Decrease In Chlorophyll Content Research Articles

AtMYB72 aggravates photosynthetic inhibition and oxidative damage in Arabidopsis thaliana leaves caused by salt stress

ABSTRACT MYB transcription factor is one of the largest families in plants. There are more and more studies on plants responding to abiotic stress through MYB transcription factors, but the mechanism of some family members responding to salt stress is unclear. In this study, physiological and transcriptome techniques were used to analyze the effects of the R2R3-MYB transcription factor AtMYB72 on the growth and development, physiological function, and key gene response of Arabidopsis thaliana. Phenotypic observation showed that the damage of overexpression strain was more serious than that of Col-0 after salt treatment, while the mutant strain showed less salt injury symptoms. Under salt stress, the decrease of chlorophyll content, the degree of photoinhibition of photosystem II (PSII) and photosystem I (PSI) and the degree of oxidative damage of overexpressed lines were significantly higher than those of Col-0. Transcriptome data showed that the number of differentially expressed genes (DEGs) induced by salt stress in overexpressed lines was significantly higher than that in Col-0. GO enrichment analysis showed that the response of AtMYB72 to salt stress was mainly by affecting gene expression in cell wall ectoplast, photosystem I and photosystem II, and other biological processes related to photosynthesis. Compared with Col-0, the overexpression of AtMYB72 under salt stress further inhibited the synthesis of chlorophyll a (Chla) and down-regulated most of the genes related to photosynthesis, which made the photosynthetic system more sensitive to salt stress. AtMYB72 also caused the outbreak of reactive oxygen species and the accumulation of malondialdehyde under salt stress, which decreased the activity and gene expression of key enzymes in SOD, POD, and AsA-GSH cycle, thus destroying the ability of antioxidant system to maintain redox balance. AtMYB72 negatively regulates the accumulation of osmotic regulatory substances such as soluble sugar (SS) and soluble protein (SP) in A. thaliana leaves under salt stress, which enhances the sensitivity of Arabidopsis leaves to salt. To sum up, MYB72 negatively regulates the salt tolerance of A. thaliana by destroying the light energy capture, electron transport, and antioxidant capacity of Arabidopsis.

PpSAUR5 promotes plant growth by regulating lignin and hormone pathways.

Peach (Prunus persica) has a high nutritional and economic value. However, its overgrowth can lead to yield loss. Regulating the growth of peach trees is challenging. The small auxin-up RNA (SAUR) gene family is the largest family of auxin-responsive genes, which play important roles in plant growth and development. However, members of this gene family are rarely reported in peach. In this study, we measured leaf area, chlorophyll and lignin content to detect the role of PpSAUR5 on growth through transgenic Arabidopsis. PpSAUR5 responds to auxin and gibberellin, promoting and inhibiting the synthesis of gibberellin and auxin, respectively. The heterologous transformation of PpSAUR5 in Arabidopsis led to enhanced growth of leaves and siliques, lightening of leaf color, decrease in chlorophyll content, increase in lignin content, abnormalities in the floral organs, and distortion of the inflorescence axis. Transcriptome data analysis of PpSAUR5 overexpression and wild-type lines revealed 854 differentially expressed genes (DEGs). GO and KEGG analyses showed that the DEGs were primarily involved in biological processes, such as cellular processes, metabolic processes, response to stimuli, and catalytic activity. These genes were mainly enriched in pathways, such as phenylalanine biosynthesis, phytohormone signaling, and MAPK signaling. In summary, these results suggested that PpSAUR5 might regulate tree vigor by modulating the synthesis of auxin and gibberellin. Future studies can use PpSAUR5 as a candidate gene to elucidate the potential regulatory mechanisms underlying peach tree vigor.

OsFK1 encodes C-14 sterol reductase, which is involved in sterol biosynthesis and affects premature aging of leaves in rice

The enzyme C-14 sterol reductase is involved in biosynthesis of brassinosteroids (BR) and sterols, as well as plant development. OsFK1, a member of the sterol biosynthesis pathway located in the endoplasmic reticulum (ER), encodes C-14 sterol reductase. However, there is little research on the function of C-14 sterol reductase in rice. Compared with the wild type, an osfk1 mutant showed dwarf phenotype and premature aging in the second leaf during the trefoil stage, and abnormal development of leaf veins during the tillering stage. The osfk1 mutant showed signs of aberrant PCD, as evidenced by TUNEL staining. This suggested that high ROS buildup caused DNA damage and ROS-mediated cell death in the mutant. The osfk1 mutant also showed decreased chlorophyll content and aberrant chloroplast structure. Sequencing of the osfk1 mutant allele revealed a non-synonymous G to A mutation in the final intron, leading to early termination. Here, we identified the OsFK1 allele, cloned it by Mutmap sequencing, and verified it by complementation. HPLC-MS/MS assays demonstrated that the osfk1 mutation caused lower phytosterol levels. These findings showed that the OsFK1 allele encoding C-14 sterol reductase is involved in phytosterol biosynthesis and mediates normal development of rice plants.

Proline and other physiological changes as an indicator of abiotic stress caused by heavy metal contamination

Heavy metal pollution due to globalization becomes the incurable hazardous problem for the agriculture productivity is due to industrialization with increased population. In this article impact of stress caused by heavy metals on shoot and root development along with phytoaccumulation was studied. The heavy metals cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb) and nickel (Ni) are taken at varying concentrations ranging from 0 to 250 ppm, while cadmium concentrations ranged from 0 to 50 ppm. The findings revealed that seed germination and plant growth were impacted due to higher percentages of these metals under study. Among them copper, nickel, lead and cadmium exhibited the most pronounced effects on chlorophyll content, root and shoot growth as well as on seed germination, moreover, the physiological analysis indicated that increasing heavy metal concentrations induced greater stress, resulting in decreased chlorophyll content and elevated proline levels, underscoring the significant impact of stress caused by heavy metals on the growth of plants. Delayed germination and growth were observed across all replicates with increased concentrations of all tested heavy metals. Despite zinc being an essential nutrient for plant growth, it was noted that it exhibited a positive effect on chlorophyll content and stimulated the production of fibrous roots, although growth was delayed at higher concentrations. The phytoaccumulation of heavy metals was analysed using atomic absorption spectroscopy (AAS) to quantify the absorption of heavy metals by seedlings, thereby assessing the accumulation or evaporation of heavy metals.

A Novel 10-Base Pair Deletion in the First Exon of GmHY2a Promotes Hypocotyl Elongation, Induces Early Maturation, and Impairs Photosynthetic Performance in Soybean.

Plants photoreceptors perceive changes in light quality and intensity and thereby regulate plant vegetative growth and reproductive development. By screening a γ irradiation-induced mutant library of the soybean (Glycine max) cultivar "Dongsheng 7", we identified Gmeny, a mutant with elongated nodes, yellowed leaves, decreased chlorophyll contents, altered photosynthetic performance, and early maturation. An analysis of bulked DNA and RNA data sampled from a population segregating for Gmeny, using the BVF-IGV pipeline established in our laboratory, identified a 10 bp deletion in the first exon of the candidate gene Glyma.02G304700. The causative mutation was verified by a variation analysis of over 500 genes in the candidate gene region and an association analysis, performed using two populations segregating for Gmeny. Glyma.02G304700 (GmHY2a) is a homolog of AtHY2a in Arabidopsis thaliana, which encodes a PΦB synthase involved in the biosynthesis of phytochrome. A transcriptome analysis of Gmeny using the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed changes in multiple functional pathways, including photosynthesis, gibberellic acid (GA) signaling, and flowering time, which may explain the observed mutant phenotypes. Further studies on the function of GmHY2a and its homologs will help us to understand its profound regulatory effects on photosynthesis, photomorphogenesis, and flowering time.

Oxyfluorfen: a novel metabolic inhibitor to select microalgal chlorophyll-deficient mutant strains for nutritional applications

Nowadays, there is an increasing demand for novel feedstocks and alternative protein sources to meet global needs. Because of their rich nutritional profiles and high protein contents, microalgae-based food products and supplements are being developed. Nonetheless, these products present organoleptic characteristics such as taste, smell and colour that are often considered unpleasant by human and animal consumers. To address this constraint, strain improvement approaches such as random mutagenesis have been used, which combined with the right selection strategy, lead to more appealing microalgal biomass. In this work, a novel selection strategy using oxyfluorfen, an inhibitor of the chlorophyll synthesis pathway, was applied for the first time to isolate chlorophyll-deficient strains of Scenedesmus rubescens and Chlorella vulgaris upon treatment with ethyl methanesulfonate (EMS). With this approach, one S. rubescens brownish (37Y01) mutant strain, as well as two C. vulgaris mutant strains, one yellow (31Y15) and one white (31W62), were obtained. S. rubescens 37Y01 displayed a reduced protein content of 19.1% dry weight (DW) compared to that of the wildtype, which presented a protein content of 25.0% DW. C. vulgaris wildtype and mutants exhibited higher protein contents, in the 42.8‐44.3% DW range, compared to Scenedesmus rubescens (p < 0.05). The selective pressure of this inhibitor allowed the selection of S. rubescens and C. vulgaris mutants displaying 55% and 95% decrease in chlorophyll content, respectively. The reduced chlorophyll content greatly improves the sensory properties and consumer acceptance of established mutants, increasing the potential of both strains as feedstocks to develop novel food products.

Ethylene accelerates maize leaf senescence in response to nitrogen deficiency by regulating chlorophyll metabolism and autophagy

Leaf senescence is an orderly and highly coordinated process, and finely regulated by ethylene and nitrogen (N), ultimately affecting grain yield and nitrogen-use efficiency (NUE). However, the underlying regulatory mechanisms on the crosstalk between ethylene- and N-regulated leaf senescence remain a mystery in maize. In this study, ethylene biosynthesis gene ZmACS7 overexpressing (OE-ZmACS7) plants were used to study the role of ethylene regulating leaf senescence in response to N deficiency, and they exhibited the premature leaf senescence accompanied by increased ethylene release, decreased chlorophyll content and Fv/Fm ratio, and accelerated chloroplast degradation. Then, we investigated the dynamics changes of transcriptome reprogramming underlying ethylene-accelerated leaf senescence in response to N deficiency. The differentially expressed genes (DEGs) involved in chlorophyll biosynthesis were significantly down-regulated, while DEGs involved in chlorophyll degradation and autophagy processes were significantly up-regulated, especially in OE-ZmACS7 plants in response to N deficiency. A gene regulatory network (GRN) was predicted during ethylene-accelerated leaf senescence in response to N deficiency. Three transcription factors (TFs) ZmHSF4, ZmbHLH106, and ZmEREB147 were identified as the key regulatory genes, which targeted chlorophyll biosynthesis gene ZmLES22, chlorophyll degradation gene ZmNYC1, and autophagy-related gene ZmATG5, respectively. Furthermore, ethylene signaling key genes might be located upstream of these TFs, generating the signaling cascade networks during ethylene-accelerated leaf senescence in response to N deficiency. Collectively, these findings improve our molecular knowledge of ethylene-accelerated maize leaf senescence in response to N deficiency, which is promising to improve NUE by manipulating the progress of leaf senescence in maize.

Energy deprivation affects nitrogen assimilation and fatty acid biosynthesis leading to leaf chlorosis under waterlogging stress in the endangered Abies koreana.

Energy deprivation triggers various physiological, biochemical and molecular changes in plants under abiotic stress. We investigated the oxidative damages in the high altitude grown conifer Korean fir (Abies koreana) exposed to waterlogging stress. Our experimental results showed that waterlogging stress led to leaf chlorosis, 35days after treatment. A significant decrease in leaf fresh weight, chlorophyll and sugar content supported this phenotypic change. Biochemical analysis showed a significant increase in leaf proline, lipid peroxidase and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical content of waterlogged plants. To elucidate the molecular mechanisms, we conducted RNA-sequencing (RNA-seq) and de novo assembly. Using RNA-seq analysis approach and filtering (P<0.05 and false discovery rate<0.001), we obtained 134 unigenes upregulated and 574 unigenes downregulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis placed the obtained differentially expressed unigenes in α-linoleic pathway, fatty acid degradation, glycosis, glycolipid metabolism and oligosaccharide biosynthesis process. Mapping of unigenes with Arabidopsis using basic local alignment search tool for nucleotides showed several critical genes in photosynthesis and carbon metabolism downregulated. Following this, we found the repression of multiple nitrogen (N) assimilation and nucleotide biosynthesis genes including purine metabolism. In addition, waterlogging stress reduced the levels of polyunsaturated fatty acids with a concomitant increase only in myristic acid. Together, our results indicate that the prolonged snowmelt may cause inability of A. koreana seedlings to lead the photosynthesis normally due to the lack of root intercellular oxygen and emphasizes a detrimental effect on the N metabolic pathway, compromising this endangered tree's ability to be fully functional under waterlogging stress.

Toxic mechanisms of the antiviral drug arbidol on microalgae in algal bloom water at transcriptomic level

Increasing antivirals in surface water caused by their excessive consumption pose serious threats to aquatic organisms. Our recent research found that the input of antiviral drug arbidol to algal bloom water can induce acute toxicity to the growth and metabolism of Microcystis aeruginosa, resulting in growth inhibition, as well as decrease in chlorophyll and ATP contents. However, the toxic mechanisms involved remained obscure, which were further investigated through transcriptomic analysis in this study. The results indicated that 885–1248 genes in algae were differentially expressed after exposure to 0.01–10.0 mg/L of arbidol, with the majority being down-regulated. Analysis of commonly down-regulated genes found that the cellular response to oxidative stress and damaged DNA bonding were affected, implying that the stress defense system and DNA repair function of algae might be damaged. The down-regulation of genes in porphyrin metabolism, photosynthesis, carbon fixation, glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation might inhibit chlorophyll synthesis, photosynthesis, and ATP supply, thereby hindering the growth and metabolism of algae. Moreover, the down-regulation of genes related to nucleotide metabolism and DNA replication might influence the reproduction of algae. These findings provided effective strategies to elucidate toxic mechanisms of contaminants on algae in algal bloom water.

Response of photosynthetic characteristics and antioxidant system in the leaves of safflower to NaCl and NaHCO3.

Compared with NaCl, NaHCO3 caused more serious oxidative damage and photosynthesis inhibition in safflower by down-regulating the expression of related genes. Salt-alkali stress is one of the important factors that limit plant growth. NaCl and sodium bicarbonate (NaHCO3) are neutral and alkaline salts, respectively. This study investigated the physiological characteristics and molecular responses of safflower (Carthamus tinctorius L.) leaves treated with 200mmolL-1 of NaCl or NaHCO3. The plants treated with NaCl treatment were less effective at inhibiting the growth of safflower, but increased the content of malondialdehyde (MDA) in leaves. Meanwhile, safflower alleviated stress damage by increasing proline (Pro), soluble protein (SP), and soluble sugar (SS). Both fresh weight and dry weight of safflower was severely decreased when it was subjected to NaHCO3 stress, and there was a significant increase in the permeability of cell membranes and the contents of osmotic regulatory substances. An enrichment analysis of the differentially expressed genes (DEGs) using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes identified significant enrichment of photosynthesis and pathways related to oxidative stress. Furthermore, a weighted gene co-expression network analysis (WGCNA) showed that the darkgreen module had the highest correlation with photosynthesis and oxidative stress traits. Large numbers of transcription factors, primarily from the MYB, GRAS, WRKY, and C2H2 families, were predicted from the genes within the darkgreen module. An analysis of physiological indicators and DEGs, it was found that under saline-alkali stress, genes related to chlorophyll synthesis enzymes were downregulated, while those related to degradation were upregulated, resulting in inhibited chlorophyll biosynthesis and decreased chlorophyll content. Additionally, NaCl and NaHCO3 stress downregulated the expression of genes related to the Calvin cycle, photosynthetic antenna proteins, and the activity of photosynthetic reaction centers to varying degrees, hindering the photosynthetic electron transfer process, suppressing photosynthesis, with NaHCO3 stress causing more pronounced adverse effects. In terms of oxidative stress, the level of reactive oxygen species (ROS) did not change significantly under the NaCl treatment, but the contents of hydrogen peroxide and the rate of production of superoxide anions increased significantly under NaHCO3 stress. In addition, treatment with NaCl upregulated the levels of expression of the key genes for superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the ascorbate-glutathione cycle, and the thioredoxin-peroxiredoxin pathway, and increased the activity of these enzymes, thus, reducing oxidative damage. Similarly, NaHCO3 stress increased the activities of SOD, CAT, and POD and the content of ascorbic acid and initiated the glutathione-S-transferase pathway to remove excess ROS but suppressed the regeneration of glutathione and the activity of peroxiredoxin. Overall, both neutral and alkaline salts inhibited the photosynthetic process of safflower, although alkaline salt caused a higher level of stress than neutral salt. Safflower alleviated the oxidative damage induced by stress by regulating its antioxidant system.

Artificial Floating Islands for the Removal of Nutrients and Improvement of the Quality of Urban Wastewater

A high amount of nutrients can be found in urban wastewater (UW), which makes it difficult to treat. The purpose of this research was to evaluate the potential of the aquatic macrophytes Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta in the treatment of UW. To evaluate the potential of each macrophyte, phytoremediation bioassays were established; the hydraulic retention time for each bioassay was 15 days. The physicochemical analysis of the water samples considered pH, turbidity, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), chemical oxygen demand (COD), total carbon (TC), phosphates (PO43-P), nitrate (NO3-N), and total nitrogen (TN). To evaluate the phytoremediation potential of each plant, the bioconcentration factors (BCFs) and translocation factors (TFs) for NO3-N and PO43-P were evaluated. Likewise, the relative growth rates (RGRs) and total chlorophyll production of the macrophytes were measured. The results showed that the highest efficiency was achieved with the bioassays with E. crassipes, with removal values of 69.7%, 68.8%, 58.7%, 69.4%, 56.3%, and 40.9% for turbidity, COD, TOC, PO43-P, NO3-N, and TN, respectively. The phytoremediation potential results showed that, for BCF, the highest value was 4.88 mg/g of PO43-P with E. crassipes, and for TF, it was 6.17 mg/g of PO43-P with S. molesta. The measurement of RGR and total chlorophyll for E. crassipes showed an increase of 0.00024 gg−1d−1 and an increase of 4.5%, respectively. On the other hand, the other macrophytes suffered decreases in chlorophyll content and RGR. Thus, E. crassipes is defined as the macrophyte with the greatest potential for the UW phytoremediation process.

Response of Grafted Olive (Olea europaea L. Cv. Coratina) to Water Deficit Conditions

Drought is one of the most damaging abiotic stresses; water deficit problem is increasingly occurring due to global climate change and negatively affects crop growth and productivity. Grafting on tolerate rootstocks is a promise approach to mitigate negative impacts of drought stress and ensure production sustainability. The present study was carried out to investigate the effect of water deficit stress on Coratina olive plants grafted on the following cultivars as rootstocks (Coratina, Koroneiki, Manzanillo, Picual and Sorani). Three water levels based on soil field capacity (FC) (100, 50% and 25% of FC) were used for water deficit treatments. Water deficit decreased shoot growth, stem diameter, leaves number and area, shoot and root weight. Leaf analysis showed marked decrease in total chlorophyll content while proline, total sugars and phenolic content increased with increasing water deficit level. The studied grafting combination differed in their response to water deficit treatments; Coratina grafted on Sorani and Koroneiki recorded higher values of growth parameters and accumulated higher amount of osmolytes (proline and total sugars) and phenolic compared to other grafted olive plants.

Mechanisms governing melon fruit skin pigmentation: Insights from transcriptome sequencing and whole-genome bisulfite sequencing analyses

Fruit skin color is a critical agronomic trait determining fruit quality, but the mechanisms governing melon (Cucumis melo L.) fruit skin pigmentation remain inadequately characterized. We performed cytological, transcriptomic, and whole-genome bisulfite sequencing (WGBS) comparative analyses on two near-isogenic lines (NILs) at different developmental stages: the green-skinned (GS) and white-skinned (WS) melon. The enriched functions among the 536 identified differentially expressed genes (DEGs) were related to chloroplast development, pigment metabolism, and photosynthetic pathway. The genes in these pathways were downregulated in the WS line, potentially contributing to the decreased chlorophyll content and abnormal chloroplast development in WS. WGBS analysis revealed that the levels of genomic DNA methylation in WS progressively exceeded those in GS as the fruits developed. The integrated analysis of the transcriptome and methylome identified DMR-associated DEGs (CHLI, CRD1, PORA, and HCAR) involved in chlorophyll metabolism. Notably, PORA exhibited downregulated expression and was hypermethylated in WS fruits during two developmental stages, showing a coordinated expression with the chlorophyll contents in developing WS and GS fruits. Furthermore, we identified a transcription factor gene, MELO3C011576, that was closely associated with the expression of PORA and chlorophyll levels across three developmental stages in both NILs. We speculate that PORA positively regulates chlorophyll biosynthesis in the two NILs, with its expression may be co-controlled by DNA methylation and transcription factors.

Involvement of BcERF109 in 1-MCP-delayed yellowing of pak choi (Brassica rapa subsp. Chinensis) via mitigation of major chlorophyll-degrading gene expression during storage

Leaf yellowing is a typical senescence symptom in postharvest pak choi (Brassica rapa subsp. Chinensis). Ethylene response factors (ERFs) are considered important regulators of leaf senescence. This study explored the likely regulatory effects of BcERF on pak choi yellowing via 1-methylcyclopropene (1-MCP) treatments. We identified an ERF transcription factor (TF), BcERF109, which may be involved in ethylene-induced pak choi yellowing. Treatment with 5.0 µL L–1 1-MCP suppressed the transcripts of chlorophyll catabolism genes (BcPPH1, BcRCCR, BcSGR2, and BcNYC1), inhibited decreases in chlorophyll content and chlorophyll fluorescence parameters, delayed chloroplast disintegration, and eventually mitigated yellowing. The treatment also blocked ethylene production and impeded the activities and transcripts of ethylene synthesis enzymes (ACC oxidase [ACO] and 1-aminocyclopropene-1-carboxylate [ACC] synthase [ACS]). In contrast, treatment with 10.0 µL L–1 ethylene accelerated pak choi yellowing, as indicated by greater ethylene production, activities and transcripts of ACO and ACS, and expression of chlorophyll catabolism genes, as well as reductions in chlorophyll content and fluorescence parameters. BcERF109 was identified as a nuclear-localised protein; its transcription levels were downregulated by 1-MCP and upregulated by ethylene. Molecular biology assays revealed that BcERF109 enhanced the transcriptional capacities of BcPPH1, BcRCCR, BcNYC1, and BcSGR2 by binding to their promoters. The transient overexpressing of BcERF109 in tobacco leaves stimulated the expression of endogenous genes (BcPPH1, BcRCCR, BcNYC1, BcSGR2, and BcERF109), leading to accelerated chlorophyll degradation and leaf yellowing. The application of 1-MCP mitigated pak choi yellowing by influencing ethylene synthesis and modulating the regulatory effects of BcERF019 on genes associated with chlorophyll catabolism. These results revealed a new regulatory mechanism involving ERF TFs in 1-MCP-induced delayed yellowing of green vegetables.

Stress-related physiological responses and ultrastructural changes in Hypoxis hemerocallidea leaves exposed to cadmium and aluminium

Hypoxis hemerocallidea is a medicinal plant containing hypoxoside (a pharmacologically active phytosterol diglucoside). This study evaluated the elemental composition in leaves of H. hemerocallidea treated with cadmium (Cd) and aluminium (Al) using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX). The impact of Cd and Al on photosynthetic pigments and performance, antioxidant activities and ultrastructure were also assessed. Corms of H. hemerocallidea were micropropagated, rooted and then exposed to varying concentrations of Cd, Al, and Cd + Al for six weeks. The SEM/EDX analysis indicated a two-fold increase in carbon content across all treated plants compared to the control. No/little Cd was detected in the leaves compared to a progressive increase in Al concentration with increasing Al treatment levels. This indicted that Al is more readily translocated to the shoots compared to Cd. Plants treated with Cd exhibited a significant decrease in total chlorophyll content accompanied by reduced photosynthetic performance and lower relative electron transport rates. Cd and Al exposure led to higher carotenoid, superoxide dismutase and malondialdehyde levels, indicating oxidative stress. Cd-treated plants displayed increased amylase activity and decreased carbohydrates content. Ultrastructural alterations occurred with exposure to Cd and Al, including abnormal swelling or disintegration of chloroplasts and thylakoid degeneration. An increase in starch grains and a decrease in plastoglobuli were also noted. In conclusion, this investigation provides evidence that both Cd and higher concentrations of Al exert detrimental effects on the ultrastructure, metabolism and photosynthetic performance of H. hemerocallidea, contributing to reduced growth and biological activity when stressed.

Effects of 5-Aminolevulinic Acid (5-ALA) on Morphological and Physiological Characteristics of Grapevine against Salt Stress

Salinity, one of the most significant abiotic stress factors restricting plant production, causes the destruction of agricultural lands and reduces productivity. In recent years, the utilization of 5-aminolevulinic acid (5-ALA) applications, which have important effects in terms of avoiding and providing tolerance to factors by impacting the physiology and metabolism of the plants, has been on the agenda. In this research, the impacts of foliar treatments of different levels of 5-ALA (0, 0.3, 0.6 and 0.9 mM) on morphological and physiological traits of 41 B American grapevine rootstocks under salinity stress (NaCl solution starting with 25 mM and reaching 150 mM concentration) were investigated. Salinity stress caused significant decreases in growth parameters, chlorophyll content, RWC and stomatal conductance, and significant increases in leaf temperature, proline and MDA content, physical damage and membrane damage degree. Under salinity stress, 0.9 mM 5-ALA treatments resulted in significant increases in shoot length (14.67 cm), root length (34.50 cm), leaf thickness (0.23 µm) leaf area (31.37 cm2), leaf number (8.67 pieces), chlorophyll content (21.83 SPAD), RWC (80.20%), proline content (0.19 μmol.g-1) and stomatal conductance (78.05 mmol.m-2.s-1); and significant decreases in physical damage degree (1.00 scale degree), membrane injury degree (15.46%) and MDA content (28.20 nmol.g-1) compared to non-ALA treatments. According to the results of this study, 5-ALA can be recommended as an alternative application to provide salinity tolerance in plants in order to reduce the damage caused by salinity stress in agricultural lands.

Exogenous melatonin delays leaves senescence and enhances saline and alkaline stress tolerance in grape seedlings

ABSTRACT Saline and alkaline stress is one of the major abiotic stresses facing agricultural production, which severely inhibits the growth and yield of plant. The application of plant growth regulators can effectively prevent crop yield reduction caused by saline and alkaline stress. Exogenous melatonin (MT) can act as a signaling molecule involved in the regulation of a variety of physiological processes in plants, has been found to play a key role in enhancing the improvement of plant tolerance to abiotic stresses. However, the effects of exogenous MT on saline and alkaline tolerance of table grape seedlings and its mechanism have not been clarified. The aim of this study was to investigate the role of exogenous MT on morphological and physiological growth of table grape seedlings ( Vitis vinifera L.) under saline and alkaline stress. The results showed that saline and alkaline stress resulted in yellowing and wilting of grape leaves and a decrease in chlorophyll content, whereas the application of exogenous MT alleviated the degradation of chlorophyll in grape seedling leaves caused by saline and alkaline stress and promoted the accumulation of soluble sugars and proline content. In addition, exogenous MT increased the activity of antioxidant enzymes, which resulted in the scavenging of reactive oxygen species (ROS) generated by saline and alkaline stress. In conclusion, exogenous MT was involved in the tolerance of grape seedlings to saline and alkaline stress, and enhanced the saline and alkaline resistance of grape seedlings to promote the growth and development of the grape industry in saline and alkaline areas.

Improving the growth, chlorophyll contents and productive tillers of wheat by exogenous application of fulvic acid under natural and heat stress conditions

Terminal thermal stress, occurring under varying climatic conditions, significantly reduces wheat yield by affecting fertilization and grain filling processes. Wheat crop damage from terminal heat stress may be lessened by the use of biostimulants. The purpose of this study is to apply fulvic acid topically to wheat in order to reduce the effects of heat stress. Wheat crops were subjected to high temperature stress during booting and initial stages of grain in in-vivo, with heat stress applied in staggered intervals in the main plot. Different concentrations of fulvic acid (water spray, 1.25 mg L-1, 2.50 mg L-1, and 3.75 mg L-1) were applied under natural and heat stress conditions during the booting and initial stages of grain of wheat. Heat stress during booting and grain filling phases notably decreased chlorophyll content, growth related parameters and productive tillers. The impact was more significant during the booting stage compared to the filling stage of grain. Application of fulvic acid at concentrations of 3.75 mg L-1 and 2.50 mg L-1 during heat stress at booting and grain filling stages substantially increased chlorophyll content and growth related parameters compared to water spray and 1.25 mg L-1 fulvic acid. These findings imply that fulvic acid applied directly to wheat under heat stress causes thermotolerance, which has a beneficial impact on biochemical and physiological processes.

High-nitrogen fertilizer alleviated adverse effects of drought stress on the growth and photosynthetic characteristics of Hosta ‘Guacamole’

BackgroundSeveral plants are facing drought stress due to climate change in recent years. In this study, we aimed to explore the effect of varying watering frequency on the growth and photosynthetic characteristics of Hosta ‘Guacamole’. Moreover, we investigated the effect of high-nitrogen and -potassium fertilizers on alleviating the impacts of drought stress on the morphology, photosynthetic characteristics, chlorophyll fluorescence, fast chlorophyll a fluorescence transient, JIP-test parameters, and enzymatic and non-enzymatic scavenging system for reactive oxygen species (ROS) in this species.ResultsLeaf senescence, decreased chlorophyll contents, limited leaf area, and reduced photosynthetic characteristics and oxygen-evolving complex (OEC) activity were observed in Hosta ‘Guacamole’ under drought stress. However, high-nitrogen fertilizer (30-10-10) could efficiently alleviate and prevent the adverse effects of drought stress. High-nitrogen fertilizer significantly increased chlorophyll contents, which was higher by 106% than drought stress. Additionally, high-nitrogen fertilizer significantly improved net photosynthetic rate and water use efficiency, which were higher by 467% and 2900% than those under drought stress. It attributes that high-nitrogen fertilizer could reduce transpiration rate of leaf cells and stomatal opening size in drought stress. On the other hand, high-nitrogen fertilizer enhanced actual photochemical efficiency of PS II and photochemical quenching coefficient, and actual photochemical efficiency of PS II significantly higher by 177% than that under drought stress. Furthermore, high-nitrogen fertilizer significantly activated OEC and ascorbate peroxidase activities, and enhanced the performance of photosystem II and photosynthetic capacity compared with high-potassium fertilizers (15-10-30).ConclusionsHigh-nitrogen fertilizer (30-10-10) could efficiently alleviate the adverse effects of drought stress in Hosta ‘Guacamole’ via enhancing OEC activity and photosynthetic performance and stimulating enzymatic ROS scavenging system.

Control of overgrowth of Potamogeton crispus in shallow lakes by light shading and artificial introductions

Potamogeton crispus is a common submersed aquatic plant in shallow lakes in China, and its overgrowth and rapid decomposing have become an important environmental problem affecting the water quality of lakes every summer. Introducing other submersed plants to substitute Potamogeton crispus can improve the structure of the aquatic plant community and to reduce the growth of Potamogeton crispus to some degree, but the effect is poor and short-lived. Considering the fact that Potamogeton crispus is sensitive to changes in light intensity, the two methods of shading the water surface and introduction of other submerged plants were used synergistically. In a large simulated experimental pool, light intensity was reduced by placing black polyethylene floating spheres on the water surface and planting three species of submerged plants, namely, Vallisneria natans, Hydrilla verticillata and Potamogeton wrightii. Changes in the physico-chemical properties of the experimental pool water and the physiological and biochemical characteristics (morphology, chlorophyll, biomass, antioxidant enzymes and malondialdehyde) of the submerged plants during the period of 0–40 d were analyzed. The results showed that: (1) After the light intensity was reduced by 85%, Potamogeton crispus seedlings showed a significant decrease in biomass and chlorophyll content and died in large numbers within 20–30 days. (2) Catalase is the main tool for Potamogeton crispus to cope with low light stress. The activities of various antioxidant enzymes and the malondialdehyde content of Potamogeton crispus showed a decreasing trend under shade conditions, but the catalase activity increased dramatically. (3) Vallisneria natans is more tolerant of low light conditions than the other two submersed plant species. Therefore, we tried to reduce the biomass of Potamogeton crispus by combing introduction of other submersed plants and shading treatment. (4) The water quality objectives remained stable over the period of the trial, indicating that short-term shading does not have a negative impact on the quality of the water quality.