CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.     

CUTICULAR ANALYSIS OF EOCENE LEAVES OF OCOTEA OBTUSIFOLIA

Dilcheb , David L. (Yale U., New Haven, Conn.) Cuticular analysis of Eocene leaves of Ocotea obtusifolia. Amer. Jour. Bot. 50(1): 1–8. IIlus. 1963.—Several specimens of Ocotea obtusifolia collected from the Eocene clays at Puryear, Tennessee, were examined in detail. The megascopic and cuticular features of the leaves are described and their variations discussed. The lower epidermis was found to be less variable and a better tool to use in the cuticular analysis of this species than the upper epidermis. The cuticle of several genera and species of modern Lauraceae were also examined. Since none could be identified with the fossil cuticle, the designation Ocotea obtusifolia as based on megascopic characters is satisfactory.     

STRUCTURE OF THE ROYAL ANN CHERRY CUTICLE AND ITS SIGNIFICANCE TO CUTICULAR PENETRATION

The structure of the Royal Ann cherry cuticle (Prunus avium L.) was determined and interpreted in the light of its possible significance to cuticular penetration by a SO₂-calcium bisulfite brine. The morphology of the cuticle was determined by standard histological and histochemical techniques. The surface structure of the cuticle was found to have a smooth to granular sheet or layer of surface wax, which when removed revealed a porous sponge-like surface. The cuticular surface showed intermittent birefringence, which increased as the fruit matured. Ectodesmata were found to occur over anticlinal walls and in guard cells on both sides of the fruit, with more on the side opposite the suture. Both sides had stomata with more occurring on the suture side. Secondary bleaching was found to alter the structure and permeability of the cuticle.     

Cuticle differentiation in the embryo of the amphipod crustacean Parhyale hawaiensis

The arthropod cuticle is a multilayered extracellular matrix produced by the epidermis during embryogenesis and moulting. Molecularly and histologically, cuticle differentiation has been extensively investigated in the embryo of the insect Drosophila melanogaster. To learn about the evolution of cuticle differentiation, we have studied the histology of cuticle differentiation during embryogenesis of the amphipod crustacean Parhyale hawaiensis, which had a common ancestor with Drosophila about 510 million years ago. The establishment of the layers of the Parhyale juvenile cuticle is largely governed by mechanisms observed in Drosophila, e.g. as in Drosophila, the synthesis and arrangement of chitin in the inner procuticle are separate processes. A major difference between the cuticle of Parhyale and Drosophila concerns the restructuring of the Parhyale dorsal epicuticle after deposition. In contrast to the uniform cuticle of the Drosophila larva, the Parhyale cuticle is subdivided into two regions, the ventral and the dorsal cuticles. Remarkably, the boundary between the ventral and dorsal cuticles is sharp suggesting active extracellular regionalisation. The present analysis of Parhyale cuticle differentiation should allow the characterisation of the cuticle-producing and -organising factors of Parhyale (by comparison with the branchiopod crustacean Daphnia pulex) in order to contribute to the elucidation of fundamental questions relevant to extracellular matrix organisation and differentiation. This work was supported by the German Research Foundation (DFG, grant number MO 1714/1-1).     

DEVELOPMENT OF THE CUTICULAR LAYERS IN ANGIOSPERM LEAVES

Schieferstein , R. H., and W. E. Loomis . (Iowa State U., Ames.) Development of the cuticular layer in angiosperm leaves. Amer. Jour. Bot. 46(9): 625–635. Illus. 1959.—The cuticularized layers of leaves and other plant surfaces consist of a primary cuticle, formed by the oxidation of oils on exposed cell walls, plus various surface and subsurface wax deposits. The primary cuticle appears to form rapidly on the walls of any living cell which is exposed to air. Surface wax is present on the mature leaves of about half of the 50 or 60 species studied. In general, wax is extruded at random through the newly formed cuticle of young leaves and accumulated in various reticulate to semicrystalline patterns. No wax pores through the cuticle or primary wall can be observed in electron-micrographs of dewaxed mature leaves. Wax accumulations on older leaves are generally subcuticular and may involve the entire epidermal wall. These deposits appear to be of considerably greater ecological significance than those on the surface. Isolated cuticular membranes from Hedera helix increased slightly in permeability to water with age of the leaf, but permeability to 2,4-D decreased 50 times. Evidence based on the patterns of cellulose in primary walls, of surface wax on growing leaves, of the appearance of the cuticle at the margins of growing epidermal cells, of the forms of the cuticle plates digested from growing and older leaves, and of the marginal location of new wax deposits on growing maize leaves is presented to support the thesis that the enlargement of the outer surface of the epidermal cells of leaves occurs at the margins of the surface. Earlier formed cuticle and wax are thus undisturbed during growth. These observations, coupled with evidence for apical growth in fibers, root hairs, etc. suggest that the primary walls of angiosperm cells are formed in specific, localized growth regions, rather than by plastic extension and apposition.     

ULTRASTRUCTURAL AND HISTOCHEMICAL CHARACTERISTICS OF THE STIGMA OF CICER ARIETINUM

The stigma of Cicer arietinum L. cv. UC-5, a self-compatible legume, is comprised of a small central region of papillate cells which exhibit a localized surface secretion at the white bud stage of development, and of surrounding peripheral cells which lack surface secretion at the white bud stage and at anthesis. The cuticle of cells of the central region is thin and smooth and is displaced from subtending cells and fragmented as a result of secretory production. The cuticle of peripheral cells is thick and rugose. Although it is also displaced by secreted material, it is not disrupted during the white bud stage of development or at anthesis. The contents of central and peripheral papillate cells are similar. Cells are densely cytoplasmic, often with starch-containing plastids. Mitochondria, Golgi bodies, and associated vesicles are abundant, along with strands of smooth and rough endoplasmic reticulum. The limited stigma surface area covered by the secretion may restrict pollen capture and retention. This limited area may partly account for the notably unsuccessful hybridization attempts to broaden the genetic base and to develop improved cultivars of Cicer.     

CONSERVATION OF MOLECULAR PREPATTERNS DURING THE EVOLUTION OF CUTICLE MORPHOLOGY IN DROSOPHILA LARVAE

We are using patterns of cuticle specialization in Drosophila larvae as models to investigate the molecular, genetic, and developmental bases of morphological evolution. Members of the virilis species group differ markedly from one another in the distribution of hairs on the dorsal surface of first instar larvae. In particular, characteristic bands of hairs cover about 20% of each trunk segment in some species but about 70% in others. These major types do not correlate with recently proposed phylogenetic relationships, suggesting that similar phenotypes have arisen independently in different lineages. The patterns of expression of several genes that control or reflect intrasegmental patterning are indistinguishable in species with very different cuticle morphologies. We conclude that, in this case, morphology probably has evolved via altered response to a conserved molecular prepattern.     

Inhibition of fatty acid desaturation impairs cuticle differentiation in Drosophila melanogaster

Previously, we showed that inhibition of the activity of fatty acid desaturases (Desat) perturbs signalling of the developmental timing hormone ecdysone in the fruit fly Drosophila melanogaster. To understand the impact of this effect on cuticle differentiation, a process regulated by ecdysone, we analysed the cuticle of D. melanogaster larvae fed with the Desat inhibitor CA10556. In these larvae, the expression of most of the key cuticle genes is normal or slightly elevated at day one of CA10556 feeding. As an exception, expression of twdlM coding for a yet uncharacterised cuticle protein is completely suppressed. The cuticle of these larvae appears to be normal at the morphological level. However, these animals are sensitive to desiccation, a trait that according to our data, among others, may be associated with reduced TwdlM amounts. At day two of CA10556 feeding, expression of most of the cuticle genes tested including twdlM is suppressed. Expression of cpr47Eb coding for a chitin‐binding protein is, by contrast, highly elevated suggesting that Cpr47Eb participates at a specific compensation program. Overall, the cuticle of these larvae is thinner than the cuticle of control larvae. Taken together, lipid desaturation is necessary for a coordinated deployment of a normal cuticle differentiation program.     

THE STIGMATIC PAPILLAE OF AMYEMA (LORANTHACEAE): DEVELOPMENTAL RESPONSES TO PROTANDRY AND SURFACE ADAPTATIONS FOR BIRD POLLINATION

The flowers of Amyema miquelii and A. miraculosum are protandrous and pollinated by birds. Their dry-type stigmatic surface is composed of unicellular papillae. At the male phase, these papillae are constricted with rugulose surfaces. During the transition to the female (pollen receptive) phase these cells expand, almost doubling in width while their surface becomes much smoother. Beneath the thin proteinaceous pellicle, the papillar wall consists of an extraordinarily thick bi-layered cuticle overlying the primary wall. The two layers of the cuticle are stained by lipid dyes, but are distinguished by their different responses to other cytochemical tests. The reaction product for the enzyme esterase is present within crenulations on the papillar surface in small amounts, and in dense deposits in the cuticular clefts at the base between papillae. Not surprisingly, pollen tubes are unable to penetrate the thick papillar cap and enter the style through these clefts. The unusual thickness of the cuticle is interpreted as an adaptive response to pollination by perching birds (passerines) probing for nectar.     

Further studies on the mechanism of oxidation of N-acetyldopamine by the cuticular enzymes from Sarcophaga bullata and other insects

In accordance with our earlier results, quinone methide formation was confirmed to be the major pathway for the oxidation of N-acetyldopamine (NADA) by cuticle-bound enzymes from Sarcophaga bullata larvae. In addition, with the use of a newly developed HPLC separation condition and cuticle prepared by gentle procedures, it could be demonstrated that 1, 2-dehydro-NADA and its dimeric oxidation products are also generated in the reaction mixture containing a high concentration of NADA albeit at a much lower amount than the NADA quinone methide water adduct, viz., N-acetylnorepinephrine (NANE). By using different buffers, it was also possible to establish the accumulation of NADA quinone in reaction mixtures containing NADA and cuticle. That the 1,2-dehydro-NADA formation is due to the action of a NADA desaturase system was established by pH and temperature studies and by differential inhibition of NANE production. Of the various cuticle examined, adult cuticle of Locusta migratoria, presclerotized cuticle of Periplaneta americana, and white puparial cases of Drosophila melanogaster exhibited more NADA desaturase activity than NANE generating activity, while the reverse was observed with the larval cuticle of Tenebrio molitor and pharate pupal cuticle of Manduca sexta. These studies indicate that both NADA quinone methide and 1, 2-dehydro NADA are formed during enzymatic activation of NADA in insect cuticle. Based on these results, a unified mechanism for β-sclerotization involving quinone methides as the reactive species is presented.     

Cuticular morphogenesis during continuous growth of the final instar larva of a moth

The larvae of the tobacco hornworm, Manduca sexta, grow continuously. During the feeding period of the fifth larval instar their weight increases ten-fold (ca. 1·2–12 g) accompanied by a four-fold expansion of the surface area of the abdominal cuticle. We have found that this cuticle contains structures which facilitate its expansion. Folds in the epicuticle (papillae) flatten as the cuticle expands. The endocuticle, in contrast, does not unfold but rather is plastically deformed. This plastic deformation is assisted by vertical structures in the cuticle (cuticular columns) which are more easily deformed than the surrounding lamellate cuticle. The head capsule cuticle, which does not expand as the larva grows, lacks papillae and cuticular columns. Thus, these are specialized structures that are reserved for cuticle that must expand as the larva grows.     

Enhancing the egg's natural defence against bacterial penetration by increasing cuticle deposition

The cuticle is a proteinaceous layer covering the avian egg and is believed to form a defence to microorganism ingress. In birds that lay eggs in challenging environments, the cuticle is thicker, suggesting evolutionary pressure; however, in poultry, selection pressure for this trait has been removed because of artificial incubation. This study aimed to quantify cuticle deposition and to estimate its genetic parameters and its role on trans‐shell penetration of bacteria. Additionally, cuticle proteins were characterised to establish whether alleles for these genes explained variation in deposition. A novel and reliable quantification was achieved using the difference in reflectance of the egg at 650 nm before and after staining with a specific dye. The heritability of this novel measurement was moderate (0.27), and bacteria penetration was dependent on the natural variation in cuticle deposition. Eggs with the best cuticle were never penetrated by bacteria (P < 0.001). The cuticle proteome consisted of six major proteins. A significant association was found between alleles of one of these protein genes, ovocleidin‐116 (MEPE), and cuticle deposition (P = 0.015) and also between alleles of estrogen receptor 1 (ESR1) gene and cuticle deposition (P = 0.008). With the heritability observed, genetic selection should be possible to increase cuticle deposition in commercial poultry, so reducing trans‐generational transmission of microorganisms and reversing the lack of selection pressure for this trait during recent domestication.     

CUTICLE THICKNESS IN PHLOX AND RESISTANCE TO POWDERY MILDEW: AN UNRELIABLE LINE OF DEFENSE

The relationship between leaf cuticle thickness and resistance to the powdery mildew Erysiphe cichoracearum was investigated for nine feral Phlox taxa. Cuticle thickness, the first potential host resistance feature, is variable within plants, although not correlated with leaf age, and both within and among taxa. There is also considerable variation within and among taxa in resistance response to artificial inoculations with a broadly compatible E. cichoracearum strain. However, no significant correlations between cuticle thickness and resistance were observed. The implications of these results for anti-mildew defenses in both feral and cultivated hosts are discussed.     

SCARABAEID BEETLE EXOCUTICLE AS AN OPTICAL ANALOGUE OF CHOLESTERIC LIQUID CRYSTALS

1. A review is given of the optical and architectural analogies between cholesteric liquid crystals and certain insect cuticles (Coleoptera: Scarabaeidae). Earlier observations on the optical properties (reflexion of circularly polarized light and high form optical rotation) are confirmed and extended. Both cholesteric liquid crystals and lamellate cuticle have helicoidal structure (Fig. i). Even though their chemistry and physical states are very different, we are justified in making the analogy, since their optical properties depend primarily on the pitch of their helicoidal architecture. 2. The unusual optical properties were located for the first time in the outer 5 to 20 μ of the exocuticle. This layer is transparent and has regular spacings in the range required for interference colours according to Bragg's law. Among Scarabaeid beetles which show interference colours, we distinguish two types of outer exocuticle. (i) Optically active cuticles which reflect circularly polarized interference colours; show high angles of form optical rotation in transmitted light; and anomalous form birefringence perpendicular to the cuticle surface (reversible by deproteinization). (2) Optically inactive cuticles which show none of the above properties and in which the form birefringence is parallel to the cuticle surface. In the electron microscope the ultrastructure of these two types of outer exocuticle is clearly different. 3. All of the optically active species reflect left hand circularly polarized light, irrespective of the wavelength of the reflected colour. They therefore appear dark when viewed through a right hand circular analyser. The sense of reflected circularly polarized light does not reverse at higher wavelengths as recorded by previous workers. (A simple treatment is given for combinations of various wavelengths with retardation plates of varying values, as used in circular analysers.) We confirm earlier reports that the sense of reflected circularly polarized light is of the opposite sense to the transmitted light. 4. Using monochromatic light we have measured the anomalous dispersion with wavelength of the magnitude of optical rotation for various optically active cuticles. The dispersion curves change from negative values at lower wavelengths to positive values at higher wavelengths, and cross the zero optical rotation axis at a wavelength (AQ) corresponding to the interference colour of each sample. There is reasonable agreement between A₀ and the interference colour calculated from ultrastructural evidence and by comparison with interference filters of known wavelength. A dispersion curve measured for a combined sample of two cuticles with different dispersion curves showed that the resultant is an algebraic summation of the two component curves. 5. We present the first experimental verification of existing mathematical treatments of anomalous form optical rotatory dispersion curves. Although these treatments were derived for cholesteric liquid crystals, they give a reasonable fit to our measured curves for cuticle. We have confirmed from our cuticle dispersion curves that a second zero value for optical rotation occurs at a wavelength higher than A₀, as predicted by the theory of Chandrasekhar and Rao (1968). This has not yet been observed in any cholesteric liquid crystal system. 6. Our evidence shows that in optically active cuticle, interference colour is determined by helicoid pitch. In Lomaptera interference coloration follows the bilateral symmetry of the insect. Hence helicoidal pitch is controlled in a bilaterally symmetrical manner. However, the sense of helicoid rotation is the same all over the beetle and is therefore bilaterally asymmetrical. This supports the view that helicoid pitch is under the local control of the epidermal cells which secrete the cuticle, whereas its sense of rotation may be determined by an extracellular self-assembly process. In view of the self-assembling properties of cholesteric liquid crystals, it is tempting to suggest that helicoidal cuticle could be formed by the stabilization of a liquid crystal. 7. We discuss in detail the differences between optically active and inactive cuticles. The constructive interference colours arising from both types are then briefly compared with other multiple layer reflecting systems in other animals. 8. A detailed comparison is made between the optics of cuticle and cholesteric liquid crystals. The optical analogy provides a two-way contact between cuticle biophysicists and liquid crystal physical chemists.     

Female ixodid ticks grow endocuticle during the rapid phase of engorgement

Lees (Proc Zool Soc Lond 121:759–772, 1952) concluded that the ixodid tick Ixodes ricinus grows endocuticle during the slow but not during the rapid, phase of engorgement, a conclusion supported by Andersen and Roepstorff (Insect Biochem Mol Biol 35:1181–1188, 2005) for the same species. In this study analysis of dimensional data and cuticle weight measurements from female ixodid ticks (Amblyomma hebraeum) were used to test this hypothesis. Both approaches showed that endocuticle growth continues during the rapid phase, tapering to zero at a fed/unfed weight ratio of ~60. Of the total mass of cuticle in the engorged tick 32–43% was formed during the rapid phase. We demonstrate that if cuticle growth stopped at the end of the slow phase, there would not be sufficient cuticle to account for the thickness of cuticle observed at the end of engorgement. This finding is consistent with prior studies of Rhipicephalus (Boophilus) microplus, and with a dimensional analysis of the cuticle thickness data of Lees for I. ricinus, in contradiction to his conclusion from an analysis of tick cuticle weight measurements. An examination of cuticle weight measurements for I. ricinus by Andersen and Roepstorff similarly supports the finding of cuticle growth during the rapid phase. All ixodid ticks undergo major body expansion, typically tenfold or more, during a rapid phase of engorgement and require sufficient cuticle at the end of that process to contain their body. The fact that cuticle grows during the rapid phase of engorgement in three species suggests that this is a general characteristic of the family Ixodidae.     

Patterns of cuticular organization in the hybrid Tsuga x jeffryi (Henry) Henry and its putative parents

The structure of the leaf cuticle of Tsuga heterophylla, T. mertensiana and their putative hybrid, T. X jeffryi, is described using light microscopy and scanning electron microscopy. In all three taxa the cuticle, from its response to varying maceration time and from sections stained in Sudan IV, shows clear evidence of two components: an outer one probably corresponding to the cuticle proper and cuticular layer and an inner spongy component separated from the outer by a cutin-deficient layer. Comparison of the three taxa indicates that T. X jeffryi agrees closely in nearly all cuticle features with T. mertensiana indicating that if the hybrid status of T. X jeffryi is correct, cuticle characters have been inherited predominantly from one parent.     

The essential role of bursicon during <Emphasis Type="Italic">Drosophila</Emphasis>development

Background  

The protective external cuticle of insects does not accommodate growth during development. To compensate for this, the insect life cycle is punctuated by a series of molts. During the molt, a new and larger cuticle is produced underneath the old cuticle. Replacement of the smaller, old cuticle culminates with ecdysis, a stereotyped sequence of shedding behaviors. Following each ecdysis, the new cuticle must expand and harden. Studies from a variety of insect species indicate that this cuticle hardening is regulated by the neuropeptide bursicon. However, genetic evidence from Drosophila melanogaster only supports such a role for bursicon after the final ecdysis, when the adult fly emerges. The research presented here investigates the role that bursicon has at stages of Drosophila development which precede adult ecdysis.     

ULTRASTRUCTURE OF THE MATURE UNGERMINATED RICE (ORYZA SATIVA) CARYOPSIS. THE CARYOPSIS COAT AND THE ALEURONE CELLS

The results of a light and electron microscopic study of the caryopsis coat and aleurone cells in ungerminated, unimbibed rice (Oryza sativa) caryopses are presented. Surrounding the rice grain is the caryopsis coat composed of the pericarp, seed coat and nucellar layers. The outermost layer, the pericarp, consists of crushed cells and is about 10 μm thick. The seed coat, interior to the pericarp, is one cell thick and has a thick cuticle. Between the seed coat cuticle and endosperm are the remains of the nucellus. The nucellus is about 2.5 μm thick and has a thick cuticle adjacent to the seed coat cuticle. Interior to the caryopsis coat is the aleurone layer of the endosperm. The aleurone completely surrounds the rice grain and is composed of two cell types—aleurone cells that surround the starchy endosperm and modified aleurone cells that surround the germ. The aleurone cells of the starchy endosperm contain many aleurone grains and lipid bodies around a centrally located nucleus. The modified aleurone cells lack aleurone grains, have fewer lipid bodies than the other aleurone cells, and contain filament bundles (fibrils). Plastids of aleurone cells exhibit a unique morphology in which the outer membranes invaginate to form tubules and vesicles within the plastid. Transfer aleurone cells are not observed in the mature rice caryopsis.     

AN ULTRASTRUCTURAL STUDY OF VEGETATIVE CELL DIVISION IN OEDOGONIUM BORISIANUM12

Vegetative cell division in Oedogonium borisianum is initiated by the formation of a 3-layered ring adjacent to the wall in the upper portion of the cell. This structure enlarges by the coalescence of vesicles. When the ring is fully developed, the parent wall splits adjacent to the ring, and the ring expands into a cylinder, which becomes the cuticle of the upper daughter cell. The lateral wall then forms between this cuticle and the plasmalemma of the cell. Concurrent with ring development and expansion, the nucleus migrates to a position in the center of the cell and karyokinesis occurs. Commencing with late telophase, evidence of transverse wall formation becomes apparent. The zone between the daughter nuclei contains a layer of microtubules in a plane parallel to the plane in which the transverse wall will develop. Subsequently a random coalescence of vesicles occurs along this plane. During the latter stages of this process, the ring expands and the plane of the transverse wall moves upward to the base of the ring cylinder. The completed transverse wall then fuses at is periphery with the newly formed lateral wall.     

Differential mechanism of oxidation of N-acetyldopamine and N-acetylnorepinephrine by cuticular phenoloxidase from Sarcophaga bullata

The mechanism of oxidation of two related sclerotizing precursors—N-acetyldopamine and N-acetylnorepinephrine—by the cuticular phenoloxidase from Sarcophaga bullata was studied and compared with mushroom tyrosinase-mediated oxidation. While the fungal enzyme readily generated the quinone products from both of these catecholamine derivatives, sarcophagid enzyme converted N-acetyldopamine to a quinone methide derivative, which was subsequently bound to the cuticle with the regeneration of o-dihydroxy phenolic function as outlined in an earlier publication [Sugumaran: Arch Insect Biochem Physiol, 8, 73 (1988)]. However, it converted N-acetylnorepinephrine to its quinone and not to the quinone methide derivative. Proteolytic digests of N-acetyldopamine-treated cuticle liberated peptides that had covalently bound catechols, while N-acetylnorepinephrine-treated cuticle did not release such peptides. Acid hydrolysis of N-acetyldopamine-treated cuticle, but not N-acetylnorepinephrine-treated cuticle liberated 2-hydroxy-3′,4′-dihydroxyacetophenone and arterenone. These results further confirm the unique conversion of N-acetyldopamine to its corresponding quinone methide derivative and N-acetylnorepinephrine to its quinone derivative by the cuticular phen-oloxidase. Significance of this differential mechanism of oxidation for sclerotization of insect cuticle is discussed.