Involvement Of Auxin Research Articles

Auxin controls local cytokinin biosynthesis in the nodal stem in apical dominance

In intact plants, the shoot apex grows predominantly and inhibits outgrowth of axillary buds. After decapitation of the shoot apex, outgrowth of axillary buds begins. This phenomenon is called an apical dominance. Although the involvement of auxin, which represses outgrowth of axillary buds, and cytokinin (CK), which promotes outgrowth of axillary buds, has been proposed, little is known about the underlying molecular mechanisms. In the present study, we demonstrated that auxin negatively regulates local CK biosynthesis in the nodal stem by controlling the expression level of the pea (Pisum sativum L.) gene adenosine phosphate-isopentenyltransferase (PsIPT), which encodes a key enzyme in CK biosynthesis. Before decapitation, PsIPT1 and PsIPT2 transcripts were undetectable; after decapitation, they were markedly induced in the nodal stem along with accumulation of CK. Expression of PsIPT was repressed by the application of indole-3-acetic acid (IAA). In excised nodal stem, PsIPT expression and CK levels also increased under IAA-free conditions. Furthermore, beta-glucuronidase expression, under the control of the PsIPT2 promoter region in transgenic Arabidopsis, was repressed by an IAA. Our results indicate that in apical dominance one role of auxin is to repress local biosynthesis of CK in the nodal stem and that, after decapitation, CKs, which are thought to be derived from the roots, are locally biosynthesized in the nodal stem rather than in the roots.

Involvement of auxin and CKs in boron deficiency induced changes in apical dominance of pea plants ( Pisum sativum L.)

It has previously been shown that boron (B) deficiency inhibits growth of the plant apex, which consequently results in a relatively weak apical dominance, and a subsequent sprouting of lateral buds. Auxin and cytokinins (CKs) are the two most important phytohormones involved in the regulation of apical dominance. In this study, the possible involvement of these two hormones in B-deficiency-induced changes in apical dominance was investigated by applying B or the synthetic CK CPPU to the shoot apex of pea plants grown in nutrient solution without B supply. Export of IAA out of the shoot apex, as well as the level of IAA, Z/ZR and isopentenyl-adenine/isopentenyl-adenosine (i-Ade/i-Ado) in the shoot apex were assayed. In addition, polar IAA transport capacity was measured in two internodes of different ages using 3H-IAA. In B-deficient plants, both the level of auxin and CKs were reduced, and the export of auxin from the shoot apex was considerably decreased relative to plants well supplied with B. Application of B to the shoot apex restored the endogenous Z/ZR and IAA level to control levels and increased the export of IAA from the shoot apex, as well as the 3H-IAA transport capacity in the newly developed internodes. Further, B application to the shoot apex inhibited lateral bud growth and stimulated lateral root formation, presumably by stimulated polar IAA transport. Applying CPPU to the shoot apex, a treatment that stimulates IAA export under adequate B supply, considerably reduced the endogenous Z/ZR concentration in the shoot apex, but had no stimulatory effect on IAA concentration and transport in B-deficient plants. A similar situation appeared to exist in lateral buds of B-deficient plants as, in contrast to plants well supplied with B, application of CKs to these plants did not stimulate lateral bud growth. In contrast to the changes of Z/ZR levels in the shoot apex, which occurred after application of B or CPPU, the levels of i-Ade/i-Ado stayed more or less constant. These results suggest that there is a complex interaction between B supply and plant hormones, with a B-deficiency-induced inhibition of IAA export from the shoot apex as one of the earliest measurable events.

The stimulating effects of ethylene and auxin on petiole elongation and on hyponastic curvature are independent processes in submerged Rumex palustris

The flooding-tolerant plant species Rumex palustris (Sm.) responds to complete submergence with stimulation of petiole elongation mediated by the gaseous hormone ethylene. We examined the involvement of auxin in petiole elongation. The manipulation of petiolar auxin levels by removing the leaf blade, or by addition of synthetic auxins or auxin transport inhibitors, led to the finding that auxin plays an important role in submergence-induced petiole elongation in R. palustris. A detailed kinetic analysis revealed a transient effect of removing the auxin source (leaf blade), explaining why earlier studies in which less frequent measurements were taken failed to identify any role for auxin in petiole elongation. We previously showed that the onset of stimulated petiole elongation depends on a more upright petiole angle being reached by means of hyponastic (upward) curvature, a differential growth process that is also regulated by ethylene and auxin. This raised the possibility that both ethylene and auxin stimulate elongation only indirectly by influencing hyponastic growth. We show here that the action of ethylene and auxin in promoting petiole elongation in submerged R. palustris is independent of the promoting effect that these hormones also exert on the hyponastic curvature of the same petiole.

Tiba inhibition of in vitro organogenesis in excised tobacco leaf explants

Abstract Triiodobenzoic acid (TIBA), an anti-auxin, was found to inhibit both shoot and root formation in cultured excised leaf explants of tobacco (Nicotiana tabacum L.). The shoot formation (SF) medium used required only exogenous cytokinin (N6-benzyladenine) and the root formation (RF) medium required both auxin (indole-3-butyric acid) and cytokinin (kinetin). By transferring the explants from SF or RF media to SF or RF media with TIBA (4.0×10−5 M), respectively or vice versa, at different times in culture, it was found that TIBA inhibition was at the time of meristemoid formation and after determination of organogenesis. This indicates that TIBA interfered with endogenous auxin involvement in organized cell division.

Ethylene and auxin control the Arabidopsis response to decreased light intensity.

Morphological responses of plants to shading have long been studied as a function of light quality, in particular the ratio of red to far red light that affects phytochrome activity. However, changes in light quantity are also expected to be important for the shading response because plants have to adapt to the reduction in overall energy input. Here, we present data on the involvement of auxin and ethylene in the response to low light intensities. Decreased light intensities coincided with increased ethylene production in Arabidopsis rosettes. This response was rapid because the plants reacted within minutes. In addition, ethylene- and auxin-insensitive mutants are impaired in their reaction to shading, which is reflected by a defect in leaf elevation and an aberrant leaf biomass allocation. On the molecular level, several auxin-inducible genes are up-regulated in wild-type Arabidopsis in response to a reduction in light intensity, including the primary auxin response gene IAA3 and a protein with similarity to AUX22 and the 1-aminocyclopropane-1-carboxylic acid synthase genes ACS6, ACS8, and ACS9 that are involved in ethylene biosynthesis. Taken together, the data show that ethylene and auxin signaling are required for the response to low light intensities.

Involvement of auxin and a homeodomain-leucine zipper I gene in rhizoid development of the moss Physcomitrella patens.

Differentiation of epidermal cells is important for plants because they are in direct contact with the environment. Rhizoids are multicellular filaments that develop from the epidermis in a wide range of plants, including pteridophytes, bryophytes, and green algae; they have similar functions to root hairs in vascular plants in that they support the plant body and are involved in water and nutrient absorption. In this study, we examined mechanisms underlying rhizoid development in the moss, Physcomitrella patens, which is the only land plant in which high-frequency gene targeting is possible. We found that rhizoid development can be split into two processes: determination and differentiation. Two types of rhizoids with distinct developmental patterns (basal and mid-stem rhizoids) were recognized. The development of basal rhizoids from epidermal cells was induced by exogenous auxin, while that of mid-stem rhizoids required an unknown factor in addition to exogenous auxin. Once an epidermal cell had acquired a rhizoid initial cell fate, expression of the homeodomain-leucine zipper I gene Pphb7 was induced. Analysis of Pphb7 disruptant lines showed that Pphb7 affects the induction of pigmentation and the increase in the number and size of chloroplasts, but not the position or number of rhizoids. This is the first report on the involvement of a homeodomain-leucine zipper I gene in epidermal cell differentiation.

Distribution of activated calmodulin in the chloronema tip cells of the moss Funaria hygrometrica

Auxin (indole-3-acetic acid) regulates caulonema differentiation as a result of gradual transitional events in the chloronema tip cells in moss protonema. This auxin action in the moss Funaria hygrometrica involves a rapid influx of calcium ions from the extracellular medium. This investigation demonstrates spatial and temporal changes in calmodulin (CaM) activation (formation of Ca(2+)-CaM complex) in the chloronema tip cells subjected to auxin treatment. Photomicroscopic localisation of the fluorescence (excitation at 365 nm and emission of 397 nm) from the tricomplex of Ca(2+)-CaM with trifluoperazine (TFP, a blocker of Ca(2+)-CaM action) shows a tip to base (tip high) gradient of Ca(2+)-CaM in the chloronema tip cells. Comparison of Ca(2+)-CaM-TFP fluorescence over time in the chloronema tip cells of wild type Funaria with the response in an auxin overproducer mutant (86.1) and an auxin deficient mutant (87.13) reveals the involvement of auxin in calmodulin activation as a rapid response prior to cell differentiation.

Phytochrome in cotyledons regulates the expression of genes in the hypocotyl through auxin-dependent and -independent pathways.

To elucidate the mechanism of plant responses to shading, we identified three promoter/enhancer trap lines (M812, J53, J59) that exhibited reporter expression in the hypocotyl in response to the end-of-day far-red light treatment. Interestingly, we found auxin-responsive genes in the vicinities of the reporter insertion sites in M812 and J53. We examined the effects of auxin on the reporter expression in these lines together with a previously identified N35 line. The results indicated that the reporter expression was induced by exogenous auxin in N35 and J53. Furthermore, an auxin transport inhibitor inhibited the responses of these lines to the end-of-day far-red light treatment, suggesting the involvement of auxin in the responses of plants to shading. By contrast, neither auxin nor the transport inhibitor affected the response in M812 and J59. Interestingly, J59 responded to ABA. Hence, ABA might be involved in the response as well. Analysis of the photoreceptive sites for the responses revealed the cotyledons, not the hypocotyl, are the major photoreceptive sites both in the auxin-responsive and ABA-responsive lines. Hence, some signals appeared to be transmitted from the cotyledons to the hypocotyl.

Involvement of auxin and cytokinins in initiation of growth of isolated pea buds

Axillary buds from the second primary scale excised from 21-day-old pea(Pisum sativum L. cv. Vladan) plants were used as a modelsystem for studying the release of buds from apical dominance. The isolatedbudswere transferred onto basal medium with or without a supplement of growthregulators and cultivated up to 24 h in short-term and up to 4weeks in long-term experiments. In both sets of experiments endogenous IAA,cytokinins and the uptake of labelled zeatin were analysed. The development ofbuds was monitored by image analysis, estimation of their weight, and byanatomical studies. Generative meristems were found in isolated axillary budsalready in 21-day-old plants at the beginning of the experimental period. Theonset of bud growth was recorded as soon as 2 h after the budexcision by image analysis. The bud growth was accompanied by a rapid transientincrease of the endogenous IAA level within the first 2 h,followedby an increase of iPA within 24 h. The uptake of the exogenouscytokinin ([3H]Z) reached its peak between the 6 and 8hafter the release from apical dominance. The cytokinin analyses of bothshort-term and long-term bud cultures revealed the increase of free cytokininsand their glucosides, indicating de novo synthesis ofcytokinins in the buds themselves.

Different pathways are involved in phosphate and iron stress-induced alterations of root epidermal cell development.

Low bioavailability of phosphorus (P) and iron (Fe) induces morphogenetic changes in roots that lead to a higher surface-to-volume ratio. In Arabidopsis, an enlargement in the absorptive surface area is achieved by an increase in the length and frequency of hairs in roots of Fe- and P-deficient plants. The extra root hairs are often located in positions that are occupied with non-hair cells under normal conditions, i.e. over a tangential wall of underlying cortical cells. An involvement of auxin and ethylene in root epidermis cell development of Fe- and P-deficient plants was inferred from phenotypical analysis of hormone-related Arabidopsis mutants and from the application of substances that interfere with either synthesis, transport, or perception of the hormones. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid or the auxin analog 2,4-D caused a marked increase in root hair density in plants of all growth types and confers a phenotype characteristic of ethylene-overproducing mutants. Hormone insensitivity and application of hormone antagonists inhibited the initiation of extranumerary root hairs induced by Fe deficiency, but did not counteract the formation of extra hairs in response to P deprivation. A model is presented summarizing putative pathways for alterations in root epidermal cell patterning induced by environmental stress.

Cell cycle regulation by plant growth regulators: involvement of auxin and cytokinin in the re-entry of Petunia protoplasts into the cell cycle.

In order to understand the mode of action of auxins and cytokinins in the induction of cell division, the effects of the two plant growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D) and N6-benzyladenine (BA) were investigated using mesophyll protoplasts of Petunia hybrida, cultivated in either complete medium or in medium deficient in cytokinin, auxin or both. Firstly we studied DNA synthesis, using 5-bromodeoxyuridine/bisbenzimide Hoechst/propidium iodide flow cytometry analyses and by the monitoring of histone H4 transcript levels. Roscovitine, a cyclin-dependent kinase (CDK) inhibitor, was found to block the cell cycle prior to entry into the S and M phases in the cultured P. hybrida protoplasts. This suggests that in Petunia cell there is a requirement for CDK activity in order to complete the G1 and G2 phases. Further experiments using roscovitine showed that neither 2,4-D nor BA were individually able to induce cell cycle progression beyond the roscovitine G1 arrest. We also monitored the phytohormonal induction of S phase by studying variations in transcript levels of the gene for mitogenactivated protein kinase (PMEK1) and transcript levels of the cell division cycle gene cdc2Pet. Only 2,4-D, and not BA, was able to stimulate PMEK1 gene transcription; thus, the more rapid S-phase induction in 2,4-D-treated protoplasts may be attributable to the activation of this transduction pathway. In contrast, both plant growth regulators were required to induce the appearance of cdc2Pet mRNA transcripts prior to S-phase engagement.

Indole-3-acetic acid elicits Ca 2+-dependent callose synthesis in the protonema of Funaria hygrometrica

Summary The present report provides an account of the possible involvement of auxin (Indole-3-acetic acid) in callose biosynthesis, prior to cell differentiation in moss protonema (chloronema to caulonema), which is primarily an auxin-controlled event. Chloronema tip cells in Funaria hygrometrica respond to IAA (5 × 10 −5 mol/L) treatment by localised callose synthesis in the basal region of the cell before changing the pattern of cell growth and subsequent division as caulonema. A qualitative comparison of the callose accumulation response in the wild strain chloronema filaments, with those of the two auxin mutants, indicates a correlation between auxin sensitivity of the specific strain and the extent of callose accumulation along the cross wall and the adjacent lateral wall of the apical cells. The percentage of responding tip cells in the three strains varied between 65 and 80 %. Least callose accumulation is observed in the auxin-insensitive mutant 86.1. The present investigations further suggest an important role of auxin-induced influx of Ca 2+ in callose synthesis, although it does not seem to be the sole factor responsible for the regulation of this process.

Transgenic white clover. Studies with the auxin-responsive promoter, GH3, in root gravitropism and lateral root development.

We report improved method for white clover (Trifolium repens) transformation using Agrobacterium tumefaciens. High efficiencies of transgenic plant production were achieved using cotyledons of imbibed mature seed. Transgenic plants were recovered routinely from over 50% of treated cotyledons. The bar gene and phosphinothricin selection was shown to be a more effective selection system than nptII (kanamycin selection) or aadA (spectinomycin selection). White clover was transformed with the soybean auxin responsive promoter, GH3, fused to the GUS gene (beta-glucuronidase) to study the involvement of auxin in root development. Analysis of 12 independent transgenic plants showed that the location and pattern of GUS expression was consistent but the levels of expression varied. The level of GH3:GUS expression in untreated plants was enhanced specifically by auxin-treatment but the pattern of expression was not altered. Expression of the GH3:GUS fusion was not enhanced by other phytohormones. A consistent GUS expression pattern was evident in untreated plants presumably in response to endogenous auxin or to differences in auxin sensitivity in various clover tissues. In untreated plants, the pattern of GH3:GUS expression was consistent with physiological responses which are regarded as being auxin-mediated. For the first time it is shown that localised spots of GH3:GUS activity occurred in root cortical tissue opposite the sites where lateral roots subsequently were initiated. Newly formed lateral roots grew towards and through these islands of GH3:GUS expression, implying the importance of auxin in controlling lateral root development. Similarly, it is demonstrated for the first time that gravistimulated roots developed a rapid (within 1 h) induction of GH3:GUS activity in tissues on the non-elongating side of the responding root and this induction occurred concurrently with root curvature. These transgenic plants could be useful tools in determining the physiological and biochemical changes that occur during auxin-mediated responses.

The contrasting role of auxin in submergence‐induced petiole elongation in two species from frequently flooded wetlands

The involvement of auxin in the submergence‐induced petiole elongation has been investigated in Rumex palustris and Ranunculus sceleratus. Both wetland species are capable of enhanced petiole elongation upon submergence or treatment with exogenous ethylene (5μl l−1). Treatment of intact Rumex palustris plants with 1‐naphthalene acetic acid (NAA) at 10−4M enhanced petiole elongation, while treatment with N‐1‐naphthylphthalamic acid (NPA) had no effect on petiole elongation. The elongation response after NAA or NPA treatment was comparable for plants in both submerged and drained conditions. Pre‐ageing of detached petioles of Rumex palustris for 3 h in light or in dark conditions had no effect on the submergence‐induced elongation. In comparison to intact plants, detached petioles of Rumex palustris, with or without lamina, did not show significant differences in responsiveness to IAA between drained or submerged conditions. This was in contrast to Ranunculus sceleratus where submergence caused a clear increase in responsiveness towards IAA. Removal of the lamina, the putative source of auxin, or treatment with NPA did not hinder the submergence‐induced elongation of detached Rumex palustris petioles, but severely inhibited elongation of detached Ranunculus sceleratus petioles. This inhibition could be restored by application of NAA, suggesting the specific involvement of auxin in the submergence response of Ranunculus sceleratus. It is concluded that, in contrast to Ranunculus sceleratus, auxin is probably not involved in the submergence‐induced petiole elongation of Rumex palustris.

The role of endogenous auxin in root initiation

This paper is the second part of a review which considers evidence for the involvement of auxin in root initiation. Part II examines the research being carried out with transformed plant tissues. Agrobacterium rhizogenes causes abundant root initiation at the site of inoculation. Ri plasmid T-DNA contains several genes which encode enzymes involved in the biosynthesis and metabolism of indole-3-acetic acid. Transfer of various fragments of the Ri plasmid has also been reported to confer increased sensitivity to auxin upon plant cells. Controlled expression of these genes in the plant genome potentially offer an insight for developmental plant physiologists into the role of plant growth substances in the process of root initiation. The importance of absolute levels of IAA in the stimulation of root initiation is discussed.

Involvement of auxin in the loss of apical dominance and plant growth potential accompanying aging of potato seed tubers

Studies were conducted to further characterize a role for auxin in the loss of apical dominance and plant growth potential that occurs during long-term storage of potato (Solanum tuberosum L.) seed tubers. Treatment of single-eye seed cores from 18-month-old seed tubers with 1-naphthaleneacetic acid (NAA) restored apical dominance and increased dry matter partitioning to roots, stems, and leaves, thus partially mitigating the deleterious effects of advanced seed-tuber age on growth potential. Conversely, NAA treatment of seed cores from 6-month-old tubers substantially inhibited plant growth. In contrast to NAA, IAA was totally ineffective at counteracting the deleterious effects of advanced tuber age on plant growth, whereas the effect of IAA on overall growth of plants from 6-month-old seed cores remained slightly inhibitory. The difference in efficacy of these two auxins appears to be related to age-induced differences in ability of tissues to transport and catabolize IAA. The specific activity of IAA oxidase (IAAox) was 4 times higher in tissue from 20-month-old seed tubers at planting and increased at a faster rate during sprouting compared with that from 8-month-old tubers. Hence, the higher potential for oxidation of IAA in tissue from older seed cores is well correlated with the inability of this auxin to alter growth. In translocation studies, etiolated sprouts from aged seed tubers showed a reduced ability to translocate [1-14C]IAA basipetally compared with those from younger tubers. Moreover, intact etiolated sprouts growing from older seed cores decarboxylated the radiolabeled IAA at a much faster rate on a dry weight basis than those from younger seed cores. The specific activities of IAAox and peroxidase in the sprout apex, sprout base, and tuber tissue from 18-month-old seed cores were substantially higher than in similar tissues from 6-month-old seed cores, and tissue concentration of the radiolabel was negatively correlated with IAAox activity. Hence, aging of potato seed tubers not only reduces the ability of sprouts to transport auxin basipetally, but it also increases the capacity for auxin catabolism during sprouting. The physiological consequence of this may be the release of lateral meristems from correlative inhibition, and in effect, reduced apical dominance and shoot growth potential during plant establishment from aged seed tubers. Key words: potato, age-reduced vigor, sprouting, apical dominance, auxin.

Effects of Light and Carbohydrate Content on Rooting of Rhizome Cuttings of Paspalum vaginatum Swartz. (Gramineae)

Summary Light and the balance between carbohydrates and auxins play an important role in rooting. The role of these factors in rooting was enhanced in cuttings kept in darkness. Light inhibits root formation especially when directed at the area where roots are initiated. In cuttings maintained in darkness there was a decrease in the carbohydrate content and an increase in rooting percentages. Treatments with sucrose increased the endogenous levels of carbohydrates of the cuttings with concomitant reduction in rooting. Experiments with indol-3yl-butyric acid and 2,3,5-triiodobenzoic acid also suggest the involvement of auxins in the rooting process.

Effects of NAA on the Occurrence of Hollow Root in the Japanese Radish (Raphanus sativus L. cv. Gensuke).

Hollowing in the root of Japanese radish (Raphanus sativus L.), a physiological disorder characterized by the lengthwise cleavage of the central stele, has been frequently associated with summer-sown crops. In this study, the involvement of auxin in the occurrence of hollow root in 'Gensuke' radish was investigated by spraying the leaves with a synthetic auxin, NAA, (α-naphthaleneacetic acid) of various concentrations at different growth periods.Daily foliar applications of NAA for 15 days during four different periods revealed that 10 mg-liter-1 NAA applied between 16 and 30 days after sowing markedly suppressed root thickening and promoted the development of hollow roots. Treatments with NAA after this period produced little or no effect, especially at 0.1 and 1 mg-liter-1. Investigation of the effects of NAA on root morphology and the development of hollowing in roots revealed that spraying with NAA from the time seedlings emerge to 30 days after sowing caused roots to form densely arranged xylem vessels, indicating a decrease in the meristematic activity of xylem parenchymatous cells.The evidence leads us to conclude that the high occurrence of hollow root in plants treated with 10 mg-liter-1 NAA results from the lowering of meristematic activity in xylem paren-chymatous among vessels because the lignify. This leads to small roots with densely arranged vessels and suppression of proliferation of parenchymatous cells which usually project from the internal surface of the air space. Consequently, the intercellular air spaces coalesce into a large hollow cavity as the root continues to thicken.

Polar Patierns of Periderm Onfogeny, Their Relationship to Leaves and Buds, and the Control of Cork Formation

Patterns of periderm ontogeny were studied in vigorously growing branches and leaders of Calotropis procera (Ait.) Ait. f., Carissa grandiflora A. DC., Ficus elastica Roxb., Ficus religiosa L. and Melia azedarach L. In all of these five woody species the periderm develops in clear polar patterns, with inhibitory zones, in which periderm formation is delayed, just beneath leaf bases and around dormant buds. A high rate of periderm production is induced by high sun irradiation in Calotropis procera. The polar patterns of periderm formation with retardation regions around leaves and buds probably indicate auxin involvement in the control mechanism of periderm differentiation. The role of both auxin and ethylene in periderm formation is discussed, as weIl as a proposed mechanism for rhytidome initiation.

Stimulation of lignification in neoformed calli induced by Agrobacterium rhizogenes on bean hypocotyls

Histological and biochemical modifications following the inoculation of bean hypocotyls with Agrobacterium rhizogenes have been studied with special emphasis on lignification. Infection with A. rhizogenes led to a swelling of the inoculated region (2 days after inoculation), giving rise to a nodular callus (4–5 days) from which transformed roots arose after 10–12 days. Time-course histochemical studies performed during callus formation have shown an increased differentiation of lignified elements concerning both direct differentiation of tracheids from cortical cells and, to a greater extent, tracheid redifferentiation in the neoformed calli. These observations have been confirmed by determinations of lignin contents and measurements of related enzyme activities. Cinnamoyl CoA reductase (E.C.1.2.1.44) and cinnamyl alcohol dehydrogenase (E.C.1.1.1.-), two specific enzymes of lignification, are rapidly stimulated with a maximum activity 8 days after inoculation in correlation with the rapid increase in amount of lignins. Hybridization experiments (Northern) demonstrate an accumulation of mRNAs corresponding to cinnamyl alcohol dehydrogenase during the callus formation. Comparative infections performed with different bacterial strains support the involvement of auxins both in tumor formation and in lignification stimulation.