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In vitro culturing can generate plants with a distorted morphology. Some distortions affect the plant's survival after transfer to an ex vitro environment, while others can affect the aesthetic value. Therefore, exogenous hormones are often applied in in vitro cultures to modulate plant architecture. In this study, it was hypothesised that regulatory effects of UV-B radiation on plant morphology can be exploited under in vitro conditions, and that UV exposure will result in sturdier, less elongated plants with more branches and smaller leaves, mediated by changes in plant hormones. Plants were grown in tissue-culture containers and exposed to ~0.22 W m−2 UV-B for 8 days. Subsequently, plants were transferred to soil and monitored for a further 7 days. Results show that UV induced a marked change in architecture with a significant increase in axillary branches, and reductions in leaf area, plant height and root weight. These changes were associated with significant alterations in concentrations of hormones, including IAA, GA7, GA3 and iP–9–G. Changes in hormone concentrations suggest a regulatory, rather than a stress response to UV-B. Therefore, it is proposed that the application of UV in in vitro culture can be an innovative approach to manipulate plant architecture. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of additional ultraviolet radiation (UV) on the main growth fluorescent lamp light on pigment content and essential oil accumulation in sweet basil (Ocimum basilicum L.). Three different UV light sources from light-emitting diodes and discharge lamps, which emit UV in the UV-A (315–400 nm), UV-B (280–315 nm) and UV-C (100–280 nm) ranges, were tested for basil plant growing. The plants, growing under additional UV-A and UV-B from mercury lamps, on the 60th growing day were higher than control plants by 90% and 53%, respectively. The fresh leaf mass of the UV-A irradiated basil plants was 2.4-fold higher than the control plant mass. The dry mass/fresh mass ratio of the UV-A and UV-B irradiated plants was higher by 45% and 35% in comparison to the control plants. Leaf area was increased by 40% and 20%, respectively. UV-C affected the anthocyanin content most strongly, they increased by 50%, whereas only by 27% and 0% under UV-A and UV-B. Any UV addition did not affect the essential oil total contents but altered the essential oil compositions. UV-A and UV-B increased the linalool proportion from 10% to 20%, and to 25%, respectively, in contrast to UV-C, which reduced it to 3%. UV-C induced the eugenol methyl ether accumulation (17%) and inhibited plant growth. Moreover, UV increased the proportion of α-guaiene, β-cubebene and α-bulnesene and decreased the proportion of sabinene and fenchone. Thus, we concluded that UV (except UV-C) used jointly with main light with PPFD 120 ± 10 μmol photons·m−2·s−1 for sweet basil cultivation may be justified to stimulate basil growth and optimize the essential oil accumulation. [ABSTRACT FROM AUTHOR]

Lamps that emit 222 nm short-wavelength ultraviolet (UV) radiation can be safely used for sterilization without harming human health. However, there are few studies on the effects of 222 nm UVC (222-UVC) radiation exposure on plants compared with the effects of germicidal lamps emitting primarily 254 nm UVC (254-UVC) radiation. We investigated the growth inhibition and cell damage caused by 222-UVC exposure to Arabidopsis plants, especially mitochondrial dynamics, which is an index of damage caused by UVB radiation. Growth inhibition resulted from 254-UVC or 222-UVC exposure depending on the dose of UVC radiation. However, with respect to the phenotype of 222-UVC-irradiated plants, the leaves curled under 1 kJ m−2 and were markedly bleached under 10 kJ m−2 compared with those of plants irradiated with 254-UVC. The cellular state, especially the mitochondrial dynamics, of epidermal and mesophyll cells of Arabidopsis leaves exposed to 254-UVC or 222-UVC radiation was investigated using Arabidopsis plants expressing mitochondrial matrix-targeted yellow fluorescent protein (MT-YFP) under the control of Pro35S to visualize the mitochondria. 222-UVC (1 or 5 kJ m−2) severely damaged the guard cells within the epidermis, and YFP signals and chloroplast autofluorescence in guard cells within the epidermis exposed to 222-UVC (1 or 5 kJ m−2) were not detected compared with those in cells exposed to 254-UVC radiation. In addition, 222-UVC irradiation led to mitochondrial fragmentation in mesophyll cells, similar to the effects of 254-UVC exposure. These results suggest that 222-UVC severely damages guard cells and epidermal cells and that such damage might have resulted in growth inhibition. [ABSTRACT FROM AUTHOR]

The photosynthetic responses of 25-day-old Arabidopsis phyA phyB double mutant (DM) compared with the wild type (WT) to UV-B radiation (1 W m − 2 , 30 min) were investigated. UV-B irradiation led to reduction of photosystem 2 (PS-2) activity and the photosynthetic rate. In plants grown under both white and red light (λ m - 660 nm) the reduction was greater in DM plants compared to the WT. Without UV-B irradiation a decrease in PS-2 activity was observed in DM grown under RL only. It is assumed that the lower content of UV-absorbing pigments and carotenoids observed in DM may be one of the reasons of reduced PS-2 resistance to UV-B. Higher decrease in activities under UV in DM plants grown under RL compared to DM plants grown under white light is likely due to the lack of activity of cryptochromes in plants grown under red light. Rates of post-stress recovery of photosynthetic activity of DM compared with WT plants under white and red light of low intensity were studied. Almost complete recovery of the activity was found which was not observed under dark conditions and in the presence of a protein synthesis inhibitor, chloramphenicol. It is assumed that phytochrome system participates in stress-protective mechanisms of the photosynthetic apparatus to UV-radiation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Grapevine showed high tolerance to UV-B. [•] Only high UV-B doses transiently reduced grapevine photosynthetic performance, inducing stomatal closure. [•] Differential responses of grapevine to short- and long-term exposures to high UV-B were revealed. [•] High UV-B doses triggered the antioxidant enzyme's response of grapevine, avoiding oxidative damage. [•] UV-B absorbing compounds strongly increased in plants acclimated to UV-B. [Copyright &y& Elsevier]

Highlights: [•] Common metabolic response to water deficit and UV-B are observed. [•] Combined action of stresses may alleviate or increase damages. [•] UV-B may enhance resistance to WD and vice versa. [•] Enhanced resistance to WD and UV-B result from interplay between metabolic shuts. [•] H2O2, NO, ABA, jasmonic acid, salicylic acid and ethylene participate in cross-talk. [Copyright &y& Elsevier]

The ascomycetous yeast Yarrowia lipolytica has been established as model system for studies of several research topics as well as for biotechnological processes in the last two decades. However, frequency of heterologous recombination is high in this yeast species, and so knockouts of genes are laborious to achieve. Therefore, the aim of this study was to check whether a reduction of non-homologous end-joining (NHEJ) of double strand breaks (DSB) results in a strong increase of proportion of homologous recombinants. The Ku70-Ku80 heterodimer is known as an essential protein complex of the NHEJ. We show that deletion of YlKU70 and/or YlKU80 results in an increase of the rate of transformants with homologous recombination (HR) up to 85 % in each case. However, it never reaches near 100 % of HR in any case as described for some other yeast. Furthermore, we demonstrated that growth of Δylku strains was similar to that of the wild-type strain. In addition, no differences were detected between the Δylku strains and the parent strain in respect to sensitivity to the mutagenic agent EMS as well as to the antibiotics hygromycin, bleomycin and nourseothricin. However, Δylku70 and Δylku80 strain showed a slightly higher sensitivity against UV rays. Thus, the new constructed Δylku strains are attractive recipient strains for homologous integration of DNA fragments and a valuable tool for directed knockouts of genes. Nevertheless, our data suggest the existence of another system of non-homologous recombination what may be subject of further investigation. [ABSTRACT FROM AUTHOR]

Polyamines (PAs) are aliphatic polycations that are widespread in living organisms. In this review, we are focusing the correlation between endogenous PA titers and physiological perturbations and on the protective role of various analogues of PAs against abiotic stresses. PAs are involved in many physiological processes, such as cell growth and development and also respond to diverse abiotic stresses. Polyamines level shifts in different ways depending on several factors, such as plant species, tolerance or sensitivity to stress, and duration of stress. Exogenously supplied PAs protected plants from abiotic stress, whereas transgenic plants overexpressing PA biosynthetic genes exhibited stress tolerance. On the other hand, loss-of-function mutant of PA biosynthetic genes, or decrease of PA titers, resulted to decrease stress tolerance. [ABSTRACT FROM AUTHOR]

Abstract: To understand the effect of pesticide and UV-B on plant non-enzymatic antioxidant system, Vigna unguiculata was exposed to different concentration of dimethoate and UV-B (30min) alone and in combination. Negative impact on V. unguiculata due to generation of superoxide radical , hydrogen peroxide (H2O2), electrolyte leakage (EC) and lipid peroxidation (MDA) was observed. Combined exposure to UV-B and dimethoate led to further increase in these parameters. The content of non-enzymatic antioxidants such as proline and flavonoids increased whereas the ascorbic acid content showed a decrease. The results suggested the role of proline and flavonoids in scavenging reactive oxygen species generated due to stress. [Copyright &y& Elsevier]

Abstract: A series of experiments were carried out to investigate photodegradation of lime wood (Tilia cordata Mill.) during artificial UV/Vis light irradiation for 600h. Photodegradation of the wood samples was evaluated by thermogravimetry throughout the irradiation period at an interval of 100h. The alteration of wood was observed by means of the peak temperatures of DTG variation and by the mass losses observed during heating, evaluated on the basis of the measured thermal data. The results obtained indicate a shifting of the DTG maxima to lower temperatures which may be related to the decreasing in the stability components during photodegradation. The values of the overall activation energies corresponding of the decomposition process progressively decreases. The decreased temperatures decomposition processes, weight losses and integral area of the peaks assigned to lignin, the increased integral area of the peaks assigned to hemicelluloses could be explained by new formed structures, mainly due to formation of reactive species. [Copyright &y& Elsevier]

Due to anthropogenic influences, solar UV-B irradiance at the earth's surface is increasing. To determine the effects of enhanced UV-B radiation on photosynthetic characteristics of Prunus dulcis, two year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-Bc), 4.42 (UV-B1), 7.32 (UV-B2) and 9.36 (UV-B3) kJ m-2. Effects of UV-B stress on a range of chlorophyll fluorescence parameters (Chl FPs), chlorophyll contents and photosynthetic gas exchange parameters were investigated. UV-B stress promoted an increase in F0 and F0 / Fm, and a decrease in Fv, Fv /Fm, Fv / F0, F0 / Fm due to its adverse effects on photosystem II activity. No significant change was observed for Fm. Enhanced UV-B radiation caused a significant inhibition of photosynthesis rate (A) at UV-B2 and UV-B3 levels and this was accompanied by a reduction in stomatal conductance (gs) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increase UV-B stress. In general, advers UV-B effects became significant at the highest tested radiation dose 9.36kj.m-2. The most sensitive indicators for UV-B stress were Fv / F0, Chl a content and A. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis. [ABSTRACT FROM AUTHOR]

Abstract: In order to understand the effect of ultraviolet-B (UV-B) radiation on plant, the accumulated amount of dry matter and the distribution of the mineral elements in the different organs of soybean seedlings treated with UV-B radiation were investigated using the inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that the accumulated amount of dry matter in root, stem and leaf of soybean seedlings treated with UV-B radiation during the stress and recovery period was lower than that of the control soybean. Moreover, the content of macroelements in the root, stem and leaf of soybean seedlings during the stress period and recovery period were decreased comparing with that of the control soybean. The change in the contents of microelements depended on the intensity of UV-B radiation, the organs of soybean and the treating period. Finally, the results from the stepwise regression analysis indicated that the content of specific microelements also affected the accumulation of dry matter in the soybean seedlings treated with UV-B radiation comparing with the contents of macroelements in the control soybean. The relationship between the contents of mineral elements and the accumulation of dry matter depended on the intensity of UV-B radiation and the organs of soybean. These results demonstrated that UV-B radiation induced the change in the distribution of mineral elements in root, stem and leaf, leading to the decrease in the accumulation of dry matter and then the inhibition of soybean growth. It was a possible effect mechanism of UV-B radiation on plant. [Copyright &y& Elsevier]

The article focuses on the effects of ultraviolet-B (UV-B) radiations to plants. It notes that the depletion of the ozone layer in the atmosphere of the Earth has increased the amount of ultraviolet radiations. UV-B induces the development of reactive oxygen species (ROS) which affects plants that causes oxidative stress, effects to antioxidants and change in gene expression of plants. Moreover, it also affects thylakoid membranes which are responsible to photosynthesis in plants.

Abstract: Anthropogenic stratospheric ozone depletion causes an increase in UVB radiation impinging on the earth''s surface, which is a threat to plants not adapted to higher UVB irradiances. Investigations were carried out among tropical marine macrophytes, Turbinaria turbinata, Sargassum polyceratium var. ovatum, Padina sanctae-crucis, Lobophora variegate, Dictyota spec., Halimeda discoidea, Udotea flabellum, Thalassia testudinum and Syringodium filiforme collected from 0.3 to 26m depths at the Belizean barrier reef, where ultraviolet radiation (UV)-irradiances are naturally high. Photoinhibition was induced under full solar, UV (UVA+UVB), and UVA only-depleted radiation conditions. Photosynthetic activity during high radiation stress and during recovery in reduced solar radiation was determined in vivo by measuring fluorescence changes using a PAM fluorometer device. Generally, UV caused an additional decrease of photosynthetic performance during high light stress which varies according to species, depth of growth and UV penetration at the site of collection; an observation in concordance with the conventional harmful UV-radiation effects on phototrophs. When solar radiation was reduced by 50%, significant photosynthetic recovery was observed. However, some shallow water species which are adapted to high UV were observed to recover less under treatment with depleted solar UVB radiation. Our result supports earlier reports that UVB causes not only negative effects on photosynthesis, but may also facilitate or induce recovery processes in aquatic macrophytes acclimated to high solar radiation which grow at the upper shoreline. Among the eulittoral macroalgae, e.g. Dictyota spec., P. sanctae-crucis, and H. discoidea and the seagrass T. testudinum, initiation of photosynthetic recovery processes in the presence of low irradiance of short UV-wavelengths may present an ecophysiological advantage compared to macrophytes which initiate photosynthetic recovery process during low light or in the absence of UV. [Copyright &y& Elsevier]

Elevated ultraviolet-B (UVB) radiation has been reported to have few effects on plants but to alter the soil microbial community composition. However, the effects on soil microorganisms have to be mediated via plants, because direct radiation effects are only plausible on the uppermost millimeters of soil. Here, we assessed secondary effects of UVB on soil microbes. The responses in the dominant plant Eriophorum russeolum, peat pore water and microbial communities in the peat were recorded at a subarctic mire in the middle of the third growing season under field exposure simulating 20% depletion in the ozone layer. The UVB treatment significantly reduced the sucrose and the total soluble sugar (sucrose+glucose+fructose) concentration of the plant leaves while increasing the sucrose concentration in the belowground storage organ rhizome. The starch concentration of the leaves was also slightly reduced by elevated UVB. In the plant roots, carbohydrate concentrations remained unaffected but the total phenolics concentration increased under elevated UVB. We suggest that the simultaneously observed decrease in bacterial growth rate and the altered bacterial community composition are due to UVB-induced changes in the plant photosynthate allocation and potential changes in root exudation. There were no effects of elevated UVB on microbial biomass, peat pore water or nutrient concentrations in the peat. The observed responses are in line with the previously reported lower ecosystem dark respiration under elevated UVB, and they signify that the changed plant tissue quality and lower bacterial activity are likely to reduce decomposition. [ABSTRACT FROM AUTHOR]

Abstract: Fifteen populations of tartary buckwheat (Fagopyrum tataricum Gaertn.) occurring in habitats with different natural UV-B levels were sampled, and the plants were exposed to enhanced UV-B radiation under field conditions simulating 25% depletion of the stratospheric ozone layer. The experimental design was a 2×15 factorial, with two levels of UV-B radiation (ambient and enhanced UV-B radiation) and plants from 15 populations. The responses of plants in growth, morphology, productivity and in the composition of photosynthetic pigments were measured. The results demonstrated that there were significant differences among populations in responses to UV-B radiation: some populations exhibited a positive effect while others were negatively affected. The UV-B effects on plant traits were correlated with the constitutive values. A principal component analysis (PCA) was used to evaluate the overall sensitivity of responses to UV-B radiation. Our results suggest that the sensitivity of plants to UV-B radiation is not only associated with the ambient UV-B level in natural habitats but also with the relative growth rate and other factors. [Copyright &y& Elsevier]

This work reports on the significance of UV-B absorbing compounds and DNA photorepair in protecting bean plants from UV-B radiation under nitrogen restriction. Bean plants grown in sterile vermiculite and irrigated periodically with a nutrient solution containing 12 or 1mM of nitrate were irradiated with 22μWcm−2 of UV-B, 4h daily during 10 days after the first trifoliate leaf was developed. This intensity was equivalent to 3.2kJm−2 per day, approximately. PAR fluence rate was 350±50μmolquantam−2 s−1. Control plants did not receive UV-B irradiation. Leaf expansion was negatively affected by both nitrate restriction and UV-B irradiation. This decrease was paralleled by a significant increase in starch, which was exacerbated by the combined action of both factors. Combined action of low nitrogen and UV-B also negatively affected the CO2 assimilation rate and the stomatal conductance. Formation of UV-B absorbing compounds was significantly increased by both UV-B irradiation and nitrogen restriction and this increase was exacerbated by the combination of both factors. No significant increase in dimer formation was detected in irradiated plants at the UV-B dose used. Significant dimer formation was only obtained by using very high UV-B intensities. This suggests that under an irradiation level of 22μWcm−2 of UV-B, which is close to natural conditions, protective mechanisms such as pigment screening and DNA photorepair were probably sufficient to prevent any dimer formation in leaves. [Copyright &y& Elsevier]

The response of Ceratophyllum demersum and Myriophyllum spicatum to three levels of UV-B radiation – reduced ( ca. 50% reduction), ambient and enhanced UV-B radiation, simulating 17% ozone depletion – is discussed. The research revealed that UV-B stimulated the production of UV-B absorbing compounds in C. demersum, but not in M. spicatum. The relative amount of UV-B absorbing compounds was about four times lower in C. demersum. Enhanced UV-B also affected respiratory potential in C. demersum (on average 3.7 mg O2/gDM/h), but no effect on M. spicatum (on average 5.5 mg O2/gDM/h) was detected. Increased need for energy revealed that UV-B radiation exerted stress in C. demersum. No changes in chlorophyll a and no disturbance to photochemical efficiency due to UV-B were observed in either species. [ABSTRACT FROM AUTHOR]

UV-B radiation on plants is now of major concern to plant biologists due to the threat to productivity in global agriculture because of stratospheric ozone depletion. Quantitative and qualitative predictions attempts of expected effects and the search for a suitable ameliorant or a stress alleviant are being met with mixed outcomes. One of the reasons for this is the complications involved in designing UV stress response experements. The study of Heijari et al. in this issue has partially resolved this issue by well designed controls. Although the proportion of UV -B stress countering effects of Se in this study was not enough to meet the criteria of Se as an ameliorant. One of the future challenges to understand Se -plant interaction will be to study its potential essentiality to the plants and to unravel the complete picture of interconversion of the Se species within the plant system. [ABSTRACT FROM AUTHOR]

A UV-B exclusion-experiment was conducted in the high Arctic Zackenberg, NE Greenland, in which Salix arctica leaves during most of the growing season were fixed perpendicular to the solar zenith angle, thereby receiving maximal solar radiation. Covered with Teflon and Mylar foil, the leaves received approximately 90 and 40% of the ambient UV-B irradiance, respectively. The effects were examined through recordings of chlorophyll a fluorescence transients, determination of biomass and analysis of total carbon and nitrogen content and amount of soluble flavonoids in the leaves. The processing of light was analysed by means of the chlorophyll a fluorescence transient, using the so-called JIP test, as evolved by Reto J. Strasser and his coworkers. Reduction of the UV-B irradiance caused a rise in many of the fluorescence parameters during July, but not in August (late season). Thus increases in the efficiency that an absorbed photon will be trapped by the PSII reaction centre with the resultant reduction of QA to QA– (ET0/ABS = FV/FM) and the efficiency that an electron residing on QA– will enter the intersystem electron transport chain (ET0/TR0) were observed in reduced UV-B. Moreover, estimated per cross-section of leaf sample, the number of active PSII reaction centres (RC/CSM) and electron transport rate (ETM/CSM) and all performance indexes (PIABS, PICSo and PICSm) were increased in reduced UV-B. The total soluble flavonoid content was highest in ambient UV-B. The treatment effects on fluorescence parameters that were directly measured (e.g. F0 and FM) and those that were derived (e.g. quantum efficiencies, parameters per PSII reaction centres and per cross-section of leaf sample) are discussed in relation to one another, in relation to daily and seasonal variation, and from the perspective of evaluating the relative importance of UV-B of donor and acceptor side capacity in Photosystem II. In conclusion, the experimental set-up and non-invasive measurements proved to be a sensitive method to screen for effects of UV-B stress. [ABSTRACT FROM AUTHOR]

This is a study of the impact of increased ultraviolet-B (UV-B) radiation on the secondary chemistry of Salix myrsinifolia (dark-leaved willow). For nearly two decades, the loss of stratospheric ozone above the high latitudes of the Northern Hemisphere has increased UV-B radiation (280–320 nm) over the long-term mean. Willows (Salicaceae) are widely distributed in these northern regions. To determine the effects of increased UV-B radiation on willows, the plantlets of three clones of S. myrsinifolia were grown under ambient (3.6 kJ m-2 day-1) or enhanced (7.18 kJ m-2 day-1) UV-B irradiance. After the 2-week indoor experiment, the concentrations of UV-B-screening phenolics (flavonoids and phenolic acids) and low-UV-B-screening phenolics (salicylates and condensed tannins) in fresh leaves were investigated and the biomass of leaves, stems and roots was determined. As expected, the total amount of flavonoids in willow leaves clearly increased when plantlets were exposed to higher UV-B irradiation. However, the degree of increase of individual compounds varied: luteolin-7-glucoside, monomethyl-monocoumaryl-luteolin-7-glucoside and one myricetin derivative increased significantly, while the apigenin-7-glucuronide increased only slightly. The enhanced UV-B also increased the amount of p-hydroxycinnamic acid derivative. The UV-B effects on other phenolic acids and tannins were minor. In contrast to the other phenolics, the amounts of two salicylates, salicin and saligenin, decreased under enhanced UV-B irradiation. Our results indicate that the concentrations of both UV-B-screening and low-UV-B-screening phenolic compounds in leaves of S. myrsinifolia may vary in response to elevated UV-B radiation. However, while the UV-B protective flavonoids and phenolic acids accumulate during UV-B exposure, the concentrations of certain salicylates decrease. [ABSTRACT FROM AUTHOR]

Examines the role of AtRAD1 plant homologue excision repair nucleases in the dark repair of ultraviolet (UV) damages and recombination. Obligatory nature of plants to sunlight and UV exposure; Expression of AtRAD1 in tissues; Discussion of the UV-dependent functions of nucleotide excision repair.

The maximum quantum yield for photosynthetic O2 evolution in red leaf coleus varieties having anthocyanin in their upper epidermis is much lower in green light and slightly lower in white light than in a green leaf variety lacking anthocyanin. A similar degree of photoinhibition occurred under excess visible light in the red versus green varieties; whereas, the red leaf varieties were less damaged by UV-B and UV-C radiation suggesting protection by anthocyanin in their epidermal tissue. [ABSTRACT FROM AUTHOR]

The molecular mechanism of plant response to UV-B radiation was studied using the nopaline synthase (nos) promoter, which has been shown to be inducible by methyl jasmonate (MJ) and reactive oxygen species (ROS). In the leaves of transgenic tobacco (Nicotiana tabacum L.) plants that carried a fusion between the nos promoter and the chloramphenicol acetyltransferase (cat) gene, 2 h of UV-B treatment resulted in a transient increase in the level of cat mRNA, a maximum being reached at 6 h after the UV-B treatment. It was also found that MJ and UV-B enhance nos promoter expression via separate pathways. Diethyldithiocarbamic acid, a potent inhibitor of jasmonate production, had little effect on UV-B stimulation of the nos promoter. In contrast, antioxidants, such as dimethylthiourea, reduced glutathione, cysteine, N-acetylcysteine and DTT, blocked UV-B induction of the nos promoter, but did not affect MJ induction of the nos promoter. These results suggest that UV-B induction of the nos promoter is mediated via a pathway that requires reactive oxygen species and is distinct from the jasmonate or MJ mediating pathway. [ABSTRACT FROM AUTHOR]