Role Of Auxin Research Articles

Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin.

Organisation and patterning of the vascular network in land plants varies in different taxonomic, developmental and environmental contexts. In leaves, the degree of vascular strand connectivity influences both light and CO2 harvesting capabilities as well as hydraulic capacity. As such, developmental mechanisms that regulate leaf venation patterning have a direct impact on physiological performance. Development of the leaf venation network requires the specification of procambial cells within the ground meristem of the primordium and subsequent proliferation and differentiation of the procambial lineage to form vascular strands. An understanding of how diverse venation patterns are manifest therefore requires mechanistic insight into how procambium is dynamically specified in a growing leaf. A role for auxin in this process was identified many years ago, but questions remain. In this review we first provide an overview of the diverse venation patterns that exist in land plants, providing an evolutionary perspective. We then focus on the developmental regulation of leaf venation patterns in angiosperms, comparing patterning in eudicots and monocots, and the role of auxin in each case. Although common themes emerge, we conclude that the developmental mechanisms elucidated in eudicots are unlikely to fully explain how parallel venation patterns in monocot leaves are elaborated.

Roles of auxin in the inhibition of shoot branching in 'Dugan' fir.

Shoot branching substantially impacts vegetative and reproductive growth as well as wood characteristics in perennial woody species by shaping the shoot system architecture. Although plant hormones have been shown to play a fundamental role in shoot branching in annual species, their corresponding actions in perennial woody plants are largely unknown, in part due to the lack of branching mutants. Here, we demonstrated the role of plant hormones in bud dormancy transition toward activation and outgrowth in woody plants by comparing the physiological and molecular changes in the apical shoot stems of 'Yangkou' 020 fir and 'Dugan' fir, two Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) clones with normal and completely abolished branching phenotypes, respectively. Our studies showed that the defect in bud outgrowth was the cause of failed shoot branching in 'Dugan' fir whereas apically derived signals acted as triggers of this ectopic bud activity. Further studies indicated that auxin played a key role in inhibiting bud outgrowth in 'Dugan' fir. During bud dormancy release, the differential auxin resistant 1/Like AUX1 (AUX1/LAX) and PIN-formed (PIN) activity resulted in an ectopic auxin/indole-3-acetic acid (IAA) accumulation in the apical shoot stem of 'Dugan' fir, which could inhibit the cell cycle in the axillary meristem by decreasing cytokinin (CK) biosynthesis but increasing abscisic acid (ABA) production and response through the signaling pathway. In contrast, during bud activation and outgrowth, the striking increase in auxin biosynthesis and PIN activity in the shoot tip of 'Dugan' fir may trigger the correlative inhibition of axillary buds by modulating the polar auxin transport stream (PATS) and connective auxin transport (CAT) in shoots, and by influencing the biosynthesis of secondary messengers, including CK, gibberellin (GA) and ABA, thereby inducing the paradormancy of axillary buds in 'Dugan' fir by apical dominance under favorable conditions. The findings of this study provide important insights into the roles of plant hormones in bud outgrowth control in perennial woody plants.

Auxin analog-induced Ca2+ signaling is independent of inhibition of endosomal aggregation in Arabidopsis roots.

Much of what we know about the role of auxin in plant development derives from exogenous manipulations of auxin distribution and signaling, using inhibitors, auxins, and auxin analogs. In this context, synthetic auxin analogs, such as 1-naphthalene acetic acid (1-NAA), are often favored over the endogenous auxin, indole-3-acetic acid (IAA), in part due to their higher stability. While such auxin analogs have proven instrumental in revealing the various faces of auxin, they display in some cases bioactivities distinct from IAA. Here, we focused on the effect of auxin analogs on the accumulation of PIN proteins in brefeldin A-sensitive endosomal aggregations (BFA bodies), and correlation with the ability to elicit Ca2+ responses. For a set of commonly used auxin analogs, we evaluated if auxin analog-induced Ca2+ signaling inhibits PIN accumulation. Not all auxin analogs elicited a Ca2+ response, and their differential ability to elicit Ca2+ responses correlated partially with their ability to inhibit BFA-body formation. However, in tir1/afb and cngc14, 1-NAA-induced Ca2+ signaling was strongly impaired, yet 1-NAA still could inhibit PIN accumulation in BFA bodies. This demonstrates that TIR1/AFB-CNGC14-dependent Ca2+ signaling does not inhibit BFA body formation in Arabidopsis roots.

The role of auxins and auxin-producing bacteria in the tolerance and accumulation of cadmium by plants.

Cadmium (Cd) is one of the most toxic heavy metals for plant physiology and development. This review discusses Cd effects on auxin biosynthesis and homeostasis, and the strategies for restoring plant growth based on exogenous auxin application. First, the two well-characterized auxin biosynthesis pathways in plants are described, as well as the effect of exogenous auxin application on plant growth. Then, review describes the impacts of Cd on the content, biosynthesis, conjugation, and oxidation of endogenous auxins, which are related to a decrease in root development, photosynthesis, and biomass production. Finally, compelling evidence of the beneficial effects of auxin-producing rhizobacteria in plants exposed to Cd is showed, focusing on photosynthesis, oxidative stress, and production of antioxidant compounds and osmolytes that counteract Cd toxicity, favoring plant growth and improve phytoremediation efficiency. Expanding our understanding of the positive effects of exogenous auxins application and the interactions between bacteria and plants growing in Cd-polluted environments will allow us to propose phytoremediation strategies for restoring environments contaminated with this metal.

Involvement of auxin in growth and stress response of cucumber

Cucumber (<italic>Cucumis sativus</italic> L.), an important vegetable, popular worldwide for its crispy texture and special flavor. Plant hormones such as auxin stands out for its dominating function in morpho- and organogenic processes, formation of organs as well as regulation of tropic responses. These developmental processes are entirely or partially dependent on auxin biosynthesis, transport, and signal transduction. In cucumber, auxin not only fine-tunes its morphogenesis but also response to environmental stress. The role of auxin in regulating different organs (root, hypocotyl, shoot, leaf, tendril, flower, and fruit) development in cucumber was reviewed in the present paper. Moreover, the role of auxin in cucumber response to biotic stresses (powdery mildew, downy mildew, and nematode infections) and abiotic stresses (heat, iron, waterlogging, cold, salinity, drought, and heavy metal stresses) was discussed. Finally, we pointed out the blind spots and future research thoughts to extend our understanding of this myriad molecule in cucumber growth and stress biology.

Promotion of Papua “Merbau” Iron Wood (Eusideroxylon Zwagerii) through in-Vitro Tissue Culture

Papua's ironwood comes from the merbau plant that inhabits the forests of Papua, one of which is in the Yapen Islands Regency, Serui City. In conventional cultivating ironwood for commercial purposes, there are various problems. When using powder and soil, a lot of sawdust is needed. In addition, the time required for planting seeds to produce shoots that are ready to be planted in the field takes a very long time of about 9-12 months. The first step in the cultivation of merbau tissue culture is to find the right formula for growth regulators. Auxins and cytokines are the right steps to stimulate merbau wood growth. It seems that the role of auxin (IAA) and cytokinin (BAP) in Murashige and Skoog media on Merbau Wood using cotyledon and meristem explants with good concentrations for shoot and plantlet formation was 1.0 mg/l IAA and 5, 0 mg/l from the latest research using hormones including NAA, Chitin and BAP in Merbau (Eusideroxylon zwageri) wood culture. NAA concentration 1 mg/l (A4B5) formed shoots and callus, A4B1 (NAA 1 mg/l; BAP 0 mg/l) resulted in organogenesis and NAA concentration 0.2 mg/l without cytokinins (A2B1) produced multiple shoots. The interaction of the combination of auxin NAA 1 mg/l with BAP 0.6 mg/l (A4B7) gave the best response in embryosomatic formation in implanted explants. While the interaction of NAA 0.2 mg/l with Kinetic 2 mg/l (A3B3) resulted in shoots and callus. The interaction of the combination of auxin NAA 1 mg/l with BAP 0.6 mg/l (A4B7) gave the best response in embryosomatic formation in implanted explants. While the interaction of NAA 0.2 mg/l with Kinetic 2 mg/l (A3B3) resulted in shoots and callus. The interaction of the combination of auxin NAA 1 mg/l with BAP 0.6 mg/l (A4B7) gave the best response in embryosomatic formation in implanted explants. While the interaction of NAA 0.2 mg/l with Kinetic 2 mg/l (A3B3) resulted in shoots and callus.

Role of Auxin and Nitrate Signaling in the Development of Root System Architecture

The plant root is an important storage organ that stores indole-3-acetic acid (IAA) from the apical meristem, as well as nitrogen, which is obtained from the external environment. IAA and nitrogen act as signaling molecules that promote root growth to obtain further resources. Fluctuations in the distribution of nitrogen in the soil environment induce plants to develop a set of strategies that effectively improve nitrogen use efficiency. Auxin integrates the information regarding the nitrate status inside and outside the plant body to reasonably distribute resources and sustainably construct the plant root system. In this review, we focus on the main factors involved in the process of nitrate- and auxin-mediated regulation of root structure to better understand how the root system integrates the internal and external information and how this information is utilized to modify the root system architecture.

Plant root development: is the classical theory for auxin-regulated root growth false?

One of the longest standing theories and, therein-based, regulation-model of plant root development, posits the inhibitory action of auxin (IAA, indolylacetic acid) on elongation growth of root cells. This effect, as induced by exogenously supplied IAA, served as the foundation stone for root growth regulation. For decades, auxin ruled the day and only allowed hormonal side players to be somehow involved, or in some way affected. However, this copiously reiterated, apparent cardinal role of auxin only applies in roots immersed in solutions; it vanishes as soon as IAA-supplied roots are not surrounded by liquid. When roots grow in humid air, exogenous IAA has no inhibitory effect on elongation growth of maize roots, regardless of whether it is applied basipetally from the top of the root or to the entire residual seedling immersed in IAA solution. Nevertheless, such treatment leads to pronounced root-borne ethylene emission and lateral rooting, illustrating and confirming thereby induced auxin presence and its effect on the root — yet, not on root cell elongation. Based on these findings, a new root growth regulatory model is proposed. In this model, it is not IAA, but IAA-triggered ethylene which plays the cardinal regulatory role — taking effect, or not — depending on the external circumstances. In this model, in water- or solution-incubated roots, IAA-dependent ethylene acts due to its accumulation within the root proper by inhibited/restrained diffusion into the liquid phase. In roots exposed to moist air or gas, there is no effect on cell elongation, since IAA-triggered ethylene diffuses out of the root without an impact on growth.

The role of auxin during early berry development in grapevine as revealed by transcript profiling from pollination to fruit set

Auxin is a key phytohormone that modulates fruit formation in many fleshy fruits through the regulation of cell division and expansion. Auxin content rapidly increases after pollination and the manipulation in its levels may lead to the parthenocarpic development. ln Vitis vinifera L., little is known about the early fruit development that encompasses from pollination to fruit set. Pollination/fertilization events trigger fruit formation, and auxin treatment mimics their effect in grape berry set. However, the role of auxin in this process at the molecular level is not well understood. To elucidate the participation of auxin in grapevine fruit formation, morphological, reproductive, and molecular events from anthesis to fruit set were described in sequential days after pollination. Exploratory RNA-seq analysis at four time points from anthesis to fruit set revealed that the highest percentage of genes induced/repressed within the hormone-related gene category were auxin-related genes. Transcript profiling showed significant transcript variations in auxin signaling and homeostasis-related genes during the early fruit development. Indole acetic acid and several auxin metabolites were present during this period. Finally, application of an inhibitor of auxin action reduced cell number and the mesocarp diameter, similarly to unpollinated berries, further confirming the key role of auxin during early berry development. This work sheds light into the molecular features of the initial fruit development and highlights the auxin participation during this stage in grapevine.

Effect of Exogenous Auxin Treatment on Cell Wall Polymers of Strawberry Fruit.

The role of auxin in the fruit-ripening process during the early developmental stages of commercial strawberry fruits (Fragaria x ananassa) has been previously described, with auxin production occurring in achenes and moving to the receptacle. Additionally, fruit softening is a consequence of the depolymerization and solubilization of cell wall components produced by the action of a group of proteins and enzymes. The aim of this study was to compare the effect of exogenous auxin treatment on the physiological properties of the cell wall-associated polysaccharide contents of strawberry fruits. We combined thermogravimetric (TG) analysis with analyses of the mRNA abundance, enzymatic activity, and physiological characteristics related to the cell wall. The samples did not show a change in fruit firmness at 48 h post-treatment; by contrast, we showed changes in the cell wall stability based on TG and differential thermogravimetric (DTG) analysis curves. Less degradation of the cell wall polymers was observed after auxin treatment at 48 h post-treatment. The results of our study indicate that auxin treatment delays the cell wall disassembly process in strawberries.

The role of auxin and sugar signaling in dominance inhibition of inflorescence growth by fruit load.

Dominance inhibition of shoot growth by fruit load is a major factor that regulates shoot architecture and limits yield in agriculture and horticulture crops. In annual plants, the inhibition of inflorescence growth by fruit load occurs at a late stage of inflorescence development termed the end of flowering transition. Physiological studies show this transition is mediated by production and export of auxin from developing fruits in close proximity to the inflorescence apex. In the meristem, cessation of inflorescence growth is controlled in part by the age-dependent pathway, which regulates the timing of arrest. Here, we show the end of flowering transition is a two-step process in Arabidopsis (Arabidopsis thaliana). The first stage is characterized by a cessation of inflorescence growth, while immature fruit continues to develop. At this stage, dominance inhibition of inflorescence growth by fruit load is associated with a selective dampening of auxin transport in the apical region of the stem. Subsequently, an increase in auxin response in the vascular tissues of the apical stem where developing fruits are attached marks the second stage for the end of flowering transition. Similar to the vegetative and floral transition, the end of flowering transition is associated with a change in sugar signaling and metabolism in the inflorescence apex. Taken together, our results suggest that during the end of flowering transition, dominance inhibition of inflorescence shoot growth by fruit load is mediated by auxin and sugar signaling.

Regulation of algal and cyanobacterial auxin production, physiology, and application in agriculture: an overview

Algal bioproducts are of growing interest to agriculture because of their biodegradable nature, ability to restore soil fertility, and capacity for plant growth regulation, nitrogen fixation, and carbon sequestration. Plants respond to a suite of growth hormones; auxins present in algal extracts or secreted exogenously by living algae may be partially responsible for the stimulation of plant growth. Auxins are a major class of phytohormones that influence plant growth and development. The roles of auxins in algae and in plants are well described, but studies on the role of auxins in plant-algae interactions remain scarce. This review summarizes the body of knowledge on the production of auxins and their physiological roles in seaweeds, cyanobacteria, and microalgae. Common and differential auxin-associated phenotypes of these algae, including the effect of growth conditions on their auxin production, are also described. Potential mechanisms by which auxins from algae mediate plant development at both phenotypic and molecular levels are also provided. Algal-derived auxins are an environmentally sustainable option for promoting plant growth and yield, but knowledge of their precise mechanisms of action is still rudimentary. Elucidating the pathways by which algal auxins stimulate plant responses and the means by which key environmental factors influence those pathways will help to harness the full potential of algal-derived auxins for agricultural development and resource conservation.

High ammonium inhibits root growth in Arabidopsis thaliana by promoting auxin conjugation rather than inhibiting auxin biosynthesis

Ammonium (NH4+) inhibits primary root (PR) growth in most plant species when present even at moderate concentrations. Previous studies have shown that transport of indole-3-acetic acid (IAA) is critical to maintaining root elongation under high-NH4+ stress. However, the precise regulation of IAA homeostasis under high-NH4+ stress (HAS) remains unclear. In this study, qRT-PCR, RNA-seq, free IAA and IAA conjugate and PR elongation measurements were conducted in genetic mutants to investigate the role of IAA biosynthesis and conjugation under HAS. Our data clearly show that HAS decreases free IAA in roots by increasing IAA inactivation but does not decrease IAA biosynthesis, and that the IAA-conjugating genes GH3.1, GH3.2, GH3.3, GH3.4, and GH3.6 function as the key genes in regulating high-NH4+ sensitivity in the roots. Furthermore, the analysis of promoter::GUS staining in situ and genetic mutants reveals that HAS promotes IAA conjugation in the elongation zone (EZ), which may be responsible for the PR inhibition observed under HAS. This study provides potential new insight into the role of auxin in the improvement of tolerance to NH4+.

Barbara G. Pickard - Queen of Plant Electrophysiology

ABSTRACT Barbara Gillespie Pickard (1936–2019) studied plant electrophysiology and mechanosensory biology for more than 50 y. Her first papers on the roles of auxin in plant tropisms were coauthored with Kenneth V. Thimann. Later, she studied plant electrophysiology. She made it clear that plant action potentials are not a peculiar feature of so-called sensitive plants, but that all plants exhibit these fast electric signals. Barbara Gillespie Pickard proposed a neuronal model for the spreading of electric signals induced by mechanical stimuli across plant tissues. In later years, she studied the stretch-activated plasma membrane channels of plants and formulated the plasma-membrane control center model. Barbara Pickard summarized all her findings in a new model of phyllotaxis involving waves of auxin fluxes and mechano-sensory signaling.

Dynamic cytokinin signalling landscapes during lateral root formation in Arabidopsis

By forming lateral roots, plants expand their root systems to improve anchorage and absorb more water and nutrients from the soil. Each phase of this developmental process in Arabidopsis is tightly regulated by dynamic and continuous signalling of the phytohormones cytokinin and auxin. While the roles of auxin in lateral root organogenesis and spatial accommodation by overlying cell layers have been well studied, insights on the importance of cytokinin is still somewhat limited. Cytokinin is a negative regulator of lateral root formation with versatile modes of action being activated at different root developmental zones. Here, we review the latest progress made towards our understanding of these spatially separated mechanisms of cytokinin-mediated signalling that shape lateral root initiation, outgrowth and emergence and highlight some of the enticing open questions.

Rapid mapping of the IAA in leaves of Arabidopsis thaliana using a simple paper-based electroanalytical device coupled with microsampling.

To deeply investigate the pivotal roles of Auxin (mainly indole-3-acetic acid, IAA), it is essential to obtain the contents of IAA in different locations of plants. It is still a challenge to quantify the levels of IAA in different sites of Arabidopsis thaliana leaves because of the small sizes. In this study, a simple paper-based electroanalytical device coupled with microsampling was used to differentiate the IAA amounts in different locations of Arabidopsis thaliana leaves. For the micro real sampling, the different areas of the thaliana leaves were retrieved by the Harris Uni-Core TM Miltex® with diameters: 1.0, 1.5, 2.5, 3.5, and 4.0 mm. The results showed that the contents of IAA can be detected from circle samples with the diameter from 1.0 to 4.0 mm. With 1.5 mm diameter sampling, the levels of IAA could be obtained in different sites of cotyledon and the first true leaf of Arabidopsis thaliana at the seedling stage. Our results suggested that the highest IAA levels were in the near petiole and lowest IAA levels in the leaf tip, which roughly agreed with those in tobacco leaves based on HPLC-MS reported before. In addition, the microsampling has a minor impact on the growth of Arabidopsis thaliana in the following especially for circle samples with the diameter 1.5 mm. This study revealed the potential application of microsampling coupled with a simple paper-based electroanalytical device for the mapping study of IAA in small plants or small tissue samples.

On how auxin, ethylene and IDA-peptide relate during mature Citrus fruit abscission

While the ethylene-auxin interactions are well documented in model dicots such as tomato (climacteric fruit) during mature fruit abscission, the process is not clearly understood in citrus (non-climacteric fruit). The mature fruit produces very little ethylene but is sensitive to ethylene treatments to induce abscission. By contrast, auxin treatments delay fruit abscission, but the particular role of auxin in the process is unknown. Since the IDA-HAE/HSL2 ethylene-independent pathway seem to regulate organ abscission in both model and crop species, we proposed that auxin treatment delays citrus fruit abscission by reactivating the basipetal auxin flux and reducing CitIDA3 expression, without modifying ethylene synthesis.Comparing orange (C. sinensis) genotypes which differ in their abscission rate, ‘Navelate’ vs. ‘Valencia Late’, we found that the force needed to detach the fruit from the tree (FDF) declines in parallel with 1) an increase of ethylene synthesis and CitIDA3 gene expression, and 2) a reduction of PIN1-like (auxin transporter) gene expresion. Further, auxin (2,4-D) treatment maintains a higher force in the abscission zone upregulating PIN1-like and AUX1-like (auxin transporter) gene expression, and downregulating CitIDA3 gene expression, but without modifying ethylene production. We conclude that the 2,4-D treatment delays citrus mature fruit abscission through an ethylene-independent pathway.

Role of auxin in horticultural fruit crops

As we know auxins were the first class of plant hormones to be discovered that use to kill weeds, promote growth and fruit quality of particular plant.in this review paper I have compile the summary of Auxin as important hormone required to carry any essential function in plant viz., delaying, early maturation, help in rooting etc. I have categorized crop in accordance with role of auxin with tropical and temperate crops, which I hope could help scientist for further breeding programme, to acknowledge the role with its pros and cons. In mango it mainly influence the girdling effect, fruit repining process, and in grape it helps in the maturation and quality maintenance of berries on the other hand in apple with the appropriate concentration it triggers the production of ethylene which eventually promotes ripening accompany it helps in the translocation of calcium which maintain the fruit quality. In guava auxin is immensely used in the form IAA and IBA which operates as a rooting hormone in this crop to hasten the growth during layering on the other hand in pear and peach its application influence the growth of primary and secondary shoot.

Auxins, the hidden player in chloroplast development

Throughout decades of plant research, the plant hormones known as auxins have been found to be of vital importance in most plant development processes. Indole-3-acetic acid (IAA) represents the most common auxin in plants and can be synthesized from its tryptophan precursor, which is synthesized in the chloroplast. The chloroplast constitutes an organelle of great relevance to plants since the photosynthesis process by which plants get most of their energy is carried out there. The role of auxins in photosynthesis has been studied for at least 50years, and in this time, it has been shown that auxins have an effect on several of the essential components and structure of the chloroplast. In recent decades, a high number of genes have been reported to be expressed in the chloroplast and some of their mutants have been shown to alter different auxin-mediated pathways. Genes in signaling pathways such as IAA/AUX, ARF, GH.3, SAUR and TIR, biosynthesis-related genes such as YUCCA and transport-related genes such as PIN have been identified among the most regulated genes in mutants related to alterations in the chloroplast. This review aims to provide a complete and updated summary of the relationship between auxins and several processes that involve the chloroplast, including chloroplast development, plant albinism, redox regulation and pigment synthesis.

Physiological Responses to Fe Deficiency in Split-Root Tomato Plants: Possible Roles of Auxin and Ethylene?

Iron (Fe) bioavailability in soils is often limited and can be further exacerbated by a non- homogeneous distribution in the soil profile, which has been demonstrated to vary both in space and time. Consequently, plants respond with morphological and physiological modifications at the root level involving a complex local and systemic signaling machinery. The present work unravels the role of two phytohormones (i.e., ethylene and auxin) and their integrated signaling in plant response to Fe deficiency. Inhibitors of auxin polar transport and of ethylene biosynthesis (N-1-naphthylphthalamic acid - NPA and aminoethoxyvinylglycine - AVG, respectively) were applied on tomato (Solanum lycopersicum L.) plants grown by the split-root technique, which allows to simulate condition of Fe heterogeneous distribution. Results showed that plants, exposed to an uneven Fe supply, triggered a complex auxin-ethylene signaling. A systemic action of auxin on FERRIC REDUCTASE OXIDASE 1 (SlFRO1) expression was revealed, while ethylene signaling was effective both locally and systemically. In addition, the investigation of Fe concentration in tissues showed that when leaves overcame Fe deficiency a Fe “steady state” was maintained. Therefore, physiological adaptation to this heterogeneous Fe supply could be mediated by the integration of the complex signaling pathways prompted by both auxin and ethylene activities.