Free Proline Content Research Articles

Hyperspectral monitoring on proline content in winter wheat under water stress

Frequent occurrence of drought disaster will seriously affect the growth and development of winter wheat (Triticum aestivum). We set different water stress treatments (80%, 60%, 45%, 35%, 30% of field water capacity) to simulate the severity of drought disaster. We measured free proline content (Pro) of winter wheat, and investigated the responses of Pro to canopy spectral reflectance under water stress. Three methods, i.e., correlation analysis and stepwise multiple linear regression (CA+SMLR), partial least squares and stepwise multiple linear regression (PLS+SMLR), and successive projections algorithm (SPA) were used to extract the hyperspectral cha-racteristic region and characteristic band of proline. Furthermore, partial least square regression (PLSR) and multiple linear regression (MLR) methods were used to establish the predicted models. The results showed that Pro content of winter wheat was higher under water stress, and that the spectral reflectance of canopy changed regularly in different bands, indicating that Pro content of winter wheat was sensitive to water stress. The content of Pro was highly correlated with the red edge of canopy spectral reflectance, with the 754, 756 and 761 nm bands being sensitive to Pro change. The PLSR model performed good, followed by the MLR model, both showing good predictive ability and high model accuracy. In general, it was feasible to monitor Pro content of winter wheat by hyperspectral technique.

Modulation of NaCl-induced osmotic, cytogenetic, oxidative and anatomic damages by coronatine treatment in onion (Allium cepa L.)

Coronatine (COR), a bacterial phytotoxin produced by Pseudomonas syringae, plays important roles in many plant growth processes. Onion bulbs were divided four groups to investigate the effects of COR against sodium chloride (NaCl) stress exposure in Allium cepa L. root tips. While control group bulbs were soaked in tap water medium, treatment group bulbs were grown in 0.15 M NaCl, 0.01 µM COR and 0.01 µM COR + 0.15 M NaCl medium, respectively. NaCl stress seriously inhibited the germination, root lenght, root number and fresh weight of the bulbs. It significantly decreased the mitotic index (MI), whereas dramatically increased the micronucleus (MN) frequency and chromosomal aberrations (CAs). Moreover, in order to determine the level of lipid peroxidation occurring in the cell membrane, malondialdehyde (MDA) content was measured and it was determined that it was at the highest level in the group germinated in NaCl medium alone. Similarly, it was revealed that the superoxide dismutase (SOD), catalase (CAT) and free proline contents in the group germinated in NaCl medium alone were higher than the other groups. On the other hand, NaCl stress caused significant injuries such as epidermis/cortex cell damage, MN formation in epidermis/cortex cells, flattened cells nuclei, unclear vascular tissue, cortex cell wall thickening, accumulation of certain chemical compounds in cortex cells and necrotic areas in the anatomical structure of bulb roots. However, exogenous COR application significantly alleviated the negative effects of NaCl stress on bulb germination and growth, antioxidant defense system, cytogenetic and anatomical structure. Thus, it has been proven that COR can be used as a protective agent against the harmful effects of NaCl on onion.

Response characteristics of root to moisture change at seedling stage of Kengyilia hirsuta.

Kengyilia hirsuta is an important pioneer plant distributed on the desertified grassland of the Qinghai-Tibet Plateau. It has strong adaptability to alpine desert habitats, so it can be used as a sand-fixing plant on sandy alpine land. To study the response mechanisms of root morphological and physiological characteristics of K. hirsuta to sandy soil moisture, 10%, 25% and 40% moisture levels were set up through potted weighing water control method. The biomass, root-shoot ratio, root architecture parameters, and biochemical parameters malondialdehyde, free proline, soluble protein, indole-3-acetic acid, abscisic acid, cytokinin, gibberellin, relative conductivity and antioxidant enzyme activities were measured in the trefoil stage, and the response mechanisms of roots at different moisture levels were analyzed. The results showed that with the increase of soil moisture, root morphological indexes such as root biomass, total root length, total root volume and total root surface increased, while the root topological index decreased continuously. The malondialdehyde content, relative conductivity, superoxide dismutase activity, peroxidase activity, catalase activity, free proline content, soluble protein content, abscisic acid content and cytokinin content at the 25% and 40% moisture levels were significantly decreased compared with the 10% level (P< 0.05). Thus, the root growth of K. hirsuta was restricted by the 10% moisture level, but supported by the 25% and 40% moisture levels. An artificial neural network revealed that total root length, total root surface area, root link average length, relative conductivity, soluble protein, free proline and moisture level were the key factors affecting root development. These research results could contribute to future agricultural sustainability.

Hedypnois cretica L. and Urospermum picroides L. Plant Growth, Nutrient Status and Quality Characteristics under Salinity Stress

The cultivation of tolerant species with low-quality irrigation water is one of the main strategies to address the lack of availability of irrigation water. In this work, the effect of salinity on plant growth, nutritional composition, and quality features of Hedypnois cretica and Urospermum picroides was tested. Fresh yield of leaves and roots of both species were severely decreased under high salinity, while the mineral profile of leaves and roots also showed a decrease in most minerals. The recorded values of K/Na and Ca/Na ratios indicate that H. cretica has a higher susceptibility to salt stress due to a higher decrease in the values of the respective ratios compared to U. picroides. Leaf pigments and total phenolic compounds content were not significantly affected by salinity, while total soluble solids and titratable acidity increased under increasing salinity in most cases. Moreover, free proline content increased with increasing salinity, while the opposite trend was recorded for nitrates’ content. In conclusion, our findings indicate that tailor-made nutrient solutions could allow the use of irrigation water of a low quality for the commercial cultivation of H. cretica and U. picroides, thus allowing their domestication and integration in cropping systems where the cultivation of conventional crops is compromised.

Proteomic and metabolomic analysis of the Eskimo-1 line on the effect of low positive temperatures

Low temperatures are a significant stressor that adversely affects plant growth and productivity. They cause mechanical damage to the aerial parts of the plant, while salinity and drought disrupt the ionic and osmotic balance of the cell. Cold damage can also occur due to extremely low temperatures that lead to irreversible damage to plant organs. Consequently, low temperatures are a limiting environmental factor for agricultural productivity. This study aimed to investigate the response of cotton seedlings (lines ESKIMO1 and Coker-312) at the 2-4 true leaf stage to low temperatures. The content of free proline and endogenous salicylic acid was measured after the plants were exposed to temperatures below the critical threshold (+4 0 С, +10 0 С, +15 0 С, and +24 0 С) for 24 and 48 hours in climatic chambers. Analysis of the results revealed changes in the amino acid and phytohormone content after 24 hours of exposure to low temperatures. Based on these findings, we conclude that these substances participate in the adaptation process, protecting plants from the damaging effects of abiotic temperature factors. These results have implications for improving plant growth and productivity under low temperature conditions.

Lack of Tocopherol Inhibits Rice Growth by Triggering an Ectopic Stress Response and the Accumulation of DELLA Protein

Although tocopherols are essential for rice development, the molecular details by which their absence affects development remain to be determined. To study how tocopherols function during rice development, we performed a transcriptome deep sequencing (RNA-seq) analysis of the rice cultivar Nipponbare (Nip) and the tocopherol-deficient mutant small grain and dwarf 1-2 (sgd1-2). We identified 563 differentially expressed genes that were enriched in Gene Ontology categories associated with metabolism, stress, cellular responses, and transcriptional regulation. We determined that the total fatty acid composition of Nip and sgd1-2 was comparable, although cell membrane penetrability in sgd1-2 was significantly higher than in Nip under optimal growth conditions, indicating that tocopherol deficiency induces cell membrane damage. The expression levels of dehydration-responsive element binding 1 (DREB1) genes and free proline content in sgd1-2 were also higher than those in Nip. We also showed that the DELLA protein SLENDER RICE1 (SLR1) accumulated in sgd1-2, resulting in significant changes in the global transcriptome. Our study confirms that the lack of tocopherol accumulation in rice induced ectopic stress responses and limited growth by enhancing SLR1 abundance through increasing SLR1 transcript levels. These results provide new insights into tocopherol during rice development.

Effects of field soil warming on the growth and physiology of Juglans mandshurica seedlings.

Global climate change will increase surface soil temperature, with consequences on plant seedling growth and population dynamics. In this study, we carried out a field experiment to investigate the effects of 2 ℃ soil warming on the growth and physiological characteristics of 1- and 2-year-old seedlings of a dominant tree species in broadleaved Korean pine forest, Juglans mandshurica. The results showed that soil warming significantly increased basal diameter, root length, total leaf area, leaf dry weight, root dry weight, total biomass, apparent photosynthetic electron transfer rate (ETR), PSⅡ actual photochemical efficiency (ΦPSⅡ), and apparent photosynthetic electrophotochemical quenching coefficient (qP) of 1-year-old seedlings by 18.3%, 66.7%, 94.4%, 105.9%, 95.8%, 37.8%, 89.5%, 100.0%, and 71.4%, respectively. Soil warming significantly increased basal diameter, total leaf area, leaf dry weight, total biomass, leaf superoxide dismutase activity, peroxidase activity, catalase activity and free proline content, ETR, ΦPSⅡ, and qP of 2-year-old seedlings by 12.5%, 180.5%, 97.3%, 42.5%, 23.9%, 20.4%, 14.9%, 20.7%, 66.7%, 283.3% and 284.6%, respectively. There was an interaction between seedling age and soil warming on the root-shoot ratio and the ΦPSⅡ and qP in chlorophyll fluorescence parameters, in that soil warming significantly reduced the root-shoot ratio of 2-year-old seedlings and that the increase of chlorophyll fluorescence parameters of 2-year-old seedlings (4.1-4.6 times) was much higher than that of 1-year-old seedlings (1.5-1.8 times). Soil warming of 2 ℃ was beneficial to the growth of 1- and 2-year-old J. mandshurica seedlings and increased their regeneration potential. In particular, 2-year-old J. mandshurica seedlings responded to soil warming by increasing leaf area, improving leaf photochemical efficiency, and enhancing protective enzyme activity to increase resistance.

Gas exchange and osmotic adjustment in cotton cultivars subjected to severe salt stress.

Salinity is harmful to crops when the concentration of soluble salts overcomes the salinity threshold of the crop, causing osmotic stress and limitations in plant growth. In this scenario, adopting tolerant cultivars is the most adequate strategy to minimize agricultural losses. However, the inheritance of tolerance depends on the genotype. From this perspective, this study assessed the tolerance to severe salt stress in 11 cotton cultivars based on gas exchange parameters and the free proline content. The cultivars were grown in a greenhouse and subjected to 34 days of saline irrigation (10 dS m-1), starting 45 days after seedling emergence (B1 phase). Plant growth was monitored weekly until the end of the salt stress period. The treatments consisted of a combination of two factors: eleven cultivars associated with two electrical conductivity levels of irrigation water (ECw: 0.3 and 10.0 dS m-1). The experimental design was in randomized blocks in a 11 × 2 factorial arrangement with three replications (66 plots), with the experimental unit consisting of one plant per plot. Salinity impacted plant growth, being reflected on the gas exchange and free proline data of most cultivars. However, BRS 286, FMT 705, BRS 416, and BRS Acácia, and CNPA 7MH withstood the effects of stress and osmotically adjusted to the salt stress conditions, thus minimizing the damage to growth. Those cultivars are the most indicated for improvement programs aiming at tolerance to salt stress based on the results found in this research.

Strigolactone (GR24) Application Positively Regulates Photosynthetic Attributes, Stress-Related Metabolites and Antioxidant Enzymatic Activities of Ornamental Sunflower (Helianthus annuus cv. Vincent’s Choice) under Salinity Stress

Strigolactones, a new group of phytohormones, are reported to improve plant tolerance to multiple abiotic stresses. A pot experiment was conducted to investigate the impact of synthetic strigolactone (GR24 at 0.001, 0.01 and 0.1 mg L−1) application on ornamental sunflowers (Helianthus annuus cv. Vincent’s Choice) grown under salt stress (150 mM NaCl). Salt stress was applied after 14 days, and SL was applied 25 days seed sowing. The results showed that amongst various GR24 concentrations, 0.01 mg L−1 proved to be superior, as it enhanced the photosynthetic rate (9.29%), transpiration rate (0.76%), stomatal conductance (77.5%), total soluble protein (0.55%) and K+ (14.63% in roots; 14.87% in shoots) and Ca2+ (12.63% in roots; 11.48% in shoots) contents under control conditions. Similarly, the leaf turgor potential (Ψp), osmotic potential (Ψs) and free proline, glycinebetaine (GB), superoxide dismutase (SOD), catalase (CAT) and peroxide (POD) contents increased by 58.17, 89.95, 159.04, 101.54, 74.42, 175.68 and 53.62%, respectively, under salt stress conditions. The leaf water potential (Ψw) decreased (−0.14%) and the malondialdehyde (MDA) content increased (16.65%) when treated with the 0.001 mg L−1 GR24 level. Meanwhile, hydrogen peroxide (H2O2) and Na+ concentrations in roots and shoots increased by 62.53%, 74.66% and 38.55% under saline conditions with a GR24 level of 0 mg L−1. Regarding the plant biomass, a GR24 level of 0.01 mg L−1 with salt stress greatly decreased the root (−47.27% and −50.45%) and shoot (−44.79% and −59.42%) fresh and dry weights, respectively, compared to control conditions. These results reveal that exogenously applied GR24 might be an effective way to mitigate the perilous impacts of salt stress in ornamental sunflower production. It is suggested that the use of molecular techniques to study different processes in which GR24 could play a vital part in various commercial floricultural crops is extremely imperative and can open novel horizons for future investigations in this exhilarating field of plant hormones.

MbICE1 Confers Drought and Cold Tolerance through Up-Regulating Antioxidant Capacity and Stress-Resistant Genes in Arabidopsis thaliana.

Malus baccata (L.) Borkh is an apple rootstock with good drought and cold resistance. The ICE gene is a key factor in the molecular mechanisms of plant drought and cold resistance. In the present research, the function of drought- and cold-induced MbICE1 of Malus baccata was investigated in Arabidopsis. According to GFP fluorescence images, MbICE1 was determined to be a nuclear protein. The MbICE1 was transferred to Arabidopsis, showing enhanced tolerance to drought and cold stresses. Under drought and cold treatments, the transgenic Arabidopsis had higher chlorophyll content and free proline content than WT plants, but the Malondialdehyde (MDA) content and electrolyte leakage (EL) were lower than those of WT plants. In addition, drought and cold led to a large accumulation of ROS (H2O2 and O2-) content in Arabidopsis, while overexpression of MbICE1 enhanced the antioxidant enzyme activity in Arabidopsis and improved the plant's resistance to stresses. Moreover, the accumulation of MbICE1 promoted the expression of AtCBF1, AtCBF2, AtCBF3, AtCOR15a, AtCOR47 and AtKIN1 genes in Arabidopsis. These data indicate that MbICE1 is a key regulator of drought and cold and can be used as a backup gene for breeding Malus rootstocks.

Salt stress in plants and amelioration strategies: alleviation of agriculture and livelihood risks after the Covid-19 pandemic.

Agriculture sustains the livelihoods of over 2.5billion people worldwide. The growing nature of disasters, the systemic nature of risk, a more recent pandemic along with abiotic stress factors are endangering our entire food system. In these stressful environment, it is widely reprimanded that strategies should be encompassed to attain increased crop yield and economic returns which would alleviate food and nutritional scarcity in developing countries. To study the physiological responses to salt stress, Vigna radiata seedlings subjected to varying levels of salt stress (0, 25, 50, 100 and 200 mM NaCl) were evaluated by tracking changes in Chl a fluorescence, pigment content, free proline and carotenoids content by HPLC. The ability of plants to adapt to salt stress is related with the plasticity and resilience of photosynthesis. As salt concentration increased, chlorophyll fluorescence indices decreased and a reduction in the PSII linear electron transport rate was observed. Chlorophyll fluorescence parameters can be used for in vitro non-invasive monitoring of plants responses to salt stress. Overall, Vigna responded to salt stress by the changes in avoidance mechanism and protective systems. Chl fluorescence indices, enzymatic contents of POD, CAT and free proline were sensitive to salt stress. The study is significant to evaluate the tolerance mechanisms of plants to salt stress and may develop insights for breeding new salt-tolerant varieties.

Impact of Irrigation with Wastewater on Accumulation of Heavy Metals in Phaseolus vulgaris L. and Its Remediation

This study investigates the effects of Spirulina platensis, Chlorella vulgaris, leaves powder of Salix alba, and ethylenediaminetetraacetic acid treatments on the biochemical and yield traits of Phaseolus plants grown under wastewater irrigation. In addition, to assess the uptake and accumulation of heavy metals into the edible plant part. Water samples were obtained from each irrigation source (fresh tap water and untreated wastewater collected from El-Rahawy drain, Giza, Egypt); the plants were treated with our treatments (3 g per kg soil) at the beginning of the experiment (mixed fully into the soil). The results observed that the irrigation of Phaseolus plants with wastewater markedly stimulated the free proline contents, total phenols, superoxide dismutase, catalase, peroxidase, polyphenol oxidase, lipid peroxidation, and abscisic acid throughout the two growth stages. Indole acetic acid, gibberellic acid, yield parameters, total soluble carbohydrate, and protein in seeds were significantly reduced. The concentrations of nickel (Ni), cadmium (Cd), lead (Pb), and cobalt (Co) in Phaseolus seeds were significantly increased beyond recommended limits set by international organizations. However, our treatments significantly reduced the contents of Ni, Cd, Pb, and Co in seeds; free proline; total phenols; superoxide dismutase; catalase; peroxidase; polyphenol oxidase; lipid peroxidation; and abscisic acid in Phaseolus plants. Moreover, indole acetic acid, gibberellic acid, all yield traits, and seed components were enhanced. This study concluded that Spirulina platensis and salix leaves powder being economically and environmentally friendly can be considered an efficient strategy to mitigate the harmful effects of wastewater on plants.

Biochemical changes, biomass production, and productivity of Triticum aestivum as a function of increasing molybdenum application

In the present study, the effects of soil-applied different molybdenum concentrations (0.1, 0.5, 2.5, 12.5 or 62.5 mg kg−1) in the form of sodium molybdate on growth performance, seed production, biochemical parameters, and uptake of Mo in wheat were investigated. Results indicate that Mo doses higher than 2.5 mg kg−1 of soil were observed to be toxic to wheat and retarded the growth as well as seed production. The change in biochemical constituents were correlated with soil Mo concentrations. Chlorophyll and carbohydrate contents increased under lower concentrations of Mo applied. In turn, Mo concentrations beyond 2.5 mg kg−1 significantly increased soluble proteins, total phenolic compounds, and free proline contents. The contents of Mo in root and shoot of wheat plants increased with increased Mo concentrations in the soil. Among the various concentrations of Mo studied, 2.5 mg kg−1 was moderately toxic while 12.5 and 62.5 mg kg−1 were highly toxic and induced stress responses to confer tolerance in wheat.

Mycosynthesis of Silica Nanoparticles Using Aspergillus niger: Control of Alternaria solani Causing Early Blight Disease, Induction of Innate Immunity and Reducing of Oxidative Stress in Eggplant.

The threats to the life and production of crops are exacerbated by climate change and the misuse of chemical pesticides. This study was designed to evaluate the effectiveness of biosynthesized silica nanoparticles (SiO2-NPs) as an alternative to pesticides against early blight disease of eggplant. Antifungal activity, disease index, photosynthetic pigments, osmolytes, oxidative stress, antioxidant enzymes activities were tested for potential tolerance of eggplant infected with Alternaria solani. Silica nanoparticles were successfully biosynthesized using Aspergillus niger through green and ecofriendly method. Results revealed that SiO2-NPs exhibited promising antifungal activity against A. solani where MIC was 62.5 µg/mL, and inhibition growth at concentration 1000 µg/mL recorded 87.8%. The disease Index (DI) as a result of infection with A. solani reached 82.5%, and as a result, a severe decrease in stem and root length and number of leaves occurred, which led to a sharp decrease in the photosynthetic pigments. However, contents of free proline, total phenol and antioxidant enzymes activity were increased in infected plants. On the other hand, the treatment with SiO2-NPs 100 ppm led to a great reduction in the disease Index (DI) by 25% and a high protection rate by 69.69%. A clear improvement in growth characteristics and a high content of chlorophyll and total carotenoids was also observed in the plants as a result of treatment with silica nanoparticles in (healthy and infected) plants. Interestingly, the noticeable rise in the content of infected and healthy plants of proline and phenols and an increase in the activity of super oxide dismutase (SOD) and polyphenol oxidase (PPO). It could be suggested that foliar application of SiO2-NPs especially 100 ppm could be commercially used as antifungal and strong inducer of plant physiological immunity against early blight disease.

Diverse responses of halophyte and glycophyte Lepidium species to the salt-mediated amelioration of nickel toxicity and accumulation.

Tolerance mechanisms employed by plants under environmental stresses can protect them against other co-occurring stresses. In this study, the effect of pre-exposure and simultaneous salt treatment on nickel (Ni) toxicity tolerance in one halophyte (L. sativum) and one glycophyte (L. latifolium) Lepidium species in hydroponics was investigated. In order to compare the species independent from their salt and Ni tolerance level, the glycophyte was subjected to lower salt and Ni concentrations and for a shorter period of time than the halophyte. Salt (NaCl) was applied at 50 and 100mM concentrations and Ni was provided at an equal free Ni2+ activity by adding 100 and 200µM Ni as single stresses, but 130 and 300µM Ni for the treatment of its combination with salt in the glycophyte and halophyte, respectively. Temporal analyses of signaling molecules revealed that the halophyte is characteristically different from the glycophyte in that it exhibits a higher constitutive level of nitric oxide and hydrogen peroxide, a longer duration of response to Ni, and its augmentation by salt. In addition to higher biomass and less Ni accumulation in salt-treated plants, the concentrations of free thiol groups, leaf pigments, proline, free and cell wall-bound phenolics contents, and the activity of phenolic metabolizing enzymes were higher in L. latifolium under the combined salt and Ni treatments than under the single Ni stress. In contrast, the biomass and most biochemical parameters of Ni-stressed L. sativum plants were not enhanced by salt treatment but rather decreased. Our findings shed light on cross-tolerance mechanisms in halophytes and uncovered halophyte survival strategies under multiple stresses.

Abscisic Acid, Paclobutrazol, and Salicylic Acid Alleviate Salt Stress in Populus talassica × Populus euphratica by Modulating Plant Root Architecture, Photosynthesis, and the Antioxidant Defense System

The exogenous plant growth regulators (PGRs) represent a useful strategy for reducing the adverse effects of salt stress in plants. In order to investigate the regulatory effect of exogenous PGRs on the salt tolerance of Populus talassica × Populus euphratica seedlings, in this study, the effects of different foliar spray concentrations of ABA (5 mg·L−1, 15 mg·L−1, 25 mg·L−1), PP333 (300 mg·L−1, 900 mg·L−1, 1500 mg·L−1), and SA (40 mg·L−1, 120 mg·L−1, 200 mg·L−1) on P. talassica × P. euphratica seedlings under salt stress (soil salt concentration of 2%) were determined. The results showed that the dry weight, total root length, root surface area, root volume, total Chl content, and photosynthetic parameters of P. talassica × P. euphratica seedlings significantly decreased under salt stress and increased their contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide anion (O2−), free proline (Pro), superoxide dismutase (SOD), and peroxidase (POD). However, ABA, PP333, and SA can mitigate the adverse effects of salt stress on these indicators. Especially, the 15 mg·L−1 ABA, 900 mg·L−1 PP333, and 120 mg·L−1 SA treatments had the best effect on alleviating salt stress, with significant increases in dry weight, root parameters, total Chl content, and the photosynthetic parameters of the P. talassica × P. euphratica seedlings, improving their photosynthetic characteristics; meanwhile, increased Pro content and enzyme activity and decreased MDA, H2O2, and O2− content protected the integrity of membrane system and enhanced the salt tolerance of the seedlings. SA resulted in a better ameliorative effect on salt stress compared to ABA and PP333.

Acer velutinum Bioss. (velvet maple) seedlings are more tolerant to water deficit than Alnus subcordata C.A. Mey. (Caucasian alder) seedlings

Drought stress is a major environmental factor limiting plant growth. Selection of drought-tolerant plants is of critical importance in vegetation restoration and forestation programs. Alnus subcordata and Acer velutinum are two valuable, dominant, and endemic species in the Hyrcanian forests. There are fast-growing species and significant diffuse-porous hardwood in afforestation and reforestation. One-year old seedlings of both species were exposed to four water shortage treatments (100, 75, 50 and 25% of field capacity (FC) chosen as control, mild, moderate, and severe) for 12 weeks. Thereafter, their morphological characteristics such as height and basal area, total and organs biomass (root, stem, and leaf), leaf area (LA), specific leaf area (SLA), leaf area ratio (LAR), as well as physiological and biochemical characteristics such as relative water content (RWC), content of chlorophyll, free proline and malondialdehyde (MDA), and superoxide dismutase (SOD) and peroxidase (POD) activity were measured. The results showed that when exposed to reduced water availability, plants’ height, basal diameter, total and organs biomass, LA, LAR, RWC and chlorophyll content decreased, but their proline concentration, MDA content, SOD, and POD activity increased in both species. The root to shoot ratio (R/S) and root mass ratio (RMR) increased at 50 and 25% FC treatments in A. subcordata, whereas no significant difference was found in A. velutinum under drought treatments. SLA increased significantly at 50% FC in A. velutinum and decreased in A. subcordata under drought treatments compared to control treatment. A. velutinum showed more proline content, RWC, POD, and lower increase in MDA content than A. subcordata under moderate treatment. Therefore, A. velutinum appears to possess a better mechanism to cope drought stress. The drought tolerance of A. velutinum may enhance its potential for climatic adaptations under drier conditions with the ongoing climatic change.

Irrigation with water enriched with seaweed extract to overcome effects of salinity in ‘New red fire’ leafy lettuce cultivation

ABSTRACT Lettuce (Lactuca sativa L.) is salt-sensitive, and salinity level can negatively affect yield. The study was conducted to investigate effect of water enriched with seaweed extract to overcome effects of salinity in ‘New Red Fire’ leafy lettuce cultivation. The highest and lowest leaf free proline content was in plants irrigated with saline water at EC 7 and 1.37 dS m−1. Increasing water EC level from 2.5 to 4 dS m−1 resulted in 9.3% increase in leaf total soluble solid content. The highest leaf vitamin C content was in plants treated by Chlorella vulgaris seaweed solution. Salinity levels could be classified into three groups: 1.37 and 2.5 dS m−1 (least damaging), 4 and 5 dS m−1 (tolerance threshold) and 7 dS m−1 (most damaging). Chlorella vulgaris seaweed solution appeared to neutralize adverse effects of salinity on plant fresh weight, free proline content, total soluble solid content, photosynthetic pigments content, radical scavenging activity, anthocyanin content, phenol and flavonoid content, peroxidase enzyme activity and leaf vitamin C content. Irrigation ‘New Red Fire’ with water enriched with Chlorella vulgaris seaweed extract is strongly recommended to overcome effects of salinity on lettuce morphological and physiological characteristics. Salinity levels higher than 5 dS m−1 can seriously damage ‘New Red Fire’ qualitative and quantitative properties.

Transcriptional analysis of grape in response to weak light stress

Grape (Vitis vinifera L.) in production is frequently exposed to inadequate light, which significantly affects its agronomic traits via inhibiting their physiological, metabolic and developmental processes. To explore the mechanism how the grape plants respond to the weak light stress, we used 'Yinhong' grape and examined their physiology-biochemistry characteristics and transcriptional profile under different levels of weak light stress. The results showed that grape seedlings upon low intensity shading treatments were not significantly affected. As the shading stress intensity was strengthened, the epidermis cells, palisade tissue, and spongy tissue in the leaves were thinner, the intercellular space between the palisade tissue and spongy tissue was larger compared with that of the control, and the activities of superoxide dismutase, catalase and peroxidase were decreased gradually. Additionally, the soluble protein content increased and the free proline content decreased gradually. Compared with the control, significant changes in plant photosynthetic characteristics and physiology-biochemistry characteristics were observed under high intensity of shading (80%). RNA-seq data showed that the differentially expressed genes between CK and T2, CK and T4, T2 and T4 were 13 913, 13 293 and 14 943, respectively. Most of the enrichment pathways were closely related with the plant's response to stress. Several signaling pathways in response to stress-resistance, e.g. JA/MYC2 pathway and MAPK signal pathway, were activated under weak light stress. The expression level of a variety of genes related to antioxidation (such as polyphenol oxidase and thioredoxin), photosynthesis (such as phytochrome) was altered under weak light stress, indicating that 'Yinhong' grape may activate the antioxidation related pathways to cope with reactive oxygen species (ROS). In addition, it may activate the expression of photosynthetic pigment and light reaction structural protein to maintain the photosynthesis activity. This research may help better understand the relevant physiological response mechanism and facilitate cultivation of grape seedlings under weak light.

The Influence of End-of-Day Blue Light on the Growth, Photosynthetic, and Metabolic Parameters of Lettuce at Different Development Stages.

This study evaluates the effect of end-of-day blue (EOD B) light on the physiological response of lettuce (Lactuca sativa, Lobjoits Green Cos) at different phenological development stages. Plants were grown in a controlled environment growth chamber (day/night temperature 21 ± 2 °C; relative air humidity 60 ± 5%) under the light of light-emitting diodes (LEDs) consisting of 5% blue (B; 450 nm), 85% red (R; 660 nm), and 10% green (G; 530 nm) photosynthetic photon flux density (PPFD) at 200 µmol m−2 s−1 for 16 h d−1 (BRG, control) for 8, 15, and 25 days (BBCH 12, BBCH 14, and BBCH 18, respectively). For the EOD B treatments, lettuce plants were additionally illuminated with 100% of B light at 30 and 60 µmol m−2 s−1 PPFD for 4 h d−1 (B30 and B60, respectively). The results show that EOD B light caused the elevated shoot elongation of lettuce plants regardless of their growth stages. However, leaf width increased only in more developed lettuce plants (BBCH 18). EOD B light negatively affected the development of new leaves and fresh weight, except for seedlings (BBCH 12). Most photosynthetic and spectral leaf indices also decreased when lettuce was treated with EOD B light, especially under the PPFD level of 60 µmol m−2 s−1. Moreover, the changes in metabolic parameters such as DPPH free radical activity, free proline content, and H+-ATPase activity in lettuce showed a plant response to unfavorable conditions to EOD B light.