Salinity-Induced Variation in Biochemical Markers Provides Insight into the Mechanisms of Salt Tolerance in Common (Phaseolus vulgaris) and Runner (P. coccineus) Beans

The evaluation of biochemical markers is important for the understanding of the mechanisms of tolerance to salinity of Phaseolus beans. We have evaluated several growth parameters in young plants of three Phaseolus vulgaris cultivars subjected to four salinity levels (0, 50, 100, and 150 mM NaCl); one cultivar of P. coccineus, a closely related species reported as more salt tolerant than common bean, was included as external reference. Biochemical parameters evaluated in leaves of young plants included the concentrations of ions (Na⁺, K⁺, and Cl⁻), osmolytes (proline, glycine betaine, and total soluble sugars), and individual soluble carbohydrates. Considerable differences were found among cultivars, salinity levels, and in their interaction for most traits. In general, the linear component of the salinity factor for the growth parameters and biochemical markers was the most important. Large differences in the salinity response were found, with P. vulgaris cultivars “The Prince” and “Maxidor” being, respectively, the most susceptible and tolerant ones. Our results support that salt stress tolerance in beans is mostly based on restriction of Na⁺ (and, to a lesser extent, also of Cl⁻) transport to shoots, and on the accumulation of myo-inositol for osmotic adjustment. These responses to stress during vegetative growth appear to be more efficient in the tolerant P. vulgaris cultivar “Maxidor”. Proline accumulation is a reliable marker of the level of salt stress affecting Phaseolus plants, but does not seem to be directly related to stress tolerance mechanisms. These results provide useful information on the responses to salinity of Phaseolus.     

HKT1;1 and HKT1;2 Na+ Transporters from Solanum galapagense Play Different Roles in the Plant Na+ Distribution under Salinity

Salt tolerance is a target trait in plant science and tomato breeding programs. Wild tomato accessions have been often explored for this purpose. Since shoot Na⁺/K⁺ is a key component of salt tolerance, RNAi-mediated knockdown isogenic lines obtained for Solanum galapagense alleles encoding both class I Na⁺ transporters HKT1;1 and HKT1;2 were used to investigate the silencing effects on the Na and K contents of the xylem sap, and source and sink organs of the scion, and their contribution to salt tolerance in all 16 rootstock/scion combinations of non-silenced and silenced lines, under two salinity treatments. The results show that SgHKT1;1 is operating differently from SgHKT1;2 regarding Na circulation in the tomato vascular system under salinity. A model was built to show that using silenced SgHKT1;1 line as rootstock would improve salt tolerance and fruit quality of varieties carrying the wild type SgHKT1;2 allele. Moreover, this increasing effect on both yield and fruit soluble solids content of silencing SgHKT1;1 could explain that a low expressing HKT1;1 variant was fixed in S. lycopersicum during domestication, and the paradox of increasing agronomic salt tolerance through silencing the HKT1;1 allele from S. galapagense, a salt adapted species.     

Effects of N fertilizer application timing on common bean production

There is usually a positive yield response when N is applied to common bean plants grown on N-poor soils. Recommendations include application of some or all of the N at planting, but growth and yield responses to later applications are not well documented. From 50 to 60kg N ha^–1 was applied at different growth stages to three bean lines during three years. All N treatments increased yield compared to the unfertilized control. Nitrogen applied during the vegetative stage produced higher seed yields than N applied at planting, flowering, during podfill or a split application. N applied at planting or during vegetative growth increased pod-set, while application at the vegetative and reproductive stages increased seed weight. Even though N application during the vegetative stage showed a negative effect on nodulation, there was a large shoot growth response. The lower yield from N applied at planting may have been caused by less shoot growth response as well as inhibited nodulation. Based on these results the best management system using N fertilizer was an application during vegetative growth. Further studies are needed to identify bean lines capable of high N₂ fixation in the presence of N and to determine optimum amounts and timing of N application to maximize biological and economic yields.     

Contribution of Exogenous Proline to Abiotic Stresses Tolerance in Plants: A Review

Abiotic stresses are the major environmental factors that play a significant role in decreasing plant yield and production potential by influencing physiological, biochemical, and molecular processes. Abiotic stresses and global population growth have prompted scientists to use beneficial strategies to ensure food security. The use of organic compounds to improve tolerance to abiotic stresses has been considered for many years. For example, the application of potential external osmotic protective compounds such as proline is one of the approaches to counteract the adverse effects of abiotic stresses on plants. Proline level increases in plants in response to environmental stress. Proline accumulation is not just a signal of tension. Rather, according to research discussed in this article, this biomolecule improves plant resistance to abiotic stress by rising photosynthesis, enzymatic and non-enzymatic antioxidant activity, regulating osmolyte concentration, and sodium and potassium homeostasis. In this review, we discuss the biosynthesis, sensing, signaling, and transport of proline and its role in the development of various plant tissues, including seeds, floral components, and vegetative tissues. Further, the impacts of exogenous proline utilization under various non-living stresses such as drought, salinity, high and low temperatures, and heavy metals have been extensively studied. Numerous various studies have shown that exogenous proline can improve plant growth, yield, and stress tolerance under adverse environmental factors.     

Foliar Application of Cerium Oxide-Salicylic Acid Nanoparticles (CeO2:SA Nanoparticles) Influences the Growth and Physiological Responses of Portulaca oleracea L. under Salinity

In the present study, the effects of foliar application of salicylic acid (100 μM), cerium oxide (50 mg L⁻¹), and cerium oxide:salicylic acid nanoparticles (CeO₂: SA-nanoparticles, 50 mg L⁻¹ + 100 μM) on the growth and physiological responses of purslane (Portulaca oleracea L.) were examined in non-saline and saline conditions (50 and 100 mM NaCl salinity). Foliar applications mitigated salinity-induced adverse effects, and the highest plant height and N, P, Mg, and Mn content were recorded in the variant with non-saline × foliar use of CeO₂: SA-nanoparticles. The highest values of fresh and dry weight were noted in the treatment with no-salinity × foliar use of CeO₂:SA-nanoparticles. The highest number of sub-branches was observed in the foliar treatments with CeO₂-nanoparticles and CeO₂:SA-nanoparticles without salinity stress, while the lowest number was noted in the 100 mM NaCl treatment. Moreover, the foliar application of CeO₂:SA-nanoparticles and cerium-oxide nanoparticles improved the total soluble solid content, K, Fe, Zn, Ca, chlorophyll a, and oil yield in the plants. The salinity of 0 and 50 mM increased the K content, 1000-seed weight, total soluble solid content, and chlorophyll b content. The use of 100 mM NaCl with no-foliar spray increased the malondialdehyde, Na, and H₂O₂ content and the Na⁺/K⁺ ratio. No-salinity and 50 mM NaCl × CeO₂: SA-nanoparticle interactions improved the anthocyanin content in plants. The phenolic content was influenced by NaCl₁₀₀ and the foliar use of CeO₂:SA-nanoparticles. The study revealed that the foliar treatment with CeO₂:SA-nanoparticles alleviated the side effects of salinity by improving the physiological responses and growth-related traits of purslane plants.     

Evaluation Releasing Efficiency of Selected Micronutrients from Natural Polymer Complex in Laboratory and Field Conditions

This work is a part of long program for producing natural polymers which is used for application in different purposes in agriculture fields. A part of this program was the preparation of various compositions of Gum Arabic (GA) and Poly vinyl alcohol (PVA) with studying its physical and chemical characters. Whereas, the present work was concerning with the evaluation of released amount of selected micronutrients from the same complex under laboratory and field conditions.

In the laboratory, the prepared complex containing copper (Cu) or manganese (Mn) separately, were tested at different pH values for releasing at intervals.

The obtained results showed the possibility of using the Mn⁺² complex at 3000 mg kg^?1. Moreover, the obtained results showed that the maximum released amount was obtained at pH 7.0. A field experiment was planed according to the resulted data obtained in laboratory.

Samples were taken for elemental analysis either from soil or plants during all growth stages likeas vegetative, flowering, bear pods, full pods and harvesting. This analysis involved some selected macro- and micro nutrients such as N, P, K, Fe and Mn either in soil or plants (straw and seed). These results proved that efficiency of Mn-complex can release 1.0 and 34.0% to soil, and plants from used complex, respectively. Some increase in most of other elements compared with untreated plants was also obtained. The presence of the absorbed Mn⁺² from this complex activate the growth of plants and consequently increased the yield of seed than untreated samples. There is a linear relationship between the amount of absorbed Mn⁺² and the growth stages of the plants. This linear relationship has significant correlation coefficient (R ² = 0.5) of Mn⁺² uptake by straw or seed plants after end of stages.     

Differential Activity of Plasma and Vacuolar Membrane Transporters Contributes to Genotypic Differences in Salinity Tolerance in a Halophyte Species,Chenopodium quinoa

Halophytes species can be used as a highly convenient model system to reveal key ionic and molecular mechanisms that confer salinity tolerance in plants. Earlier, we reported that quinoa (Chenopodium quinoa Willd.), a facultative C3 halophyte species, can efficiently control the activity of slow (SV) and fast (FV) tonoplast channels to match specific growth conditions by ensuring that most of accumulated Na⁺ is safely locked in the vacuole (Bonales-Alatorre et al. (2013) Plant Physiology). This work extends these finding by comparing the properties of tonoplast FV and SV channels in two quinoa genotypes contrasting in their salinity tolerance. The work is complemented by studies of the kinetics of net ion fluxes across the plasma membrane of quinoa leaf mesophyll tissue. Our results suggest that multiple mechanisms contribute towards genotypic differences in salinity tolerance in quinoa. These include: (i) a higher rate of Na⁺ exclusion from leaf mesophyll; (ii) maintenance of low cytosolic Na⁺ levels; (iii) better K⁺ retention in the leaf mesophyll; (iv) a high rate of H⁺ pumping, which increases the ability of mesophyll cells to restore their membrane potential; and (v) the ability to reduce the activity of SV and FV channels under saline conditions. These mechanisms appear to be highly orchestrated, thus enabling the remarkable overall salinity tolerance of quinoa species.     

Salinity Stress Alters the Secondary Metabolic Profile of M. sativa,M. arborea and Their Hybrid (Alborea)

Increased soil salinity, and therefore accumulation of ions, is one of the major abiotic stresses of cultivated plants that negatively affect their growth and yield. Among Medicago species, only Medicago truncatula, which is a model plant, has been extensively studied, while research regarding salinity responses of two important forage legumes of Medicago sativa (M. sativa) and Medicago arborea (M. arborea) has been limited. In the present work, differences between M. arborea, M. sativa and their hybrid Alborea were studied regarding growth parameters and metabolomic responses. The entries were subjected to three different treatments: (1) no NaCl application (control plants), (2) continuous application of 100 mM NaCl (acute stress) and (3) gradual application of NaCl at concentrations of 50-75-150 mM by increasing NaCl concentration every 10 days. According to the results, M. arborea maintained steady growth in all three treatments and appeared to be more resistant to salinity. Furthermore, results clearly demonstrated that M. arborea presented a different metabolic profile from that of M. sativa and their hybrid. In general, it was found that under acute and gradual stress, M. sativa overexpressed saponins in the shoots while M. arborea overexpressed saponins in the roots, which is the part of the plant where most of the saponins are produced and overexpressed. Alborea did not perform well, as more metabolites were downregulated than upregulated when subjected to salinity stress. Finally, saponins and hydroxycinnamic acids were key players of increased salinity tolerance.     

An ABA Functional Analogue B2 Enhanced Salt Tolerance by Inducing the Root Elongation and Reducing Peroxidation Damage in Maize Seedlings

Salt stress negatively affects maize growth and yield. Application of plant growth regulator is an effective way to improve crop salt tolerance, therefore reducing yield loss by salt stress. Here, we used a novel plant growth regulator B2, which is a functional analogue of ABA. With the aim to determine whether B2 alleviates salt stress on maize, we studied its function under hydroponic conditions. When the second leaf was fully developed, it was pretreated with 100 µM ABA, 0.01 µM B2, 0.1 µM B2, and 1 µM B2, independently. After 5 days treatment, NaCl was added into the nutrient solution for salt stress. Our results showed that B2 could enhance salt tolerance in maize, especially when the concentration was 1.0 µMol·L⁻¹. Exogenous application of B2 significantly enhanced root growth, and the root/shoot ratio increased by 7.6% after 6 days treatment under salt stress. Compared with control, the ABA level also decreased by 31% after 6 days, which might have resulted in the root development. What is more, B2 maintained higher photosynthetic capacity in maize leaves under salt stress conditions and increased the activity of antioxidant enzymes and decreased the generation rate of reactive oxygen species by 16.48%. On the other hand, B2 can enhance its water absorption ability by increasing the expression of aquaporin genes ZmPIP1-1 and ZmPIP1-5. In conclusion, the novel plant growth regulator B2 can effectively improve the salt tolerance in maize.     

Profiles of Cytokinins Metabolic Genes and Endogenous Cytokinins Dynamics during Shoot Multiplication In Vitro of Phalaenopsis

Shoot multiplication induced by exogenous cytokinins (CKs) has been commonly used in Phalaenopsis micropropagation for commercial production. Despite this, mechanisms of CKs action on shoot multiplication remain unclear in Phalaenopsis. In this study, we first identified key CKs metabolic genes, including six isopentenyltransferase (PaIPTs), six cytokinin riboside 5′ monophosphate phosphoribohydrolase (PaLOGs), and six cytokinin dehydrogenase (PaCKXs), from the Phalaenopsis genome. Then, we investigated expression profiles of these CKs metabolic genes and endogenous CKs dynamics in shoot proliferation by thidiazuron (TDZ) treatments (an artificial plant growth regulator with strong cytokinin-like activity). Our data showed that these CKs metabolic genes have organ-specific expression patterns. The shoot proliferation in vitro was effectively promoted with increased TDZ concentrations. Following TDZ treatments, the highly expressed CKs metabolic genes in micropropagated shoots were PaIPT1, PaLOG2, and PaCKX4. By 30 days of culture, TDZ treatments significantly induced CK-ribosides levels in micropropagated shoots, such as tZR and iPR (2000-fold and 200-fold, respectively) as compared to the controls, whereas cZR showed only a 10-fold increase. Overexpression of PaIPT1 and PaLOG2 by agroinfiltration assays resulted in increased CK-ribosides levels in tobacco leaves, while overexpression of PaCKX4 resulted in decreased CK-ribosides levels. These findings suggest de novo biosynthesis of CKs induced by TDZ, primarily in elevation of tZR and iPR levels. Our results provide a better understanding of CKs metabolism in Phalaenopsis micropropagation.     

Mechanistic Insights into Potassium-Conferred Drought Stress Tolerance in Cultivated and Tibetan Wild Barley: Differential Osmoregulation,Nutrient Retention,Secondary Metabolism and Antioxidative Defense Capacity

Keeping the significance of potassium (K) nutrition in focus, this study explores the genotypic responses of two wild Tibetan barley genotypes (drought tolerant XZ5 and drought sensitive XZ54) and one drought tolerant barley cv. Tadmor, under the exposure of polyethylene glycol-induced drought stress. The results revealed that drought and K deprivation attenuated overall plant growth in all the tested genotypes; however, XZ5 was least affected due to its ability to retain K in its tissues which could be attributed to the smallest reductions of photosynthetic parameters, relative chlorophyll contents and the lowest Na⁺/K⁺ ratios in all treatments. Our results also indicate that higher H⁺/K⁺-ATPase activity (enhancement of 1.6 and 1.3-fold for shoot; 1.4 and 2.5-fold for root), higher shoot K⁺ (2 and 2.3-fold) and Ca²⁺ content (1.5 and 1.7-fold), better maintenance of turgor pressure by osmolyte accumulation and enhanced antioxidative performance to scavenge ROS, ultimately suppress lipid peroxidation (in shoots: 4% and 35%; in roots 4% and 20% less) and bestow higher tolerance to XZ5 against drought stress in comparison with Tadmor and XZ54, respectively. Conclusively, this study adds further evidence to support the concept that Tibetan wild barley genotypes that utilize K efficiently could serve as a valuable genetic resource for the provision of genes for improved K metabolism in addition to those for combating drought stress, thereby enabling the development of elite barley lines better tolerant of abiotic stresses.