Reduced Leaf Chlorophyll Content Research Articles

Characterization of the gibberellic oxidase gene SdGA20ox1 in Sophora davidii (Franch.) skeels and interaction protein screening.

Gibberellin 20-oxidases (GA20oxs) are multifunctional enzymes involved in regulating gibberellin (GA) biosynthesis and controlling plant growth. We identified and characterized the GA20ox1 gene in a plant height mutant of Sophora davidii, referred to as SdGA20ox1. This gene was expressed in root, stem, and leaf tissues of the adult S. davidii plant height mutant, with the highest expression observed in the stem. The expression of SdGA20ox1 was regulated by various exogenous hormones. Overexpression of SdGA20ox1 in Arabidopsis resulted in significant elongation of hypocotyl and root length in seedlings, earlier flowering, smaller leaves, reduced leaf chlorophyll content, lighter leaf color, a significant increase in adult plant height, and other phenotypes. Additionally, transgenic plants exhibited a substantial increase in biologically active endogenous GAs (GA1, GA3, and GA4) content, indicating that overexpression of SdGA20ox1 accelerates plant growth and development. Using a yeast two-hybrid (Y2H) screen, we identified two SdGA20ox1-interacting proteins: the ethylene receptor EIN4 (11430582) and the rbcS (11416005) protein. These interactions suggest a potential regulatory mechanism for S. davidii growth. Our findings provide new insights into the role of SdGA20ox1 and its interacting proteins in regulating the growth and development of S. davidii.

A missense mutation in the barley Xan-h gene encoding the Mg-chelatase subunit I leads to a viable pale green line with reduced daily transpiration rate

Key messageThe barley mutant xan-h.chli-1 shows phenotypic features, such as reduced leaf chlorophyll content and daily transpiration rate, typical of wild barley accessions and landraces adapted to arid climatic conditions.The pale green trait, i.e. reduced chlorophyll content, has been shown to increase the efficiency of photosynthesis and biomass accumulation when photosynthetic microorganisms and tobacco plants are cultivated at high densities. Here, we assess the effects of reducing leaf chlorophyll content in barley by altering the chlorophyll biosynthesis pathway (CBP). To this end, we have isolated and characterised the pale green barley mutant xan-h.chli-1, which carries a missense mutation in the Xan-h gene for subunit I of Mg-chelatase (HvCHLI), the first enzyme in the CBP. Intriguingly, xan-h.chli-1 is the only known viable homozygous mutant at the Xan-h locus in barley. The Arg298Lys amino-acid substitution in the ATP-binding cleft causes a slight decrease in HvCHLI protein abundance and a marked reduction in Mg-chelatase activity. Under controlled growth conditions, mutant plants display reduced accumulation of antenna and photosystem core subunits, together with reduced photosystem II yield relative to wild-type under moderate illumination, and consistently higher than wild-type levels at high light intensities. Moreover, the reduced content of leaf chlorophyll is associated with a stable reduction in daily transpiration rate, and slight decreases in total biomass accumulation and water-use efficiency, reminiscent of phenotypic features of wild barley accessions and landraces that thrive under arid climatic conditions.

Winter Durum Wheat Disease Severity Detection with Field Spectroscopy in Phenotyping Experiment at Leaf and Canopy Level

Accurate disease severity assessment is critical for plant breeders, as it directly impacts crop yield. While hyperspectral remote sensing has shown promise for disease severity assessment in breeding experiments, most studies have focused on either leaf or canopy levels, neglecting the valuable insights gained from a combined approach. Moreover, many studies have centered on experiments involving a single disease and a few genotypes. However, this approach needs to accurately represent the challenges encountered in field conditions, where multiple diseases could occur simultaneously. To address these gaps, our current study analyses a combination of diseases, yellow rust, brown rust, and yellow leaf spots, collectively evaluated as the percentage of the diseased leaf area relative to the total leaf area (DA) at both leaf and canopy levels, using hyperspectral data from an ASD field spectrometer. We quantitatively estimate overall disease severity across fifty-two winter durum wheat genotypes categorized into early (medium milk) and late (late milk) groups based on the phenophase. Chlorophyll content (CC) within each group is studied concerning infection response, and a correlation analysis is conducted for each group with nine vegetation indices (VI) known for their sensitivity to rust and leaf spot infection in wheat. Subsequent parametric (linear and polynomial) and nonparametric (partial least squares and kernel ridge) regression analyses were performed using all available spectral bands. We found a significant reduction in Leaf CC (>30%) in the late group and Canopy CC (<10%) for both groups. YROI and LRDSI_1 are the VIs that exhibited notable and strong negative correlations with Leaf CC in the late group, with a Pearson coefficient of −0.73 and −0.72, respectively. Interestingly, spectral signatures between the early and late disease groups at both leaf and canopy levels exhibit opposite trends. The regression analysis showed we could retrieve leaf CC only for the late group, with R2 of 0.63 and 0.42 for the cross-validation and test datasets, respectively. Canopy CC retrieval required separate models for each group: the late group achieved R2 of 0.61 and 0.37 (cross-validation and test), while the early group achieved R2 of 0.48 and 0.50. Similar trends were observed for canopy DA, with separate models for early and late groups achieving comparable R2 values of 0.53 and 0.51 (cross-validation) and 0.35 and 0.36 (test), respectively. All of our models had medium accuracy and tended to overfit. In this study, we analyzed the spectral response mechanism associated with durum wheat diseases, offering a novel crop disease severity assessment approach. Additionally, our findings serve as a foundation for detecting resistant wheat varieties, which is the most economical and environmentally friendly management strategy for wheat leaf diseases on a large scale in the future.

Reduction of Dispersant Pollutant (Linear Alkylbenzene Sulfonate) by Mangrove Plant (Rhizophora mucronata)

Linear alkylbenzene sulfonate (LAS) is the main component of dispersants that function as cleaners of various materials. The increasing use of LAS causes this compound to dominantly pollute coastal waters. Phytoremediation is the most environmentally safe alternative to physical and chemical methods. One of the potential plants as a phytoremediator is Rhyzophora mucronata. This research is an experiment as an application of LAS pollutant control by Rhyzophora Mucronata (R. Mucronata) plants in waters. After acclimatization and preliminary tests, the implementation of LAS phytoremediation tests by R. Mucronata plants in seawater media was carried out at concentrations of A1: 25 mg/L, A2: 100 mg/L, A3: 175 mg/L, A4: 250 mg/L, and A5: 325 mg/L and control (Control without plants) as a simulation of the presence of pollutants in coastal waters. The method used was a completely randomized design (CRD) with one treatment and 3 replications. The reduction of LAS concentration in the test media and its effect on R Mucronata leaf chlorophyll and dissolved oxygen were analyzed at week 2 to week 4. The analysis results showed that LAS compounds could be reduced to 91.48% at week 2 and 97.40% at week 4. Plant Water quality parameters (dissolved oxygen, temperature and pH) were measured daily. Based on the study results, LAS can be reduced by R. Mucronata plants 87-90.4% in week 2 and 95.1-97.4% in week 4. LAS exclusion by plants had a significant impact on the reduction of leaf chlorophyll content until week 4. LAS reduction by R. Mucronata in the media can increase dissolved oxygen content as an indication of improved water quality. R. Mucronata plants can be used as an alternative to control LAS pollution in waters

A novel semi-empirical model for crop leaf area index retrieval using SAR co- and cross-polarizations

The retrieval of continuous leaf area index (LAI) in space and time from remote sensing is beneficial for cropland monitoring and management. Synthetic Aperture Radar (SAR) with the advantages of all-weather operation and fine spatial resolutions has been utilized in various agricultural applications. Although the water cloud model (WCM) has been extensively used for LAI estimation over croplands, it is modified for application to crop canopies with large gaps. The requirement of prior information on soil moisture is also a hinderance for the model application. In this study, WCM is theoretically modified to consider the correlation of active microwave propagation through the canopy in downward and upward directions. Such a modification is particularly important for sparse vegetation with large gaps between crop plants in the early stage of the growing season. A parameter with explicit physical meaning, i.e. the full-vegetation backscattering coefficient, was defined to simplify our model scheme and make the model applicable for the whole growing season. In addition, a physics-based SAR data processing scheme is developed to entangle the influences of LAI and soil moisture on SAR backscatter by taking advantage of the multiple polarizations of RADARSAT-2 (R2) SAR data. In this way, LAI was estimated using modified WCM without the prior knowledge of soil moisture. To evaluate LAI retrieved from the R2 datasets (R2 LAI), ground-based LAI measurements were made at the experimental area of SMAPVEX16-MB in Canada with twenty approximately 800 m х 800 m plots in soybeans and corn. R2 LAI was well correlated to these ground-based LAI (n = 15, R2 = 0.63, RMSE = 0.99 m2·m−2 for soybeans; n = 5, R2 = 0.66, RMSE = 1.20 m2·m−2 for corn). LAI was also retrieved from optical data acquired by Sentinel-2/MSI (S2), denoted as S2 LAI. The R2 LAI and S2 LAI are well correlated and achieved coefficients of determination (R2) of 0.76 and 0.71 and root mean square errors (RMSE) of 1.1 and 1.4 m2·m−2 for soybeans and corn, respectively. The seasonal variations of R2 LAI and S2 LAI are generally similar except at the end of the growing season when S2 LAI is considerably larger than R2 LAI. S2 LAI followed the trend of the reduction in leaf chlorophyll content, while R2 LAI reduced only slightly due to the decrease in leaf water content near the end the growing season. R2 LAI represents the total standing leaf area useful for surface energy balance estimation, while S2 LAI responds to green leaf area useful for crop productivity modeling.

Multi-omics analyses reveal new insights into nutritional quality changes of alfalfa leaves during the flowering period.

High-quality alfalfa is an indispensable resource for animal husbandry and sustainable development. Its nutritional quality changes dramatically during its life cycle and, at present, no molecular mechanisms for nutrient metabolic variation in alfalfa leaves at different growth stages have been clearly reported. We have used correlation and network analyses of the alfalfa leaf metabolome, proteome, and transcriptome to explore chlorophyll, flavonoid, and amino acid content at two development stages: budding stage (BS) and full-bloom stage (FBS). A high correlation between the expression of biosynthetic genes and their metabolites revealed significant reductions in metabolite content as the plant matured from BS to FBS. l-Glutamate, the first molecule of chlorophyll biosynthesis, decreased, and the expression of HemA, which controls the transformation of glutamyl-tRNA to glutamate 1-semialdehyde, was down-regulated, leading to a reduction in leaf chlorophyll content. Flavonoids also decreased, driven at least in part by increased expression of the gene encoding CYP75B1: flavonoid 3'-monooxygenase, which catalyzes the hydroxylation of dihydroflavonols and flavonols, resulting in degradation of flavonoids. Expression of NITRILASE 2 (NIT2) and Methyltransferase B (metB), which regulate amino acid metabolism and influence the expression of genes of the glycolysis-TCA pathway, were down-regulated, causing amino acid content in alfalfa leaves to decrease at FBS. This study provides new insights into the complex regulatory network governing the content and decrease of chlorophyll, amino acids, flavonoids, and other nutrients in alfalfa leaves during maturation. These results further provide a theoretical basis for the generation of alfalfa varieties exhibiting higher nutritional quality, high-yield cultivation, and a timely harvest.

Foliar Spray of Micronutrients Alleviates Heat and Moisture Stress in Lentil (Lens culinaris Medik) Grown Under Rainfed Field Conditions.

The simultaneous occurrence of high temperature and moisture stress during the reproductive stage of lentil (Lens culinaris Medik) constrains yield potential by disrupting the plant defense system. We studied the detrimental outcomes of heat and moisture stress on rainfed lentils under residual moisture in a field experiment conducted on clay loam soil (Aeric Haplaquept) in eastern India from 2018 to 2019 and from 2019 to 2020 in winter seasons. Lentil was sown on two dates (November and December) to expose the later sowing to higher temperatures and moisture stress. Foliar sprays of boron (0.2% B), zinc (0.5% Zn), and iron (0.5% Fe) were applied individually or in combination at the pre-flowering and pod development stages. High temperatures increased malondialdehyde (MDA) content due to membrane degradation and reduced leaf chlorophyll content, net photosynthetic rate, stomatal conductance, water potential, and yield (kg ha–1). The nutrient treatments affected the growth and physiology of stressed lentil plants. The B+Fe treatment outperformed the other nutrient treatments for both sowing dates, increasing peroxidase (POX) and ascorbate peroxidase (APX) activities, chlorophyll content, net photosynthetic rate, stomatal conductance, relative leaf water content (RLWC), seed filling duration, seed growth rate, and yield per hectare. The B+Fe treatment increased seed yield by 35–38% in late-sown lentils (December). In addition, the micronutrient treatments positively impacted physiological responses under heat and moisture stress with B+Fe and B+Fe+Zn alleviating heat and moisture stress-induced perturbations. Moreover, the exogenous nutrients helped in improving physiochemical attributes, such as chlorophyll content, net photosynthetic rate, stomatal conductance, water potential, seed filling duration, and seed growth rate.

Freezing induces an increase in leaf spectral transmittance of forest understorey and alpine forbs

Evergreen plants growing at high latitudes or high elevations may experience freezing events in their photosynthetic tissues. Freezing events can have physical and physiological effects on the leaves which alter leaf optical properties affecting remote and proximal sensing parameters. We froze leaves of six alpine plant species (Soldanella alpina, Ranunculus kuepferi, Luzula nutans, Gentiana acaulis, Geum montanum, and Centaurea uniflora) and three evergreen forest understorey species (Hepatica nobilis, Fragaria vesca and Oxalis acetosella), and assessed their spectral transmittance and optically measured pigments, as well as photochemical efficiency of photosystem II (PSII) as an indicator of freezing damage. Upon freezing, leaves of all the species transmitted more photosynthetically active radiation (PAR) and some species had increased ultraviolet-A (UV-A) transmittance. These differences were less pronounced in alpine than in understorey species, which may be related to higher chlorophyll degradation, visible as reduced leaf chlorophyll content upon freezing in the latter species. Among these understorey forbs, the thin leaves of O. acetosella displayed the largest reduction in chlorophyll (−79%). This study provides insights into how freezing changes the leaf optical properties of wild plants which could be used to set a baseline for upscaling optical reflectance data from remote sensing. Changes in leaf transmittance may also serve to indicate photosynthetic sufficiency and physiological tolerance of freezing events, but experimental research is required to establish this functional association.Graphical abstract

Maternal drought stress on Persian oak (Quercus brantii Lindl.) affects susceptibility to single and combined drought and biotic stress in offspring

Zagros woodlands in Iran are threatened by the decline of Persian oak (Quercus brantii) trees. Although the main cause of tree mortality is drought stress, bacterial pathogens such as Brenneria goodwinii also contribute to tree dieback. Maternal effects were studied in a drought-affected environment. We investigated if the susceptibility of Q. brantii seedlings to single and combined B. goodwinii and drought stresses depends on the health status of mother trees. Plants were grown from seeds collected from non-stressed healthy and drought-stressed unhealthy trees. Root weight and belowground to aboveground weight ratios were significantly higher in offspring of unhealthy mother trees, suggesting that drought stress regulated the performance of Q. brantii in the subsequent generation. Brenneria goodwinii followed by drought had synergistic negative effects on seedlings (reduced plant growth, reduced xylem vessel size and reduced relative water content of tissues) and induced more injury (reduced leaf chlorophyll content and increased root electrolyte leakage) in offspring of unhealthy trees. Increased adaptation to drought in plants germinating from drought-stressed trees was observed and the effects persisted over the vegetative period, after the plants were rewatered. The results provide a first evidence of transgenerational plasticity in response to drought stress in trees. It is concluded that the health status of trees influences the response of offspring to combined stress.

Morphological and Molecular Characterization of Soybean (Glycine max L.) Genotypes undre Salt Stress

Three advanced lines (SB02, SB05, SB07) along with one tolerant (Lokon) and one susceptible check (Asswt) of soybean (Glycine max L.) were assessed for salt tolerance in terms of morpho-physiological traits and molecular markers (SSR). The experiment was conducted at seedling stage with four salinity treatments namely 0, 8, 12 and 16 dSm-1 following Completely Randomized design. All the genotypes displayed considerable reduction in their morphological traits, least affecting the tolerant one. None of the genotypes were survived at 12 and 16 dSm-1 stress condition. Among the lines tested, SB-02 and SB-05 were identified as salt tolerant at 8 dSm-1 based on salinity susceptibility index (SSI) scoring. These genotypes suffered less in reduction of leaf chlorophyll content (SPAD) and increase of Na+/K+ than the susceptible genotypes. For all the traits viz. shoot length, root length, total length, shoot fresh weiht, root fresh weight, shoot dry weight, root dry weight, total fresh weight, total dry weight, percent live leaves, chlorophyll content and Na+/K+ ratio, the phenotypic coefficient of variation (PCV) was higher than that of genotypic coefficient of variation (GCV). All the traits studied showed medium to high heritability ranging between 43.81% (SPAD) to 96.65% (shoot length). The genotypes were grouped into two clusters considering both Euclidian distance and Unweighted Pair Group Method with Arithmetic Mean analysis. Lokon, SB-02 and SB-05 are on the same cluster as tolerant, and SB-7 and Asset on the other as susceptible to salt stress. The molecular pattern using by SSR marker displayed an average number of 3.33 alleles per locus with PIC (Polymorphism Information Content) values ranged from 0.2688 (sat_655 and satt728) to 0.7680 (sat_210). The highest gene diversity was observed in sat_210 and satt237 and the lowest in sat_655 and satt728 with a mean diversity of 0.5733. The genotypes Lokon, SB-02 and SB-05 could be suggested as a potential germplasm source of QTL (Quantitative Trait Loci) analysis for the development of salt tolerant soybean variety. Ann. Bangladesh Agric. (2020) 24(2): 33-46

Potassium Application Positively Modulates Physiological Responses of Cocoa Seedlings to Drought Stress

With increasing frequency and intensity of dry spells in the cocoa production zones of West Africa, strategies for mitigating impact of water stress on cocoa seedling survival are urgently required. We investigated the effects of applied potassium on biomass accumulation, physiological processes and survival of cocoa varieties subjected to water stress in pot experiments in a gauzehouse facility. Four levels of potassium (0, 1, 2, or 3 g/plant as muriate of potash) were used. Soil water stress reduced plant biomass accumulation (shoot and roots), relative water content (RWC), chlorophyll content and fluorescence. Leaf phenol and proline contents were increased under water stress. Additionally, compared to the well-watered conditions, soils under water stress treatments had higher contents of exchangeable potassium and available phosphorus at the end of the experimental period. Potassium applied under well-watered conditions reduced leaf chlorophyll content and fluorescence and increased leaf electrolyte leakage, but improved the growth and integrity of physiological functions under soil water stress. Potassium addition increased biomass partitioning to roots, improved RWC and leaf membrane stability, and significantly improved cocoa seedling survival under water stress. Under water stress, the variety with the highest seedling mortality accumulated the highest contents of phenol and proline. A significant effect of variety on plant physiological functions was observed. Generally, varieties with PA 7 parentage had higher biomass partitioning to roots and better seedling survival under soil moisture stress. Proportion of biomass partitioned to roots, RWC, chlorophyll fluorescence and leaf electrolyte leakage appear to be the most reliable indicators of cocoa seedling tolerance to drought.

Strigolactone could enhances gas-exchange through augmented antioxidant defense system in Salvia nemorosa L. plants subjected to saline conditions stress

Salvia is one of the most important herbs that is of universal pharmacological value whose production may be restricted by salt stress. Although the role of phytohormones in modulating the harmful effects of salinity has been investigated, insufficient information has been reported on the positive effects of strigolactone (SL). Therefore, to evaluate the plant reaction to salinity when associated with SL treatments, S. nemorosa were subjected to four levels of salinity (0, 100, 200 and 300 mM NaCl) and five levels of SL (0. 0.1, 0.2, 0.3 and 0.4 μM) under greenhouse conditions. The outcomes demonstrated that salinity reduced the plant growth rate and foliar applied SL significantly prevented salinity stress-induced loss of growth. Increasing salinity significantly reduced leaf chlorophyll content, Fv/Fm and gas exchange parameters and these negative effects could be mitigated by SL application. Providing salt stressed Salvia plants with various levels of SL mostly accompanied with a slow but significant decrease in the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR). When different concentrations of salinity stress were imposed, increasing levels of SL up to 0.3 μM resulted in lower total phenol content and reduced glutathione (GSH) compared with the plants exposed to salinity alone. When plants were subjected to 100 mM NaCl, SL treatment at 0.3 μM indicated the highest essential oil yield (0.4 g plant−1). The modulatory effect of SL treatments in reducing the deleterious effects of NaCl toxicity could be attributed to more proline accumulation and decreased activity of antioxidant enzymes which improved salt tolerance of Salvia nemorosa.

A Cd/Zn Co-hyperaccumulator and Pb accumulator, Sedum alfredii, is of high Cu tolerance

High sensitivity towards Cu toxicity is problematic when using some hyperaccumulator plants for phytoremediation of soils with mixed contamination of Cu. Sedum alfredii, a Cd/Zn co-hyperaccumulator and Pb accumulator, is widely used for remediation of Cd, Zn, and Pb co-contaminated soils in China. In this paper, the tolerance and accumulation ability of S. alfredii towards Cu stress and its potential for phytoremediation of multi-metal polluted soils have been studied. Both the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii accumulated high Cu in the roots and translocated minimal Cu to the shoots, and Cu in the stems and leaves mostly restricted in the vascular tissues (phloem zone). The HE plants, however, exhibited high Cu resistance with stimulated lateral root growth and increased chlorophyll content under 10 μM Cu treatment. XANES analysis showed that Cu in HE roots comprised Cu2+ (46.7%), Cu-histidine (35.2%) and Cu-cell wall (18.1%). The NHE under Cu stress showed decreased biomass, reduced leaf chlorophyll content, altered root architecture, and higher Cu localized to root cell wall as compared with the HEs. Potted HE plants thrived six months in multi-metal contaminated soils including 3897 mg kg−1 available Cu. In conclusion, HE S alfredii is highly tolerant toward Cu due to metal homeostasis in root cells. Therefore, this plant has great potential to remediate Zn, Cd, and Pb contaminated soils those also contain high levels of Cu.

Effect of Nitrogen Fertilizers on Yield and Antioxidant Enzymes of Basil (Ocimum basilicum L.) under Water Stress Conditions

Water scarcity in Iran has always been a limiting factor for crop and horticultural production. Under these conditions, the nutrient uptake and metabolism processes of plants are different and can reduce growth. To study water stress (at three levels) and six fertilizer regimes (Nitrogen fertilizer requirement by a combination of vermicompost and urea fertilizer) on the quantitative yield of experimental basil (Ocimum basilicum L.). Results showed that water deficit treatment reduced leaf chlorophyll content, leaf soluble proteins, shoot dry weight and essential oil yield. The highest concentration of total chlorophyll and leaf soluble protein was obtained in normal irrigation and fertilizer regime of 1 ton vermicompost. And water deficit stress reduced these two traits. The lowest activity of antioxidant enzymes was obtained under non-stress conditions. Increasing of water deficit stress increased the activity of these antioxidants among fertilizer treatments. The highest activity of this antioxidant was obtained in non-fertilizer treatment and by adding vermicompost fertilizer to fertilizer treatment of this antioxidant. Forks also declined. The shoot dry weight and essential oil yield decreased under water deficit stress. Increasing vermicompost share in fertilizer treatments led to increased yield. The percentage of essential oil increased with moderate irrigation and decreased again with severe irrigation. In general, the results showed that vermicompost had a positive effect on both vegetative and physiological traits of the plant. Keywords: Catalase, Compost, Peroxidase, Secondary metabolites, Urea fertilizer DOI: 10.7176/JSTR/5-11-12

Mapping of genomic regions associated with arsenic toxicity stress in a backcross breeding populations of rice (Oryza sativa L.)

BackgroundArsenic (As) is an unwanted toxic mineral that threatens the major rice-growing regions in the world, especially in South Asia. Rice production in Bangladesh and India depends on As-contaminated groundwater sources for irrigating paddy fields, resulting in elevated amounts of As in the topsoil. Arsenic accumulating in rice plants has a significant negative effect on human and animal health. Here, we present a quantitative trait locus (QTL) mapping study to identify candidate genes conferring As toxicity tolerance and accumulation in rice (Oryza sativa L.) seedlings. An early backcross breeding population consisting of 194 lines derived from a cross between WTR1 (indica) and Hao-an-nong (japonica) was grown in hydroponics for 25 days, from the seventh day exposed to an environmentally relevant concentration of 10 ppm As.ResultsArsenic toxicity leads to significantly negative plant responses, including reduced biomass, stunted plant growth, reduced leaf chlorophyll content, and increased shoot As concentration ranging from 9 to 20 mg kg− 1. Marker-trait association was determined for seven As-related traits using 704 single nucleotide polymorphism (SNP) markers generated from a 6 K SNP-array. One QTL was mapped on chromosome 1 for relative chlorophyll content, two QTLs for As content in roots were mapped on chromosome 8, and six QTLs for As content in shoots were mapped on chromosomes 2, 5, 6, and 9. Using the whole-genome sequence of the parents, we narrowed down the number of candidate genes associated with the QTL intervals based on the existence of a non-synonymous mutation in genes between the parental lines. Also, by using publicly available gene expression profiles for As stress, we further narrowed down the number of candidate genes in the QTL intervals by comparing the expression profiles of genes under As stress and control conditions. Twenty-five genes showing transcription regulation were considered as candidate gene nominees for As toxicity-related traits.ConclusionsOur study provides insight into the genetic basis of As tolerance and uptake in the early seedling stage of rice. Comparing our findings with the previously reported QTLs for As toxicity stress in rice, we identified some novel and co-localized QTLs associated with As stress. Also, the mapped QTLs harbor gene models of known function associated with stress responses, metal homeostasis, and transporter activity in rice. Overall, our findings will assist breeders with initial marker information to develop suitable varieties for As-contaminated ecosystems.

Effect of phosphorus concentration on the photochemical stability of PSII and CO2 assimilation in Pistacia vera L. and Pistacia atlantica Desf.

A greenhouse pot experiment was conducted at the faculty of sciences of Gafsa to evaluate the effect of phosphorus treatment on two pistachio species. The seedlings of Pistacia vera and Pistacia atlantica were subjected to six levels of phosphoric acid (P2O5) (0, 5, 15, 30, 60 and 120 ppm). Stomatal conductance, net photosynthesis, chlorophyll fluorescence (OJIP) and total chlorophyll content were measured after 1, 2, 3, 6, 8, 9 and 12 weeks of treatment. During the experiment, phosphorus application at 5 ppm increased photosynthesis and stomatal conductance, relative to the treatment 0 ppm only in P. atlantica. However, phosphorus supply at 60 and 120 ppm induced toxicity leading to an inhibition of CO2 photo-assimilation rate, an alteration of photosystem II (PSII) structure and function and reduction in leaf chlorophyll content in both species. The (OJIP) transient showed complex changes in O-J, J-I and I–P phases of fluorescence. Due to phosphorus toxicity, both donor and acceptor sides of PSII were damaged, electron transport perturbed and chlorophyll pigment reduced which resulted in the fall of CO2 photo-assimilation rate, followed by mortality in both species.

Biochemical, Physiological and Anatomical Mechanisms of Adaptation of Callistemon citrinus and Viburnum lucidum to NaCl and CaCl2 Salinization.

Callistemon citrinus and Viburnum lucidum are appreciated and widespread ornamental shrubs for their abundant flowering and/or brilliant foliage. The intrinsic tolerance to drought/salinity supports their use in urban areas and in xeriscaping. Despite adaptive responses of these ornamental species to sodium chloride (NaCl) have been extensively explored, little is known on the effects of other salt solution, yet iso-osmotic, on their growth, mineral composition and metabolism. The present research was aimed to assess responses at the biochemical, physiological and anatomical levels to iso-osmotic salt solutions of NaCl and CaCl2 to discriminate the effects of osmotic stress and ion toxicity. The two ornamental species developed different salt-tolerance mechanisms depending on the salinity sources. The growth parameters and biomass production decreased under salinization in both ornamental species, independently of the type of salt, with a detrimental effect of CaCl2 on C. citrinus. The adaptive mechanisms adopted by the two ornamental species to counteract the NaCl salinity were similar, and the decline in growth was mostly related to stomatal limitations of net CO2 assimilation rate, together with the reduction in leaf chlorophyll content (SPAD index). The stronger reduction of C. citrinus growth compared to V. lucidum, was due to an exacerbated reduction in net photosynthetic rate, driven by both stomatal and non stomatal limitations. In similar conditions, V. lucidum exhibited other additional adaptive response, such as modification in leaf functional anatomical traits, mostly related to the reduction in the stomata size allowing plants a better control of stomata opening than in C. citrinus. However, C. citrinus plants displayed an increased ability to retain higher Cl- levels in leaves than in roots under CaCl2 salinity compared to V. lucidum, thus, indicating a further attempt to counteract chloride toxicity through an increased vacuolar compartmentalization and to take advantages of them as chip osmotica.

Effects of drought stress on growth, grain filling duration, yield and quality attributes of barley (Hordeum vulgare L.)

A pot experiment was conducted to investigate the effect of drought stress at start of anthesis (applied by adjusting the field capacities at 100, 50 and 30%) on barley growth, grain filling duration, grain shape, yield and quality attributes. The effect of drought stress was more prominent on plant fresh biomass accumulation, grain yield and grain filling duration. However, it produced non-significant effect on total number of tillers and grain protein contents. With the increasing intensity of drought stress, barley growth and yield traits significantly diminished. Water stress gradually shortened the plant height and biomass accumulation but the difference was more prominent in fresh biomass accumulation (– 45%) over dry biomass accumulation. The field capacity of 30% caused 29 - 41% reduction in leaf chlorophyll content and 10 - 27% in grain quality traits. Root fresh and dry biomass accumulation decreased by drought stress while root length increased. Drought stress produced uneven grain size that resulted in lower grain yield (42%) specially at 30% field capacity. This reduction in yield was also due to the decreased grain filling duration (38 d) at 30% field capacity as compared to 100% field capacity. So, it may be concluded that drought stress affected barley yield through impaired grain development and grain filling duration. The results of present study are satisfactory and needed further exploration about the physiological mechanism and management strategies to overcome drought stress related yield losses in barley crop.

Combined effect of water inundation and heavy metals on the photosynthesis and physiology of Spartina alterniflora

The frequency and duration of tidal flooding significantly influence the bioavailability of heavy metals (HMs) in sediment and hence exert toxicological effects on coastal wetland plants. In this study, the combined effects of different water inundation times (3, 6, 9, and 12 h) and HMs (Cu, Zn, Pb, and Cr) on the photosynthesis and physiology of Spartina alterniflora were investigated under greenhouse conditions. Results showed that S. alterniflora was somehow tolerant to the combined HMs treatments, and only the highest level of HM treatment decreased leaf chlorophyll content. Furthermore, the plants did not show any signs of victimization. Different times of water inundation with HMs did not exert any significant effect on the malonaldehyde (MDA) and chlorophyll contents in the leaves of S. alterniflora at day 20. Prolonged water inundation time at day 60 significantly reduced leaf chlorophyll content with the decrease in leaf photosynthetic rate, which was accompanied by a significant increase in the intercellular concentration of CO2. At day 60, abscisic acid dose-dependently increased along the different water inundation times, indicating that this phytohormone is involved in plant responses to flooding stress. Peroxidase (POD), superoxide dismutase (SOD), and ascorbate peroxidase (APX), showed different responses to the combined treatment of water inundation and HMs at different times. At day 20, the long duration of water inundation and HMs treatments (9 h+HMs and/or 12 h+HMs) significantly increased enzyme activity in the leaves compared with the control group (6 h). At day 60, the POD and SOD activities in the leaves of S. alterniflora decreased with prolonged water inundation time, and root APX activity significantly decreased compared with the 6 h water inundation treatment.

Direct effect of acid rain on leaf chlorophyll content of terrestrial plants in China

Anthropogenic emissions of acid precursors in China have resulted in widespread acid rain since the 1980s. Although efforts have been made to assess the indirect, soil mediated ecological effects of acid rain, a systematic assessment of the direct foliage injury by acid rain across terrestrial plants is lacking. Leaf chlorophyll content is an important indicator of direct foliage damage and strongly related to plant productivity. We synthesized data from published literature on experiments of simulated acid rain, by directly exposing plants to acid solutions with varying pH levels, to assess the direct effect of acid rain on leaf chlorophyll content across 67 terrestrial plants in China. Our results indicate that acid rain substantially reduces leaf chlorophyll content by 6.71% per pH unit across the recorded plant species. The direct reduction of leaf chlorophyll content due to acid rain exposure showed no significant difference across calcicole, ubiquist or calcifuge species, implying that soil acidity preference does not influence the sensitivity to leaf injury by acid rain. On average, the direct effects of acid rain on leaf chlorophyll on trees, shrubs and herbs were comparable. The effects, however varied across functional groups and economic use types. Specifically, leaf chlorophyll content of deciduous species was more sensitive to acid rain in comparison to evergreen species. Moreover, vegetables and fruit trees were more sensitive to acid rain than other economically used plants. Our findings imply a potential production reduction and economic loss due to the direct foliage damage by acid rain.