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

BACKGROUND: Several 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. RESULTS: Leaf 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). CONCLUSIONS: High-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.

Effects of different light conditions on morphological, anatomical, photosynthetic and biochemical parameters of Cypripedium macranthos Sw.

In this study, the morphological (plant height, leaf length and width, stem diameter and leaf number), anatomical (epidermal cell density and thickness, Stomatal length and width), photosynthetic (net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration, relative humidity, leaf temperature and chlorophyll fluorescence parameters) and biochemical parameters (the content of soluble sugar, soluble protein, proline, malondialdehyde and electrical conductivity) of Cypripedium macranthos Sw. in Changbai Mountain were determined under different light conditions (L10, L30, L50, L100). The results showed that morphological values including plant height, leaf area, stem diameter and leaf number of C. macranthos were smaller under the condition of full light at L100. The epidermal cell density and epidermal thickness of C. macranthos were the highest under L30 and L50 treatments, respectively. It had the highest net photosynthetic rate (Pn) and chlorophyll content under L50 treatment. Meanwhile, correlation analysis indicated that photosynthetically active radiation (PAR) and water use efficiency (WUE) were the main factors influencing Pn. C. macranthos accumulated more soluble sugars and soluble proteins under L100 treatment, while the degree of membrane peroxidation was the highest and the plant was severely damaged. In summary, the adaptability of C. macranthos to light conditions is ranked as follows L50 > L30 > L10 > L100. Appropriate light conditions for C. macranthos are 30%-50% of full light, which should be taken into account in protection and cultivation.

Differential Transcription Profiling Reveals the MicroRNAs Involved in Alleviating Damage to Photosynthesis under Drought Stress during the Grain Filling Stage in Wheat.

To explore the possible novel microRNA (miRNA) regulatory pathways in Zhengmai 1860, a newly cultivated drought-tolerant wheat (Triticum aestivum L.) cultivar, miRNA transcriptome sequencing of the flag leaves of Zhengmai 1860, drought-sensitive variety Zhoumai 18, and drought-resistant variety Bainong 207 was performed during the grain filling stage. We also observed changes in the chloroplast ultrastructure, phytohormone levels, and antioxidant- and photosynthesis-related physiological indicators in three wheat varieties. The results showed that the flag leaves of the drought-tolerant variety Zhengmai 1860 had higher chlorophyll contents and net photosynthetic rates than those of Zhoumai 18 under drought stress during the grain filling stage; in addition, the chloroplast structure was more complete. However, there was no significant difference between Zhengmai 1860 and Bainong 207. MiRNA transcriptome analysis revealed that the differential expression of the miRNAs and mRNAs exhibited variable specificity. The KEGG pathway enrichment results indicated that most of the genes were enriched in the MAPK signaling pathway, plant hormone signal transduction, photosynthetic antennae protein, and amino acid and carbohydrate metabolism. In the drought-tolerant cultivar Zhengmai 1860, tae-miR408 was targeted to regulate the allene oxide synthase (AOS) gene, inhibit its expression, reduce the AOS content, and decrease the synthesis of jasmonic acid (JA) and abscisic acid (ABA). The results of this study suggest that Zhengmai 1860 could improve the photosynthetic performance of flag leaves by inhibiting the expression of genes involved in the JA pathway through miRNAs under drought conditions. Moreover, multiple miRNAs may target chlorophyll, antioxidant enzymes, phytohormone signal transduction, and other related pathways; thus, it is possible to provide a more theoretical basis for wheat molecular breeding.

Photosynthetic characteristics and genetic mapping of a new yellow leaf mutant crm1 in Brassica napus.

Chlorophyll is one of the key factors for photosynthesis and plays an important role in plant growth and development. We previously isolated an EMS mutagenized rapeseed chlorophyll-reduced mutant (crm1), which had yellow leaf, reduced chlorophyll content and fewer thylakoid stacks. Here, we found that crm1 showed attenuated utilization efficiency of both light energy and CO2 but enhanced heat dissipation efficiency and greater tolerance to high-light intensity. BSA-Seq analysis identified a single nucleotide change (C to T) and (G to A) in the third exon of the BnaA01G0094500ZS and BnaC01G0116100ZS, respectively. These two genes encode the magnesium chelatase subunit I 1 (CHLI1) that catalyzes the insertion of magnesium into protoporphyrin IX, a pivotal step in chlorophyll synthesis. The mutation sites resulted in an amino acid substitution P144S and G128E within the AAA+ domain of the CHLI1 protein. Two KASP markers were developed and co-segregated with the yellow leaf phenotype in segregating F2 population. Loss of BnaA01.CHLI1 and BnaC01.CHLI1 by CRISPR/Cas9 gene editing recapitulated the mutant phenotype. BnaA01.CHLI1 and BnaC01.CHLI1 were located in chloroplast and highly expressed in the leaves. Furthermore, RNA-seq analyses revealed the expression of chlorophyll synthesis-related genes were upregulated in the crm1 mutant. These findings provide a new insight into the regulatory mechanism of chlorophyll synthesis in rapeseed and suggest a novel target for improving the photosynthetic efficiency and tolerance to high-light intensity in crops. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01429-6.

Copper stress-induced phytotoxicity associated with photosynthetic characteristics and lignin metabolism in wheat seedlings.

Copper (Cu) pollution is one of environmental problems that adversely affects the growth and development of plants. However, knowledge of lignin metabolism associated with Cu-induced phytotoxicity mechanism is insufficient. The objective of this study was to reveal the mechanisms underlying Cu-induced phytotoxicity by evaluating changes in the photosynthetic characteristics and lignin metabolism in the seedlings of wheat cultivar 'Longchun 30'. Treatment with varying concentrations of Cu clearly retarded seedling growth, as demonstrated by a reduction in the growth parameters. Cu exposure reduced the photosynthetic pigment content, gas exchange parameters, and chlorophyll fluorescence parameters, including the maximum photosynthetic efficiency, potential efficiency of photosystem II (PS II), photochemical efficiency of PS II in light, photochemical quenching, actual photochemical efficiency, quantum yield of PS II electron transport, and electron transport rate, but notably increased the nonphotochemical quenching and quantum yield of regulatory energy dissipation. Additionally, a significant increase was observed in the amount of cell wall lignin in wheat leaves and roots under Cu exposure. This increase was positively associated with the up-regulation of enzymes related to lignin synthesis, such as phenylalanine ammonia-lyase, 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, laccase, cell wall bound (CW-bound) guaiacol peroxidase, and CW-bound conifer alcohol peroxidase, and TaPAL, Ta4CL, TaCAD, and TaLAC expression. Correlation analysis revealed that lignin levels in the cell wall were negatively correlated with the growth of wheat leaves and roots. Taken together, Cu exposure inhibited photosynthesis in wheat seedlings, resulting from a reduction in photosynthetic pigment content, light energy conversion, and photosynthetic electron transport in the leaves of Cu-stressed seedlings, and the Cu-inhibitory effect on seedling growth was related to the inhibition of photosynthesis and an increase in cell wall lignification.

Identification of Photosynthesis Characteristics and Chlorophyll Metabolism in Leaves of Citrus Cultivar (Harumi) with Varying Degrees of Chlorosis.

In autumn and spring, citrus leaves with a Ponkan (Citrus reticulata Blanco cv. Ponkan) genetic background (Harumi, Daya, etc.) are prone to abnormal physiological chlorosis. The effects of different degrees of chlorosis (normal, mild, moderate and severe) on photosynthesis and the chlorophyll metabolism of leaves of Citrus cultivar (Harumi) were studied via field experiment. Compared with severe chlorotic leaves, the results showed that chlorosis could break leaf metabolism balance, including reduced chlorophyll content, photosynthetic parameters, antioxidant enzyme activity and enzyme activity related to chlorophyll synthesis, increased catalase and decreased enzyme activity. In addition, the content of chlorophyll synthesis precursors showed an overall downward trend expected for uroporphyrinogen III. Furthermore, the relative expression of genes for chlorophyll synthesis (HEMA1, HEME2, HEMG1 and CHLH) was down-regulated to some extent and chlorophyll degradation (CAO, CLH, PPH, PAO and SGR) showed the opposite trend with increased chlorosis. Changes in degradation were more significant. In general, the chlorosis of Harumi leaves might be related to the blocked transformation of uroporphyrinogen III (Urogen III) to coproporphyrinogen III (Coprogen III), the weakening of antioxidant enzyme system activity, the weakening of chlorophyll synthesis and the enhancement in degradation.

Effect of soil water-phosphorus coupling on the photosynthetic capacity of Robinia pseudoacacia L. seedlings in semi-arid areas of the Loess Plateau, China.

Afforestation can improve soil erosion in the ecologically fragile areas of the Loess Plateau; however, the amount of water and phosphorus fertilizer that can promote vegetation survival is unclear, which hinders the improvement of the local ecological environment and the waste of water and fertilizer. In this study, based on field surveys, water and fertilizer control tests on Robinia pseudoacacia L. seedlings in experimental fields, and fitting CO2 response curves to R. pseudoacacia seedlings using a Li-6400 portable photosynthesizer, we measured their leaf nutrient contents and calculated resource use efficiency. The results showed that (1) under the same moisture gradient, except for photosynthetic phosphorus utilization efficiency (PPUE), light use efficiency (LUE), water use efficiency (WUE), carbon utilization efficiency (CUE), and photosynthetic nitrogen use efficiency (PNUE) all increased with increasing phosphorus fertilizer application. Under the same phosphorus fertilizer gradient, WUE increased with decreasing water application, and LUE, CUE, PNUE, and PPUE all reached the maximum at 55-60% of field water holding capacity. (2) Net photosynthetic rate (Pn) of R. pseudoacacia seedlings increased with increasing intercellular carbon dioxide concentration (Ci), and as Ci continued to increase, the increase in Pn became slower, but no maximal electron transport rate (TPU) occurred. Under the same CO2 concentration, Pn reached a maximum at 55-60% of field water holding capacity and phosphorus fertilizer at 30 gPm-2·a-1. (3) Leaf maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), daily respiration (Rd), stomatal conductance (Gs), and mesophyll conductance (Gm) reached their maximum at 30 gPm-2·a-1 of phosphorus fertilizer. Vcmax, Jmax, and Rd reached their maximum at 55-60% of field water holding capacity; Gs and Gm reached their maximum at 75-80% of field water holding capacity. (4) The higher the soil phosphorus content, the lower the biochemical (lb), stomatal (ls), and mesophyll (lm). With the increase of soil moisture, lb and ls are higher, and lm is lower. (5) Structural equation modeling showed that water-phosphorus coupling had a less direct effect on Rd and a more direct impact on Gs and Gm. Relative photosynthetic limitation directly affected the photosynthetic rate, indicating that water and phosphorus affected the photosynthetic rate through relative plant limitation. It was concluded that the resource use efficiency and photosynthetic capacity reached the maximum when 55-60% of field water holding capacity was maintained, and phosphorus fertilization was at 30 gP m-2·a-1. Therefore, maintaining suitable soil moisture and phosphorus fertilizer levels in the semi-arid zone of the Loess Plateau can improve the photosynthetic capacity of R. pseudoacacia seedlings.

Phytotoxicity response of sugar beet (Beta vulgaris L.) seedlings to herbicide fomesafen in soil.

Fomesafen is the most widely used herbicide in the soybean field. However, there are urgent practical challenges with the long-term persistence of fomesafen in soil and its effects on the subsequent crops in agricultural production. Therefore, pot experiments were conducted to study the effects of fomesafen residues (0-0.05 mg kg-1) on growth, photosynthetic characteristics, and the antioxidant defense system of sugar beet seedlings. The results showed that with the increase of fomesafen residues, the phytotoxicity index increased, while the plant height, leaf area, root length, root volume, and dry weight of sugar beet decreased. Photosynthetic pigment content, net photosynthetic rate (Pn), maximum photosynthetic efficiency (Fv/Fm), and actual photosynthetic efficiency (Y(II)) declined with a dose-dependent manner of fomesafen, but the intercellular CO2 concentration (Ci) and non-photochemical quenching coefficient (NPQ) increased under fomesafen. On the other hand, the residues of fomesafen increased the content of malondialdehyde (MDA) and membrane permeability by aggravating oxidative stress and triggering the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO). In addition, sugar beet seedlings were significantly sensitive to fomesafen as the concentration of fomesafen in the soil was up to 0.025 mg kg-1. In conclusion, the present study showed that fomesafen residues in the soil could affect the morphophysiology and photosynthetic performance of sugar beet. This study is beneficial for understanding the effects of the herbicide fomesafen residues on non-target crops.

Exogenous Melatonin Enhances Photosynthetic Capacity and Related Gene Expression in A Dose-Dependent Manner in the Tea Plant (Camellia sinensis (L.) Kuntze).

The enhancement of photosynthesis of tea leaves can increase tea yield. In order to explore the regulation mechanism of exogenous melatonin (MT) on the photosynthetic characteristics of tea plants, tea variety 'Zhongcha 108' was used as the experimental material in this study. The effects of different concentrations (0, 0.2, 0.3, 0.4 mM) of melatonin on the chlorophyll (Chl) content, stomatal opening, photosynthetic and fluorescence parameters, antioxidant enzyme activity, and related gene expression of tea plants were detected and analyzed. The results showed that under 0.2-mM MT treatment, chlorophyll (Chl) content, photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) improved, accompanied by a decrease in stomata density and increase in stomata area. Zero point two millimolar MT increased Chl fluorescence level and superoxide dismutase (SOD) activity, and reduced hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, indicating that MT alleviated PSII inhibition and improved photochemical efficiency. At the same time, 0.2 mM MT induced the expression of genes involved in photosynthesis and chlorophyll metabolism to varying degrees. The study demonstrated that MT can effectively enhance the photosynthetic capacity of tea plants in a dose-dependent manner. These results may promote a comprehensive understanding of the potential regulatory mechanism of exogenous MT on photosynthesis in tea plants.

[Effect of light intensity on growth, accumulation of ginsenosides, and expression of related enzyme genes of Panax quinquefolius].

Appropriate light intensity is favorable for the photosynthesis, biomass accumulation, key enzyme activity, and secondary metabolite synthesis of medicinal plants. This study aims to explore the influence of light intensity on growth and quality of Panax quinquefolius. To be specific, sand culture experiment was carried out in a greenhouse under the light intensity of 40, 80, 120, and 160 µmol·m~(-2)·s~(-1), respectively. The growth indexes, photosynthetic characteristics, content of 6 ginsenosides of the 3-year-old P. quinquefolius were determined, and the expression of ginsenoside synthesis-related enzyme genes in leaves, main roots, and fibrous roots was determined. The results showed that the P. quinquefolius growing at 80 µmol·m~(-2)·s~(-1) light intensity had the most biomass and the highest net photosynthetic rate. The total biomass of P. quinquefolius treated with 120 µmol·m~(-2)·s~(-1) light intensity was slightly lower than that with 80 µmol·m~(-2)·s~(-1). The root-to-shoot ratio in the treatment with 120 µmol·m~(-2)·s~(-1) light intensity was up to 6.86, higher than those in other treatments(P<0.05),and the ginsenoside content in both aboveground and underground parts of P. quinquefolius in this treatment was the highest, which was possibly associated with the high expression of farnesylpyrophosphate synthase(FPS), squalene synthase(SQS), squalene epoxidase(SQE), oxidosqualene cyclase(OSC), dammarenediol-Ⅱ synthase(DS), and P450 genes in leaves and SQE and DS genes in main roots. In addition, light intensities of 120 and 160 µmol·m~(-2)·s~(-1) could promote PPD-type ginsenoside synthesis in leaves by triggering up-regulation of the expression of upstream ginsenoside synthesis genes. The decrease in underground biomass accumulation of the P. quinquefolius grown under weak light(40 µmol·m~(-2)·s~(-1)) and strong light(160 µmol·m~(-2)·s~(-1)) was possibly attributed to the low net photosynthetic rate, stomatal conductance, and transpiration rate in leaves. In the meantime, the low expression of SQS, SQE, OSC, and DS genes in the main roots might led to the decrease in ginsenoside content. However, there was no significant correlation between the ginsenoside content and the expression of synthesis-related genes in the fibrous roots of P. quinquefolius. Therefore, the light intensity of 80 and 120 µmol·m~(-2)·s~(-1) is beneficial to improving yield and quality of P. quinquefolius. The above findings contributed to a theoretical basis for reasonable shading in P. quinquefolius cultivation, which is of great significance for improving the yield and quality of P. quinquefolius through light regulation.

Increase in lipid productivity and photosynthetic activities during distillery wastewater decolorization by Chlorella vulgaris cultures.

Finding an eco-friendly process for the decolorization of distillery wastewaters is a major concern. This study shows that the Chlorella vulgaris CCAP 211/19 strain can be used for color removal and direct production of oleaginous biomass. A response surface method was used for determining optimal operating conditions, including the dilution factor of industrial wastewater. The highest daily light supply values were the most efficient for color removal. The analysis of the microalgae physiological status confirmed that these colored waters could have a photoprotective action. Moreover, the increase in photosystem 2 activities of C. vulgaris CCAP 211/19 strain after short-term incubations in the presence of a synthetic melanoidin confirmed that this fraction is involved in the enhancement of lipid-enriched biomass production. The results show for the first time the stimulation effect of a melanoidin fraction on the lipid content and productivity by C. vulgaris. These results suggest that this approach may be used to design a closed loop, including water and CO2 recycling for the wastewater dilution and photosynthetic carbon fixation, respectively, while providing biomass for useful renewable algae-based feedstocks of potential interest for a distillery process. KEY POINTS: • Chlorella vulgaris cultures can be used for decolorization of distillery wastewaters. • Diluted distillery wastewaters stimulate biomass and lipid productivities. • Melanoidins, as well as distillery wastewater, stimulate photosynthetic activities.

Changes in photosynthetic traits and their responses to increasing fertilization rates in soybean (Glycine max (L.) Merr.) during decades of genetic improvement.

BACKROUND: Changes in photosynthetic traits (PTs) during the long-term genetic improvement of soybean (Glycine max (L.) Merr.) yield have been studied, but detailed information on whether PT responses to environmental stress have improved, and their correlations with seed yield, are still unknown. Our objectives were to describe the changes in soybean PTs - leaf area index (LAI), leaf chlorophyll content (Chl), net photosynthetic rate (PN ), stomatal conductance (gs ), and transpiration rate (E) - during decades of genetic improvement, and to detect whether the responses to increasing fertilizer application rates (FRs) of the PTs of 13 different soybean cultivars released in various decades differed. RESULTS: All of the soybean PTs increased significantly along with the year in which each cultivar was released, under different FR treatments, indicating that PTs have improved during decades of genetic breeding. Medium FR (nitrogen) treatment (150 kg ha -1 ) increased PT values, to different extents, at all the investigated growth stages. Leaf area index, Chl, and PN of the old and middle cultivar groups at the full bloom (R2), full seed (R6), and beginning maturity (R7) stages decreased significantly under high FR treatment (300 kg ha-1 ) compared with the medium FR treatment. The former had no effect on any of the PTs of new cultivar group, or had promotive effects. Thus, the photosynthetic capacities of the new cultivars are more tolerant to high FR-related stress than older cultivars. CONCLUSIONS: The photosynthetic capacities, and tolerance to high FR-related stress, of soybean cultivars that were released in different years improved after long-term genetic breeding. © 2021 Society of Chemical Industry.

Physiological and comparative proteomic analysis provides new insights into the effects of shade stress in maize (Zea mays L.).

BACKGROUND: Shade stress, a universal abiotic stress, suppresses plant growth and production seriously. However, little is known regarding the protein regulatory networks under shade stress. To better characterize the proteomic changes of maize leaves under shade stress, 60% shade (S) and supplementary lighting (L) on cloudy daylight from tasseling stage to physiological maturity stage were designed, the ambient sunlight treatment was used as control (CK). Isobaric tag for relative and absolute quantification (iTRAQ) technology was used to determine the proteome profiles in leaves. RESULTS: Shading significantly decreased the SPAD value, net photosynthetic rate, and grain yield. During two experimental years, grain yields of S were reduced by 48 and 47%, and L increased by 6 and 11%, compared to CK. In total, 3958 proteins were identified by iTRAQ, and 2745 proteins were quantified including 349 proteins showed at least 1.2-fold changes in expression levels between treatments and CK. The differentially expressed proteins were classified into photosynthesis, stress defense, energy production, signal transduction, and protein and amino acid metabolism using the Web Gene Ontology Annotation Plot online tool. In addition, these proteins showed significant enrichment of the chloroplasts (58%) and cytosol (21%) for subcellular localization. CONCLUSIONS: 60% shade induced the expression of proteins involved in photosynthetic electron transport chain (especially light-harvesting complex) and stress/defense/detoxification. However, the proteins related to calvin cycle, starch and sucrose metabolisms, glycolysis, TCA cycle, and ribosome and protein synthesis were dramatically depressed. Together, our results might help to provide a valuable resource for protein function analysis and also clarify the proteomic and physiological mechanism of maize underlying shade stress.

Photosynthetic characteristics and chloroplast ultrastructure of welsh onion (Allium fistulosum L.) grown under different LED wavelengths.

BACKGROUND: The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 µmol/m2·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) plants. RESULTS: Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate (Pn) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate (E) and stomatal conductance (Gs) were the highest in the B treatment, and the intercellular CO2 concentration (Ci) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv'/Fm'), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. CONCLUSIONS: White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Effect of different light intensity on physiology, antioxidant capacity and photosynthetic characteristics on wheat seedlings under high CO2 concentration in a closed artificial ecosystem.

The growth of plants under high carbon dioxide (CO2) concentrations (≥ 1000 ppm) is explored for the climate change and the bioregenerative life support system (BLSS) environment of long-duration space missions. Wheat (Triticum aestivum L.) is a grass cultivated for cereal grain-a global staple food including astronauts. Light and CO2 are both indispensable conditions for wheat seedlings. This study provides insights on the physiology, antioxidant capacity and photosynthetic characteristics of wheat seedlings under a range of photosynthetic photon flux densities in a closed system simulating BLSS with high CO2 concentration. We found that the Fv/Fm, Fv/F0, chlorophyll content, intrinsic water use efficiencies (WUEi), membrane stability index (MSI), and malondialdehyde (MDA) of wheat seedlings grown under an intermediate light intensity of 600 µmol m-2 s-1 environment were all largest. Interestingly, the high light intensity of 1200 mol m-2 s-1 treatment group exhibits the highest net photosynthetic rate but the lowest MDA content. The stomatal conductance and F0 of high light intensity of 1000 µmol m-2 s-1 treatment group were both significantly higher than that of other groups. Our study provides basic knowledge on the wheat growth in different environments, especially in a closed ecosystem with artificial lights.

Physiological and transcriptome analysis reveal molecular mechanism in Salvia miltiorrhiza leaves of near-isogenic male fertile lines and male sterile lines.

BACKGROUND: Our previous study finds that male sterility in Salvia miltiorrhiza could result in stunted growth and reduced biomass, but their molecular mechanisms have not yet been revealed. In this article, we investigate the underlying mechanism of male sterility and its impact on plant growth and metabolic yield by using physiological analysis and mRNA sequencing (RNA-Seq). RESULTS: In this study, transcriptomic and physiological analysis were performed to identify the mechanism of male sterility in mutants and its impact on plant growth and metabolic yield. Through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, it is found that the pathways are mainly enriched in processes including organ development, primary metabolic process and secondary metabolic process. Physiological analysis show that the chloroplast structure of male sterile mutants of S. miltiorrhiza is abnormally developed, which could result in decrease in leaf gas exchange (A, E and gs), chlorophyll fluorescence (Fv, Fm and Fv/Fm), and the chlorophyll content. Expression level of 7 differentially expressed genes involved in photosynthesis-related pathways is downregulated in male sterile lines of S. miltiorrhiza, which could explain the corresponding phenotypic changes in chlorophyll fluorescence, chlorophyll content and leaf gas exchange. Transcriptomic analysis establishes the role of disproportionating enzyme 1 (DPE1) as catalyzing the degradation of starch, and the role of sucrose synthase 3 (SUS3) and cytosolic invertase 2 (CINV2) as catalyzing the degradation of sucrose in the S. miltiorrhiza mutants. The results also confirm that phenylalanine ammonialyase (PAL) is involved in the biosynthesis of rosmarinic acid and salvianolic acid B, and flavone synthase (FLS) is an important enzyme catalyzing steps of flavonoid biosynthesis. CONCLUSIONS: Our results from the physiological and transcriptome analysis reveal underlying mechanism of plant growth and metabolic yield in male sterile mutants, and provide insight into the crop yield of S. miltiorrhiza.

Effect of soil aeration on root morphology and photosynthetic characteristics of potted tomato plants (Solanum lycopersicum) at different NaCl salinity levels.

BACKGROUND: Salt stress is one of the environmental factors that greatly limits crop production worldwide because high salt concentrations in the soil affect morphological responses and physiological and metabolic processes, including root morphology and photosynthetic characteristics. Soil aeration has been reported to accelerate the growth of plants and increase crop yield. The objective of this study was to examine the effects of 3 NaCl salinity levels (28, 74 and 120 mM) and 3 aeration volume levels (2.3, 4.6 and 7.0 L/pot) versus non-aeration and salinity treatments on the root morphology, photosynthetic characteristics and chlorophyll content of potted tomato plants. RESULTS: The results showed that both aeration volume and salinity level affected the root parameters, photosynthetic characteristics and chlorophyll content of potted tomato plants. The total length, surface area and volume of roots increased with the increase in aeration volume under each NaCl stress level. The effect was more marked in the fine roots (especially in ≤1 mm diameter roots). Under each NaCl stress level, the photosynthetic rate and chlorophyll content of tomato significantly increased in response to the aeration treatments. The net photosynthetic rate and chlorophyll a and t content increased by 39.6, 26.9, and 17.9%, respectively, at 7.0 L/pot aeration volume compared with no aeration in the 28 mM NaCl treatment. We also found that aeration could reduce the death rate of potted tomato plants under high salinity stress conditions (120 mM NaCl). CONCLUSIONS: The results suggest that the negative effect of NaCl stress can be offset by soil aeration. Soil aeration can promote root growth and increase the photosynthetic rate and chlorophyll content, thus promoting plant growth and reducing the plant death rate under NaCl stress conditions.

Effects of Pseudomonas alkylphenolica KL28 on immobilization of Hg in soil and accumulation of Hg in cultivated plant.

OBJECTIVE: The available content of mercury (Hg) in farmland soil is directly related to the safety of agricultural products. Meanwhile, humans may accumulate high concentrations of Hg through the food chain, resulting in health damage. Regarding the remediation technologies of Hg-contaminated soil, research and development is mainly concentrated on the immobilisation of Hg in soil and efficient extraction by accumulators. Therefore, in this work, the highly Hg-tolerant strain Pseudomonas alkylphenolica KL28 was used to study the removal effect of Hg in a solution, immobilization effect of Hg in soil, and its effect on growth, Hg accumulation and photosynthetic characteristics of Brassica campestris L. RESULTS: KL28 could effectively remove Hg2+ in the solution, with the removal ratio of 96.0% at 24 h. This strain could reduce decreases in shoots' and roots' dry weights by 31% and 16%, respectively, at a Hg concentration of 20 mg/L. The available Hg in the soil decreased to 4.7-9.4% in 8 days treated with KL28 bacterial solution at a dosage of 100 L/hm2. Meanwhile, with increases in Hg concentrations, Fv/Fm, Y(II), Y(I) and Y(NPQ) in the leaves of B. campestris showed a downward trend while Y(ND) and Y(NO) displayed an upward trend. Under the stress of 20 mg/L Hg2+, KL28 could reduce the Fv/Fm from 11.2 to 6.1%. CONCLUSIONS: KL28 could effectively remove Hg in the solution, immobilize Hg in soil, promote growth, decrease Hg accumulation and affect photosynthetic characteristics of B. campestris, indicating its potential use in Hg contaminated soils.

Interactive effects of single, binary and trinary trace metals (lead, zinc and copper) on the physiological responses of Kandelia obovata seedlings.

Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive effects of heavy metals on growth, photosynthetic parameters, lipid peroxidation and compatible osmolytes were studied in Kandelia obovata grown for 5 months in sediment treated with combinations of lead (Pb), zinc (Zn) and copper (Cu). The results showed no significant reduction of biomass under heavy metal stresses, except for decreased root biomass under higher Pb + Cu treatment, indicating high tolerance of K. obovata to heavy metal stress. Only the photosynthetic parameters, including net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), decreased with increasing concentration of treatments (except for Pb + Cu and Pb + Zn + Cu). Trinary treatment (Pb + Zn + Cu) increased biomass and the photosynthetic parameters when compared to the external addition of binary metals. In the roots, biomass and soluble sugar content were lower under binary than trinary treatments, indicating that the combination of Zn and Cu exhibited improved effects of alleviating toxicity than each of them alone in Pb-containing combined treatments. In the leaves, Zn-containing combined treatments significantly decreased malondialdehyde (MDA), soluble sugar and proline content in low concentration, while Pb + Cu treatments significantly increased these parameters (P < 0.05). The correlation analysis showed that leaf MDA and proline content were negatively correlated with Zn concentration (P < 0.05). Zn could alleviate the effects of combined heavy metal stress, and Pb + Cu treatment showed synergistic effects in leaves. The positive correlations between MDA content and the osmotic parameters showed that osmotic stress and lipid membranes oxidation exist simultaneously under multiple heavy metal stresses. Therefore, biomass, Tr, leaf MDA, leaf proline content and soluble sugar content could indicate metal mixture toxicity to mangrove seedlings.

[Response of growth and photosynthetic characteristics of Polygonatum cyrtonema to shading conditions].

The purpose of this experiment was to study the effects of different shading conditions on the growth,physiological characteristics and biomass allocation of Polygonatum cyrtonema,which offered a theoretical basis for its cultivation.Different light environments(100%,80%,60% and 35% light transmittance) were simulated with shading treatments.Growth and photosynthetic indexes of P.cyrtonema were measured and the variances were analyzed.The results show that shading decreased superoxide anion radical(O-·2)production rate and hydrogen peroxide(H_2O_2) accumulation,kept the activity of SOD,POD and CAT enzyme at a high level.Furthermore,The content of chlorophyll a and chlorophyll b,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),maximal photochemical efficiency of photosystem Ⅱ(Fv/Fm),photochemical quenching index(q P) and effective quantum yield of photosystem II(ΦPSⅡ) of P.cyrtonema were increased while the intercellular CO2 concentration(Ci),Foand NPQ were decreased by shading.Shading is beneficial to P.cyrtonema growth,can increase the total biomass P.cyrtonema.The allocation proportion of biomass on the aerial portion of P.cyrtonema increased but underground parts decreased with increasing shading conditions.In this study,P.cyrtonema can grow well in shading conditions,shading is beneficial to the formation of the yield and quality of the rhizomes of P.cyrtonema,especially in 65% light transmittance.