IAA Treatment Research Articles

Transcript Profiles of Auxin Efflux Carrier and IAA-Amido Synthetase Genes Suggest the Role of Auxin on Apple (<i>Malus</i> × <i>domestica</i>) Fruit Maturation Patterns

Auxin has been suggested to play an essential role in regulating apple fruit maturation and ripening, though the molecular function of auxin and its interaction with ethylene during apple fruit development are largely unknown. To understand the function of auxin during apple fruit maturation and ripening, auxin efflux carrier and IAA-amido synthetase encoding genes were identified from the apple genome based on the results of previous microarray analysis. The expression patterns of these genes were analyzed using qRT-PCR during 10 - 12 weeks of fruit maturation for two apple cultivars: “Golden Delicious” (GD) and “Cripps Pink” (CP), which have the distinct patterns of maturation progression. Our results showed that the expressions of auxin efflux carrier and IAA-amido synthetase genes have a correlation with the timing of ethylene biosynthesis pathway activation in both cultivars. The earlier and stronger expression of MdGH3.102 and MdAECFP1 in the fruit of GD, a mid-season cultivar, correlates with the earlier activation of a pre-climacteric ethylene biosynthesis gene of MdACS3, compared with that in CP, a late-ripening apple cultivar. Results of exogenous IAA treatment indicated that the expression patterns of the genes were regulated in a fruit maturity dependent manner. Our results suggested that the dynamics of the auxin level in apple fruit cortex could be one of the key factors influencing the timing of ethylene biosynthesis pathway activation and consequently contributed to the control of the apple maturation progression.

GmPRP2 promoter drives root-preferential expression in transgenic Arabidopsis and soybean hairy roots.

BackgroundPromoters play important roles in gene expression and function. There are three basic types of promoters: constitutive, specific, and inducible. Constitutive promoters are widely used in genetic engineering, but these promoters have limitations. Inducible promoters are activated by specific inducers. Tissue-specific promoters are a type of specific promoters that drive gene expression in specific tissues or organs. Here, we cloned and characterized the GmPRP2 promoter from soybean. The expression pattern indicated that this promoter is root-preferential in transgenic Arabidopsis and the hairy roots of soybean. It can be used to improve the root resistance or tolerance to pathogens, pests, malnutrition and other abiotic stresses which cause extensive annual losses in soybean production.ResultsThe GmPRP2 promoter (GmPRP2p-1062) was isolated from soybean cv. Williams 82. Sequence analysis revealed that this promoter contains many cis-acting elements, including root-specific motifs. The GmPRP2p-1062 and its 5’-deletion fragments were fused with the GUS reporter gene and introduced into Arabidopsis and the hairy roots of soybean to further determine promoter activity. Histochemical analysis in transgenic Arabidopsis showed that GUS activity was mainly detected in roots and hypocotyls in all deletion fragments except GmPRP2p-471 (a 5’-deletion fragment of GmPRP2p-1062 with 471 bp length). GUS activity was higher in transgenic Arabidopsis and hairy roots with GmPRP2p-1062 and GmPRP2p-852 (a 5’-deletion fragment of GmPRP2p-1062 with 852 bp length) constructs than the other two constructs. GUS activity was enhanced by NaCl, PEG, IAA and JM treatments and decreased by SA, ABA and GA treatments in transgenic Arabidopsis.ConclusionsGmPRP2p-1062 is a root-preferential promoter, and its core fragment for root-preferential expression might lie between −369 and +1. GmPRP2p-852 may be useful in the genetic engineering of novel soybean cultivars in the future.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0245-z) contains supplementary material, which is available to authorized users.

Improvement of embryo rescue technique using 4-chloroindole-3 acetic acid in combination with in vivo grafting to overcome barriers in lentil interspecific crosses

Widening the genetic base of minor grain legume crops such as lentil (Lens culinaris Medik.) is important for achieving future gains in productivity. In order to access genes from wild lentil species embryo rescue techniques are required to overcome reproductive barriers. Removing the seed coat from developing 14-day old immature hybrid seeds and culturing the interspecific zygotic embryos in medium containing auxin 4-chloroindole-3 acetic acid (4-Cl-IAA) improved successful hybrid recovery. Addition of 4-Cl-IAA to media also increased shoot proliferation when combined with a low concentration of zeatin. No significant difference in shoot elongation was observed between 4-Cl-IAA or IAA treatments. Hybrid shoots were then successfully grafted in vivo onto faba bean rootstocks. Hybrids were obtained from crosses of L. culinaris with L. tomentosus Ladiz., L. lamottei Czef., and L. odemensis Ladiz. This efficient and simple embryo rescue protocol resulted in seed production of large interspecific F2 populations from inherently weak zygotic embryos produced from wide hybridization.

Effects of indole-3-acetic, kinetin and spermidine assisted with EDDS on metal accumulation and tolerance mechanisms in ramie (Boehmeria nivea (L.) Gaud.)

The effects and mechanisms of indole-3-acetic (IAA), kinetin (KN) and spermidine (Spd) assisted with ethylenediamine disuccinic acid (EDDS) on Cd and Pb accumulation in ramie were investigated by a pot experiment. In the first stage, the optimum concentrations of IAA, KN, and Spd were determined. And the effects of IAA, KN, and Spd at their optimum concentration on the antioxidant enzymes, non-enzymatic antioxidants, and metal accumulation in ramie were evaluated in the secondary stage. The results show that the translocation factor (TF) of Cd and Pb were increased by approximately 47 and 112%, respectively, at the presence of KN in combination with EDDS. In comparison with IAA treatment, Cd and Pb in root symplast were increased, approximately 2.02 and 2.62 times upon the combined application of IAA and EDDS. In addition, the contents of antioxidant enzymes and non-enzymatic antioxidant were increased dramatically through the addition of IAA, KN, and Spd plus EDDS. On the whole, IAA, KN, and Spd assisted with EDDS could significantly alleviate the oxidative stress induced by Cd and Pb in ramie.

Surgical treatment of interrupted aortic arch associated with ventricular septal defect and patent ductus arteriosus in patients over one year of age

Background Interrupted aortic arch (IAA) is a rare congenital anomaly affecting 1.5% of infants with congenital heart disease. Neonatal repair of IAA is required to avoid irreversible pulmonary vascular lesion. However, in China, patients with IAA associated with ventricular septal defect (VSD) and patent ductus arteriosus (PDA) over one year of age are common. So we investigated the outcome of surgical treatment of IAA with VSD and PDA in patients over one year of age. Methods From January 2009 to December 2012, 19 patients with IAA have undergone complete single–stage repair. The patients’ mean age was 4.4 years, ranging 1 to 15 years; and their mean weight was 12.8 kg, ranging 4.2 to 36.0 kg. Fifteen IAA were type A, four were type B. Preoperative cardiac catheterization data were available from all patients. Mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) were measured. The measurements of postoperative pulmonary artery pressure were taken in the operating room at the end of the case. All patients underwent echocardiographic examinations before discharged from the hospital. In addition, cardiac catheterization and echocardiographic examinations were performed during follow–up. Selective brain perfusion through the innominate artery during aortic arch reconstruction was used in all patients. Mean follow–up was (1.6±0.8) years. Results There were two hospital deaths (2/19, 11%). One patient died of pulmonary hypertension crisis, and another died of postoperative low cardiac output. Five cases had other main postoperative complications but no postoperative neurologic complications. Seventeen survivors were followed up, and there were no late deaths or reoperation. Mean cross–clamp duration was (85±22) minutes and selective brain perfusion duration was (34±11) minutes. Two patients required delayed sternal closure at two days postoperatively. Intensive care unit and hospital stays were (9±8) days and (47±24) days, respectively. Pressure gradients across the anastomosis at most recent follow up were less than 22 mmHg. mPAP regressed significantly from preoperative (62.1±8.1) mmHg to postoperative (37.3±11.3) mmHg (P <0.001) and (24.2±6.0) mmHg at six months after discharged from the hospital (P <0.001). The pulmonary vascular resistance also regressed significantly from preoperative (1 501.4±335.7) dyn·s·cm–5 to (485.0±215.1) dyn·s·cm–5 at six months after discharged from the hospital (P <0.001). The majority of the seventeen patients (89%) were in New York Heart Association (NYHA) class I, and 11% remained in NYHA class II. Conclusions Single–stage repair of patients with IAA, VSD and PDA over one year of age can have good surgical results and functional outcomes. Assessment and treatment of pulmonary artery pressure pre–operatively and postoperatively was crucial. mPAP and pulmonary vascular resistance may have regress significantly compared to preoperative values.

Over-expression of SlCycA3 gene in Arabidopsis accelerated the cell cycle transition.

We characterised an A-type cyclin SlCycA3 (AJ243453) from tomato (Solanum lycopersicum L.). Phylogenetic analysis based on the deduced amino acid sequence revealed that SlCycA3 was 71% identical to A3-type cyclin in Nicotiana tabacum L. (CAA63540), 48% identical to its homologue found in Arabidopsis thaliana (NP_199122), and 48% identical to its homologue in Pisum sativum L. (CAB77269). SlCycA3 gene was transformed into Arabidopsis plants in order to study its function. The hypocotyl length of transgenic plants was approximately half the length of wild-type plants, and the cell size in the transgenic lines was also smaller. The transgenic plants had longer roots than the wild type. Overexpression of SlCycA3 gene accelerated the cell cycle from G1/S transition to early M-phase, thereby accelerating the cell division. When the plants were treated with IAA and 3-indolebutyric acid (IBA) for 2 days, the transgenic plants produced more lateral roots than wild type. Treatment with IBA significantly increased the cell number in the G2-phase in transgenic plants compared with wild type after treatment for 10 days, whereas the proportion of cells in the S-phase was strongly increased by IAA treatment both in wild-type and transgenic plants. These results suggest a possible key role for cyclin in regulating root growth and development and provide some evidence of cell division underlying hormone treatment in plants.

Impact of IAA, GA 3 , and ABA on Negative Root Phototropism and Root Growth of Rice

The objective of this research was to investigate the relationship between rice roots negative phototropism and endogenous plant hormone levels, as well as the impact of exogenous hormones on rice root growth. The adventitious roots and primary roots of conventional cultivars Yangdao 6(indica), Nipponbare(japonica), Zhonghua 11(japonica) and its OsPIN1 a over expressed transgenic seedlings were used to observe the process of root negative phototropism, measure contents of endogenous auxin(IAA), gibberellin(GA3) and abscisic acid(ABA) in the bending part of root tips, and investigate the impact of exogenous hormones to rice root morphology and anatomy. Results indicated that seedling roots of both Yangdao 6 and Nipponbare had negative phototropism, and the lateral roots and adventitious roots of Yangdao 6 showed stronger negative phototropism. Plant hormones and negative phototropism of rice root and root development are closely linked. Under unilateral illumination, endogenous IAA, GA3 and ABA levels declined. The content of these phytohormones in the irradiated side was lower than that in the shaded side. The treatment of unilateral light and exogenous IAA induced a large number of root hairs in Yangdao 6. Compared with conventional rice, the angle of negative phototropism was lager in OsPIN1 a transgenic plant. There was no direct relationship between exogenous GA3 and ABA treatments and root negative phototropism of rice. Exogenous ABA inhibited root growth obviously. The total absorption surface area, root number and root length per plant were significantly reduced by ABA treatment. The treatment of 10 μmol L–1ABA not only caused a dysplasia of both meristematic and elongation zone but also promoted the development of the central vascular tissue in root tips.

Carbon-11 Reveals Opposing Roles of Auxin and Salicylic Acid in Regulating Leaf Physiology, Leaf Metabolism, and Resource Allocation Patterns that Impact Root Growth in Zea mays

Auxin (IAA) is an important regulator of plant development and root differentiation. Although recent studies indicate that salicylic acid (SA) may also be important in this context by interfering with IAA signaling, comparatively little is known about its impact on the plant’s physiology, metabolism, and growth characteristics. Using carbon-11, a short-lived radioisotope (t 1/2 = 20.4 min) administered as 11CO2 to maize plants (B73), we measured changes in these functions using SA and IAA treatments. IAA application decreased total root biomass, though it increased lateral root growth at the expense of primary root elongation. IAA-mediated inhibition of root growth was correlated with decreased 11CO2 fixation, photosystem II (PSII) efficiency, and total leaf carbon export of 11C-photoassimilates and their allocation belowground. Furthermore, IAA application increased leaf starch content. On the other hand, SA application increased total root biomass, 11CO2 fixation, PSII efficiency, and leaf carbon export of 11C-photoassimilates, but it decreased leaf starch content. IAA and SA induction patterns were also examined after root-herbivore attack by Diabrotica virgifera to place possible hormone crosstalk into a realistic environmental context. We found that 4 days after infestation, IAA was induced in the midzone and root tip, whereas SA was induced only in the upper proximal zone of damaged roots. We conclude that antagonistic crosstalk exists between IAA and SA which can affect the development of maize plants, particularly through alteration of the root system’s architecture, and we propose that the integration of both signals may shape the plant’s response to environmental stress.

COMMERCIAL PRODUCTION OF GLOBE ARTICHOKE (CYNARA SCOLYMUS L.) IN-VITRO

This work was carried out in the Laboratory of tissue culture Arid Land Agriculture Research Unit (ALARU) Faculty of Agriculture Ain Shams University during the two autumn seasons of 2006 and 2008 in two separated experiments. First: Micropropagation of globe artichoke (Cynara scolymus L.).Second: Acclimatization of plantlets produced from tissue culture condition to the open field. First experiment: data cleared that there is a relationship between the size of shoot-tip and the percentage of survival regenerated and the time needed to regenerate shoots however increasing the size of shoot tip explants from 2 to 5 cm led to a gradual increase in both survival and regenerated shoot percentage. And at the same time reduce the number of days needed to configured healthy shoots. Culturing the shoot tips explants in the media containing the ascorbic acid or citric acid led to a reduction of browning percentagIncreasing the levels of both cytokinins (BA and Kn) from 2.5 to 10.0 mg/L was sufficient to enhance the capability of explants to produce more shoots especially at high level but unfortunately the highest level of both cytokinins (10.0 mg/L) led to obtain callus formation beside shoots production which is undesirable. There are relationship between number of subculture and rates of shoots productions. Increasing the number of subcultures till fifth times increased gradually the number of shoot production and decreased shoot length. IBA added to the media for rooting the regenerated shoots encouraged the root formation (number and length|) than IAA treatments. On the other side addition of activated charcoal to the nutrient media is very important for enhancement root formationConcerning of the second experiment (acclimatization) data reported that culturing the plantlets produced from tissue culture in pots contained vermiculite either alone or in combination with other compounds gave the highest transplants survival percentage (60 - 90 % ) than other substrate treatments.

Influence of exogenous IAA and GA on seed germination, vigor and their endogenous levels in Cunninghamia lanceolata

To improve seed germination of Chinese fir (Cunninghamia lanceolata (Lamb) Hook), IAA and GA3 treatments were applied. The most significant promotion by IAA and GA3 occurred at the concentration of 10−4 M and 10−5 M, respectively. 10−4 M IAA treatment increased germination rate, germination index, seedling length, seedling weight by 41%, 47%, 30%, 28% compared to the control, and 12%, 23%, 15%, 11% compared to target moist chilling. Seed vigor and endogenous hormone levels were analyzed to elucidate the physiological mechanisms. Electrical conductivity test showed that electrolyte leakage rate of the control seeds was 10.4 µS.cm−2.g−1 while it was decreased to 5.6 µS.cm−2.g−1 after 10−4 M IAA soaking. Furthermore, oxygen sensing test showed that 10−4 M IAA treatment increased oxygen metabolism rate (OMR) by 17% and it reduced increased metabolism time (IMT) by 31%, critical oxygen pressure (COP) by 62%, relative germination time (RGT) by 36%, suggesting that IAA promoted seed respiration. In addition, gas chromatography/mass spectrometry analysis showed that IAA soaking reduced endogenous IAA levels by 32% while it increased endogenous GA1 contents by 347%, suggesting that feedback inhibition of IAA biosynthesis and promotion of GA1 biosynthesis might be involved in seed vigor and germination improvement.

Rapid auxin-induced nitric oxide accumulation and subsequent tyrosine nitration of proteins during adventitious root formation in sunflower hypocotyls

Using NO specific probe (MNIP-Cu), rapid nitric oxide (NO) accumulation as a response to auxin (IAA) treatment has been observed in the protoplasts from the hypocotyls of sunflower seedlings (Helianthus annuus L.). Incubation of protoplasts in presence of NPA (auxin efflux blocker) and PTIO (NO scavenger) leads to significant reduction in NO accumulation, indicating that NO signals represent an early signaling event during auxin-induced response. A surge in NO production has also been demonstrated in whole hypocotyl explants showing adventitious root (AR) development. Evidence of tyrosine nitration of cytosolic proteins as a consequence of NO accumulation has been provided by western blot analysis and immunolocalization in the sections of AR producing hypocotyl segments. Most abundant anti-nitrotyrosine labeling is evident in proteins ranging from 25–80 kDa. Tyrosine nitration of a particular protein (25 kDa) is completely absent in presence of NPA (which suppresses AR formation). Similar lack of tyrosine nitration of this protein is also evident in other conditions which do not allow AR differentiation. Immunofluorescent localization experiments have revealed that non-inductive treatments (such as PTIO) for AR develpoment from hypocotyl segments coincide with symplastic and apoplastic localization of tyrosine nitrated proteins in the xylem elements, in contrast with negligible (and mainly apoplastic) nitration of proteins in the interfascicular cells and phloem elements. Application of NPA does not affect tyrosine nitration of proteins even in the presence of an external source of NO (SNP). Tyrosine nitrated proteins are abundant around the nuclei in the actively dividing cells of the root primordium. Thus, NO-modulated rapid response to IAA treatment through differential distribution of tyrosine nitrated proteins is evident as an inherent aspect of the AR development.

Overexpression of Malus xiaojinensis CS1 gene in tobacco affects plant development and increases iron stress tolerance

Iron is one of the essential micronutrients required by all plants and citric acid is considered to be the chelate substance in the long distance transport of iron. The expression of MxCS1 was enriched in active organs—leaf, root and phloem, which was strongly affected by Fe stress and IAA treatment, and weakly by ABA treatment in Malus xiaojinensis seedlings. This gene was introduced into the nongraminaceous plant tobacco, which promotes the synthesis of citrate synthase and increases the content of citric acid. Overexpression of MxCS1 improved Fe stress tolerance in transgenic tobacco and flowers presented morphological abnormalities. Increased expression of MxCS1 in transgenic tobacco plants also resulted in early-flowering and increased concentrations of Fe, Mn, Cu, and Zn in young leaves and flowers. In addition to its role in long-distance metal transport, citric acid may be involved in the regulation of metal transfer within cells. These results suggest that citric acid excess influenced the functions of metal-requiring proteins, including some transcription factors.

Tiller formation in rice is altered by overexpression of OsIAGLU gene encoding an IAA-conjugating enzyme or exogenous treatment of free IAA

Optimization of plant architecture is important for cultivation and yield of cereal crops in the field. Tillering is an essential factor used to determine the overall architecture of cereal crops. It has long been recognized that the development of branching patterns is controlled by the level and distribution of auxin within a plant. To better understand the relationship between auxin levels and tillering in rice, we examined rice plants with increased or decreased levels of free IAA. To decrease IAA levels, we selected the rice IAA-glucose synthase gene (OsIAGLU) from the rice genome database based on high sequence homology with IAA-glucose synthase from maize (ZmIAGLU), which is known to generate IAAglucose conjugate from free IAA. The OsIAGLU gene driven by the Cauliflower Mosaic Virus 35S promoter was transformed into a rice cultivar to generate transgenic rice plants constitutively over-expressing this gene. The number of tillers and panicles significantly increased in the transgenic lines compared to the wild-type plants, while plant height and panicle length decreased. These results indicate that decreased levels of free IAA likely enhance tiller formation in rice. To increase levels of free IAA, we treated rice plants with three different concentrations of exogenous IAA (1 μM, 10 μM and 100 μM) twice a week by spraying. Exogenous IAA treatment at concentrations of 10 μM and 100 μM significantly reduced tiller number in three different rice cultivars. These results indicate that exogenously applied IAA inhibits shoot branching in rice. Overall, auxin tightly controls tiller formation in rice in a negative way.

Transcript profiling of microRNAs during the early development of the maize brace root via Solexa sequencing

To characterize the microRNAs that contribute to the development of brace root, Solexa high-throughput sequencing of three libraries derived from tissues of node (N), nodes with just-emerged brace roots (NR), and nodes with just-emerged brace roots after IAA treatment (NRI) was performed. Total 650,793, 957,303 and 1,082,948 genome-matched unique reads were obtained in N, NR and NRI libraries, respectively. Further analysis confirmed the authenticity of 137 known miRNAs and the discovery of 159 novel miRNAs in maize. 14 conserved and 16 novel miRNAs differentially expressed in brace root, as well as 15 target genes, were identified and validated by qRT-PCR during maize brace root development. Moreover, we identified 9 miRNA precursor-matched novel sRNAs that may form miRNA clusters, as well as 24nt siRNAs in the three libraries. In addition, we suggest that auxin represent a regulator in brace root development and can be regulated at the posttranscriptional level by miRNAs.

Superoxide production induced by short-term exposure of barley roots to cadmium, auxin, alloxan and sodium dodecyl sulfate

Abiotic stress-induced superoxide generation depending on its localization, level, duration and presumably also on the action of other signals may lead to different stress responses. The purpose of this study was to analyze the alterations in superoxide generation and morphogenesis following short-term Cd, IAA and alloxan treatments, during stress and recovery period in barley root tips. At low Cd concentration the transient accumulation of superoxide in the epidermal cells was accompanied by root growth inhibition and radial expansion of cortical cells in the elongation zone of root tips. These morphological changes were very similar to the externally applied IAA-induced responses. However, the role of superoxide generated in the epidermal cells by low concentration of Cd and IAA is probably alone not sufficient for the induction of these processes. SDS as an activator of NOX activity caused a strong accumulation of superoxide in the epidermal cells along the whole root apex but without any changes in root morphology and growth. On the other hand, higher Cd concentrations as well as alloxan stimulated the generation of superoxide in the cortical tissue of the elongation zone of root tip, which was accompanied by the induction of cell death. Our results suggest that enhanced superoxide generation, depending on its localization, level, duration and presumably also on the action of other signals, may lead to altered root morphology (15 μM Cd or IAA), root growth inhibition (alloxan), transient root growth cessation (30 μM Cd) or to the death of cells/root at higher (60 μM) Cd concentrations.

Genome-wide analysis of SAUR gene family in Solanaceae species

The plant hormone auxin plays a vital role in regulating many aspects of plant growth and development. Small auxin up-regulated RNAs (SAURs) are primary auxin response genes hypothesized to be involved in auxin signaling pathway, but their functions remain unclear. Here, a genome-wide search for SAUR gene homologues in Solanaceae species identified 99 and 134 members of SAUR gene family from tomato and potato, respectively. Phylogenetic analysis indicated that the SAUR proteins from Arabidopsis, rice, sorghum, tomato and potato were divided into four major groups with 16 subgroups. Among them, 25 histidine-rich SAURs genes with metal-binding characteristics were found in Arabidopsis, sorghum and Solanaceae species, but not in rice. Using tomato as a model, a comprehensive overview of SAUR gene family is presented, including the gene structures, phylogeny and chromosome locations. Quantitative real-time PCR analysis indicated that 11 randomly selected SlSAUR genes in tomato could be expressed at least in one of the tomato organs/tissues tested. However, different SlSAUR genes displayed distinctive expression levels. SlSAUR16 and SlSAUR71 exhibited highly tissue-specific expression patterns. Almost all of the detected SlSAURs showed an accumulating pattern of mRNA along tomato flower and fruit development. Some of them displayed differential response to exogenous IAA treatment. The abiotic (cold, salt and drought) stresses significantly modified transcript levels of SlSAURs genes. Most of them were down-regulated in response to abiotic stresses (drought, heat and salinity), but SlSAUR58, as a histidine-rich SAUR gene, was up-regulated after salt treatment, indicating that it may play a specific role in the salt signaling transduction pathway. Our comparative analysis provides some basic genomic information for the SAUR genes in the Solanaceae species and will pave the way for deciphering their function during plant development.

Effect of plant growth regulators on growth, flowering and corm production of gladiolus cv. Snow Princess

The earliness in sprouting was observed with all the treatments of IAA and GA3 irrespective of the concentrations, however, the earliest (10.00 days) was recorded in corms dipped in GA3 (1 000 ppm). GA3 was found to be the best in increasing the floret diameter, number of florets/spike, rachis length and field durability of spike and in earliness to flowering. The number of cormels/plant and volume were highly increased by IAA treatment. Both IAA and GA3 were found equally effective in increasing the weight of corm and cormels, diameter of the corm and propagation coefficient, spike length, leaf area and early sprouting of the corms. Among the different modes of application, soaking treatment helps in the efficient absorption of the growth regulator solutions and its effect on sprouting and early vegetative growth is pronounced whereas spraying influences the corm characters and to some extent the flowering behaviour. Soaking + spraying treatment had lasting effect throughout the crop period and hence was superior to all other treatments.

Auxin-responsive grape Aux/IAA9 regulates transgenic Arabidopsis plant growth

We report the characterization of VvIAA9, an auxin/indole-3-acetic acid (Aux/IAA) protein, in grapevine (Vitis vinifera L.). VvIAA9 was expressed abundantly in leaves and berries. VvIAA9 transcription was drastically upregulated from anthesis to onset of ripening (termed véraison), in which berry diameter rapidly increased. Treatment with exogenous IAA induced VvIAA9 expression in grape leaves, suggesting that VvIAA9 is an auxin-responsive Aux/IAA protein. The overexpression of VvIAA9 in Arabidopsis thaliana promoted plant growth, including rapid floral transition. However, no morphological differences were observed between the control plant and the VvIAA9-overexpressing plant. The overexpression of VvIAA9 in Arabidopsis plants rendered the plants hyposensitive to exogenous IAA. The exogenous IAA treatment did not induce VvIAA9-overexpressing Arabidopsis plant growth and expression of IAA-responsive HAT2. Taken together, we conclude that grape Aux/IAA9 protein is likely to play a crucial role as a plant growth regulator.

Regulation of auxin response by miR393-targeted transport inhibitor response protein 1 is involved in normal development in Arabidopsis

miR393, which is encoded by MIR393a and MIR393b in Arabidopsis, post-transcriptionally regulates mRNAs for the F-box auxin receptors TIR1 (Transport Inhibitor Response Protein 1), AFB1 (Auxin Signaling F-box Protein 1), AFB2 and AFB3. However, biological functions of the miR393-TIR1/AFBs module in auxin response and plant development is not fully understood. In the study herein, we demonstrate that miR393 accumulated in response to exogenous IAA treatment, and its induction was due to enhanced MIR393b transcription but not MIR393a. Overexpression of a miR393-resistant form of TIR1 (mTIR1) enhanced auxin sensitivity and led to pleiotropic effects on plant development including inhibition of primary root growth, overproduction of lateral roots, altered leave phenotype and delayed flowering. Furthermore, miR393 level was increased in 35S:mTIR1 plant, suggesting that TIR1 promoted the expression of miR393 by a feedback loop. The interaction between miR393 and its target indicates a fine adjustment to the roles of the miR393-TIR1 module, which is required for auxin responses in plant development.

Abiotic stress–induced inhibition of root growth and ascorbic acid oxidase activity in barley root tip is associated with enhanced generation of hydrogen peroxide

Using short-term treatments, the aim of this study was to analyze the role of hydrogen peroxide in the regulation of AAO activity during Cd, Cu or IAA treatments in barley root tips. For analysis individual barley root segments were obtained by the gradual cutting of each root from the tip to the base 1, 2, 3 or 6 h after short-term treatments. Already a short 30 min exposure of barley roots to Cd induced significant root growth inhibition in a Cd concentration dependent manner, which was accompanied by a marked reduction of AAO activity. At Cu concentration which had no effect on the root growth a significant increase in AAO activity was observed. This increased AAO activity was detected only in ionically-bound CW fraction. In contrast, Cu at higher concentration and IAA inhibited both ionically-bound CW AAO isozymes. Prompt inhibition of AAO activity immediately after short-term treatment was observed only in the case of H2O2 treatment suggesting that H2O2 may act as an inhibitor of AAO. This was further supported by the observation that all Cd-, Cu- or IAA-induced root growth and AAO activity inhibition in barley roots was connected with an elevated production of H2O2.