Changes in growth, physiological parameters and the hormonal status of Myrtus communis L. plants irrigated with water with different chemical compositions

Reclaimed water reuse system on water quality, growth of irrigated crops, and impact of ecology: case study in Taiwan

In rapidly urbanized regions, the development of sustainable and resilient urban agriculture is essential to reduce environmental pollution and ensure reusable resources. The purpose of this study was to design, implement, and analyze the effects of reclaimed water reuse systems on crop growth, water purification, and ecology. A simulated experimental field near the side of Li Tse Lake at MingDao University in Changhua County, Taiwan, was chosen as the research field. A reclaimed water reuse system was established to collect domestic sewage discharged from the student dormitory, and a soil filter bed and plants in the system were used to purify the sewage, so as to detect its effects on water quality, soil, plant growth, and ecology throughout the year. According to the results, the water purified by the reclaimed water reuse system met the agricultural irrigation water quality criteria. While the soil filter bed showed that the purified water was alkaline and had low electrical conductivity, this did not affect plant growth. In the reclaimed water reuse system, the cultivation of fruiting and leafy vegetables increased the habitats of a number of organisms, and a total of 49 families of arthropods in 13 orders were found. This study showed that the reclaimed water reuse system could not only purify water and promote water reuse but also improve the ecology and develop the potential for food production.

Analysis of Salinity Tolerance in Tomato Introgression Lines Based on Morpho-Physiological and Molecular Traits

The development of salt-tolerant tomato genotypes is a basic requirement to overcome the challenges of tomato production under salinity in the field or soil-free farming. Two groups of eight tomato introgression lines (ILs) each, were evaluated for salinity tolerance. Group-I and the group-II resulted from the following crosses respectively: Solanum lycopersicum cv-6203 × Solanum habrochaites and Solanum lycopersicum M82 × Solanum pennellii. Salt tolerance level was assessed based on a germination percentage under NaCl (0, 75, 100 mM) and in the vegetative stage using a hydroponic growing system (0, 120 mM NaCl). One line from group I (TA1648) and three lines from group II (IL2-1, IL2-3, and IL8-3) were shown to be salt-tolerant since their germination percentages were significantly higher at 75 and 100 mM NaCl than that of their respective cultivated parents cvE6203 and cvM82. Using the hydroponic system, IL TA1648 and IL 2-3 showed the highest value of plant growth traits and chlorophyll concentration. The expression level of eight salt-responsive genes in the leaves and roots of salt-tolerant ILs (TA1648 and IL 2-3) was estimated. Interestingly, SlSOS1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated in leaves of both TA1648 and IL 2-3 genotypes under NaCl stress. While SlHKT1.1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated under salt stress in the roots of both TA1648 and IL 2-3 genotypes. Furthermore, SlSOS2 and SlSOS3 genes were upregulated in TA1648 root and downregulated in IL 2-3. On the contrary, SlSOS1 and SlHKT1.2 genes were upregulated in the IL 2-3 root and downregulated in the TA1648 root. Monitoring of ILs revealed that some of them have inherited salt tolerance from S. habrochaites and S. pennellii genetic background. These ILs can be used in tomato breeding programs to develop salt-tolerant tomatoes or as rootstocks in grafting techniques under saline irrigation conditions.

Effect of Pisolithus tinctorious on Physiological and Hormonal Traits in Cistus Plants to Water Deficit: Relationships among Water Status, Photosynthetic Activity and Plant Quality

Cistus species can form ectomycorrhizae and arbuscular mycorrhizal fungus that can bring benefits when plants are under water stress conditions. However, the application of some ectomycorrhizae on the water uptake under drought through physiological traits and hormonal regulation is less known. The experiment was performed during three months in a growth chamber with Cistus albidus plants in which the combined effect of the ectomycorrhiza Pisolithus tinctorious inoculation and two irrigation treatments (control and water-stressed plants) were applied. Irrigation absence caused significant decrease in aerial growth and tended to decrease soil water potential at the root surface, leading to a decrease in leaf water potential. Under these conditions, the abscisic acid and salicylic acid content increased while the precursor of ethylene decreased. Although the mycorrhization percentages were not high, the inoculation of P. tinctorious improved the water status and slightly cushioned the rise in leaf temperature of water-stressed plants. The ectomycorrhiza decreased the scopoletin values in leaves of plants subjected to deficit irrigation, indicating that inoculated plants had been able to synthesize defense mechanisms. Therefore, Pisolithus tinctorious alleviated some of the harmful effects of water scarcity in Cistus plants, being its use a sustainable option in gardening or restoration projects.

Functional annotations of ESTs of Stevia rebaudiana involved in abiotic stress signaling through computational approach

Stevia rebaudiana (Bertoni) is known as a natural sweetener plant to produced steviol glycosides. The steviol glycosides biosynthesis is limited in S. rebaudiana plants due to the alteration in the environmental circumstances such as drought, cold, salt and light. These environmental circumstances are a common side-effect in plants affecting the plant growth, metabolism and yield of secondary metabolites. Due to absence of complete genome annotations, the plant metabolites signaling is difficult in order to get the exact enzymatic flow to the product. In this article, we have analyzed the ESTs of S. rebaudiana and predicted their role in plant signaling in term of cis-regulatory elements, their biological function respect to abiotic stress. Further, the predicted abiotic stress responsive factors were also analyzed in order to predict the relevant genes or proteins function in comparison with the genome of Arabidopsis thaliana. Total 5,548 ESTs of stevia were retrieved from NCBI database. EST-contigs assembled from 5393 were 619 contigs and 2,894 singletons elements were identified by assembler program. Due to short expressed sequences related to singletons, it is excluded for further study. Further, retrieved ESTs were resulted in to 619 EST-contigs by using the clustering method. Out of 619, 15 contigs belongs to transcription factor families while 292 contigs, belongs to five enzyme classes. Out of 619 contigs, the 529 contigs showing the correct gene ontology in term of biological process (BP), molecular Functions (MF) and cellular component (CC). Further, these contigs were also screened for metabolic pathways analyses using KEG database. In this, 390 metabolic pathways and 67 involved for signal transduction were identified from 619 contigs. The co-expression analysis was revealed by gene investigators and STRING 10.0 with 0.40 correlations and 0.9 mutual connection. In projected PPI network, the recognized factors (WD40-like protein, MYB-HB like, AP2-EREBP, C2H2, Hap3/NF-YB, bHLH, C2C2-CO-like, CW-Zn, FHA-SMAD, Nin like, SBP3, TIFY, Tc-PD, Znf-B and bIP) belong to plant signaling and MAPK signaling pathways. These TFs introduce as a candidate genes responsive factors may lead to enhanced plant growth and metabolism by overexpression.

Biochemical study of the effect of stress conditions on the mandelonitrile-associated salicylic acid biosynthesis in peach

Salicylic acid (SA) plays a central role in plant responses to environmental stresses. In a recent study, we suggested a third pathway for SA biosynthesis from mandelonitrile (MD) in peach plants. This pathway is an alternative to the phenylalanine ammonia-lyase pathway and links SA biosynthesis and cyanogenesis. In the present work, using biochemical approaches, we studied the effect of salt stress and Plum pox virus (PPV) infection on this proposed SA biosynthetic pathway from MD. Peach plants were submitted to salt stress and Plum pox virus (PPV) infection. We studied the levels of SA and its intermediates/precursors (phenylalanine, MD, amygdalin and benzoic acid) in in vitro shoots. Moreover, in peach seedlings, we analysed the content of H₂ O₂ -related enzymes, SA and the stress-related hormones abscisic acid and jasmonic acid. We showed that the contribution of this SA biosynthetic pathway from MD to the total SA pool does not seem to be important under the stress conditions assayed. Nevertheless, MD treatment not only affected the SA content, but also had a pleiotropic effect on abscisic acid and jasmonic acid levels. Furthermore, MD modulates the antioxidative metabolism via SA-dependent or -independent redox-related signalling pathways. Even though the proposed SA biosynthetic pathway seems to be functional under stress conditions, MD, and hence cyanogenic glycosides, may be operating more broadly than by influencing SA pathways and signalling. Thus, the physiological function of the proposed SA biosynthetic pathway remains to be elucidated.

Characterization of natural genetic variation identifies multiple genes involved in salt tolerance in maize

Progressive decline in irrigation water is forcing farmers to use brackish water which increases soil salinity and exposes the crop plants to salinity. Maize, one of the most important crops, is sensitive to salinity. Salt tolerance is a complex trait controlled by a number of physiological and biochemical processes. Scant information is available on the genetic architecture of salt tolerance in maize. We evaluated 399 inbred lines for six early vigor shoot and root traits upon exposure of 18-day seedlings to salinity (EC_iw = 16 dS m^-1) stress. Contrasting response of shoot and root growth to salinity indicated a meticulous reprogramming of resource partitioning by the plants to cope with the stress. The genomic analysis identified 57 single nucleotide polymorphisms (SNP) associated with early vigor traits. Candidate genes systematically associated with each SNP include both previously known and novel genes. Important candidates include a late embryogenesis protein, a divalent ion symporter, a proton extrusion protein, an RNA-binding protein, a casein kinase 1, and an AP2/EREBP transcription factor. The late embryogenesis protein is associated with both shoot and root length, indicating a coordinated change in resource allocation upon salt stress. Identification of a casein kinase 1 indicates an important role for Ser/Thr kinases in salt tolerance. Validation of eight candidates based on expression in a salt-tolerant and a salt-sensitive inbred line supported their role in salt tolerance. The candidate genes identified in this investigation provide a foundation for dissecting genetic and molecular regulation of salt tolerance in maize and related grasses.

The Salt-Stress Response of the Transgenic Plum Line J8-1 and Its Interaction with the Salicylic Acid Biosynthetic Pathway from Mandelonitrile

Salinity is considered as one of the most important abiotic challenges that affect crop productivity. Plant hormones, including salicylic acid (SA), are key factors in the defence signalling output triggered during plant responses against environmental stresses. We have previously reported in peach a new SA biosynthetic pathway from mandelonitrile (MD), the molecule at the hub of the cyanogenic glucoside turnover in Prunus sp. In this work, we have studied whether this new SA biosynthetic pathway is also present in plum and the possible role this pathway plays in plant plasticity under salinity, focusing on the transgenic plum line J8-1, which displays stress tolerance via an enhanced antioxidant capacity. The SA biosynthesis from MD in non-transgenic and J8-1 micropropagated plum shoots was studied by metabolomics. Then the response of J8-1 to salt stress in presence of MD or Phe (MD precursor) was assayed by measuring: chlorophyll content and fluorescence parameters, stress related hormones, levels of non-enzymatic antioxidants, the expression of two genes coding redox-related proteins, and the content of soluble nutrients. The results from in vitro assays suggest that the SA synthesis from the MD pathway demonstrated in peach is not clearly present in plum, at least under the tested conditions. Nevertheless, in J8-1 NaCl-stressed seedlings, an increase in SA was recorded as a result of the MD treatment, suggesting that MD could be involved in the SA biosynthesis under NaCl stress conditions in plum plants. We have also shown that the plum line J8-1 was tolerant to NaCl under greenhouse conditions, and this response was quite similar in MD-treated plants. Nevertheless, the MD treatment produced an increase in SA, jasmonic acid (JA) and reduced ascorbate (ASC) contents, as well as in the coefficient of non-photochemical quenching (qN) and the gene expression of Non-Expressor of Pathogenesis-Related 1 (NPR1) and thioredoxin H (TrxH) under salinity conditions. This response suggested a crosstalk between different signalling pathways (NPR1/Trx and SA/JA) leading to salinity tolerance in the transgenic plum line J8-1.

The effect of mandelonitrile, a recently described salicylic acid precursor, on peach plant response against abiotic and biotic stresses

In a previous work, we observed that mandelonitrile (MD), which controls cyanogenic glycoside turnover, is involved in salicylic acid (SA) biosynthesis in peach plants. In order to gain knowledge about the possible roles of this SA biosynthetic pathway, this current study looks at the effect of MD and phenylalanine (Phe; MD precursor) treatments on peach plant performance from an agronomic point of view. Abiotic (2 g·l^-1 NaCl) and biotic (Plum pox virus, PPV) stresses were assayed. We recorded the following chlorophyll fluorescence parameters: quantum yield of photochemical energy conversion in PSII [Y(II)], photochemical quenching (qP) and quantum yield of regulated non-photochemical energy loss in PSII and its coefficient [Y(NPQ) and qN]. In addition, considering that environmental stresses lead to nutritional disorders, we determined the soluble K⁺ , Ca²⁺ , Na⁺ and Cl^- concentrations in NaCl-stressed seedlings. In PPV-infected seedlings, we recorded the Ca²⁺ level, which has been suggested to play critical roles in regulating SA-related plant defence responses against pathogens. The MD treatment lessened the effect of both stresses on plant development. In addition, an increase in non-photochemical quenching parameters was observed in MD-treated seedlings, suggesting a safer dissipation of excess energy under stress conditions. In NaCl-stressed peach seedlings both treatments stimulated the accumulation of phytotoxic ions in roots, whereas in PPV-infected seedlings MD increased Ca²⁺ content. Our results suggest that MD and Phe influence the response of peach seedlings to the deleterious effects of salt and PPV infection stresses.

Counteractive mechanism (s) of salicylic acid in response to lead toxicity in Brassica juncea (L.) Czern. cv. Varuna

Salicylic acid alleviates lead toxicity in Brassica juncea (L.) by promoting growth under non-stress and activating stress-defense mechanism (s) under lead stress conditions. It also boosts the ascorbate-glutathione cycle and thus helps in minimizing oxidative and DNA damage. Brassica juncea plants were exposed to different concentrations (0, 500, 1000 and 2000 mg kg^-1) of lead (Pb) and subsequently sprayed with 0.5 mM of salicylic acid (SA) to check for morphological and leaf gas exchange parameters like transpiration rate (E), stomatal conductance (GH₂O), net photosynthetic rate (A) and maximum quantum yield of PS II (F_v/F_m). Leaf epidermis by scanning electron microscopy (SEM), enzymatic and non-enzymatic components of ascorbate-glutathione (AsA-GSH) cycle, DNA damage by comet assay, lipid peroxidation and endogenous SA quantification by HPLC were analyzed. Lead accumulation in root, shoot and its sub-cellular distribution ratio (SDR) and localization was also determined using atomic absorption spectroscopy (AAS) and rhodizonate-dye staining method, respectively. Results revealed that notable amount of Pb was accumulated in root and shoot in dose-dependent manner which significantly (P ≤ 0.05) posed the toxicity on the majority of morphological parameters, structural integrity of epidermal and guard cells, photosynthetic pigments, malondialdehyde (MDA) and H₂O₂ content. Notable decrease in leaf gas exchange parameters, F_v/F_m, poor performance of AsA-GSH cycle and striking amount of DNA damage, was found as well. However, SA revoked Pb toxicity to a great extent by promoting growth, chlorophyll content, improving the A, F_v/F_m, boosting the overall performance of AsA-GSH cycle and by lessening the DNA damage.

Plant Responses to Salt Stress: Adaptive Mechanisms

This review deals with the adaptive mechanisms that plants can implement to cope with the challenge of salt stress. Plants tolerant to NaCl implement a series of adaptations to acclimate to salinity, including morphological, physiological and biochemical changes. These changes include increases in the root/canopy ratio and in the chlorophyll content in addition to changes in the leaf anatomy that ultimately lead to preventing leaf ion toxicity, thus maintaining the water status in order to limit water loss and protect the photosynthesis process. Furthermore, we deal with the effect of salt stress on photosynthesis and chlorophyll fluorescence and some of the mechanisms thought to protect the photosynthetic machinery, including the xanthophyll cycle, photorespiration pathway, and water-water cycle. Finally, we also provide an updated discussion on salt-induced oxidative stress at the subcellular level and its effect on the antioxidant machinery in both salt-tolerant and salt-sensitive plants. The aim is to extend our understanding of how salinity may affect the physiological characteristics of plants.

The long-term resistance mechanisms, critical irrigation threshold and relief capacity shown by Eugenia myrtifolia plants in response to saline reclaimed water

Salts present in irrigation water are serious problems for commercial horticulture, particularly in semi-arid regions. Reclaimed water (RW) typically contains, among others elements, high levels of salts, boron and heavy metal. Phytotoxic ion accumulation in the substrate has been linked to different electric conductivities of the treatments. Based on these premises, we studied the long-term effect of three reclaimed water treatments with different saline concentrations on Eugenia myrtifolia plants. We also looked at the ability of these plants to recover when no drainage was applied. The RW with the highest electric conductivity (RW3, EC = 6.96 dS m^-1) provoked a number of responses to salinity in these plants, including: 1) accumulation and extrusion of phytotoxic ions in roots; 2) a decrease in the shoot/root ratio, leaf area, number of leaves; 3) a decrease in root hydraulic conductivity, leaf water potential, the relative water content of leaves, leaf stomatal conductance, the leaf photosynthetic rate, water-use efficiency and accumulated evapotranspiration in order to limit water loss; and 4) changes in the antioxidant defence mechanisms. These different responses induced oxidative stress, which can explain the damage caused in the membranes, leading to the death of RW3 plants during the relief period. The behaviour observed in RW2 plants was slightly better compared with RW3 plants, although at the end of the experiment about 55% of the RW2 plants also died, however RW containing low salinity level (RW1, EC = 2.97 dS m^-1) can be effective for plant irrigation.