Synthetic Auxin Research Articles

Auxin-activated MdARF5 induces the expression of ethylene biosynthetic genes to initiate apple fruit ripening.

Summary The gaseous plant hormone ethylene induces the ripening of climacteric fruit, including apple (Malus domestica). Another phytohormone, auxin, is known to promote ethylene production in many horticultural crops, but the regulatory mechanism remains unclear.Here, we found that auxin application induces ethylene production in apple fruit before the stage of commercial harvest, when they are not otherwise capable of ripening naturally.The expression of MdARF5, a member of the auxin response factor transcription factor (TF) family involved in the auxin signaling pathway, was enhanced by treatment with the synthetic auxin naphthaleneacetic acid (NAA). Further studies revealed that MdARF5 binds to the promoter of MdERF2, encoding a TF in the ethylene signaling pathway, as well as the promoters of two 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) genes (MdACS3a and MdACS1) and an ACC oxidase (ACO) gene, MdACO1, all of which encode key steps in ethylene biosynthesis, thereby inducing their expression. We also observed that auxin‐induced ethylene production was dependent on the methylation of the MdACS3a promoter.Our findings reveal that auxin induces ethylene biosynthesis in apple fruit through activation of MdARF5 expression.

Transcriptomics in Erigeron canadensis reveals rapid photosynthetic and hormonal responses to auxin herbicide application.

The perception pathway for endogenous auxin has been well described, yet the mode of action of synthetic auxin herbicides, used for >70 years, remains uncharacterized. We utilized transcriptomics and targeted physiological studies to investigate the unknown rapid response to synthetic auxin herbicides in the globally problematic weed species Erigeron canadensis. Synthetic auxin herbicide application consistently and rapidly down-regulated the photosynthetic machinery. At the same time, there was considerable perturbation to the expression of many genes related to phytohormone metabolism and perception. In particular, auxin herbicide application enhanced the expression of the key abscisic acid biosynthetic gene, 9-cis-epoxycarotenoid deoxygenase (NCED). The increase in NCED expression following auxin herbicide application led to a rapid biosynthesis of abscisic acid (ABA). This increase in ABA levels was independent of a loss of cell turgor or an increase in ethylene levels, both proposed triggers for rapid ABA biosynthesis. The levels of ABA in the leaf after auxin herbicide application continued to increase as plants approached death, up to >3-fold higher than in the leaves of plants that were drought stressed. We propose a new model in which synthetic auxin herbicides trigger plant death by the whole-scale, rapid, down-regulation of photosynthetic processes and an increase in ABA levels through up-regulation of NCED expression, independent of ethylene levels or a loss of cell turgor.

Effects of auxin derivatives on phenotypic plasticity and stress tolerance in five species of the green algaDesmodesmus(Chlorophyceae, Chlorophyta)

Green microalgae of the genus Desmodesmus are characterized by a high degree of phenotypic plasticity (i.e. colony morphology), allowing them to be truly cosmopolitan and withstand environmental fluctuations. This flexibility enables Desmodesmus to produce a phenotype–environment match across a range of environments broader compared to algae with more fixed phenotypes. Indoles and their derivatives are a well-known crucial class of heterocyclic compounds and are widespread in different species of plants, animals, and microorganisms. Indole-3-acetic acid (IAA) is the most common, naturally occurring plant hormone of the auxin class. IAA may behave as a signaling molecule in microorganisms, and the physiological cues of IAA may also trigger phenotypic plasticity responses in Desmodesmus. In this study, we demonstrated that the changes in colonial morphs (cells per coenobium) of five species of the green alga Desmodesmus were specific to IAA but not to the chemically more stable synthetic auxins, naphthalene-1-acetic acid and 2,4-dichlorophenoxyacetic acid. Moreover, inhibitors of auxin biosynthesis and polar auxin transport inhibited cell division. Notably, different algal species (even different intraspecific strains) exhibited phenotypic plasticity different to that correlated to IAA. Thus, the plasticity involving individual-level heterogeneity in morphological characteristics may be crucial for microalgae to adapt to changing or novel conditions, and IAA treatment potentially increases the tolerance of Desmodesmus algae to several stress conditions. In summary, our results provide circumstantial evidence for the hypothesized role of IAA as a diffusible signal in the communication between the microalga and microorganisms. This information is crucial for elucidation of the role of plant hormones in plankton ecology.

Sugar enhances waterlogging-induced adventitious root formation in cucumber by promoting auxin transport and signalling.

Waterlogging is a severe environmental stress that causes severe crop productivity losses. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots (ARs) that enhance gas exchange. Little is known about the role of light and sugars in the waterlogging-induced production of ARs. The role of these factors in AR production was therefore studied in cucumber seedlings grown in the absence or presence of waterlogging and different light conditions. The effect of photosynthesis was studied by removing the shoots of the seedlings and replacing them with exogenous applications of sucrose or stachyose. Shoot removal inhibited AR emergence and elongation. However, the exogenous application of sugars fully restored AR emergence and partially restored root elongation. The exogenous application of a synthetic auxin restored AR emergence but not AR elongation. Transcriptome profiling analysis was used to determine the effects of light on gene expression in the hypocotyls under these conditions. The levels of transcripts encoding proteins involved in auxin transport and signalling were higher in the light and following the exogenous application of sucrose and stachyose. These results show that the waterlogging-induced emergence of ARs is regulated by the interaction between sugars and auxin, whereas AR elongation depends only on sugars alone.

Lipophilicity of tryptophan, its metabolites and derivatives measured by thin-layer chromatography

Fourteen compounds, including tryptophan and its metabolites: kynurenine pathway products (kynurenine, kynurenic acid, 3-hydroxykynurenine), auxin pathway products (indoleacetic acid, indolepropionic acid, indolebutyric acid, indolepyruvic acid), serotonin pathway products (5-hydroxytryptophan, serotonin, melatonin), tryptamine, as well as two synthetic auxin analogs (naphtyl-1-acetamide and naphthalene-1-acetic acid) were chromatographed on RP8 plates using binary mobile phases containing 8 concentrations of methanol as a modifier. The resulting retention data was fitted to linear Soczewiński–Wachtmeister models, obtaining experimental lipophilicity indices, which were then compared with computational lipophilicities calculated with 6 algorithms (ALOGPs, AClogP, ALOGP, MLOGP, XLOGP2 and XLOGP3) using regression and multivariate (principal component analysis) approach. It was confirmed that hydroxylation lowers the lipophilicity, whereas adding one homologous aliphatic CH2, exchange of amino group to keto group (or its loss) increases the lipophilicity. Kynurenic acid has lower lipophilicity than kynurenine under investigated conditions due to its ionization, which is opposite to computational results based on non-ionized molecule. The obtained results can be useful in explaining the biochemical and pharmacological phenomena related to these compounds.

Control of Umbelliferae in Grassland and Pasture, a new herbicide containing ArylexTM active

Anthriscus sylvestris is a perennial or biennial herbaceous plant in permanent grassland and pasture. With its half rosette it is able to displace valuable forage grasses and has only a medium feed value. At present, no effective and long-lasting solutions with selective acting herbicides is available against it and other hard-to-control weeds of the Umbelliferae family. ArylexTM active (halauxifen-methyl) is a new active ingredient in the subgroup of aryl picolinates belonging to synthetic auxins. Herbicides containing this active ingredient have been marketed in Germany since 2018 for weed control in cereals. For the use in grassland and pasture GF-3635 is now under development by Corteva Agriscience in Germany and other European countries. It is a premix of Arylex, fluroxypyr and triclopyr and contains at the 1.5 L/ha maximum use rate 10 g/ha Arylex, 300 g/ha Fluroxypyr and 300 g/ha triclopyr. GF-3635 is thus a further development of the Product Starane Ranger® available since 2005, Ranger® since 2012 respectively, with equal amounts of fluroxypyr and triclopyr per hectare. It can be safely applied during the whole vegetation period, does not harm valuable grass species and has no negative impact on yield quantity and Forage quality. GF-3635 controls A. sylvestris, Heracleum sphondylium, Plantago lanceolata, Ranunculus acris, Ranunculus repens, Rumex crispus, Rumex obtusifolius, Taraxacum officinale and Urtica dioica.

Natural Variation in Adventitious Rooting in the Alpine Perennial Arabis alpina.

Arctic alpine species follow a mixed clonal-sexual reproductive strategy based on the environmental conditions at flowering. Here, we explored the natural variation for adventitious root formation among genotypes of the alpine perennial Arabis alpina that show differences in flowering habit. We scored the presence of adventitious roots on the hypocotyl, main stem and axillary branches on plants growing in a long-day greenhouse. We also assessed natural variation for adventitious rooting in response to foliar auxin spray. In both experimental approaches, we did not detect a correlation between adventitious rooting and flowering habit. In the greenhouse, and without the application of synthetic auxin, the accession Wca showed higher propensity to produce adventitious roots on the main stem compared to the other accessions. The transcript accumulation of the A. alpina homologue of the auxin inducible GH3.3 gene (AaGH3.3) on stems correlated with the adventitious rooting phenotype of Wca. Synthetic auxin, 1-Naphthaleneacetic acid (1-NAA), enhanced the number of plants with adventitious roots on the main stem and axillary branches. A. alpina plants showed an age-, dosage- and genotype-dependent response to 1-NAA. Among the genotypes tested, the accession Dor was insensitive to auxin and Wca responded to auxin on axillary branches.

Effects of exogenous auxin on stem cutting growth of tea (Camellia sinensis)

Root growth rate of a stem cutting was affected by the auxin levels absorbed by the stem cutting. Level of endogenous auxin was insufficient to stimulate the root growth, so that exogenous auxin should be applied. As synthetic auxin was highly expensive, natural auxin sources gained more attention recently to be used. This study was aimed to determine the best source of exogenous auxin triggering the stem cutting growth of tea (Camellia sinensis). This research was conducted using a completely randomized design with four replicates of each treatment. Source of exogenous auxin used in this study consisted of both synthetic (IBA and Rootone-F™) and natural (goat urine and shallot tuber extract) types. These exogenous auxins were applied into the tea stem cutting before planting through dipping method. Growth parameters related to root, shoot and leaf development were observed. Data were evaluated statistically using one-way anova. Application of 6.000 ppm IBA enhanced the rooting percentage and leaf area. Increase of root length was found in the stem cutting treated with 10% goat urine. These results suggested that each type of exogenous auxin stimulated the root growth in a different way. Therefore, proportional combination of these auxin sources might provide a greater support on root growth of tea stem cutting.

Forecasting the potential of apple fruitlet drop by in-situ Vis-NIR spectroscopy

Apple trees (Malus domestica Borkh.) tend to exhibit a biennial cycle: a heavy-flowering year with an excessive amount of low-quality fruits is followed by a year with scarce flowering and low fruit load. Chemical thinning is currently the only viable solution in large commercial operations to ensure adequate yield. However, most thinners are effective only in the first few weeks following bloom and thinning efficiency depends on numerous factors and is difficult to predict. Forecasting the expected fruitlet drop after an initial thinner application would help perform corrections with the subsequent application. In this study, we used in-situ spectroscopy in the visible and near-infrared (Vis-NIR) range to forecast fruitlets drop rate. The study was carried out on “Golden Delicious” apple trees during two growing seasons – in April 2017 and April 2018. As commonly done in commercial orchards, the fruitlet drop was amplified by the application of synthetic auxins 1-naphthaleneacetic acid (NAA) and its amide (NAD). Fruitlets were tagged and monitored in situ every 2–4 days by measuring reflectance over the 400–1000 nm range. Special care was taken to assess sunlight interference during the measurement and correct it using a custom post-processing procedure. Measurements at 4–12 days after NAA/NAD treatment (days after treatment - DAT) were used to forecast fruitlet drop by 20–26 DAT (prediction dates). Principal component analysis (PCA(was carried out, followed by a classification algorithm (linear or quadratic discriminant analysis). Performing measurements on 4 DAT proved too early to predict fruitlet drop with satisfactory reliability (forecast accuracy 65%). Measurements at 6–12 DAT resulted in forecast accuracies of 80–97%, depending on the selected dates. The method offers a non-destructive prediction of apple fruitlet drop rate, which could lead to the development of a low-cost device that could help manage chemical thinning.

Genome-wide identification, molecular evolution, and expression analysis provide new insights into the APETALA2/ethylene responsive factor (AP2/ERF) superfamily in Dimocarpus longan Lour

BackgroundThe APETALA2/ethylene responsive factor (AP2/ERF) superfamily members are transcription factors that regulate diverse developmental processes and stress responses in plants. They have been identified in many plants. However, little is known about the AP2/ERF superfamily in longan (Dimocarpus longan Lour.), which is an important tropical/subtropical evergreen fruit tree that produces a variety of bioactive compounds with rich nutritional and medicinal value. We conducted a genome-wide analysis of the AP2/ERF superfamily and its roles in somatic embryogenesis (SE) and developmental processes in longan.ResultsA genome-wide survey of the AP2/ERF superfamily was carried out to discover its evolution and function in longan. We identified 125 longan AP2/ERF genes and classified them into the ERF (101 members), AP2 (19 members), RAV (four members) families, and one Soloist. The AP2 and Soloist genes contained one to ten introns, whereas 87 genes in the ERF and RAV families had no introns. Hormone signaling molecules such as methyl jasmonate (MeJA), abscisic acid (ABA), gibberellin, auxin, and salicylic acid (SA), and stress response cis-acting element low-temperature (55) and defense (49) boxes also were identified. We detected diverse single nucleotide polymorphisms (SNPs) between the ‘Hong He Zi’ (HHZ) and ‘SI JI MI’ (SJM) cultivars. The number of insertions and deletions (InDels) was far fewer than SNPs. The AP2 family members exhibited more alternative splicing (AS) events in different developmental processes of longan than members of the other families. Expression pattern analysis revealed that some AP2/ERF members regulated early SE and developmental processes in longan seed, root, and flower, and responded to exogenous hormones such as MeJA, SA, and ABA, and 2,4-D, a synthetic auxin. Protein interaction predictions indicated that the Baby Boom (BBM) transcription factor, which was up-regulated at the transcriptional level in early SE, may interact with the LALF/AGL15 network.ConclusionsThe comprehensive analysis of molecular evolution and expression patterns suggested that the AP2/ERF superfamily may plays an important role in longan, especially in early SE, and in seed, root, flower, and young fruit. This systematic analysis provides a foundation for further functional characterization of the AP2/ERF superfamily with the aim of longan improvement.

Application of synthetic auxin herbicides to suppress seed viability of Italian ryegrass (Lolium perenne ssp. multiflorum) in tall fescue seed production

AbstractItalian ryegrass is one of the most troublesome weeds worldwide because of the rapid evolution of herbicide resistance in this species. Oregon tall fescue seed production requires high seed purity, demanding good control of Italian ryegrass. The necessity to control herbicide-resistant Italian ryegrass and maintain tall fescue seed purity created interest in new chemical management options. The objectives of this study were to assess the effects of synthetic auxin herbicides on seed viability of Italian ryegrass biotypes and the feasibility of this management strategy for use in tall fescue seed production. Eight treatments of synthetic auxin herbicides were applied to Italian ryegrass and tall fescue at two growth stages (boot and anthesis): dicamba (1.0 and 2.2 kg ae ha−1), 2,4-D (1.1 and 2.2 kg ae ha−1), aminopyralid (0.5 kg ae ha−1), dicamba + 2.4-D (0.8 + 1.1 kg ae ha−1), 2.4-D + clopyralid (1.1 + 0.3 kg ae ha−1), and halauxifen-methyl + florasulam (0.4 kg ae ha−1 + 0.4 kg ai ha−1). Aminopyralid applied at boot and anthesis stages of Italian ryegrass reduced seed viability. Aminopyralid treatments reduced seed viability and weight of Italian ryegrass more than 50% compared to the control. Four biotypes from different locations in western Oregon with different types of herbicide resistance were sprayed, and differences in aminopyralid effect among Italian ryegrass biotypes were documented. Aminopyralid reduced the speed of germination by 1 to 2 d. Aminopyralid treatments had a greater effect when applied at the anthesis stage and had a greater negative impact on tall fescue. Tall fescue plants were more susceptible to aminopyralid, so this management practice is not feasible for tall fescue seed production. Future studies are needed to understand the physiological mechanisms involved in the reduced seed viability and to define an optimum aminopyralid rate for different Italian ryegrass biotypes.

Autophagy mediates temporary reprogramming and dedifferentiation in plant somatic cells.

Somatic cells acclimate to changes in the environment by temporary reprogramming. Much has been learned about transcription factors that induce these cell-state switches in both plants and animals, but how cells rapidly modulate their proteome remains elusive. Here, we show rapid induction of autophagy during temporary reprogramming in plants triggered by phytohormones, immune, and danger signals. Quantitative proteomics following sequential reprogramming revealed that autophagy is required for timely decay of previous cellular states and for tweaking the proteome to acclimate to the new conditions. Signatures of previous cellular programs thus persist in autophagy-deficient cells, affecting cellular decision-making. Concordantly, autophagy-deficient cells fail to acclimatize to dynamic climate changes. Similarly, they have defects in dedifferentiating into pluripotent stem cells, and redifferentiation during organogenesis. These observations indicate that autophagy mediates cell-state switches that underlie somatic cell reprogramming in plants and possibly other organisms, and thereby promotes phenotypic plasticity.

Chemically induced male sterility in common wheat mediated by Aegilops cytoplasm

Several approaches have been proposed, in the past, for the development of hybrid wheat varieties. Nevertheless, common wheat hybrids today account for less than 1% of the world's wheat production. The reason for the limited success of hybrid wheat varieties is the fact that to date, a simple and efficient system for the production of hybrid seed has not been developed. A two-line system using photoperiod-sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa Boiss. cytoplasm seems to be very promising way to produce hybrid wheat seed on large scale. Non-desirable side effects of PCMS system are the unreliable sterility of the male sterile lines under different latitudes. Therefore, we tried to connect male sterility system based on Ae. crassa cytoplasm with chemical induction of male sterility. The presented results reveal that the majority of male sterility genes are conserved in the Ae. crassa cytoplasm and that their effects can be promoted by chemical signals, such as synthetic auxins (e.g., 2,4-Dichlorophenoxyacetic acid). Our research work represents the development of a novel male sterility system which is controlled by chemical signals (e.g., synthetic auxins and their pro-herbicide analogues) and mediated by Ae. crassa cytoplasm.

Rapid Degradation of Caenorhabditis elegans Proteins at Single-Cell Resolution with a Synthetic Auxin.

As developmental biologists in the age of genome editing, we now have access to an ever-increasing array of tools to manipulate endogenous gene expression. The auxin-inducible degradation system allows for spatial and temporal control of protein degradation via a hormone-inducible Arabidopsis F-box protein, transport inhibitor response 1 (TIR1). In the presence of auxin, TIR1 serves as a substrate-recognition component of the E3 ubiquitin ligase complex SKP1-CUL1-F-box (SCF), ubiquitinating auxin-inducible degron (AID)-tagged proteins for proteasomal degradation. Here, we optimize the Caenorhabditis elegans AID system by utilizing 1-naphthaleneacetic acid (NAA), an indole-free synthetic analog of the natural auxin indole-3-acetic acid (IAA). We take advantage of the photostability of NAA to demonstrate via quantitative high-resolution microscopy that rapid degradation of target proteins can be detected in single cells within 30 min of exposure. Additionally, we show that NAA works robustly in both standard growth media and physiological buffer. We also demonstrate that K-NAA, the water-soluble, potassium salt of NAA, can be combined with microfluidics for targeted protein degradation in C. elegans larvae. We provide insight into how the AID system functions in C. elegans by determining that TIR1 depends on C. elegans SKR-1/2, CUL-1, and RBX-1 to degrade target proteins. Finally, we present highly penetrant defects from NAA-mediated degradation of the FTZ-F1 nuclear hormone receptor, NHR-25, during C. elegans uterine-vulval development. Together, this work improves our use and understanding of the AID system for dissecting gene function at the single-cell level during C. elegans development.

SYNTHESIS AND PHYTOTOXIC PROFILE OF A NEW TETRAOXANE DESIGNED FROM A COMMERCIAL AUXIN

Modern agriculture relies on the massive use of agrochemicals, including herbicides. Despite their effectiveness, a continuous use of herbicides sharing the same target has resulted in the selection of weed biotypes resistant to such chemicals. To cope with this problem, the development of new herbicides is an urgent requirement. In this work we applied the Active compound Derivatization Method (ADM) strategy to develop a new tetraoxane (5), derived from the synthetic auxin 2-(naphtalen-1-yl)acetic acid (NAA). Greenhouse bioassays showed that 5 caused chlorosis, necrosis and leaf epinasty in Cucumis sativa. Furthermore, this compound, at the concentration of 1.25 x 10-5 mol L-1, inhibited the growth of important weeds such as Bidens pilosa, Iponomea acuminate, Solanum americanum and Althernantera ficoidea. For some weeds, the compound effect was higher or comparable to those caused by commercial glyphosate and imazethapyr. In addition, degradation studies revealed that 5 is transformed into NAA. The results also showed that 5 could act as photosynthesis inhibitor and as an auxin herbicide. In summary, we have discovered a new compound that may be a useful lead for the development of a commercial herbicide.

English

Plant growth and development is significantly influenced by phytohormones – endogenous molecules present naturally in plants. The best known plant hormones are auxins and cytokinins. This study examined the possible effect of externally applied plant hormone analogues (growth regulators): 1-naphthyl acetic acid (NAA) and 6-benzyl aminopurine (BAP) on industrial fibre hemp (Cannabis sativa L., variety Bialobrzeskie). Plants were treated with three different concentrations of NAA (5, 10 and 20 mg/l) and three different concentrations of BAP (10, 25 and 50 mg/l). Morphological and physiological characteristics, such as apical dominance, shoot branching, fibre properties, and flavonoid content were evaluated. The chosen variety of hemp had a significant response to exogenous application of growth regulators, as has been observed with other plant species. Most notably, completely understood and controlled synthetic auxin tretament has a potential to increase the bark fibre yield of hemp.

Auxin-mediated Protein Degradation in Caenorhabditis elegans.

The auxin-inducible degron (AID) technology was recently adapted for use in the nematode Caenorhabditis elegans. Rapid degradation of C. elegans proteins tagged with an AID is mediated by a plant-specific F-box protein, transport inhibitor response 1 (TIR1), and occurs only in the presence of the phytohormone auxin. The first iteration of this technology elicited protein degradation in C. elegans through a naturally occurring form of auxin, indole-3-acetic acid (IAA). Here, we present a protocol that uses 1-naphthaleneacetic acid, potassium salt (K-NAA), an indole-free synthetic auxin analog. At equal concentration, K-NAA is as effective as IAA in standard nematode growth media (NGM). K-NAA is also effective in physiological buffer (M9), allowing for high-throughput experimentation. The main advantages of K-NAA are twofold: first, its photostability prevents light-induced compound degradation during storage and the production of toxic indole-derivatives during fluorescence microscopy of live cells; and second, its water solubility eliminates the need of using ethanol to dissolve the auxin compound, a solvent that may confound C. elegans lifespan and behavioral assays. In this protocol, we describe our method of degrading C. elegans proteins using K-NAA on solid and in liquid media, as well as our method of analyzing protein degradation.

Agroecological aspects of application of Pseudomonas sp. DA1.2 in overcoming herbicidal stress in wheat

This article submits results of laboratory and field experiments on the effect of an auxin-producing bacterial strain Pseudomonas sp. DA1.2 in comparison with Pseudomonas koreensis IB-4 on wheat plants in conjunction with the “Chistalan” herbicide treatment. Our work shows the positive effect of bacterial treatments on plant growth, the relative water content in leaves and the role of bacteria in the redistribution of ABA and IAA in wheat shoots under conditions of herbicidal stress. Application of Pseudomonas sp. DA1.2 together with the herbicide in the field of the steppe zone led to an increase in yield by 20% relative to the control variant. This bacterial strain helps to overcome herbicidal stress and is a promising agent for improving the technology of using synthetic auxins herbicides.

Impact of 2,4-D and potato (Solanum tuberosum L.) tuber age on anthocyanin content of skin and phellem anatomy of Red Norland

Attractive appearance is highly desirable for fresh market red-skinned potatoes. Red potatoes derive their skin color from anthocyanins. Some growers attempt to enhance red potato skin color by treating vines with the synthetic auxin 2,4-D. In this study, 2,4-D was applied twice at early bloom stage to ‘Red Norland’ potatoes and tubers were harvested weekly until plants senesced. 2,4-D rapidly increased anthocyanin quantity and altered anthocyanin composition. Average tuber mass at the final harvest was less for the 2,4-D-treatment than untreated controls. Elevated anthocyanin content resulting from 2,4-D persisted through 3 months storage. 2,4-D-treated potatoes did not differ from untreated controls in the number and depth of red pigmented cells in the phellem. Thus, changes in periderm cell division and expansion may not contribute to the 2,4-D response of ‘Red Norland’. Instead, the data suggest that 2,4-D application initiated a rapid change in anthocyanin accumulation that persisted into storage.

Synthetic auxins concentration and application time modulates seed yield and quality of carrot by altering the umbel order

Quality seed is an essential prerequisite to achieve good yield of a crop. Carrot (Daucus carota) seed quality is affected due to uneven maturation of seeds produced in different umbel orders. Seed quality can be improved by altering the umbel order. Auxins play role in apical dominance and thus can be tested to suppress tertiary umbels in carrot seed crop. A study was conducted to explore the potential of synthetic auxins on alteration of umbel order in carrot seed crop. Significant differences were recorded among different concentrations (0, 100, 200 or 300 mg L−1) of plant growth regulators for growth, yield and seed quality. All growth related traits were improved when Indole acetic acid (IAA) was applied three times at 300 mg L−1. Naphthalene acetic acid (NAA) at 200 mg L−1 or IAA at 100 mg L−1 applied at three times, viz. planting of stecklings (PoS) + 15 days after PoS + 30 days after PoS significantly enhanced number of secondary umbels by suppressing the tertiary umbels. Seed yield and 1000-seed weight of primary, secondary and tertiary umbels was maximum for NAA or IAA at 100 mg L-1 applied three times. Seed quality attributes, viz., final germination, vigour index, enzymatic activity i.e. Superoxide dismutase (SOD), Peroxidase (POD), Catalase (CAT), total antioxidants and total phenolic contents from seeds of primary, secondary and tertiary umbels were increased when three applications of IAA or NAA were done at 200 mg L−1. Moreover, three times application of IAA or NAA at 200 mg L−1 not only minimized the conductivity of seed leachates and malondialdehyde contents from seeds of primary and secondary umbels but also in tertiary umbels seeds. It was concluded that three times foliar application of IAA or NAA at 100 or 200 mg L−1, till 30 days after planting of stecklings, can be effectively used to modify umbel order and hence to increase yield and seed quality. Therefore, seed companies and growers may apply IAA or NAA at 200 mg L−1 for obtaining higher yield of good quality carrot seed.