Photosynthesis in leaves of the juvenile and adult phase of ivy (Hedera helix)

Abstract Photosynthetic and anatomical parameters of leaves from the juvenile and adult part of an ivy plant (Hedera helix L.) have been determined and compared with each other. Light-saturated net photosynthesis (per unit leaf area) was about 1.5 times higher in adult leaves than in juvenile ones. The lower photosynthetic capacity of juvenile leaves was caused by a lower stomatal and especially a lower residual conductance to the CO₂-transfer. This corresponds with anatomical features of the leaves, i.e. lower stomatal frequency, fewer chloroplasts per cell, and – most important – thinner leaves, as well as with a less efficient photosynthetic apparatus measured as Hill reaction of isolated broken chloroplasts and activity of ribulose bisphosphate carboxylase. No differences in the respiration in light (relative to net photosynthesis) and in the CO₂-compensation concentration could be detected between the two leaf types. These observed anatomical and photosynthetic parameters of the juvenile and adult ivy leaves resemble those reported for shade and sun leaves, respectively, although the leaves investigated originated from the same light environment.     

Photosynthesis in frost-hardened and frost-stressed leaves of Hedera helix L.

Abstract The purpose of this study was to determine the respective extents to which winter reduction of photosynthetic capacity in ivy (Hedera helix L.) is caused by direct frost injury to the photosynthetic apparatus and by preceding protoplasmic changes connected with the acquisition of frost tolerance. Potted juvenile ivy plants were placed in the open under natural weather conditions whilst others were hardened under controlled conditions and subjected to the desired frost stress. Low non-freezing temperatures induced frost tolerance in ivy leaves down to about – 12°C (50% injury = TL₅₀) without impairing net photosynthetic rate as measured under standard conditions (20°C, light saturation, natural CO₂ level; = Standard-F_n. Only if the leaves froze (below ? 3°C to ?4°C) was a reversible inhibition of Standard-F_n observed. As long as the temperatures did not fall below approximately ?8°C the inhibition was small and Standard-F_n reached about 80–90% of the control. In this case the stomatal opening narrowed, giving a poorer supply of CO₂ to the mesophyll cells. Maximal frost tolerance (TL_5O?20°C to ?24°C) developed only with severe frosts below about ? 10°C. After such frosts, Standard-F_n was reduced to less than 20% of the control. The dependence of the rate of net photosynthesis on the internal CO₂ concentration showed a lower initial slope, thus indicating disturbances of chloroplast functions. However, neither in outdoor plants nor in those artificially frosted at – 20°C could there be found an appreciable inhibition of the electron transport capacity from H₂O to dichlorophenol indophenol or of ribulose bisphosphate carboxylase. If intact, severely frosted ivy plants were then held at higher temperatures (20/15°C), Standard-F_n recovered completely in approximately 10 d. Furthermore, following a frost period with temperatures down to ?12°C, mild weather caused a distinct improvement in Standard-F_n in outdoor plants, and there was no loss of maximum frost tolerance. Thus it can be concluded that the inhibition of Standard-F_n after severe frosts is not due to the development of maximal frost tolerance, but rather may be attributed to frost damage to the photosynthetic apparatus.     

Function of leaf hamamelitol as a compatible solute during water stress treatment of Hedera helix L.

Hamamelitol is an unusual branched-chain sugar alcohol previously suggested to function as a leaf compatible solute. In this study, we have examined the leaf metabolism and intracelluiar compartmentalization of hamamelitol and other soluble sugars during long-term water stress treatment of Hedera helix (English ivy). Total leaf hamamelitol content was relatively low in greenhouse control plants, but increased 2-fold during water stress treatment to levels approaching those observed in field-grown plants (6–7 μmol g^?1 fresh weight). Using density gradient fractionation with non-aqueous solvents, we showed that hamamelitol occurs primarily in the cytoplasm and vacuoles of leaf mesophyll cells. During water stress treatment most of the increase in leaf hamamelitol occurred in the mesophyll cytoplasm, compensating osmotically for a decrease in cytoplasmic sucrose concentration. The maximum concentration of cytoplasmic hamamelitol was 155 mol m^?3 and occurred in field-grown plants. Labelling experiments showed that hamamelitol is slowly synthesized from ¹⁴CO₂ in leaves of H. helix, but is very long-lived (estimated t_1/2 of 4 years). Together, these data indicate that hamamelitol probably functions during long-term stress conditions as an osmotically active, compatible solute in plant leaves. We suggest that the signal for enhanced accumulation of hamamelitol during the water stress treatment was initiated by decreased plant growth and increased leaf sucrose hydrolysis.     

Increase in CO2 concentration could alter the response of Hedera helix to climate change

Increasing CO₂ concentration ([CO₂]) is likely to affect future species distributions, in interaction with other climate change drivers. However, current modeling approaches still seldom consider interactions between climatic factors and the importance of these interactions therefore remains mostly unexplored. Here, we combined dendrochronological and modeling approaches to study the interactive effects of increasing [CO₂] and temperature on the distribution of one of the main European liana species, Hedera helix. We combined a classical continent‐wide species distribution modeling approach with a case study using H. helix and Quercus cerris tree rings, where we explored the long‐term influence of a variety of climate drivers, including increasing [CO₂], and their interactions, on secondary growth. Finally, we explored how our findings could influence the model predictions. Climate‐only model predictions showed a small decrease in habitat suitability for H. helix in Europe; however, this was accompanied by a strong shift in the distribution toward the north and east. Our growth ring data suggested that H. helix can benefit from high [CO₂] under warm conditions, more than its tree hosts, which showed a weaker response to [CO₂] coupled with higher cavitation risk under high temperature. Increasing [CO₂] might therefore offset the negative effects of high temperatures on H. helix, and we illustrate how this might translate into maintenance of H. helix in warmer areas. Our results highlight the need to consider carbon fertilization and interactions between climate variables in ecological modeling. Combining dendrochronological analyses with spatial distribution modeling may provide opportunities to refine predictions of how climate change will affect species distributions.     

Growth promotion of ivy (Hedera helix L.) by paclobutrazol

Paclobutrazol was applied to juvenile ivy plants in an attempt to induce the mature form by the inhibition of gibberellin biosynthesis. Contrary to expectation, shoot elongation and adventitious root formation on aerial shoots were promoted.     

Differential expression of a chlorophyll a/b binding protein gene and a proline rich protein gene in juvenile and mature phase English ivy (Hedera helix)

Two cDNA clones representing mRNAs which are differentially expressed during in vitro culture of juvenile and mature leaf petioles of English ivy ( Hedera helix L.) were isolated by differential screening. The mRNA represented by clone HW101 is expressed at a higher level in untreated juvenile than in untreated mature in-vitro-cultured petioles. Treatment of petioles with α-naphthaleneacetic acid (NAA) at the initiation of culture decreases HW101 mRNA levels in juvenile but not mature, petioles. In intact plants. HW101 mRNA is expressed at a higher level in juvenile laminae, petioles and stems than in identical tissues of mature plants. DNA sequence analysis indicates that HW1O1 cDNA is significantly similar to a light harvesting chlorophyll a/b binding protein gene ( Lhcb ) of pea. The gene represented by the second clone. HW103, is expressed at a higher level in mature than in juvenile in-vitro-cultured petisoles. Treatment of petioles with NAA at the initiation of culture decreases HW103 mRNA levels in chronologically young mature but not older mature and juvenile petioles. However, expression of the HW103 gene is not detectable in petioles, or in any other vegetative organ tested, immediately after excision. It is, however, expressed in developing seeds. In otherwise intact plants, the HW103 gene is expressed in wounded petioles of mature plants 5 days after wounding but not in wounded petioles of juvenile plants. It is also expressed at a higher level in wounded stems of mature plants than in those of juvenile plants. However, it is not expressed in wounded lamina of either juvenile or mature plants. DNA sequence analysis indicates that HW103 cDNA is similar to a cell wall proline rich protein (PRP) gene of soybean. This is the first report of differential expression of a PRP gene in tissues from juvenile and mature plants. Southern blot analysis of nuclear DNA of H. helix shows that both HW101 and HW103 are members of small gene families.     

Cuticular waxes from ivy leaves (Hedera helix L.): analysis of high-molecular-weight esters

Soluble waxes were extracted from the cuticle of ivy (Hedera helix L.) leaves with dichloromethane in a yield of ca. 13%. The cuticular waxes were directly analysed by GC-MS, high-temperature GC-MS and ESI-MS/MS. The GC-MS analysis showed mostly n-alkanols (45.3%), monoacids (18.8%), triterpenes (9.7%), n-aldehydes (8.7%) and n-alkanes (7.7%). The high-temperature GC-MS and the ESI-MS/MS analyses showed the presence of ester waxes, namely alkyl alkanoates and alkyl coumarates. Alkyl alkanoates comprised esters of the hexadecanoic acid with n-alkanols ranging from C16 to C34. Alkyl coumarates included esters of coumaric acid with n-alkanols ranging from C16 to C32. The cuticular waxes were hydrolysed and the resulting organic and aqueous phases analysed by GC-MS. The hydrolysate showed a major increase in the quantities of n-alkanols, hexadecanoic acid and coumaric acid derived from the alkyl and acyl moieties from the ester waxes. A content of ester waxes of 38% was estimated based on the results from the GC-MS analysis of the non-hydrolysed and hydrolysed cuticular waxes. Alkyl alkanoates were analysed by ESI-MS/MS as [M + Li]+ adduct ions and the alkyl coumarates as [M - H]- deprotonated ions. The ESI-MS/MS analysis allowed the detection of a wider range of ester waxes than high-temperature GC-MS, and was shown to be a useful technique for the qualitative analysis of ester waxes from plant cuticles.     

常春藤在室内生长适宜光照范围的研究

研究了常春藤(Hedera helix)适宜生长的光照范围问题。根据光的分布,选择房间内具有代表性的光区进行栽培试验。在18~28℃,RH31%~70%条件下。经栽培80 d后,用LI-6400测定其不同光强下的光合特性,计算光补偿点、光饱和点、最大净光合速率。同时测定不同试验区的叶面积、叶片数的生长量。结果表明:常春藤在18~28℃及RH31%~70%室内条件下,光照为大于3.1至小于834.3 μmol·m^-2·s^-1(155~41 715 lx)可以生长。     

Ontogenetic and seasonal development of wax composition and cuticular transpiration of ivy (Hedera helix L.) sun and shade leaves

The ontogenetic and seasonal development of wax composition and cuticular transpiration of sun and shade leaves of ivy (Hedera helix L.) was analysed by investigating leaves varying in age between 4 and 202 d. It was discovered that the total amount of solvent-extractable wax was composed of two distinct fractions, separable by column chromatography: (i) a less polar or apolar monomeric wax fraction consisting of the typical linear, long-chain aliphatics usually described as cuticular wax components and (ii) a polar, oligomeric wax fraction consisting of primary alcohols and acids mostly esterified to C₁₂-, C₁₄- and C₁₆-ω-hydroxyfatty acids. The apolar wax fraction, which could be analysed directly by gas chromatography coupled with mass spectrometry (GC-MS), exhibited pronounced seasonal changes in composition. Wax amounts in the apolar fraction reached a maximum after about 30 d and gradually decreased again during the remaining period of the season investigated. In contrast, the polar wax fraction, which was analysable by GC-MS only after transesterification, rapidly increased early in the season, reaching a plateau after 40 d, and then remained constant during the rest of the season. Thus, total amounts of solvent-extractable cuticular waxes, which can be determined gravimetrically, will only be detected by GC-MS after fractionation and transesterification, a methodological approach rarely applied in the past in cuticular wax analysis. Additionally, investigation of the cutin polymer matrix after depolymerisation through transesterification, revealed that only those primary alcohols and acids forming an essential part of the apolar and the polar wax fractions were esterified during the investigated season and incorporated in increasing amounts into the cutin polymer matrix (matrix-bound wax fraction). Thus, it can be concluded that a complete analysis of cuticular wax of ivy and its seasonal development can only be achieved if all the relevant fractions (i) the less polar or apolar, (ii) the polar and (iii) the wax fraction bound to the cutin polymer matrix are investigated. Cuticular transpiration rapidly decreased within the first 30 d and essentially remained constant during the rest of the season. Thus, changes in cuticular water permeability were closely correlated with the most prominent changes in wax amounts and composition occurring during the first 30 d of ontogenetic leaf development. However, during the remainder of the year, up to 202 d, cuticular transport properties remained constant, although significant quantitative and qualitative changes in cuticular wax composition continued to occur. Thus, our study clearly demonstrated that there will be no simple relationship between chemical composition of cuticular waxes and transport properties of isolated ivy leaf cuticles. Received: 2 March 1998 / Accepted: 26 June 1998     

Hepatoprotective and antioxidant effects of Hedera helix extract on acetaminophen induced oxidative stress and hepatotoxicity in mice

ABSTRACT

Exposure to high doses of acetaminophen is the most common cause of drug induced liver injury. We investigated the protective effects of Hedera helix extract against acetaminophen induced oxidative stress and hepatotoxicity using a mouse model. We used two control groups: group A was given 0.9% NaCl, group B was an acetaminophen control that was given a single injection of 600 mg/kg acetaminophen. T1?T4 groups were pretreated orally with different doses of H. helix extract. The mice were sacrificed and blood samples were collected to estimate the levels of glutathione peroxidase (GPx), malondialdehyde (MDA), superoxide dismutase (SOD) and total bilirubin. Liver samples also were used for histopathological studies. We found that acetaminophen significantly increased the levels of serum ALP, ALT, AST and MDA, and also significantly reduced the antioxidant factors, CAT, GPX and SOD. H. helix extract treatment produced a significant reduction in the levels of ALP, ALT, AST and MDA in serum and restored the levels of CAT, GPX and SOD to control levels. The histopathological findings were consistent with the biochemical findings. H. helix extract exhibited antioxidant and hepatoprotective effects against acetaminophen induced liver damage.     

Palynological and chemical volatile components of typically autumnal honeys of the western Mediterranean

Measurements and observations of pollen grains of varying structure before and after dehiscence of the anther sac illustrate large magnitudes of harmomegathic changes in volume and shape. Such changes are compared for colpate, porate, and colporate grains, and it is suggested that the nature of the harmomegathal action may serve to distinguish colpi or furrows from pores. Consideration of the requirement to allow harmomegathy while preventing wall collapse may provide at least partial explanation for evolution of the internal structure and external sculpturing of pollen grain walls.     

Observational study on the tolerability and safety of film-coated tablets containing ivy extract (Prospan Cough Tablets) in the treatment of colds accompanied by coughing

The only saponin drug currently prescribed in any significant amount in monotherapy medicines is ivy. This post-marketing surveillance study (PMSS) aimed at investigating the tolerability and safety of film-coated tablets containing ivy leaves dry extract (extracting medium: ethanol 30%, DER 5-7.5:1 [Prospan^® Cough Tablets]) under practice conditions. Adults and children aged 11-85 years of both genders were included. A total of 330 patients suffering from colds accompanied by coughing or from chronic, inflammatory bronchial diseases were scheduled to undergo treatment for a period of at least seven days. The tolerability of the tablets was rated by means of questionnaires.The results of this PMSS reflect the good to very good tolerability of the tablets in the global assessment by both, the practitioner (98.5%) and by the patient (96.4%). This is one of the reasons for the high acceptance and compliance (rated as ‘good’ in 98.8% of all cases). The safety not only regarding the administration form but also regarding the active substance is thus underlined once again.     

Callus and shoot formation in organ and tissue cultures of Hedera helix L., English ivy

When shoots of young plants of hemp (Cannabis sativa L.) and spinach (Spinacea oleracea L.) were cultured as cuttings and allowed to regenerate advenitious roots, ca. 80–85% became female (formed pistillate flowers) regardless of whether the leaves were left on the plants or were cut off (except for the 2–3 uppermost ones) after the beginning of adventitious-root formation. But when the leaves were cut off and the cuttings treated with gibberellic acid (GA₃, 25 mg/l) ca. 77–80% of the plants became male (formed staminate flowers). The result was quite similar when roots and leaves of young hemp plants were removed at the same time and the cuttings treated with GA₃. It is suggested that the leaves play an essential role in sex expression in hemp and spinach and that this role is related to gibberellin synthesis in the leaves.     

Light acclimation in leaves of the juvenile and adult life phases of ivy (Hedera helix)

Hoflacher, H. and Bauer, H. 1982. Light acclimation in leaves of the juvenile and adult life phases of ivy (Hedera helix). – Physiol. Plant. 56: 177–182. Light acclimation was investigated during the juvenile and adult life phases of the whole-plant-development in Hedera helix L. For this purpose, cuttings of the juvenile and adult parts of one single parent plant were grown under low-light (PAR 30–50 μmol photons m^?2 s^?1) and high-light (PAR 300–500 μmol m^?2 s^?1) conditions: CO₂ exchange, chloroplast functions, and specific anatomy of fully developed leaves differentiated under these conditions were determined. In juvenile plants the leaves formed under low and high light had light-saturated rates of net photosynthesis of 6.5 and 11.1 mg CO₂ (dm leaf area)^?2 h^?1, respectively. In adult plants the rates were 9.4 and 22.2 mg dm^?2 h^?1, indicating a more pronounced capacity for acclimation to strong light in the adult life phase. Higher photosynthetic capacities were accompanied by higher conductances for the CO₂ transfer through the stomata, leading to almost the same CO₂ concentration in the intercellular spaces. Thus, stomatal conductances were not primarily responsible for the different photo-synthetic capacities. The higher rates in adult and high-light grown leaves were mainly the result of formation of thicker leaves with more chloroplasts per unit leaf area. Expressed per chloroplast, the photosynthetic capacity, the Hill reaction, and the activity of ribulose bisphosphate carboxylase were almost identical in plants grown in low-light and high-light. Measurements of photosynthetic capacity and thickness of leaves of Hedera sampled from field habitats with contrasting light regimes confirm the results of growth chamber studies. It is, therefore, concluded that both life phases of Hedera are capable of acclimating to strong light, but that during the juvenile phase this capacity is not fully developed.     

Photoinhibition of photosynthesis under natural conditions in ivy (Hedera helix L.) growing in an understory of deciduous trees

We investigated to what extent south-exposed leaves (E-leaves) of the evergreen ivy (Hedera helix L.) growing in the shadow of two deciduous trees suffered from photoinhibition of photosynthesis when leaf-shedding started in autumn. Since air temperatures drop concomitantly with increase in light levels, changes in photosynthetic parameters (apparent quantum yield, _i and maximal photosynthetic capacity of O₂ evolution, P_max; chlorophyll-a fluorescence at room temperature) as well as pigment composition were compared with those in north-exposed leaves of the same clone (N-leaves; photosynthetic photon flux density PPFD< 100 mol · m^–2 · s^–2) and phenotypic sun leaves (S-leaves; PPFD up to 2000 mol · m^–2 · s^–1).In leaves exposed to drastic light changes during winter (E-leaves) strong photoinhibition of photosynthesis could be observed as soon as the incident PPFD increased in autumn. In contrast, in N-leaves the ratio of variable fluorescence to maximum fluorescence (F_V/F_Mm) and _i did not decline appreciably prior to severe frosts (up to -12° C) in January. At this time, _i was reduced to a similar extent in all leaves, from about 0.073 mol O₂ · mol^–1 photons before stress to about 0.020. Changes in _i were linearly correlated with changes in f_v/f_m (r = 0.955). The strong reduction in F_V/F_M on exposure to stress was caused by quenching in F_M. The initial fluorescence (F₀), however, was also quenched in all leaves. The diminished fluorescence yield was accompanied by an increase in zeaxanthin content. These effects indicate that winter stress in ivy primarily induces an increase in non-radiative energy-dissipation followed by photoinhibitory damage of PSII. Although a pronounced photooxidative bleaching of chloroplast pigments occurred in January (especially in E-leaves), photosynthetic parameters recovered completely in spring. Thus, the reduction in potential photosynthetic yield in winter may be up to three times greater in leaves subjected to increasing light levels than in leaves not exposed to a changing light environment.Abbreviations and Symbols F₀, F_M initial and maximal fluorescence yield when all PSII centres are open and closed - F_V variable fluorescence (F_M-F₀) - P_max maximal photosynthetic capacity at 1000 umol · m^–2 · s^–1 PPFD and CO₂ saturation - PPFD photosynthetic photon flux density - _i apparent quantum yield of photosynthetic O₂ evolution - E-leaves, N-leaves shade leaves exposed, not exposed to drastic light changes during winter - S-leaves sun leaves from an open ivy stand Dedicated to Professor Otto Härtel on the occasion of his 80th birthdayThis work was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung.     

Photosynthetic light acclimation in fully developed leaves of the juvenile and adult life phases of Hedera helix

The aim of this study was to investigate the extent to which fully developed leaves of Hedera helix L. are capable of acclimating to new light conditions and how this ability is determined by the life phase of the plant. To this end juvenile and adult plants were transferred from a low (L) to a moderately high (H) light regime and vice versa and changes of photosynthetic gas exchange, RuBP carboxylase (EC 4.1.1.39) activity and specific anatomy were monitored in leaves that were fully developed prior to the transfer.
Immediately after transfer from L to H there was a decrease in the rate of net photosynthesis (F_n). This photoinhibition was particularly pronounced in leaves of the adult life phase. F_n recovered after 10 to 20 days at H, and 40 to 65 days after transfer the rate exceeded that of control plants by about 20% in leaves of the adult life phase and by about 50% in leaves of the juvenile life phase. If H plants were transferred to L, F_n had declined only slightly after 30 to 40 days and regained its initial level within a few days, when the plants were returned to the original high light regime.
The increased rates of F_n per unit leaf area in leaves transferred from L to H were associated with higher light levels necessary to saturate F_n, higher carboxylation efficiencies, higher contents of soluble protein and higher activities of RuBP carboxylase, whereas the quantum yield did not change. Although fully differentiated before transfer, the leaves had formed a further cell layer in the palisade parenchyma. Related to leaf volume there was no increase in F_n.
Our results indicate that in the adult life phase of ivy phenotypie light acclimation occurs mainly during leaf development, whereas in juvenile plants fully expanded leaves still possess a rather wide modulativc acclimation plasticity.     

Structure, attachment properties, and ecological importance of the attachment system of English ivy (Hedera helix)

Root climbers such as English ivy (Hedera helix) rely on specialized adventitious roots for attachment, enabling the plants to climb on a wide range of natural and artificial substrates. Despite their importance for the climbing habit, the biomechanical properties of these specialized adventitious roots compared with standard roots and their performance in the attachment to different host species or inert substrates have not been studied. Here organs and tissues involved in the attachment are characterized and their significance in regard to a broader functional and ecological aspect is discussed. Depending on the substrate, the root clusters show different types of failure modes at various frequencies, demonstrating the close interaction between the climber and its substrates. With a Young's Modulus of 109.2 MPa, the attachment roots are relatively stiff for non-woody roots. The central cylinders of the attachment roots show a high tensile strength of 38 MPa and a very high extensibility of 34%. In host trees naturally co-distributed with English ivy, a 'balanced' occurrence of failure of the attachment system of the climber and the bark of the host is found, suggesting a co-evolution of climber and host. Maximum loads of root clusters normalized by the number of roots match those of individually tested attachment roots. In comparison with most subterranean roots the properties and structure of the attachment roots of English ivy show distinct differences. There exist similarities to the properties found for roots of Galium aparine, suggesting a trend in not fully self-supporting plants towards a higher extensibility.     

Responses of ivy (Hedera helix L.) to combinations of gibberellic acid,paclobutrazol and abscisic acid

A reduction in concentration of gibberellins has been implicated in the phase change from juvenile to mature forms of ivy (Hedera helix L.). Attempts were made to increase the effective internal concentration of gibberellins by exogenous application of GA₃, and to decrease them by various applications of abscisic acid (ABA) and paclobutrazol (PP333), alone or in combination with GA₃. ABA and GA₃ were fed directly into the xylem of ivy plants by a wick system (a less drastic procedure than the defoliation or decapitation used by earlier workers) whereas PP333 was applied as a soil drench.Mature ivy responded to the application of GA₃ by reversion to the juvenile form, although this reversion was incomplete with respect to leaf lobing and red (anthocyanin) pigmentation and could occur spontaneously without the application of GA₃. Contrary to expectation, applications of ABA and PP333 caused the stimulation of growth in juvenile ivy. No adult characteristics were induced. As similar concentrations of ABA and PP333 produced severe retardation of growth (which could be alleviated by the application of GA₃) in other species, it is suggested that ivy may be an unsuitable model system for the investigation of phase change in woody plants.     

Functional morphology and biomechanics of cuticular fracture at the elytrophoral autotomy plane of the scaleworm Alentia gelatinosa (Annelida: Polynoidae)

Abstract. Autotomy of the elytra (scales) in the annelid Alentia gelatinosa occurs at a breakage plane near the junction between the elytron and its elytrophore (stalk), and requires fracture of the external epidermal cuticle. The mechanism of cuticular fracture was investigated by light and electron microscopy, glycoconjugate histochemistry, direct observation of autotomy in isolated preparations, and mechanical tests. The breakage plane crosses the elytrophoral wall at a cuticular thickening and passes through the subelytral cavity between the elytron and the terminal septum of the elytrophore. At the cuticular breakage zone (CBZ), the collagenous framework of the normal cuticle is replaced with non‐collagenous microfibrils. The CBZ has a complex glycoconjugate composition and includes a strongly sulfated, uronic acid‐containing glycosaminoglycan and a high proportion of disulfide or sulfydryl linkages. Tonofilament‐rich epidermal cells (tendon cells) are attached to the thick cuticle on the dorsal and ventral sides of the CBZ. Dorsal tendon cells have long processes that extend into the elytron near the roof of the subelytral cavity. Ventral tendon cells are linked by connective tissue to the longitudinal and terminal sphincter muscles of the elytrophore. Mechanical tests showed that the elytrophoral wall is not inherently weaker at the autotomy plane than elsewhere. It is hypothesized that at autotomy (i) contractile force generated by the sphincter muscle is transmitted through elytrophoral tendon cells to the ventral side of the CBZ and (ii) contraction of the longitudinal and main circular muscles of the elytrophore increases hydrostatic pressure in its lumen, everts the terminal septum, and generates tension that is transmitted through elytral tendon cells to the dorsal side of the CBZ. This results in stress concentration at the basal edge of the CBZ and initiates fracture. The distinctive microstructure and macromolecular composition of the CBZ may reduce its fracture toughness and make it more susceptible to brittle failure.