Biological N fixation performed by moss-associated cyanobacteria is among the main sources of new nitrogen (N) input in pristine subarctic ecosystems. Yet, until now there has been a lack of knowledge on the drivers of biological N fixation on small spatial scales (moss segment) in relation to the drivers at larger scales (moisture ecosystem). To investigate this, we assessed the capacity of N fixation along shoots of two common moss species, and collected along a steep precipitation gradient in the Subarctic. Furthermore, concentrations of nutrients and pH were analysed along the same moss shoot-gradients. We found the highest nitrogenase activity in collected at the location with the highest mean annual precipitation. Nitrogenase activity varied significantly along the moss shoots, and between species and location along the precipitation gradient. had the highest nitrogenase activity in the middle segments, while for , it was highest in the lowest segments (below 3 cm). Contents of iron, molybdenum and N generally increased with moss segment depth, but phosphorus concentrations decreased and pH was stable across segments. Taken together, the factors that drive nitrogenase activity at small scales differ between moss species, whereas precipitation predominantly controls nitrogenase activity at larger scales (across habitats).

All land plants modulate their growth and physiology through intricate signaling cascades. The majority of these are at least modulated-and often triggered-by phytohormones. Over the past decade, it has become apparent that some phytohormones have an evolutionary origin that runs deeper than plant terrestrialization-many emerged in the streptophyte algal progenitors of land plants. Ethylene is such a case. Here we synthesize the current knowledge on the evolution of the phytohormone ethylene and speculate about its deeply conserved role in adjusting stress responses of streptophytes for more than half a billion years of evolution.

As a result of global warming and climate change, the number and intensity of weather events such as droughts, heat waves, and floods are increasing, resulting in major losses in crop yield worldwide. Combined with the accumulation of different pollutants, this situation is leading to a gradual increase in the complexity of environmental factors affecting plants. We recently used the term 'multifactorial stress combination' (MFSC) to describe the impact of three or more stressors occurring simultaneously or sequentially on plants. Here, we show that a MFSC of six different abiotic stressors (high light, heat, nitrogen deficiency, paraquat, cadmium, and salinity) has a negative impact on the growth, photosystem II function, and photosynthetic activity of mature tomato plants. We further reveal a negative correlation between proline accumulation and the increasing number of stress factors combined, suggesting that proline could have an adverse effect on plants during MFSC. Our findings further indicate that alterations in hormonal levels and stomatal responses are stress/stress combination-dependent, and that a tomato mutant deficient in jasmonic acid accumulation is more sensitive to high light and its combinations with salinity and/or paraquat. Taken together, our study reveals that the effects of MFSC on tomato plants are broad, that photosynthesis and proline accumulation are especially vulnerable to MFSC, and that jasmonic acid is required for tomato acclimation to MFSCs involving high light, salinity and paraquat.

Temperature is one of the key abiotic factors during the life of plants, especially in the Arctic region which is currently experiencing rapid climate change. We evaluated plant traits and environmental variables determining leaf temperature in tundra shrubs and volatile organic compound (VOC) emissions with field measurements on deciduous tundra shrubs, and and evergreen and . Higher leaf-to-air temperature difference was observed in evergreen, compared to deciduous shrubs. Evergreen shrubs also showed continuously increasing photosynthesis with increasing temperature, suggesting high thermal tolerance. For the deciduous species, the optimum temperature for net photosynthesis was between our measurement temperatures of 24 °C and 38 °C. Air temperature and vapor pressure deficit were the most important variables influencing leaf temperature and VOC emissions in all the studied plants, along with stomatal density and specific leaf area in the deciduous shrubs. Using climate data and emission factors from our measurements, we modelled total seasonal tundra shrub VOC emissions of 0.3-2.3 g m over the main growing season. Our results showed higher-than-expected temperature optima for photosynthesis and VOC emission and demonstrated the relative importance of plant traits and local environments in determining leaf temperature and VOC emissions in a subarctic tundra.

(PV) and (PQ) are reported to hyperaccumulate arsenic (As) when grown in Asrich soil. Yet, little is known about the impact of their unique As accumulation mechanisms on As transformations and cycling at the soil-root interface. Using a combined approach of two-dimensional (2D), sub-mm scale solute imaging of arsenite (As), arsenate (As), phosphorus (P), manganese (Mn), iron (Fe) and oxygen (O), we found localized patterns of As/As redox transformations in the PV rhizosphere (As/As ratio of 0.57) compared to bulk soil (As/As ratio of ≤0.04). Our data indicate that the high As root uptake, translocation and accumulation from the As-rich experimental soil (2080 mg kg) to PV fronds (6986 mg kg) induced As detoxification via As reduction and As root efflux, leading to As accumulation and re-oxidation to As in the rhizosphere porewater. This As cycling mechanism is linked to the reduction of O2 and Mn (oxyhydr)oxides resulting in decreased O2 levels and increased Mn solubilization along roots. Compared to PV, we found 4-fold lower As translocation to PQ fronds (1611 mg kg), 2-fold lower As depletion in the PQ rhizosphere, and no As efflux from PQ roots, suggesting that PQ efficiently controls As uptake to avoid toxic As levels in roots. Analysis of root exudates obtained from soil-grown PV showed that As acquisition by PV roots was not associated with phytic acid release. Our study demonstrates that two closely-related As-accumulating ferns have distinct mechanisms for As uptake modulating As cycling in As-rich environments.

Ozone and wounding are key abiotic factors but, their interactive effects on temporal changes in terpene synthase gene expression and emission responses are poorly understood. Here, we applied combined acute ozone and wounding stresses to the constitutive isoprenoid-emitter and studied how isoprene, 1,8-cineole, and isoledene synthase genes were regulated, and how the gene expression was associated with temporal changes in photosynthetic characteristics, product emission rates, and stomatal ozone uptake through recovery phase. Photosynthetic characteristics and emission rate of isoprene, 1,8-cineole, and isoledene were synergistically altered, while three TPS gene expressions were antagonistically altered by combined stress applications. A time-delay analysis indicated that the best correspondences between gene expression and product emission rates were observed for 0 h time-shift for wounding and 0-2 h time-shifts for separate ozone, and combined ozone and wounding treatments. The best correspondence between ozone uptake and gene expression was observed for 0-4 h time-shifts for separate ozone and combined ozone and wounding treatments. Overall, this study demonstrated that expression profiles of isoprene, the monoterpene 1,8-cineole, and the sesquiterpene isoledene synthase genes differentially influenced their corresponding product emissions for separate and combined ozone and wounding treatments through recovery.

Reduction-oxidation (redox) reactions, in which electrons move from a donor to an acceptor, are the functional heart of photosynthesis. It is not surprising therefore that reactive oxygen species (ROS) are generated in abundance by photosynthesis, providing a plethora of redox signals as well as functioning as essential regulators of energy and metabolic fluxes. Chloroplasts are equipped with an elaborate and multifaceted protective network that allows photosynthesis to function with high productivity even in resource-limited natural environments. This includes numerous antioxidants with overlapping functions that provide enormous flexibility in redox control. ROS are an integral part of the repertoire of chloroplast signals that are transferred to the nucleus to convey essential information concerning redox pressure within the electron transport chain. Current evidence suggests that there is specificity in the gene-expression profiles triggered by the different ROS signals, so that singlet oxygen triggers programs related to over excitation of photosystem (PS) II while superoxide and hydrogen peroxide promote the expression of other suites of genes that may serve to alleviate electron pressure on the reducing side of PSI. Not all chloroplasts are equal in their signaling functions, with some sub-populations appearing to have better contacts/access to the nucleus than others to promote genetic and epigenetic responses. While the concept that light-induced increases in ROS result in damage to PSII and photoinhibition is embedded in the photosynthesis literature, there is little consensus concerning the extent to which such oxidative damage happens in nature. Slowly reversible decreases in photosynthetic capacity are not necessarily the result of light-induced damage to PSII reaction centers.

We measured the bulk grain concentrations of arsenic (As), along with rubidium (Rb) and strontium (Sr) as indicators of phloem and xylem transport respectively, in rice ( cv. ) pulsed with arsenate at two exposure levels for 5 day periods at progressively later stages of grain fill, between anthesis and maturity, through the cut flag leaf. We compared these to unexposed (negative) controls and positive controls; pulsed with dimethylarsinic acid (DMA). We collected elemental maps of As and micronutrient elements (Fe, Zn, Mn, Cu and Ni) from developing grains of rice. Exposures were either 25 or 100 μg/ml arsenate (As(V)) at various stages of grain development, compared to 25 μg/ml dimethylarsinic acid (DMA); the most efficiently transported As species identified in rice. We used the spatial distribution of arsenic in the grain to infer the presence of As transporters. By exposing grains through the flag leaf rather than via the roots, we were able to measure arsenic transport into the grain during filling under controlled conditions. Exposure to 100 μg/ml As(V) resulted in widespread As localization in both embryo and endosperm, especially in grains exposed to As at later stages of panicle development. This suggests loss of selective transport, likely to be the result of As toxicity. At 25 μg/ml As(V), As colocalized with Mn in the ovular vascular trace (OVT). Exposure to either As(V) or DMA reduced grain Fe, an effect more pronounced when exposure occurred earlier in grain development. The abundance of Cu and Zn were also reduced by As. Arsenic exposure later in grain development caused higher grain As concentrations, indicating the existence of As transporters whose efficiency increases during grain fill. We conclude that localization of As in the grain is a product of both As species and exposure concentration, and that high As(V) translocation from the flag leaf can result in high As concentrations in the endosperm.

Both ozone and wounding constitute two key abiotic stress factors, but their interactive effects on plant constitutive and stress-elicited volatile (VOC) emissions are poorly understood. Furthermore, the information on time-dependent modifications in VOC release during recovery from a combined stress is very limited. We studied the modifications in photosynthetic characteristics and constitutive and stress-induced volatile emissions in response to single and combined applications of acute ozone (4, 5, and 6 ppm) and wounding treatments through recovery (0.5-75 h) in a constitutive isoprene and mono- and sesquiterpene emitter . Overall, the photosynthetic characteristics were surprisingly resistant to all ozone and wounding treatments. Constitutive isoprene emissions were strongly upregulated by ozone and combined ozone and wounding treatments and remained high through recovery phase, but wounding applied alone reduced isoprene emission. All stress treatments enhanced emissions of lipoxygenase pathway volatiles (LOX), mono- and sesquiterpenes, saturated aldehydes (C7-C10), benzenoids, and geranylgeranyl diphosphate (GGDP) pathway volatiles. Once elicited, GGDP volatile, saturated aldehyde and benzenoid emissions remained high through the recovery period. In contrast, LOX emissions, and total mono- and sesquiterpene emissions decreased through recovery period. However, secondary rises in total sesquiterpene emissions at 75 h and in total monoterpenes at 25-50 h were observed. Overall, acute ozone and wounding treatments synergistically altered gas exchange characteristics and stress volatile emissions. Through the treatments and recovery period, stomatal ozone uptake rate and volatile emission rates were poorly correlated, reflecting possible ozone-scavenging effect of volatiles and thus, reduction of effective ozone dose and elicitation of induced defense by the acute ozone concentrations applied. These results underscore the important role of interactive stresses on both constitutive and induced volatile emission responses.

Gypsy moth ( L., Lymantriinae) is a major pest of pedunculate oak () forests in Europe, but how its infections scale with foliage physiological characteristics, in particular with photosynthesis rates and emissions of volatile organic compounds has not been studied. Differently from the majority of insect herbivores, large larvae of rapidly consume leaf area, and can also bite through tough tissues, including secondary and primary leaf veins. Given the rapid and devastating feeding responses, we hypothesized that infection of leaves by leads to disproportionate scaling of leaf photosynthesis and constitutive isoprene emissions with damaged leaf area, and to less prominent enhancements of induced volatile release. Leaves with 0% (control) to 50% of leaf area removed by larvae were studied. Across this range of infection severity, all physiological characteristics were quantitatively correlated with the degree of damage, but all these traits changed disproportionately with the degree of damage. The net assimilation rate was reduced by almost 10-fold and constitutive isoprene emissions by more than 7-fold, whereas the emissions of green leaf volatiles, monoterpenes, methyl salicylate and the homoterpene (3)-4,8-dimethy-1,3,7-nonatriene scaled negatively and almost linearly with net assimilation rate through damage treatments. This study demonstrates that feeding by large insect herbivores disproportionately alters photosynthetic rate and constitutive isoprene emissions. Furthermore, the leaves have a surprisingly large capacity for enhancement of induced emissions even when foliage photosynthetic function is severely impaired.

The early culmination of maximum radial growth (RG) in late spring has been found in several coniferous species in a dry inner Alpine environment. We hypothesized that an early decrease in RG is an adaptation to cope with drought stress, which might require an early switch of carbon (C) allocation to belowground organs. To test this hypothesis, we experimentally subjected six-year-old Norway spruce saplings (tree height: 1.35 m; n = 80 trees) to two levels of soil water availability (watered versus drought conditions) and manipulated tree C status by physically blocking phloem transport at three girdling dates (GD). The influence of C availability and drought on tree growth (radial and shoot growth; root biomass) in response to girdling was analyzed in both treatments. Non-structural carbohydrates (NSCs, soluble sugars and starch) were measured in the stem, root and current leader to evaluate changes in tree C status due to girdling. The main finding was a significant increase in RG of the girdled trees compared to the controls above the girdling zone (UZ). At all girdling dates the RG increase was significantly more intense in the drought-stressed compared with watered trees (. 3.3 and 1.9-fold higher compared with controls in the drought-stressed and watered trees, respectively), most likely indicating that an early switch of C allocation to belowground occurs as an adaptation to maintain tree water status under drought conditions. Reactivation of the cambium after the cessation of its regular activity was detected in UZ in drought-stressed trees, while below the girdling zone no xylem formation was found and the NSC content was strikingly reduced. Irrespective of water availability, girdling before growth onset significantly reduced the progression of bud break ( < 0.05) and the length of the current leader shoot by -47% ( < 0.01) indicating a reduction in xylem hydraulic conductance, which was corroborated by significantly reduced xylem sap flow ( < 0.001). Based on our findings, we conclude that during the growing season drought stress prioritizes an early switch of C allocation to the root system as an adaptation to maintain adequate tree water status in drought-prone environments.

Carotenoids constitute a major target of chloroplastic photooxidative reactions, leading to the formation of several oxidized derivatives and cleavage products, some of which are volatile (VCCPs). Among them, β-cyclocitral (β-CC), at least, is a retrograde signaling molecule that modulates the activity of many key physiological processes. In the present work, we aimed to study whether β-CC and other VCCPs are released into the atmosphere from photosynthetic tissues. To overcome stomatal limitations, the foliose chlorolichen was used as the model system, and the emissions of biogenic volatiles, induced by heat and wounding stresses, were monitored by proton-transfer reaction time-of-flight mass-spectrometry (PTR-TOF-MS) and gas-chromatography (GC-MS). Prior to stress treatments, VCCPs were emitted constitutively, accounting for 1.3 % of the total volatile release, with β-CC being the most abundant VCCP. Heat and wounding stresses induced a burst of volatile release, including VCCPs, and a loss of carotenoids. Under heat stress, the production of β-CC correlated positively with temperature. However the enhancement of production of VCCPs was the lowest among all the groups of volatiles analyzed. Given that the rates of carotenoid loss were three orders of magnitude higher than the release rates of VCCPs and that these compounds only represent a minor fraction in the blend of volatiles, it seems unlikely that VCCPs might represent a global stress signal capable of diffusing through the atmosphere to different neighboring individuals.

Plants frequently experience heat ramps of various severities, but how and to what degree plant metabolic activity recovers from mild and severe heat stress is poorly understood. In this study, we exposed the constitutive terpene emitter, leaves to mild (37 and 41 °C), moderate (46 °C) and severe (49 °C) heat ramps of 5 min. and monitored foliage photosynthetic activity, lipoxygenase pathway volatile (LOX), and mono- and sesquiterpene emissions and expression of two terpene synthase genes, β-phellandrene synthase and ()-β-caryophyllene/α-humulene synthase, through a 24 h recovery period upon return to pre-stress conditions. Leaf monoterpene emissions were dominated by β-phellandrene and sesquiterpene emissions by ()-β-caryophyllene, and thus, these two terpene synthase genes were representative for the two volatile terpene classes. Photosynthetic characteristics partly recovered under moderate heat stress, and very limited recovery was observed under severe stress. All stress treatments resulted in elicitation of LOX emissions that declined during recovery. Enhanced mono- and sesquiterpene emissions were observed immediately after the heat treatment, but the emissions decreased even to below the control treatment during recovery between 2-10 h, and raised again by 24 h. The expression of β-phellandrene and ()-β-caryophyllene synthase genes decreased between 2-10 h after heat stress, and recovered to pre-stress level in mild heat stress treatment by 24 h. Overall, this study demonstrates a highly sensitive heat response of terpenoid synthesis that is mainly controlled by gene level responses under mild stress, while severe stress leads to non-recoverable declines in foliage physiological and gene expression activities.

Diverse plant functions (e.g. growth, storage, defense and anti-stress mechanisms) use elements disproportionally. We hypothesized that plants growing under different abiotic and biotic conditions would shift their elemental compositions in response to a very severe drought. We tested this hypothesis by investigating the changes in foliar stoichiometry and species composition from a very severe drought. We also tested the effects of previous droughts (acclimation) on this response. Different species growing in the same community responded more similarly to a very severe drought than did individual species growing in different communities. The stoichiometric shifts were thus more community-dependent than species-dependent. The results also suggested that plants grown in monoculture were less stoichiometrically plastic during the drought than plants grown in a more diverse community. Previous exposure to long-term drought treatments in the same communities did not significantly affect the stoichiometric shifts during the new drought. Differential use of resources may have been responsible for these responses. Monocultured plants, which used the same resources in similar proportions, had more difficulty avoiding direct competition when the resources became scarcer. Moreover, each species tested had a particular elemental composition in all communities and climatic treatments. The differences in foliar elemental compositions were largest between plant functional groups (shrubs and grasses) and smallest among species within the same functional group. Global principal components analyses (PCAs) identified a general tendency for all species, independently of the community in which they grew, toward lower concentrations of K, N, P, Mg and S, and to higher concentrations of C and Fe as the drought advanced. This study has demonstrated the utility of analyses of differences and shifts in plant elemental composition for understanding the processes underlying the responses of plants to changes in biotic and abiotic environmental conditions.

Over-wintering reproductive buds of many woody plants survive frost by supercooling. The bud tissues are isolated from acropetally advancing ice by the presence of ice barriers that restrict ice growth. Plants living in alpine environments also face the risk of ice formation in summer months. Little knowledge exists, how reproductive structures of woody alpine plants are protected from frost injury during episodic summer frosts. In order to address this question, frost resistance of three common dwarf shrubs, , and was measured and ice formation and propagation were monitored in twigs bearing reproductive shoots during various stages of reproductive development (bud, anthesis, and fruit) throughout the alpine summer. Results indicated that, in the investigated species, ice barriers were present at all reproductive stages, isolating the reproductive shoots from ice advancing from the subtending vegetative shoot. Additionally, in the reproductive stems ice nucleating agents that are active at warm, sub-zero temperatures, were absent. The ice barriers were 100% effective, with the exception of , where in 13% of the total observations, the ice barrier failed. The ice barriers were localized at the base of the pedicel, at the anatomical junction of the vegetative and reproductive shoot. There, structural aspects of the tissue impede or prevent ice from advancing from the frozen stem into the pedicel of the reproductive shoot. Under the experimental conditions used in this study, ice nucleation initially occurred in the stem of the vegetative shoot at species-specific mean temperatures in the range of -4.7 to -5.8 °C. Reproductive shoots, however, remained supercooled and ice free down to a range of -7.2 to -18.2 °C or even below -22 °C, the lowest temperature applied in the study. This level of supercooling is sufficient to prevent freezing of reproductive structures at the lowest air temperature occurring at the altitude of the upper distribution boundary of the natural habitat of the investigated species which is between -8 and -10 °C in summer. Frost resistance assays indicated that reproductive shoots are much less frost resistant than vegetative stems, and in contrast to vegetative shoots, are not ice tolerant. Supercooling of reproductive shoots in alpine, woody plant species is an effective mechanism that protects developing offspring from potential frost damage resulting from episodic summer freezing events.

Earlier, we established that a major drought tolerance QTL on linkage group 2 of pearl millet is also associated with reduced salt uptake and enhanced growth under salt stress. Present study was undertaken to re-assess the performance of drought tolerant (PRLT 2/89-33) and drought sensitive (H 77/833-2) parents along with two QTL-NILs (ICMR 01029 and ICMR 01040), under salinity stress specifically imposed during post-flowering growth stages when plants had developed their ion sinks in full. Time course changes in ionic accumulation and their compartmentalization in different plant parts was studied, specifically to monitor and capture changes conferred by the two alleles at this QTL, at small intervals. Amongst different plant parts, higher accumulation of toxic ion Na was recorded in roots. Further, the Na concentration in roots of the testcross hybrid of the drought-sensitive parent (H 77/833-2) reached its maximum at ECiw 15 dS m within 24 h after salinity imposition, whereas it continued to increase with time in the testcross hybrids of the drought tolerant parent PRLT 2/89-33 as well as those of its QTL-NILs (ICMR 01029 and ICMR 01004) and reached at its maximum at 120 h stage. Comparison of differential distribution of toxic ions in individual leaves revealed that Na ions were not uniformly distributed in the leaves of the drought-tolerant parent and drought-tolerant QTL-NILs; but accumulated preferentially in the older leaves, whereas the hybrid of the drought-sensitive parent showed significantly higher Na concentration in all main stem leaves irrespective of their age. Dynamics of chlorophyll and proline concentration variation studied under salt stress at late flowering stages revealed a greater reduction, almost twice, in both leaf chlorophyll and proline concentrations in younger leaves in the hybrids of the sensitive parent as compared to the tolerant parent and QTL NILs. Imposition of salinity stress even at flowering stage affected the yield performance in pearl millet, wherein higher yield was recorded in drought tolerant parent and the two QTL-NILs compared to drought sensitive parent.

Plant volatile organic compounds (VOCs) elicited in response to herbivory can serve as cues for parasitic and predatory insects, but the modification of VOC elicitation responses under interacting abiotic stresses is poorly known. We studied foliage VOC emissions in the deciduous tree induced by feeding by the larvae of green alder sawfly () under well-watered and drought-stressed conditions Drought strongly curbed photosynthesis rate and stomatal conductance, but there were no effects of insect feeding on photosynthetic characteristics. Feeding induced emissions of volatile products of lipoxygenase pathway and monoterpenes, and emissions of stress marker compounds ()-β-ocimene and homoterpene DMNT. The emissions were more strongly elicited and reached a maximum value earlier in drought-stressed plants. In addition, methyl salicylate emissions were elicited in herbivory-fed drought-stressed plants. Herbivores were more strongly attracted to well-watered plants and consumed more than a four-fold greater fraction of leaf area than they consumed from drought-treated plants. Overall, this study demonstrates an important priming effect of drought, suggesting that plants under combined drought/herbivory stress are more resistant to herbivores.

Using iron-deprived (-Fe) chlorotic as well as green iron-deficient (5 μM Fe) and iron-sufficient supplied (50 μM Fe) leaves of young hydroponically reared plants, we explored iron deficiency effects on triggering programmed cell death (PCD) phenomena. Iron deficiency increased superoxide anion but decreased hydroxyl radical (•OH) formation (TBARS levels). Impaired photosystem II efficiency led to hydrogen peroxide accumulation in chloroplasts; NADPH oxidase activity, however, remained on the same level in all treatments. Non-autolytic PCD was observed especially in the chlorotic leaf of iron-deprived plants, to a lesser extent in iron-deficient plants. It correlated with higher DNAse-, alkaline protease- and caspase-3-like activities, DNA fragmentation and chromatin condensation, hydrogen peroxide accumulation and higher superoxide dismutase activity. A significant decrease in catalase activity together with rising levels of dehydroascorbic acid indicated a strong disturbance of the redox homeostasis, which, however, was not caused by •OH formation in concordance with the fact that iron is required to catalyse the Fenton reaction leading to •OH generation. This study documents the chain of events that contributes to the development of non-autolytic PCD in advanced stages of iron deficiency in leaves.

Safeners are agrochemicals which enhance tolerance to herbicides in cereals including wheat ( L.) by elevating the expression of xenobiotic detoxifying enzymes, such as glutathione transferases (GSTs). When wheat plants were spray-treated with three safener chemistries, namely cloquintocet mexyl, mefenpyr diethyl and fenchlorazole ethyl, an apparently identical subset of GSTs derived from the tau, phi and lambda classes accumulated in the foliage. Treatment with the closely related mefenpyr diethyl and fenchlorazole ethyl enhanced seedling shoot growth, but this effect was not determined with the chemically unrelated cloquintocet mexyl. Focussing on cloquintocet mexyl, treatments were found to only give a transient induction of GSTs, with the period of elevation being dose dependent. Examining the role of safener metabolism in controlling these responses, it was determined that cloquintocet mexyl was rapidly hydrolysed to the respective carboxylic acid. Studies with cloquintocet showed that the acid was equally effective at inducing GSTs as the ester and appeared to be the active safener. Studies on the tissue induction of GSTs showed that whilst phi and tau class enzymes were induced in all tissues, the induction of the lambda enzymes was restricted to the meristems. To test the potential protective effects of cloquintocet mexyl in wheat on chemicals other than herbicides, seeds were pre-soaked in safeners prior to sowing on soil containing oil and a range of heavy metals. Whilst untreated seeds were unable to germinate on the contaminated soil, safener treatments resulted in seedlings briefly growing before succumbing to the pollutants. Our results show that safeners exert a range of protective and growth promoting activities in wheat that extend beyond enhancing tolerance to herbicides.

Thunb. is an edible herb with a variety of pharmacological activities, but only limited information is available about its response towards potassium supplementation. Sterile plantlets were cultured in media with different potassium levels, and parameters related to growth, foliar potassium, water and chlorophyll contents, photosynthesis, transpiration, HO contents and antioxidative enzyme activities were determined after a month. Results showed that 1.28 mM potassium was the optimum for as highest values of dry weight, shoot height, root length and number were obtained at this concentration. The optimum potassium concentration resulted in the maximum net photosynthetic rate which could be associated with the highest chlorophyll content rather than limited stomatal conductance. The supply of surplus potassium resulted in higher content of foliar potassium, but negatively correlated with the biomass. Both potassium starvation (0 mM) and high potassium (>1.28 mM) could lead to water loss through high transpiration rate and low water absorption, respectively, and resulted in HO accumulation and increased activities of catalase and peroxidase, which suggested induction of oxidative stress. Moreover, showed the minimum of HO content and the maximum of superoxide dismutase activity on 1.28 mM potassium, implying its role in inducing tolerance against oxidative stress.

Three plant growth-promoting bacteria (PGPB; ES4, RIZO1, and Cd) were tested for their ability to enhance plant growth and development of the native Sonoran Desert shrub quailbush () and for their effect on the native bacterial community in moderately acidic, high-metal content (AHMT) and in neutral, low metal content natural tailings (NLMT) in controlled greenhouse experiments. Inoculation of quailbush with all three PGPB significantly enhanced plant growth parameters, such as germination, root length, dry weight of shoots and roots, and root/shoot ratio in both types of tailings. The effect of inoculation on the indigenous bacterial community by the most successful PGPB ES4 was evaluated by denaturating gradient gel electrophoresis (PCR-DGGE) fingerprinting and root colonization was followed by specific fluorescent in situ hybridization (FISH). Inoculation with this strain significantly changed the bacterial community over a period of 60 days. FISH analysis showed that the preferred site of colonization was the root tips and root elongation area. This study shows that inoculation of native perennial plants with PGPB can be used for developing technologies for phytostabilizing mine tailings.