Involvement Of Plant Hormones Research Articles

Investigation of stimulated growth effect by application of L-aspartic acid on poplar

Poplar is an important resource for the production of wood-based products. L-aspartic acid (Asp) is a proteinogenesis amino acid that plays a critical role in cell growth modulation and stress response. Also, Asp is widespread in the commonly used amino acid-based biostimulant products. However, its effects on poplars remain largely unknown. To address this issue, we applied different concentrations of Asp to poplar seedlings under N reduction conditions (simulating low N availability status), and assessed the effects of Asp on poplar growth and development. Our results showed that supplement of Asp at an appropriate concentration, that is, 0.5 mM in the present study, had the best growth-promoting effect on poplars. It significantly increased poplar biomass and height, and simultaneously elevated the photosynthetic parameters, the chlorophyll content and total free amino acid content, as well as the activity of N metabolism-related enzymes in poplars-treated with Asp in comparision with the control plants without Asp addition. Furthermore, the expression of Asp-metabolism pathway genes (AspAT1, AspAT6, AspAT10, AK1, ASS1 and ASS2), key chlorophyll synthesis gene (LHCB3) and cell division gene (CYCD3) was all dramatically upregulated in response to Asp application, suggesting that Asp-induced effect invoked photosynthesis activation and metabolism reprogramming. More interestingly, our results showed that the levels of various phytohormones, such as auxin and cytokinins were remarkably altered, and key auxin transport gene (PIN1c-2), auxin conjugation gene (GH3.6–2) were induced by Asp treatment, indicative of the possible involvement of plant hormones under the effect of Asp, especially fine-tuning auxin homeostasis by forming IAA-Asp conjugates to store auxin and catabolizing IAA-Asp to release auxin, may account for Asp-mediated growth modulation to an extent in poplars. Our study provides a novo insight into the growth promotion effect of Asp on poplars, especially, when the N source is limited, even though the underlying mechanism of Asp-induced stimulation action needs further in-depth investigation.

Plant Hormones in Phytoplasma Infected Plants.

Phytoplasmas are bacterial plant pathogens that need a plant host and an insect vector for their spread and survival. In plants, the physiological responses that phytoplasmas trigger result in symptom development through effects on hormonal, nutritional, and stress signaling pathways, and the interactions between these. In this review, recent advances on the involvement of plant hormones together with their known and deduced roles in plants infected with phytoplasmas are discussed. Several studies have directly, or in many cases indirectly, addressed plant hormone systems in phytoplasma-infected plants. These have provided accumulating evidence that phytoplasmas extensively affect plant hormone pathways. Phytoplasmas thus, with disturbing complex plant hormone networks, suppress plant immunity and modify plant structure, while optimizing their nutrient acquisition and facilitating their colonization of the plants, and their dissemination among plants by their insect vectors.

Common and specific responses to availability of mineral nutrients and water.

Changes in resource (mineral nutrients and water) availability, due to their heterogeneous distribution in space and time, affect plant development. Plants need to sense these changes to optimize growth and biomass allocation by integrating root and shoot growth. Since a limited supply of water or nutrients can elicit similar physiological responses (the relative activation of root growth at the expense of shoot growth), similar underlying mechanisms may affect perception and acquisition of either nutrients or water. This review compares root and shoot responses to availability of different macronutrients and water. Attention is given to the roles of root-to-shoot signalling and shoot-to-root signalling, with regard to coordinating changes in root and shoot growth and development. Involvement of plant hormones in regulating physiological responses such as stomatal and hydraulic conductance is revealed by measuring the effects of resource availability on phytohormone concentrations in roots and shoots, and their flow between roots and shoots in xylem and phloem saps. More specific evidence can be obtained by measuring the physiological responses of genotypes with altered hormone responses or concentrations. We discuss the similarity and diversity of changes in shoot growth, allocation to root growth, and root architecture under changes in water, nitrate, and phosphorus availability, and the possible involvement of abscisic acid, indole-acetic acid, and cytokinin in their regulation. A better understanding of these mechanisms may contribute to better crop management for efficient use of these resources and to selecting crops for improved performance under suboptimal soil conditions.

Systemic resistance induced in Arabidopsis thaliana by Trichoderma asperellum SKT‐1, a microbial pesticide of seedborne diseases of rice

Trichoderma asperellum SKT-1 is a microbial pesticide of seedborne diseases of rice. To investigate the mechanisms of disease suppression in SKT-1, the ability to induce systemic resistance by SKT-1, or its cell-free culture filtrate (CF), was tested using Arabidopsis thaliana Col-0 plants. Both SKT-1 and its CF elicit an induced systemic resistance against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 in Col-0 plants. Involvement of plant hormones in the induced resistance by SKT-1 and CF was assessed using Arabidopsis genotypes such as the jasmonic acid (JA)-resistant mutant jar1, the ethylene (ET)-resistant mutant etr1, the plant impaired in salicylic acid (SA) signalling transgenic NahG and the mutant npr1 impaired in NPR1 activity. In soil experiments using SKT-1, no significant disease suppression effect was observed in NahG transgenic plants or npr1 mutant plants. Expression levels of SA-inducible genes such as PR-1, PR-2 and PR-5 increased substantially in the leaves of Col-0 plants. Expression levels of JA/ET-induced genes such as PDF1.2a, PR-3, PR-4 and AtVsp1 were also induced, but the levels were not as high as for SA-inducible genes. In a hydroponic experiment using CF from SKT-1, all Arabidopsis genotypes showed an induced systemic resistance by CF and increased expression levels of JA/ET- and SA-inducible genes in leaves of CF-treated plants. The SA signalling pathway is important in inducing systemic resistance to colonisation by SKT-1, and both SA and JA/ET signalling pathways combine in the signalling of induced resistance by CF. These results indicate that the response of A. thaliana is different from that found in root treatments with barley grain inoculum and CF from SKT-1.

Involvement of Plant Hormones in the Gravitropic Response of Floating Rice Pulvini and Effect of Submergence on the Response

Involvement of Plant Hormones in the Gravitropic Response of Floating Rice Pulvini and Effect of Submergence on the Response

Multiple hormone analysis indicates involvement of jasmonate signalling in the early defence of potato to potato virus Y<sup>NTN</sup>

The involvement of plant hormones in the very early response of plants to virus infection was studied in potato plants (Solanum tuberosum L.) infected with potato virus YNTN (PVYNTN). Endogenous plant hormones and compounds mediating a stress response (JA-jasmonic acid, OPDA-12-oxo phytodienoic acid, SA-salicylic acid, IAA-indole-3-acetic acid, ABA-abscisic acid) were simultaneously quantified in susceptible cv. DĂŠsirĂŠe and resistant cv. SantĂŠ, one and three hours after inoculation. Of the hormones analysed, only the contents of endogenous JA and its precursor OPDA changed in a way that could be clearly connected with the early resistant response. In comparison to susceptible cultivar, a much more pronounced increase of JA was detected in virus-inoculated leaves of resistant cultivar at both time points. The same trend of changes was also observed with OPDA. However, there were no significant changes of JA and its precursor in upper intact systemic leaves and roots, at either time point. These findings implicate the jasmonate signalling pathway in a very early local but not systemic resistant defence of potato to PVYNTN.

Transcriptome Analysis of Arabidopsis Clubroots Indicate a Key Role for Cytokinins in Disease Development

The clubroot disease of the family Brassicaceae is caused by the obligate biotrophic protist Plasmodiophora brassicae. Infected roots undergo a developmental switch that results in the formation of aberrant roots (clubs). To investigate host gene expression during the development of the disease, we have used the Arabidopsis ATH1 genome array. Two timepoints were chosen, an early timepoint at which the pathogen has colonized the root but has induced only very limited change of host cell and root morphology and a later timepoint at which more than 60% of the host root cells were colonized and root morphology was drastically altered. At both timepoints, more than 1,000 genes were differentially expressed in infected versus control roots. These included genes associated with growth and cell cycle, sugar phosphate metabolism, and defense. The involvement of plant hormones in club development was further supported; genes involved in auxin homeostasis, such as nitrilases and members of the GH3 family, were upregulated, whereas genes involved in cytokinin homeostasis (cytokinin synthases and cytokinin oxidases/dehydrogenases) were already strongly downregulated at the early timepoint. Cytokinin oxidase/dehydrogenase overexpressing lines were disease resistant, clearly indicating the importance of cytokinin as a key factor in clubroot disease development.

Involvement of Plant Hormones and Plant Growth Regulators on in vitro Somatic Embryogenesis

In spite of the importance attained by somatic embryogenesis and of the many studies that have been conducted on this developmental process, there are still many aspects that are not fully understood. Among those features, the involvement of plant hormones and plant growth regulators on deTermining the conversion of somatic onto embryogenic tissues, and on allowing progression and maturation of somatic embryos, are far away from being completely comprehended. Part of these difficulties relies on the frequent appearance of contradictory results when studying the effect of a particular stimulus over a specific stage in somatic embryogenesis. Recent progress achieved on understanding the interaction between exogenously added plant growth regulators over the concentration of endogenous hormones, together with the involvement of sensitivity of the tissues to particular hormone groups, might help clarifying the occurrence of divergent patterns in somatic embryogenesis, and in tissue culture in general. The aspects described above, emphasizing on the effect of the concentration of plant hormones and of the addition of plant growth regulators during the different phases of somatic embryogenesis, will be reviewed in this paper. Citations will be limited to review articles as much as possible and to individual articles only in those cases in which very specific or recent information is presented.

Induction of tomato stress protein mRNAs by ethephon, 2,6-dichloroisonicotinic acid and salicylate

To study the possible involvement of plant hormones in the synthesis of stress proteins in tomato upon inoculation with Cladosporium fulvum, we investigated the induction of mRNAs encoding PR proteins and ethylene biosynthesis enzymes by ethephon, 2,6-dichloroisonicotinic acid (INA) and salicylic acid (SA) by northern blot analysis. Ethephon slightly induced some but not all mRNAs encoding intra- and extracellular PR proteins. INA induced all PR protein mRNAs analysed, except for intracellular chitinase and extracellular PR-4. SA induced all PR protein mRNAs analyzed, except for intracellular chitinase and osmotin. None of the inducers affected the expression of ACC synthase mRNA, whereas all three induced ethylene-forming enzyme (EFE) mRNA.

Hormonal regulation of gene expression

The involvement of plant hormones in the regulation of gene expression is well-recognized. Current research using molecular approaches has resulted in the isolation and characterization of a number of hormone-responsive genes and cDNAs. These genes are proving to be valuable molecular probes to study the mode of action of plant hormones. This review will briefly describe some recent molecular data from selected hormone-responsive plant systems. Results of these studies indicate potential complexity in the regulation of these genes. These results and future challenges are discussed.

Osmoregulation and membrane-mediated responses to altered water potential in plant cells

Plant cells respond to short-term stress dehydration by modification of internal Ψ π such that an inward gradient of Ψ ω is maintained. In response to lowered Ψ ω, increases in internal Ψ π are created by alteration of cell inorganic ions and small organic solute content. Passive movement of water follows, changing cell hydration and forcing the plasma membrane against the elastic cell wall. The stretched cell wall presses against the cell contents, creating a hydrostatic pressure, Ψ π, which tends to force water out of the cell. The resulting hydrostatic pressure eventually comes into equilibrium with forces bringing water into the cell, largely Ψ π, and the net flow of water ceases. The mechanism for sensing cell Ψ ω changes is unknown but the initial event must be physical, not biochemical. The method of translation of such physical events into biochemical actions is also unknown but the Zimmermann model provides a means of signal transduction and amplification, through the alteration of membrane parameters, which could account for the observed changes. As for animal cells, cell levels of Ca 2+ are important for their regulation of membrane P j in these responses but unlike osmoregulation in higher animals, the involvement of plant hormones in these responses have not been clearly established. However, the important role of plant cell limiting membranes in plant cell osmoregulation responses seems obvious.

Plant hormones and water stress

In recent years, the involvement of plant hormones has become a subject of interest in plant water relations. The interest was initially stimulated by research into leaf ageing and plant senescence and the role of cytokinins in these processes. Plant water stress and some other stresses enhance senescence. They also bring about reduction in the levels of endogenous cytokinins. Exogenous cytokinins retard leaf senescence and may stimulate stomatal opening. Later, interest in the subject gained momentum from the various observations of the role of abscisic acid in stomatal opening. Abscisic acid brings about rapid stomatal closure, and its endogenous levels in leaves increase rapidly when plants are subjected to water stress or several other stresses. Hypotheses and data relevant to the possible role of hormones in plants subjected to environmental stresses are presented and discussed.