Decline In Chlorophyll Content Research Articles

Plant growth regulators improve the yield of white lupin (Lupinus albus) by enhancing the plant morpho-physiological functions and photosynthesis under salt stress

BackgroundWhite lupin (Lupinus albus L.) is a multi-purpose, climate resilient, pulse crop with exceptionally high protein content that makes it a suitable alternative of soybean in livestock feed. Although white lupin grows well on marginal sandy soils, previous studies have reported its sensitivity towards salinity stress. This experiment aims to assess the influence of salinity stress and mitigating role of plant growth regulators (PGRs) on performance of white lupin.MethodologyThe white lupin plants were sown in pots maintained at three salinity levels (1, 3 and 4.5 dS m− 1) throughout the growing season and foliar sprayed with different PGRs, including ascorbic acid, potassium chloride, boric acid, ammonium molybdate and methionine at sowing, four weeks after emergence and at the initiation of flowering. Foliar spray of distilled water and salinity level of 1 dS m− 1 were maintained as control treatments. Data were recorded for seed germination indices, plant growth, antioxidant enzymes and photosynthetic efficiency variables.ResultsThe severe salinity stress (4.5 dS m− 1) reduced the germination indices by 9–50%, plant growth traits by 26–54%, root nodulation by 12–26%, grain development by 44–53%, antioxidant enzymes activity by 13–153% and photosynthetic attributes by 1–8% compared to control (1 dS m− 1). Different PGRs improved several morpho-physiological attributes in a varied manner. The application of potassium chloride improved seed vigour index by 53%, while ascorbic acid improved root nodulation by 12% and number of pods per cluster by 75% at the severe salinity level. The foliar application of PGRs also displayed a recovery of 140% in the activity of superoxide dismutase and 70% in catalase. The application of multi zinc displayed an improvement of 37% in plant relative chlorophyll, while ascorbic acid brought an increase of 25% in non-photochemical quenching and 21% in photochemical quenching coefficient at the severe salinity level. On contrary, the application of PGRs brought a relatively modest improvement (8–13%) in quantum yield of photosystem II at slight to moderate (3 dS m− 1) salinity stress. The correlation analysis confirmed a partial contribution of leaf area and seed vigour index to overall photosynthetic efficiency of white lupin.ConclusionsClearly, salinity exerted a negative impact on white lupin through a decline in chlorophyll content, activity of antioxidant enzymes and efficiency of photosynthetic apparatus. However, PGRs, especially ascorbic acid and potassium chloride considerably improved white lupin growth and development by mitigating the negative effects of salinity stress.

Acute toxicity of salicylic acid and its derivatives on the diatom Phaeodactylum tricornutum: Physico-Biochemical and transcriptomic insights

Salicylate pollutants (SAs) poses a serious threat to marine ecosystems as emerging contaminants. However, the toxic effects of SAs on marine phytoplankton, as well as the potential mechanisms and their ecological risks linked with them, are remain largely unknown. In this study, we aimed to evaluate the toxic effects of salicylic acid (SA) and its 5-substituted derivatives (5-sSA) on the marine diatom Phaeodactylum tricornutum, as well as the potential molecular mechanism involved in the toxicity. Physiological assays conducted on P. tricornutum revealed significant changes in photosynthetic pigments, chlorophyll fluorescence parameters, and antioxidant enzyme activities. The results showed that exposure of P. tricornutum to SAs caused a significant decline in chlorophyll contents and damage to the photosystem II (PSII) core resulting in the decline of photosynthesis. Although the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, oxidative damage occurred. Transcriptome analysis showed that a large number of differentially expresses genes (DEGs) were significantly enriched in metabolic pathways such as porphyrin metabolism, terpenoid backbone biosynthesis, and carbon fixation in photosynthetic organisms after SA and 5-BrSA treatments. In addition, key genes in transcriptomic metabolic pathways were further analyzed and validated using weighted correlation network analysis (WGCNA) and real-time fluorescence quantitative PCR (qPCR). Considering the above results, SAs mainly inhibit the processes of photosynthesis by repressing the expression of genes involved in secondary metabolite synthesis and photosynthetic carbon sequestration pathways, thus exerting toxic effects on algal cells. The results of the study will provide key data for understanding the ecological risk and toxicity mechanisms of SA pollutants.

Low temperature and high humidity affect dynamics of chlorophyll biosynthesis and secondary metabolites in Cucumber.

During the cold season, low temperature (LT) and high relative humidity (HRH) are significant environmental factors in greenhouses and plastic tunnels, often hindering plant growth and development. The chlorophyll (Chl) biosynthesis inhibitory mechanisms under LT and HRH stress are still widely unclear. To understand how cucumbers seedlings respond to LT and HRH stress, we investigated the impact of these stressors on Chl biosynthesis. Our results revealed that individual LT, HRH and combined LT + HRH stress conditions affected chlorophyll a, b, total chlorophyll and carotenoid content, reducing the levels of these pigments. The levels of Chlorophyll precursors were also markedly reduced under LT and HRH stresses, with the greatest reduction observed in cucumber seedlings exposed to LT + HRH conditions (9/5℃, 95%HRH). The activities of glutamate-1-semialdehyde transaminase (GSA-AT), ALA dehydratase (ALAD), Mg-chelatase, and protochlorophyllide oxidoreductase (POR) were increased under individual LT, HRH, conditions but decreased by combination of LT + HRH stress condition. In addition, Chl biosynthesis related genes (except PBG) were upregulated by the HRH stress but were significantly downregulated under the LT + HRH stress condition in cucumber seedlings. Furthermore, the content of phenols, flavonoids and phenolic acids (cinnamic acid and caffeic acid) were significantly surged under LT + HRH treatment over the control. Histochemical observation showed higher O2- and H2O2 content in cucumber leaves during the LT and HRH stress. The results indicate that LT + HRH stress significantly impairs chlorophyll biosynthesis in cucumber seedlings by drastically reducing pigment accumulation, altering enzyme activity and gene expression. Additionally, LT + HRH stress induces oxidative damage, which further exacerbates the decline in chlorophyll content and affects overall cucumber metabolism.

Comparative Analysis of Phytohormone Biosynthesis Genes Responses to Long-Term High Light in Tolerant and Sensitive Wheat Cultivars.

Phytohormones are vital for developmental processes, from organ initiation to senescence, and are key regulators of growth, development, and photosynthesis. In natural environments, plants often experience high light (HL) intensities coupled with elevated temperatures, which pose significant threats to agricultural production. However, the response of phytohormone-related genes to long-term HL exposure remains unclear. Here, we examined the expression levels of genes involved in the biosynthesis of ten phytohormones, including gibberellins, cytokinins, salicylic acid, jasmonic acid, abscisic acid, brassinosteroids, indole-3-acetic acid, strigolactones, nitric oxide, and ethylene, in two winter wheat cultivars, Xiaoyan 54 (XY54, HL tolerant) and Jing 411 (J411, HL sensitive), when transferred from low light to HL for 2-8 days. Under HL, most genes were markedly inhibited, while a few, such as TaGA2ox, TaAAO3, TaLOG1, and TaPAL2, were induced in both varieties. Interestingly, TaGA2ox2 and TaAAO3 expression positively correlated with sugar content but negatively with chlorophyll content and TaAGP expression. In addition, we observed that both varieties experienced a sharp decline in chlorophyll content and photosynthesis performance after prolonged HL exposure, with J411 showing significantly more sensitivity than XY54. Hierarchical clustering analysis classified the phytohormone genes into the following three groups: Group 1 included six genes highly expressed in J411; Group 2 contained 25 genes drastically suppressed by HL in both varieties; and Group 3 contained three genes highly expressed in XY54. Notably, abscisic acid (ABA), and jasmonic acid (JA) biosynthesis genes and their content were significantly higher, while gibberellins (GA) content was lower in XY54 than J411. Together, these results suggest that the differential expression and content of GA, ABA, and JA play crucial roles in the contrasting responses of tolerant and sensitive wheat cultivars to leaf senescence induced by long-term HL. This study enhances our understanding of the mechanisms underlying HL tolerance in wheat and can guide the development of more resilient wheat varieties.

Toxicity of CuFe and Co-doped CuFe layered double hydroxides on algae: Insights into synthesis, growth inhibition, morphological changes, and antioxidative enzyme responses

Layered double hydroxides (LDH) are widely used in a variety of industries due to their unique structural characteristics. It is essential to comprehend the environmental behavior and toxicological impacts of these substances to address potential risks caused by LDH release into the environment. In this study, CuFe and Cobalt (Co)-doped CuFe LDHs were synthesized and their toxicities to Chlorella vulgaris were investigated. In the scanning electron microscope images, the Co-doped and undoped catalysts appeared as uniformly dispersed flakes. The X-ray diffraction pattern of the Co-doped CuFe LDH confirmed the successful incorporation of Co into the crystalline lattice of the LDH. The growth of C. vulgaris was negatively affected by the presence of 1 mg/L LDHs, with membrane damage and cell wrinkling observed with 20 mg/L. The CuFe LDH-exposed algae exhibited a significantly greater decline in chlorophyll content compared to that of the Co-doped LDH-exposed algae. However, superoxide dismutase activity was elevated in algal cells exposed to the Co-doped CuFe LDH. Catalase activity increased up to 20 mg/L, followed by a decline at higher doses in CuFe LDH-exposed cells. From an ecological perspective, the lack of increased toxicity after Co doping is favorable for aquatic life. The extensive characterization, together with a rigorous toxicity assessment, provides new information about the environmental safety of cobalt doping to aid in the development of safer and more sustainable LDH-based products.

Exogenous melatonin delays programmed cell death in broccoli via maintenance of ROS homeostasis and reduction of mitochondrial dysfunction

Plant senescence is the final period of the plant life cycle and represents a programmed cell death (PCD) process. Melatonin, a versatile signaling molecule, exhibits potent free radical scavenging properties and actively participates in cellular antioxidant systems, effectively retarding plant senescence throughout its development. In order to illustrate the impact of melatonin on PCD during senescence, we examined the effects of exogenous melatonin at 80 μmol L−1 on PCD and mitochondrial function in broccoli bud cells at 25 ℃. The findings revealed that melatonin treatment not only maintained the morphological integrity of chloroplasts and mitochondria but also attenuated the decline in chlorophyll content by reducing the expression of genes that metabolize chlorophyll, including BoPPH, BoPAO, and BoSGR1. In comparison to the control group, the treatment decreased the content of H2O2 and the rate of O2- production in mitochondria and simultaneously enhanced the activities of ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), resulting in effective maintenance of reactive oxygen species (ROS) homeostasis and reduction of the level of lipid peroxidation in broccoli buds during senescence. Meanwhile, exogenous melatonin treatment up-regulated alternative oxidase (AOX) activity and its gene expression while delayed the reduction of cytochrome oxidase (COX) activity and restrained the over-opening of mitochondrial permeability transition pores (MPTP). Additionally, exogenous melatonin decelerated the increase in membrane potential and prevented mitochondria from releasing excess cytochrome c (Cyt c) into the cytoplasm. Taken together, the results indicate that melatonin treatment delayed mitochondrial dysfunction, preserved mitochondrial ROS homeostasis, and consequently postponed the initiation of PCD, ultimately inhibiting senescence in broccoli.

Integrated transcriptome and metabolome analysis unveils the mechanism of color-transition in Edgeworthia chrysantha tepals

BackgroundEdgeworthia chrysantha, a deciduous shrub endemic to China, is known for its high ornamental value, extensive cultivation history, and wide-ranging applications. However, theoretical research on this plant is severely lacking. While its flowering process displays striking color transitions from green (S1) to yellow (S2) and then to white (S3), the scientific exploration of this phenomenon is limited, and the underlying regulatory mechanisms are yet to be elucidated.ResultsCorrelation analysis between phenotypic measurements and pigment content revealed that carotenoids and chlorophyll are the key pigments responsible for the color changes. Metabolomic analysis of carotenoids demonstrated that lutein and β-carotene were present at higher levels in S1, while S2 exhibited increased diversity and quantity of carotenoids compared to other stages. Notably, antheraxanthin, zeaxanthin, lycopene, and α-cryptoxanthin showed significant increases. In S3, apart from the colorless phytoene, other carotenoid metabolites were significantly reduced to extremely low levels. Transcriptomic data indicated that PSY, Z-ISO, crtZ, ZEP, PDS and ZDS are key genes involved in carotenoid biosynthesis and accumulation, while NCED plays a crucial role in carotenoid degradation. SGR was identified as a key gene contributing to the progressive decline in chlorophyll content. Additionally, three transcription factors potentially regulating carotenoid metabolism were also identified.ConclusionsThis study represents the first systematic investigation, spanning from phenotypic to molecular levels, of the color-changing phenomenon in E. chrysantha. The study elucidates the crucial pigments, metabolites, genes, and transcription factors responsible for flower color changes during the flowering process, thereby providing preliminary understanding of the intrinsic regulatory mechanisms. These findings establish a theoretical foundation for the genetic improvement of flower color in E. chrysantha.

Phytotoxic Effects of Tetracycline and its Removal Using Canna indica in a Hydroponic System.

Wetland plants are gaining interest as potential agents for removing emerging contaminants. However, there have been limited studies examining the ability of these plant species to remove antibiotics and their tolerance to stress. This study aimed to investigate the potential of Canna indica, an indigenous wetland plant species in India, for tetracycline-induced oxidative stress, antioxidant activity, and removal of antibiotics from nutrient media and domestic wastewater. Canna indica exhibited a removal rate of approximately 91.05 ± 0.18% for tetracycline in antibiotic containing nutrient media and 87.97 ± 0.39% in domestic wastewater. Notably, the exposure to the drug during the 30 d reaction period led to the accumulation of reactive oxygen species in the plant tissues. Consequently, there was a decline in chlorophyll content, alongside an increase in antioxidant activity, membrane permeability, and K + ion leakage. These findings emphasize the importance of monitoring tolerance levels induced by antibiotics in plant species. Thus, monitoring the antibiotic-induced-tolerance levels in plant species is crucial for maintaining plant health and effectively managing abiotic stress, ensuring efficient recovery and facilitating an effective wetland treatment system.

Genome-wide identification of PLATZ genes related to cadmium tolerance in Populus trichocarpa and characterization of the role of PtPLATZ3 in phytoremediation of cadmium

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific zinc finger transcription factors that perform critical functions in plant development and resistance. However, the function of PLATZs in heavy metal tolerance has not yet been investigated. Moreover, only a few PLATZ proteins have been functionally characterized in tree species. In this study, we identified 18 PtPLATZ genes in Populus trichocarpa, an important woody model plant, and classified them into five groups. PtPLATZ genes attributed to the same clade usually possess similar exon-intron structures containing two or three introns, as well as a similar motif composition. Furthermore, chromosomal location analysis indicated an uneven distribution of PtPLATZ genes on 13 of the 19 Populus chromosomes. Promoter cis-acting element prediction and gene expression analysis showed that PtPLATZ genes were highly responsive to heavy metal stress. Heterologous yeast expression revealed that PtPLATZ1, PtPLATZ2, PtPLATZ3, PtPLATZ4, PtPLATZ8 and PtPLATZ9 are significantly involved in Cd tolerance. In addition, transgenic expression of PtPLATZ3 significantly enhanced Cd tolerance and accumulation, slowed the decline in chlorophyll content, maintained membrane integrity in Populus, and increased the expression of genes related to Cd tolerance and accumulation. In conclusion, our results suggest the potential of PtPLATZ3 to improve Cd tolerance and accumulation in Populus, which is of great significance for phytoremediation.

PsbA gene over-expression and enhanced metabolism conferring resistance to atrazine in Commelina communis

Commelina communis L. is a troublesome weed in agronomic fields and increasingly threatens the yield security of corn in north-eastern China. Previously, we found that a C. communis population (JL-1) has evolved resistance to atrazine. Although the potential genetic and enzymic differences contributing to atrazine resistance in this population have been investigated, the specific molecular mechanisms underlying C. communis resistance are still poorly understood. Here, the expression level of the target gene PsbA and the non-target-site resistance (NTSR) mechanism for this population were studied. The results showed that the decline in chlorophyll content in JL-1 leaves was less than in the susceptible JS-10 population following atrazine treatment. JL-1 exhibited an enhanced expression of the PsbA gene compared with JS-10 of 7.28- and 14.28-fold higher at 0 and 24 h after treatment with atrazine, respectively. The cytochrome P450 monooxygenase (P450) inhibitor piperonyl butoxide (PBO) increased the phytotoxicity of atrazine in both populations of C. communis. Seven candidate genes associated with NTSR of Jl-1 were identified through RNA-seq and validated by quantitative real-time PCR, including 5 upregulated genes involved in herbicide metabolism. In addition, the activities of glutathione S-transferases and P450s in JL-1 were increased compared with JS-10. Collectively, PsbA gene overexpression and enhanced metabolism are likely to be responsible for JL-1 resistance to atrazine.

Melatonin delays leaf senescence and improves cucumber yield by modulating chlorophyll degradation and photoinhibition of PSII and PSI

Decreases in chlorophyll and photosynthetic efficiency co-occur during aging and leaf senescence. Here, we report the positive functions of melatonin (MT) in delaying leaf senescence in cucumber plants. The results showed that natural leaf senescence induced the accumulation of endogenous MT and that spraying MT delayed leaf senescence in a concentration-dependent manner. Moreover, application of MT and transient overexpression of CsASMT, the key gene in MT synthesis, both suppressed leaf senescence simulated by darkness. This was evidenced by a decrease in expression of the senescence-related gene SAG12 and the cell death-related gene PDCD, an increase in chlorophyll content in terms of downregulation of chlorophyll-degradation genes and normal chloroplast structure, and higher activity of PSI and PSII reaction centers, electron transfer efficiency and photosynthesis-associated protein levels, compared with these measures in the H2O-treated seedlings. In addition, the data from field spraying experiments demonstrated that MT indeed alleviated the decline in chlorophyll content and increased photosynthetic efficiency in both functional and senescent leaves, which ultimately promoted the growth and yield of cucumber in the solar greenhouse. Together, these results indicate that MT acts as a positive regulator to downregulate SAG12 and PDCD mRNA abundances and alleviate damage to the photosynthetic apparatus by suppressing chloroplast disintegration and photosynthesis-associated protein degradation during leaf senescence.

Drought-Induced Oxidative Stress in Pearl Millet (Cenchrus americanus L.) at Seedling Stage: Survival Mechanisms through Alteration of Morphophysiological and Antioxidants Activity.

We report the impact of drought stress on pearl millet during the early seedling stage and its survival mechanism. Drought stress imposed for a period of 7, 14 and 21 days showed considerable changes in morphophysiological attributes, which were evident by a decline in seedling elongation, fresh and dry biomass, and relative water content (RWC) and degradation of chlorophyll pigment. Besides this, visible chlorosis lesions were observed in leaves as compared to the control. As compared to the respective controls, a nearly 60% decline in chlorophyll content was recorded after 14 and 21 days of drought stress. In both root and shoot, drought stress raised the reactive oxygen species (ROS) levels. Both H2O2 and O2●− levels were significantly elevated along with a significant increase in lipid peroxidation in both roots and shoots, which clearly indicated ROS-induced oxidative stress. Concomitant with the increase in ROS levels and malondialdehyde (MDA) content in roots, membrane integrity was also lost, which clearly indicated ROS-induced peroxidation of membrane lipids. The activities of antioxidant enzymes and levels of non-enzymatic antioxidants were significant (p ≤ 0.001). After 7, 14 and 21 days of drought stress, activities of all the antioxidant enzymes viz., catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and glutathione reductase (GR) were inhibited, clearly indicating a loss of antioxidant defense machinery. Likewise, the levels of ascorbate (AsA) and reduced glutathione (GSH) levels declined significantly (p ≤ 0.01). Our results reveal that, being tolerant to arid climatic conditions, pearl millet is highly susceptible to drought stress at the early seedling stage.

Fate of carbamazepine and its effect on physiological characteristics of wetland plant species in the hydroponic system

Plants play a cardinal role in removing various pollutants through the synergistic interaction with filling materials and microbes of constructed wetlands (CWs). However, the information regarding the selection of plant species to remove pharmaceutically active compounds (PhACs) is not adequate. The present study attempted to select an appropriate plant species for CWs, considering their characteristics and physiological response to PhACs. In this regard, batch hydroponics studies were carried out to assess the removal, fate, and antioxidative response of carbamazepine (CBZ) in four wetland plant species (Canna indica, Colocasia esculenta, Phragmites australis, and Chrysopogon zizanioides). The specific uptake potential of CBZ (in terms of plant dry biomass) was found to be in the order: C. indica (14.48 mg/g) >P. australis (11.71 mg/g) >C. esculenta (8.67 mg/g) >C. zizanioides (6.04 mg/g). The results showed that exposure to CBZ (0–30 days) caused an accumulation of reactive oxygen species (ROS) in the plant tissues, causing a decline in chlorophyll content, root activity, and increased oxidative stress. However, the selected plants could recover from the oxidative damages to a certain extent in the recuperation phase (31–60 days). C. indica exhibited relatively lesser ROS accumulation and oxidative damage during the experimental phase than other selected plants. The study also showed that plant biomass, transpiration rate, chlorophyll content, root exudates, and root activity influenced the removal of CBZ by various plants (r – 0.76 to 0.98, P < 0.05). The mass balance analysis indicated that a significant proportion of CBZ (49.2 to 72.7 %) underwent metabolism in the plant tissues. Apart from higher removal, lesser accumulation, and lower oxidation stress, multi-criteria decision analysis showed that C. indica is a potential plant species for the removal of CBZ.

Mucilaginibacter sp. K Improves Growth and Induces Salt Tolerance in Nonhost Plants via Multilevel Mechanisms.

Soil salinity negatively modulates plant growth and development, contributing to severe decreases in the growth and production of crops. Mucilaginibacter sp. K is a root endophytic bacterium that was previously reported by our laboratory to stimulate growth and confer salt tolerance in Arabidopsis (Arabidopsis thaliana). The main purpose of the present study is to elucidate the physiological and molecular machinery responsible for the prospective salt tolerance as imparted by Mucilaginibacter sp. K. We first report that auxin, gibberellin, and MPK6 signalings were required for strain K-induced growth promotion and salt tolerance in Arabidopsis. Then, this strain was assessed as a remediation strategy to improve maize performance under salinity stress. Under normal growth conditions, the seed vigor index, nitrogen content, and plant growth were significantly improved in maize. After NaCl exposure, strain K significantly promoted the growth of maize seedlings, ameliorated decline in chlorophyll content and reduced accretion of MDA and ROS compared with the control. The possible mechanisms involved in salt resistance in maize could be the improved activities of SOD and POD (antioxidative system) and SPS (sucrose biosynthesis), upregulated content of total soluble sugar and ABA, and reduced Na+ accumulation. These physiological changes were then confirmed by induced gene expression for ion transportation, photosynthesis, ABA biosynthesis, and carbon metabolism. In summary, these results suggest that strain K promotes plant growth through increases in photosynthesis and auxin- and MPK6-dependent pathways; it also bestows salt resistance on plants through protection against oxidative toxicity, Na+ imbalance, and osmotic stress, along with the activation of auxin-, gibberellin-, and MPK6-dependent signaling pathways. This is the first detailed report of maize growth promotion by a Mucilaginibacter sp. strain from wild plant. This strain could be used as a favorable biofertilizer and a salinity stress alleviator for maize, with further ascertainment as to its reliability of performance under field conditions and in the presence of salt stress.

Impact of dust accumulation on the physiological functioning of selected herbaceous plants of Delhi, India.

Plants are now widely recognized for their potential role in improving the air quality by dispersion and deposition of atmospheric dust particles. However, suspended dust particles negatively affect plant growth and physiological development. The present study aims to assess the amount of dust accumulation on the leaf surface and to evaluate the effect of foliar dust on leaf gas exchange parameters, photosynthetic pigment, and metabolite content of five roadside herbaceous plant species (Amaranthus viridis, Achyranthes aspera, Acalypha indica, Parthenium hysterophorus, Trianthema portulacastrum). Two sites (site I and site II) were selected that differed in their surrounding anthropogenic activities and dust pollution levels. Results showed that the average amount of dust accumulated on the leaf surface was significantly greater in plants grown at the polluted site. Among the five species examined, the highest amount of foliar dust load was observed for A. aspera (0.49mgcm-2). Dust accumulation caused substantial changes in plant physiology as indicated by the significant decline in chlorophyll content, photosynthetic rate, stomatal conductivity, and transpiration rate in plants grown at the polluted site. Moreover, an increase in antioxidant activity, total ascorbate, and metabolite content, responsible for maintaining plant defense, was higher in plants at polluted site. Biochemical response of the individual plants studied was variable, which suggests that different plants adopted different mechanisms to cope with the stress induced by dust particles.

The role of PAP4/FSD3 and PAP9/FSD2 in heat stress responses of chloroplast genes

Chloroplasts’ mechanisms of adaptation to elevated temperatures are largely determined by the gene expression of the plastid transcription apparatus. Gene disruption of iron-containing superoxide dismutase PAP4/FSD3 and PAP9/FSD2, which are parts of the DNA–RNA polymerase complex of plastids, contributed to a decrease in resistance to oxidative stress caused by the prolonged action of elevated temperatures (5 days, 30 °C). Under heat stress conditions, pap4/fsd3 and pap9/fsd2 mutants showed a decline in chlorophyll content and photosynthesis level, as measured by photosynthetic parameters, and a different amplitude of HSP gene response to heat stress. The expression of nuclear- and plastid-encoded photosynthesis genes and corresponding proteins was strongly inhibited in the mutants as compared with wild-type plants and was further suppressed or displayed no additional changes at 30 °C. NEP-dependent plastid genes, as well as NEP genes RPOTp and RPOTmp, were also downregulated in the mutants by high temperature or remained stable, unlike in wild-type seedlings where these genes were strongly upregulated. The results obtained correspond to the concept of the complex effect of various forms of reactive oxygen species under all types of stresses, including heat stress, and confirm the hypothesis of a new regulatory function in plastid transcription acquired by enzymatic proteins during evolution.

Flowering and Non-Flowering Spur Leaf Characteristics of 'Amasya' Apple and Its Comparison with Other Cultivars

Understanding the attributes of spur leaves in apple trees is essential to gain more insight into the complex process of fruit development and quality. However, limited literature is available about the spur leaf characteristics of the 'Amasya' apple cultivar. In this work, the Soil Plant Analysis Development (SPAD) and leaf area were investigated in flowering and non-flowering spur leaves of 'Amasya' and six common apple cultivars. Significant differences among cultivars were observed for the SPAD and spur leaf area. The median SPAD readings in 'Amasya' were 32.63 and 26.23 for the flowering and non-flowering spurs, respectively, which were the relatively low values among studied cultivars. The maximum SPAD value was measured in flowering spurs of 'Cripps Pink' (45.03). SPAD values were found to be lower in non-flowering spurs compared with flowering ones for all the studied cultivars, which confirms that decline in chlorophyll content coincided with a gradual decline in productivity. A notably significantly lower spur leaf area was found in 'Amasya', whereas the highest spur leaf area was in 'Cripps Pink'. However, no statistical difference was observed between flowering and non-flowering spur leaf areas within the same cultivars. The present results provided a general framework of SPAD and spur leaf areas in 'Amasya' and other apple cultivars when spurs had flowers or not. Knowledge of these characteristics provides a basis for building a model related to yield elaboration of apple trees.

不同抗旱性甘薯品种叶片生理性状差异及抗旱指标筛选

<p id="C3">Field experiments were conducted under a rain proof shelter using 15 sweetpotato cultivars with well-watered and drought stress treatments. Leaf physiological characteristics of different sweetpotato cultivars under drought stress were studied. The results showed that the leaf area index of all varieties decreased in different degrees under drought stress, which evaluating the difference of drought tolerance in varieties. Cluster analysis of drought resistance coefficient revealed that 15 sweetpotato cultivars were classified into three drought resistant types. The drought-tolerant cultivars were Jishu 21, Jishu 25, Jixu 23, Jishu 15, and Yanshu 25. The moderate drought-tolerant cultivars were Xushu 18, Jishu 26, Beijing 553, Jizishu 2, and Jishu 18. The drought-sensitive cultivars were Zhengshu 20, Jizishu 3, Jishu 22, Jizishu 1, and Ayamaraski. The correlation analysis between leaf area index and drought resistance coefficient demonstrated that the drought-tolerant cultivars could maintain higher leaf area index under drought stress, while the leaf area index under well-watered could not reflect the drought resistance. Drought stress resulted in the decline of chlorophyll content, the relative water content of functional leaves, and the increase of relative electrical conductivity of functional leaves. Under drought stress, the chlorophyll content and relative water content of functional leaves were significantly positively correlated with drought resistance in different cultivars, while the relative electrical conductivity of functional leaves was significantly negatively correlated with the drought resistance of sweetpotato varieties. In summary, leaf area index, chlorophyll content, relative water content, and relative electrical conductivity of functional leaves could be used as comprehensive evaluation indexes for identifying drought resistance of sweetpotato cultivars.

Improvement in drought tolerance in bread wheat is related to an improvement in osmolyte production, antioxidant enzyme activities, and gaseous exchange.

Water deficit stress negatively affects wheat growth, physiology, and yield. In lab and hydroponic experiments, osmotic stress levels (control, −2, −4, −6 and −8 Bars) created by PEG-6000, caused a significant decline in germination, mean germination time, root, shoot, and coleoptile length in both wheat genotypes examined. Germination was inhibited more in Wafaq-2001 than in Chakwal-50. Wafaq-2001 showed a higher susceptibility index based on root and shoot dry weight than did Chakwal-50. Wheat plants exhibited osmotic adjustment through the accumulation of proline, soluble sugars, soluble proteins, and free amino acids, and increased antioxidation activities of superoxide dismutase, peroxidase, catalase, and malondialdehyde. Increasing water deficit stress caused a linear decline in chlorophyll contents, leaf membrane stability, and relative water content in all wheat plants, with Wafaq-2001 showing a more severe negative impact on these parameters with increasing stress levels. The results suggest the possibility of utilizing some of these parameters as quantitative indicators of water stress tolerance in plants. Gas exchange measurements (photosynthesis, transpiration, stomatal conductance), leaf osmotic potential, water potential, and yield attributes decreased more abruptly with increasing water deficit, whereas leaf cuticular wax content increased in both genotypes, with more severe impacts on Wagaq-2001. More reduction in biochemical, physiological, and yield attributes was observed in Wafaq-2001 than was observed in Chakwal-50. Based on these results, we can conclude that Chakwal-50 is a more drought-tolerant genotype, and has excellent potential for future use in breeding programs to improve wheat drought tolerance.

Improving growth and photosynthetic performance of drought stressed tomato by application of nano-organic fertilizer involves up-regulation of nitrogen, antioxidant and osmolyte metabolism

Organic fertilizer usage is been introduced into agricultural practices for preventing the damaging effects of chemical fertilizers. Present study investigated the beneficial role of organic fertilizer (nano-vermicompost) on the growth, oxidative stress parameters, antioxidant and nitrogen metabolism, osmolyte accumulation and mineral elements in tomato under drought stress. Drought stress resulted in reduced growth and biomass accumulation by triggering oxidative stress due to excess accumulation of reactive oxygen species (ROS) and reduced mineral uptake. Application of nano-vermicompost proved significantly beneficial in improving growth and mitigating the drought induced growth decline. Nano-vermicompost increased growth and dry matter content and ameliorated the decline in chlorophyll contents, photosynthesis and PSII activity more significantly at higher concentration (100 mg kg−1 soil). ROS accumulation was significantly reduced by nano-vermicompost application thereby enhancing the membrane stability under normal as well as drought conditions. Furthermore, lipid peroxidation and activities of protease and lypoxygenase were significantly reduced. Drought up-regulated antioxidant system and application of nano-vermicompost further enhanced the activities of antioxidant enzymes and the contents of non-enzymatic antioxidant components. Accumulation of osmolytes including proline, glycine betaine and sugars increased significantly due to nano-vermicompost application. Besides, decline in the activity of nitrate reductase and content of essential mineral elements like nitrogen, potassium and phosphorous was also ameliorated by nano-vermicompost application.