Ontogenetics of QTL: the genetic architecture of trichome density over time in Arabidopsis thaliana

Although much is known about the molecular genetic basis of trichome development in Arabidopsis thaliana, less is known about the underlying genetic basis of continuous variation in a trait known to be of adaptive importance: trichome density. The density of leaf trichomes is known to be a major determinant of herbivore damage in natural populations of A. thaliana and herbivores are a significant selective force on genetic variation for trichome density. A number of developmental changes occur during ontogeny in A. thaliana, including changes in trichome density. I used multiple interval mapping (MIM) analysis to identify QTL responsible for trichome density on both juvenile leaves and adult leaves in replicate, independent trials and asked whether those QTL changed with ontogeny. In both juvenile and adult leaves, I detected a single major QTL on chromosome 2 that explained much of the genetic variance. Although additional QTL were detected, there were no consistent differences in the genetic architecture of trichome density measured on juvenile and adult leaves. The finding of a single QTL of major effect for a trait of known adaptive importance suggests that genes of major effect may play an important role in adaptation.     

日本刀角瓢虫对不同番茄品种的产卵选择性及其影响因素

【目的】明确日本刀角瓢虫Serangium japonicum对叶毛密度和类型不同的番茄Lycopersiconesculentum品种的产卵选择性。【方法】以4个番茄品种(砧木101、闽粉樱1号、砧木301和以色列超级金刚)作为日本刀角瓢虫的寄主植物,观察番茄叶片背面超微结构,统计叶片背面叶毛类型及密度;用叶蝶法和植株法测定日本刀角瓢虫雌成虫在带烟粉虱Bemisia tabaci卵的4个番茄品种上的产卵量占比;并测定日本刀角瓢虫在这4个番茄品种叶片上的子代及成虫表现(生长发育、繁殖和捕食能力)以及对叶片的附着力,雌成虫对4个番茄品种健康叶片和受烟粉虱为害叶片的气味选择以及4个番茄品种叶碟和植株上日本刀角瓢虫卵被同类捕食的风险。【结果】4个番茄品种叶片背面叶毛类型均具有非腺毛和腺毛,其中,非腺毛有Ⅱ, Ⅲ和Ⅴ型,腺毛有Ⅰ, Ⅳ Ⅵ和Ⅶ型,且均以Ⅴ型非腺毛密度最高。以色列超级金刚叶片背面的叶毛密度显著低于其他3个供试番茄品种。日本刀角瓢虫偏好在以色列超级金刚上产卵,在以色列超级金刚、砧木101和闽粉樱1号上的繁殖力(165~223.92粒/雌)显著高于在砧木301上的(2809粒/雌)。日本刀角瓢虫子代由卵发育至成虫的历期在闽粉樱1号上最短(15.73 d),在砧木101上最长(23.00 d)。日本刀角瓢虫在4个番茄品种上的产卵选择性与子代表现及亲代表现无显著相关性,而与日本刀角瓢虫卵的被捕食风险存在显著正相关关系。日本刀角瓢虫在4个番茄品种上的产卵选择性与日本刀角瓢虫对番茄叶片的附着力及番茄叶片上各类型叶毛密度均无显著相关性。番茄的7种叶毛类型其叶毛密度在4个番茄品种上都存在显著差异,除番茄Ⅰ型腺毛密度与日本刀角瓢虫的繁殖力(30 d内单雌产卵量)存在显著负相关关系外,其他6种类型的叶毛密度与日本刀角瓢虫子代表现及亲代表现均无显著相关性。日本刀角瓢虫雌成虫对4个番茄品种的气味无明显偏好。日本刀角瓢虫卵在4个番茄品种叶蝶和植株上的被捕食比例差异显著。【结论】日本刀角瓢虫雌成虫偏好在叶毛密度低的番茄品种叶片上产卵,番茄腺毛对日本刀角瓢虫成虫生命活动影响显著。     

Arabidopsis ketoacyl‐CoA synthase 16 (KCS16) forms C36/C38 acyl precursors for leaf trichome and pavement surface wax

The aliphatic waxes sealing plant surfaces against environmental stress are generated by fatty acid elongase complexes, each containing a β‐ketoacyl‐CoA synthase (KCS) enzyme that catalyses a crucial condensation forming a new C─C bond to extend the carbon backbone. The relatively high abundance of C₃₅ and C₃₇ alkanes derived from C₃₆ and C₃₈ acyl‐CoAs in Arabidopsis leaf trichomes (relative to other epidermis cells) suggests differences in the elongation machineries of different epidermis cell types, possibly involving KCS16, a condensing enzyme expressed preferentially in trichomes. Here, KCS16 was found expressed primarily in Arabidopsis rosette leaves, flowers and siliques, and the corresponding protein was localized to the endoplasmic reticulum. The cuticular waxes on young leaves and isolated leaf trichomes of ksc16 loss‐of‐function mutants were depleted of C₃₅ and C₃₇ alkanes and alkenes, whereas expression of Arabidopsis KCS16 in yeast and ectopic overexpression in Arabidopsis resulted in accumulation of C₃₆ and C₃₈ fatty acid products. Taken together, our results show that KCS16 is the sole enzyme catalysing the elongation of C₃₄ to C₃₈ acyl‐CoAs in Arabidopsis leaf trichomes and that it contributes to the formation of extra‐long compounds in adjacent pavement cells.     

Lima bean–lady beetle interactions: hooked trichomes affect survival of <Emphasis Type="Italic">Stethorus punctillum</Emphasis> larvae

We tested the hypothesis that Lima bean Phaseolus lunatus L. (Henderson cultivar) trichome density affects the survival of the acariphagous lady beetle Stethorus punctillum Weise. When isolated throughout larval development, 10% or less of S. punctillum larvae reared on two-spotted spider mite Tetranychus urticae Koch on small (rather than large) P. lunatus leaves survived until pupation. Although other factors might have contributed to larval mortality, we demonstrated that survival rate was related to trichome density (i.e., number of hooked trichomes per cm on the underside of leaves). Trichome density was greatest on the underside of small leaves and least on large leaves, indicating that survival rate increased as trichome density decreased. Hooked trichomes impaled S. punctillum larvae more often at the apex of the abdomen than at any other body part. Hooked trichomes also trapped S. punctillum adults, but they always managed to free themselves. This study highlights the negative effect of Lima bean hooked trichomes on a predacious lady beetle that attacks the two-spotted spider mite.     

Trichome micromorphology in Turkish species of Ziziphora (Lamiaceae)

Ziziphora L. is represented by 5 species and 2 subspecies in the flora of Turkey: Z. clinopodioides, Z. capitata, Z. persica, Z. tenuior, Z. taurica subsp. taurica, Z. taurica subsp. cleonioides. It is difficult to distinguish between some Ziziphora taxa because of their morphological similarities. In this study, the leaf and calyx trichomes of Ziziphora taxa in Turkey were studied in order to assess anatomical variations that may serve as distinguishing characters. Their micromorphological features were surveyed by scanning electron microscopy (SEM) and light microscopy (LM). Trichomes on leaves and calyx can be divided into two general types: non‐glandular trichomes and glandular (secretory) trichomes. The non‐ glandular trichomes are simple, acicular or curved with cuticular micropapillae. They usually consist of one or more additional cells. The glandular trichomes are divided into two types: peltate and capitate and Ziziphora taxa can easily be distinguished by presence/absence, density and types of glandular trichomes on leaves and calyx. The peltate trichomes consist of 12 or 18 secretory head cells in a single disc; four or six central cells surrounded by eight or twelve peripheral ones. Peltate trichomes are absent on the adaxial leaf surface of Z. capitata and Z. persica. Two types of capitate trichomes are present in Ziziphora. The capitate trichomes are only absent on the calyx surface of Z. persica. In addition, the trichome micromorphology provides some support for separating the two subspecies of Z. taurica. In conclusion, Ziziphora taxa can easily be distinguished by cell number, cell shape presence/absence and density of the glandular trichomes on leaves and calyx.     

A nuclear mutation blocking initiation of the lamina in leaves of Nicotiana syhestris

Isolation of a nuclear recessive mutation (lam-1) blocking initiation of the lamina in leaves of Nicotiana sylvestris Speg. et Comes is described. Histological analysis of the mutant apex demonstrates a defect in establishment of meristematic activity along the margins of emerging primordia, the earliest cytological event in lamina formation. Mutant leaves grow to their normal length (about 30 cm) but fail to expand. Transverse sections show that mutant leaves are essentially naked midribs, lacking the characteristic cell types of the wild-type mesophyll. In the absence of lateral expansion, all secondary veins develop along the longitudinal axis, producing abnormal parallel venation. The mutant is defective in phase transition and grows indefinitely as a juvenile vegetative rosette. Exogenous gibberellic acid induces rapid stem elongation and flowering, but does not correct the lamina defect, indicating that juvenile arrest is a pleiotropic consequence of a gibberellin deficiency in bladeless leaves. The calyx, corolla and gynoecium in mutant flowers show defects in lateral development, indicating that the lam-1 gene plays a crucial role in development of floral organs as well as leaves.Abbreviations GA gibberellin - GA₃ gibberellic acid - WT wildtype The technical assistance of Regan Perry is gratefully acknowledged.     

Two new endemic species of Ophiorrhiza L. (Rubiaceae: Ophiorrhizeae) from Davao Oriental,Philippines

Two new species of Ophiorrhiza collected from Mt Hamiguitan Range Wildlife Sanctuary in Davao Oriental, Philippines, are herein described and illustrated. Ophiorrhiza erythropilosa is the third Philippine species possessing involucral bracts and is further characterized by its predominantly villose stems that appear red due to strikingly red-violet trichomes, subpersistent bifid stipules, linear involucral bracts without prominent midrib, and 4 mm long urceolate corolla that is villose outside and lightly puberulous inside. Ophiorrhiza hamiguitanensis is characterized by its coriaceous, lanceolate leaves with attenuate apex and base, brochidodromous venation, subpersistent bilobed stipules with slightly recurved acute tips, presence of 1.5–2.5 mm long linear ensiform bracts, heterostylous flowers, clavate calyces and broadly obcordate capsules.     

EARLY HISTOGENESIS OF THE ADULT LEAVES OF DARLINGTONIA CALIFORNICA (SARRACENIACEAE) AND ITS BEARING ON THE NATURE OF EPIASCIDIATE FOLIAR APPENDAGES

In order to assess the validity of various interpretations of tubular leaves of angiosperms, a histogenetic study of the ontogeny of adult leaves of Darlingtonia californica was undertaken. The adult leaf of Darlingtonia is characterized by a sheathing leaf base, an elongate ascidium, an overarching hood, and two “fishtail” appendages which arise near the leaf apex. A keellike growth, with two rows of alternate vascular bundles, traverses the tube from base to mouth. Ontogenetic studies show that the primordium arises by a monopodial rather than a sympodial mode of growth as previously reported. After the formation of a small, erect primordium, a restricted adaxial meristem is initiated that expands both adaxially and upwards. This “querzone” serves, in effect, to congenitally combine the two primordial margins during its extension. Growth and maturation of the subjacent portions cause tubular elongation in the leaf. Primordial apical divisions are later replaced by more general intercalary growth with acropetal and centrifugal maturation. The hood and fishtails are established early in ontogeny by adaxial growth of the primordial apex and subsequent activation of juxtaposed localized meristems. Comparative morphology has established that the epiascidiate leaf is a foliar appendage that undergoes certain specific morphogenetic modifications. It has a structural relationship to ensiform appendages of Acacia and Acorus as well as to peltate foliar organs. The early ontogeny of Darlingtonia leaves is considered to be homologous with other epiascidiate foliar organs, including some supposedly primitive carpels.     

Structure and development of stellate trichomes in Andradea ftoribunda Fr. Allem. (Nyctaginaceae)

LOURO, R. P., MIGUENS, F. C. & MACHADO, R. D., 1992. Structure and development of stellate trichomes in Andradea ftoribunda Fr. Allem. (Nyctaginaceae). Trichomes occur on both faces of young leaves. They are peltate-stellate on the abaxial face, and comprise a stalk and radiating cells with a rudimentary central apex. On the adaxial face the trichomes arc stellate with a large apex comprising one to three cells. In both cases the stalk is formed by three to six cells of which the most distal may contain a tannoid substance. In the adult leaf only the abaxial surface exhibits stellate trichomes, with two to three celled stalks. The central region of radial cells is depressed. On the adaxial side the hairs are shed during maturation of the leaf.     

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 ROLES OF HETEROCHRONY AND HETEROBLASTY IN THE DIVERSIFICATION OF LEAF SHAPES IN BEGONIA DREGEI (BEGONIACEAE)

The relationship between shape variation in the transitional series of leaves and in adult leaves was examined in seedlings of seven morphs of Begonia dregei using several quantitative methods of shape analysis. There is variation in the shape of adult leaves among individuals as well as in juvenile leaves within individuals in B. dregei. As an individual grows, there is a gradual transition in leaf shape from the symmetrical, oval, smooth-margined leaves through a series of more than ten transitional leaves to a stable adult leaf shape. There appear to be two basic patterns to the acquisition of adult traits. Traits that differ among morphs are acquired gradually throughout the entire transitional series while those that are similar among morphs are acquired by about leaf 5 and remain stable through the later juvenile leaves. There is no identity of leaf shape between the earlier leaves of some morphs and the later leaves of others. Evolutionary diversification in adult leaf morphology in this species is not related to simple changes in ontogeny of the whole plant.     

Microarray analysis of vegetative phase change in maize

Vegetative phase change is the developmental transition from the juvenile phase to the adult phase in which a plant becomes competent for sexual reproduction. The gain of ability to flower is often accompanied by changes in patterns of differentiation in newly forming vegetative organs. In maize, juvenile leaves differ from adult leaves in morphology, anatomy and cell wall composition. Whereas the normal sequence of juvenile followed by adult is repeated with every sexual generation, this sequence can be altered in maize by the isolation and culture of the shoot apex from an adult phase plant: an 'adult' meristem so treated reverts to forming juvenile vegetative organs. To begin to unravel the as-yet poorly understood molecular mechanisms underlying phase change in maize, we compared gene expression in two juvenile sample types, leaf 4 and culture-derived leaves 3 or 4, with an adult sample type (leaf 9) using cDNA microarrays. All samples were leaf primordia at plastochron 6. A gene was scored as 'phase induced' if it was up- or downregulated in both juvenile sample types, compared with the adult sample type, with at least a twofold change in gene expression at a P-value of < or =0.005. Some 221 expressed sequence tags (ESTs) were upregulated in juveniles, and 28 ESTs were upregulated in adults. The largest class of juvenile-induced genes was comprised of those involved in photosynthesis, suggesting that maize plants are primed for energy production early in vegetative growth by the developmental induction of photosynthetic genes.     

THE CUTICULAR ANATOMY OF FRENELOPSIS VARIANS FROM THE LOWER CRETACEOUS OF CENTRAL TEXAS

Stem fragments identified as Frenelopsis varions Fontaine have been found in the Lower Cretaceous (Albian) of central Texas. The cuticle is extremely thick and characterized by 5–6 subsidiary cells with papillae overarching the stomatal chamber. Guard cells are deeply sunken below the epidermis. Stomatal complexes are arranged in axial rows extending from the base of an internode to its apex. The rows of stomata continue into the sheathing leaf where the rows curve towards the leaf apex. The epidermis of F. varions was apparently long persistent and underwent prolonged growth. Axial rows of stomata are frequently disrupted resulting in a random pattern of stomata. A single, highly reduced, sheathing leaf is present at each node. The margin of the leaf has numerous unicellular trichomes and extends to form a slightly triangular blade.     

THE ONTOGENY OF THE INFLORESCENCE AND FLOWER OF LIQUIDAMBAR STYRACIFLUA L. (HAMAMELIDACEAE)

A developmental study of the inflorescence of Liquidambar styraciflua L. was conducted to clarify morphological discrepancies reported in the literature. Salient features of development are: 1) the inflorescence apex results from the conversion of a terminal, vegetative apex; 2) partial inflorescence apices arise as ellipsoid structures in axils of leaves, bracts, or transitional phyllomes; 3) development of male heads is acropetal whereas female heads differentiate basipetally; 4) the partial inflorescence apex becomes segmented into several distinct subunits indicating an axillary branch system of the third order; 5) distinct individual floral primordia are initiated on the subunits; 6) a complete absence of perianth development; 7) inception of carpel primordia in flowers of lower male heads as well as female heads, but a failure of the gynoecium to develop beyond an incipient stage in male heads; and 8) development of sterile structures around the base of the styles of only female flowers near the time of anthesis. Carpellary characteristics of the sterile structures are described, their morphological nature is discussed, and the phylogenetic position of Liquidambar is evaluated.     

Reproductive strategy of an invasive thistle: effects of adults on seedling survival

Invasive species are known for their ability to form monocultures that exclude native species, yet intraspecific interactions among invasives have not been well studied. Cynara cardunculus (L.) is an invasive perennial thistle that establishes high-density populations in coastal California grasslands. We examined the natural distribution of C. cardunculus seedlings in an established population and found that nearly 100% of seedlings grew within 2 m of adults despite an expected distribution peak at 3 m from source plants based on measured dispersal distances. We then investigated the role of mature plants in seedling survival and establishment with regard to live vegetation, litter, and seedling distance by planting seedlings at increasing distances around adults and applying removal treatments to the focal adult rosettes. We applied control (no removal), adult rosette removal (live leaves), litter removal (dead leaves), and adult rosette plus litter removal (all aboveground plant material) treatments. Seedlings experienced a higher rate of survival, measured by senescence date, and establishment, measured by return rate the following year, with all adult rosette removal treatments. Inhibition by adult rosettes was reduced with distance to 60–80 cm from the rosette, and there was little effect of adult plants between 80 and 200 cm. These results suggest that adult rosettes may inhibit conspecific seedlings at very close distances but provide a favorable environment for seedlings within nearby interspaces. This pattern may contribute to the creation and maintenance of high-density populations in C. cardunculus. Land managers seeking to control this species may improve long-term effectiveness by expanding management efforts to include a 2 m radius around adult plants and treating within 5 months of seedling emergence to prevent recruitment rather than treating adults alone.     

COMPARISON OF SHOOT APEX DYNAMICS AND EARLY LEAF ONTOGENY IN TWO SPECIES OF SARACA (LEGUMINOSAE)

Shoot apices of Saraca indica produce adult leaves that have 4 to 6 pairs of leaflets, whereas those of S. bijuga usually have only 2 pairs. In both species one leaflet pair is found during the juvenile phase. Juvenility lasts many plastochrons in S. bijuga but is restricted to a few in S. indica. The shoot apical meristems of these two taxa are similar in structure, cell number, and cell size; however, the shoot apex of Saraca bijuga is slightly more stratified, having 2–3 tunica layers as opposed to 1–2 in S. indica. For most of the plastochron the apical meristem in both species is situated laterally at the base of the most recently formed leaf. A newly forming primordium and its internode shift the apical meristem upward unilaterally; the meristem passes through a brief apical dome stage and becomes positioned 180° from its origin at the beginning of the plastochron. Hence, there is a true pendulum meristem in both species. In S. bijuga the maximum length of the youngest leaf primordium, just prior to the formation of its successor, is twice that of S. indica. The internodes immediately below the shoot apex and the axillary buds develop more rapidly in S. bijuga than in S. indica. It is suggested that the bijugate leaf of S. bijuga represents a case of neoteny in plants.     

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.     

Walking pattern of Trichogramma nubilale Ertle & Davis (Hymenoptera; Trichogrammatidae) on various surfaces

The leaf surfaces on which mass-reared Trichogramma spp. are released for augmentative biological control may be an important factor effecting the success of these releases. We observed and recorded the walking pattern of Trichogramma nubilale females on leaves of Zea mays, Canna × generalis (Canna lilly), Silphium perfoliatum (cup plant), Abutilon theophrasti (velvetleaf), Schizachyruim scoparium (little bluestem), a smooth and a fuzzy polyester material, and waxed paper. For each surface type, a total of 10 mated, 1–2 days old, naive and fed females were observed and their walking path was traced. Females walked fastest on waxed paper and leaves of S. scoparium and slowest on leaves of A. theophrasti and the fuzzy material. Turning rates were high on Canna × generalis and waxed paper. In general, walking speed was negatively affected by the presence and density of trichomes and possibly the lack of leaf veins. The effect of surface structures, such as trichomes is likely to scale to the body size of the searching parasitoid. Parasitoids can walk over short trichomes, but short directionally pointed trichomes (as on S. scoparium) can guide the search paths in certain directions. The effects of long trichomes may depend on trichome density relative to the parasitoid body length. When trichome density is on the same order of magnitude as 1/L² (Z. mays), wasps will stand between trichomes, and will frequently run into trichomes, which will retard walking speeds and increase turning.