Increase In Chlorophyll Fluorescence Research Articles

Exploring the Adaptation of Native Shrub Species to Different Levels of Shading: Augmenting their Sustainable Exploitation Framework

Abstract The environmental adaptation potential of regional wild germplasm resources should be investigated in a species-specific manner in terms of the sustainable exploitation of underutilized native species. In the current work, three fruit/ornamental shrub species (Rosa canina L., Sambucus nigra L. and Cornus sanguinea L.) originating from regional wild germplasm of Greece with a previously set domestication framework have been investigated in terms of their environmental adaptation to different levels of shading. To this end, targeted experimentation was conducted on ex situ adapted material by applying different shading levels (0%, 30% and 60% shading) in purpose-built netting tunnels. Rosa canina showed similar growth patterns among the shading levels applied but with increased chlorophyll fluorescence patterns and increased abaxial leaf stomatal density with increased shading. Sambucus nigra showed similar results to R. canina in photosynthetic efficiency and leaf stomatal density but with additional effects on plant growth patterns. Cornus sanguinea, on the other hand, was not affected by shading level in the measured parameters. These results outline the adaptation potential in a species-specific manner of the studied species to shading in terms of adding novel exploitation options for agroecosystems, agroforestry, and landscape management in peri-urban green spaces and peri-urban forest understory enrichment to mitigate climate change impacts in temperate and semi-arid climates. Study Implications: This study explores the adaptation potential to increasing levels of shading of ex situ adapted germplasm of wild origin of three underutilized shrub species with known multifaceted value. The work builds on the sustainable utilization framework of the focal species in terms of novel exploitation options in landscape management for peri-urban green spaces and peri-urban forest understory enrichment for enhancing biodiversity and soil erosion protection. Therefore, this work offers an example of an underlying research line towards systematized screening and utilization of wild plant species for climate change impact mitigation in agroecosystems, agroforestry, and landscape management in temperate semi-arid climates.

Effect of foliar applications of aminolevulinic acid (bulk and nano-encapsulated) on bell pepper under heat stress

Plant growth and production can be adversely affected by high temperature stress, which is defined as an increase in temperature over a threshold level. 5-aminolevulinic acid (ALA) can be used as a beneficial growth regulator in agriculture, particularly for plants experiencing abiotic stress. The efficacy of exogenous two form ALA application (bulk and nanoencapsulated) was investigated in a factorial experiment based on a completely randomized block design with 12 replications. In this study, different temperatures (optimal temperature 25 °C, and high temperature 35 °C) and different ALA treatments were used (control, 1 mM of ALA, and 1 mM Nano-encapsulated N-ALA). The study revealed that elevated temperatures of 35 °C had an adverse impact on the majority of bell pepper growth characteristics. Nevertheless, the application of ALA and N-ALA significantly enhanced the growth characteristics under these conditions. In contrast to the conditions at 25 °C, the concentrations of potassium (K), proline, electrolyte leakage (EL), glucose, and fructose exhibited an increase at 35 °C. However, both forms of ALA were effective in mitigating these adverse effects. Comparatively, the control treatment showed elevated levels of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) enzymes, along with increased malondialdehyde (MDA) levels compared to the ALA treatment. The treatment with ALA resulted in the highest fresh weight and shoot length at 35 °C compared to N-ALA. Conversely, at the same temperature, N-ALA led to a 17 % increase in chlorophyll fluorescence and a 32 % increase in DPPH compared to ALA. In summary, the application of both ALA and Nano-encapsulated N-ALA effectively mitigates the adverse effects of exposure to 35 °C on bell pepper growth and biochemical parameters.

Graphene enhances artemisinin production in the traditional medicinal plant Artemisia annua via dynamic physiological processes and miRNA regulation

We investigated the effects of graphene on the model herb Artemisia annua, which is renowned for producing artemisinin, a widely used pharmacological compound. Seedling growth and biomass were promoted when A. annua was cultivated with low concentrations of graphene, an effect which was attributed to a 1.4-fold increase in nitrogen uptake, a 15%–22% increase in chlorophyll fluorescence, and greater abundance of carbon cycling–related bacteria. Exposure to 10 or 20 mg/L graphene resulted in a ∼60% increase in H2O2, and graphene could act as a catalyst accelerator, leading to a 9-fold increase in catalase (CAT) activity in vitro and thereby maintaining reactive oxygen species (ROS) homeostasis. Importantly, graphene exposure led to an 80% increase in the density of glandular secreting trichomes (GSTs), in which artemisinin is biosynthesized and stored. This contributed to a 5% increase in artemisinin content in mature leaves. Interestingly, expression of miR828 was reduced by both graphene and H2O2 treatments, resulting in induction of its target gene AaMYB17, a positive regulator of GST initiation. Subsequent molecular and genetic assays showed that graphene-induced H2O2 inhibits micro-RNA (miRNA) biogenesis through Dicers and regulates the miR828–AaMYB17 module, thus affecting GST density. Our results suggest that graphene may contribute to yield improvement in A. annua via dynamic physiological processes together with miRNA regulation, and it may thus represent a new cultivation strategy for increasing yield capacity through nanobiotechnology.

β-Cyclocitric acid enhances drought tolerance in peach (Prunus persica) seedlings.

The β-cyclocitric acid (β-CCA) is a bioactive apocarotenoid previously shown to improve drought tolerance in annual plants. However, the underlying molecular mechanism of this process remains largely elusive. Moreover, the question about the activity of β-CCA in perennial fruit crops is still open. Here, we found that treatment of β-CCA enhances drought tolerance in peach seedlings. The application of β-CCA significantly increased the relative water content and root activity and reduced the electrolyte leakage of peach seedlings under drought stress. Moreover, treatment with β-CCA under drought stress increased chlorophyll fluorescence, indicating a positive effect on photosynthesis, while also enhancing superoxide dismutase and peroxidase activity and reducing reactive oxygen species (ROS) levels. Consistent with these alterations, transcriptome analysis revealed an up-regulation of photosynthesis and antioxidant-related genes upon the application of β-CCA under drought stress. We also detected an induction in genes related to detoxification, environmental adaptation, primary metabolism, phytohormone, phenylpropanoid and the biosynthesis of cutin, suberine and wax, which might contribute to the induction of drought resistance. Altogether, our study reveals that β-CCA positively modulates peach drought tolerance, which is mainly mediated by enhancing photosynthesis and reducing ROS, indicating the potential of utilizing β-CCA for drought control in peach and perhaps other fruit crops.

Effects of Hemlock Woolly Adelgid Control Using Imidacloprid on Leaf-Level Physiology of Eastern Hemlock

Widespread mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) has been occurring due to the introduction of hemlock woolly adelgid (Adelges tsugae Annand) (HWA), threatening millions of hectares of hemlock-dominated forests in the eastern United States. HWA feeds at the base of needles and removes stored carbohydrates, which can impact leaf-level physiology, contributing to the decline of the tree. However, these physiological mechanisms in HWA-infested hemlocks are still not clearly understood. We investigated hemlock leaf physiology year-round at three forested sites with various degrees of infestation. At each site, half the trees were treated with imidacloprid (Merit® 2 F, Bayer, Kansas City, MO, USA) while the rest were left untreated. Imidacloprid is widely used to control HWA but can itself have phytotoxic effects. After one growing season, there was an increase in photosynthetic rates (7.5%, p = 0.0163) and stomatal conductance (7.1%, p = 0.0163) across sites in the trees treated with imidacloprid. After two years, the imidacloprid treatment also increased bud break from 22.5% to 88.7% at Fishburn (the most severely impacted site) and from 22.7% to 58.9% at Mountain Lake (the least impacted site), and slightly increased chlorophyll fluorescence for treated trees at Fishburn. Chemical treatment also slightly increased water use efficiency at Mountain Lake. These results suggest that HWA is causing tree mortality largely through a reduction in leaf area caused by decreasing bud break and also by a slight, but significant, reduction in leaf-level photosynthesis and stomatal conductance.

Genetic mapping identified three hotspot genomic regions and candidate genes controlling heat tolerance-related traits in groundnut.

Groundnut productivity and quality have been impeded by rising temperatures in semi-arid environments. Hence, understanding the effects and molecular mechanisms of heat stress tolerance will aid in tackling yield losses. In this context, a recombinant inbred line (RIL) population was developed and phenotyped for eight seasons at three locations for agronomic, phenological, and physiological traits under heat stress. A genetic map was constructed using genotyping-by-sequencing with 478 single-nucleotide polymorphism (SNP) loci spanning a map distance of 1,961.39 cM. Quantitative trait locus (QTL) analysis using phenotypic and genotypic data identified 45 major main-effect QTLs for 21 traits. Intriguingly, three QTL clusters (Cluster-1-Ah03, Cluster-2-Ah12, and Cluster-3-Ah20) harbor more than half of the major QTLs (30/45, 66.6%) for various heat tolerant traits, explaining 10.4%-38.6%, 10.6%-44.6%, and 10.1%-49.5% of phenotypic variance, respectively. Furthermore, important candidate genes encoding DHHC-type zinc finger family protein (arahy.J0Y6Y5), peptide transporter 1 (arahy.8ZMT0C), pentatricopeptide repeat-containing protein (arahy.4A4JE9), Ulp1 protease family (arahy.X568GS), Kelch repeat F-box protein (arahy.I7X4PC), FRIGIDA-like protein (arahy.0C3V8Z), and post-illumination chlorophyll fluorescence increase (arahy.92ZGJC) were the underlying three QTL clusters. The putative functions of these genes suggested their involvement in seed development, regulating plant architecture, yield, genesis and growth of plants, flowering time regulation, and photosynthesis. Our results could provide a platform for further fine mapping, gene discovery, and developing markers for genomics-assisted breeding to develop heat-tolerant groundnut varieties.

The Effect of Chitosan on Plant Physiology, Wound Response, and Fruit Quality of Tomato.

In agriculture, chitosan has become popular as a metabolic enhancer; however, no deep information has been obtained yet regarding its mechanisms on vegetative tissues. This work was conducted to test the impact of chitosan applied at different plant growth stages on plant development, physiology, and response to wounding as well as fruit shape and composition. Five concentrations of chitosan were tested on tomato. The most effective chitosan doses that increased leaf number, leaf area, plant biomass, and stomatal conductance were 0.75 and 1 mg mL-1. Chitosan (1 mg mL-1) applied as foliar spray increased the levels of jasmonoyl-isoleucine and abscisic acid in wounded roots. The application of this dose at vegetative and flowering stages increased chlorophyll fluorescence (Fv/Fm) values, whereas application at the fruit maturation stage reduced the Fv/Fm values. This decline was positively correlated with fruit shape and negatively correlated with the pH and the content of soluble sugars, lycopene, total flavonoids, and nitrogen in fruits. Moreover, the levels of primary metabolites derived from glycolysis, such as inositol phosphate, lactic acid, and ascorbic acid, increased in response to treatment of plants with 1 mg mL-1- chitosan. Thus, chitosan application affects various plant processes by influencing stomata aperture, cell division and expansion, fruit maturation, mineral assimilation, and defense responses.

Unprecedented summer hypoxia in southern Cape Cod Bay: an ecological response to regional climate change?

Abstract. In late summer 2019 and 2020 bottom waters in southern Cape Cod Bay (CCB) became depleted of dissolved oxygen (DO), with documented benthic mortality in both years. Hypoxic conditions formed in relatively shallow water where the strong seasonal thermocline intersected the sea floor, both limiting vertical mixing and concentrating biological oxygen demand (BOD) over a very thin bottom boundary layer. In both 2019 and 2020, anomalously high sub-surface phytoplankton blooms were observed, and the biomass from these blooms provided the fuel to deplete sub-pycnocline waters of DO. The increased chlorophyll fluorescence was accompanied by a corresponding decrease in sub-pycnocline nutrients, suggesting that prior to 2019 physical conditions were unfavorable for the utilization of these deep nutrients by the late-summer phytoplankton community. It is hypothesized that significant alteration of physical conditions in CCB during late summer, which is the result of regional climate change, has favored the recent increase in sub-surface phytoplankton production. These changes include rapidly warming waters and significant shifts in summer wind direction, both of which impact the intensity and vertical distribution of thermal stratification and vertical mixing within the water column. These changes in water column structure are not only more susceptible to hypoxia but also have significant implications for phytoplankton dynamics, potentially allowing for intense late-summer blooms of Karenia mikimotoi, a species new to the area. K. mikimotoi had not been detected in CCB or adjacent waters prior to 2017; however, increasing cell densities have been reported in subsequent years, consistent with a rapidly changing ecosystem.

Application of plant growth-promoting rhizobacteria combined with compost as a management strategy against Verticillium dahliae in tomato

This study aimed to evaluate the effect of plant growth-promoting rhizobacteria (PGPR) and compost, applied alone or in combination, on tomato resistance to vascular wilt caused by Verticillium dahliae. Improved management of vascular wilt is important for enhanced productivity of greenhouse-grown susceptible tomato plants. The application of compost and PGPR resulted in a reduction in infection parameters compared with untreated plants inoculated with the pathogen, as well as activation of plant defence mechanisms. In the presence of the pathogen, compost application significantly improved the total fresh and dry weights by 97% and 71%, respectively, compared with pathogen-inoculated controls. The combination of compost with PGPR significantly increased chlorophyll fluorescence and stomatal conductance compared with the infected-control. In addition, the combination of compost and PGPR reduced the accumulation of stress markers such as malondialdehyde and hydrogen peroxide by 48% and 77%, respectively, and promoted the activity of antioxidant enzymes. Fruit yield and quality were also significantly improved relative to the control. The results suggest that compost applied alone or in combination with PGPR helps to suppress vascular wilt and to improve the yield and quality of tomatoes.

Biphasic effects of typical chlorinated organophosphorus flame retardants on Microcystis aeruginosa

The potential accumulation of chlorinated organophosphorus flame retardants (Cl-OPFRs) in aquatic environments sparked interest in studying the effects of Cl-OPFRs on cyanobacterial blooms. In this work, two common Cl-OPFRs, tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tris(2-chloroethyl) phosphate (TCEP), induced dose-dependent biphasic effect on bloom-forming M. aeruginosa. The hormetic response to low-dose Cl-OPFRs was associated with the upregulation of the type I NADH dehydrogenase (NDH-1) complex and its mediated cyclic electron transfer (CET) pathway, as reflected by a transient post-illumination increase in chlorophyll fluorescence, the dark reduction of P700+ and the change of NDH-1-related gene expression. The increased CET activity and carotenoid content jointly reduced the intracellular ROS production, facilitating cyanobacterial growth. Conversely, a higher concentration of both Cl-OPFRs induced severe inhibition of growth and photosynthetic oxygen-evolving activity through an imbalance between PSII and PSI. Toxic-dose Cl-OPFRs inhibited state transition and fixed cells into the State I with a higher PSII/PSI ratio, as indicated by chlorophyll fluorescence induction, 77 K fluorescence emission spectra and photosystem stoichiometry. The elevated PSII/PSI ratio created an imbalance between the two photosystems and eventually lead to ROS overproduction, which generate adverse effects on cell growth. This work provides important insights into the hormetic mechanism of Cl-OPFRs on Microcystis aeruginosa and their potential roles in harmful cyanobacteria blooms.

Rendimento quântico, clorofila e dano celular em maracujazeiro-amarelo sob estratégias de irrigação com água salobra e potássio

Abstract The occurrence of water sources with high concentrations of salts in the semiarid region of Northeast Brazil stands out as a limiting factor in the cultivation of irrigated yellow passion fruit. Thus the search for irrigation strategies with brackish water is fundamental for the sustainability of irrigated crops. The objective of the present study was to determine the quantum yield, chlorophyll levels, and cell damage in yellow passion fruit cultivated under different irrigation strategies with brackish water and potassium fertilization. The experiment was conducted under field conditions in São Domingos - PB, Brazil, adopting a randomized block design in a 6×2 factorial scheme, consisting of six strategies of use of brackish water applied in the different phenological stages of crop and two doses of potassium (60 and 100% of the recommendation), with four replicates. Two levels of irrigation water salinity were used, with low (1.3 dS m-1) and high electrical conductivity (4.0 dS m-1). The potassium dose of 100% recommendation corresponds to the application of 345 g of K2O per plant per year. The use of brackish water (4.0 dS m-1) increased chlorophyll fluorescence and negatively affected the photosynthetic pigments of yellow passion fruit, regardless of the phenological stage. Salt stress intensified intercellular electrolyte leakage in passion fruit plants under higher dose of potassium. Our results show that fertilization equivalent to 100% of the potassium recommendation is excessive for yellow passion fruit ‘BRS GA1’ in the tropical semiarid region under salt stress conditions.

Increased CO2 Relevant to Future Ocean Acidification Alleviates the Sensitivity of a Red Macroalgae to Solar Ultraviolet Irradiance by Modulating the Synergy Between Photosystems II and I.

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO2 levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO2 concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O2-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (Fk) of Kautsky curves relative to the amplitude of FJ−Fo (Wk) and a decrease of the maximum quantum yield of PSII (Fv/Fm). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO2 assimilation. When the algal thalli were grown under increased CO2 and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO2 levels and OA.

Applying foliar magnesium enhances wheat growth in acidic soil by stimulating exudation of malate and citrate

Aluminium toxicity in acidic soils adversely affects wheat growth. Foliar-applied magnesium (Mg) contributes to mitigating soil acidity stress in wheat, but the mechanisms are unknown. This study explored the mechanism of foliar-Mg mediated enhancement of wheat growth in acidic soil. Two contrasting near-isogenic wheat (Triticum aestivum L.) genotypes differing in Al resistance (Al-sensitive ES8 and Al-resistant ET8) were grown to the vegetative stage (Zadoks 24) in a reconstituted acidic soil (pH0.1 M CaCl2 4.0) profile with three rates of foliar Mg (0, 200 and 500 mg Mg L− 1 using MgSO4.7H2O). Magnesium was applied to the foliage twice [14 and 28 days after sowing (DAS)], and plant growth and root exuded carboxylates were measured up to 42 DAS. Applying 200 mg Mg L− 1 to the foliage increased organic acid anion exudation from wheat roots by ~ 2-fold compared to 0 foliar Mg treated plants. The Al-resistant wheat genotype exuded 1.3-fold more malate and citrate from roots than the Al-sensitive genotype in the absence of foliar Mg. Malate exudation was delayed relative to citrate following foliar Mg application. The foliar-applied Mg increased shoot and root dry weight (by ~ 38 %), total root length (by ~ 33 %) and intrinsic water-use efficiency (by ~ 80 %) compared to plants treated with no Mg. Applying foliar Mg decreased soil acidity stress (as shown by a significant increase in chlorophyll fluorescence Fv/Fm ratio) in wheat compared to 0 foliar Mg. Increased malate and citrate exudation is the underlying mechanism of enhanced wheat growth following foliar Mg application under acidic soil conditions.

Evaluating the efficacy of chitosan and salicylic acid on photosynthetic pigments and antioxidant enzymes towards resistance of mango malformation

The mango malformation is an ambiguous malady of mango (Mangifera indica L.) with tremendous economic importance throughout the mango growing regions. The effect of different concentrations of chitosan and salicylic acid on photosynthetic pigments and antioxidant enzyme responses towards the resistance of mango malformation was investigated. The experiment was carried out in on seven-year-old trees of two different mango cultivars Amrapali (moderately susceptible to mango malformation) and Dashehari (moderately resistant to mango malformation) with seven treatments and three replications during February and March 2019-2020. The foliar application of chitosan and salicylic acid was done at three different stages i.e. prior to panicle emergence, pre blooming and full bloom. The pooled data over the years 2019 and 2020 revealed that the highest chlorophyll fluorescence and photosynthetic pigments in Dashehari as compared to Amrapali. However, Amrapali was recorded maximum malformation (%). Chitosan (0.50%) shows the maximum increase in chlorophyll fluorescence, leaf area, photosynthetic pigments, proline and total phenol contents in both the varieties over control. On the contrary, antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase were reported higher in both the varieties at 0.40% salicylic acid which, was statistically at par with 0.50% chitosan treatment. However, the catalase activity decreases at lower concentration and increases at high concentration of chitosan and salicylic acid. Therefore, it was concluded that protective application of either chitosan or salicylic acid prior to panicle emergence, pre blooming and full bloom reduced the negative effect of mango malformation and elevated the defense induced antioxidant activities to confer resistance to floral malformation.

Slr0320 Is Crucial for Optimal Function of Photosystem II during High Light Acclimation in Synechocystis sp. PCC 6803.

Upon exposure of photosynthetic organisms to high light (HL), several HL acclimation responses are triggered. Herein, we identified a novel gene, slr0320, critical for HL acclimation in Synechocystis sp. PCC 6803. The growth rate of the Δslr0320 mutant was similar to wild type (WT) under normal light (NL) but severely declined under HL. Net photosynthesis of the mutant was lower under HL, but maximum photosystem II (PSII) activity was higher under NL and HL. Immunodetection revealed the accumulation and assembly of PSII were similar between WT and the mutant. Chlorophyll fluorescence traces showed the stable fluorescence of the mutant under light was much higher. Kinetics of single flash-induced chlorophyll fluorescence increase and decay revealed the slower electron transfer from QA to QB in the mutant. These data indicate that, in the Δslr0320 mutant, the number of functional PSIIs was comparable to WT even under HL but the electron transfer between QA and QB was inefficient. Quantitative proteomics and real-time PCR revealed that expression profiles of psbL, psbH and psbI were significantly altered in the Δslr0320 mutant. Thus, Slr0320 protein plays critical roles in optimizing PSII activity during HL acclimation and is essential for PSII electron transfer from QA to QB.

Ocean Acidification and Warming Lead to Increased Growth and Altered Chloroplast Morphology in the Thermo-Tolerant Alga Symbiochlorum hainanensis.

Ocean acidification and warming affect the growth and predominance of algae. However, the effects of ocean acidification and warming on the growth and gene transcription of thermo-tolerant algae are poorly understood. Here we determined the effects of elevated temperature (H) and acidification (A) on a recently discovered coral-associated thermo-tolerant alga Symbiochlorum hainanensis by culturing it under two temperature settings (26.0 and 32.0°C) crossed with two pH levels (8.16 and 7.81). The results showed that the growth of S. hainanensis was positively affected by H, A, and the combined treatment (AH). However, no superimposition effect of H and A on the growth of S. hainanensis was observed under AH. The analysis of chlorophyll fluorescence, pigment content, and subcellular morphology indicated that the chloroplast morphogenesis (enlargement) along with the increase of chlorophyll fluorescence and pigment content of S. hainanensis might be a universal mechanism for promoting the growth of S. hainanensis. Transcriptomic profiles revealed the effect of elevated temperature on the response of S. hainanensis to acidification involved in the down-regulation of photosynthesis- and carbohydrate metabolism-related genes but not the up-regulation of genes related to antioxidant and ubiquitination processes. Overall, this study firstly reports the growth, morphology, and molecular response of the thermo-tolerant alga S. hainanensis to future climate changes, suggesting the predominance of S. hainanensis in its associated corals and/or coral reefs in the future.

Subtle changes in solar radiation under a green-to-red conversion film affect the photosynthetic performance and chlorophyll fluorescence of sweet pepper

Although spectrum conversion films are used to improve the photosynthetic efficiency and, ultimately, crop growth, the effects of the modified spectrum on photosynthetic traits in plants have not yet been sufficiently reported. The objective of this study was to investigate the changes in photosynthetic performance and chlorophyll fluorescence of sweet pepper (Capsicum annuum L.) under a green-to-red conversion (GtR) film. The GtR-modified spectrum increased the dry mass and decreased the petiole length. The photosynthetic light-response curves were significantly improved, and the gap of the maximum photosynthetic rates increased over time after covering. The GtR-modified spectrum significantly increased chlorophyll fluorescence parameters in the JIP-test, such as parameters related to the reduction of end electron acceptors on the PSI acceptor side, the efficiency for electron transport in PSII, and the performance indexes. Our data indicated that the GtR-modified spectrum promotes electron transfer around PSI, improving photosynthetic performance and growth.

Overexpression of MdIAA24 improves apple drought resistance by positively regulating strigolactone biosynthesis and mycorrhization.

Most land plant species have the ability to establish a symbiosis with arbuscular mycorrhizal (AM) fungi. These fungi penetrate into root cortical cells and form branched structures (known as arbuscules) for nutrient exchange. We cloned the MdIAA24 from apple (Malus domestica) following its up-regulation during AM symbiosis. Results demonstrate the positive impact of the overexpression (OE) of MdIAA24 in apple on AM colonization. We observed the strigolactone (SL) synthesis genes, including MdD27, MdCCD7, MdCCD8a, MdCCD8b and MdMAXa, to be up-regulated in the OE lines. Thus, the OE lines exhibited both a higher SL content and colonization rate. Furthermore, we observed that the OE lines were able to maintain better growth parameters under AM inoculation conditions. Under drought stress with the AM inoculation, the OE lines were less damaged, which was demonstrated by a higher relative water content, a lower relative electrolytic leakage, a greater osmotic adjustment, a higher reactive oxygen species scavenging ability, an improved gas exchange capacity and an increased chlorophyll fluorescence performance. Our findings demonstrate that the OE of MdIAA24 in apple positively regulates the synthesis of SL and the formation of arbuscules as a drought stress coping mechanism.

Blue Light Acclimation Reduces the Photoinhibition of Phalaenopsis aphrodite (Moth Orchid).

The moth orchid is an important ornamental crop. It is very sensitive to high light irradiation due to photoinhibition. In this study, young orchid tissue culture seedlings and 2.5” potted plants pretreated under blue light (BL, λmax = 450 nm) at 100 µmol m−2 s−1 for 12 days (BL acclimation) were found to have an increased tolerance to high light irradiation. After BL acclimation, orchids had an increased anthocyanin accumulation, enhanced chloroplast avoidance, and increased chlorophyll fluorescence capacity whenever they were exposed to high light of 1000 μmol m−2 s−1 for two weeks (HL). They had higher Fv/Fm, electron transport rate (ETR), chlorophyll content, catalase activity and sucrose content when compared to the control without BL acclimation. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) showed that transcript levels of phototropins, D1, RbcS, PEPCK, Catalase and SUT2 were upregulated in the BL-acclimated orchids. Consequently, BL acclimation orchids had better growth when compared to the control under long-term high light stress. In summary, this study provides a solution, i.e., BL acclimation, to reduce moth orchid photoinhibition and enhance growth before transplantation of the young tissue culture seedlings and potted plants into greenhouses, where they usually suffer from a high light fluctuation problem.

Physiological changes associated with enhanced cold resistance during maize (Zea mays) germination and seedling growth in response to exogenous calcium

Maize (Zea mays L.) is one of the most important crops worldwide. However, low temperature limits seed germination and seedling growth of maize, which can in turn affect grain yield. The calcium ion (Ca2+) is the second messenger involved in the response to environmental-stimuli-induced signal transduction networks. The underlying physiological mechanisms related to the effects of exogenous Ca2+ treatment of different maize cultivars under low temperature are unclear. We selected two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. Y478, for studying the effects of Ca2+ on seed germination, photosynthesis, antioxidant enzymes and the osmotic regulation of seedling resistance to low temperature. The optimal concentration of CaCl2 was 80 mmol L–1, which significantly improved the germination percentage at temperatures <10°C. Application of CaCl2 at this concentration under cold stress mitigated the degree of membrane injury and improved the antioxidant enzyme system through reduced relative electrolyte conductivity and malondialdehyde content, increased the soluble protein content, and enhanced superoxide dismutase and peroxidase activity. CaCl2 also significantly increased chlorophyll fluorescence indicators (Fv/Fo, Fv/Fm) and the photosynthetic rate. We conclude that exogenous CaCl2 at a concentration of 80 mmol L–1 protects the function and structure of the membrane and photosystems, improves antioxidant enzyme activity and increases osmotic regulatory substances under cold stress. These results improve our understanding of the mechanisms of Ca2+ and contribute to the development of cold-tolerant maize varieties.