Synergistic effect of DFMO and 2,4-D on regeneration of Tabernaemontana persicariaefolia jacq in vitro

Callus cultures of Tabernaemontana persicariaefolia, (Apocynaceae), an endangered species endemic to the Mascarene Islands, were established from leaf explants on MS medium containing either 5 mg·l⁻¹ 2,4-D and 0.5 mg·l⁻¹ BA or 5 mg·l⁻¹ 2,4-D, 0.5 mg·l⁻¹ BA and 200 mg·l⁻¹ DFMO. Histological studies showed regenerating nodules resembling globular embryos in calli after 4 weeks on the DFMO medium. Green shoot formation was achieved by sequential subculture of the induced calli on media with gradually decreasing 2,4-D concentrations (5→1→0 mg·l⁻¹). Regeneration was greatly stimulated in the presence of DFMO. The first emergence of shoots occured 3 weeks earlier than in untreated callus cultures.     

沙枣组织脱分化培养与快繁体系建立的研究

研究了以沙枣的种子为外植体诱导形成愈伤组织以及植株再生的过程,对培养中出现的愈伤组织和不定芽的类型进行了探讨。通过正交试验及单因素试验方法,确定了沙枣快繁体系的最适培养方案：①诱导材料：苗期为10 d的沙枣无菌苗子叶;②有效愈伤组织诱导培养基：MS+NAA 0.5 mg·L^-1+BA 2.0 mg·L^-1+3%蔗糖;③有效芽的分化培养基：MS+NAA 0.1 mg·L^-1+BA1.0 mg·L^-1+3% 蔗糖;④壮苗培养基：MS+NAA 0.1mg·L^-1+BA 1.0 mg·L^-1+GA 30.2 mg·L^-1+3%蔗糖;⑤生根培养基：1/2MS+ABT生根粉（1号）1.0 mg·L^-1+1.5%蔗糖。     

Rhizome induction and plantlet regeneration of Cymbidium goeringii from flower bud cultures in vitro

Apical flower buds of Cymbidium goeringli Reichenbach fil. (ca 2 mm long) exeised from infloreseences (ca 5 cm long) were explanted on modified Murashige & Skoog medium (=MS medium) supplemented with N⁶-benzyladenine (BA) and -naphthaleneacetic acid (NAA). Within 107 days of culture, swelling growth, chlorophyll synthesis, and subsequent rhizome differentiation were observed. MS medium containing 0.1 mg l^-1 BA and 10 mg l^-1 NAA was found to be optimal for initiating rhizome development and subsequent plantlet regeneration.Explants cultured on MS medium supplemented with 1 mg l^-1 NAA alone formed a mass of rhizome branches. Multiple shoots of rhizome branches were induced from apical segments when rhizomes were transferred to MS medium containing 0.1 mg l^-1 BA and 10 mg l^-1 NAA.Abbreviations NAA -naphthaleneacetic acid - BA N⁶-benzyladenine     

Micropropagation ofCereus peruvianus mill. (cactaceae) by areole activation

Summary Currently,Cereus peruvianus plants can be rapidly clonedin vitro via adventitious organogenesis using callus cultures; however, somaclonal variation is a problem. A method is described herein using lateral bud explants to produce multiple shoots for clonal propagation. Apical and lateral explants were cultured on MS (Murashige and Skoog, 1962) media with factorial combinations of the auxins indole-3-acetic acid (IAA), 1-naphthaleneacetic acid (NAA), and cytokinins 6-ben-zyladenine (BA) and N-(2-furanyl-methyl)-1-purine-6 amine (kinetin) at the concentrations 0.0, 0.01, 0.1, 1.0 mg“l⁻¹. Positive results were obtained from the lateral explants in all conditions tested, but apical explants did not respond toin vitro multiplication ofC. peruvianus cactus at all growth regulator combinations tested. Formation of axillary shoots inC. peruvianus seems most frequent in medium containing BA at 1.0 mg·l⁻¹ (4.44 μM) and IAA or NAA at 1.0 mg·l⁻¹ (5.71 μM or 5.37 μM respectively), but the frequency of shoot formation in the BA or kinetin and NAA or IAA combinations indicated that any of the combinations tested can be used for multiplication ofC. peruvianus plants regenerated from callus tissue culture. Root formation occurred in all (100%) of the cactus shoots after 9 wk in the same culture medium. All the cacti that developed at the different auxin and cytokin combinations continued growth after transfer to a potting mix of red earth (Paleudult) and ground river sand (1∶1).     

褐纹报春苣苔组织培养与快速繁殖

褐纹报春苣苔(Primulina glandaceistriata)是一种极具观赏价值的喀斯特地区野生花卉,目前尚未有褐纹报春苣苔组培快繁的研究报道。该研究以褐纹报春苣苔的叶片为外植体,通过两种途径建立其组培快繁体系。结果表明:适宜的不定芽诱导培养基为MS+6-BA 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1),适宜的不定芽增殖培养基为MS+ZT 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1)+活性炭0.05 g·L~(-1),增殖系数为11.09;适宜的愈伤组织诱导培养基为MS+TDZ 2.0 mg·L~(-1)+NAA 0.10 mg·L~(-1),适宜的愈伤组织分化培养基为MS+ZT 1.0 mg·L~(-1)+NAA 0.10mg·L~(-1),分化系数为12.46;适宜的生根培养基为1/2MS+IBA 0.1 mg·L~(-1)+活性炭0.05 g·L~(-1)或1/2MS+IBA0.5 mg·L~(-1)+活性炭0.05 g·L~(-1),生根率为100%。该研究结果成功建立了褐纹报春苣苔的组培快繁体系,为今后褐纹报春苣苔的种苗繁殖和遗传转化提供了技术支持。     

The interaction of auxin and cytokinin in the induction of phenylalanine ammonia-lyase in suspension cultures of Phaseolus vulgaris

The dependence of phenylalanine ammonialyase (PAL) induction in bean suspension cultures on the concentration of naphthylacetic acid (NAA) and kinetin has been investigated and the timing of the effect of each hormone has been determined. NAA was required at an optimal concentration of 1 mg l^-1 2 days prior to the increase in PAL activity. Kinetin caused a prapid stimulation of the rate of PAL induction and the total amount of PAL induced in a concentration range of 0.1–0.5 mg l^-1 when it was supplied to the cells immediately prior to the expected rise in PAL activity. The inhibitory effect of 2 mg l^-1 NAA on PAL induction was overcome by an increased concentration of kinetin.Abbreviations NAA naphthylacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3yl acetic acid - PAL phenylalanine ammonia-lyase (EC 4.3.1.5.)     

Lignin synthesis and its related enzymes as markers of tracheary-element differentiation in single cells isolated from the mesophyll of Zinnia elegans

Mesophyll cells isolated from Zinnia elegans L. cv. Canary Bird were cultured for 96 h in a liquid medium containing 0.1 mg l^-1 -naphthaleneacetic acid and 1 mg l^-1 benzyladenine in which both differentiation of tracheary elements (TE) and cell division were induced, or in a medium containing 0.1 mg l^-1 -naphthaleneacetic acid and 0.001 mg l^-1 benzyladenine, in which cell division was induced but TE differentiation was not. Lignification was found to occur only in the former medium, fairly synchronously after 76 h of culture, 5 h later than the onset of visible secondary wall thickening. Changes in the soluble phenolics were not correlated with TE differentiation. Of three important enzymes which have been reported to play a role in TE differentiation, the activity of phenylalanine ammonia-lyase (EC 4.3.1.5) in the TE-inductive culture was higher than that in the control culture between 72 and 96 h of culture, when TE differentiation progressed and lignin was synthesized actively. O-Methyltransferase (EC 2.1.1.6) activity was higher in the control culture than in the TE-inductive culture, indicating that this enzyme was not a marker enzyme of TE differentiation. The activities of peroxidases (EC 1.11.1.7), one extractable and the other nonextractable, with CaCl₂ from the cell walls, reached peaks at 72 h (just before lignification) and 84 h of culture (active lignin synthesis), respectively, in the TE-inductive culture only, whereas the activity of soluble peroxidase showed a similar pattern of increase in the TE-inductive to the control culture. These results indicate that phenylalanine ammonia-lyase and peroxidase bound to the cell walls can be marker proteins for the differentiation of TE.Abbreviations OMT O-methyltransferase - PO peroxidase - PAL phenylalanine ammonia-lyase - TE tracheary element(s)     

杜仲叶片愈伤组织诱导的激素优化研究

以杜仲优树L33的幼叶为材料,在B5培养基上添加不同浓度的生长素与细胞分裂素进行愈伤组织诱导研究,结果表明：无激素的培养基上不能诱导出愈伤组织,单独加入2,4-D、NAA和IBA均可诱导出愈伤组织,以0.5 mg·L^-1 2,4-D、0.5～1.0 mg·L^-1 NAA、1.0 mg·L^-1 IBA出愈率最高,达100%,且愈伤组织生长较好;在适宜浓度的生长素的培养基上加入细胞分裂素时,KT的加入对愈伤组织的诱导及生长起抑制作用;1.0 mg·L^-1 NAA+0.3～0.5 mg·L^-1 BA与1.0 mg·L^-1 IBA+0.3～0.5 mg·L^-1 BA 的组合可明显促进愈伤组织的诱导和生长,适合进一步继代培养。     

青海野生黑果枸杞再生体系的建立及遗传稳定性分析

以野生黑果枸杞(Lycium ruthenicum Murr.)的无菌苗叶片作为外植体,建立了两条再生体系:一条是经愈伤组织再分化的间接再生体系,一条是不经愈伤组织再分化的直接再生体系。并采用流式细胞术(FCM)及ISSR分子标记技术对两种途径再生苗进行了遗传稳定性分析。结果表明:(1)最佳愈伤组织诱导培养基为MS+1.5 mg·L-12,4-二氯苯氧乙酸(2,4-D),诱导率达100%;最佳分化培养基为MS+1.5 mg·L-16-苄氨基腺嘌呤(6-BA)+0.1 mg·L-1吲哚-3-丁酸(IBA),1 g愈伤组织上的平均不定芽数为39.4个。(2)叶片直接诱导不定芽的最佳培养基为MS+0.5 mg·L-16-BA+0.3 mg·L-1α-萘乙酸(NAA),不定芽诱导率为92.9%,每个外植体上平均不定芽数为18.1个。(3)两条途径再生的不定芽在不含植物生长调节剂的MS培养基上,2周内均可正常生根。(4)FCM结果显示亲本苗及2种再生苗均为二倍体。(5)ISSR分析表明,间接再生苗的平均遗传相似性系数为0.84,直接再生苗的平均遗传相似性系数为0.91,直接再生体系是一种更加快速高效的繁殖方法。     

广西五种绞股蓝属植物离体快繁与种质保存研究

以绞股蓝属植物的带芽茎段为材料,研究不同6-BA浓度与NAA 0.02mg·L-1组合对其诱导、分化和增殖的影响,并建立离体快繁体系。结果表明:MS+6-BA 2.0mg·L-1+NAA 0.02mg·L-1最适宜初代诱导,MS+6-BA 2.0mg·L-1+NAA 0.02mg·L-1最适合扁果绞股蓝的增殖培养,而MS+6-BA 1.5mg·L-1+NAA0.02mg·L-1是其它四种植物增殖的最佳培养基,在1/2MS+NAA 1.0mg·L-1上的生根率均达100%。1/2MS与蔗糖40g·L-1对五种植物的保存效果均最好;添加生长抑制剂能有效减缓生长速度,最佳生长抑制剂为ABA和CCC,浓度均为1.0mg·L-1,其中CCC能适合多个物种,连续保存360d的存活率均在94.5%以上;PP333不适合五种植物的保存。活力检测表明,各种质经保存后增殖、生根能力均未下降。     

Somatic embryogenesis from mature zygotic embryos of Distylium chinense (Fr.) Diels and assessment of genetic fidelity of regenerated plants by SRAP markers

The objective was to establish an efficient regeneration protocol for Distylium chinense based on somatic embryogenesis and evaluate the genetic stability of plants regenerated in vitro. To induce callus mature zygotic embryos were cultured on Murashige and Skoog’s (MS) medium that was supplemented with different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and N⁶-benzyladenine (BA). After 20 days, the highest rate of callus formation (88.9 %) occurred on MS medium supplemented with 0.5 mg l^?1 2,4-D and 0.1 mg l^?1 BA. It was observed that light-yellow, compact, dry, nodular embryogenic calli had formed. These calli were then subcultured on fresh MS medium supplemented with 0.1 mg l^?1 BA and 0.5 mg l^?1 α-naphthaleneacetic acid (NAA) for proliferation for an additional 30 days. To induce somatic embryos and plant regeneration, the embryogenic callus was transferred to fresh MS medium that was supplemented with different concentrations of BA and NAA. After 30 days, 0.5 mg l^?1 BA in combination with 0.5 mg l^?1 NAA produced the best result in terms of somatic embryogenesis (%), shoot differentiation (%), number of shoots per callus and shoot length. Next, the plantlets were transferred to the field for 5 weeks and a 95 % survival rate was observed. The sequence-related amplified polymorphism markers confirmed genetic stability of plants regenerated in vitro. To our knowledge, this is the first report that describes a plant regeneration protocol for D. chinense via somatic embryogenesis to be used for germplasm conservation and commercial cultivation.     

Induction of haploid callus and embryogenesis in in vitro cultured anthers of mulberry (Morus indica)

Anthers of Morus indica L., with microspores at the uninucleate stage were cultured; and the influence of temperature and kinetin pretreatment on induction of androgenic calluses was examined. The effects of various pretreatments revealed that 24 h cold pretreatment increased the percentage of cultures inducing callus. First microspore division was observed after 16 to 20 days of culture. Th anthers split and developed embryogenic calluses on MB medium supplemented with NAA (0.5 mg l^–1 and BA (1.0 mg l^–1)) using 8% sucrose. Rhizogenesis was induced on medium supplemented with NAA and BA (each 0.5 mg l^–1) with reduced myo-inositol (75 mg l^–1). Cytological study of induced roots confirmed the haploid nature of calluses. Different type of embryos were initiated upon transfer of calluses to medium supplemented with NAA, BA (each 0.5 mg l^–1), 2,4-d (1.0 mg l^–1) and PVP (600 mg l^–1). These embryoids further developed roots on removal of 2,4-d from the medium and developed precociously without developing cotyledons and formed elongated shoots.Abbreviations BA 6 benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - FAA formalin: Acetic acid: Alcohol - GA₃ gibberellic acid - IBA indole-3-butyric acid - MB modifed Bourgin (Qian et al., 1982) - NAA 1-naphthalene acetic acid - PVP polyvinylpyrrolidone - RFS-135 rainfed selection 135 - SE standard error     

广藿香叶盘法高效再生体系主要影响因素的研究

广藿香是重要的芳香药用植物,利用基因工程技术对广藿香进行品种改良,需要建立一个高效的广藿香植株再生体系。该研究以广藿香无菌苗叶片为材料,将叶盘外植体分别置于不同条件下培养,观察、统计其再生植株的数量及生长状况。通过研究15~50 d的苗龄、第2~4节上的叶及培养基中2,4-D、NAA、BA和KT的浓度和配比等因素对广藿香叶盘再生植株的影响,在此基础上优化培养条件,建立广藿香高效再生体系。结果表明:广藿香无菌苗的苗龄、叶片在茎上的着生位置以及培养基中的植物生长调节物质浓度和配比都对广藿香的植株再生有显著影响;优化培养条件为以培养30 d的广藿香无菌苗顶芽下第2对展开叶片切割的叶盘为外植体,在含0.1 mg·L-1NAA和0.5 mg·L-1BA的MS培养基中培养28 d,叶盘的不定芽发生频率达到100%,单个叶盘的平均再生芽数为96.5个,经生根培养及温室炼苗,再生植株的移栽成活率达到96%。广藿香叶盘植株再生体系的建立为其基因转化研究及优良品种的快速繁育奠定了基础。     

Morphogenesis and tissue cultures of three citrus species

Studies were performed to define tissue culture techniques and culture conditions for morphogenesis, callus culture and plantlet culture of sweet orange (Citrus sinensis (L.) Osb.), citron (C. medica L.) and lime (C. aurantifolia) (Christm. Swing). The optimal concentrations of NAA to induce root formation on stem segments were 10 mg l^-1 for sweet orange and lime, and 3 mg l^-1 for citron. The optimal BA concentration for shoot and bud proliferation was 3 mg l^-1 for sweet orange and citron, and 1 mg l^-1 for lime. Callus initiation was accomplished in a culture medium containing 10 mg l^-1 NAA and 0.25 mg l^-1 BA. Callus was maintained by periodical subculture into the same medium supplemented with 10% (v:v) organge juice. In vitro plantlets of the three species were obtained by rooting of shoots developed from bud cultures, and of citron and lime by development of shoots from root cultures. The plants were successfully established on soil.     

Propagation of rose speciesin vitro

Summary Several rose species (Rosa rugosa, R. wichuraiana, R. setigera, R. laevigata, R. banksiae, R. roxburghii, R. odorata) and interspecific hybrids were cultured to determine the appropriate concentrations of nutrients and growth regulators for shoot proliferation and root initiation. Cultured shoot tips and lateral buds from different genotypes proliferated multiple shoots on a basal medium [Murashige and Skoog (MS) salts, vitamins, glycine, sucrose, and agar] supplemented with 0 μM to 17.8 μM (4 mg·l⁻¹) 6-benzyladenine (BA) and 0 μM to 0.54 μM (0.1 mg·l⁻¹) naphthalene, acetic acid (NAA). The ability of the explants to proliferate shoots and initiate roots was affected by the genotype, the nodal position of the explant, the strength of the MS basal salts, and the growth regulators used. The buds nearest the apex exhibited the slowest rate of development. Most species had the highest shoot proliferation when cultured on basal MS medium supplemented with 8.9 μM (2 mg·l⁻¹) BA, but the degree varied by species. Root development was enhanced by lowering the concentration of MS salts. With difficult-to-root species, rooting was improved by supplementing the media with 11.4 μM (2 mg·l⁻¹) indole-3-acetic acid (IAA) or by giving them a 7-d dark treatment at 10°C.     

Micropropagation studies inCeropegia SPP

Summary The purpose of this study was to developin vitro techniques for conserving wild and endemic species ofCeropegia by mass multiplication for subsequent reintroduction in their natural habitat. Micropropagation involving a combination of axillary bud culture, shoot multiplication, somatic embryogenesis andin vitro tuber formation forCeropegia jainii, a rare plant of the Indian sub continent,C. bulbosa var.bulbosa andC. bulbosa var.lushii, common species, was developed. Nodal explants from all species were cultured on 0.5 MS medium with 8.8 μM (2 mg·l⁻¹) N⁶-benzyl aminopurine (BA) to regenerate the axillary buds. These produced multiple shoots when transferred to multiplication medium consisting of 0.5 MS medium with 2.2 μM (0.5 mg·l⁻¹) BA, or microtubers when transferred to 0.5 MS medium with 22.2 μM (5 mg·l⁻¹) BA and 23.2 μM (5 mg·l⁻¹) kinetin.In vitro flowering occurred inC. jainii and not in the other two varieties when the plants were cultured on multiplication media with spermine at 0.25 μM (50 μg·l⁻¹) as an additive. Shoot pieces produced callus on MS medium with 9.05 μM (2 mg·l⁻¹) 2,4-dichlorophenoxy acetic acid. Regeneration of the calli by somatic embryogenesis was achieved when they were transferred to 0.5 MS medium with 2.2 μM (0.5 mg·l⁻¹) BA. Rooting of the shoots was possible both byin vitro andex vitro means.     

银杏愈伤组织诱导的多因子正交试验研究

采用正交试验设计法,研究了NAA、KT、2,4-D、蔗糖浓度和不同外植体类型等因素对银杏愈伤组织诱导的影响。结果表明:不同外植体类型对银杏愈伤组织诱导率影响最大,KT和NAA其次,2,4-D和蔗糖浓度最小。银杏愈伤组织诱导最佳培养基为MS+NAA 0.5 mg·L-1+KT 0.5 mg·L-1+蔗糖40 g·L-1,最佳外植体为茎段,其愈伤组织诱导率可达100%。     

In vitro clonal propagation of an aromatic medicinal herb Ocimum basilicum L. (sweet basil) by axillary shoot proliferation

Summary An efficient protocol for in vitro propagation of an aromatic and medicinal herb Ocimum basilicum L. (sweet basil) through axillary shoot proliferation from nodal explants, collected from field-grown plants, is described. High frequency bud break and maximum number of axillary shoot formation was induced in the nodal explants on Murashige and Skoog (1962) medium (MS) containing N⁶-benzyladenine (BA). The nodal explants required the presence of BA at a higher concentration (1.0 mg·l⁻¹, 4.4 μM) at the initial stage of bud break; however, further growth and proliferation required transfer to a medium containing BA at a relatively low concentration (0.25 mg·gl⁻¹, 1.1 μM). Gibberellic (GA₃) at 0.4 mg·l⁻¹ (1.2 μM) added to the medium along with BA (1.0 mg·l⁻¹, 4.4 μM) markedly enhanced the frequency of bud break. The shoot clumps that were maintained on the proliferating medium for longer durations, developed inflorescences and flowered in vitro. The shoots formed in vitro were rooted on half-strength MS supplemented with 1.0 mg·l⁻¹ (5.0 μM) indole-3-butyric acid (IBA). Rooted plantlets were successfully acclimated in vermi-compost inside a growth chamber and eventually established in soil. All regenerated plants were identical to the donor plants with respect to vegetative and floral morphology.     

Shoot organogenesis and plantlet regeneration from hypocotyl-derived cell suspensions of a tree legume, Dalbergia sissoo Roxb

Summary A complete and efficient protocol is presented for plant regeneration from cell-suspension cultures of Dalbergia sissoo Roxb., an economically important leguminous tree. Factors influencing callus initiation, establishment of cell-suspension culture, callus formation from embredded microcolonies, and shoot organogenesis from suspension-derived callus were identified. Of the two different auxins tested, callus induction was better on a medium containing naphthalene acetic acid (NAA). The percentage of callus induction increased considerably when NAA at 2.0 mg l⁻¹ (10.8 μM) was added in conjunction with 0.5 mg l⁻¹ (2.2 μM) N⁶-benzyladenine (BA). Of the three different explants evaluated for callus induction, hypocotyl segments were most responsive. Friable hypocotyl-derived callus from the second subculture passage was used to initiate the cell-suspension culture. Optimum growth of the cell suspension was observed in MS medium supplemented with the same growth regulators as described above for callus induction, with an initial inoculum cell density of 1%. The plating efficiency of the microcolonies was greatly influenced by harvesting time and the gelling agent used for plating. Efficiency was highest (93%) with cells harvested at their exponential growth phase and plated in 1.2 g l⁻¹ Phytagel. Shoot organogenesis from callus cultures was higher on a medium supplemented with a combination of BA and NAA than on BA alone. Seventy-one per cent of cultures exhibited shoot-bud differentiation on a medium containing 3.0 mg l⁻¹ (13.3 μM) BA and 0.5 mg l⁻¹ (2.7 μM) NAA. Regenerated shoots were rooted on half-strength MS medium containing 1 mg l⁻¹ each of indole-3-acetic acid (5.7 μM), indole-3-butyric acid (4.9 μM) and indole-3-propionic acid (5.3 μM). Plantlets were acclimated and established in soil.     

L-Phenylalanine ammonia-lyase fromPhaseolus vulgaris: Modulation of the levels of active enzyme bytrans-cinnamic acid

The extractable activity ofl-phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) in cell suspension cultures of bean (Phaseolus vulgaris) is greatly induced following exposure to an elicitor preparation from the cell walls of the phytopathogenic fungusColletotrichum lindemuthianum. Following exogenous application oftrans-cinnamic acid (the product of the PAL reaction) to elicitor-induced cells, the activity of the enzyme rapidly declines. Loss of enzyme activity is accompanied by inhibition of the rate of synthesis of PAL subunits, as determined by [³⁵S]methionine pulse-labelling followed by specific immunoprecipitation; this is insufficient to account for the rapid loss of PAL enzyme activity. Pulse-chase and immune blotting experiments indicate that cinnamic acid does not affect the rate of degradation of enzyme subunits, but rather mediates inactivation of the enzyme. A non-dialysable factor from cinnamicacid-treated bean cells stimulates removal of PAL activity from enzyme extracts in vitro; this effect is dependent on the presence of cinnamic acid. Such loss of enzyme activity in vitro is accompanied by an apparent loss or reduction of the dehydroalanine residue of the enzyme's active site, as detected by active-site-specific tritiation, although levels of immunoprecipitable enzyme subunits do not decrease. Furthermore, cinnamic-acid-mediated loss of enzyme activity in vivo is accompanied, in pulse-chase experiments, by a greater relative loss of³⁵S-labelled enzyme subunits precipitated by an immobilised active-site affinity ligand than of subunits precipitated with anti-immunoglobulin G. It is therefore suggested that a possible mechanism for cinnamic-acid-mediated removal of PAL activity may involve modification of the dehydroalanine residue of the enzyme's active site.Abbreviations AOPP l--aminoxy--phenylpropionic acid - CA trans-cinnamic acid - PAGE polyacrylamide gel electrophoresis - PAL l-phenylalanine ammonia-lyase - SDS sodium dodecyl sulphate