Analía Llanes

A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation

A new PGPR (plant growth promoting rhizobacteria) strain was isolated from soybean seeds and the bacterial mechanisms related to plant growth promotion were evaluated and characterized. Isolates were genotypically compared and identified by amplification of partial sequences of 16S DNAr as Bacillus amyloliquefaciens strain LL2012. Isolates were grown until exponential growth phase to evaluate the atmospheric nitrogen fixation, enzymatic activities, phosphate solubilization, siderophores and phytohormones production. LL2012 strain was able to grow and to produce high levels of auxin, gibberellins and salicylic acid in chemically defined medium. Co-inoculation of soybean plants with LL2012 strain and the natural symbiont (Bradyrhizobium japonicum) altered plant growth parameters and significantly improved nodulation. Our results show that the association of LL2012 with B. japonicum, enhanced the capacity of the latter to colonize plant roots and increase the number of nodules, which make the co-inoculation technique attractive for use in commercial inoculant formulations following proper field evaluation.

Drought and salinity alter endogenous hormonal profiles at the seed germination phase

The most critical phase in plant life is seed germination, which is influenced by environmental factors. Drought and salinity are key environmental factors that affect seed germination. Reduction or alterations of germination when seeds are exposed to these factors have been shown to be due to either the adverse effects of water limitation and/or specific ion toxicity on metabolism. Phytohormones are chemical messengers produced within the plant that control its growth and development in response to environmental cues; small fluctuations of phytohormone levels alter the cellular dynamics and, hence, play a central role in regulating plant growth responses to these environmental factors. To integrate current knowledge, the present review focuses on the involvement of endogenous phytohormones in plant adaptative responses to drought and salinity at one of the plants developmental phases.

Differential effects of sodium salts on the germination of a native halophytic species from South America: Prosopis strombulifera (Lam.) Benth

Prosopis strombulifera is a halophytic shrub frequently found in the salinized areas of central Argentina. Interactions between temperature, ionic and osmotic components of salinity, and seed germination in this species are discussed in this chapter. Besides the osmotic effect, specific ion effects of salts play an important role in seed germination causing toxicity to the embryo. In saline soils where P. strombulifera is frequent, NaCl and Na2SO4 proportions are similar. Germination experiments with both salts, their iso-osmotic anionic and cationic mixtures and polyethylene glycol (PEG) were performed at 30°C and 35°C; the germination percentages registered with PEG were lower than those obtained with iso-osmotic Na-based monosaline solutions at osmotic potential (Ψo) of -1.2 MPa and lower, but greater than those in the salt mixtures, indicating that seeds were mainly affected by an osmotic effect rather than by ionic toxicity at 35°C. The salt mixture accentuated ion toxicity showing that germination is inhibited by a combination of osmotic and ionic effects, the latter having greater influence at very high salt concentrations. The excess of Cl- or SO4 2- anions in both cationic mixtures produced equal magnitude of toxicity on the seeds. Although a deleterious effect of potassium was also observed, the anionic effects were evidently much more marked. From Ψo of -1.2 MPa and lower, germination inhibition increased when salt concentration increased as the ionic effects were additive to osmotic effects. The germination percentages obtained with monosaline solutions at 35°C were superior to those obtained at 30°C, indicating that temperature played an important role in the germination response of this species by diminishing the osmotic effect of salt only in the case of monosaline solutions; however, the toxic effect of ions was accentuated when they were combined. Nevertheless, a partial reversion of sulfate toxicity was observed when seeds were placed in anionic salt mixtures at 30°C, demonstrating the differential effects of temperature on the osmotic and ionic components of salinity.

The American Halophyte Prosopis strombulifera, a New Potential Source to Confer Salt Tolerance to Crops

Salinity imposes a major environmental threat to agriculture and its adverse impact has become the most serious problem in vast regions of the earth surface. The combination of population growth and land degradation are of such significance that plant salt tolerance improvement has become an urgent need for the future of agriculture. Generation of salt tolerant crops requires a clear understanding of the complex mechanism of abiotic stress resistance in key species. Evolutionary processes under saline conditions gave rise to halophytes which have evolved adaptive traits to cope with the salinity of the environment. They include some specific biochemical, physiological and molecular mechanisms, on one hand, and a capability of natural association with different microorganisms called Plant Stress-Homeo-regulating Rhizobacteria (PSHR), on the other. However, a complete understanding of these processes is still lacking despite the intensive research conducted during the last decade. The genus Prosopis includes many important arboreal and shrub-like species that are present in saline zones of the Americas and some of them are considered to be unique terrestrial species due to their combined ability to fix nitrogen and grow under high-salinity conditions. The shrub Prosopis strombulifera (Lam) Benth. is distributed from the Arizona desert (U.S.A.) to Patagonia (Argentina) and is especially abundant in the salinized areas of central Argentina. This species showed a halophytic response to NaCl surviving up to 1 M NaCl in in-vitro experiments, but in contrast, a strong growth inhibition at lower Na2SO4 concentrations. These differential responses to the most abundant salts present in most salinized soils make this species an excellent model to study salt-tolerance mechanisms in halophytic plants. This chapter provides an overview of different salt tolerance mechanisms in the native halophyte Prosopis strombulifera, which may be considered a new useful source to improve crop salt tolerance through two biotechnological strategies: considering P. strombulifera as a natural gene donor to improve the genetic salt tolerance of low tolerant crops, and considering this species and its rhizosphere as natural sources of PSHR microorganisms capable of physiologically improving salt tolerance in crops.

Metabolomic Approach to Understand Plant Adaptations to Water and Salt Stress

Abstract Plants are sessile organisms unable to escape from regularly changing environmental conditions that affect their growth and development; thus their survival depends upon adaptive responses. These adaptive features have been observed in plants exposed to abiotic stress, including morphophysiological, biochemical, and molecular. Moreover, the regulation of metabolic pathways activated by stresses can be characterized through the profile of metabolites involved in them. Therefore several compounds or metabolites with extraordinarily large chemical complexity play different functions in intricate metabolic networks. Consequently, the complex molecular regulatory system involved in plant response to abiotic stress can be understood through high-throughput “omic” techniques, such as metabolomics. At present, metabolomics is a new tool for increasing our knowledge about specific metabolites playing crucial roles in plant responses to environmental stresses, particularly salinity and drought. In fact, several researchers have reported that plants exposed to salinity or water stress show alterations in certain metabolites, such as primary metabolites (osmolytes, osmoprotectants) and secondary metabolites (defense metabolites). However, not all plant species synthesize all kinds of metabolites; some species accumulate very low quantities of some of these metabolites, whereas some others do not do so at all. Indeed, the flux through a metabolic pathway rather than the accumulation of a specific metabolite per se might contribute to stress tolerance. In addition, alterations in secondary metabolites cannot be inferred only from variations in their primary metabolite precursors but is usually a result of a complex regulatory process. In this chapter, we review the recent progress in the field of metabolomics, including the analytical technologies, highlighting changes in specific metabolites induced by salt and water stress and discussing the meaning of specific and nonspecific responses to these stresses. This approach could lead to new insights into understanding plant water and salt stress adaptations for future application in biotechnology.

What is known about phytohormones in halophytes? A review

Phytohormones participate in many aspects of the plant life cycle, including responses to biotic and abiotic stresses. They play a key role in plant responses to the environment with direct bearing on a plant’s fitness for adaptation and reproduction. In recent years, there have been major advances in our understanding of the role of phytohormones in halophytic plants. The variability in maximal salinity level that halophytes can tolerate makes it difficult to characterize the specific traits responsible for salt tolerance. However, the most evident effect of salinity is growth disturbance, and growth is directly governed by phytohormones. Phytohormones such as abscisic acid, salicylic acid ethylene and jasmonates are traditionally related to stress responses, while the involvement of cytokinins, gibberellins and auxins has started to be analyzed. Polyamines, although they can’t be considered phytohormones because of the high concentrations required for cell responses, have been proposed as a new category of plant growth regulators involved in several plant processes and stress responses. This review integrates the advances in the knowledge about phytohormones in halophytes and their participation in salt tolerance.

Morphophysiology and Biochemistry of Prosopis strombulifera Under Salinity. Are Halophytes Tolerant to All Salts

Prosopis genus is an important member of semiarid, arid and saline environments around the world. This genus includes shrubs and trees that exhibit a high economic and ecological potential in different American regions. These plants are considered to be unique terrestrial species due to their combined ability to fix nitrogen and grow under high-salinity conditions. The South American halophyte, Prosopis strombulifera (Lam) Benth, is distributed from the Arizona desert (U.S.A.) to Patagonia (Argentina) and is especially abundant in the salinized areas of central Argentina. The soil of these areas is characterized by similar proportions of NaCl and Na2SO4. P. strombulifera species showed a halophytic response to NaCl surviving up to 1 M NaCl in in-vitro experiments, but in contrast, a strong growth inhibition at lower Na2SO4 concentrations was observed. These differential responses to the most abundant salts present in salinized soils of Argentina make this species an excellent model to study salt-tolerance mechanisms in halophytic plants. This chapter provides an overview of different salt tolerance mechanisms in the American halophyte Prosopis strombulifera, especially phytohormone pattern, oxidative responses and production of biomolecules. This halophyte may be considered as a new useful genetic source to improve crop salt tolerance and a promising plant as source of natural products for pharmaceutical industry.