Methyl jasmonate is a more effective senescence-promoting factor in Cucurbita pepo (zucchini) cotyledons when compared with darkness at the early stage of senescence

Gene expression pattern and taxane biosynthesis in a cell suspension culture of Taxus baccata L. subjected to light and a phenylalanine ammonia lyase (PAL) inhibitor

Taxus baccata L. cell culture is a promising commercial method for the production of taxanes with anti-cancer activities. In the present study, a T. baccata cell suspension culture was exposed to white light and 2-aminoindan-2-phosphonic acid (AIP), a phenylalanine ammonia lyase (PAL) inhibitor, and the effects of this treatment on cell growth, PAL activity, total phenol content (TPC), total flavonoid content (TFC), taxane production and the expression of some key taxane biosynthetic genes (DXS, GGPPS, T13OH, BAPT, DBTNBT) as well as the PAL were studied. Light reduced cell growth, whereas AIP slightly improved it. Light increased PAL activity up to 2.7-fold relative to darkness. The highest TPC (24.89 mg GAE/g DW) and TFC (66.94 mg RUE/g DW) were observed in cultures treated with light and AIP. Light treatment also resulted in the maximum content of total taxanes (154.78 μg/g DW), increasing extracellular paclitaxel and cephalomannin (3.3-fold) and intracellular 10-deacetyl paclitaxel (2.5-fold). Light significantly increased the expression level of PAL, DBTNBT, BAPT, and T13αOH genes, whereas it had no effect on the expression of DXS, a gene active at the beginning of the taxane biosynthetic pathway. AIP had no significant effect on the expression of the target genes. In conclusion, the light-induced activation of PAL transcription and altered expression of relevant biosynthetic genes reduced cell growth and increased the content of total phenolic compounds and taxanes. These findings can be applied to improve taxane production in controlled cultures and bioreactors.

Leaf metabolic signatures induced by real and simulated herbivory in black mustard (Brassica nigra)

INTRODUCTION

The oxylipin methyl jasmonate (MeJA) is a plant hormone active in response signalling and defence against herbivores. Although MeJA is applied experimentally to mimic herbivory and induce plant defences, its downstream effects on the plant metabolome are largely uncharacterized, especially in the context of primary growth and tissue-specificity of the response.

OBJECTIVES

We investigated the effects of MeJA-simulated and real caterpillar herbivory on the foliar metabolome of the wild plant Brassica nigra and monitored the herbivore-induced responses in relation to leaf ontogeny.

METHODS

As single or multiple herbivory treatments, MeJA- and mock-sprayed plants were consecutively exposed to caterpillars or left untreated. Gas chromatography (GC) and liquid chromatography (LC) time-of-flight mass-spectrometry (TOF-MS) were combined to analyse foliar compounds, including central primary and specialized defensive plant metabolites.

RESULTS

Plant responses were stronger in young leaves, which simultaneously induced higher chlorophyll levels. Both MeJA and caterpillar herbivory induced similar, but not identical, accumulation of tricarboxylic acids (TCAs), glucosinolates (GSLs) and phenylpropanoids (PPs), but only caterpillar feeding led to depletion of amino acids. MeJA followed by caterpillars caused higher induction of defence compounds, including a three-fold increase in the major defence compound allyl-GSL (sinigrin). When feeding on MeJA-treated plants, caterpillars gained less weight indicative of the reduced host-plant quality and enhanced resistance.

CONCLUSIONS

The metabolomics approach showed that plant responses induced by herbivory extend beyond the regulation of defence metabolism and are tightly modulated throughout leaf development. This leads to a new understanding of the plant metabolic potential that can be exploited for future plant protection strategies.

The effect of light, phenylalanine and methyl jasmonate, alone or in combination, on growth and secondary metabolism in cell suspension cultures of Vitis vinifera

The cultivated grapevine V. vinifera is a rich source of stilbene compounds such as resveratrol, which are widely believed to provide dietary protection against the development of cardiovascular disease and some forms of cancer. Elicitation is a well-known strategy to increase commercial production of natural products in plant cell suspension culture systems. Callus tissues obtained from berry slices of V. vinifera cv. Shahani grown on an optimized medium were used to develop cell suspension cultures used to study the effects of elicitation on stilbene synthesis. The effect of two light regimes (135.1 μmol. s^-1 m^-2 radiation, and dark), the concentration of phenylalanine (Phe; 0, 0.1, 0.5 and 1 mM) and of methyl jasmonate elicitor (MeJA; 0 and 25 μM), alone or in combination, were tested. The results showed that cultures grown in darkness resulted in significantly higher levels of the accumulation of total stilbenes (resveratrol + piceid) compared with the high light condition. The combined treatments of dark +1 mM Phe and dark +25 μM MeJA induced the synthesis of high levels of total phenolics, total flavonoids and total stilbenes. Finally, the combined elicitation of dark +1 mM Phe + 25 μM MeJA gave the highest synergistic coefficient (1.24) and proved to be the most effective treatment for the production of total phenolics, total flavonoids, and total stilbenes with mean contents of 384.80 mg GA/g DW, 527.62 mg catechin/g DW and 188.34 μg/g DW, respectively. The results of our study suggest that the combinations of dark together with MeJA and/or Phe can be used as an efficient method for the future scale-up of V. vinifera cell cultures for the production of high value stilbene compounds in a bioreactor system.

Methyl Jasmonate-Induced Lipidomic and Biochemical Alterations in the Intertidal Macroalga Gracilaria dura (Gracilariaceae, Rhodophyta)

The role of exogenously added methyl jasmonate (MeJA), a lipid-derived signaling compound, in inducing oxidative stress in the marine red macroalga Gracilaria dura was investigated. MeJA at a concentration of 1-100 µM was a strong stimulant of reactive oxygen species (H(2)O(2), HO· and O(2) (·-)) (P < 0.05) causing considerable oxidative stress in G. dura. This further led to lipid peroxidation and degradation of the pigments Chl a and phycocyanin, with a concomitant increase in phycoerythrin. The MeJA-induced oxidative burst also led to the induction of a fatty acid oxidation cascade, resulting in the synthesis of hydroxy-oxylipins and the up-regulation of the 13-lipoxygenase pathway. Electrospray ionization-mass spectrometry-based shotgun lipidomic analysis revealed that monogalactosyldiacylglycerol (a chloroplastic glycerolipid) and phosphatidylcholine (extrachloroplastidic phopholipid) were the most affected lipid classes. The degradation of 18:3-fatty acid-containing monogalactosyldiacylglycerol inferred that it provided fatty acyl chains for the biosynthesis of 13-hydroperoxylinolenic acid, which was further directed towards either the jasmonate pathway or other alternative pathways of the fatty acid oxidation cascade, analogous to higher plants. Also, G. dura modulated the lipid acyl chains in such a way that no significant change was observed in the fatty acid profile of the treated thalli as compared with those of the control, except for C16:0, C16:1 (n-9), C20:3 (n-6) and C20:4 (n-6) (P < 0.05). Furthermore, MeJA caused the accumulation of phenolic compounds and the up-regulation of enzymes involved in secondary metabolism such as polyphenol oxidase, shikimate dehydrogenase and phenylalanine ammonia-lyase, indicating a shift towards secondary metabolism as a defense strategy to combat the induced oxidative stress.

Methyl jasmonate as modulator of Cd toxicity in Capsicum frutescens var. fasciculatum seedlings

Methyl jasmonate (MeJA) elicits protective effects as form of plant response to abiotic stress. However, related studies on plant response to metal stress are insufficient. This study aimed to examine the effects of MeJA on growth and physiological responses of Capsicum frutescens seedlings exposed to cadmium (Cd) stress. The study was performed in an artificial climate chamber. Results showed that 50 mg L⁻¹ Cd significantly impaired the growth of the seedlings by increasing leaf MDA content and decreasing chlorophyll b. These effects were significantly mitigated by MeJA at low concentrations (0.1 µmol L⁻¹). The dry weights of different plant parts, chlorophyll content, and leaf catalase and ascorbate peroxidase activities were increased by a low MeJA concentration (0.1 µmol L⁻¹) but were decreased by a high MeJA concentration (1000 µmol L⁻¹). Significant increases in endogenous jasmonic acid were observed at 48 h after the samples were treated with Cd and 0.1 µmol L⁻¹ MeJA. These results suggested that low exogenous MeJA concentrations exhibited protective effects on the growth and physiology of C. frutescens seedlings under Cd stress.

Phytohormones and microRNAs as sensors and regulators of leaf senescence: assigning macro roles to small molecules

Ageing or senescence is an intricate and highly synchronized developmental phase in the life of plant parts including leaf. Senescence not only means death of a plant part, but during this process, different macromolecules undergo degradation and the resulting components are transported to other parts of the plant. During the period from when a leaf is young and green to the stage when it senesces, a multitude of factors such as hormones, environmental factors and senescence associated genes (SAGs) are involved. Plant hormones including salicylic acid, abscisic acid, jasmonic acid and ethylene advance leaf senescence, whereas others like cytokinins, gibberellins, and auxins delay this process. The environmental factors which generally affect plant development and growth, can hasten senescence, the examples being nutrient dearth, water stress, pathogen attack, radiations, high temperature and light intensity, waterlogging, and air, water or soil contamination. Other important influences include carbohydrate accumulation and high carbon/nitrogen level. To date, although several genes involved in this complex process have been identified, still not much information exists in the literature on the signalling mechanism of leaf senescence. Now, the Arabidopsis mutants have paved our way and opened new vistas to elucidate the signalling mechanism of leaf senescence for which various mutants are being utilized. Recent studies demonstrating the role of microRNAs in leaf senescence have reinforced our knowledge of this intricate process. This review provides a comprehensive and critical analysis of the information gained particularly on the roles of several plant growth regulators and microRNAs in regulation of leaf senescence.

COMPARISON OF METHYL JASMONATE AND CADMIUM EFFECT ON SELECTED PHYSIOLOGICAL PARAMETERS IN SCENEDESMUS QUADRICAUDA (CHLOROPHYTA, CHLOROPHYCEAE)(1)

Effect of methyl jasmonate (MeJA) in the concentrations of 10 or 100 μM on selected physiological parameters in Scenedesmus quadricauda (Turp.) Bréb. after 24 h of exposure was studied. Results were compared with the application of general toxic metal (cadmium, Cd) to identify MeJA-specific responses. Accumulation of reactive oxygen species (ROS; hydrogen peroxide and superoxide) was the most elevated by 10 μM MeJA and 100 μM Cd, while total chls showed decrease (Cd) and increase (MeJA) in these variants. The amount of carotenoids and cell viability were affected neither by MeJA nor by Cd application. The sum of free amino acids was considerably elevated by 10 μM Cd (increase in histidine, threonine, arginine, leucine, and lysine mainly) but depleted by 100 μM MeJA (14 from 17 compounds decreased), while accumulation of soluble proteins was unaffected by Cd and enhanced by MeJA. Cadmium application reduced the amount of Ca and also Mg in the case of 100 μM Cd, while MeJA had no effect on the content of mineral nutrients. Total Cd content reached 557 and 1,334 μg · g(-1) dry weight (dwt) in 10 and 100 μM Cd variant, respectively. Intracellular Cd uptake was ca. 55% from total Cd content in both Cd variants. The present findings are discussed in the context of the available literature, and possible explanations are suggested.

Methyl jasmonate, gibberellic acid, and auxin affect transcription and transcript accumulation of chloroplast genes in barley

Phytohormones control growth and development of plants. Their effects on the expression of nuclear genes are well investigated. Although they influence plastid-related processes, it is largely unknown whether phytohormones exert their control also by regulating the expression of plastid/chloroplast genes. We have therefore studied the effects of methyl jasmonate (MeJA), gibberellic acid (GA(3)), an auxin (indole-3-acetic acid, IAA), a brassinosteroid (24-epibrassinolide, BR) and a cytokinin (6-benzyladenine) on transcription (run-on assays) and transcript levels (RNA blot hybridization) of chloroplast genes after incubation of detached barley leaves in hormone solutions. BR was the only hormone without significant influence on chloroplast transcription. It showed, however, a weak reducing effect on transcript accumulation. MeJA, IAA and GA(3) repressed both transcription and transcript accumulation, while BA counteracted the effects of the other hormones. Effects of phytohormones on transcription differed in several cases from their influence on transcript levels suggesting that hormones may act via separate signaling pathways on transcription and transcript accumulation in chloroplasts. We observed striking differences in the response of chloroplast gene expression on phytohormones between the lower (young cells) and the upper segments (oldest cells) of barley leaves. Quantity and quality of the hormone effects on chloroplast gene expression seem to depend therefore on the age and/or developmental stage of the cells. As the individual chloroplast genes responded in different ways on phytohormone treatment, gene- and transcript-specific factors should be involved. Our data suggest that phytohormones adjust gene expression in the nucleo-cytoplasmic compartment and in plastids/chloroplasts in response to internal and external cues.

Proteomic identification of differentially expressed proteins in Arabidopsis in response to methyl jasmonate

Jasmonates (JAs) are the well characterized fatty acid-derived cyclopentanone signals involved in the plant response to biotic and abiotic stresses. JAs have been shown to regulate many aspects of plant metabolism, including glucosinolate biosynthesis. Glucosinolates are natural plant products that function in defense against herbivores and pathogens. In this study, we applied a proteomic approach to gain insight into the physiological processes, including glucosinolate metabolism, in response to methyl jasmonate (MeJA). We identified 194 differentially expressed protein spots that contained proteins that participated in a wide range of physiological processes. Functional classification analysis showed that photosynthesis and carbohydrate anabolism were repressed after MeJA treatment, while carbohydrate catabolism was up-regulated. Additionally, proteins related to the JA biosynthesis pathway, stress and defense, and secondary metabolism were up-regulated. Among the differentially expressed proteins, many were involved in oxidative tolerance. The results indicate that MeJA elicited a defense response at the proteome level through a mechanism of redirecting growth-related metabolism to defense-related metabolism.

Senescence progression in a single darkened cotyledon depends on the light status of the other cotyledon in Cucurbita pepo (zucchini) seedlings: potential involvement of cytokinins and cytokinin oxidase/dehydrogenase activity

Darkness mediates different senescence-related responses depending on the targeting of dark treatment (whole plants or individual leaves) and on the organs that perceive the signal (leaves or cotyledons). As no data are available on the potential role of darkness to promote senescence when applied to individual cotyledons, we have investigated how darkness affects the progression of senescence in either a single or both individually darkened cotyledons of young 10-day-old Cucurbita pepo (zucchini) seedlings. Strong acceleration of senescence was observed when both cotyledons were darkened as judged by the damage in their anatomical structure, deterioration of chloroplast ultrastructure in parallel with decreased photosynthetic rate and photochemical quantum efficiency of PSII. In addition, the endogenous levels of cytokinins (CKs) and IAA were strongly reduced. In a single individually darkened cotyledon, the structure and function of the photosynthetic apparatus as well as the contents of endogenous CKs and IAA were much less affected by darkness, thus suggesting inhibitory effect of the illuminated cotyledon on the senescence of the darkened one. Apparently, the effect of darkness to accelerate/delay senescence in a single darkened cotyledon depends on the light status of the other cotyledon from the pair. The close positive correlation between CK content and the activity of CK oxidase/dehydrogenase (CKX; EC 1.4.3.18/1.5.99.12) suggested that CKX was essentially involved in the mechanisms of downregulation of endogenous CK levels. Our results indicated that CKX-regulated CK signaling could be a possible regulatory mechanism controlling senescence in individually darkened cotyledons.