Evaluation of drought-tolerant varieties based on root system architecture in cotton (Gossypium hirsutum L.).

BACKGROUND: Root system architecture (RSA) exhibits significant genetic variability and is closely associated with drought tolerance. However, the evaluation of drought-tolerant cotton cultivars based on RSA in the field conditions is still underexplored. RESULTS: So, this study conducted a comprehensive analysis of drought tolerance based on physiological and morphological traits (i.e., aboveground and RSA, and yield) within a rain-out shelter, with two water treatments: well-watered (75 ± 5% soil relative water content) and drought stress (50 ± 5% soil relative water content). The results showed that principal component analysis identified six principal components, including highlighting the importance of root traits and canopy parameters in influencing drought tolerance. Moreover, the systematic cluster analysis was used to classify 80 cultivars into 5 categories, including drought-tolerant cultivars, relatively drought-tolerant cultivars, intermediate cultivars, relatively drought-sensitive cultivars, and drought-sensitive cultivars. Further validation of the drought tolerance index showed that the yield drought tolerance index and biomass drought tolerance index of the drought-tolerant cultivars were 8.97 and 5.05 times higher than those of the drought-sensitive cultivars, respectively. CONCLUSIONS: The RSA of drought-tolerant cultivars was characterised by a significant increase in average length-all lateral roots, a significant decrease in average lateral root emergence angle and a moderate root/shoot ratio. In contrast, the drought-sensitive cultivars showed a significant decrease in average length-all lateral roots and a significant increase in both average lateral root emergence angle and root/shoot ratio. It is therefore more comprehensive and accurate to assess field crop drought tolerance by considering root performance.

Xylem conduit deformation across vascular plants: an evolutionary spandrel or protective valve?

The hydraulic system of vascular plants and its integrity is essential for plant survival. To transport water under tension, the walls of xylem conduits must approximate rigid pipes. Against this expectation, conduit deformation has been reported in the leaves of a few species and hypothesized to function as a 'circuit breaker' against embolism. Experimental evidence is lacking, and its generality is unknown. We demonstrated the role of conduit deformation in protecting the upstream xylem from embolism through experiments on three species and surveyed a diverse selection of vascular plants for conduit deformation in leaves. Conduit deformation in minor veins occurred before embolism during slow dehydration. When leaves were exposed to transient increases in transpiration, conduit deformation was accompanied by large water potential differences from leaf to stem and minimal embolism in the upstream xylem. In the three species tested, collapsible vein endings provided clear protection of upstream xylem from embolism during transient increases in transpiration. We found conduit deformation in diverse vascular plants, including 11 eudicots, ginkgo, a cycad, a fern, a bamboo, and a grass species, but not in two bamboo and a palm species, demonstrating that the potential for 'circuit breaker' functionality may be widespread across vascular plants.

You are what you eat: nutrient and water relations between mistletoes and hosts.

Mistletoes play important roles in biogeochemical cycles. Although many studies have compared nutrient concentrations between mistletoes and their hosts, no general patterns have been found and the nutrient uptake mechanisms in mistletoes have not been fully resolved. To address the water and nutrient relations in mistletoes compared with their hosts, we measured 11 nutrient elements, two isotope ratios and two leaf morphological traits for 11 mistletoe and 104 host species from four sites across a large environmental gradient in southwest China. Mistletoes had significantly higher phosphorus, potassium, and boron concentrations, nitrogen isotope ratio, and lower carbon isotope ratio (δ13 C) indicative of lower water-use efficiency than hosts, but other elements were similar to those in hosts. Sites explained most of the variation in the multidimensional trait space. With increasing host nitrogen concentration, both mistletoe δ13 C and the difference between mistletoe and host δ13 C increased, providing evidence to support the 'nitrogen parasitism hypothesis'. Host nutrient concentrations were the best predictors for that of the mistletoe nutrient elements in most cases. Our results highlight the important roles of environmental conditions and host nutrient status in determining mistletoe nutrient pools, which together explain their trophic interactions with hosts in subtropical and tropical ecosystems.

Cell- and noncell-autonomous AUXIN RESPONSE FACTOR3 controls meristem proliferation and phyllotactic patterns.

In cell-cell communication, noncell-autonomous transcription factors play vital roles in controlling plant stem cell fate. We previously reported that AUXIN RESPONSE FACTOR3 (ARF3), a member of the ARF family with critical roles in floral meristem maintenance and determinacy, has a distinct accumulation pattern that differs from the expression domain of its encoding gene in the shoot apical meristem (SAM). However, the biological meaning of this difference is obscure. Here, we demonstrate that ARF3 expression in Arabidopsis (Arabidopsis thaliana) is mainly activated at the periphery of the SAM by auxin where ARF3 cell autonomously regulates the expression of meristem-organ boundary-specific genes, such as CUP-SHAPED COTYLEDON1-3 (CUC1-3), BLADE ON PETIOLE1-2 (BOP1-2), and TARGETS UNDER ETTIN CONTROL3 (TEC3) to regulate the arrangement of organs in regular pattern, a phenomenon referred to as phyllotaxis. We also show that ARF3 is translocated into the organizing center where it represses cytokinin activity and WUSCHEL expression to regulate meristem activity noncell-autonomously. Therefore, ARF3 acts as a molecular link that mediates the interaction of auxin and cytokinin signaling in the SAM while coordinating the balance between meristem maintenance and organogenesis. Our findings reveal an ARF3-mediated coordination mechanism through cell-cell communication in dynamic SAM maintenance.

An exploratory steady-state redox model of photosynthetic linear electron transport for use in complete modelling of photosynthesis for broad applications.

A photochemical model of photosynthetic electron transport (PET) is needed to integrate photophysics, photochemistry, and biochemistry to determine redox conditions of electron carriers and enzymes for plant stress assessment and mechanistically link sun-induced chlorophyll fluorescence to carbon assimilation for remotely sensing photosynthesis. Towards this goal, we derived photochemical equations governing the states and redox reactions of complexes and electron carriers along the PET chain. These equations allow the redox conditions of the mobile plastoquinone pool and the cytochrome b6 f complex (Cyt) to be inferred with typical fluorometry. The equations agreed well with fluorometry measurements from diverse C3 /C4 species across environments in the relationship between the PET rate and fraction of open photosystem II reaction centres. We found the oxidation of plastoquinol by Cyt is the bottleneck of PET, and genetically improving the oxidation of plastoquinol by Cyt may enhance the efficiency of PET and photosynthesis across species. Redox reactions and photochemical and biochemical interactions are highly redundant in their complex controls of PET. Although individual reaction rate constants cannot be resolved, they appear in parameter groups which can be collectively inferred with fluorometry measurements for broad applications. The new photochemical model developed enables advances in different fronts of photosynthesis research.

Leaves as bottlenecks: The contribution of tree leaves to hydraulic resistance within the soil-plant-atmosphere continuum.

Within vascular plants, the partitioning of hydraulic resistance along the soil-to-leaf continuum affects transpiration and its response to environmental conditions. In trees, the fractional contribution of leaf hydraulic resistance (Rleaf ) to total soil-to-leaf hydraulic resistance (Rtotal ), or fRleaf (=Rleaf /Rtotal ), is thought to be large, but this has not been tested comprehensively. We compiled a multibiome data set of fRleaf using new and previously published measurements of pressure differences within trees in situ. Across 80 samples, fRleaf averaged 0.51 (95% confidence interval [CI] = 0.46-0.57) and it declined with tree height. We also used the allometric relationship between field-based measurements of soil-to-leaf hydraulic conductance and laboratory-based measurements of leaf hydraulic conductance to compute the average fRleaf for 19 tree samples, which was 0.40 (95% CI = 0.29-0.56). The in situ technique produces a more accurate descriptor of fRleaf because it accounts for dynamic leaf hydraulic conductance. Both approaches demonstrate the outsized role of leaves in controlling tree hydrodynamics. A larger fRleaf may help stems from loss of hydraulic conductance. Thus, the decline in fRleaf with tree height would contribute to greater drought vulnerability in taller trees and potentially to their observed disproportionate drought mortality.

Mixed infections with new emerging viruses associated with jujube mosaic disease.

BACKGROUND: Jujube is an economically important fruit tree and native to China. Viral disease is a new threat to jujube production, and several new viruses have been identified infecting jujube plants. During our field survey, jujube mosaic disease was widely distributed in Beijing, but the associated causal agents are still unknown. METHODS: Small RNA deep sequencing was conducted to identify the candidate viruses associated with jujube mosaic. Further complete genome sequences of the viruses were cloned, and the genomic characterization of each virus was analyzed. The field distribution of these viruses was further explored with PCR/RT-PCR detection of field samples. RESULTS: Mixed infection of four viruses was identified in a plant sample with the symptom of mosaic and leaf twisting, including the previously reported jujube yellow mottle-associated virus (JYMaV), persimmon ampelovirus (PAmpV), a new badnavirus tentatively named jujube-associated badnavirus (JaBV), and a new secovirus tentatively named jujube-associated secovirus (JaSV). PAmpV-jujube was 14,093 nt in length with seven putative open reading frames (ORFs) and shared highest (79.4%) nucleotide (nt) sequence identity with PAmpV PBs3. Recombination analysis showed that PAmpV-jujube was a recombinant originating from plum bark necrosis stem pitting-associated virus isolates nanjing (KC590347) and bark (EF546442). JaBV was 6449 bp in length with conserved genomic organization typical of badnaviruses. The conserved RT and RNAse H region shared highest 67.6% nt sequence identity with jujube mosaic-associated virus, which was below the 80% nt sequence identity value used as the species demarcation threshold in Badnavirus. The genome of JaSV composed of two RNA molecules of 5878 and 3337 nts in length, excluding the polyA tails. Each genome segment contained one large ORF that shared homology and phylogenetic identity with members of the family Secoviridae. Field survey showed JYMaV and JaBV were widely distributed in jujube trees in Beijing. CONCLUSION: Two new viruses were identified from jujube plants, and mixed infections of JYMaV and JaBV were common in jujube in Beijing.

First report of bean common mosaic virus naturally infecting rice bean (Vigna umbellata) in China.

Rice bean [Vigna umbellata (Thunb.) Ohwi et Ohashi] is a traditional grain legume in Asia. From 2020 and 2021, approximately 15% plants exhibiting virus-like symptoms of mosaic, crumpling, and stunting were observed in two rice bean fields in Changping district, Beijing, China. To unveil the viral agent(s) leading to the disease symptoms, leaf samples from nine symptomatic plants were collected, and used for total RNA extraction with RNAprep pure plant kit (DP432, Tiangen Biotech, Beijing, China). The RNA samples were then subjected to reverse transcription (RT)-PCR testing with degenerate primers targeting the partial NIb gene of potyvirus (Marie-Jeanne et al. 2000) as well as the respective specific primer pairs for 18 viruses that are known to infect Fabaceae crops (Suppl Table S1). While none of the 18 target viruses was detected from any of the samples, a fragment of 327 bp was obtained from each of the diseased leaf samples, but not from healthy plants, with the degenerate potyvirus primer pair. The suspected potyvirus-amplicons were Sanger sequenced at SinoGenMax (SinoGenoMax Co., Ltd. Beijing, China). BLASTn analysis of the sequences showed that they shared 100% nt identity with themselves and 99.1% with the partial NIb gene of bean common mosaic virus (BCMV; Potyvirus; Potyviridae) isolate BCMV-Az (accession no. KP903372). To confirm the BCMV identity of the virus as well as its molecular characteristics, a fragment around 3,388 bp corresponding to NIa, NIb, CP and 3'UTR of BCMV genome was amplified from 4 diseased samples with the primer pair BCMV-F (5'-AGCAAGTCAATTTACAAGGGACTTC-3') and BCMV-R (5'-GGAACAACAAACATTGCCGTAGCTAC-3') (Li et al., 2014). Five independent clones from each diseased sample (20 clones in total) were Sanger sequenced, and all showed 100% identity with each other. One representative sequence has been deposited in GenBank under the accession number OP422522. BLASTn analysis showed that the sequence shares >98% identity with a number of BCMV sequences in GenBank (e.g., 98.9% with KP903372, the isolate BCMV-Az), thus confirming the BCMV identity of the virus. Further analysis of plants (n = 88) resulting from seeds of the 9 abovementioned diseased plants revealed an infection rate of 41% based on symptoms and RT-PCR assay with the degenerate primers, demonstrating the seed transmissibility of the virus in rice bean. The virus isolate is also mechanical transmissible as mechanical inoculation of 10 healthy rice bean plants led to the successful infection of four plants, which showed mosaic symptoms and tested positive for BCMV with RT-PCR assay with BCMV-specific primers reported in Manjunatha et al. (2014). BCMV can infect many leguminous plants, such as azuki bean (Vigna angularis) (Li et al., 2014), yam bean (Pachyrhizus erosus) (Han et al., 2023), and mungbean (Vigna radiata) (Cui et al. 2014). However, to the best of our knowledge, this is the first report that BCMV naturally infects rice bean in China. Further attention should be paid to this emerging viral disease, and proper measures need to be developed and implemented to minimize the spread of the virus in bean crops in the region.

Morphological and Physiological Mechanisms of Melatonin on Delaying Drought-Induced Leaf Senescence in Cotton.

Leaf senescence reduces the photosynthetic capacity of leaves, thus significantly affecting the growth, development, and yield formation of cotton. Melatonin (MT) is a multipotent substance proven to delay leaf senescence. However, its potential mechanism in delaying leaf senescence induced by abiotic stress remains unclear. This study aimed to explore the effect of MT on delaying drought-induced leaf senescence in cotton seedlings and to clarify its morphological and physiological mechanisms. Drought stress upregulated the leaf senescence marker genes, destroyed the photosystem, and led to excessive accumulation of reactive oxygen species (ROS, e.g., H2O2 and O2-), thus accelerating leaf senescence. However, leaf senescence was significantly delayed when 100 µM MT was sprayed on the leaves of the cotton seedlings. The delay was embodied by the increased chlorophyll content, photosynthetic capacity, and antioxidant enzyme activities, as well as decreased H2O2, O2-, and abscisic acid (ABA) contents by 34.44%, 37.68%, and 29.32%, respectively. MT significantly down-regulated chlorophyll degradation-related genes and senescence marker genes (GhNAC12 and GhWRKY27/71). In addition, MT reduced the chloroplast damage caused by drought-induced leaf senescence and maintained the integrity of the chloroplast lamellae structure under drought stress. The findings of this study collectively suggest that MT can effectively enhance the antioxidant enzyme system, improve photosynthetic efficiency, reduce chlorophyll degradation and ROS accumulation, and inhibit ABA synthesis, thereby delaying drought-induced leaf senescence in cotton.

Granal thylakoid structure and function: explaining an enduring mystery of higher plants.

In higher plants, photosystems II and I are found in grana stacks and unstacked stroma lamellae, respectively. To connect them, electron carriers negotiate tortuous multi-media paths and are subject to macromolecular blocking. Why does evolution select an apparently unnecessary, inefficient bipartition? Here we systematically explain this perplexing phenomenon. We propose that grana stacks, acting like bellows in accordions, increase the degree of ultrastructural control on photosynthesis through thylakoid swelling/shrinking induced by osmotic water fluxes. This control coordinates with variations in stomatal conductance and the turgor of guard cells, which act like an accordion's air button. Thylakoid ultrastructural dynamics regulate macromolecular blocking/collision probability, direct diffusional pathlengths, division of function of Cytochrome b6 f complex between linear and cyclic electron transport, luminal pH via osmotic water fluxes, and the separation of pH dynamics between granal and lamellar lumens in response to environmental variations. With the two functionally asymmetrical photosystems located distantly from each other, the ultrastructural control, nonphotochemical quenching, and carbon-reaction feedbacks maximally cooperate to balance electron transport with gas exchange, provide homeostasis in fluctuating light environments, and protect photosystems in drought. Grana stacks represent a dry/high irradiance adaptation of photosynthetic machinery to improve fitness in challenging land environments. Our theory unifies many well-known but seemingly unconnected phenomena of thylakoid structure and function in higher plants.

The physiological basis for estimating photosynthesis from Chla fluorescence.

Solar-induced Chl fluorescence (SIF) offers the potential to curb large uncertainties in the estimation of photosynthesis across biomes and climates, and at different spatiotemporal scales. However, it remains unclear how SIF should be used to mechanistically estimate photosynthesis. In this study, we built a quantitative framework for the estimation of photosynthesis, based on a mechanistic light reaction model with the Chla fluorescence of Photosystem II (SIFPSII ) as an input (MLR-SIF). Utilizing 29 C3 and C4 plant species that are representative of major plant biomes across the globe, we confirmed the validity of this framework at the leaf level. The MLR-SIF model is capable of accurately reproducing photosynthesis for all C3 and C4 species under diverse light, temperature, and CO2 conditions. We further tested the robustness of the MLR-SIF model using Monte Carlo simulations, and found that photosynthesis estimates were much less sensitive to parameter uncertainties relative to the conventional Farquhar, von Caemmerer, Berry (FvCB) model because of the additional independent information contained in SIFPSII . Once inferred from direct observables of SIF, SIFPSII provides 'parameter savings' to the MLR-SIF model, compared to the mechanistically equivalent FvCB model, and thus avoids the uncertainties arising as a result of imperfect model parameterization. Our findings set the stage for future efforts to employ SIF mechanistically to improve photosynthesis estimates across a variety of scales, functional groups, and environmental conditions.

Development of one-step multiplex RT-PCR assay for rapid simultaneous detection of five RNA viruses and Acidovorax citrulli in major cucurbitaceous crops in China.

Cucurbitaceous fruits and vegetables are important crops. Viral and bacterial diseases cause substantial economic losses to cucurbit crops globally. For rapid detection of these pathogens and improved disease control, a one-step multiplex reverse-transcription polymerase chain reaction (mRT-PCR) system was created. This method allowed for the concurrent detection of Tobacco mosaic virus (TMV), Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV), Cucumber green mottle mosaic virus (CGMMV), Cucumber mosaic virus (CMV), and Acidovorax citrulli. Five pairs of specific primers were created according to the conserved regions around the coat protein (CP) genes of each virus, and one pair was based on the A. citrulli internal transcribed spacer (ITS). To limit false negatives, one pair of primers, created based on the Transcriptional elongation factor 1-α (EF1-α) from the major cucurbitaceous crop species, was put into the mRT-PCR reaction system. Primer concentrations, annealing temperature, extension time, and amplification cycles were optimized. Anticipated fragments of 152 bp (TMV), 205 bp (ZYMV), 318 bp (WMV), 419 bp (CGMMV), 529 bp (CMV), 662 bp (A. citrulli), and 821 bp (EF1-α) were amplified by the multiplex RT-PCR system, and their origin was established via DNA sequencing. This method was successfully used to examine field-collected seed samples of cucurbitaceous crops from China. The results demonstrated that the one-step mRT-PCR technique is a quick, efficient, and sensitive assay for the concurrent detection of six pathogens of cucurbits. It provides a method for monitoring and preventing these diseases.

First report of tomato spotted wilt virus infecting water dropwort in China.

Water dropwort (Oenanthe javanica) is an aquatic perennial plant that has been cultivated in many regions in Asia for thousands of years. In China, it is an economically important vegetable that has been consumed as food, while also being used as a folk remedy to alleviate diseases (Liu et al., 2021). In 2021, during a disease survey of a greenhouse in Beijing, China, chlorotic spots were detected on many water dropwort plants (Fig. S1A). Twenty-seven water dropwort samples were collected for the extraction of total RNA using the TRIzol reagent (Invitrogen, USA). High-quality RNA samples from three water dropwort plants were combined and used as the template for constructing a single small RNA library (BGI-Shenzhen Company, China). The Velvet 1.0.5 software was used to assemble the clean reads (18 to 28 nt) into larger contigs, which were then compared with the nucleotide sequences in the National Center database using the BLASTn algorithm. Thirty-eight contigs matched sequences in the tomato spotted wilt virus (TSWV) genome. No other viruses were detected. Twenty-seven leaf samples were analyzed in an enzyme-linked immunosorbent assay (ELISA) with anti-TSWV antibody (Agdia, USA), which revealed 17 positive reaction. Two sets of primer pairs targeting different parts of the S RNA (Table S1) was used to verify the TSWV infection on water dropwort by reverse transcription (RT)-PCR followed by Sanger sequencing (BGI-Shenzhen, China). The TSWV target sequences were amplified from 17 samples, which was consistent with the ELISA results. The sequenced 861-bp PCR product shared 99.8% nucleotide sequence identity with TSWV isolate MR-01 (MG593199), while the 441-bp amplicon shared a 99.2% nucleotide sequence identity with MR-01 (MG593199). To obtain the whole genome sequence of TSWV (S, M, and L RNA sequences), specific RT-PCR primers were designed (Table S1) and used to amplify their respective fragments from one representative sample (TSWV-water dropwort). The amplified products were inserted into PCE2TA/Blunt-Zero vector (Vazyme Biotech Co., Ltd, China) and then sequenced (BGI-Shenzhen, China). The S, M, and L RNA sequences were determined to be 2,952 nt (accession no. OM154969), 4,776 nt (accession no. OM154970), and 8,914 nt (accession no. OM154971), respectively. BLASTn analysis demonstrated that the whole genome sequence was highly conserved. The nucleotide identities between this isolate and other TSWV isolates ranged from 98.6% to 99.6% (S RNA), 98.9% to 99.2% (M RNA), and 97.3% to 98.7% (L RNA). Using MEGA 7.0, the phylogenetic relationships of TSWV were determined on the basis of the S, M, and L RNA full-length sequences (Kumar et al., 2016). In the S RNA derived phylogenetic tree, the water dropwort isolate was closely related to the MR-01 isolate from the USA (MG593199). In the M RNA and L RNA derived phylogenetic trees, the water dropwort isolate formed a branch with only a TSWV isolate from eggplant. Additionally, the M and L RNA sequences were most similar to sequences in TSWV isolates from China and Korea, respectively (Fig. S1B). To the best of our knowledge, this is the first report of water dropwort as a natural host for TSWV in China and the second report worldwide since the first finding in the Korea (Kil et al. 2020). TSWV has caused serious problems on many crops in the world, and the infection of TSWV on water dropwort in a greenhouse should not be looked lightly. Firstly, the virus can be passed on from generation to generation in infected water dropwort due to the vegetative propagation mode of the plant in production, thus threaten the production of this vegetable crop. In addition, infected water dropwort may serve as a reservoir for the virus, thus potentially posing a threat for causing TSWV spread in the affected greenhouses. The author(s) declare no conflict of interest. Funding: This research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (QNJJ202131, KJCX20200212, and KJCX20200113). References: Kil et al. 2020. Plant Pathol. J. 36: 67-75 Kumar et al. 2016. Mol Biol Evol, 33: 1870-1874 Liu et al. 2021. Horticulture Research. 8:1-17.

Effects of Exogenous Melatonin on Root Physiology, Transcriptome and Metabolome of Cotton Seedlings under Salt Stress.

Root systems are the key organs through which plants absorb water and nutrients and perceive the soil environment and thus are easily damaged by salt stress. Melatonin can alleviate stress-induced damage to roots. The present study investigated the effects of exogenous melatonin on the root physiology, transcriptome and metabolome of cotton seedlings under salt stress. Salt stress was observed to damage the cell structure and disorder the physiological system of cotton seedling roots. After subjecting melatonin-soaked seeds to salt stress, the activities of SOD, CAT and POD in cotton seedling roots increased by 10-25%, 50-60% and 50-60%, respectively. The accumulation of H2O2 and MDA were significantly decreased by 30-60% and 30-50%, respectively. The contents of soluble sugar, soluble protein and K+ increased by 15-30%, 15-30% and 20-50%, respectively, while the Na+ content was significantly reduced. Melatonin also increased auxin (by 20-40%), brassinosteroids (by 5-40%) and gibberellin (by 5-35%) and promoted melatonin content and root activity. Exogenous melatonin maintained the integrity of root cells and increased the number of organelles. Transcriptomic and metabolomic results showed that exogenous melatonin could mitigate the salt-stress-induced inhibition of plant root development by regulating the reactive oxygen species scavenging system; ABC transporter synthesis; plant hormone signal transduction, endogenous melatonin gene expression; and the expression of the transcription factors MYB, TGA and WRKY33. These results provide a new direction and empirical basis for improving crop salt tolerance with melatonin.

Distribution of mercury and methylmercury in river water and sediment of typical manganese mining area.

Manganese (Mn) ores contain substantial concentrations of mercury (Hg), and mining and smelting of Mn ores can bring Hg into the surrounding aquatic environment through atmospheric deposition, leaching of electrolytic Mn residue and Mn gangue dump. However, limited is known that how these processes influence the environmental behaviors of Hg in waterbody. Therefore, the seasonal distribution and existing form of Hg in water and sediment in one Mn ore area in Xiushan County, Chongqing were investigated. Our results showed that the mean Hg and methylmercury (MeHg) concentrations in water (n=35) were 5.8 ± 4.6 ng/L and 0.22 ± 0.14 ng/L, respectively. The mean Hg concentrations in retained riverbed and fluvial bank sediment (n=35) were 0.74 ± 0.26 mg/kg and 0.63 ± 0.27 mg/kg, respectively (the mean MeHg concentrations were 0.64 ± 0.40 µg/kg and 0.51 ± 0.30 µg/kg, respectively). It indicated that the mining and smelting of Mn ores were the main sources of anthropogenic Hg, and Mn may inhibit Hg methylation in rivers in Mn ore areas. Mercury in the bound to iron/ Mn (Fe/Mn) oxides of low crystallinity fraction (Hg-OX) accounted for 4.01% and 5.25% of the total Hg concentrations in the retained riverbed and fluvial bank sediment, respectively. The amount of Hg bound to Fe/Mn oxides in sediment increased significantly due to the manganese mining activities in the investigated area. Therefore, it could be hypothesized that high Hg concentrations in river sediment in Mn mining areas are closely related to high Mn concentration in sediment.

Low-cost and efficient confocal imaging method for arabidopsis flower.

For an extensive period of time apical meristem (SAM) has been considered as a mysterious organ, due to its small, hidden and dynamic structure. Confocal imaging, combined with fluorescent reporters, enables researchers to unveil the mechanisms underlying cellular activities, such as gene expression, cell division, growth patterns and cell-cell communications. Recently, a series of protocols were developed for confocal imaging of inflorescence meristem (IM) and floral meristem (FM). However, the requirement of high configuration, such as the need of a water-dipping lens without coverslip and the specialized turrets associated with fixed-stage microscopes, impedes the wide adoption of these methods. We exploited an improved object slide and matching method aiming to decrease the configuration requirement. Following this protocol, various dry microscope lenses can be selected with flexibility for building 3D images of IM and FM.

Hydraulic prediction of drought-induced plant dieback and top-kill depends on leaf habit and growth form.

Hydraulic failure caused by severe drought contributes to aboveground dieback and whole-plant death. The extent to which dieback or whole-plant death can be predicted by plant hydraulic traits has rarely been tested among species with different leaf habits and/or growth forms. We investigated 19 hydraulic traits in 40 woody species in a tropical savanna and their potential correlations with drought response during an extreme drought event during the El Niño-Southern Oscillation in 2015. Plant hydraulic trait variation was partitioned substantially by leaf habit but not growth form along a trade-off axis between traits that support drought tolerance versus avoidance. Semi-deciduous species and shrubs had the highest branch dieback and top-kill (complete aboveground death) among the leaf habits or growth forms. Dieback and top-kill were well explained by combining hydraulic traits with leaf habit and growth form, suggesting integrating life history traits with hydraulic traits will yield better predictions.

Exogenous melatonin improves the salt tolerance of cotton by removing active oxygen and protecting photosynthetic organs.

BACKGROUND: As damage to the ecological environment continues to increase amid unreasonable amounts of irrigation, soil salinization has become a major challenge to agricultural development. Melatonin (MT) is a pleiotropic signal molecule and indole hormone, which alleviates the damage of abiotic stress to plants. MT has been confirmed to eliminate reactive oxygen species (ROS) by improving the antioxidant system and reducing oxidative damage under adversity. However, the mechanism by which exogenous MT mediates salt tolerance by regulating the photosynthetic capacity and ion balance of cotton seedlings still remains unknown. In this study, the regulatory effects of MT on the photosynthetic system, osmotic modulators, chloroplast, and anatomical structure of cotton seedlings were determined under 0-500 µM MT treatments with salt stress induced by treatment with 150 mM NaCl. RESULTS: Salt stress reduces the chlorophyll content, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, PSII photochemical efficiency, PSII actual photochemical quantum yield, the apparent electron transfer efficiency, stomata opening, and biomass. In addition, it increases non-photochemical quenching. All of these responses were effectively alleviated by exogenous treatment with MT. Exogenous MT reduces oxidative damage and lipid peroxidation by reducing salt-induced ROS and protects the plasma membrane from oxidative toxicity. MT also reduces the osmotic pressure by reducing the salt-induced accumulation of Na+ and increasing the contents of K+ and proline. Exogenous MT can facilitate stomatal opening and protect the integrity of cotton chloroplast grana lamella structure and mitochondria under salt stress, protect the photosynthetic system of plants, and improve their biomass. An anatomical analysis of leaves and stems showed that MT can improve xylem and phloem and other properties and aides in the transportation of water, inorganic salts, and organic substances. Therefore, the application of MT attenuates salt-induced stress damage to plants. Treatment with exogenous MT positively increased the salt tolerance of cotton seedlings by improving their photosynthetic capacity, stomatal characteristics, ion balance, osmotic substance biosynthetic pathways, and chloroplast and anatomical structures (xylem vessels and phloem vessels). CONCLUSIONS: Our study attributes help to protect the structural stability of photosynthetic organs and increase the amount of material accumulation, thereby reducing salt-induced secondary stress. The mechanisms of MT-induced plant tolerance to salt stress provide a theoretical basis for the use of MT to alleviate salt stress caused by unreasonable irrigation, fertilization, and climate change.

The hydraulic architecture of an arborescent monocot: ontogeny-related adjustments in vessel size and leaf area compensate for increased resistance.

Bamboos are arborescent monocotyledons that have no secondary growth, but can continually produce conduits with diameters appropriate to the current size of the plant. Here, we studied bamboo hydraulic architecture to address the mechanisms involved in compensating for the increase in hydraulic resistance during ontogeny. We measured the hydraulic weighted vessel diameters (Dh ) at different distances from the apex along the stem of Bambusa textilis. The hydraulic resistance of different components and individuals of different heights were quantified using the high-pressure flowmeter method. The Dh showed tip-to-base widening with a scaling exponent in the range of those reported for trees. Although theoretical hydraulic conductivity decreased from base-to-tip, leaf-specific conductivity did not change. Leaves contributed the most to the whole-shoot hydraulic resistance, followed by the leaf-bearing branches. Roots contributed c. 13% to whole-plant resistance. Interestingly, taller individuals showed lower whole-shoot resistance owing to an increased number of resistances in parallel (side-branches), while leaf-specific resistance was independent of plant size. Tip-to-base vessel widening and height-independent constant leaf-specific conductance could be mechanisms for hydraulic optimization in B. textilis. Similar patterns have also been found in woody plants with secondary growth, but this bamboo exhibits them without secondary growth.

Quantifying vulnerability to embolism in tropical trees and lianas using five methods: can discrepancies be explained by xylem structural traits?

Vulnerability curves (VCs) describe the loss of hydraulic conductance against increasing xylem tension, providing valuable insights about the response of plant water transport to water stress. Techniques to construct VCs have been developed and modified continuously, but controversies continue. We compared VCs constructed using the bench-top dehydration (BD), air-injection-flow (AI), pneumatic-air-discharge (PAD), optical (OP) and X-ray-computed microtomography (MicroCT) methods for tropical trees and lianas with contrasting vessel lengths. The PAD method generated highly vulnerable VCs, the AI method intermediate VCs, whereas the BD, OP and MicroCT methods produced comparable and more resistant VCs. Vessel-length and diameter accounted for the overestimation ratio of vulnerability estimated using the AI but not the PAD method. Compared with directly measured midday embolism levels, the PAD and AI methods substantially overestimated embolism, whereas the BD, MicroCT and OP methods provided more reasonable estimations. Cut-open vessels, uncertainties in maximum air volume estimations, sample-length effects, tissue cracks and shrinkage together may impede the reliability of the PAD method. In conclusion, we validate the BD, OP and MicroCT methods for tropical plants, whereas the PAD and AI need further mechanistic testing. Therefore, applications of VCs in estimating plant responses to drought need to be cautious.