STEM ANATOMY OF PARTHENIUM ARGENTATUM,P. INCANUM AND THEIR NATURAL HYBRIDS

Guayule (Parthenium argentatum Gray) contains rubber in the parenchymatous cells of stems and roots. Stem anatomy of P. argentatum is described along with that of P. incanum H.B.K. (mariola). Anatomy of these species differs significantly. Phloem rays in both species increase in width by cell division and expansion; however, the increase observed in mariola is less as compared to that in guayule. Axial xylem parenchyma in guayule is generally a two-cell strand as compared to the fusiform axial xylem parenchyma observed in mariola. Vascular ray cells and cells of the pith region of guayule are parenchymatous, whereas those of mariola are sclerenchymatous. As a result of introgression between guayule and mariola, three forms of guayule exist in the native stands of Mexico. Morphological differences between these guayule plants have been described previously. The stem anatomy of these three groups of plants differ importantly. Group I guayule plants, least introgressed by mariola, have taller rays with the cells of pith region and vascular rays parenchymatous. Group III plants, highly introgressed by mariola, have a few to many cells of vascular rays and pith with lignified secondary walls and shorter rays. Many of the anatomical characteristics of group II plants, somewhat introgressed by mariola, are intermediate between group I and III plants.     

Distribution of elements on tobacco trichomes and leaves under cadmium and sodium stresses

When tobacco (Nicotiana tabacum) plants are exposed to toxic level of cadmium (0.2 mM Cd), their trichomes actively excrete crystals (Choi et al., 2001). In this study, we investigated the distribution of Cd and NaCI on trichomes and leaf surfaces. Energy dispersive x-ray (EDX) analysis revealed that, under toxic Cd stress, crystals exudated from the trichomes contained high amounts of Ca, Mg, and Cd, as well as low levels of P, S, and Mn. Electron spectroscopic imaging (ESI) from trichomes and attached crystals showed that these crystals emitted denser radiation energy for Ca and Cd than did the head cells of the trichomes. However, no Cd was detected on the trichome surface itself or within the leaf epidermis. In contrast, treatment with salt (NaCI) did not stimulate crystal formation; instead, it induced the abnormal expansion of trichome cells. Although Na was not accumulated within the crystals, a considerable amount of both Na and CI was sequestered within the stalk cells of the long trichomes. Therefore, we believe that tobacco trichomes play an important role in Cd crystal exudation through crystallization, but that, under NaCI stress, the long trichomes sequester those elements within their stalks.     

GLANDULAR STRUCTURES OF HOLOCARPHA AND THEIR ONTOGENY

Carlquist , Sherwin . (Rancho Santa Ana Botanic Garden, Claremont, California.) Glandular structures of Holocarpha and their ontogeny. Amer. Jour. Bot. 46(4): 300–308. Illus. 1959.—Two types of advanced glandular structures occur in the 4 species of the genus Holocarpha. Sessile disk-shaped glands occur at the tips of upper leaves and of involucral and receptacular bracts. Unlike all other glandular structures of Madinae which have been investigated, these originate from several protodermal initials rather than a single one. These glands, however, represent modifications of a glandular trichome. The other type of glandular structure, termed hollow-stalked trichome here, occurs on the outer surface of involucral and receptacular bracts. These trichomes originate from a single cell but differ from others in the formation of a hollow stalk, the wall of which is one cell in thickness. Mesophyll of the bract, often with an included vascular bundle, is present as an intrusion into the base of the hollow stalk. Corresponding to the advanced nature of the glandular structures, the leaves show specializations in the “inrolling” of margins. Upper leaves have a cylindrical organization of vascular tissue, whereas basal leaves are “normal” and leaves of the main stem are intermediate. The species of Holocarpha differ in certain details of leaf anatomy and structure of hollow-stalked trichomes. The systematic distribution of these is given. The essential unity of the various glandular structures of Madinae is discussed both in terms of mature structure and ontogeny, and the steps in the evolution of these are suggested.     

Glandular trichomes of Ceratotheca triloba (Pedaliaceae): morphology, histochemistry and ultrastructure

This study was initiated to characterize the distribution, morphology, secretion mode, histochemistry and ultrastructure of the glandular trichomes of Ceratotheca triloba using light and electron microscopy. Its leaves bear two morphologically distinct glandular trichomes. The first type has long trichome with 8-12 basal cells of pedestal, 3-14 stalk cells, a neck cell and a head of four cells in one layer. The second type has short trichome comprising one or two basal epidermal cells, a unicellular or bicellular stalk and a multicellular head of two to eight cells. There is a marked circular area in the upper part of each head cell of the long trichome. This area is provided with micropores to exudate directly the secretory product onto the leaf surface by an eccrine pathway. The secretory product has copious amount of dark microbodies arising from plastids which are positive to Sudan tests and osmium tetroxide for unsaturated lipids. The secretion mode of short trichomes is granulocrine and involves two morphologically and histochemically distinct vesicle types: small Golgi-derived vesicles which are positive to Ruthenium Red test for mucilaginous polysaccharides; the second type is dark large microbodies similar to that of long trichomes with low quantity. These two types are stored in numerous peripheral vacuoles and discharge their contents accompanied by the formation of irregular invaginations of the plasmalemma inside the vacuoles via reverse pinocytosis. These two secretion modes of long and short trichomes are reported for the first time in the family Pedaliaceae. The long trichomes have more unsaturated lipids, while the short trichomes contain more mucilaginous polysaccharides.     

Leaf beetle grazing does not induce willow trichome defence in the coppicing willow Salix viminalis

Abstract 1 Willows are frequently attacked and defoliated by adult leaf beetles (Phratora vulgatissima L.) early in the season and the plants are then attacked again when new larvae emerge. The native willow Salix cinerea has previously been shown to respond to adult grazing by producing new leaves with an increased trichome density. Subsequent larval feeding was reduced on new leaves. This type of induced plant response may reduce insect damage and could potentially be utilized for plant protection in agricultural systems. 2 Here, we investigated if the willow species most commonly used for biomass production in short rotation coppice, Salix viminalis, also responds to adult beetle grazing by increasing trichome density. Larval performance and feeding behaviour on plants previously exposed to adult beetles was compared with that on undefoliated control plants in a greenhouse. 3 We found an overall decrease in trichome density within all the plants (i.e. trichome density was lower on new leaves compared to that for older basal leaves on S. viminalis). However, leaves of beetle defoliated plants had a higher trichome density compared to control plants. Larval growth and feeding was not affected by this difference between treatments. Larvae appeared to remove trichomes when feeding on S. viminalis, a behaviour that might explain the lack of difference between treatments.     

Leaf trichomes influence predatory mite densities through dispersal behavior

Habitat complexity can mediate interactions among predators and herbivores and influences arthropod population density and community structure. The abundance of many predatory mites (Acari: Phytoseiidae) is positively associated with abundance of non‐glandular trichomes. We hypothesized that (1) increasing the complexity (trichome density mimicked with cotton fiber patches) of the habitat that predatory mites encounter on leaves would reduce adult dispersal from plants, and (2) increasing habitat complexity would reduce the time that mites spend walking. Typhlodromus pyri Scheuten retention on plants increased linearly in the presence of trichome mimics; mites placed on plants lacking leaf trichomes showed a behavioral response that led to active dispersal. Phytoseiid retention increased with both fiber patch size and fiber density within patches. Moving fiber patches from the underside of the leaf to the upper leaf surface did not change phytoseiid retention but did alter egg distribution, suggesting trichomes do not exclusively influence phytoseiid behavior. Phytoseiid activity level as measured by the amount of time spent walking did not decrease with the addition of fibers. Overall, increasing habitat complexity in the form of non‐glandular trichomes strongly reduced T. pyri dispersal behavior; the predatory mites showed a consistent preference for complex trichome‐rich habitat that was manifest both rapidly and in absence of predators. Hence, the frequently observed pattern of population‐level accumulation of phytoseiids on trichome‐rich plants appears to be driven by a behavioral response to the presence and abundance of non‐glandular trichomes on the leaf surface manifested in the level of dispersal and/or retention. The primary implication of phytoseiid–habitat interactions for biocontrol programs is that where plants have no trichomes, T. pyri will not establish. Whether this behavioral response pattern is a general response of phytoseiids to leaf trichomes or varies with species is a question that remains unanswered.     

6-Benzylaminopurine treatment induces increased pubescence on wheat leaves

The epidermis of wheat (Triticum aestivum L.) leaves contains trichomes that contribute to resistance to insect pests and drought tolerance. In the present study, we examined the effects of 6-benzylaminopurine (BA) and methyl jasmonate (MeJA) treatment on trichome development on the leaves of wheat cv. Norin 61 seedlings. Without phytohormone treatment, trichomes on the adaxial leaf surface were short (90 μm) and their density was low (3.6 trichomes/mm²). Both BA and MeJA treatments significantly increased the density of trichomes, and there were no significant differences between the phytohormone treatments. BA treatment increased trichome length to five times as long as that in the control, whereas MeJA treatment did not significantly affect trichome length. Since BA treatment concurrently increased the DNA content of the nuclei in trichome cells, endoreduplication of the nuclei is probably involved in trichome enlargement. These results indicate that even wheat cultivars with short trichomes retain the mechanisms for trichome enlargement and stimuli such as BA application can induce increased pubescence on wheat leaves.     

Ficus carica L. leaf anatomy: Trichomes and solid inclusions

Ficus carica L., a typical plant of the Mediterranean environment, presents leaves covered by an extensive indumentum, and a mesophyll full of solid inclusions. The morphology and ultrastructure of the trichomes, calcium carbonate cystoliths and silicified structures of leaves of F. carica cv Dottato were investigated with light, confocal, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. At the same time, histochemical reactions were also employed to analyse the indumentum composed by glandular and non-glandular trichomes by applying chemical reagents and fluorescence microscopy. Non-glandular and glandular trichomes, capitate, are described. Non-glandular trichomes are unicellular simple, spine-like and present different morphology and sizes. The capitate glandular trichomes are present on leaf adaxial and abaxial surface and consist of one-celled stalk and 3/4 cells spherical head. Histochemical characterisation of leaf hairs revealed the presence of flavonoids, while glandular trichome head cells showed a complex mixture of alkaloids, essential oil and flavonoids. Cu and Al were found in the constitutive structures, spike and dome, of the cystoliths. Several epidermal cells and non-glandular trichomes were silicified. Leaf hairs, trichomes secretions, solid inclusions and silicification of F. carica leaf have significant roles to play in relation to leaf protection from external factors, including high-intensity radiation, herbivores or pathogens.     

Relationship between physical leaf characteristics and growth and survival of polyphagous grasshopper nymphs, <Emphasis Type="Italic">Parapodisma subastris</Emphasis> (Orthoptera: Catantopidae)

Common types of plant defense mechanisms are thought to affect the host ranges of polyphagous herbivorous insects, yet few studies have examined the relationship between host plant suitability for polyphagous insects and defense against them. We investigated the suitability of the 19 plant species growing in the habitat of the polyphagous grasshopper, Parapodisma subastris, to determine the relationship between the physical characteristics of leaves and the growth and survival of grasshopper nymphs. We examined leaf toughness, trichome density, and length. Nymph survival was greater on plants with characteristics ranging from soft leaves and dense trichomes to tough leaves and few trichomes than on plants with soft leaves and few trichomes. The exception was Rorippa indica, a plant with soft leaves and few trichomes that uses biotic defense, on which nymph survival was maximal. Higher-quality plants that share common physical characteristics over families may favor polyphagy by grasshoppers that possess ability to overcome the physical defense easily with their robust mandibles.An erratum to this article can be found at     

THE LEAF OF CALYCADENIA AND ITS GLANDULAR APPENDAGES

Carlquist , Sherwin . (Rancho Santa Ana Botanic Garden, Claremont, Calif.) The leaf of Calycadenia and its glandular appendages. Amer. Jour. Bot. 46(2) : 70-80. Illus. 1959.—Large tack-shaped glands are characteristic of the leaves of Calycadenia which are associated with the inflorescence. These glands may be divided into those which are terminal on leaves and those which occur laterally on the surface of the leaf. Lateral glands show stages early in their development which are identical with those of simpler trichomes of Madinae. Terminal glands, which possess more vascularization of the stalk, show a more modified form of development. Vascularization is not derived from protoderm, but from more deeply-seated cells. These cells are included in a zone of elongation which forms the stalk. Vascular bundles may extend to the base of glands which lack vascularization in their stalks. Tack-shaped glands are considered an advanced form of trichome in which internal tissues of the leaf are involved. Within the genus Calycadenia, ontogenetic and comparative studies suggest that the following characters are advanced: reduction to a single terminal gland, “inrolling” of margins to form a cylinder of bundles, concomitant with a central core of fibers or a pectic channel. Systematic distribution of gland occurrence and of types of foliar structure are given.     

Light, conventional and environmental scanning electron microscopy of the trichomes of Cucurbita pepo subsp. pepo var. styriaca and histochemistry of glandular secretory products

BACKGROUND AND AIMS: In the present study, the differences between glandular and non-glandular trichomes, the secretory process and the method of secretion were studied. Previous studies on leaves of Styrian oil pumpkin (Cucurbia pepo var. styriaca) plants have shown that four morphologically and ontogenetically independent glandular and non-glandular trichome types and one bristle hair type can be distinguished. The four types of trichomes can be categorized into three glandular trichome types: type I, a short-stalked trichome with four head cells including a 'middle-cell', two stalk cells and one basal cell; type II, a long-stalked trichome with two head cells, a 'neck-cell' region and a long stalk area; type IV, a 'stipitate-capitate' trichome with a mesophyll cell basement, a short stalk and a multicellular head; type III, a non-glandular 'columnar-digit' trichome, which consists of two head cells continuous with three-celled stalk, and the basal cell. METHODS: The histochemical studies (the main classes of metabolite in secreted material of glandular trichomes) were conducted in fresh and fixed hand sections, using the following tests: Sudan black B, Nile blue A, osmium tetroxide, neutral red, Naturstoffreagent A, FSA (fuchsin-safranin-astra blue), NADI (naphthol + dimethylparaphenylenediamine) and ruthenium red. Each suggested differences in the intercalations during the ontogenetical development of each trichome during the development stage. KEY RESULTS: The histochemical reactions revealed the main components of the materials secreted by all types of trichomes, which include lipids, flavones and terpenes and the different cell wall compositions. Glandular secretions were observed during environmental scanning electron microscopy (ESEM) and the trichomes compared with those seen by conventional scanning electron microscopy (CSEM). CONCLUSIONS: Scanning electron microscopy and histochemical analysis demonstrated that each of the trichomes studied produced and released secretory products in a characteristic way.     

DEVELOPMENT,STRUCTURE AND FUNCTION OF SECRETORY TRICHOMES IN PSYCHOTRIA BACTERIOPHILA (RUBIACEAE)

Mucilage-secreting dendroid trichomes develop from the adaxial epidermis of young stipules surrounding the shoot apex. Each trichome consists of a multicellular stalk from which radiate many branch cells. The trichome has no cuticle and the branch cell walls distally are loose cellulosic frameworks. Dictyosomes produce vesicles whose products are secreted through the plasma-lemma and cell wall. Enlarged portions of the ER are frequently associated with dictyosomes and may be part of the system for synthesis and transport of secretion products. Bacteria, which later occur in leaf nodules, are present in the mucilage surrounding trichomes and young leaves. The latter develop stomata through which the bacteria enter. As stipules and leaves grow out of the apical region, the secretory trichomes degenerate and are replaced by non-secretory ones.     

Oviposition,larval survival and leaf damage by the willow leaf blotch miner,Micrurapteryx salicifoliella,in relation to leaf trichomes across 10 Salix species

1. Foliar trichomes clearly reduce chewing damage and efficiency of movement by some insect herbivores, but the effect of trichomes on insect oviposition is less well characterised. Trichomes are likely to have particularly strong, negative effects on species that require secure attachment of the egg to the leaf epidermis for successful transition to the feeding stage – a group that includes many leaf mining insects. 2. One such species, Micrurapteryx salicifoliella, must initially enter leaf cells directly from an egg adhered to the cuticle, but later instars can move between leaves and initiate new mines from the leaf exterior. 3. Natural patterns of occurrence by M. salicifoliella were quantified on 10 sympatric Salix species varying in trichome expression to test whether trichomes were associated with reduced oviposition, larval survival and leaf damage. 4. Mean egg density and leaf mining damage were negatively related to mean trichome density across Salix species. Survival of M. salicifoliella from egg to pupa was positively related to trichome density, suggesting that initiation of new mines by late‐instar larvae was not adversely affected by trichomes. There was no evidence that trichomes benefited leaf miner larvae indirectly by decreasing density‐dependent mortality; rather, the positive relationship between trichome density and larval survival may reflect less effective chemical defence by Salix species expressing high trichome density. 5. The results suggest that foliar trichomes serve as an effective defence against M. salicifoliella by deterring oviposition, but do not reduce the survivorship of those individuals that successfully transition from egg to larva.     

Artificial Defoliation Induces Trichome Production in the Tropical Shrub Cnidoscolus aconitifolius (Euphorbiaceae)1

Induction of plant defenses and their spatial variability are key subjects in the field of ecology and evolution of defensive traits in plants. Nevertheless, induction has been more commonly studied under controlled environments, ignoring other factors that might influence this process in natural settings. The main goal of this study was to determine if artificial defoliation induces trichome production in three natural populations of the tropical shrub Cnidoscolus aconitifolius. First, we performed trichome counts for each population before imposing artificial defoliation to assess differences in trichome loads between populations. Trichome densities (trichomes/cm²) were quantified for leaf blades, petioles, and flower stalks. To determine if defoliation induced trichome production, three defoliation treatments (0% leaves defoliated or controls, 50% of total leaves defoliated, and 100% defoliation) were applied once at the beginning of the reproductive season. Trichome counts were performed on each structure every ～20 d during a 3‐mo period after the application of treatments. Trichome counts showed significant differences in trichome densities between populations for all three structures. In turn, artificial defoliation increased trichome density. Significant differences among treatments were found for trichome densities on leaf blades and petioles. In both these structures, the 100 percent defoliation treatment differed significantly from control plants, presenting higher trichome densities. In addition, the treatment × population interaction was not significant for leaf blades and petioles, indicating that induction is a generalized response in this species, at least at the study sites. These results indicate that trichomes in C. aconitifolius are inducible due to defoliation.     

Nonglandular leaf trichomes as short-term inducible defense of the grey alder,Alnus incana (L.), against the chrysomelid beetle,Agelastica alni L.

Summary The grey alder compensates leaf area losses due to insect grazing by continuously producing new leaves throughout the vegetative period. Different degrees of defoliation were attained experimentally by a controlled release of the oligophagous beetle Agelastica alni on arbitrarily selected trees from a homogenous population of young alders. The reduction in leaf area per tree significantly influenced the density of leaf trichomes, assessed 10–30 days later, on newly sprouting leaves only. Cross-correlations between leaf area reduction and trichome density were strongest for leaves which completed unfolding 14–21 days after damage. Dualchoice assays suggested a negative influence of trichomes on oviposition rate of A. alni. Removal of trichomes by shaving demonstrated the highly significant effect of trichomes on feeding behavior of adults and larvae in dual-choice assays. The role of the induced increase in trichome density as a possible short-term defense reaction against herbivorous insects is discussed.     

The taxonomic value of leaf anatomy and trichome morphology of the genus Cyclotrichium (Lamiaceae) in Turkey

The genus Cyclotrichium (Boiss.) Manden. & Scheng. is represented by six species in Turkey: C. glabrescens, C. leucotrichum, C. longiflorum, C. niveum, C. origanifolium and C. stamineum. They are aromatic perennial subshrubs used as spices or herbal teas in traditional Turkish medicine. The leaf anatomy and tomentum morphology of leaves and calyces of Cyclotrichium species in Turkey was investigated by scanning electron microscopy (SEM) and light microscopy (LM). The investigated species have equifacial (C. niveum, C. origanifolium) or bifacial leaves (C. glabressens, C. leucotrichum, C. longiflorum, C. stamineum). All species have peltate and capitate glandular, and simple (all species) or branched (C. niveum) eglandular trichomes and diacytic stomata. Peltate trichomes consist of a basal cell embedded in the epidermis, a stalk cell, and a broad 12 (–13)‐celled secretory head arranged in two concentric circles. The capitate trichomes observed in Cyclotrichium can be grouped into five types, differing in structure and size. They consist of either a pear‐shaped or globose unicellular head and uni‐or bicellular stalk, or a bicellular head and bicellular stalk. The density of peltate, capitate and eglandular trichomes differs between species. Peltate trichomes are densely spaced only on the calyx and on the leaf surface of C. niveum and C. origanifolium and on the abaxial leaf surface of C. longiflorum and C. stamineum. The significance of trichome architecture for taxonomy in Cyclotrichium and Lamiaceae in general is discussed.     

Resource availability and the trichome defenses of tomato plants

We conducted two experiments to determine how resource availability influenced allocation by tomato (Lycopersicon esculentum) to trichomes, and how different patterns of trichome allocation by plants grown in different resource environments might then influence the behavior of tobacco hornworm (Manduca sexta) caterpillars. In the first experiment we used high and low levels of light and water, and then, using scanning electron microscopy, determined trichome densities on the leaves and stems. We sampled leaves and stems at several places throughout the plant to determine whether there were within-plant differences in allocation to trichomes. The results of the first experiment showed that resource availability influenced allocation to trichome growth. Patterns in high and low-light supported both the growth-differentiation balance hypothesis (GDBH) and the carbon-nutrient balance hypothesis (CNBH). However, the GDBH was not supported by differences among water treatments. Contrary, to predictions of the GDBH, plants with intermediate growth did not have the highest trichome densities, and plants with similar growth differed in trichome density. Possible biological and artifactual explanations are discussed. The first experiment also showed that there was within-plant variation in allocation to trichomes, and that plant resource availability may influence within-plant variation in allocation to trichomes. In the second experiment, we grew plants in high and low-light, and then monitored the behavior of tobacco hornworms on the stems of these plants in the laboratory. This experiment demonstrated that the light environment that tomato plants were grown in influenced the resting behavior of caterpillars. Furthermore, it demonstrated that both glandular and non-glandular trichomes impeded caterpillars from searching for food. Overall, this study indicated that plant resource availability can influence allocation to trichome defenses, and that these differences may affect insect herbivores.