Salt-treated Plants Research Articles

English

This work aims to identify the impacts of vermicompost leachate (VCL) toward its salt resistance stress in plants. Young Capsicum annuum L seedlings were subjected to salinity (160 mM NaCl added to a nutrient solution) over a course of seven days during or following the adding of 7 mL L−1 VCL. The exposure to salt stress resulted in a notable decrease of dry and fresh leaf weights, K+ concentrations, and leaf water content; whereas leaf and root Na+ concentrations were remarkably increased. Furthermore, the salt stress yielded reduced instantaneous transpiration, net photosynthesis, maximum PSII photochemistry efficiency, stomatal conductance (gs) in the state of photochemical quenching, dark adaptation, and photochemical efficiency of PSII (ΦPSII). Moreover, VCL application in the state of salt stress led to an increase of leaf fresh weight and gs, while the leaf osmotic potential remained consistent regardless of the proline content increase seen in the salt-treated plants. Meanwhile, it minimized the Na+ concentration in the leaves by 21.4%, and increased in the roots by 16.9%. Accordingly, a pre-treatment regiment with VCL and the ensuing salt stress yielded higher efficiency compared to its concomitant application with salt stress due to the pre-treatment recording the highest osmotic adjustment. VCL pre-treatment resulted in sugar concentration in the roots (9.3 µmol g−1 FW) and the maximum level of proline in the leaves (51 µmol g−1 FW). Additionally, the fluorescence-linked parameter reaffirmed superior outcomes for the PSII stability and efficiency in the case of VCL pre-treatment on salt-stressed plants in contrast to those subjected to concurrent VCL salt stress exposure. Hence, VCL is proven to be an effective defense medium towards enhancing the property of salt-stress resistance in bell peppers. Key words: Vermicompost leachate (VCL), priming, bell pepper, Sodium, NaCl.

Growth regulation of Desmostachya bipinnata by organ-specific biomass, water relations, and ion allocation responses to improve salt resistance

Salt resistance strategies in Desmostachya bipinnata may be a function of coordinated organ specific responses for growth and developmental stages. It may provide clues to improve salt tolerance in conventional crops. The effects of NaCl concentrations (100, 200, 300 and 400 mM) on growth, water relations, organic compound (proline and sugar) accumulation, ion-flux and nutrient selectivity both in root [adventitious (RA) and mature (RM) root] and shoot [juvenile (LJ) and adult (LA) leaves] organs were investigated. Decreases in biomass were observed under saline treatments higher than 100 mM NaCl. The lower amount of biomass is considered to be a survival strategy under harsh conditions due to reallocation of energy in the plant. D. bipinnata regulated water flux (OP, osmotic potential, in the following order: LJ > LA > RM > RA) to allow water uptake from soil under hyperosmotic conditions. Na+ was largely accumulated in roots followed by LA and LJ. This ion excluding strategy is common in monocots to protect photosynthetic tissues. Salt-treated plants retained more Ca2+ and Mg2+ in roots than in shoots, while K+ allocation was not affected by salinity. This may be due to selective transport in the case of K+ and increasing use efficiency for Ca2+ and Mg2+. Whole plant responses generally are organ-specific based on salinity concentrations. Our findings suggest that different organs of D. bipinnata coordinated with each other for biomass partitioning, OP gradient, Na+ distribution, K+ selective transport, nutrient use efficiency, and sugar and proline allocation to achieve better yields in moderately saline areas for fodder/forage production.

Paclobutrazol induced non-enzymatic antioxidants and polyamine levels in soybean plants grown under salinity stress

Paclobutrazol (PBZ) is a member of the triazole family of plant growth regulators and is known to protect crops from environmental stresses such as salinity and drought. It plays a role in maintaining water balance, photosynthesis capacity and enhancing antioxidant enzyme activities. Despite the well-documented effects of PBZ on antioxidant defence in soybean plants, the changes in non-enzymatic antioxidants and endogenous polyamines in the PBZ-treated plants grown under salinity stress are still not studied. Herewith, the study aimed to clarify the effects of PBZ on these molecules. For this purpose, the combined effect of salt (250 mM NaCl) and three different concentrations of PBZ (5, 10 and 20 ppm) on soybean (Glycine max L.) plants were studied. Proline, hydroxyl radical (OH.) scavenging capacity, non-enzymatic antioxidants (anthocyanin, flavonoid, phenolic and free thiol-containing compounds) and polyamines spermine, spermidine, and putrescine were investigated in the treated plants. We found that the PBZ (10 ppm) treatment was the most effective concentration to counteract oxidative stress due to NaCl in soybean seedlings. It significantly increased hydroxyl radical scavenging activity, proline, total phenolics, flavonoids, and conjugated polyamine content compared to those found in salt-treated plants only. For the first time, our study showed that PBZ could induce the non-enzymatic antioxidant defence in soybean plants grown under salt stress conditions.

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Salinity stress inhibits plant growth by affecting morphological, photosynthesis, antioxidant phenomena, and nitrogen metabolism, among other physiological and biochemical processes. In this study, the effects of pre-soaking Wheat and Mung grains in aqueous extract of Cissus quadrangularis on growth, and antioxidant activity of salt-treated plants, were investigated. The pre-soaking of grains in extract demonstrated a significant enhancement in growth parameters. The activity of superoxide dismutase (SOD), guaiacol peroxidise (GPOX), and ascorbate peroxidase (APX), catalase (CAT) increased with increasing the concentration of C. quadrangularis extract up to 3%w/v while decreasing when at a higher concentration of 10%w/v. The estimation of bioactive compound Proline also observes higher concentrations at 3%w/v under treatment with different salt stress. Therefore, the study suggested that seed priming with plant extract is an effective technique to improve the growth of Wheat and Mung seedlings under salt stress conditions.

Wpływ działania stresu solnego na wzrost i aktywność fotosyntezy roślin bazylii pospolitej (Ocimum basilicum L.)

The study evaluated basil plants’ response (var. Sweet Green) to increased concentrations of sodium chloride (NaCl) and macro- and micronutrients in the medium. The following variants were used: ½ Hoagland nutrient solution containing NaCl (0, 80 and 160 mM) and 4/2 Hoagland solution with 0 mM NaCl. Biometric and physiological parameters were measured 20 days after saline application. The application of 160 mM NaCl in nutrient solution caused the suppression of basil plants’ growth. The height of plants was decreased by 22% and the length of the roots was less by 60%. Control plants had 68% greater leaf area than those grown in the medium with 160 mM NaCl. Compared to the control, basil grown in ½ Hoagland solution with 80 mM NaCl and 4/2 Hoagland solution with 0 mM NaCl had leaf area reduced by 43.4% and 48.2%, respectively. A single plant’s highest fresh weight was found in the control variant (17.78 g) and the lowest in the ½ Hoagland solution with 160 mM NaCl (5.14 g). A negative effect of 160 mM NaCl in solution on the leaf gas exchange of salt-treated plants was found. At the same time, no negative influence of salinity on the content of photosynthetic pigments was found. The addition of NaCl into Hoagland solution did not affect the maximum photochemical efficiency (Fv/Fm) but modified the actual activity of Photosystem II (PSII). Increasing the concentration of macro- and microelements in the nutrient solution (4/2 of Hoagland and 0 mM NaCl) had a significantly lower negative effect on the growth and photosynthetic activity of basil plants.

Alleviative effects of Fara-darmani Consciousness Field on Triticum aestivum L. under salinity stress.

Background: The Fara-darmani Consciousness Field was founded by Mohammad Ali Taheri. It is a novel field and is described similarly to the field of gravity, or the electromagnetic field. This field is neither matter nor energy, and therefore does not possess a quantity. Even though there is no direct scientific evidence for the Consciousness Field, it is possible to investigate its effects on objects through controlled experiments. The aim of the present work was to study the alleviative effects of the Fara-darmani Consciousness Field on common wheat Triticum aestivum L. var Star under salt stress. Methods: Plants were grown under 0 mM NaCl (control) and 150 mM NaCl with or without the influence of Fara-darmani Consciousness Field for 3 weeks. Chlorophyll, hydrogen peroxide (H 2O 2), malondialdehyde (MDA) content and activity of antioxidant enzymes such as superoxide dismutase (SOD),polyphenol oxidase (PPO), and peroxidase (POX) were measured in all groups of plants. Results: In the salt-treated plants under the influence of the Fara-darmani Consciousness Field, the contents of total chlorophyll, as well as a and b chlorophyll forms, were elevated compared with the salt-treated plants without Fara-darmani CF (34.8%, 17.8%, and 169% respectively). Additionally, Fara-darmani increased H 2O 2 (57%) and the activity of SOD and PPO by 220% and 168%, respectively, under salinity compared with the salt-treated plants without Fara-darmani CF. MDA content and activity of peroxidase were decreased by 12.5% and 34%, respectively. Conclusion: These results suggest the Fara-darmani Consciousness Field as a qualitative intervention strategy to withstand salt stress in plants, by increasing the contents of chlorophyll, antioxidant enzyme activities, and decreasing MDA content under salinity.

Increased soil salinity has no effect on the host preference and suitability of the Tamarix biological control agent, Diorhabda carinulata

ABSTRACT Tamarix species are major terrestrial riparian invaders in South Africa. The biocontrol agent, Diorhabda carinulata (Coleoptera: Chrysomelidae), was tested as the initial candidate agent in South Africa due to its success against invasive Tamarix in North America. The ability of Tamarix to grow across a broad soil salinity gradient may affect its suitability as a host for D. carinulata, and influence its invasive capability. Therefore, the effect of increased soil salinity was considered a potential influential factor on the host preference of D. carinulata and the suitability of the host plant for the beetle. Choice tests were conducted by exposing beetles to salt-treated and untreated plants of both the invasive alien T. chinensis x T. ramosissima hybrid and indigenous T. usneoides. Leaf chlorophyll content and relative water content were used as a proxy to measure how increased soil salinity affected the health of the Tamarix taxa. Adult host selection and oviposition, and subsequent larval survival and development of D. carinulata on salt-treated and untreated plants were not different on either the invasive hybrid or T. usneoides. Under salt stress, T. usneoides exhibited a greater reduction only in chlorophyll content compared to the invasive hybrid. Increased soil salinity thus does not alter the host preference of D. carinulata, or the suitability of the Tamarix taxa as host plants. The invasive alien Tamarix taxa may be less susceptible to salt-induced stress than T. usneoides, which could be contributing to its invasiveness in South Africa.

Phytohormone signaling pathway for eliciting leaf phenolic synthesis in honeysuckle (Lonicera japonica Thunb.) under coastal saline environment

To date, it remains unclear how saline stress induces leaf phenolic synthesis in honeysuckle (Lonicera japonica Thunb.), a traditional Chinese medicinal crop. This study was to investigate hormone signaling for salt-induced leaf phenolic synthesis in honeysuckle from molecular, physiological and ecological levels by pot experiments and field trials. As a major ingredient of soil salinity in coastal land, NaCl was used in salt treatment for simulating coastal saline environment. NaCl stress significantly increased leaf abscisic acid (ABA) and salicylic acid (SA) concentrations, potentiated leaf phenolic synthesis by elevating phenylalanine ammonia-lyase (PAL) activity and PALs transcription, and enhanced leaf phenolic accumulation. Under NaCl stress, tungstate and paclobutrazol pretreatments inhibited leaf ABA and SA accumulation, respectively, and lowered PAL activity, PALs transcription, and phenolic accumulation. Thus, ABA and SA participated in transducing salt-induced leaf phenolic synthesis. Paclobutrazol pretreatment hardly influenced leaf ABA concentration in salt-treated plants, but tungstate pretreatment abated salt-induced leaf SA accumulation, indicating that ABA was an upstream signal of SA. Under NaCl stress, SA application restored leaf SA level with no effect on ABA level but incompletely restored PAL activity and phenolic accumulation in tungstate-pretreated plants, confirming the downstream role of SA and implying the existence of other downstream signals. Leaf ABA and SA concentrations were higher in plants in coastal saline plots than non-saline plots, and the roles of ABA and SA in mediating salt-induced leaf phenolic synthesis passed ecological test, according to a significant positive correlation of leaf ABA and SA levels with phenolic concentration. In conclusion, ABA acted as an upstream signal of SA to elicit leaf phenolic synthesis in honeysuckle under coastal saline environment.

Salt Tolerance of Hydrangea Plants Varied among Species and Cultivar within a Species

A greenhouse study was conducted to assess the relative salt tolerance of 11 cultivars of hydrangea: Hydrangea macrophylla ‘Ayesha’, ‘Emotion’, ‘Mathilda Gutges’, ‘Merritt’s Supreme’ and ‘Passion’; H. paniculata ‘Interhydia’ and ‘Bulk’; H. quercifolia ‘Snowflake’; H. serrata ‘Preciosa’; and H. serrata × macrophylla ‘Sabrina’ and ‘Selina’. Plants were treated with a nutrient solution at an electrical conductivity (EC) of 1.0 dS·m−1, and nutrient solution-based saline solutions at an EC of 5.0 dS·m−1 (EC 5) or 10 dS·m−1 (EC 10). The study was repeated in time (Experiments 1 and 2). In both experiments, by the fourth week after treatment, ‘Bulk’ plants in EC 10 exhibited severe salt damage with most of them dead. ‘Interhydia’ was also sensitive, showing severe salt damage in EC 10 with a high mortality rate by the end of the experiment. The leaf area and total shoot dry weight (DW) of all cultivars in EC 5 and EC 10 treatments were significantly reduced compared to the control. Leaf sodium (Na+) and chloride (Cl−) concentrations were negatively correlated with visual quality, leaf area and shoot DW. The salt-sensitive cultivars ‘Bulk’, ‘Interhydia’ and ‘Snowflake’ had inherently low leaf Na+ and Cl− concentrations in both control and salt-treated plants compared to other cultivars. Salt tolerance varied among species and cultivars within H. macrophylla. Among the 11 cultivars, H. macrophylla ‘Ayesha’ and two hybrids, ‘Sabrina’ and ‘Selina’, were relatively salt-tolerant. H. macrophylla ‘Merritt’s Supreme’ and ‘Mathilda’ were moderately tolerant. H. paniculata ‘Bulk’ was the most sensitive, followed by H. paniculata ‘Interhydia’, and then by H. serrata ‘Preciosa’ and H. macrophylla ‘Passion’, as evidenced by high mortality and severe salt damage symptoms. H. quercifolia ‘Snowflake’ and H. macrophylla ‘Emotion’ were moderately salt-sensitive.

Alleviative effects of Fara-darmani Consciousness Field on Triticum aestivum L. under salinity stress

Background: The Fara-darmani Consciousness Field was founded by Mohammad Ali Taheri. It is a novel field and is described similarly to the field of gravity, or the electromagnetic field. This field is neither matter nor energy, and therefore does not possess a quantity. Even though there is no direct scientific evidence for the Consciousness Field, it is possible to investigate its effects on objects through controlled experiments. The aim of the present work was to study the alleviative effects of the Fara-darmani Consciousness Field on common wheat Triticum aestivum L. var Star under salt stress. Methods: Plants were grown under 0 mM NaCl (control) and 150 mM NaCl with or without the influence of Fara-darmani Consciousness Field for 3 weeks. Chlorophyll, hydrogen peroxide (H2O2), malondialdehyde (MDA) content and activity of antioxidant enzymes such as superoxide dismutase (SOD),polyphenol oxidase (PPO), and peroxidase (POX) were measured in all groups of plants. Results: In the salt-treated plants under the influence of the Fara-darmani Consciousness Field, the contents of total chlorophyll, as well as a and b chlorophyll forms, were elevated compared with the salt-treated plants without Fara-darmani CF (34.8%, 17.8%, and 169% respectively). Additionally, Fara-darmani increased H2O2 (57%) and the activity of SOD and PPO by 220% and 168%, respectively, under salinity compared with the salt-treated plants without Fara-darmani CF. MDA content and activity of peroxidase were decreased by 12.5% and 34%, respectively. Conclusion: These results suggest the Fara-darmani Consciousness Field as a qualitative intervention strategy to withstand salt stress in plants, by increasing the contents of chlorophyll, antioxidant enzyme activities, and decreasing MDA content under salinity.

Enhanced thermotolerance of photosystem II by elevated pore-water salinity in the coastal marsh graminoid Sporobolus pumilus

In coastal marsh ecosystems, high salinities, anoxic waterlogged soils, and elevated summer temperatures often promote physiological strain that results in only a few tolerant halophytic species. Although not well understood, plant physiological responses to multiple stressors can be complex and may involve intensifying or offsetting reactions. In this study, we investigated physiological responses to combined salinity and high temperature in the coastal marsh graminoid Sporobolus pumilus (syn. Spartina patens). Specifically, we considered changes in plant-water relations and Photosystem II (PSII) behavior (involving chlorophyll [chl] a fluorescence) in heat-shocked plants that were acclimated to different salinities (0, 15, and 30 psu). Higher salinities fostered lower stomatal conductance (g), lower leaf-water potential (Ψleaf) and lower tissue-water content (θ), as well as decreased potential quantum yield (Fv/Fm) and decreased excitation energy capture efficiencies of open reaction centers (Fv’/Fm’). Heat-shocked plants acclimated to freshwater only had decreased Fv/Fm and PSII performance index (PIABS). Interestingly, there were no changes in chl a fluorescent outputs in heat-shocked plants acclimated to moderate salinities, and minimal changes in plants acclimated to high salinities. Approximately 25% of the heat-shocked S. pumilus in freshwater revealed a K-step in their polyphasic chl a fluorescent transients (OJIP procedure); K-steps were not observed in salt-treated plants. This suggests that, for plants residing in freshwater, heat-shock promoted disturbances in the PSII reaction centers and, in some cases, disrupted the oxygen-evolving complex. These PSII disruptions were either absent or less intense in salinity-treated plants, indicating that acclimation to environmental salts may provide PSII thermostability in S. pumilus.

Maternal environment alters dead pericarp biochemical properties of the desert annual plant Anastatica hierochuntica L.

The dead organs enclosing embryos (DOEEs) emerge as central components of the dispersal unit (DU) capable for long-term storage of active proteins and other substances that affect seed performance and fate. We studied the effect of maternal environment (salt and salt+heat) on progeny DU (dry indehiscent fruit) focusing on pericarp properties of Anastatica hierochuntica. Stressed plants displayed increased seed abortion and low level and rate of germination. Hydrated pericarps released antimicrobial factors and allelopathic substances that inhibit germination of heterologous species. Proteome analysis of dead pericarps revealed hundreds of proteins, among them nucleases, chitinases and proteins involved in reactive oxygen species detoxification and cell wall modification. Salt treatment altered the composition and level of proteins stored in the pericarp. We observed changes in protein profile released from seeds of salt-treated plants with a notable increase in a small anti-fungal protein, defensin. The levels of phytohormones including IAA, ABA and salicylic acid were reduced in dead pericarps of stressed plants. The data presented here highlighted the predominant effects of maternal environment on progeny DUs of the desert plant A. hierochuntica, particularly on pericarp properties, which in turn might affect seed performance and fate, soil fertility and consequently plant biodiversity.

The developmental and metabolic effects of different magnesium dozes in pepper plants under salt stress

Morphological and biochemical effects of different magnesium (Mg) doses on pepper plants under salt stress were investigated in this study. Experiments were conducted under controlled conditions of a climate cabin at 25 oC temperature, 70% relative humidity and 16/8 hours light/dark photoperiod. The developmental and metabolic effects of different magnesium doses in plants under salt stress were investigated by examining leaf antioxidant enzyme activities, Malondialdehyde (MDA) levels and chlorophyll contents. Seedlings of ‘Demre’ pepper cultivar (Capsicum annuum L. cv. ‘Demre’) were grown in Hoagland nutrient solution supplemented with 100 mM NaCl to generate salt stress. Besides salt treatments, different Mg doses (Mg 1 = 24.64 ppm, Mg 2 = 49.28 ppm, Mg 3 = 73.92 ppm, Mg 4 = 98.56 ppm, Mg 5 = 123.20 ppm) were applied to plants. On the 20th day of salt treatments, the total weight of the plants which is one of the growths and development parameters of pepper plants was measured, and plant samples were taken for analyses. A slight increase was observed in total weights of salt-treated plants with increasing Mg doses. The greatest plant weight was obtained from Mg 4 + salt treatments. It was observed that increasing Mg doses had positive effects on the development of plants under salt stress. Chlorophyll contents and antioxidant enzymes activities increased and MDA (malondialdehyde) levels, the product of lipid peroxidation, which indicates the amount of damage to plant cells, decreased with increasing Mg doses. Present measurements and analyses and resultant findings revealed that Mg treatments at increasing doses partially alleviated negative effects of salt stress on pepper seedlings.

EFFECTS OF SALT STRESS ON PLANT GROWTH AND BIOMASS ALLOCATION IN SOME WETLAND GRASS SPECIES IN THE MEKONG DELTA

Salt stress causes serious damage to many cellular and physiological processes that leads to yield reduction. The study induced salt stress using Hoagland solution added NaCl to evaluate its effects on plant growth and biomass allocation of some wetland grass species in order to identify salt-tolerant species for replacing and/or supplementing rice/grass in rice-shrimp model and salt-affected area in the Mekong Delta. The study also seeks to evaluate the response of leaf chlorophyll (SPAD unit) and proline content in salt-treated plants to varying application of salinity. Typha orientalis, Lepironia articulata, Eleocharis dulcis and Scirpus littoralis were studied in hydroponics condition with four levels of NaCl of 5, 10, 15, 20‰ and the control treatment (without adding NaCl). The experiment was arranged in a completely randomized design with 3 replications. The salt-treated plants showed visually clear responses of inhibited growth under salt stress condition compared to the control plants. Among the four studied species, T. orientalis produced the highest dry shoot biomass (15.5 g DW/plant), while E. dulcis had the lowest value (2.8 g DW/plant). However, only T. orientalis showed significantly decreased in biomass as salinity increased with 9.3 and 4.6 times lower of fresh and dry biomass in plants grown at the salinity level of 20‰ compared to those grown in the control treatment. The other three plant species did not affect by salinity levels. The results indicated that S. littoralis, L. articulata and E. dulcis could tolerate at high salinity of 20‰ (eq. to the EC value in the nutrient solution of 38.0 dS/m) and could be potential candidate to grow in the rice-shrimp model or in the salt-affected soils.

Na+ transporter HKT1;2 reduces flower Na+ content and considerably mitigates the decline in tomato fruit yields under saline conditions

Genes encoding HKT1-like Na+ transporters play a key role in the salinity tolerance mechanism in Arabidopsis and other plant species by retrieving Na+ from the xylem of different organs and tissues. In this study, we investigated the role of two HKT1;2 allelic variants in tomato salt tolerance in relation to vegetative growth and fruit yield in plants subjected to salt treatment in a commercial greenhouse under real production conditions. We used two near-isogenic lines (NILs), homozygous for either the Solanum lycopersicum (NIL17) or S. cheesmaniae (NIL14) allele, at HKT1;2 loci and their respective RNAi-Sl/ScHKT1;2 lines. The results obtained show that both ScHKT1;2- and SlHKT1;2-silenced lines display hypersensitivity to salinity associated with an altered leaf Na+/K+ ratio, thus confirming that HKT1;2 plays an important role in Na+ homeostasis and salinity tolerance in tomato. Both silenced lines also showed Na+ over-accumulation and a slight, but significant, reduction in K+ content in the flower tissues of salt-treated plants and consequently a higher Na+/K+ ratio as compared to the respective unsilenced lines. This altered Na+/K+ ratio in flower tissues is associated with a sharp reduction in fruit yield, measured as total fresh weight and number of fruits, in both silenced lines under salinity conditions. Our findings demonstrate that Na+ transporter HKT1;2 protects the flower against Na+ toxicity and mitigates the reduction in tomato fruit yield under salinity conditions.

Predicting Biomass and Yield in a Tomato Phenotyping Experiment Using UAV Imagery and Random Forest.

Biomass and yield are key variables for assessing the production and performance of agricultural systems. Modeling and predicting the biomass and yield of individual plants at the farm scale represents a major challenge in precision agriculture, particularly when salinity and other abiotic stresses may play a role. Here, we evaluate a diversity panel of the wild tomato species (Solanum pimpinellifolium) through both field and unmanned aerial vehicle (UAV)-based phenotyping of 600 control and 600 salt-treated plants. The study objective was to predict fresh shoot mass, tomato fruit numbers, and yield mass at harvest based on a range of variables derived from the UAV imagery. UAV-based red–green–blue (RGB) imageries collected 1, 2, 4, 6, 7, and 8 weeks before harvest were also used to determine if prediction accuracies varied between control and salt-treated plants. Multispectral UAV-based imagery was also collected 1 and 2 weeks prior to harvest to further explore predictive insights. In order to estimate the end of season biomass and yield, a random forest machine learning approach was implemented using UAV-imagery-derived predictors as input variables. Shape features derived from the UAV, such as plant area, border length, width, and length, were found to have the highest importance in the predictions, followed by vegetation indices and the entropy texture measure. The multispectral UAV imagery collected 2 weeks prior to harvest produced the highest explained variances for fresh shoot mass (87.95%), fruit numbers (63.88%), and yield mass per plant (66.51%). The RGB UAV imagery produced very similar results to those of the multispectral UAV dataset, with the explained variance reducing as a function of increasing time to harvest. The results showed that predicting the yield of salt-stressed plants produced higher accuracies when the models excluded control plants, whereas predicting the yield of control plants was not affected by the inclusion of salt-stressed plants within the models. This research demonstrates that it is possible to predict the average biomass and yield up to 8 weeks prior to harvest within 4.23% of field-based measurements and up to 4 weeks prior to harvest at the individual plant level. Results from this work may be useful in providing guidance for yield forecasting of healthy and salt-stressed tomato plants, which in turn may inform growing practices, logistical planning, and sales operations.

Salinity sensitivity and mycorrhizal responsiveness of polyphenolics in ‘Siam Queen’ basil grown in soilless substrate

The effects of salinity on basil (Ocimum basilicum L. ‘Siam Queen’) phenolic composition was evaluated by exposing plants to either no (Control), low, or moderate levels of salinity induced by NaCl or CaCl2in a soilless substrate. Plants in the control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis (Blaszk., Wubet, Renker, & Buscot) C. Walker & A. Schler. Salinity had no influence on fresh weight (FW) of non-inoculated plants at 41 d, but by 75 d plants treated with salt had lower FW than non-salinized controls. Salinity altered the polyphenolic profile of basil plants by reducing accumulation of several polyphenolics and increasing accumulation of two polyphenolics. In general, the effect of salinity on reducing phenolic accumulation was similar between the two salt types. Non-inoculated plants treated with salt had lower concentrations of caffeic acid (P5), chicoric acid (P7), caffeic acid derivative (P8), and rosmarinic acid (P11) than non-salinized controls at both harvests and lower concentrations of caffeic acid derivative (P1), caftaric acid derivative (P2), cinnamyl malic acid (P3), and feruloyl tartaric acid (P4) at 75 d. Salinity from both salts enhanced accumulation of quercetin-rutinoside (P9) in leaves and stems and CaCl2 also enhanced accumulation of cinnamic acid derivative (P10) in stems. Salinity had a greater influence on minor polyphenolics, particularly at 75 d, when these polyphenolics were more prevalent in non-salinized controls than in plants treated with salt. Inoculation with AMF had no influence on FW at 41 d, but by 75 d increased FW in non-salinized controls and salt-treated plants by ∼10 %. The influence of AMF on specific phenolic concentrations and phenolic profiles varied among harvest dates and salt treatments. In general, AMF inoculation had a greater influence on phenolic concentrations in non-salinized controls at 41 d than at 75 d and in salt-treated plants at 75 d than at 41 d. In salt-treated plants, AMF increased FW and accumulation of several polyphenolics, but did not completely mitigate the negative effects of salinity on FW or phenolic composition. Our results indicate that salinity can alter polyphenolic composition of ‘Siam Queen’ basil even when it has no influence on productivity (FW). While basil productivity may be more sensitive to NaCl than CaCl2 as plants age, the effects of these two salts on polyphenolics were similar. This highlights the importance of considering the effects of salinity and plant age on both crop productivity and quality.

Silicon Confers Soybean Resistance to Salinity Stress Through Regulation of Reactive Oxygen and Reactive Nitrogen Species.

Salt stress is one of the major abiotic stressors that causes huge losses to the agricultural industry worldwide. Different strategies have been adopted over time to mitigate the negative impact of salt stress on plants and reclaim salt-affected lands. In the current study, we used silicon (Si) as a tool for salinity alleviation in soybean and investigated the influence of exogenous Si application on the regulation of reactive oxygen and reactive nitrogen species and other salt stress–related parameters of the treated plants. Our results revealed that the canopy temperature was much higher in sole NaCl–treated plants but declined in Si + NaCl–treated plants. Furthermore, the chlorophyll contents decreased with sole NaCl treatment, whereas Si + NaCl–treated plants showed improved chlorophyll contents. In addition, Si application normalized the photosynthetic responses, such as transpiration rate (E) and net photosynthesis rate (PN) in salt-treated plants, and reduced the activity of ascorbate peroxidase and glutathione under salt stress. The expression levels of antioxidant-related genes GmCAT1, GmCAT2, and GmAPX1 started to decline at 12 h after addition of Si to NaCl-treated plants. Similarly, the S-nitrosothiol and nitric oxide (NO)–related genes were upregulated in the salt stress condition but reduced after Si supplementation. Si application downregulated genes associated with reactive oxygen species and reactive nitrogen species and reduced enzymatic and non-enzymatic antioxidants of the treated plants. Results of the current study conclude that Si mitigated the adverse effects of NaCl-induced stress by modulating the crosstalk between antioxidants and NO scavengers. It is suggested that Si may be used in agricultural systems for alleviating salt stress.

Early effects of salt stress on the physiological and oxidative status of the halophyte Lobularia maritima.

Soil salinity is an abiotic stress that reduces agricultural productivity. For decades, halophytes have been studied to elucidate the physiological and biochemical processes involved in alleviating cellular ionic imbalance and conferring salt tolerance. Recently, several interesting genes with proven influence on salt tolerance were isolated from the Mediterranean halophyte Lobularia maritima (L.) Desv. A better understanding of salt response in this species is needed to exploit its potential as a source of stress-related genes. We report the characterisation of L. maritima's response to increasing NaCl concentrations (100-400 mM) at the physiological, biochemical and molecular levels. L. maritima growth was unaffected by salinity up to 100 mM NaCl and it was able to survive at 400 mM NaCl without exhibiting visual symptoms of damage. Lobularia maritima showed a Na+ and K+ accumulation pattern typical of a salt-includer halophyte, with higher contents of Na+ in the leaves and K+ in the roots of salt-treated plants. The expression profiles of NHX1, SOS1, HKT1, KT1 and VHA-E1 in salt-treated plants matched this Na+ and K+ accumulation pattern, suggesting an important role for these transporters in the regulation of ion homeostasis in leaves and roots of L. maritima. A concomitant stimulation in phenolic biosynthesis and antioxidant enzyme activity was observed under moderate salinity, suggesting a potential link between the production of polyphenolic antioxidants and protection against salt stress in L. maritima. Our findings indicate that the halophyte L. maritima can rapidly develop physiological and antioxidant mechanisms to adapt to salt and manage oxidative stress.

Three-dimensional anatomy of mesophyll cells in rice leaf tissue by serial section light microscopy

ABSTRACT2D sections of rice (Oryza sativa L.) mesophyll cells are complex and the cell interior contains a large volume of chloroplasts. Furthermore, the structure of chloroplasts changes in response to salt stress. In this study, we used a 3D reconstruction method based on serial section light microscopy to analyze a wide range of structures in leaf tissues and compared the intracellular structure of mesophyll cells of rice under normal and salt-treated conditions. The 3D reconstructed models revealed that mesophyll cells appeared as ellipsoid discs with several lobes around the cell periphery, with the volumes showing no significant difference between control and salt-treated plants. The chloroplast structure in the whole mesophyll cell was altered under salt stress, showing a reduced coverage area, whereas their volumes did not differ between treatments. These findings suggest that 3D reconstruction based on serial light micrographs can reveal the morphology of cells and chloroplasts in plant tissue.