Involvement of inorganic elements in tissue reunion in the hypocotyl cortex of Cucumis sativus

Cucumber (Cucumis sativus L.) hypocotyls were transversely cut to half their diameter, and morphological analyses of the tissue-reunion process in the cortex were conducted to elucidate the involvement of root-derived factors. Cell division in the cortex commenced 3 days after cutting, and the cortex was nearly fully united within 7 days. In shoots from which the roots were removed and which were cultured in water, cell division occurred during tissue reunion; however, thick-wall layer formed in the reunion region, and intrusive cell elongation and interdigitation of cortex cells at the cut surface did not occur, even after 7 days. Interdigitation of cells, followed by normal tissue reunion, was observed in shoots from which the roots were removed and which were cultured in squash xylem sap or Murashige and Skoog (MS) medium. The same effect was observed with the simultaneous application of B, Mn, and Zn, which are the major inorganic microelements of MS medium. Our results suggest that application of these inorganic elements, which are taken up from the soil and transferred to the xylem sap, are required for interdigitation of cells during tissue reunion in the cortex of cucumber hypocotyls, possibly because they are required for cell wall function and metabolism.Asahina M and Gocho Y equally contributed to this work.     

Interplay between SCARECROW, GA and LIKE HETEROCHROMATIN PROTEIN 1 in ground tissue patterning in the Arabidopsis root

Regulated cell division is critical for the development of multi-cellular organisms. In the Arabidopsis root, SCARECROW (SCR) is required for the first cell division, but represses the subsequent, longitudinal asymmetric cell divisions that generate the two cell types of the ground tissue – cortex and endodermis. To elucidate the molecular basis of the role of SCR in ground tissue patterning, we screened for SCR-interacting proteins using the yeast two-hybrid method. A number of putative SCR-interacting proteins were identified, among them LIKE HETEROCHROMATIN PROTEIN 1 (LHP1). In lhp1 mutants, a second longitudinal asymmetric cell division occurs in the ground tissue earlier than in wild-type plants. Similar to the scr mutant, this premature middle cortex phenotype is suppressed by the phytohormone gibberellin (GA). We provide evidence that the N-terminal domain of SCR is required for the interaction between SCR and LHP1 as well as with other interacting partners, and that this domain is essential for repression of asymmetric cell divisions. Consistent with a role for GA in cortex proliferation, mutants of key GA signaling components produce a middle cortex precociously. Intriguingly, we found that the spindly (spy) mutant has a similar middle cortex phenotype. As SPY homologs in animals physically interact with histone deacetylase, we examined the role of histone deacetylation in middle cortex formation. We show that inhibition of histone deacetylase activity causes premature middle cortex formation in wild-type roots. Together, these results suggest that epigenetic regulation is probably the common basis for SCR and GA activity in cortex cell proliferation.     

Reversal of 5-fluorodeoxyuridine-caused growth inhibition in intact and excised etiolated hypocotyls of Sinapis alba L. by thymidine

Summary The elongation growth in etiolated, intact seedlings and excised hypocotyl segments of Sinapis alba is inhibited by FdUrd in the same fashion, and in either case there is a direct correlation between FdUrd concentration and inhibition of elongation growth. Removal of the roots reduced elongation; however, the percentage inhibition by FdUrd remained the same. Therefore, the growth inhibition by FdUrd is not a consequence of root growth inhibition.The growth inhibition in excised hypocotyls cultured on synthetic media is inversely proportional to the size of the segments, and of the seedlings from which they are taken. Elongation of the smaller segments is more sensitive to FdUrd than that of the larger ones. Anatomical observations showed that the inhibition of growth elongation by FdUrd in the hypocotyl segments is due to inhibition of cell elongation, and not of cell division. Root formation is inhibited in all isolated segments.The growth inhibition by FdUrd could be reversed by dThd but not by uridine, and this reversibility depended upon the FdUrd concentration. When FdUrd inhibition is partial (up to 10^-7M) relatively high dThd concentration (up to 100 fold) are required for complete reversal; when inhibition is maximal relatively lower dThd concentrations effect a complete or near-complete reversal. Irreversible, unspecific effects of FdUrd were not found.These experiments confirm that DNA synthesis is involved in cell elongation of the hypocotyls even when the apical meristem and roots are removed, and that the growth inhibition by FdUrd is not a nonspecific, toxic effect.Abbreviations FdUrd 5-fluorodeoxyuridine - dThd thymidine     

Sensitivity of cell division and cell elongation to low water potentials in soybean hypocotyls

Summary The response of cell division and cell elongation to low cell water potentials was studied in etiolated, intact soybean hypocotyls desiccated either by withholding water from seedlings or by subjecting hypocotyls to pressure. Measurements of hypocotyl water potential and osmotic potential indicated that desiccation by withholding water resulted in osmotic adjustment of the hypocotyls so that turgor remained almost constant. The adjustment appeared to involve transport of solutes from the cotyledons to the hypocotyl and permitted growth of the seedlings at water potentials which would have been strongly inhibitory had adjustment not occurred. Growth was ultimately inhibited in hypocotyls due to inhibition of cell division and cell elongation to a similar degree. The inhibition of cell elongation appeared to result from a change in the minimum turgor necessary for growth. On the other hand, when intact hypocotyls were exposed to pressure for 3 h, osmotic adjustment did not occur, turgor decreased, and the sensitivity of growth to low cell water potentials increased, presumably due to inhibition of cell elongation. Thus, although cell division was sensitive to low cell water potentials in soybean hypocotyls, cell elongation had either the same sensitivity or was more sensitive, depending on whether the tissue adjusted osmotically. Osmotic adjustment of hypocotyls may represent a mechanism for preserving growth in seedlings germinating in desiccated soil.Supported by a grant from the Illinois Agricultural Experiment Station, University of Illinois and grant 1-T1-GM-1380 from the United States Public Health Service.     

Selection in Vitro for NaCI-tolerance in Vitis rupestris Scheele

Suspension cultures were made from the vegetative tissues ofanthers of the grape rootstock Vitis rupestris Scheele cv. RupestrisSt George. Cell lines and somatic embryos were isolated whichgrew in agitated liquid media containing up to 150 mM NaCl.Exposure to NaCl (50–100 mM) promoted outgrowth of secondarysomatic embryos but inhibited development of plantlets. Withinsomatic embryos the cotyledon and hypocotyl tissues were moretolerant of NaCl than root tissues. Elongation of the radiclein embryos in the presence of NaCl (50 mM) was associated withnecrosis and death of root tissue but hypocotyls and cotyledonsremained viable and continued to produce callus and secondarysomatic embryos. The usefulness of the cell culture approachin selecting for salt tolerance is questioned.     

Cytological studies on the antimetabolite action of 2, 6-diaminopurine in Vicia faba roots

At a concentration of 9.6 x 10(-5)M, 2,6-diaminopurine (DAP) completely inhibited cell enlargement, cell division, and DNA synthesis (determined by microphotometric measurement of Feulgen dye) in Vicia faba roots. Inhibition of cell enlargement was partially reversed by adenine, guanine, xanthine, adenosine, and desoxyadenosine. Guanine and the nucleosides gave the greatest reversal, suggesting that one point of DAP action upon cell enlargement is a disruption of nucleoside or nucleotide metabolism, possibly during pentosenucleic acid synthesis. DAP inhibited cell division by preventing onset of prophase. At the concentrations used it had no significant effect on the rate or appearance of mitoses in progress. Inhibition of entrance into prophase was not directly due to inhibition of DNA synthesis since approximately half of the inhibited nuclei had the doubled (4C) amount of DNA. Adenine competitively reversed DAP inhibition of cell division, giving an inhibition index of about 0.5. Guanine gave a slight reversal while xanthine, hypoxanthine, adenosine, and desoxyadenosine were inactive. A basic need for free adenine for the onset of mitosis was suggested by this reversal pattern. Meristems treated with DAP contained almost no nuclei with intermediate amounts of DNA, indicating that DAP prevented the onset of DNA synthesis while allowing that underway to reach completion. The inhibition of DNA synthesis was reversed by adenine, adenosine, and desoxyadenosine although synthesis appeared to proceed at a slower rate in reversals than in controls. Inhibition of DNA synthesis by DAP is probably through nucleoside or nucleotide metabolism. A small general depression of DNA content of nuclei in the reversal treatments was observed. This deviation from DNA "constancy" cannot be adequately explained at present although it may be a result of direct incorporation of DAP into DNA. The possible purine precursor, 4-amino-5-imidazolecarboxamide gave no reversal of DAP inhibition of cell elongation and cell division and only a slight possible reversal of inhibition of DNA synthesis.     

Light-controlled growth of the maize seedling mesocotyl: Mechanical cell-wall changes in the elongation zone and related changes in lignification

Cell extension in the mesocotyl elongation zone (MEZ) of maize ( Zea mays L.) seedlings is inhibited by light. The growth inhibition by blue light in the MEZ was reversible upon transfer to darkness. This experimental system was used for investigating the modification of mechanical cell-wall properties and the role of cell-wall lignification in cell elongation. The occurrence of lignin in the cortex and vascular bundle tissues of the MEZ was demonstrated by the isolation of diagnostic monomers released after thioacidolysis of the cell walls. Concomitantly with the inhibition of growth, blue light induces an increase in cell-wall stiffness (tensile modulus) as well as an increase in extractable lignin in the outer MEZ tissues (cortex+epidermis). Both effects are reversed when growth is resumed in the MEZ in darkness after a period of growth inhibition induced by 3 h light. In the vascular bundle light produces no comparable change in lignin content. Appearance and disappearance of phenylpropanoid material in MEZ cell walls in the light, or in darkness following a brief light treatment, respectively, can be visualized under the fluorescence microscope by characteristic changes in autofluorescence of tissue sections upon excitation with UV radiation. It is concluded from these results that light-induced lignification of primary walls is involved in cell-wall stiffening and thus inhibition of elongation growth in the MEZ of maize seedlings. Resumption of growth upon redarkening may be initiated by wall loosening in the uppermost MEZ region which displaces the lignified cell walls towards the lower mesocotyl region.     

Influence of ethylene and Ag+ on hypocotyl growth in etiolated lupin seedlings. Effects on cell growth and division

Lupin seeds treated with 1-amino-cyclopropane-1-carboxylic acid (ACC) or2-chloroethylphosphonic acid (CEPA) produced hypocotyls showing a typicalethylene growth response (reduced elongation and increased thickness), whichcould be efficiently counteracted by the presence of silver thiosulfate (STS).The fact that ACC and CEPA stimulated the ethylene produced in different zonesalong the hypocotyls suggests that these compounds, which are stored in theseeds during treatment, were transported to and along the hypocotyl. The same istrue in hypocotyls from STS-treated seeds, which indicates that stress ethyleneis induced by metal toxicity. CEPA was more effective than ACC in both producingethylene and influencing growth due to the high capacity of the hypocotyl toconjugate ACC. At the same time that CEPA inhibited hypocotyl elongation, thehypocotyl diameter increased and ethylene production exceeded the maximum valueof the control. The subsequent recovery of hypocotyl elongation coincided with adecrease in ethylene production and involved cell elongation. The final celllength was similar (in ACC-) or higher (in CEPA-treated plants) than in thecontrol, although the hypocotyls were shorter in both cases, while the number ofcells per column was reduced to half that observed in the control. Thisinhibition of cell division caused by ethylene was selective since the number ofcell layers did not change. The variations in cell diameter in the epidermisand, especially, in the cortex and pith were correlated with the variations inhypocotyl diameter produced by ACC, CEPA and STS. The results show that theethylene-induced hypocotyl thickening was irreversible and mainly due to anincrease in cell diameter, while the inhibition of hypocotyl elongation wasreversible and involved irreversible inhibition of cell division and,paradoxically, stimulation of cell elongation to produce cells longer than thoseof the control.     

The role of cytokinins in rooting of stem slices cut from apple microcuttings

ABSTRACT

We examined the role of cytokinins in rooting of 1-mm stem slices cut from microcuttings of the apple rootstock ‘Jork 9?s. Various types of cytokinins inhibited the rooting of apple stem slices to different extents. Highest inhibition was obtained with thidiazuron and benzylaminopurine. Remarkably, isopentenyladenine and isopentenyladenosine enhanced rooting at low concentration (at the optimal concentration of 0.1 μM by 53 and 19%, respectively). We also examined the effect of lovastatin and simvastatin. These drugs are putative cytokinin-synthesis inhibitors. Both inhibited rooting and inhibition was partially reversed by simultaneous addition of zeatin. Moreover, in the presence of lovastatin a higher concentration of zeatin had to be applied to achieve inhibition of rooting than in the absence of the drug. This data indicates that these compounds indeed inhibited cytokinin synthesis. One-day pulses with lovastatin strongly blocked rooting when given just after cutting the slices but had no effect after that. Adding zeatin simultaneously reversed inhibition completely. In conclusion, our data confirm that cytokinins may strongly inhibit rooting but they also show that at low concentration, certain cytokinins enhance rooting. Moreover, synthesis of cytokinin is essential during root formation. We hypothesise that cell division initiated by a relatively high endogenous level of cytokinins just after cutting the slices is a necessary, initial step in adventitious root formation.     

Growth Inhibition, Turgor Maintenance, and Changes in Yield Threshold after Cessation of Solute Import in Pea Epicotyls

The dependence of stem elongation on solute import was investigated in etiolated pea seedlings (Pisum sativum L. var Alaska) by excising the cotyledons. Stem elongation was inhibited by 60% within 5 hours of excision. Dry weight accumulation into the growing region stopped and osmotic pressure of the cell sap declined by 0.14 megapascal over 5 hours. Attempts to assay phloem transport via ethylenediaminetetraacetate-enhanced exudation from cut stems revealed no effect of cotyledon excision, indicating that the technique measured artifactual leakage from cells. Despite the drop in cell osmotic pressure, turgor pressure (measured directly via a pressure probe) did not decline. Turgor maintenance is postulated to occur via uptake of solutes from the free space, thereby maintaining the osmotic pressure difference across the cell membrane. Cell wall properties were measured by the pressure-block stress relaxation technique. Results indicate that growth inhibition after cotyledon excision was mediated primarily via an increase in the wall yield threshold.     

Cell elongation and cell division in elongating lettuce hypocotyl sections

The roles of cell division and cell elongation in the growth of sections excised from hypocotyls of lettuce (Lactuca sativa L. cv. Arctic) were investigated. Elongation of sections incubated in the light is inhibited compared to dark-grown sections and this inhibition is reversed by gibberellic acid (GA₃). The elongation of both dark-grown and GA₃-treated, light-grown sections can be enhanced by 10mM KCl. Under all conditions of incubation, elongation growth is greatest in the uppermost quarter of the hypocotyl section while the basal quarter does not elongate. In darkness the two apical segments of sections marked into four equal parts grow at the same rate, while in light, growth of the apical segment exceeds that of the second segment. Cell division in cortical or epidermal cells, as measured by mitotic index or cell number, is not affected by illumination conditions nor by GA₃ or KCl treatments. Although -irradiation and FUDR pretreatment eliminate or cause a marked reduction in cell division in the excised hypocotyl, sections from seeds irradiated with -rays or incubated in 5-fluorodeoxyuridine elongate in response to GA₃ and KCl treatment as do sections from non-pretreated controls. Therefore, since neither GA₃ nor darkness affect celldivision activity and since treatments which eliminate or significantly reduce cell division do not affect growth, we conclude that the effect of GA₃ and darkness in this material is to increase cell elongation.Abbreviations FUDR 5-fluorodeoxyuridine - GA(s) gibberellin(s) - GA₃ gibberellic acid     

Growth and gibberellin a(1) metabolism in excised lettuce hypocotyls

Excised lettuce (Lactuca sativa L. cv. Arctic) hypocotyls retain the ability to elongate in response to exogenously supplied gibberellic acid and gibberellin A(1) (GA(1)). We have studied the relationship between metabolism of GA(1) and elongation in this tissue. In 24 hours at 28 C, hypocotyls treated with 3 mum GA(1) double in length while controls elongate less than 45%. After an exogenous hormone supply is removed, hypocotyls continue to grow faster than untreated controls, although as the hormone application time is decreased, the GA(1) concentration required to effect a given length change increases. [(3)H]GA(1) was used to determine rates of hormone uptake, efflux, and metabolism. In the presence of [(3)H]GA(1), hypocotyls accumulate and metabolize lable for at least 24 hours. When the exogenous label is removed, the amount of acidic GA in the hypocotyl declines rapidly to a constant level while ethyl acetate-insoluble metabolites increase rapidly to a constant level. Lable accumulation and metabolism at any time are proportional to the external GA(1) concentration below 50 mum GA(1). Chromatographic analysis of radioactive compounds present in tissue extracts suggests that unaltered GA(1) is the major component of the acidic ethyl acetate-soluble fraction, and gibberellin A(8) is a minor component. The ethyl acetate-insoluble fraction appears to contain an unidentified GA(1) metabolite with chromatographic properties similar to those of GA(1). The strong retention of accumulated GA(1) confirms the possibility of a continuing requirement for GA(1) during the sustained response to a GA(1) "pulse" but raises the question of accessibility of the stored hormone for growth promotion.     

Culture of Cotyledon and Hypocotyl Protoplasts from True Potato Seedlings in Solanum tuberosum L.

Culture of protoplast using cotyledon and hypocotyl as the donor tissue from true potato seedlings (TPSs) of 3 breeding lines (DTO-33, ND 860-2 and BN 9815-3) of Solanum tuberosum L. was studied. The cotyledons and hypocotyls of TPSs just extended were excised and digested in an enzyme solution containing 1 % cellulase and 0. 5 % macerozyme for 17—20 h after vacuum infiltration of the tissue in the solution. The protoplasts were cultured in an improved liquid medium and transferred onto solid media for callus culture and shoot regeneration. Some factors affecting the efficiency of cotyledon and hypocotyl protoplast culture were studied. The results showed that using the cotyledons and hypocotyls as donor tissues for protoplast isolation and culture in potato, the division frequency of protoplast derived cells was significantly higher than that using the leaves and shoot-tips of the test-tube plantlets: the yield and quality of the protoplast from TPSs cultured under continuous high light intensity (3000 Ix) were much higher than the TPSs cultured under low light intensity (1000 Ix), and no intact protoplast was ever obtained from the TPSs cultured in continuous dark condition. Vacuum infiltration of the cotyledon and hypocotyl segments in enzyme solution before digestion increased protoplast yield. The yield of protoplasts from hypocotyl tissue was significantly higher than from the cotyledon, but there was no significant difference in quality between the protoplast derived from the two tissues. The significance, advantages and shortcomings of using the cotyledons and hypocotyls as the donor tissues for isolation and culture of potato protoplasts are dicussed.     

Cell elongation, turgor and osmotic pressure in developing sunflower hypocotyls

The relationship between cell elongation, change in turgor andcell osmotic pressure was investigated in the sub-apical regionof hypocotyls of developing sunflower seedlings (Helianthusannuus L.) that were grown in continuous white light. Cell turgorwas measured with the pressure probe. The same hypocotyl sectionswere used for determination of osmotic pressure of the tissuesap. Acceleration of cell elongation during the early phaseof growth was accompanied by a 25% decrease in both turgor andosmotic pressure. During the linear phase of growth both pressuresremained largely constant. The difference between turgor andosmotic pressure (water potential) was –0.10 to –0.13MPa. Excision of one cotyledon had no effect on growth, turgorand osmotic pressure. However, after removal of both cotyledonscell elongation ceased and a substantial decrease in both pressureswas measured. In addition, we determined the longitudinal tissuepressure in seedlings from which one or both cotyledons hadbeen removed. Tissue pressure and turgor were very similar quantitiesunder all experimental conditions. Our results demonstrate thatturgor and cell osmotic pressure show a parallel change duringdevelopment of the stem. Cessation of cell elongation afterremoval of the cotyledons is attributable to a decrease in turgor(tissue) pressure, which provides the driving force for growthin the hypocotyl of the intact plant. Key words: Cell elongation, Helianthus annuus, osmotic pressure, tissue pressure, turgor     

Modification of cell wall polysaccharides during cell elongation in Phaseolus vulgaris hypocotyls

The effect of gibberellic acid (GA) and naphthylacetic acid (NAA) on hypocotyl elongation and cell wall polysaccharides was studied using Phaseolus vulgaris seedlings grown in light condition. The hypocotyl was demarcated into two segments — one near the root was called lower and the one near the cotyledon was called upper. The upper segment showed a typical sigmoidal growth curve while lower segment did not show any growth at all. GA promoted the growth of upper segment while NAA showed clear inhibition in both the segments. Xyloglucan content showed a clear inverse correlation with growth. Pectic polysaccharides did not show a clear trend, though showed an initial inverse correlation with growth. It is concluded that degradation of low and high molecular weight xyloglucans are involved in cell wall loosening which in turn may be responsible for the elongation growth of Phaseolus hypocotyls in light.     

Synthesis of new glycyrrhetinic acid (GA) derivatives and their effects on tyrosinase activity

To synthesize glycyrrhetinic acid (GA) derivatives (3, 4, 5, 10, 13, 14, 15, and 16), we first removed the ketonic group in the C-11 position, and the carboxylic function at the C-30 position was kept intact, reduced to an alcohol, or transformed to an aldehyde corresponding derivatives 10 and 13. Glycyrrhetinic acid (GA) derivatives (3, 4, 5, 15, and 16) were coupled with 4-amino piperpyridine derivatives (12 and 14) and 4-fluorobenzyl bromide at C-30 carboxylic acid position of glycyrrhetinic acid. In subsequent tyrosinase assays, we found that GA derivatives 4, 5, and 16 were not active at early time points, but strongly inhibited tyrosinase activity at late time points. Of the GA derivatives examined, derivative 5 was most active, with an IC₅₀ value of 50 μM after 2 h reaction. IC₅₀ values of derivatives 4 and 16 were 120 and 170 μM, respectively. Further kinetic data indicated that these derivatives are slow-binding inhibitors of tyrosinase. The time-dependent inhibition was reversed when vitamin C or kojic acid was used, that is, both compounds showed active inhibition at early time points. These results suggest that GA derivatives are much more stable than vitamin C or kojic acid, although their intrinsic inhibitory potentials are relatively low. Higher stability and activity suggest that GA derivative 5 might be a useful candidate for skin whitening.     

Control by cytokinins of the cellular behavior in the plate meristem of zucchini cotyledons

The temporal and spatial effects of exogenous cytokinins on both cell expansion and division activity in the plate meristem of cultured zucchini cotyledons were studied. N ⁶-benzylaminopurine (1–100 μM) and N-(2-chloro-4pyridyl)-N′-phenylurea (4PU-30) (0.1–100 μM) greatly stimulated the cell growth and division. They provoked multiple cell cycles, formation of larger clusters of daughter cells and an increase of the final number of cells. Both cytokinins led to earlier achievement of final cotyledon size and shortened the cell doubling time. By contrast to the purine cytokinin, phenylurea cytokinin 4PU-30 enlarged the cotyledon predominantly in length. Zeatin and kinetin were less effective, particularly in stimulating cell expansion. In low concentrations, all cytokinins were more effective in stimulating division activity rather than expansion. The cells in the cotyledon margins displayed a higher division activity, especially when treated with exogenous cytokinins. The final cotyledon and cluster areas were not of the strict proportional dependence upon the number of their cells. These results provide a novel example where stimulated cell division fails to evoke a respective increase in the final organ size.     

Ethylene effects on cambial activity and cell wall formation in hypocotyls of Picea abies seedlings

Ethylene regulation of cell division in the vascular cambium and cell wall formation was studied in hypocotyls of Norway spruce ( Picea abies [L.] Karst.) seedlings. Cuttings from 6-week-old seedlings were placed in water culture to which compounds affecting the synthesis and action of ethylene were added. After a 3-week treatment period, growth, ethylene production, morphology and cell wall composition of the hypocotyls were determined. Addition of high concentrations of the potent ethylene releasing agent 2-chloroethylphosphonic acid (ethrel), which increased ethylene emission by more than twice compared to control plants, inhibited the expansion of xylem cells while stimulating the incorporation of cell wall material, especially cellulose. Addition of small amounts of ethrel, which slightly stimulated ethylene emission, led to increases in the size of xylem cells, the amount of phloem tissue and the number of intercellular spaces in the cortex, and thus to increased hypocotyl diameter. However, no significant change in cell wall composition was detected. When ethylene production was decreased by adding Co²⁺ to the nutrient solution, differentiation of new xylem was disturbed, but the rate of cell division was not affected. Although the incorporation of cell wall material was inhibited, the proportions of lignin and cellulose in the wall appeared to remain unchanged. Silver ions stimulated the expansion of both xylem and cortex cells, but had no significant effect on cell wall formation. We conclude that ethylene has a role in regulating the incorporation of wall carbohydrates.     

Effect of Chlorsulfuron on Morphogenetic and Disordered Cell Division in Cultures of Passiflora edulis

We examined the effects of a sulfonylurea herbicide, chlorsulfuron, which is known as a potent inhibitor of plant cell division, on morphogenetic cell division and disorganized cell division using the culture system of multiple shoot primordia and callus of Passiflora edulis. The multiple shoot primordia tissue treated with chlorsulfuron failed to achieve shoot morphogenesis, and a large part of the tissue was necrotized during the posttreatment culture, even when it was washed and transferred to chlorsulfuron-free medium. The inhibition of Passiflora shoot morphogenesis by chlorsulfuron was not reversed by the simultaneous addition of branched amino acids, which are known to reverse the inhibitory effect of chlorsulfuron. In contrast, the same treatment of chlorsulfuron on the callus did not kill the cells, although the growth resumption was retarded by a prolonged lag period. The addition of branched amino acids enhanced the recovery growth of the chlorsulfuron-treated callus. These results suggest that the inhibition of disorganized cell division (callus growth) by chlorsulfuron is reversible, whereas morphogenetic cell division (shoot morphogenesis), which is under complex regulation, is inhibited irreversibly by chlorsulfuron. Qualitative differences between morphogenetic cell division and disordered simple proliferative cell division are discussed. Received November 17, 1997; accepted June 4, 1998