Application Of IAA Research Articles

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.

Cytokinins: Determinants of Sink Storage Ability

A new study demonstrates that storage organ formation can be induced in the axillary meristem of non-tuberizing plants by ectopic expression of the cytokinin biosynthetic gene LONELY GUY (LOG1).

Effect of foliar application of IAA And GA on sex expression, yield attributes and yield of bitter gourd (Momordica Charantia L.)

Three concentrations of each of IAA viz. 2.5 (T1), 5.0 (T2) and 10 (T3) ppm and GA3 viz. 2.5 (T4), 5.0 (T5) and 10 (T6) ppm were applied as foliar spray on bitter gourd. Results showed a positive stimulatory effect in the increase of female flowers at T3 where the male to female sex ratio was the lowest. The number of fruits, fresh weight of fruits and yield per plant were also found to be the highest at T3. DOI: http://dx.doi.org/10.3329/cujbs.v5i1.13370 The Chittagong Univ. J. B. Sci.,Vol. 5(1 &2):55-62, 2010

Arabidopsis thalianaplants differentially modulate auxin biosynthesis and transport during defense responses to the necrotrophic pathogenAlternaria brassicicola

Although the role of auxin in biotrophic pathogenesis has been extensively studied, relatively little is known about its role in plant resistance to necrotrophs. Arabidopsis thaliana mutants defective in different aspects of the auxin pathway are generally more susceptible than wild-type plants to the necrotrophic pathogen Alternaria brassicicola. We show that A. brassicicola infection up-regulates auxin biosynthesis and down-regulates the auxin transport capacities of infected plants, these effects being partially dependent on JA signaling. We also show that these effects of A. brassicicola infection together lead to an enhanced auxin response in host plants. Application of IAA and MeJA together synergistically induces the expression of defense marker genes PDF1.2 (PLANT DEFENSIN 1.2) and HEL (HEVEIN-LIKE), suggesting that enhancement of JA-dependent defense signaling may be part of the auxin-mediated defense mechanism involved in resistance to necrotrophic pathogens. Our results provide molecular evidence supporting the hypothesis that JA and auxin interact positively in regulating plant resistance to necrotrophic pathogens and that activation of auxin signaling by JA may contribute to plant resistance to necrotrophic pathogens.

Identification of defense-related genes newly-associated with tomato flower abscission

The current abscission model suggests the formation of a post-abscission trans-differentiation of a protective layer as the last step of the process. The present report expands the repertoire of genes activated in the tomato flower abscission zone (AZ), which are likely to be involved in defense responses. We identified four different defense-related genes, including: Cysteine-type endopeptidase, α-Dioxygenase 1 (α-DOX1), HopW-1-1-Interacting protein2 (WIN2), and Stomatal-derived factor-2 (SDF2), that are newly-associated with the late stage of the abscission process. The late expression of these genes, induced at 8-14 h after flower removal when pedicel abscission was already in progress, was AZ-specific, and was inhibited by treatments that prevented pedicel abscission, including 1-methylcyclopropene pretreatment or IAA application. This information supports the activation of different defense responses and strategies at the late abscission stages, which may enable efficient protection of the exposed tissue toward different environmental stresses.

Effects of mother tree ages, different rooting mediums, light conditions and auxin treatments on rooting behaviour of Dalbergia sissoo branch cuttings

Dalbergia sissoo Roxb. is one of the promising multipurpose tree species of South Asia. Most of the plantations of D. sissoo from seeds are facing severe threats due to the die-back disease, which ultimately causes death of this potential tree-species within a few months. Vegetative propagation could avoid the die-back disease. Thirty mother trees of different age-groups of D. sissoo were selected for evaluating the rooting behaviour of branch cuttings from D. sissoo as influenced by auxins (IAA or IBA at 100, 200, 500 mg·L−1), ages of mother trees (10, 4 and 2 years old) and different environment conditions, i.e., different mediums (soil and sand) or light conditions (in shade and open condition). The results show that application of IAA and IBA induced more numbers of cuttings (collected from 10-year-old mother trees) to root compared to control. Branch cuttings of D. sissoo collected from 10-year-old mother trees and planted in soil bed in open conditions had 100.0% of cuttings to root in IAA (100 mg·L−1) and IBA (200 mg·L−1) treatments. Both rooting medium (Soil and sand) influenced significantly (p<0.05) on rooting response of branch cuttings. Soil medium was found to achieve maximum no. of branch cuttings to root, compared to sand medium.

Auxin transport in maize roots in response to localized nitrate supply

background and aims: Roots typically respond to localized nitrate by enhancing lateral-root growth. Polar auxin transport has important roles in lateral-root formation and growth; however, it is a matter of debate whether or how auxin plays a role in the localized response of lateral roots to nitrate. Treating maize (Zea mays) in a split-root system, auxin levels were quantified directly and polar transport was assayed by the movement of [(3)H]IAA. The effects of exogenous auxin and polar auxin transport inhibitors were also examined. Auxin levels in roots decreased more in the nitrate-fed compartment than in the nitrate-free compartment and nitrate treatment appeared to inhibit shoot-to-root auxin transport. However, exogenous application of IAA only partially reduced the stimulatory effect of localized nitrate, and auxin level in the roots was similarly reduced by local applications of ammonium that did not stimulate lateral-root growth. It is concluded that local applications of nitrate reduced shoot-to-root auxin transport and decreased auxin concentration in roots to a level more suitable for lateral-root growth. However, alteration of root auxin level alone is not sufficient to stimulate lateral-root growth.

Effect of growth hormones, seasons and age of cuttings on sprouting and rooting response of three medicinal tree species of Garhwal Himalaya

Hard wood and juvenile cuttings of Aegle marmelos, Sapindus mukorossi and Terminalia bellirica were tested for their capacity to form roots. Cuttings were treated with different concentrations of auxins (IAA, IBA, NAA and 2, 4-D) in four seasons (spring, summer, rainy and winter). Hard wood cuttings of S. mukorossi rooted only in spring season whereas juvenile cuttings of the same species rooted in three seasons (spring, summer and rainy). Hard wood cuttings of the T. bellirica showed only callus formation in spring season whereas the juvenile cutting of T. bellirica proved callus as well as root formation in the same season. A. marmelos failed either to sprout or root throughout the four seasons. Exogenous application of IAA and IBA induced profuse rooting in S. mukorossi and T. bellirica.

Strigolactones’ Effect on Root Growth and Root-Hair Elongation May Be Mediated by Auxin-Efflux Carriers

Strigolactones are a new group of plant hormones that play a pivotal role in the regulation of aboveground plant architecture. However, the mechanisms governing their regulation of plant growth and development are unknown. We characterized the effect of a synthetic strigolactone (GR24) on tomato (Solanum lycopersicon) roots and present evidence for its relationship with the plant hormone auxin. We demonstrate that strigolactones interfere with the inhibitory effect of exogenously applied auxin on root elongation. This GR24-induced root elongation is conveyed via an increase in root cell length accompanied by a reduction in cell diameter, and it occurs despite strigolactone’s reduction of cell division (detected as reduction of CYCB1;1 transcript). In addition, high concentrations of strigolactone lead to asymmetric root growth and inhibition of root-hair elongation. Exogenous application of NAA or IAA was unable to restore symmetric root growth and root-hair elongation in the presence of strigolactone. However, application of NPA, an auxin-efflux inhibitor, did restore root-hair elongation in the presence of strigolactone. Similarly, exogenous application of 2,4-D, a synthetic auxin that is not secreted by efflux carriers, restored root-hair elongation and symmetric growth in the presence of strigolactone. Nevertheless, 2,4-D was unable to prevent root elongation by strigolactones. Therefore, strigolactones’ effect on root growth and root-hair elongation appears to be mediated via an effect on auxin-efflux carriers. Nevertheless, more than one mechanism may govern strigolactones’ effect on root growth.

Cloud Computing: Distributed Internet Computing for IT and Scientific Research

Cloud computing is a disruptive technology with profound implications not only for Internet services but also for the IT sector as a whole. Its emergence promises to streamline the on-demand provisioning of software, hardware, and data as a service, achieving economies of scale in IT solutions' deployment and operation. This issue's articles tackle topics including architecture and management of cloud computing infrastructures, SaaS and IaaS applications, discovery of services and data in cloud computing infrastructures, and cross-platform interoperability. Still, several outstanding issues exist, particularly related to SLAs, security and privacy, and power efficiency. Other open issues include ownership, data transfer bottlenecks, performance unpredictability, reliability, and software licensing issues. Finally, hosted applications' business models must show a clear pathway to monetizing cloud computing. Several companies have already built Internet consumer services such as search, social networking, Web email, and online commerce that use cloud computing infrastructure. Above all, cloud computing's still unknown "killer application" will determine many of the challenges and the solutions we must develop to make this technology work in practice.

Effects of top excision on the potassium accumulation and expression of potassium channel genes in tobacco

The effects of the removal of the shoot apex of tobacco on the relative transcript levels of potassium channel genes, determined by real-time PCR, and on the relationship between the expression of genes encoding potassium channels and potassium concentration, were studied. The results from the study indicated that comparatively more assimilates of photosynthesis were allocated to the apex in control plants than in both decapitated and IAA-treated decapitated plants. By contrast, dry matter in the upper leaves, roots, and stems in both decapitated and IAA-treated plants was significantly increased relative to control plants. The potassium level in whole plants decreased post-decapitation compared with control plants, and so did the potassium concentration in middle and upper leaves, stem, and roots. Expression of NKT1, NtKC1, NTORK1, and NKT2 was inhibited by decapitation in tobacco leaves with a gradual reduction after decapitation, but was induced in roots. The relative expression of NKT1, NTORK1, and NKT2 in tobacco leaves was higher than that in roots, whereas the expression of NtKC1 was higher in roots. The levels of inhibition and induction of NKT1, NtKC1, NTORK1, and NKT2 in leaves and roots, respectively, associated with decapitation were reduced by the application of IAA on the cut surface of the decapitated stem. Further results showed that the level of endogenous auxin IAA in decapitated plants, which dropped in leaves and increased in roots by 140.7% at 14 d compared with the control plant, might be attributed to the change in the expression of potassium channel genes. The results suggest that there is a reciprocal relationship among endogenous auxin IAA, expression of potassium channel genes and potassium accumulation. They further imply that the endogenous IAA probably plays a role in regulating the expression of potassium channel genes, and that variations in expression of these genes affected the accumulation and distribution of potassium in tobacco.

EFFECT OF TRANSPLANT AGE AND SOME GROWTH REGULATORS ON PRODUCTIVITY OF CANOLA CROP.

Two field experiments were carried out at El-Gemmeiza Agric. Res. Station, Gharbia Governorate, during 2005 / 2006 and 2006 / 2007 seasons, to study the effect of transplanting canola seedling at different ages (30, 45 and 60 days as well as direct seeding) and preplanting soaking canola transplants, in GA3, IAA and NAA and without dipping (control treatment), on growth, yield and yield attributes of canola seeds (Srew 4). The treatment took of stages of 30 days from seeding the seeding were soaked for 24 hours just before transplanting using control without soaking. Results indicated that, the differences between transplanting treatments as well as direct seeding for number of days to 50% flowering, plant height (cm), number of branches / plant, fruiting zone length, seed yield / plant (g), 1000 – seed weight (g), seed yield kg/fad. and oil seed percentage were significant in the two seasons. Transplanting canola plants at 45 days old gave the highest values for all attributes studied in both seasons, except No. of branches/plant and oil percentage. While, transplanting after 30 days produced the highest values for number of branches / plant and seed oil percentage in the two seasons. The minimum values of the above attributes studied were obtained by sowing seed directly. IAA application significantly increased all attributes studied in first and second seasons. Interaction between transplanting and soaking treatments showed significant increase for all attributes studied except number of branches / plant, 1000 – seed weight (g) and seed oil percentage in both seasons.

Ethylene and IAA interactions in the inhibition of photoperiodic flower induction of Pharbitis nil

It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis.

Roles of Auxin and Cytokinin in Soybean Pod Setting

Soybean plants differentiate abundant floral buds, but most of them fail to grow pods and abort during development. Many studies indicated promotive effects of exogenously applied cytokinin on pod setting, but the effects of auxin application on pod set are ambiguous. In this study, we examined the changes in the concentrations of endogenous auxin and cytokinin in racemes and the effects of application of the two hormones on pod setting to clarify the role of auxin and cytokinin in soybean pod setting. The long-raceme soybean genotype IX93-100 was grown in pots and in the field. The auxin (IAA, indoleacetic acid) concentration in racemes was high for a long period from pre-anthesis to 9 days after anthesis (DAA) of the first flower on a raceme, but the cytokinin concentration was high for a short period, with a peak at 9 DAA. The IAA concentration was higher in distal portions of racemes, but the cytokinin concentration was higher in basal portions of racemes. In pot-grown plants, IAA applied to racemes tended to reduce the number of flowers and pods. In contrast, 6-benzylaminopurine (BA) applied to racemes before anthesis tended to reduce the number of flowers and pods, and that applied around 7 DAA significantly increased the pod-set percentage. However, these effects of IAA and BA application were slight in field-grown plants. These results indicate that the concentration of endogenous auxin and cytokinin in racemes changes in a different manner, and that cytokinins have a positive, and auxin a negative effect on pod setting when respective hormones are applied to racemes after the anthesis stage.

Characterizations and fine mapping of a mutant gene for high tillering and dwarf in rice (Oryza sativa L.)

A rice htd-1 mutant, related to tillering and dwarfing, was characterized. We show that the htd-1 mutant increases its tiller number by releasing axillary buds from dormant stage rather than by initiating more axillary buds. The dwarf is caused by averagely reducing each internode and panicle. Based on this dwarfing pattern, the htd-1 mutant could be grouped into dn-type dwarf defined by Takeda (Gamma Field Symp 16:1, 1977). In addition, the dwarfing of the htd-1 mutant was found independent of GA based on the analyses of two GA-mediated processes. Based on the quantitative determination of IAA and ABA and application of the two hormones exogenously to the seedlings, we inferred that the high tillering capacity of the htd-1 mutant should not be attributed to a defect in the synthesis of IAA or ABA. The genetic analysis of the htd-1 mutant indicated that the phenotypes of high tillering and dwarf were controlled by a recessive gene, termed htd1. By map-based cloning, the htd1 gene was fine mapped in a 30-kb DNA region on chromosome 4. Sequencing the target DNA region and comparing the counterpart DNA sequences between the htd-1 mutant and other rice varieties revealed a nucleotide substitution corresponding to an amino acid substitution from prolin to leucine in a predicted rice gene, OsCCD7, the rice orthologous gene of AtMAX3/CCD7. With the evidence of the association between the presence of one amino acid change in OsCCD7 and the abnormal phenotypes of the htd-1 mutant, OsCCD7 was identified as the candidate of the HTD1 gene.

Ameliorative Effect of Chlormequat Chloride and IAA on Drought Stressed Plants of Cymbopogon Martinii and C. winterianus

Responses of Cymbopogon martinii and C. winterianus to drought stress and chlormequat chloride and IAA application are compared. These two species are important source of essential oil production in drought regions. For both species and their cultivars relative water content (RWC), herbage yield and oil amount decreased under drought, while oil biosynthesis increased. Oil concentration increased significantly under drought in C. winterianus while peroxidase activity increased in C. martinii. Amount of geraniol increased under drought stress in C. martinii while citronellal and geraniol accumulation decreased in C. winterianus. Ameliorative effects of chlormequat chloride and IAA were observed in drought stressed plants of both species. Herbage yield increased significantly in chlormequat chloride and IAA treated stressed plants of C. winterianus, while oil concentration increased in C. martinii. Ameliorative effect of IAA in increasing oil yield was significant in drought stressed plants of both the species. Changes in various morpho-physiological traits indicated that chlormequat chloride and IAA can partially alleviate the detrimental effect of drought in these aromatic grasses.

Hormone-induced protection of sunflower photosynthetic apparatus against copper toxicity

The effects of excess Cu as affected by the application of exogenous hormones (gibberellic acid - GA3 and indole-3-acetic acid - IAA) with respect to sunflower (Helianthus annuus L.) growth, physiology, and metabolism were studied. Application of 100 μM IAA lessened the toxic effects of 80 μM Cu in roots indicating greater root length and root hair formation, while addition of 100 μM GA3 ameliorated the toxic effect mainly to the shoot. The content of photosynthetic pigments significantly declined under Cu stress, whereas application of hormones led to a substantial preservation of chlorophylls and carotenoids. Under Cu stress, the rate constant of energy trapping by photosystem 2 (PS2) reaction centres (RCs) was reduced as a result of physical dissociation of the light-harvesting complex (LHC) from PS2 core, while application of IAA and especially GA3 resulted in stability of the LHC of PS2 RCs. The drop in net photosynthetic (PN) and transpiration (E) rates with preserved or slightly reduced variable to maximum fluorescence ratio (Fv/Fm) in the presence of 80 μM Cu could be explained by a possible inhibition of the enzymatic processes in the Calvin cycle. Application of 100 μM IAA and 100 μM GA3 lessened Cu effects mainly on PN. Water use efficiency was also improved under hormone exposure.

Effects of IAA and IAA precursors on the development, mineral nutrition, IAA content and free polyamine content of pepper plants cultivated in hydroponic conditions

The effect of IAA and two IAA precursors, l-tryptophan (Trp) and indole (Ind), on the growth, mineral nutrition and potential development under stress conditions of intact pepper plants cultivated in hydroponic conditions, has been studied. To this end, the growth of both shoots and roots, the plant content of both IAA and free polyamines and the content in leaves and roots of macronutrients and micronutrients have been evaluated. Both Trp and Ind presented a similar pattern of action to that of IAA regarding both plant development and mineral uptake. The application of Ind and Trp at the highest dose (10 −3 M) was associated with significant increases of IAA content in roots. The application of IAA and IAA precursors was associated with an increase in Spermine and a decrease in Putrescine in leaves, thus suggesting the conversion of Putrescine into Spermidine and Spermine, which in turn could be associated with better plant development under stress. Both Trp and Ind showed auxin-like effects likely due to their conversion into IAA within the plant. However, further studies carried out under axenic conditions are needed in order to clarify this question.

Leaf growth and K+/Na+ ratio as an indication of the salt tolerance of three sorghum cultivars grown under salinity stress and IAA treatment

The salt tolerance of three sorghum (Sorghum bicolor L.) cultivars (Dorado, Hagen Shandawil and Giza 113) and their responses to shoot spraying with 25 ppm IAA were studied. Salinity stress induced substantial differences between the three sorghum cultivars in the leaf area, dry mass, relative water content and tolerance index of the leaves. Dorado and Hagen Shandawil tolerated salinity up to 88 and 44 mM NaCl, respectively, but above this level, and at all salinity levels in Giza 113, a significant reduction in these parameters was recorded. The rate of reduction was lower in Dorado than in Hagen Shandawil and Giza 113, allowing the sequence Dorado ? Hagen Shandawil ? Giza 113 to be established for the tolerance of these cultivars to salinity. The differences in the tolerance of the sorghum cultivars were associated with large differences in K+ rather than in Na+, which was found to be similar in the whole plant. The youngest leaf was able to maintain a higher K+ content than the oldest leaf. Consequently the K+/Na+ ratios were higher in the most salt-tolerant cultivar Dorado than in the other sorghum cultivars, and in the youngest than in the oldest leaf. In conformity with this mechanism, the stimulatory effect of the exogenous application of IAA was mostly associated with a higher K+/Na+ ratio. Shoot spraying with IAA partially alleviated the inhibitory effect of salinity on leaf growth and on the K+ and Ca2+ contents, especially at low and moderate levels of salinity, while it markedly retarded the accumulation of Na+ in the different organs of sorghum cultivars. Abbreviations: LA: Leaf area, DM: Dry mass, I Indole acetic acid, RWC: Relative water content,TI: Tolerance index

Repressed ethylene production in the gynoecium of long-lasting flowers of the carnation 'White Candle': role of the gynoecium in carnation flower senescence.

Ethylene production and expression of ethylene biosynthetic genes was investigated in senescing flowers of carnation (Dianthus caryophyllus L.) cultivars 'White Candle (WC)' and 'Light Pink Barbara (LPB)', with long and short vase-lives, respectively. Ethylene production from the gynoecium and petals of senescing 'WC' flowers was below the limit of detection, in agreement with the repressed ethylene production from the whole flowers. However, exogenous ethylene treatment caused the accumulation of transcripts for DC-ACS1 and DC-ACO1 genes in both the gynoecium and petals, resulting in ethylene production from the flowers. Moreover, application of ABA or IAA, which are known to exhibit their action through the induction of ethylene synthesis in the gynoecium, to 'WC' flowers from their cut stem-end induced ethylene production and wilting in the flowers. These findings suggested that, in 'WC' flowers the mechanism of ethylene biosynthesis, i.e. the induction of expression of genes for ethylene biosynthesis and the action of resulting enzymes, was not defective, but that its function was repressed during natural senescence. Transcripts of DC-ACO1, DC-ACS3, and DC-ACS1 were present in the gynoecium of senescing 'LPB' flowers. In the gynoecium of senescing 'WC' flowers, however, the DC-ACO1 transcript was present, but the DC-ACS1 transcript was absent and the DC-ACS3 transcript was detected only in a small amount; the latter two were associated with the low rate of ethylene production in the gynoecium of 'WC' flowers. These findings indicated that the repressed ethylene production in 'WC' flowers during natural senescence is caused by the repressed ethylene production in the gynoecium, giving further support for the role of the gynoecium in regulating petal senescence in carnation flowers.