The causes for barley root growth retardation in the presence of ammonium and glutamate

In barley (Hordeum vulgare L.) seedlings, the rate of root growth, osmotic pressure (Π), hydraulic conductance (L _p), and longitudinal (δl) and transverse (δD/D) extensibility of root cells were measured. The seedlings were grown on Knop solution with nitrate or without nitrate with addition of 5–10 mM NH₄⁺ or 0.5–1.0 mM glutamate. Root growth retardation on the 1st–4th days of exposure to NH₄⁺ was determined by a decrease in δl in the zone of elongation, whereas root thickening was evidently related to an increase in Π. Biphasic dynamics of δl in the presence of NH₄⁺ was imitated by medium acidification near the root surface to pH 3.7, which confirms a conclusion, we have done earlier, about a non-monotonous pH-dependence of longitudinal extensibility. Root growth retardation during the first day of exposure to Glu was also determined by a decrease in the δl, which was, however, accompanied by an increase in the δD/D and L _p. Fast Glu-induced changes of measured root parameters were imitated by root exposure to oryzalin, ionomycin, and inhibitors of the H⁺-pump. It was supposed that a decrease in δl in the presence of NH₄⁺ and Glu was related to cortical microtubule disorganization with the involvement of cytosolic calcium Ca_cyt²⁺. A decrease in the δD/D and L _p in the presence of NH₄⁺ was related to apoplast acidification and a high activity of the plasmalemmal H⁺-pump. An increase in the δD/D and L _p in the presence of Glu indicates the inhibition of the plasmalemmal H⁺-pump. On the 2nd–4th days of exposure to Glu, root growth ceased, as distinct from treatment with NH₄⁺. This complete root growth inhibition by Glu was possibly related to a rapid uptake of Ca²⁺ through Glu-sensitive Ca²⁺-channels, Ca²⁺-dependent inhibition of the plasmalemmal H⁺-pump, and a decrease in mitotic activity.     

Biochemical mechanism of ulcer development under stressful conditions

Using the model of acute immobilizing stress in rats it has been established that the content of N-acetylneuraminic acid, hexoses connected with protein, acid glycosaminoglycanes and fucouse in a structure of gastric mucus increases alongside with growth of proteolytic enzymes activity in it. The received results justify an important role of noncollagenic proteins and proteolytic enzymes in provision of resistancy of stomach mucous membrane and mechanisms of stressory ulcers development.     

Plx1 is required for chromosomal DNA replication under stressful conditions

Polo-like kinase (Plk)1 is required for mitosis progression. However, although Plk1 is expressed throughout the cell cycle, its function during S-phase is unknown. Using Xenopus laevis egg extracts, we demonstrate that Plx1, the Xenopus orthologue of Plk1, is required for DNA replication in the presence of stalled replication forks induced by aphidicolin, etoposide or reduced levels of DNA-bound Mcm complexes. Plx1 binds to chromatin and suppresses the ATM/ATR-dependent intra-S-phase checkpoint that inhibits origin firing. This allows Cdc45 loading and derepression of DNA replication initiation. Checkpoint activation increases Plx1 binding to the Mcm complex through its Polo box domain. Plx1 recruitment to chromatin is independent of checkpoint mediators Tipin and Claspin. Instead, ATR-dependent phosphorylation of serine 92 of Mcm2 is required for the recruitment of Plx1 to chromatin and for the recovery of DNA replication under stress. Depletion of Plx1 leads to accumulation of chromosomal breakage that is prevented by the addition of recombinant Plx1. These data suggest that Plx1 promotes genome stability by regulating DNA replication under stressful conditions.     

Enhanced survival of pluripotent stem cells under stressful conditions

Comment on: Ardehali R, et al. Proc Natl Acad Sci USA. 2011; 108:3282-7.     

Expression of epidermal growth factor in transgenic mice causes growth retardation

The epidermal growth factor (EGF) family of peptides signals through the erbB family of receptor tyrosine kinases and plays important roles in development and tumorigenesis. Both EGF and transforming growth factor (TGF)-alpha only bind to erbB1 and activate it. The precursor of EGF is distinct from that of TGF-alpha in having eight additional EGF-like repeats. We have recently shown that the EGF precursor without these repeats is biologically active and leads to hypospermatogenesis in transgenic mice. Here we present evidence that the growth of transgenic mice widely expressing this engineered EGF precursor is also stunted. These mice were consistently born at half the normal weight and reached almost 80% of normal weight at adulthood. The mechanism involved a reduction of serum insulin-like growth factor-binding protein-3. Chondrocyte development in the growth plate was affected, and osteoblasts accumulated in the endosteum and periosteum. Besides these novel findings on the in vivo effects of EGF on bone development, we observed no sign of tumor formation in our transgenic animals. In contrast to previous reports on TGF-alpha transgenic mice, we show that the biological functions of EGF and TGF-alpha are clearly distinct.     

Effect of soil strength on root growth under different water conditions

The objective of this study was to determine the effects of soil water and soil strength on root growth in situations where the individual effects of both of these factors were important. Three grain legumes were grown from pre-germinated seeds for five days on 50-mm compacted columns of two major soils of Sri Lanka. Four or five levels of bulk density (1.1 to 1.8 Mg.m^–3) and five or six levels of matric potential (–0.02 to–2.0 MPa) were used.Soil strength and matric potential effects on root growth were independently significant for most crop and soil combinations. Under high (wet) matric potential (>–0.77 MPa) soil conditions, the effect of soil water on root growth was evident only in its effect on soil strength. Bulk density had a significant effect on root growth independent of soil strength and matric potential in three cases.For all crops and soils, root penetration was 80% of the maximum or greater when the average soil strength (soil water not limiting) was 0.75 MPa or less, and when the average matric potential (soil strength not limiting) was –0.77 MPa or greater (wetter). Root penetration was 20% of the maximum or less when the soil strength was greater than 3.30 MPa (soil water not limiting), and when matric potential (soil strength not limiting) was less than –3.57 MPa. The use of pre-germinated seeds, which contained imbibed water, combined with a lack of water loss from the closed chambers containing the plants is the probable cause for the very low (–3.57 MPa) matric potential that allowed root growth at 20% of the maximum.     

Wheat root growth and seasonal water use as affected by irrigation under shallow water table conditions

Summary Irrigation experiments with wheat (Triticum aestivum L.) in clay loam, silty clay loam and the silty clay loam. Contrary to this, irrigation at late jointing, and late jointing and milk stages produced deepest root system in the loam. Roots followed the receding water table. was greatest in the loam. Avoiding irrigation at late jointing stage caused shifting of the zone of peak root density downwards and concentration of roots near water table both in the clay loam and the silty clay loam. Contrary to this, irrigation at late jointing, and late jointing and milk stages produced deepest root system in the loam. Roots followed the receding water table. Seasonal evapotranspiration (E) was affected by number of irrigations and water table depths. Water table contribution ranged from 61.6–64.5% of the total E in clay loam, from 39.0–46.8% of the total E in silty clay loam and from 4.0–8.1% of the total E in loam. Irrigations after late jointing contributed largely to the drainage. Yield was significantly higher in the treatments with scheduled irrigations at crown root initiation and late jointing stages in the clay loam and silty clay loam and at crown root initiation, late jointing and milk stages in the loam. This research has been financed in part by a grant made by USDA, ARS, authorized by Public Law-480     

Development of isoform selective PI3-kinase inhibitors as pharmacological tools for elucidating the PI3K pathway

Using a parallel synthesis approach to target a non-conserved region of the PI3K catalytic domain a pan-PI3K inhibitor 1 was elaborated to provide alpha, delta and gamma isoform selective Class I PI3K inhibitors 21, 24, 26 and 27. The compounds had good cellular activity and were selective against protein kinases and other members of the PI3K superfamily including mTOR and DNA-PK.     

A root hairless barley mutant for elucidating genetic of root hairs and phosphorus uptake

This paper reports a new barley mutant missing root hairs. The mutant was spontaneously discovered among the population of wild type (Pallas, a spring barley cultivar), producing normal, 0.8 mm long root hairs. We have called the mutant bald root barley (brb). Root anatomical studies confirmed the lack of root hairs on mutant roots. Amplified Fragment Length Polymorphism (AFLP) analyses of the genomes of the mutant and Pallas supported that the brb mutant has its genetic background in Pallas. The segregation ratio of selfed F₂ plants, resulting from mutant and Pallas outcross, was 1:3 (–root hairs:+root hairs), suggesting a monogenic recessive mode of inheritance.In rhizosphere studies, Pallas absorbed nearly two times more phosphorus (P) than the mutant. Most of available inorganic P in the root hair zone (0.8 mm) of Pallas was depleted, as indicated by the uniform P depletion profile near its roots. The acid phosphatase (Apase) activity near the roots of Pallas was higher and Pallas mobilised more organic P in the rhizosphere than the mutant. The higher Apase activity near Pallas roots also suggests a link between root hair formation and rhizosphere Apase activity. Hence, root hairs are important for increasing plant P uptake of inorganic as well as mobilisation of organic P in soils.Laboratory, pot and field studies showed that barley cultivars with longer root hairs (1.10 mm), extracted more P from rhizosphere soil, absorbed more P in low-P field (Olsen P=14 mg P kg^–1 soil), and produced more shoot biomass than shorter root hair cultivars (0.63 mm). Especially in low-P soil, the differences in root hair length and P uptake among the cultivars were significantly larger. Based on the results, the perspectives of genetic analysis of root hairs and their importance in P uptake and field performance of cereals are discussed.     

Insulin-like growth factor-binding protein-1: an evolutionarily conserved fine tuner of insulin-like growth factor action under catabolic and stressful conditions

The insulin-like growth factor-binding proteins (IGFBPs) are evolutionarily conserved components of the insulin-like growth factor (IGF) system. The six forms of IGFBPs (IGFBP-1–6) bind the IGF ligands (IGF-1 and -2) with high affinity and regulate the IGFs available to their receptors, therefore providing additional flexibilities in regulating IGF signalling. IGFBP-1, the first identified member of the IGFBP family is highly inducible under a variety of catabolic conditions, such as food deprivation, malnutrition, stress, injury and hypoxia. Recent in vivo studies have indicated that the induced IGFBP-1 serves as a molecular switch by restricting IGF signalling and diverts the limited energy resources away from growth and development towards those metabolic processes essential for survival. This article reviews the recent understandings of the molecular basis of IGFBP-1 regulation and its biological functions, as revealed through research in mammalian and fish models.     

Plant hormone signaling and modulation of DNA repair under stressful conditions

The role played by phytohormone signaling in the modulation of DNA repair gene and the resulting effects on plant adaptation to genotoxic stress are poorly investigated. Information has been gathered using the Arabidopsis ABA (abscisic acid) overly sensitive mutant abo4-1, defective in the DNA polymerase ε function that is required for DNA repair and recombination. Similarly, phytohormone-mediated regulation of the Ku genes, encoding the Ku heterodimer protein involved in DNA repair, cell cycle control and telomere homeostasis has been demonstrated, highlighting a scenario in which hormones might affect genome stability by modulating the frequency of homologous recombination, favoring plant adaptation to genotoxic stress. Within this context, the characterisation of Arabidopsis AtKu mutants allowed disclosing novel connections between DNA repair and phytohormone networks. Another intriguing aspect deals with the emerging correlation between plant defense response and the mechanisms responsible for genome stability. There is increasing evidence that systemic acquired resistance (SAR) and homologous recombination share common elements represented by proteins involved in DNA repair and chromatin remodeling. This hypothesis is supported by the finding that volatile compounds, such as methyl salicylate (MeSA) and methyl jasmonate (MeJA), participating in the plant-to-plant communication can trigger genome instability in response to genotoxic stress agents. Phytohormone-mediated control of genome stability involves also chromatin remodeling, thus expanding the range of molecular targets. The present review describes the most significant advances in this specific research field, in the attempt to provide a better comprehension of how plant hormones modulate DNA repair proteins as a function of stress.     

Induction of Escherichia coli chromosomal mazEF by stressful conditions causes an irreversible loss of viability

mazEF is a stress-induced toxin-antitoxin module located on the chromosomes of many bacteria. Here we induced Escherichia coli chromosomal mazEF by various stressful conditions. We found an irreversible loss of viability, which is the basic characteristic of cell death. These results further support our previous conclusion that E. coli mazEF mediation of cell death is not a passive process, but an active and genetically "programmed" death response.     

Phenotypic heterogeneity as key factor for growth and survival under oligotrophic conditions

Productivity-poor oligotrophic environments are plentiful on earth. Yet it is not well understood how organisms maintain population sizes under these extreme conditions. Most scenarios consider the adaptation of a single microorganism (isogenic) at the cellular level, which increases their fitness in such an environment. However, in oligotrophic environments, the adaptation of microorganisms at population level – that is, the ability of living cells to differentiate into subtypes with specialized attributes leading to the coexistence of different phenotypes in isogenic populations – remains a little-explored area of microbiology research. In this study, we performed experiments to demonstrate that an isogenic population differentiated to two subpopulations under low energy-flux in chemostats. Fluorescence cytometry and turnover rates revealed that these subpopulations differ in their nucleic acid content and metabolic activity. A mechanistic modelling framework for the dynamic adaptation of microorganisms with the consideration of their ability to switch between different phenotypes was experimentally calibrated and validated. Simulation of hypothetical scenarios suggests that responsive diversification upon a change in energy availability offers a competitive advantage over homogenous adaptation for maintaining viability and metabolic activity with time.     

Triacontanol as a dynamic growth regulator for plants under diverse environmental conditions

Triacontanol (TRIA) being an endogenous plant growth regulator facilitates numerous plant metabolic activities leading to better growth and development. Moreover, TRIA plays essential roles in alleviating the stress-accrued alterations in crop plants via modulating the activation of the stress tolerance mechanisms. The present article critically focuses on the role of exogenously applied TRIA in morpho-physiology and biochemistry of plants for example, in terms of growth, photosynthesis, enzymatic activity, biofuel synthesis, yield and quality under normal and stressful conditions. This article also enlightens the mode of action of TRIA and its interaction with other phytohormones in regulating the physio-biochemical processes in counteracting the stress-induced damages in plants.

     

Effects of hydroxyproline on the growth of excised root segments of Pisum sativum under aseptic conditions

Summary The cis and trans isomers of 4-hydroxy-l-proline stimulated the extension growth of excised 2–4 mm pea root segments during culture. Increase in the uptake and subsequent incorporation of [¹⁴c]leucine into proteins was inhibited by both l-isomers, and so also were changes in chloride uptake capacity and in protein metabolism measured in terms of invertase and peroxidase activities. Changes in [¹⁴C]proline uptake and incorporation, and in respiration, were unaffected. Proline had no effect on changes in extension growth or protein metabolism but did prevent the effects of both hydroxyproline isomers. Azetidine-2-carboxylic acid inhibited extension growth and all the aspects of protein metabolism studied, the effects again being all prevented by proline. It is suggested that hydroxyproline enhances growth by interfering with protein synthesis in the cell walls.     

The growth and differentiation of root cap columella cells and the proper root grown in the stationary conditions and under clinorotation

The results of light- and electron-microscopic investigations of root apices of Beta vulgaris 3-day-old seedlings grown in the stationary conditions and under clinorotation are presented. It was shown that ultrastructure and topography of organelles in root cap statocytes (graviperceptive cells) and in the cells of distal elongation zone clearly reflected the different direction in their growth and differentiation in space and time in dependence on specialization and functions. Cell growth and genetically determined differentiation occur similarly to control, although certain differences in ultrastructure are evident on metabolism changes.     

Exaggerated root respiration accounts for growth retardation in a starchless mutant of Arabidopsis thaliana

The knock‐out mutation of plastidial phosphoglucomutase (pgm) causes a starchless phenotype in Arabidopsis thaliana, and results in a severe growth reduction of plants cultivated under diurnal conditions. It has been speculated that high soluble sugar levels accumulating during the light phase in leaf mesophyll might cause a reduction of photosynthetic activity or that shortage of reduced carbon during the night is the reason for the slow biomass gain of pgm. Separate simultaneous measurements of leaf net photosynthesis and root respiration demonstrate that photosynthetic activity per unit fresh weight is not reduced in pgm, whereas root respiration is strongly elevated. Comparison with a mutant defective in the dominating vacuolar invertase (AtβFruct4) revealed that high sucrose concentration in the cytosol, but not in the vacuole, of leaf cells is responsible for elevated assimilate transport to the root. Increased sugar supply to the root, as observed in pgm mutants, forces substantial respiratory losses. Because root respiration accounts for 80% of total plant respiration under long‐day conditions, this gives rise to retarded biomass formation. In contrast, reduced vacuolar invertase activity leads to reduced net photosynthesis in the shoot and lowered root respiration, and affords an increased root/shoot ratio. The results demonstrate that roots have very limited capacity for carbon storage but exert rigid control of supply for their maintenance metabolism.     

Magnesium mobility in soils as a challenge for soil and plant analysis, magnesium fertilization and root uptake under adverse growth conditions

Background

Due to its unique chemistry magnesium (Mg) is subject to various cycling processes in agricultural ecosystems. This high mobility of Mg needs to be considered for crop nutrition in sustainable agricultural systems. The Mg mobility in soils and plants and its consequences for crop nutrition are understood, but recent findings in crop Mg uptake, translocation and physiology particularly under adverse growth conditions give new insights into the importance of Mg in crop production.

Scope

The aim of this review is to combine the knowledge on the origin and mobility of Mg in soils with the role of Mg in plant stress physiology and recent evidence on the principles of crop Mg uptake. The question is addressed whether the progress made in Mg research, particularly on the role of Mg in stress physiology, makes a revision of the development of Mg fertilization recommendations necessary.

Conclusions

New insights into Mg uptake and utilization but particularly into the role of Mg in increasing crop tolerance to various stresses indicate changes in the crop Mg demand under adverse growth conditions. Future work should incorporate these findings in optimization of site-specific balanced fertilization programs particularly under stress conditions.