attenuates GA-biosynthetic and increases GA-catabolic gene expression leading to a reduction in bioactive GAs. Vice versa, GA activated ABA catabolism mainly in mycorrhizal roots. The negative impact of GA3 on arbuscule abundance in wild-type plants is partially offset by treatment with ABA and the application of a GA biosynthesis inhibitor rescued the arbuscule abundance in the ABA-deficient sitiens mutant. These findings, coupled with the evidence that ABA application leads to reduce bioactive GA1, support the hypothesis that ABA could act modifying bioactive GA level to regulate AM. Taken together, our results suggest that these hormones perform essential functions and antagonize each other by oppositely regulating AM formation in tomato roots.

• Keywords
• abscisic acid, arbuscular mycorrhiza, gibberellins, plant hormones, symbiosis, tomato,
• Publication type
• Journal Article MeSH

The herbicide 2,4-D exhibits an auxinic activity and therefore can be used as a synthetic and traceable analog to study auxin-related responses. Here we identified that not only exogenous 2,4-D but also its amide-linked metabolite 2,4-D-Glu displayed an inhibitory effect on plant growth via the TIR1/AFB auxin-mediated signaling pathway. To further investigate 2,4-D metabolite conversion, identity and activity, we have developed a novel purification procedure based on the combination of ion exchange and immuno-specific sorbents combined with a sensitive liquid chromatography-mass spectrometry method. In 2,4-D treated samples, 2,4-D-Glu and 2,4-D-Asp were detected at 100-fold lower concentrations compared to 2,4-D levels, showing that 2,4-D can be metabolized in the plant. Moreover, 2,4-D-Asp and 2,4-D-Glu were identified as reversible forms of 2,4-D homeostasis that can be converted to free 2,4-D. This work paves the way to new studies of auxin action in plant development.

• MeSH
• Arabidopsis drug effects   growth & development   metabolism   MeSH
• F-Box Proteins genetics   metabolism   MeSH
• Herbicides pharmacology   MeSH
• Homeostasis MeSH
• Plant Roots drug effects   growth & development   metabolism   MeSH
• 2,4-Dichlorophenoxyacetic Acid pharmacology   MeSH
• Indoleacetic Acids metabolism   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Receptors, Cell Surface genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Growth Regulators pharmacology   MeSH
• Seedlings drug effects   growth & development   metabolism   MeSH
• Signal Transduction drug effects   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• F-Box Proteins MeSH
• Herbicides MeSH
• 2,4-Dichlorophenoxyacetic Acid MeSH
• Indoleacetic Acids MeSH
• Arabidopsis Proteins MeSH
• Receptors, Cell Surface MeSH
• Plant Growth Regulators MeSH
• TIR1 protein, Arabidopsis MeSH Browser

Habituated embryogenic line of pumpkin contained more CKs and IAA, but less ABA than the non-habituated line. Pronounced hypomethylation correlated with the absence of 2,4-D, addition of 5-azaC, and the process of habituation. A comparative analysis between habituated and non-habituated embryogenic cultures of pumpkin (Cucurbita pepo L.) in relation to endogenous phytohormones, global DNA methylation, and developmental and regeneration capacities of the cultures was conducted. The analysis revealed more cytokinins (CKs) and indole-3-acetic acid (IAA), but less abscisic acid (ABA) in the habituated HEC line than in the non-habituated DEC line. Ribosides and ribotides were the most abundant CK forms in both HEC and DEC lines (75.9 and 57.6 %, respectively). HEC contained more free-base CKs (5.8 vs. 3.2 %), whereas DEC contained considerably more O-glycosides (39.1 vs. 18.3 %). Although prevalence of IAA was common for both lines, relative ratio of CKs and ABA differed between DEC and HEC lines. ABA was prevailing over CKs in DEC, while CKs prevailed over ABA in HEC line. Taking into account the importance of ABA for embryo maturation, the reduced endogenous ABA content in HEC line might be the reason for a 5-fold reduction in regeneration capacity compared to DEC. Both habituated and non-habituated embryogenic lines were highly methylated in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D). Pronounced hypomethylation correlated with the absence of 2,4-D, addition of 5-azacytidine (5-azaC), but also with the process of habituation. The habituated line was resistant to the effect of hypomethylation drug 5-azaC and remained highly methylated even after the addition of 5-azaC. Also, 5-azaC did not change the developmental pattern in the habituated line, indicating the existence of separate mechanisms by which 2,4-D influences global DNA methylation in comparison to habituation-related global DNA methylation.

• Keywords
• ABA, CKs, DNA methylation, Habituation, IAA, Somatic embryogenesis,
• MeSH
• Azacitidine pharmacology   MeSH
• Cucurbita drug effects   embryology   genetics   MeSH
• Cytokinins metabolism   MeSH
• Epigenesis, Genetic drug effects   MeSH
• Herbicides pharmacology   MeSH
• Enzyme Inhibitors pharmacology   MeSH
• 2,4-Dichlorophenoxyacetic Acid pharmacology   MeSH
• Abscisic Acid metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• DNA Methylation drug effects   MeSH
• Plant Growth Regulators metabolism   MeSH
• Plant Somatic Embryogenesis Techniques MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Azacitidine MeSH
• Cytokinins MeSH
• Herbicides MeSH
• indoleacetic acid MeSH Browser
• Enzyme Inhibitors MeSH
• 2,4-Dichlorophenoxyacetic Acid MeSH
• Abscisic Acid MeSH
• Indoleacetic Acids MeSH
• Plant Growth Regulators MeSH

Plant hormones act as chemical messengers in the regulation of myriads of physiological processes that occur in plants. To date, nine groups of plant hormones have been identified and more will probably be discovered. Furthermore, members of each group may participate in the regulation of physiological responses in planta both alone and in concert with members of either the same group or other groups. The ideal way to study biochemical processes involving these signalling molecules is 'hormone profiling', i.e. quantification of not only the hormones themselves, but also their biosynthetic precursors and metabolites in plant tissues. However, this is highly challenging since trace amounts of all of these substances are present in highly complex plant matrices. Here, we review advances, current trends and future perspectives in the analysis of all currently known plant hormones and the associated problems of extracting them from plant tissues and separating them from the numerous potentially interfering compounds.

• MeSH
• Plant Growth Regulators * chemistry   isolation & purification   MeSH
• Plants chemistry   MeSH
• Signal Transduction MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Plant Growth Regulators * MeSH

BACKGROUND AND AIMS: Nitric oxide (NO) is involved in the signalling and regulation of plant growth and development and responses to biotic and abiotic stresses. The photoperiod-sensitive mutant 7B-1 in tomato (Solanum lycopersicum) showing abscisic acid (ABA) overproduction and blue light (BL)-specific tolerance to osmotic stress represents a valuable model to study the interaction between light, hormones and stress signalling. The role of NO as a regulator of seed germination and ABA-dependent responses to osmotic stress was explored in wild-type and 7B-1 tomato under white light (WL) and BL. METHODS: Germination data were obtained from the incubation of seeds on germinating media of different composition. Histochemical analysis of NO production in germinating seeds was performed by fluorescence microscopy using a cell-permeable NO probe, and endogenous ABA was analysed by mass spectrometry. KEY RESULTS: The NO donor S-nitrosoglutathione stimulated seed germination, whereas the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) had an inhibitory effect. Under WL in both genotypes, PTIO strongly suppressed germination stimulated by fluridone, an ABA inhibitor. The stimulatory effect of the NO donor was also observed under osmotic stress for 7B-1 seeds under WL and BL. Seed germination inhibited by osmotic stress was restored by fluridone under WL, but less so under BL, in both genotypes. This effect of fluridone was further modulated by the NO donor and NO scavenger, but only to a minor extent. Fluorescence microscopy using the cell-permeable NO probe DAF-FM DA (4-amino-5-methylamino-2',7'-difluorofluorescein diacetate) revealed a higher level of NO in stressed 7B-1 compared with wild-type seeds. CONCLUSIONS: As well as defective BL signalling, the differential NO-dependent responses of the 7B-1 mutant are probably associated with its high endogenous ABA concentration and related impact on hormonal cross-talk in germinating seeds. These data confirm that light-controlled seed germination and stress responses include NO-dependent signalling.

• MeSH
• Models, Biological MeSH
• Cyclic N-Oxides pharmacology   MeSH
• Nitric Oxide Donors pharmacology   MeSH
• Fluoresceins analysis   MeSH
• Stress, Physiological * drug effects   radiation effects   MeSH
• Imidazoles pharmacology   MeSH
• Kinetics MeSH
• Germination * drug effects   radiation effects   MeSH
• Abscisic Acid metabolism   MeSH
• Mutation MeSH
• Osmosis drug effects   radiation effects   MeSH
• Nitric Oxide pharmacology   MeSH
• Pyridones pharmacology   MeSH
• Gene Expression Regulation, Plant drug effects   radiation effects   MeSH
• Plant Growth Regulators metabolism   MeSH
• S-Nitrosoglutathione pharmacology   MeSH
• Free Radical Scavengers pharmacology   MeSH
• Seeds drug effects   genetics   physiology   radiation effects   MeSH
• Signal Transduction drug effects   radiation effects   MeSH
• Solanum lycopersicum drug effects   genetics   physiology   radiation effects   MeSH
• Light * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide MeSH Browser
• 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate MeSH Browser
• Cyclic N-Oxides MeSH
• Nitric Oxide Donors MeSH
• Fluoresceins MeSH
• fluridone MeSH Browser
• Imidazoles MeSH
• Abscisic Acid MeSH
• Nitric Oxide MeSH
• Pyridones MeSH
• Plant Growth Regulators MeSH
• S-Nitrosoglutathione MeSH
• Free Radical Scavengers MeSH