Coleoptile Sections Research Articles

Hormesis in Plants: The Role of Oxidative Stress, Auxins and Photosynthesis in Corn Treated with Cd or Pb.

Hormesis, which describes the stimulatory effect of low doses of toxic substances on growth, is a well-known phenomenon in the plant and animal kingdoms. However, the mechanisms that are involved in this phenomenon are still poorly understood. We performed preliminary studies on corn coleoptile sections, which showed a positive correlation between the stimulation of growth by Cd or Pb and an increase in the auxin and H2O2 content in the coleoptile sections. Subsequently, we grew corn seedlings in hydroponic culture and tested a wide range of Cd or Pb concentrations in order to determine hormetic growth stimulation. In these seedlings the gas exchange and the chlorophyll a fluorescence, as well as the content of chlorophyll, flavonol, auxin and hydrogen peroxide, were measured. We found that during the hormetic stimulation of growth, the response of the photosynthetic apparatus to Cd and Pb differed significantly. While the application of Cd mostly caused a decrease in various photosynthetic parameters, the application of Pb stimulated some of them. Nevertheless, we discovered that the common features of the hormetic stimulation of shoot growth by heavy metals are an increase in the auxin and flavonol content and the maintenance of hydrogen peroxide at the same level as the control plants.

Growth-limiting proteins in maize coleoptiles and the auxin-brassinosteroid hypothesis of mesocotyl elongation.

The shoot of grass coleoptiles consists of the mesocotyl, the node, and the coleoptile (with enclosed primary leaf). Since the 1930s, it is known that auxin (indole-3-acetic acid, IAA), produced in the tip of the coleoptile, is the central regulator of turgor-driven organ growth. Fifty years ago, it was discovered that antibiotics that suppress protein biosynthesis, such as cycloheximide, inhibit auxin (IAA)-induced cell elongation in excised sections of coleoptiles and stems. Based on such inhibitor studies, the concept of "growth-limiting proteins (GLPs)" emerged that was subsequently elaborated and modified. Here, we summarize the history of this idea with reference to IAA-mediated shoot elongation in maize (Zea mays) seedlings and recent studies on the molecular mechanism underlying auxin action in Arabidopsis thaliana. In addition, the analysis of light-induced inhibition of shoot elongation in intact corn seedlings is discussed. We propose a concept to account for the GLP-mediated epidermal wall-loosening process in coleoptile segments and present a more general model of growth regulation in intact maize seedlings. Quantitative proteomic and genomic studies led to a refinement of the classic "GLP concept" to explain phytohormone-mediated cell elongation at the molecular level (i.e., the recently proposed theory of a "central growth regulation network," CGRN). Novel data show that mesocotyl elongation not only depends on auxin but also on brassinosteroids (BRs). However, the biochemical key processes that regulate the IAA/BR-mediated loosening of the expansion-limiting epidermal wall(s) have not yet been elucidated.

Tissue culture characteristics of maize (Zea mays L.) haploid coleoptile sections.

Doubled haploid (DH) technology, which is used for rapidly purifying genetic resources, is a key technology in modern maize breeding. The present study evaluated the tissue culture characteristics of maize haploid coleoptile sections, in order to provide a new way of haploid doubling. With 20 combinations of haploid coleoptile sections, obtained by hybridization within Reid, Tangsipingtou, and Term-tropical groups, as explants, we analyzed the induction and differentiation rate of callus, observed the number of root tip chromosomes in regenerated plants, and analyzed the pollen fertility. In addition, we used 47 SSR markers to analyze the genotypes of regenerated plants. The Reid and Tangsipingtou groups had significantly higher induction rates of haploid coleoptile callus compared to the Term-tropical group. Fifteen haploid plants were obtained which had 10 chromosomes in the root tips as assessed by I-KI staining. It was also noticed that the pollen of pollinated anthers were partially fertile. The haploid plants had genetic stability and showed no variation. The Reid and Tangsipingtou groups had good culture characteristics of haploid coleoptile sections, while the Term-tropical group had poor culture characteristics. Genotypes of haploid plants generated by tissue culture were evidenced to come from recombinant types of parents. Thus, this study established a tissue culture system of maize haploid coleoptile.

Growth response of coleoptile sections of several Polish varieties of wheat to some growth-regulators

Growth response of coleoptile sections of several Polish varieties of wheat to some growth-regulators

Resin acids as the potential growth-affecting component of pine oleoresin

The nonvolatile fraction of the oleoresin of <i>Pinus sihestris</i> L. was found to contain substances which inhibit growth of wheat ceoleoptile and oat mesocotyl sections in standard bioassays. The inhibition is mainly confined to the fraction of resin acids. Among the seven authentic resin acids tested, the effects of dehydroabietic and abietic acids were most sifgnificant. Palustric, pimaric and isopimaric acids were not effective in the wheat coleoptile section straight growth test. None of the substances, in the amounts tested, except for extremely high concentration, exerted an inhibitory effect on natural or IAA-induced elongation of pine hypocotyl sections. Neither was an inhibitory effect discovered in the microbiological test with the <i>Aspergillus niger</i> van Tiegh. The results obtained with pine hypocotyl sections, allow the conclusion that resin acids interfering with the results of standard bioassays are probably not effective as inhibitory factors in the regulation of pine tissue growth.

Rapid auxin‐mediated changes in the proteome of the epidermal cells in rye coleoptiles: implications for the initiation of growth

In axial organs of juvenile plants, the phytohormone auxin (indole-3-acetic acid, IAA) rapidly mediates cell wall loosening and hence promotes turgor-driven elongation. In this study, we used rye (Secale cereale) coleoptile sections to investigate possible effects of IAA on the proteome of the cells. In a first set of experiments, we document that IAA causes organ elongation via promotion of expansion of the rigid outer wall of the outer epidermis. A quantitative comparison of the proteome (membrane-associated proteins), using two-dimensional difference gel electrophoresis (2-D DIGE), revealed that, within 2 h of auxin treatment, at least 16 protein spots were up- or down-regulated by IAA. These proteins were identified using reverse-phase liquid chromatography electrospray tandem mass spectrometry. Four of these proteins were detected in the growth-controlling outer epidermis and were further analysed. One epidermal polypeptide, a small Ras-related GTP-binding protein, was rapidly down-regulated by IAA (after 0.5 h of incubation) by -35% compared to the control. Concomitantly, a subunit of the 26S proteasome was up-regulated by IAA (+30% within 1 h). In addition, this protein displayed IAA-mediated post-translational modification. The implications of these rapid auxin effects with respect to signal transduction and IAA-mediated secretion of glycoproteins (osmiophilic nano-particles) into the growth-controlling outer epidermal wall are discussed.

ChemInform Abstract: Synthesis, Biological Activity and Metabolism of N-Hydroxytryptophan.

Abstract N -Hydroxytryptophan (α-hydroxyamino-β-indolyl-3-propionic acid) was chemically synthesized. On a mole basis, its relative biological activity in comparison with indole-3-acetic acid at sub-optimal concentrations is: oat coleoptile curvature test=0.129; oat first internode test=0.089 and linseed root growth inhibition test=0.022. Infiltration of N -hydroxytryptophan into oat coleoptile sections leads to the production of indoleacetaldehyde oxime, indoleacetaldehyde and indoleacetic acid. It is suggested that tryptophan could be metabolized in oat coleoptiles to indole-3-acetic acid via N -hydroxytryptophan, indoleacetaldehyde oxime and indoleacetaldehyde.

Degradation Studies on Benzoxazinoids. Soil Degradation Dynamics of (2R)-2-O-β-d-Glucopyranosyl-4-hydroxy-(2H)- 1,4-benzoxazin-3(4H)-one (DIBOA-Glc) and Its Degradation Products, Phytotoxic Allelochemicals from Gramineae

Wheat (Triticum aestivum L.) has been found to possess allelopathic potential and studies have been conduced to apply wheat allelopathy for biological weed control. 2,4-Dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) is a common product found in wheat, corn, and rye exudates and it can be released to the environment by that way. In this report, the stability of DIBOA is studied in two soils from crop lands of wheat cv. Astron and cv. Ritmo. These varieties were selected by their concentrations of DIBOA and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA) from aerial parts and by the bioactivities of their aqueous extracts in the growth of wheat coleoptile sections. The degradation rate of DIBOA in these soils was measured in laboratory tests during 90 h by high-pressure liquid chromatography methods. These analyses demonstrate that DIBOA was transformed primarily into 2-benzoxazolinone (BOA). This transformation was similar in both soil types with an average half-life of 43 h. The degradation studies for BOA show its biotransformation to 2-aminophenoxazin-3-one (APO) with a half-life of 2.5 days. Therefore, BOA is an intermediate product in the biotransformation from DIBOA to APO in these wheat crop soils and is consistent with previous findings. APO was not degraded after three months in soil, suggesting that its degradation rate in soil is very slow.

A New Inhibitor of Auxin-induced Growth, 5-Chloro-6methoxy-2-benzoxazolinone, from Light-grown Shoots of Maize Seedlings

A new inhibitor of auxin-induced growth was isolated from light-grown shoots of maize seedlings (Zea mays L.) and its chemical structure was determined by spectral data as 5-chloro-6-methoxy-2-benzoxazolinone. It inhibited the auxin-induced growth of coleoptile sections of Avena seedlings, and the growth of shoots and roots of maize seedlings at concentrations higher than 1 and 3 and 10 gmol/L, respectively; the doses required for 20 % growth inhibition were 14.7, 15.8 and 292 gmol/L, respectively. The activity of the inhibitor was higher than that of its analogue, 6-methoxy-2-benzoxazolinone. These results suggest that a new growth inhibitor, 5-chloro-6-methoxy-2-benzoxazolinone, may be involved in the inhibition of auxin-induced growth, which may be one of the causes of inhibition of the growth of maize seedlings.

Physiological effects of narciclasine from the mucilage of Narcissus tazetta L. bulbs

An inhibitor was isolated from the secreted mucilage of Narcissus tazetta L. bulbs. Based on X-ray analysis, the inhibitor was identified as narciclasine (NCS), an Amaryllidaceae alkaloid. NCS inhibited seed germination and seedling growth of rice and Chinese cabbage in a dose-dependent manner. NCS interacted with plant hormones in some physiological responses. Indole-3-acetic acid could not overcome the inhibition of elongation of wheat coleoptile sections caused by NCS. NCS suppressed the gibberellin-induced α-amylase production in barley seeds and cytokinin-induced expansion and greening of excised radish cotyledons.

Effect of auxinhormone lanthanide complexes on the growth of wheat coleoptile.

Naphthalene-1-acetic acid (HNAA), dichlorophenoxy acetic acid (HDAA), and indole-3-acetic acid (HIAA) are auxinhormones that can affect the growth of plants. The lanthanide complexes of the above auxinhormone LnA3 x 3H2O (Ln = La3+, Ce3+, Sm3+, Er3+, Yb3+; HA = HNAA, HDAA, HIAA; A = NAA-, DAA-, IAA-) were synthesized and are characterized in this paper. The solubility and IR spectra of these complexes were also studied. Experiments of the effects of LnCl3 x nH2O, HA, and LnA3 x 3H2O on the growth rate of wheat coleoptile sections show, that LnCl3 x nH2O promotes the growth of wheat coleoptile when this compounds concentration is lower than 2 x 10(-5) M and the promotion is very significant when the concentration of Ln3+ is lower than 8 x 10(-6) M. It was also found that the effect of LnA3 x 3H2O on the growth of wheat coleoptile is stronger than that of LnCl3 x nH2O and HA, which indicates that the combination of Ln3+ with HA act synergistically.

Light-induced auxin-inhibiting substance from sunflower seedlings

A plant growth-inhibiting substance was isolated from de-etiolated sunflower ( Helianthus annuus) seedlings. Its structure was identified as 8-epixanthatin from IR, 1H NMR and EI mass spectra. 8-Epixanthatin was detected in sunflower and burweed shoots, but not in lettuce, radish, oat and corn. 8-Epixanthatin inhibited auxin-induced growth of sunflower hypocotyl and oat coleoptile sections at concentrations higher than 100 μM and 30 μM, respectively, and the elongation of cress roots at concentrations higher than 30 μM. However, it did not affect gibberellin-induced growth of lettuce hypocotyls and second leaf sheaths of rice at the various concentrations used. The light-grown seedlings were observed to contain a higher level of 8-epixanthatin than the dark control, and the difference in its level was noticeable before the growth inhibition by light appeared. These results suggest that 8-epixanthatin with its auxin-inhibiting activity might contribute to the light-induced growth inhibition of sunflower seedlings.

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.

Antibodies against distinct ABP1 regions modify auxin binding to ABP1 and change the physiological auxin response of maize coleoptile cections

Summary Twelve peptides spanning the whole maize ABP1 sequence were synthesized and coupled to sepharose. Peptide — specific antibodies were purified from and ABP1 IgGs on peptide affinity columns, and binding of NAA to purified ABP1 in the presence of the IgGs was assayed. Of all the antibodies tested, only three increased the KD of auxin binding. Correspondingly, auxin-caused pH shift of the incubation medium by coleoptile sections was strongly influenced by these three antibodies. In addition, antibodies directed against the peptides corresponding to the N- and the C-terminus were also able to reduce the auxin-induced pH drop.

Decarboxylation of lndole‐3‐Acetic Acid and Inhibition of Growth in Avena sativa Seedlings by Plant‐Derived Photosensitizers*

Abstract— A number of plant phototoxins, when supplemented with UVA (320–400 nm) radiation, are capable of sensitizing the decomposition of indole‐3‐acetic acid (IAA), as measured by release of 14CO2 from carboxyl‐labeled IAA. Alpha‐terthienyl (αT) and harmine caused significant rates of IAA decarboxylation at concentrations as low as 1 nM and were approximately 80% as effective as riboflavin and flavin mononucleotide. Partial inhibition by sodium azide indicates that the aT‐induced decarboxylation of IAA is predominately, but not entirely, a type II reaction mediated by singlet oxygen. Based on changes in UV ab sorption spectra, it appears that the hormones gibberellic acid, abscisic acid and 6‐benzylaminopurine (a cytokinin) are less susceptible to photosensitized decomposition than is IAA. Alpha‐terthienyl plus UVA also inhibited elongation growth and reduced endogenous IAA levels in Avena sativa L. coleoptile sections and promoted senescence in intact Avena seedlings. These results confirm the allelopathic potential of plant photosensitizers such as αT and indicate that the phytohormone IAA may represent an additional target for the action of photosensitizers.

A new auxin-inhibiting substance, 4-Cl-6,7-dimethoxy-2-benzoxazolinone, from light-grown maize shoots

Two auxin-inhibiting substances were isolated from light-grown maize shoots. One was a new compound and determined from its spectral data as 4-Cl-6,7-dimethoxy-2-benzoxazolinone (Cl-DMBOA). Another was identified from its spectral data as a known compound, 6,7-dimethoxy-2-benzoxazolinone (DMBOA). Above concentrations of 10 −5 M, Cl-DMBOA inhibited the auxin-inducing elongation in the Avena coleoptile section test. Its inhibitory activity was almost comparable to that of DMBOA and higher than that of 6-methoxy-2-benzoxazolinone (MBOA) which we previously isolated.

Arabinogalactan proteins in maize coleoptiles: developmental relationship to cell death during xylem differentiation but not to extension growth†

The spatial and temporal expression of arabinogalactan proteins (AGPs) in the coleoptile of maize seedlings was investigated with monoclonal antibodies (MAC207, JIM13, JIM14) raised against particular AGP epitopes in carrot. MAC207 binds to a buffer-soluble AGP fraction of 90-210 kDa that also reacts with beta-glucosyl Yariv reagent and the lectin RCA120. Immunogold-labelling showed that the MAC207 epitope is exclusively localized in the plasma membrane. JIM13 binds to a 120 kDa component of the buffer-soluble AGP fraction localized in the plasma membrane of future sclerenchyma cells and secondary-wall thickenings of future tracheids of vascular bundles. JIM14 binds to a 50 kDa component of the salt-extractable fraction from cell walls localized in the innermost wall layer of sclerenchyma cells. These AGP epitopes demonstrate different temporal expression patterns which do not correlate with extension growth. Auxin had no effect on the amount of soluble AGP from coleoptile sections, containing the growth-controlling epidermis but no vascular bundles, as measured by crossed electrophoresis. Moreover, incorporation of radioactive arabinose, galactose or proline into this fraction was not stimulated by auxin. These results contradict the hypothesis that AGPs function as wall-loosening agents in auxin-mediated extension growth. The results are compatible with the notion that AGPs serve as developmental markers defining particular features of future cell differentiation. The specific association of the epitopes recognized by JIM13 and JIM14 with disintegrating cells suggests that the related AGPs identify those cells of the coleoptile which are committed to programmed cell death.

Characteristics and implications of prolonged fusicoccin‐induced growth of Avena coleoptile sections

A study has been made of the prolonged growth of Avena coleoptile sections in response to fusicoccin (FC), a phytotoxin that promotes apoplastic acidification. The final amount of FC-induced growth is a function of the FC concentration. Removal of the epidermis speeds up the initial rate of elongation and shortens the duration of the response, without affecting the total amount of extension. A suboptimal FC concentration (7 x 10(-8) M) which induces the same rate of proton excretion as does optimal indoleacetic acid (IAA) (1 x 10(-5) M), causes elongation which is 60-75% of that induced by IAA in 4 h or 50-65% in 7 h. This suggests that acid-induced extension could make a major contribution to auxin-induced growth for at least 7 h.

Characteristics and implications of prolonged fusicoccin-induced growth of Avena coleoptile sections

Characteristics and implications of prolonged fusicoccin-induced growth of Avena coleoptile sections

Epidermal Growth Factor Interacts with Indole-3-Acetic Acid and Promotes Coleoptile Growth

We used coleoptile sections of Avena sativa, Sorghum bicolor, and Zea mays seedlings to examine interactions between epidermal growth factor (EGF) and indole-3-acetic acid (IAA) that may affect plant growth and development. Our 24-h bioassays employed three controls ranging in dilution from 10−4 to 10−8 g ml−1: (1) 50 mM potassium-phosphate buffer solution (pH=6.0), (2) bovine serum albumin, a nonspecific protein; and (3) IAA; plus two treatments: (1) mouse epidermal growth factor (EGF) ranging from 10−6 to 10−10gml−1, and (2) EGF + IAA. In all three species growth in IAA, EGF, and EGF + IAA treatments showed significant increases over controls; EGF+IAA showed significant increases in growth over IAA alone. As the concentrations of IAA decreased, the EGF and IAA interaction became more pronounced. At the highest IAA concentrations, EGF + IAA increased growth rates ca. 2% to 39%, whereas at lower IAA concentrations EGF + IAA promoted growth as much as 121%, thereby lowering the normal IAA physiological set point up to three or four orders of magnitude. Our data suggest that an interaction between EGF and IAA may allow plants to recognize and respond to animal biochemical messengers, resulting in changes in plant cell elongation that ultimately may alter plant growth patterns.