Coleoptile Elongation Research Articles

Effects of γ-irradiation on elongation and indole-3-acetic acid level of maize (Zea mays) coleoptiles

The effects of γ-irradiation on elongation and the level of indole-3-acetic acid (IAA) of maize (Zea mays) coleoptiles were investigated. When 3-day-old seedlings of maize were exposed to γ-radiation lower than 1 kGy, a temporal retardation of coleoptile elongation was induced. This retardation was at least partly ascribed to a temporal decrease in the amount of free IAA in coleoptile tips on the basis of the following facts: (1) the reactivity to IAA of the elongating coleoptile cells was not altered by irradiation; (2) endogenous IAA level in the tip of irradiated coleoptiles was at first unchanged, but then declined before returning to nearly the same level as that of the non-irradiated control; and (3) the amount of IAA that diffused from coleoptile tip sections showed a similar pattern to that of endogenous IAA. The rate of conversion between free and conjugated IAA was not significantly affected by irradiation. These results suggest that a temporal inhibition of maize coleoptile elongation induced by γ-irradiation can be ascribed to the reduction of endogenous IAA level in the coleoptile tip, and this may originate from the modulation in the rate of IAA biosynthesis or catabolism.

58 Elongation of wheat coleoptile was promoted by brassinolide and suppressed by brassinazole

58 Elongation of wheat coleoptile was promoted by brassinolide and suppressed by brassinazole

Elongation of wheat coleoptile was promoted by brassinolide and suppressed by brassinazole.

Elongation of wheat coleoptile was promoted by brassinolide and suppressed by brassinazole.

Scavenger Properties of Synthetic Naphthenic Methyl Esters

To study the scavenger properties four naphthenic methyl esters were synthesized. The abilities of the compounds to act as radical scavengers were investigated in an experimental epinephrine/adrenochrome model using enzymic and non-enzymic systems. We found that our particular compounds exhibited radical scavenger activity and superoxide-dismutase activity inhibition. Investigated compounds also showed physiological activity. In the auxin test one compound induced elongation of the wheat coleoptile by 35%.

In rice, Oryzalin and abscisic acid differentially affect tubulin mRNA and protein levels

The effect of the anti-microtubular drug Oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on growth and elongation of rice (Oryza sativa L. cv. Arborio) roots and coleoptiles was investigated. At 100 nM, Oryzalin strongly reduced primary root elongation, caused loss of cell anisotropy and the disappearance of the cortical microtubule array. Under these conditions the amounts of alpha- and beta-tubulin protein, but not mRNA, were heavily reduced. Similar data were also obtained in coleoptile segments treated with different concentrations of Oryzalin. However, when coleoptile elongation was inhibited by cis-abscisic acid, remarkable decreases in alpha- and beta-tubulin accumulation were observed to occur at the mRNA level but not at the protein level. The transcriptional decreases could be reversed by re-addition of 3-indole acetic acid. Altogether, these data indicate that rice tubulin accumulation can be controlled at different levels, mRNA or protein, in response to Oryzalin or abscisic acid treatments.

Assessing biological activity of agricultural biostimulants: Bioassays for plant growth regulators in three soil additives

Laboratory bioassays were used to investigate plant growth‐regulating effects of three different experimental soil additives, designated EXP95, W91, and Z96. A yeast growth test was used as a general assay of bioactivity, responses to soil additives were compared to those of known plant growth regulators [indoleacetic acid (IAA), gibberellic acid (GA3), and kinetin]. A corn coleoptile elongation test was used to assay for auxin‐like activity and a dwarf pea bioassay was used for gibberellin‐like activity. The three soil additives were tested at five solution concentrations ranging from 1 to 10,000 ppm (by volume). All three soil additives stimulated yeast growth, depending on the concentration of the test solutions. However, all three soil additives inhibited plant growth in the two plant bioassays. Although this study clearly demonstrated that the three soil additives had significant biological activity at very low concentrations, there was little evidence for auxin‐like or gibberellin‐like activity.

Inheritance of the First Internode Elongation due to Deep-Seeding and Ethylene Treatment in Wheat.

It has been shown that deep-seeding and ethylene stimulate the elongation of the first internodes in wheat seedlings. In the present study, patterns of inheritance in the elongation of wheat first internodes and coleoptiles responding to deep-seeding and ethylene were examined using three crosses. Length of the coleoptile in F2 segregants showed a simple unimodal distribution resembling a normal distribution both in deep-seeded and ethylene-treated plants. Except in one cross, however, length of the first internode in F2 segregants showed a unimodal distributions with large transgressive segregation on the shorter length side in deep-seeded plants and the longer side exceeding the length of parents' first internodes in ethylene-treated plants. These results suggest that ability of plants to respond to ethylene, a regulatory factor for the elongation of the first internode in wheat, can be changed througb genetic recombination.

In growing epidermal cells of rye coleoptiles microtubules are associated with the nuclei

Summary The localization and pattern of microtubules in post-mitotic epidermal cells of coleoptiles of rye seedlings ( Secale cerdale L.) were examined by means of immuno-fluorescence and confocal laser scanning microscopy. In 2-day-old etiolated coleoptiles, which grow by cell elongation, microtubules (MTs) were associated with the nuclei of the cells. In growing 3- and 4-day-old etiolated coleoptiles cortical MTs were observed that were arranged in parallel bundles oriented transverse to the axis of elongation. Cessation of coleoptile elongation was accompanied by a reorientation of the cortical MTs into an oblique and longitudinal direction. Our results support the hypothesis that in growing, non-dividing epidermal cells MTs originate at the nuclear surface or within the nucleus. This organelle may function as a major microtubule nucleating center in the cells of the juvenile rye coleoptile.

Protein synthesis and Golgi-mediated vesicle traffic is not required to maintain a polarised membrane voltage in the presence of auxin

The contribution of protein synthesis and secretion to indol acetic acid (IAA) induced polarisation of the plasma membrane voltage (V M) was investigated. TheV M of coleoptiles fromZea mays was measured in the presence of known inhibitors of protein- and RNA synthesis, as well as those of Golgi-mediated vesicle secretion. Inhibitors were applied under conditions at which they are known to abolish IAA stimulated H+ secretion and cell elongation effectively. Cycloheximide (CHI), an inhibitor of protein synthesis, caused depolarisation ofV M with a half maximal concentration of approximately 20 μM. At 100 μM CHI,V M depolarised to a new stable voltage with a half time of 9.8 ± 0.6 min. The temporal similarity of CHI-induced depolarisation and cessation of coleoptile elongation suggests that the induced change inV M underlies inhibition of elongation. CHI evoked membrane depolarisation to a final voltage of about −100 mV irrespective of the presence or absence of auxin in the external medium. Thus, CHI probably affected constitutive membrane transport properties independently of IAA-induced modulation of transport proteins. Cordycepin (COR), an inhibitor of RNA synthesis, had no significant effect at 400 μM onV M of IAA-treated cells, suggesting that gene transcription for transport- or regulatory protein synthesis was not essential for IAA-generated polarisation ofV M. Brefeldin-A (BFA), an inhibitor of Golgi-mediated vesicle secretion in maize coleoptiles, had no perceivable effect at 20 mg/1 onV M of IAA-treated coleoptile cells, demonstrating that constitutive or IAA-stimulated protein secretion was not essential for the mechanism underlying IAA-evokedV M polarisation. Hence, IAA-stimulated and COR/BFA-depressed H+ extrusion in elongating coleoptiles may not be entirely mediated by auxin-enhanced ATPase activity.

Comparative Physiological Effects of Quinclorac and Auxins, and Light Involvement in Quinclorac-Induced Chlorosis in Corn Leaves

The physiological effects of the herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) in corn and the involvement of light on the herbicide-induced chlorosis were investigated. Quinclorac was highly inhibitory to corn growth. However, different from the tested auxins, quinclorac showed no promotion in an auxinic activity assay (corn coleoptile elongation). Quinclorac induced significantly lower amounts of ethylene in corn coleoptile sections compared with IAA, NAA, and 2,4-D under darkness. Furthermore, quinclorac did not bind with a putative corn membrane-bound auxin receptor. Quinclorac caused chlorotic discoloration in the youngest leaf under light. When the quinclorac-treated corn leaf disks were continuously exposed to light, a significant decrease in total chlorophyll content was observed. No decrease in total chlorophyll content of the herbicide-treated leaf disks under dark conditions was detected. There was a significant correlation between light intensity and the reduction in total chlorophyll content of the leaf disks induced by quinclorac. Moreover, quinclorac considerably increased ethylene production in leaf disks under light conditions, whereas no enhancement of ethylene production in the dark was observed. 2,4-D slightly stimulated ethylene production under both the light and dark conditions. There was a high negative correlation between quinclorac-induced ethylene production and total chlorophyll content in quinclorac-treated leaf disks. These results suggest that the physiological actions of quinclorac applied to corn are not necessarily the same as 2,4-D and other auxins. Ethylene biosynthetic reaction may be closely related with the major herbicidal action of quinclorac, similar to that of 2,4-D. However, our data indicate that the quinclorac-enhanced ethylene biosynthetic reaction and the herbicide-induced chlorosis in corn leaves are light dependent.

Comparison of Reversal of Abscisic Acid-Induced Inhibition of Seed Germination and Seedling Growth of Some Gramineae and Liliaceae Members by Kinetin and Gibberellic Acid

The degrees of reversal of the known inhibitory effect of abscisic acid (ABA) on seed germination and seedling growth by kinetin and gibberellic acid (GA3) were compared. For this purpose, the seeds of five members of Gramineae and three of Liliaceae were germinated in Petri dishes containing ABA and its combinations with kinetin and/or GA3 at 20¼C in continuous darkness for 7 days. At the end of the study, which investigated relative effectiveness in reversing the inhibitory properties of ABA on percentages of seed germination, coleoptile emergence and the time course of germination, it was determined that while GA3 alone and kinetin + GA3 for the most part had the same degree of effectiveness in Gramineae, GA3 alone was more effective in the other cases and in all cases had an effect far superior to that of kinetin alone. Kinetin was generally ineffective within these parameters. In overcoming ABA inhibition of radicle elongation, although GA3 and kinetin + GA3 were generally equally effective in barley and wheat, GA3 was superior in the other cases. Kinetin alone was largely ineffective in this parameter as well. Although the kinetin + GA3 combination was more effective than GA3 alone in overcoming ABA inhibition of coleoptile elongation in barley and wheat cultivars, GA3 alone was for the most part more effective in the other species. Kinetin alone was either successful to a lesser extent or entirely unsuccessful. In this parameter as well, GA3 had a well above that of kinetin. It is concluded from the findings that GA3 may be far more effective than kinetin in overcoming ABA inhibition of seed germination and seedling growth in Gramineae and Liliaceae.

Physiology and Genetics of Submergence Tolerance in Rice

We review a multidisciplinary approach to improve flooding tolerance in rice and, specifically, tolerance of complete submergence. Environmental characterizations in India and Thailand suggest that limited gas diffusion and, sometimes, low irradiance are the most important factors contributing to plant mortality. This supports the view that submergence tolerance of rice seedlings is related to maintenance of energy supply partly through fast rates of alcoholic fermentation which require high levels of carbohydrates. In germinating seeds, rates of coleoptile elongation during anoxia are highly correlated with rates of alcoholic fermentation and carbohydrate supply for energy production. In older seedlings, survival during submergence is highly correlated with carbohydrate supply. Optimization of growth vs. maintenance processes affects survival because elongation growth competes for energy and carbohydrate reserves essential for maintenance processes. This was demonstrated by experiments using: (a) cultivar comparisons, (b) growth regulators and (c) dwarf-mutants. Hence, submergence tolerance of 14-d-old rice seedlings can increase by up to 98 % during 10 d submergence when elongation growth is reduced in these three ways. This is consistent with the observation that submergence tolerance and elongation ability rarely occur in the same genotype. Plant breeding has produced elite lines with up to four-fold greater yields and submergence tolerance equal to the world's most tolerant cultivars, but successful introduction of these elite lines in the field is elusive. Recent production of double haploid populations differing in submergence tolerance permitted testing of the physiological and genetic linkage of traits, or genes, with submergence tolerance. Genetics research with segregating populations of 15- to 50d-old seedlings demonstrated (a) there is one dominant gene for submergence tolerance and (b) this gene is present in three out of four of the world's most tolerant rice cultivars. This suggests that a common factor related to tolerance of limited gas diffusion, (e.g. one of the enzymes of alcoholic fermentation) may be responsible for genotypic differences in submergence tolerance of rice. An alternative possibility is that a gene for a transcription factor is involved in the expression of a multiple gene cascade that confers submergence tolerance. C 1997 Annals of Botany Company

Opposite effects of fusicoccin and IAA on putrescine synthesis of rice coleop tiles

Changes in polyamine biosynthesis and elongation of etiolated rice coleoptiles (Oryza sativa L. cv. Taichung Native 1) in response to fusicoccin (FC) and indoleacetic acid (IAA) were investigated. FC stimulated coleoptile elongation at concentrations higher than 1 μM but caused a decrease in the levels of free putrescine, spermidine and sper‐mine, as well as in the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50). The extent to which FC caused these effects was dependent on its concentration. Treatment with 100 μM IAA also induced coleoptile elongation and resulted in a decrease in free spermidine/sper‐mine and SAMDC activity. However, treatment with IAA resulted in an increase in free putrescine levels and ADC activity. The extent of coleoptile elongation and putrescine accumulation also depended on IAA concentration. α‐Difluoromethylarginine (DFMA), an irreversible inhibitor of ADC. but not α‐difluoromethylornithine (DFMO). an irreversible inhibitor of ODC (EC 4.1.1.17), inhibited the LAA‐stimulated coleoptile elongation and putrescine accumulation. Addition of putrescine could not reverse the effect of DFMA.

In vivo evidence for the involvement of phospholipase A and protein kinase in the signal transduction pathway for auxin‐induced corn coleoptile elongation

Auxin‐induced elongation of com coleoptiles is accompanied by cell wall acidification, which depends upon H+‐pump activity. We tested the hypothesis that phospholipase A and a protein kinase are involved in the pathway of auxin signal transduction leading to H+ secretion, and elongation of corn coleoptiles. Initially, the pH of the bath solution at 50–100 μm from the surface of a coleoptile segment (pHo) ranged between 4.8 and 6.6 when measured with an H+‐sensitive microelectrode. Twenty or 50 μM lysophosphatidylcholine, 50 μM linolenic acid or 50 μM arachidonic acid induced a decline in pHo by 0.3 to 2.1 units. The effect was blocked by 1 mM vanadate, suggesting that lysophosphatidylcholine or linolenic acid induced acidification of the apoplast by activating the H+‐pump. Lysophosphatidylcholine and linolenic acid also accelerated the elongation rate of the coleoptiles. While linolenic acid and arachidonic acid, highly unsaturated fatty acids, promoted pHo decrease and coleoptile elongation, linoleic acid, oleic acid, and stearic acid, fatty acids with a lesser extent of unsaturation, had no such effects. The effects of lysophosphatidylcholine, linolenic acid, and arachidonic acid on H+ secretion were not additive to that of indoleacetic acid (IAA), suggesting that lysophospholipids, fatty acids and auxin use similar pathways for the activation of the H+‐pump. The phospholipase A2 inhibitors, aristolochic acid and manoalide, inhibited the IAA‐induced pHo decrease and coleoptile elongation. The general protein kinase inhibitors, H‐7 or staurosporine, blocked the IAA‐ or lysophosphatidylcholine‐induced decrease in pHo. H‐7 also inhibited the coleoptile elongation induced by IAA or lysophosphatidylcholine. These results support the hypothesis that phospholipase A is activated by auxin, and that the products of the enzyme, lysophospholipids and fatty acids, induce acidification of the apoplast by activating the H+‐pump through a mechanism involving a protein kinase, which in turn promotes com coleoptile elongation.

In vivo evidence for the involvement of phospholipase A and protein kinase in the signal transduction pathway for auxin-induced corn coleoptile elongation

In vivo evidence for the involvement of phospholipase A and protein kinase in the signal transduction pathway for auxin-induced corn coleoptile elongation

Changes in cellular osmotic potential and mechanical properties of cell walls during light‐induced inhibition of cell elongation in maize coleoptiles

The growth rate of maize (Zea mays L. cv. Cross Bantam T51) coleoptiles in the dark was highest at the basal zone and decreased towards the tip. Growth was strongly inhibited by white fluorescent light (5 W m−2), especially in the basal zone of coleoptiles. Light irradiation caused an increase in the values of stress‐relaxation parameters, the minimum stress‐relaxation time and the relaxation rate and a decrease in the extensibility (strain/stress) of the cell walls at all zones. In addition, during growth, the accumulation of osmotic solutes was strongly inhibited by white light irradiation, resulting in an increased osmotic potential. The influences of white light on the mechanical properties of the cell wall and the osmotic potential of the tissue sap were most prominent in the basal zone. Significant correlations were observed between the increment of coleoptile length and the mechanical properties of the cell walls or the osmotic potential of the tissue sap and osmotic solutes content. Furthermore, light inhibited the outward bending of split coleoptile segments. These facts suggest that white light inhibits elongation of maize coleoptiles by modifying both the mechanical properties of the cell walls and cellular osmotic potential, which control the rate of water uptake.

In vitro binding affinities of 4-chloro-, 2-methyl-, 4-methyl-, and 4-ethylindoleacetic acid to auxin-binding protein 1 (ABP1) correlate with their growth-stimulating activities

4-Chlorindole-3-acetic acid (4-CI-IAA), an endogenous auxin in certain plant species of Fabaceae, has a higher efficiency in stimulating cell elongation of grass coleoptiles compared with indole-3-acetic acid (IAA), particularly at low concentrations. However, some investigations reported a 1,000-fold discrepancy between growth stimulation and binding affinity of 4-CI-IAA to auxin-binding protein 1 (ABP1) from maize. Here we report binding data of 4-CI-IAA and three alkylated IAA derivatives using purified ABP1 in equilibrium dialysis. There is a clear correlation between the growth-promoting effects and the binding affinity to ABP1 of the different IAA analogues measured by competition of [3H]naphthalene-1-acetic acid binding. Our data are consistent with the hypothesis that ABP1 mediates auxin-induced cell elongation.

Small inward rectifying K+ channels in coleoptiles: inhibition by external Ca2+ and function in cell elongation.

Plant growth requires a continuous supply of intracellular solutes in order to drive cell elongation. Ion fluxes through the plasma membrane provide a substantial portion of the required solutes. Here, patch clamp techniques have been used to investigate the electrical properties of the plasma membrane in protoplasts from the rapid growing tip of maize coleoptiles. Inward currents have been measured in the whole cell configuration from protoplasts of the outer epidermis and from the cortex. These currents are essentially mediated by K+ channels with a unitary conductance of about 12 pS. The activity of these channels was stimulated by negative membrane voltage and inhibited by extracellular Ca2+ and/or tetraethylammonium-CI (TEA). The kinetics of voltage- and Ca(2+)-gating of these channels have been determined experimentally in some detail (steady-state and relaxation kinetics). Various models have been tested for their ability to describe these experimental data in straightforward terms of mass action. As a first approach, the most appropriate model turned out to consist of an active state which can equilibrate with two inactive states via independent first order reactions: a fast inactivation/activation by Ca(2+)-binding and -release, respectively (rate constants >> 10(3) sec-1) and a slower inactivation/activation by positive/negative voltage, respectively (voltage-dependent rate constants in the range of 10(3) sec-1). With 10 mM K+ and 1 mM Ca2+ in the external solution, intact coleoptile cells have a membrane voltage (V) of -105 +/- 7 mV. At this V, the density and open probability of the inward-rectifying channels is sufficient to mediate K+ uptake required for cell elongation. Extracellular TEA or Ca2+, which inhibit the K+ inward conductance, also inhibit elongation of auxin-depleted coleoptile segments in acidic solution. The comparable effects of Ca2+ and TEA on both processes and the similar Ca2+ concentration required for half maximal inhibition of growth (4.3 mM Ca2+) and for conductance (1.2 mM Ca2+) suggest that K+ uptake through the inward rectifier provides essential amounts of solute for osmotic driven elongation of maize coleoptiles.

Cessation of cell elongation in rye coleoptiles is accompanied by a loss of cell-wall plasticity

The mechanism by which endogenous cessation of coleoptile elongation after emergence of the primary leaf is brought about was investigated in rye seedlings (Secale cereale L.) that were either grown in darkness or irradiated with continuous white light. In 3-d-old etiolated (growing) coleoptiles a turgor pressure of 0.59 MPa was measured. In 6-d-old coleoptiles, which had ceased to elongate, cell turgor was 0.51 MPa and thus only 13% lower than in the rapidly growing organ. Hence, the driving force for growth (turgor) is largely maintained. Cell-wall plasticity (E pl ) and elasticity (E el ) were determined with a constant-load extensiometer both in vivo (turgid coleoptile segments) and in vitro (frozen-thawed samples). Cessation of coleoptile elongation was correlated with a 95% reduction in E pl , whereas E el , was only slightly affected. Extension kinetics were measured with living and frozen-thawed segments cut from growing and non-growing coleoptiles. The corresponding stress-strain (load-extension) curves indicate that the cell wall of the growing coleoptile behaves like an elastic-plastic material whereas that of the non-growing organ shows the behaviour of an elastic solid. These data demonstate that E pl , represents a true plastic (irreversible) deformation of the cell wall. It is concluded that cessation of coleoptile growth after emergence of the primary leaf is attributable to a loss of cell-wall plasticity. Hence, a mechanical stiffening of the cell wall and not a loss of turgor pressure may be responsible for the deceleration of cell elongation in the rye coleoptile.

A microtubule‐associated protein in maize is expressed during phytochrome‐induced cell elongation

Plants can adapt their shape to environmental stimuli. This response is mediated by the reorganization of cortical microtubules, a unique element of the cytoskeleton. However, the molecular base of this response has remained obscure so far. In an attempt to solve this problem, signal-dependent changes in the pattern of microtubule-binding proteins were analysed during coleoptile elongation in maize, that is, under the control of the plant photoreceptor phytochrome. Two putative MAPs of 100 kDa (P100) and 50 kDa apparent molecular weights were identified in cytosolic extracts from non-elongating and elongating cells. Both proteins co-assembled with endogenous tubulin, bound to neurotubules and were immunologically related to the neural MAP tau: the P100 protein, depending on the physiological situation, was manifest as a double band and was always found to be heat-stable. In contrast, the 50 kDa MAP was heat-stable only for particular tissues and physiological treatments. The P100 protein was present in all tissues, however in a reduced amount in elongating coleoptiles. The 50 kDa MAP was expressed exclusively upon induction of phytochrome-dependent cell elongation. As shown by immunofluorescence double-staining, an epitope shared by both proteins colocalized with cortical microtubules in situ, but exclusively in elongating cells. In non-elongating cells, only the nuclei were stained. Partially purified nuclei from elongating cells were enriched in P100, whereas the 50 kDa MAP became enriched in a partially purified plasma membrane fraction.