Differenciation cellulaire et composés sulfhydrylés acido-solubles de la racine de Lens culinaris Med.

Cell differentiation and acid-soluble sulfhydryl compounds in the root of Lens culinaris. Med. — The content of acid-soluble sulfhydryl compounds (SH + S-S) is determined amperometrically in tissues of the Lens root. Two distinct zones are analysed: first the meristematic one (0 to 1.6 mm from the tip) and secondly the elongating one (1.6 to 3.7 mm). Measurements concerned the first 80 hours of the root growth. SH/S-S ratio is minimum in the meristematic ZONE. Connections seem to exist between the growth rate and the amount of SH compounds in the elongating zone. These facts suggest that the increase of cytoplasmic SH is associated with the reduction of protein-disulfur-bridges, which account for t he intermicrofibrilar bindings in the cell wall. The effects of auxins (indoleacetic acid and naphtylacetic acid) treatments are also studied. They are strictly localized in the apical zone and their intensity depends upon the auxin concentration. SH-level is rising: this is due partially to a reduction of acid-soluble S-S.     

Meristem-Specific Suppression of Mitosis and a Global Switch in Gene Expression in the Root Cap of Pea by Endogenous Signals

Two functionally distinct sets of meristematic cells exist within root tips of pea (Pisum sativum): the root apical meristem, which gives rise to the body of the root; and the root cap meristem, which gives rise to cells that differentiate progressively through the cap and separate ultimately from its periphery as border cells. When a specific number of border cells has accumulated on the root cap periphery, mitosis within the root cap meristem, but not the apical meristem, is suppressed. When border cells are removed by immersion of the root tip in water, a transient induction of mitosis in the root cap meristem can be detected starting within 5 min. A corresponding switch in gene expression throughout the root cap occurs in parallel with the increase in mitosis, and new border cells begin to separate from the root cap periphery within 1 h. The induction of renewed border cell production is inhibited by incubating root tips in extracellular material released from border cells. The results are consistent with the hypothesis that operation of the root cap meristem and consequent turnover of the root cap is self-regulated by a signal from border cells.     

Triaziflam and Diaminotriazine derivatives affect enantioselectively multiple herbicide target sites

Enantiomers of triaziflam and structurally related diaminotriazines were synthesized and their herbicidal mode of action was investigated. The compounds caused light and dark-dependent effects in multiple test systems including heterotrophic cleaver and photoautotrophic algal cell suspensions, the Hill reaction of isolated thylakoids and germinating cress seeds. Dose-response experiments revealed that the (S)-enantiomers of the compounds preferentially inhibited photosystem II electron transport (PET) and algae growth with efficacies similar to that of the herbicide atrazine. In contrast, the (R)-enantiomers of the diaminotriazines were up to 100 times more potent inhibitors of growth in cleaver cell suspensions and cress seedlings in the dark than the (S)-enantiomers. The most active compound, the (R)-enantiomer of triaziflam, inhibited shoot and root elongation of cress and maize seedlings at concentrations below 1 microM. The meristematic root tips swelled into a club shape which is typical for the action of mitotic disrupter herbicides and cellulose biosynthesis inhibitors. Microscopic examination using histochemical techniques revealed that triaziflam (R)-enantiomer blocks cell division in maize root tips 4 h after treatment. The chromosomes proceeded to a condensed state of prometaphase but were unable to progress further in the mitotic cycle. Disruption of mitosis was accompanied by a loss of spindle and phragmoplast micotubule arrays. Concomitantly, cortical microtubules decreased which could lead to isodiametric cell growth and consequently to root swelling. In addition, a decline in cellulose deposition in cell walls was found 24 h after treatment. Compared to the (R)-form, triaziflam (S)-enantiomer was clearly less active. The results suggest that triaziflam and related diaminotriazines affect enantioselectively multiple sites of action which include PET inhibitory activity, mitotic disruption by inhibiting microtubule formation and inhibition of cellulose synthesis.     

Regulation of Mitosis in Roots by their Caps

WHEN the meristematic cells of root tips are damaged by surgery, X-rays or various chemical treatments, the cells of the quiescent centre (Fig. 1) are stimulated into mitosis. These cells normally have an average rate of mitosis about one-tenth of that of their neighbours more than half of them are not in mitotic cycles and, of those that are, some have a “fast” cycle three or four times as long as those of their neighbours¹. After X-irradiation there is an immediate response in the quiescent centre that suggests that the balance in cell proliferation between different regions of the meristem is not a simple competition effect. One stimulatory action is the removal of the root cap² and I have now found that the cap exerts a complex effect on mitosis in the rest of the meristem.     

Multinucleate plant cells: I. Aneuploidy in a proliferating population

A new method for the production of multinucleate plant cells in meristematic populations is described. This method involves the aneuploidy induction of nuclei of a same cell. Allium cepa root tips were chemically treated, and the multinucleate cells obtained were scored at interphase and mitosis. When meristematic cells are treated with γ-hexachlorocyclohexane in appropriate culture conditions, the anaphase chromatids are distributed into discrete unbalanced groups. This phenomenon has been profited for inducing viable multinucleate cells with aneuploid nuclei after cytokinesis inhibition with caffeine.     

Changes in hormonal balance and meristematic activity in primary root tips on the slowly rotating clinostat and their effect on the development of the rapeseed root system

The morphometry of the root system, the meristematic activity and the level of indole-3-acetic acid (IAA), abscisic acid (ABA) and zeatin in the primary root tips of rapeseed seedlings were analyzed as functions of time on a slowly rotating clinostat (1 rpm) or in the vertical controls (1 rpm). The fresh weight of the root system was 30% higher throughout the growth period (25 days) in clinorotated seedlings. Morphometric analysis showed that the increase in biomass on the clinostat was due to greater primary root growth, earlier initiation and greater elongation of the secondary roots, which could be observed even in 5-day-old seedlings. However, after 15 days, the growth of the primary root slowed on the clinostat, whereas secondary roots still grew faster in clinorotated plants than in the controls. At this time, the secondary roots began to be initiated closer to the root tip on the clinostat than in the control. Analysis of the meristematic activity and determination of the levels in IAA, ABA and zeatin in the primary root tips demonstrated that after 5 days on the clinostat, the increased length of the primary root could be the consequence of higher meristematic activity and coincided with an increase in both IAA and ABA concentrations. After 15 days on the clinostat, a marked increase in IAA, ABA and zeatin, which probably reached supraoptimal levels, seems to cause a progressive disturbance of the meristematic cells, inducing a decrease of primary root growth between 15 and 25 days. These modifications in the hormonal balance and the perturbation of the meristematic activity on the clinostat were followed by a loss of apical dominance, which was responsible for the early initiation of secondary roots, the greater elongation of the root system and the emergence of the lateral roots near the tip of the primary root.     

Enhanced lipoxygenase activity is involved in the stress response but not in the harmful lipid peroxidation and cell death of short-term cadmium-treated barley root tip

Root growth inhibition and radial root swelling were the characteristic symptoms of barley root tips after the short-term exposure of roots to 15 and 30 μM Cd. Higher Cd concentrations caused extensive cell death and root growth arrest. Enhanced lipid peroxidation was observed as early as 1 h after the short-term treatment in a Cd concentration-dependent manner. In contrast to lipid peroxidation, the induction of lipoxygenase activity was detected only 3 h after the exposure of roots to 15 or 30 μM Cd. In addition, it was not observed in 60 μM Cd-treated root tips. The highest lipoxygenase activity was detected 6 h after 15 μM Cd treatment in the meristematic and elongation zone of root tip and was probably associated with the radial expansion of cells. Our results indicate that the upregulation of lipoxygenase is an important component of stress response in barley roots to toxic Cd. It is probably involved in the morphological stress response of root tips or/and in the alleviation of Cd-induced toxic alterations in plant cell membranes, but it is not responsible for the Cd-induced harmful lipid peroxidation and cell death.     

Characterization of a cytosolic nucleoside diphosphate kinase associated with cell division and growth in potato

A cDNA encoding Solanum chacoense cytosolic NDPK (NDPK1, EC 2.7.4.6) was isolated. The open reading frame encoded a 148 amino acid protein that shares homology with other cytosolic NDPKs including a conserved N-terminal domain. S. chacoense NDPK1 was expressed in Escherichia coli as a 6×His-tagged protein and purified by affinity chromatography. The recombinant protein exhibited a pattern of abortive complex formation suggesting that the enzyme is strongly regulated by the NTP/NDP ratio. A polyclonal antibody generated against recombinant NDPK1 was specific for the cytosolic isoform in Solanum tuberosum as shown from immunoprecipitation experiments and immunoblot analysis of chloroplasts and mitochondria preparations. NDPK activity and NDPK1 protein were found at different levels in various vegetative and reproductive tissues. DEAE fractogel analyses of NDPK activity in root tips, leaves, tubers and cell cultures suggest that NDPK1 constitutes the bulk of extractable NDPK activity in all these organs. NDPK activity and NDPK1 protein levels raised during the exponential growth phase of potato cell cultures whereas no rise in activity or NDPK1 protein was observed when sucrose concentration in the culture was manipulated to limit growth. Activity measurements, immunoblot analysis as well as immunolocalization experiments performed on potato root tips and shoot apical buds demonstrated that NDPK1 was predominantly localized in the meristematic zones and provascular tissues of the apical regions. These data suggest that NDPK1 plays a specific role in the supply of UTP during early growth of plant meristematic and provascular tissues.     

The effect of lead on Allium cepa L.

The effect of lead on Allium cepa L. at concentrations of 0.1, 1.0, 10, 50, 100 and 200 ppm were studied. Analysis focused on root growth, frequency of mitosis in a meristematic zone, and chromosomal aberrations. It was observed that lead reduces root growth and the frequency of mitotic cells in meristematic zones, and increases the frequency of aberrant cells. The intensity of the effects is a function of lead concentration.     

The Influence of Colchicine on Initiation and Early Development of Adventitious Roots

The first sign of adventitious root formation in the petiole of the primary leaves of Phaseolus vulgaris after treatment with IAA was the dedifferentiation of mature parenchyma cells next to strands of sieve elements and companion cells. Colchicine strongly inhibited this dedifferentiation. Treatment with colchicine 3 days after treatment with IAA, caused the groups of meristematic cells formed to grow by cell enlargement only. Groups of more than about 30 meristematic cells changed into recognizable root primordia during this growth. Groups with a smaller number of meristematic cells extended also in size but did not form a recognizable root primordium.     

QUANTITATIVE STUDIES OF THE ROOT APICAL MERISTEM OF EQUISETUM SCIRPOIDES

An investigation was made of the meristematic activity of the apical cell, its immediate derivatives (merophytes), and of other selected cell populations of the root of Equisetum scirpoides Michx. The plane of the first division of a derivative of the apical cell is radiallongitudinal, which provides evidence that merophytes immediately adjacent to the apical cell cannot be the ultimate root initials. The apical cell is as active mitotically in roots 20–40 mm long as it is in roots that are 0.25–1 mm in length. The mitotic activity of the apical cell and of other cell populations was determined from the mitotic index, and from determination of the durations of the cell cycle and of mitosis of the apical cell by using the colchicine method of metaphase accumulation. Microspectrophotometric measurements of DNA content indicated that there was no consistent increase in DNA (endopolyploidy) in the apical cell or in the other meristematic cells as roots increased in length. Conclusion: there is no evidence that the apical cell becomes quiescent or undergoes endopolyploidy as a root increases in length.     

Inhibition of maize primary root elongation by spermidine: Effect on cell shape and mitotic index

Spermidine applied for 18 h to intact maize seedlings through their roots reduces root growth 70%, and the effect is reversible. Histological observations of longitudinal sections of 0.4-cm root apical segments from 2-day-old maize seedlings grown for 18 h in 0.5 m CaSO₄ solution with or without 1 mm spermidine contribute to the explanation of spermidine-dependent slow root growth. In the meristematic zone a strong reduction of the mitotic index and in the elongation zone an inhibition of cell elongation occur simultaneously. Cell shape analysis along the growth axis of the maize root apex expressed in terms of form factor (FCircle) values substantiates the dual effect of spermidine on mitotic activity and cell elongation.Abbreviations PA polyamine(s) - Spm spermine - Spd spermidine     

Regulation of Root Growth in Lactuca sativa L. Seedlings by the Ent-Kaurane Diterpenoid Epinodosin

Epinodosin, an ent-kaurane diterpenoid isolated from Isodon japonica var. galaucocalyx, had a biphasic, dose-dependent effect on root growth and a strong inhibitory effect on root hair development in Lactuca sativa L. seedlings. Lower levels of epinodosin (25–100 μM) significantly promoted root growth, but higher concentrations (150–200 μM), by contrast, had inhibitory effects. In addition, all of the tested concentrations (20–80 μM) inhibited root hair development of lettuce seedlings in a dose-dependent manner. Further investigations on the underlying mechanism revealed that the promotion effect of epinodosin (25–100 μM) resulted from increasing the cell length in the mature region and enhancing the mitotic activity of meristematic cells in lettuce seedling root tips. On the other hand, epinodosin at higher concentrations inhibited root growth by strongly affecting both the cell length in the mature region and the division of meristematic cells. Comet assay analysis demonstrated that the decrease of mitotic activity of root meristematic cells was due to DNA damage induced by higher levels of epinodosin.     

Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham

Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.—J. exp. Bot. 36: 1504–1513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. ‘Victory’)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m^–3 DCPA, 1·0–5·0 mmol m^–3propham, and 50–500 mmol m^–3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham     

An ArabidopsisSUPERMAN-like gene,AtZFP12, Expressed at Shoot Organ Boundaries Suppresses cell Growth.

Arabidopsis SUPERMAN (SUP) and its family members have been implicated in flower organogenesis and plant morphogenesis via the regulation of division or growth of cells. In this study, we characterized a new SUP-like zinc finger gene (AtZFP12). This gene is expressed around the bases of the axillary buds and at the junction between the inflorescence axis and flower stalks. It is also expressed at the boundary between the meristematic and elongation zones in root tips. Overexpression of its cDNA in transgenicArabidopsis reduced cell expansion, resulting in dwarfed plant growth. These results suggest the potential role ofAtZFP12 in the regulation of cell growth during the establishment of SOB in the shoot and transition zones in root tips.     

EFFECTS OF BORON DEFICIENCY ON MITOSIS AND INCORPORATION OF TRITIATED THYMIDINE INTO NUCLEI OF SUNFLOWER ROOT TIPS

Boron deprivation has multiple effects upon root growth within 6 hr after this essential micronutrient is withheld. Root elongation is inhibited and this response has been attributed to a cessation of mitosis and DNA synthesis. Our preliminary results using an autoradiographic analysis of sunflower roots labeled with [³H]-thymidine demonstrated no difference in label distribution between +/-B root tips. We found that mitosis in inhibited in -B roots but does not completely cease. Scintillation counting of whole root tips shows that boron-deficient roots up to 72 hr of treatment incorporate radioactive label at a level comparable to that of the controls. Because mitosis and presumably DNA synthesis are affected by prolonged boron deficiency, these results may be brought about by a change in membrane integrity or permeability. We propose that effects of boron deprivation on DNA synthesis and mitosis in sunflower are secondary and that primary events involve alterations in cellular membranes.     

Changes in onion root development induced by the inhibition of peptidyl-prolyl hydroxylase and influence of the ascorbate system on cell division and elongation

Post-translational hydroxylation of peptide-bound proline residues, catalyzed by peptidyl-prolyl-4 hydroxylase (EC 1.14.11.2) using ascorbate as co-substrate, is a key event in the maturation of a number of cell wall-associated hydroxyproline-rich glycoproteins (HRGPs), including extensins and arabinogalactan-proteins, which are involved in the processes of wall stiffening, signalling and cell proliferation. Allium cepa L. roots treated with 3,4-DL-dehydroproline (DP), a specific inhibitor of peptidyl-prolyl hydroxylase, showed a 56% decrease in the hydroxyproline content of HRGP. Administration of DP strongly affected the organization of specialized zones of root development, with a marked reduction of the post-mitotic isodiametric growth zone, early extension of cells leaving the meristematic zone and a huge increase in cell size. Electron-microscopy analysis showed dramatic alterations both to the organization of newly formed cell walls and to the adhesion of the plasma membranes to the cell walls. Moreover, DP administration inhibited cell cycle progression. Root tips grown in the presence of DP also showed an increase both in ascorbate content (+53%) and ascorbate-specific peroxidase activity in the cytosol (+72%), and a decrease in extracellular “secretory” peroxidase activity (−73%). The possible interaction between HRGPs and the ascorbate system in the regulation of both cell division and extension is discussed. Received: 14 October 1998 / Accepted: 31 May 1999     

Inhibitory action of auxin on root elongation not mediated by ethylene

The inhibitory effects of indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) on elongation growth of pea (Pisum sativum L.) seedling roots were investigated in relation to the effects of these compounds on ethylene production by the root tips. When added to the growth solution both compounds caused a progressively increasing inhibition of growth within the concentration range of 0.01 to 1 micromolar. However, only ACC increased ethylene production in root tips excised from the treated seedlings after 24 hours. High auxin concentrations caused a transitory increase of ethylene production during a few hours in the beginning of the treatment period, but even in 1 micromolar IAA this increase was too low to have any appreciable effect on growth. ACC, but not IAA, caused growth curvatures, typical of ethylene treatment, in the root tips. IAA caused conspicuous swelling of the root tips while ACC did not. Cobalt and silver ions reversed the growth inhibitory effects induced by ACC but did not counteract the inhibition of elongation or swelling caused by IAA. The growth effects caused by the ACC treatments were obviously due to ethylene production. We found no evidence to indicate that the growth inhibition or swelling caused by IAA is mediated by ethylene. It is concluded that the inhibitory action of IAA on root growth is caused by this auxin per se.     

The influence of H2S on reproduction rate in paramecium caudatum

Conclusion Sulfhydryl in H₂S and Na₂S in proper concentration, accelerates the reproduction rate ofParamecium caudatum. This fact is further support for the thesis ofHammett that the -SH group is an essential stimulus to growth by increase in cell number.     

Induction of polyploidy and C-tumours after treatingAllium cepa root tips with the herbicide “Treflan”

Treflan has the ability to induce polyploidy inAllium cepa root tips. The frequency of polyploidy was reduced after allowing the roots to recover, which indicates that the process of polyploidy is a reversible one, if we apply Treflan for a short time (4 h). As soon as the chemioal is removed from the cells, they go on with their normal way in division. It was found that the concentration 350 × 10^-5 ml Treflan per 100 ml water is an effective concentration in producing polyploidy in the roots ofAllium cepa. Treflan induced C-tumours in root tips ofAllium cepa. Two types of enlargement were noticed, complete swelling along the majority of root tips and complete swelling with a certain enlargement immediately after 2 mm terminal tips. The histological examination of these zones revealed that swellings were due to cell enlargement both in meristematic and in tumour zones. This conclusion was evidenced by the results obtained from the nucleoplasmic index.