Leaf Abscisic Acid Research Articles

RING-box proteins regulate leaf senescence and stomatal closure via repression of ABA transporter gene ABCG40.

Plant hormone abscisic acid (ABA) plays an indispensable role in the control of leaf senescence, during which ABA signaling depends on its biosynthesis. Nevertheless, the role of ABA transport in leaf senescence remains unknown. Here, we identified two novel RING-box protein-encoding genes UBIQUITIN LIGASE of SENESCENCE 1 and 2 (ULS1 and ULS2) involved in leaf senescence. Lack of ULS1 and ULS2 accelerates leaf senescence, which is specifically promoted by ABA treatment. Furthermore, the expression of senescence-related genes is significantly affected in mature leaves of uls1/uls2 double mutant (versus wild type (WT)) in an ABA-dependent manner, and the ABA content is substantially increased. ULS1 and ULS2 are mainly expressed in the guard cells and aging leaves, and the expression is induced by ABA. Further RNA-seq and quantitative proteomics of ubiquitination reveal that ABA transporter ABCG40 is highly expressed in uls1/uls2 mutant versus WT, though it is not the direct target of ULS1/2. Finally, we show that the acceleration of leaf senescence, the increase of leaf ABA content, and the promotion of stomatal closure in uls1/usl2 mutant are suppressed by abcg40 loss-of-function mutation. These results indicate that ULS1 and ULS2 function in feedback inhibition of ABCG40-dependent ABA transport during ABA-induced leaf senescence and stomatal closure.

H2O2 participates in ABA regulation of grafting-induced chilling tolerance in cucumber.

Rootstock provides more abscisic acid (ABA) content to scions to increase the chilling tolerance of seedlings. H2O2 is involved in ABA regulation of grafting-induced chilling tolerance of cucumber. Here we examined the role of ABA in the response of grafted cucumber to chilling stress. The data showed chilling induced an increase in leaf and root ABA content and there was a positive correlation between ABA content and the chilling tolerance of the varieties. The increase of ABA content and NCED mRNA abundance in the leaf of both Cs/Cs (self-root) and Cs/Cm (grafted with pumpkin as rootstock) showed a delay under aerial stress compared with those under whole plant and root-zone stress. Intriguingly, an increase in ABA in xylem was found under whole-plant and root-zone chilling stress but was not detected under aerial stress, implying the increases in ABA content in leaves were mainly from root ABA transportation. Compared to Cs/Cs, a higher ABA content and NCED mRNA abundance were observed in Cs/Cm, which showed that Cm could output more ABA than Cs. The removal of endogenous ABA decreased the difference in chilling tolerance induced by Cm, as evidenced by the observed similar oxidative stress levels and photosynthetic capacity between Cs/Cs and Cs/Cm after chilling stress. Moreover, we found that the H2O2 signal in grafted cucumber could respond to chilling stress earlier than the H2O2 signal in self-rooted cucumber. The inhibition of endogenous H2O2 decreased the chilling tolerance of grafted cucumber induced by ABA by reducing photosynthesis and the mRNA abundance of CBF1 and COR. Thus, our results indicate that H2O2, as the downstream signal, participated in the rootstock-induced chilling tolerance of grafted seedlings induced by ABA.

Stomatal behaviour and endogenous phytohormones promotes intrinsic water use efficiency differently in cotton under drought

The coordination between phytohormones regulation, stomatal behaviour (stomatal index and opening/closing) and gas exchange are potent determinants of plant survival under drought stress. However, we found a knowledge gap in the mechanism regulating the fine-tuning of these features during drought. In order to address this we evaluated gas exchange, stomatal behaviour and endogenous phytohormones content in two cotton varieties (LRA-5166 and NBRI-67) differing in drought sensitivity during water deficit conditions. Variety specific differences were recorded in net photosynthesis rate (A), transpiration rate (E) and stomatal conductance (gs) with significantly less decrease in drought tolerant LRA-5166 than drought sensitive NBRI-67. The abscisic acid (ABA) accumulation was significantly increased in LRA-5166 while reduced in NBRI-67 under water deficit, which was accompanied by relatively less reduced 6-benzylaminopurine (6-BAP) level in LRA-5166 than NBRI-67.Thus, improved ABA/6-BAP ratio was observed in both the varieties of cotton. Critically, LRA- 5166 has reduced stomatal index, aperture size and significantly higher A and intrinsic water use efficiency (WUEi), thus higher drought tolerance than NBRI-67. Furthermore, we found that endogenous ABA predominantly maintains the stomatal behaviour and regulates its physiology either by antagonizing 6-BAP or alone to coordinate with water deficit signals. Overall, our findings describe a new insight as to how drought modulates endogenous ABA and 6-BAP homeostasis in cotton leaf and the mechanism of stomatal regulation by ABA and 6-BAP in cotton.

Nanopotassium, Nanosilicon, and Biochar Applications Improve Potato Salt Tolerance by Modulating Photosynthesis, Water Status, and Biochemical Constituents

Salinity is one of the main environmental stresses, and it affects potato growth and productivity in arid and semiarid regions by disturbing physiological process, such as the photosynthesis rate, the absorption of essential nutrients and water, plant hormonal functions, and vital metabolic pathways. Few studies are available on the application of combined nanomaterials to mitigate salinity stress on potato plants (Solanum tuberosum L. cv. Diamont). In order to assess the effects of the sole or combined application of silicon (Si) and potassium (K) nanoparticles and biochar (Bc) on the agro-physiological properties and biochemical constituents of potato plants grown in saline soil, two open-field experiments were executed on a randomized complete block design (RCBD), with five replicates. The results show that the biochar application and nanoelements (n-K and n-Si) significantly improved the plant heights, the fresh and dry plant biomasses, the numbers of stems/plant, the leaf relative water content, the leaf chlorophyll content, the photosynthetic rate (Pn), the leaf stomatal conductance (Gc), and the tuber yields, compared to the untreated potato plants (CT). Moreover, the nanoelements and biochar improved the content of the endogenous elements of the plant tissues (N, P, K, Mg, Fe, Mn, and B), the leaf proline, and the leaf gibberellic acid (GA3), in addition to reducing the leaf abscisic acid content (ABA), the activity of catalase (CAT), and the peroxidase (POD) and polyphenol oxidase (PPO) in the leaves of salt-stressed potato plants. The combined treatment achieved maximum plant growth parameters, physiological parameters, and nutrient concentrations, and minimum transpiration rates (Tr), leaf abscisic acid content (ABA), and activities of the leaf antioxidant enzymes (CAT, POD, and PPO). Furthermore, the combined treatment also showed the highest tuber yield and tuber quality, including the contents of carbohydrates, proteins, and the endogenous nutrients of the tuber tissues (N, P, and K), and the lowest starch content. Moreover, Pearson’s correlation showed that the plant growth and the tuber yields of potato plants significantly and positively correlated with the photosynthesis rate, the internal CO2 concentration, the relative water content, the proline, the chlorophyll content, and the GA3, and that they were negatively correlated with the leaf Na content, PPO, CAT, ABA, MDA, and Tr. It might be concluded that nanoelement (n-K and n-Si) and biochar applications are a promising method to enhance the plant growth and crop productivity of potato plants grown under salinity conditions.

Long-distance control of pumpkin rootstock over cucumber scion under drought stress as revealed by transcriptome sequencing and mobile mRNAs identifications.

Grafting with pumpkin rootstock is commonly used not only to improve the quality of cucumber fruits but also to confer biotic or abiotic stress tolerance. However, the molecular mechanism of the response of grafted cucumbers to drought stress and the possible roles of mobile mRNAs in improving stress tolerance have remained obscure. Hence, we conducted transcriptome sequencing and combined it with morphophysiological experiments to compare the response of homografts (cucumber as scion and rootstock) and heterografts (cucumber as scion and pumpkin as rootstock) to drought stress. After applying drought stress, homografts and heterografts expressed 2960 and 3088 genes, respectively, in response to the stress. The differentially expressed genes identified in heterografts under drought stress were categorized into different stress-responsive groups, such as carbohydrate metabolism (involved in osmotic adjustment by sugar accumulation), lipid and cell wall metabolism (involved in cell membrane integrity by a reduction in lipid peroxidation), redox homeostasis (increased antioxidant enzyme activities), phytohormone (increased abscisic acid content), protein kinases, and transcription factors, using MapMan software. Earlier and greater H2O2 accumulation in xylem below the graft union was accompanied by leaf abscisic acid accumulation in heterografts in response to drought stress. Greater leaf abscisic acid helped heterografted cucumbers to sense and respond to drought stress earlier than homografts. The timely response of heterografts to drought stress led to the maintenance of higher water content in the leaves even in the late stage of drought stress. The mobile mRNAs identified in heterografts were mostly related to photosynthesis, which would be the possible reason for improved chlorophyll content and maximum photochemical efficiency of photosystem II (Fv/Fm). The existence of some stress-responsive pumpkin (rootstock) mRNAs in cucumber (scion), such as heat shock protein (HSP70, a well-known stress-responsive gene), led to higher proline accumulation than in homografts. Expression of mobile and immobile stress-responsive mRNAs and timely response of heterografts to drought stress could improve drought tolerance in pumpkin-rooted plants.

Exogenous Abscisic Acid Priming Modulates Water Relation Responses of Two Tomato Genotypes With Contrasting Endogenous Abscisic Acid Levels to Progressive Soil Drying Under Elevated CO2.

Plants have evolved multiple strategies to survive and adapt when confronting the changing climate, including elevated CO2 concentration (e[CO2]) and intensified drought stress. To explore the role of abscisic acid (ABA) in modulating the response of plant water relation characteristics to progressive drought under ambient (a[CO2], 400 ppm) and e[CO2] (800 ppm) growth environments, two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (AC) and its ABA-deficient mutant (flacca), were grown in pots, treated with or without exogenous ABA, and exposed to progressive soil drying until all plant available water in the pot was depleted. The results showed that exogenous ABA application improved leaf water potential, osmotic potential, and leaf turgor and increased leaf ABA concentrations ([ABA]leaf) in AC and flacca. In both genotypes, exogenous ABA application decreased stomatal pore aperture and stomatal conductance (gs), though these effects were less pronounced in e[CO2]-grown AC and gs of ABA-treated flacca was gradually increased until a soil water threshold after which gs started to decline. In addition, ABA-treated flacca showed a partly restored stomatal drought response even when the accumulation of [ABA]leaf was vanished, implying [ABA]leaf might be not directly responsible for the decreased gs. During soil drying, [ABA]leaf remained higher in e[CO2]-grown plants compared with those under a[CO2], and a high xylem sap ABA concentration was also noticed in the ABA-treated flacca especially under e[CO2], suggesting that e[CO2] might exert an effect on ABA degradation and/or redistribution. Collectively, a fine-tune ABA homeostasis under combined e[CO2] and drought stress allowed plants to optimize leaf gas exchange and plant water relations, yet more detailed research regarding ABA metabolism is still needed to fully explore the role of ABA in mediating plant physiological response to future drier and CO2-enriched climate.

Root endophytic fungus Piriformospora indica and zinc attenuate cold stress in grapevine by influencing leaf phytochemicals and minerals content

The effects of Piriformospora indica (Pi) inoculation and zinc (Zn) soil- application on mitigation of cold stress in grapevine (Vitis vinifera L. cv Sultana) plants were investigated. Fungal mycelium (1% w/v) suspension was added to each cutting and Zn (5.0 mg/l Zn-EDTA) applied to each pot every 15 day. At the end of experiment, half of the pots (control and Pi and Zn-treated vines) were subjected to 4 °C for 24 h. The remaining vines in each treatment group were kept at 24 °C. Cold stress (4 °C) markedly decrease leaf photosynthetic pigments and relative water content however, Pi and Zn resulted in higher stability of photosynthetic pigments and higher relative water content in treated vines compared to control vines. Cold stress increased leaf electrolyte leakage (EL), lipid peroxidation and hydrogen peroxide contents in vines, whereas Pi colonization and Zn treatments considerably reduced their levels. Moreover, leaf superoxide dismutase, catalase, guaiacol peroxidase, and ascorbate peroxidase activities markedly increased in Pi- and Zn-treated vines under cold stress. Decreasing the temperature from 24 to 4 °C increased leaf abscisic acid (ABA), polyamines (PAs), soluble carbohydrate, proline, soluble proteins and total phenol content in all vines. However, vines treated with Pi + Zn showed marked increases in these compounds compared to control vines under cold stress. The leaf nutrient content of vines under low temperature stress decreased compared to those grown at 24 °C. However, this decrease in leaf nutrient was affected lesser in vines inoculated with Pi and Zn. Therefore, application of Pi and Zn allowed chilled vines to absorb higher nutrient during normal temperatures, enabling them to attenuate cold stress by increase in osmoregulants, antioxidant enzymes activity and plant growth regulators (ABA and PAs) in their tissues.

Effects of salt stress on plant growth, abscisic acid and salicylic acid in own-rooted cultivars of Vitis vinifera L.

Aim of study: In most areas of vineyards worldwide, cultivars are frequently grafted on specific rootstocks to avoid Daktulosphaira vitifoliae pest attack. Nevertheless, the absence of this pest in Canary Islands allowed the chance to conserve and cultivate traditional or new own-rooted genotypes without the requirement of the rootstocks. To investigate the responses of own-rooted genotypes of Vitis vinifera L. to salt stress conditions, ‘Castellana Negra’ (‘CN’) and ‘Negramoll’ (‘Ne’) were used with the aim to characterize their morphological and physiological responses.Area of study: Canary Islands, Spain.Material and methods: The effects of NaCl stress on growth, abscisic acid (ABA), salicylic acid (SA) and proline were assessed in ‘CN’ and ‘Ne’ under greenhouse conditions.Main results: In ‘CN’, the decrease of leaf number in stressed plants was lower and started eleven days later than in ‘Ne’. Salt stress also reduced stomatal conductance (gs), although such decrease took place earlier in ‘CN’ than in ‘Ne’. ABA and SA concentrations in ‘CN’ leaves were 2-fold higher than those of ‘Ne’. Salt stress increased leaf ABA and SA content in both genotypes, compared to control. In conclusion, ABA and SA appear to be involved in grapevines responses to salinity and suggest that exogenous SA could be useful to mitigate the stress impacts.Research highlights: ‘CN’ exhibited a better response than ‘Ne’ through the delay of salt injury establishment, and the dissimilar responses between ‘CN’ and ‘Ne’ seem to be associated to the higher accumulation of ABA and SA under salt stress.

Agronomic and physiological responses of potato subjected to soil compaction and/or drying

AbstractCompact and dry soils impede root growth and restrict plant water availability, respectively, potentially causing leaf water deficit. Although both stresses likely co‐occur in the field and limit yield, little is known about their combined impact on plant growth and physiology over a whole season, especially in a tuberous crop like potato. Field‐grown potato (Solanum tuberosum L. var. 'Maris Piper') was exposed to factorial combination of deficit irrigation (watering when soil moisture deficit reached 60 vs. 25 mm) and soil compaction (compacted with heavy machinery vs. uncompacted), with plant growth and leaf physiology measured weekly. Shoot growth was restricted by adverse soil conditions, while leaf water status, photosynthesis rates and leaf abscisic acid (ABA) levels did not vary significantly between treatments. Across all treatments, final yield was linearly correlated (R2 = 0.71) to mid‐season shoot biomass. Compared to well‐watered plants growing in loose soil, soil compaction, deficit irrigation and their combination decreased final tuber yield similarly, by 23%–34%. Surprisingly, tuber size distribution was more dependent on irrigation management than on soil strength. Plants exposed to deficit irrigation produced more, smaller potatoes than their respective control. Thus, low soil water availability and/or compact soil caused these field‐grown potatoes to restrict shoot growth rather than limit leaf gas exchange. Further research is needed to understand the role of hormonal signalling in regulating tuber growth when plants are exposed to compact and dry soils.

NCED expression is related to increased ABA biosynthesis and stomatal closure under aluminum stress

Aluminum (Al)-induced decrease in leaf hydration has been associated with low gas exchange, especially stomatal conductance (gs). However, the mechanisms explaining these responses are unclear. Citrus limonia was exposed to 0 and 1480 μM Al in nutrient solution for 90 days to test whether the low gs and leaf hydration in plants exposed to Al is associated with increased 9-cis-epoxycarotenoid dioxygenase (NCED) gene expression and abscisic acid (ABA) biosynthesis. Relative leaf water content (RWC), water potential (Ψw) and gas exchange in the leaves, as well as leaf and root ClNCED3, ClNCED1 and ClNCED5 expression and accumulation of ABA and its metabolites (phaseic acid, dihydrophaseic acid, (+)-7′-hydroxy-ABA and ABA-β-d-glucosyl ester) were measured. Aluminum up-regulated ClNCED3 and induced ABA accumulation in the roots before impairments in leaf water status (low Ψw, RWC and gs) could be observed. Leaf ABA concentration increased from 7 to 90 days and this could be partially explained by the up-regulation of ClNCED3, ClNCED1 and ClNCED5 in this organ. Stomatal closure occurred concomitantly with the increase of ABA concentration, and this result provides further evidence of the role of ABA modulation of plant hydration under Al stress.

НАКОПЛЕНИЕ, РАСПРЕДЕЛЕНИЕ И ФУНКЦИОНАЛЬНАЯ РОЛЬ АБК ПРИ КРАТКОВРЕМЕННОМ ДЕЙСТВИИ ЗАСОЛЕНИЯ НА РАСТЕНИЯ ПШЕНИЦЫ

Local effects on plant roots or shoots are accompanied by a change of plant hormones concentration providing signal transduction in plants and their adaptation to changing environmental conditions. It is known that plants respond to drought stress by increasing the concentration of abscisic acid (ABA) in xylem sap which leads to decrease in stomatal conductance to prevent plant water loss from transpirational pathways. Earlier, we found a rapid leaf ABA accumulation in barley and wheat plants under influence of the shortterm salinity. However, the mechanism of the salt stress induced rapid accumulation of abscisic acid in plant leaves remained unclear. The aim of this study was to investigate whether the salt-induced rapid accumulation of abscisic acid in the leaves was the result of its inflow from the roots (as a root signal). In our experiments the short-term salinity did not increase but decreased the concentration of abscisic acid in xylem sap of wheat plants. Thus, detected accumulation of ABA in the leaves did not result from an increase in its inflow from the roots. Apparently leaf ABA accumulation already detected in 15 min after the onset of salinity stress could be a local reaction due to its metabolism in the shoot itself. The decrease in the leaf water potential could induce the change of abscisic acid metabolism pathways in the shoot that led to the accumulation of this hormone. A small short-term accumulation of ABA in the roots did not lead to an increase in their hydraulic conductivity.

Effect of deficit irrigation scheduling and planting pattern on leaf water status and radiation use efficiency of winter wheat

AbstractDrought and water shortages have always been great challenges for agricultural production in the North China Plain. To explore appropriate irrigation regimes and planting patterns in this area, a field experiment was conducted for winter wheat (Triticum aestivum L.) from 2014 to 2016. Three irrigation treatments of 50 mm irrigation at growth stage of jointing (GS34) and heading (GS48, W1), 100 mm irrigation at GS34 (W2) and 100 mm irrigation at GS34 and GS48 (W3) combined with uniform (U), double–double (DD) and furrow‐ridge (F) planting patterns were designed. The tillers number, leaf water status, spike characteristics and radiation use efficiency (RUE) were measured. Results showed that compared with W2, W3 significantly reduced leaf abscisic acid (ABA) content and increased tillers number, spikelets spike−1, yield components and RUE, while W1 produced more tillers number, leaf relative water content (LRWC) and water potential (Lψ) only in the late growth stage, yield components and RUE. The DD significantly increased tillers number, LRWC, Lψ, leaf osmotic potential, spike length, spikes m−2, grains spike−1 and RUE, and reduced the ABA content compared with U. Considering the serious water shortage in the North China Plain, 50 mm irrigation at jointing and heading stages combined with DD is a worthy cultivation measure for sustainable agriculture at water‐deficit condition.

Effects of Plant Growth Promoting Rhizobacteria on the Content of Abscisic Acid and Salt Resistance of Wheat Plants.

Although salinity inhibits plant growth, application of appropriate rhizosphere bacteria can diminish this negative effect. We studied one possible mechanism that may underlie this beneficial response. Wheat plants were inoculated with Bacillus subtilis IB-22 and Pseudomonas mandelii IB-Ki14 and their consequences for growth, water relations, and concentrations of the hormone abscisic acid (ABA) were followed in the presence of soil salinity. Salinity alone increased ABA concentration in wheat leaves and roots and this was associated with decreased stomatal conductance, but also with chlorophyll loss. Bacterial treatment raised ABA concentrations in roots, suppressed accumulation of leaf ABA, decreased chlorophyll loss, and promoted leaf area and transpiration. However, water balance was maintained due to increased water uptake by inoculated plants, brought about in part by a larger root system. The effect may be the outcome of ABA action since the hormone is known to maintain root extension in stressed plants. Root ABA concentration was highest in salt-stressed plants inoculated with B. subtilis and this contributed to greater root hydraulic conductivity. We conclude that bacteria can raise salt resistance in wheat by increasing root ABA, resulting in larger root systems that can also possess enhanced hydraulic conductivity thereby supporting better-hydrated leaves.

Physiological and transcriptional responses of Alternaria alternata induced abnormal leaf senescence in Pyrus pyrifolia

In the Yangtze Valley of China, Pyrus pyrifolia is known by the name sand pear and often suffers abnormal, early leaf senescence and premature defoliation, which causes serious yield loss and poor fruit quality. In this study, the relationship of Alternaria alternata with abnormally senesced leaves (ASLs) was analyzed by physiological and molecular method. Using data from the P. pyrifolia cultivars ‘Huanghua’ and ‘Suisho’, we found that A. alternata inoculation caused early leaf senescence. Restricted foliar nutrient redistributions were observed in ASLs, such as nitrogen (N) and phosphorus (P). Higher abscisic acid (ABA) levels were induced in the tissues of the leaf mesophyll, veins and stalks of ASLs, and higher concentrations of indole-3-acetic acid (IAA) and H2O2 were induced in the tissues of leaf mesophylls and veins of ASLs, while an opposite trend was observed in the tissues of leaf veins. Quantitative real-time PCR (qRT-PCR) consistently demonstrated that ASLs upregulated the expression of ABA biosynthesis genes (e.g., PyNCED3, PyZEP and PyAAO3), and the catabolism gene (PyABA8′OH), whereas PyBG and PyDXS showed opposite trends. Based on the leaf senescence database (LSD) 3.0, 42 senescence-associated genes (SAGs) that induced differential expression by A. alternata inoculations were enriched for P. pyrifolia cv. ‘Hongfeng’, which has high susceptibility to A. alternata and readily exhibits early leaf senescence. These results showed that A. alternata infection is one of major factors for abnormal leaf senescence and ABA signaling involved in this pathogenic process.

Significance of root hairs for plant performance under contrasting field conditions and water deficit.

Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in a less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder's dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

Ozone impairs the response of isoprene emission to foliar nitrogen and phosphorus in poplar

Tropospheric ozone (O3) impairs physiological processes of plants while nitrogen (N) deposition may cause imbalances in soil N and other nutrients such as phosphorus (P) suggesting an increase of P demand for plants. However, the combined effect of O3, soil N and P on isoprene emission from leaves has never been tested. We therefore examined isoprene emission in leaves of Oxford poplar clone exposed to O3 (ambient, AA [35.0 nmol mol−1 as daily mean]; 1.5 × AA; 2.0 × AA), soil N (0 and 80 kg N ha−1) and soil P (0, 40 and 80 kg P ha−1) in July and September in a Free-Air Controlled Exposure (FACE) facility. We also investigated the response of isoprene emission to foliar N, P and abscisic acid (ABA) contents in September because the 2-C-methylerythritol-5-phosphate (MEP) pathway of isoprenoid biosynthesis produces ABA. We found that O3 increased isoprene emission in July, which was associated to increased dark respiration, suggesting an activation of metabolism against O3 stress as an initial response. However, O3 decreased isoprene emission in September which was associated to reduced net photosynthesis. In September, isoprene emission was positively correlated with leaf N content and negatively correlated with leaf P content in AA. However, no response of isoprene emission to foliar N and P was found in elevated O3, suggesting that the isoprene responses to foliar N and P depended on the O3 exposure levels. Isoprene emission rate in 1.5 × AA and 2.0 × AA increased with increasing leaf ABA content, indicating accelerated senescence of injured leaves to favor new leaf growth when high O3 and nutritional availability in the soil were combined. Even though foliar N and P usually act as a proxy for isoprene emission rate, the impact of recent abiotic factors such as O3 should be always considered for modeling isoprene emission under climate change.

Phytohormone signaling pathway for eliciting leaf phenolic synthesis in honeysuckle (Lonicera japonica Thunb.) under coastal saline environment

To date, it remains unclear how saline stress induces leaf phenolic synthesis in honeysuckle (Lonicera japonica Thunb.), a traditional Chinese medicinal crop. This study was to investigate hormone signaling for salt-induced leaf phenolic synthesis in honeysuckle from molecular, physiological and ecological levels by pot experiments and field trials. As a major ingredient of soil salinity in coastal land, NaCl was used in salt treatment for simulating coastal saline environment. NaCl stress significantly increased leaf abscisic acid (ABA) and salicylic acid (SA) concentrations, potentiated leaf phenolic synthesis by elevating phenylalanine ammonia-lyase (PAL) activity and PALs transcription, and enhanced leaf phenolic accumulation. Under NaCl stress, tungstate and paclobutrazol pretreatments inhibited leaf ABA and SA accumulation, respectively, and lowered PAL activity, PALs transcription, and phenolic accumulation. Thus, ABA and SA participated in transducing salt-induced leaf phenolic synthesis. Paclobutrazol pretreatment hardly influenced leaf ABA concentration in salt-treated plants, but tungstate pretreatment abated salt-induced leaf SA accumulation, indicating that ABA was an upstream signal of SA. Under NaCl stress, SA application restored leaf SA level with no effect on ABA level but incompletely restored PAL activity and phenolic accumulation in tungstate-pretreated plants, confirming the downstream role of SA and implying the existence of other downstream signals. Leaf ABA and SA concentrations were higher in plants in coastal saline plots than non-saline plots, and the roles of ABA and SA in mediating salt-induced leaf phenolic synthesis passed ecological test, according to a significant positive correlation of leaf ABA and SA levels with phenolic concentration. In conclusion, ABA acted as an upstream signal of SA to elicit leaf phenolic synthesis in honeysuckle under coastal saline environment.

Activities of leaf and spike carbohydrate-metabolic and antioxidant enzymes are linked with yield performance in three spring wheat genotypes grown under well-watered and drought conditions

BackgroundTo improve our understanding about the physiological mechanism of grain yield reduction at anthesis, three spring wheat genotypes [L1 (advanced line), L2 (Vorobey) and L3 (Punjab-11)] having contrasting yield potential under drought in field were investigated under controlled greenhouse conditions, drought stress was imposed at anthesis stage by withholding irrigation until all plant available water was depleted, while well-watered control plants were kept at 95% pot water holding capacity.ResultsCompared to genotype L1 and L2, pronounced decrease in grain number (NGS), grain yield (GY) and harvest index (HI) were found in genotype L3, mainly due to its greater kernel abortion (KA) under drought. A significant positive correlation of leaf monodehydroascorbate reductase (MDHAR) with both NGS and HI was observed. In contrast, significant negative correlations of glutathione S-transferase (GST) and vacuolar invertase (vacInv) both within source and sink were found with NGS and HI. Likewise, a significant negative correlation of leaf abscisic acid (ABA) with NGS was noticed. Moreover, leaf aldolase and cell wall peroxidase (cwPOX) activities were significantly and positively associated with thousand kernel weight (TKW).ConclusionDistinct physiological markers correlating with yield traits and higher activity of leaf aldolase and cwPOX may be chosen as predictive biomarkers for higher TKW. Also, higher activity of MDHAR within the leaf can be selected as a predictive biomarker for higher NGS in wheat under drought. Whereas, lower activity of vacInv and GST both within leaf and spike can be selected as biomarkers for higher NGS and HI. The results highlighted the role of antioxidant and carbohydrate-metabolic enzymes in the modulation of source-sink balance in wheat crops, which could be used as bio-signatures for breeding and selection of drought-resilient wheat genotypes for a future drier climate.

Rhizobacteria Inoculation Effects on Phytohormone Status of Potato Microclones Cultivated In Vitro under Osmotic Stress

Water deficits inhibit plant growth and decrease crop productivity. Remedies are needed to counter this increasingly urgent problem in practical farming. One possible approach is to utilize rhizobacteria known to increase plant resistance to abiotic and other stresses. We therefore studied the effects of inoculating the culture medium of potato microplants grown in vitro with Azospirillum brasilense Sp245 or Ochrobactrum cytisi IPA7.2. Growth and hormone content of the plants were evaluated under stress-free conditions and under a water deficit imposed with polyethylene glycol (PEG 6000). Inoculation with either bacterium promoted the growth in terms of leaf mass accumulation. The effects were associated with increased concentrations of auxin and cytokinin hormones in the leaves and stems and with suppression of an increase in the leaf abscisic acid that PEG treatment otherwise promoted in the potato microplants. O. cytisi IPA7.2 had a greater growth-stimulating effect than A. brasilense Sp245 on stressed plants, while A. brasilense Sp245 was more effective in unstressed plants. The effects were likely to be the result of changes to the plant’s hormonal balance brought about by the bacteria.

Differences in carbon and nitrogen metabolism between male and female Populus cathayana in response to deficient nitrogen.

Sexual dimorphism occurs regarding carbon and nitrogen metabolic processes in response to nitrogen supply. Differences in fixation and remobilization of carbon and allocation and assimilation of nitrogen between sexes may differ under severe defoliation. The dioecious species Populus cathayana was studied after two defoliation treatments with two N levels. Males had a higher capacity of carbon fixation because of higher gas exchange and fluorescence traits of leaves after severe long-term defoliation under deficient N. Males had higher leaf abscisic acid, stomatal conductance and leaf sucrose phosphate synthase activity increasing transport of sucrose to sinks. Males had a higher carbon sink than females, because under N-deficient conditions, males accumulated >131.10% and 90.65% root starch than males in the control, whereas females accumulated >40.55% and 52.81%, respectively, than females in the control group. Males allocated less non-protein N (NNon-p) to leaves, having higher nitrogen use efficiency (photosynthetic nitrogen use efficiency), higher glutamate dehydrogenase (GDH) and higher leaf GDH expression, even after long-term severe defoliation under deficient N. Females had higher leaf jasmonic acid concentration and NNon-p. The present study suggested that females allocated more carbon and nitrogen to defense chemicals than males after long-term severe defoliation under deficient N.