Intercellular power transmission along trichomes of cyanobacteria

An attempt at demonstrating lateral power transmission over millimeter distances along a coupling membrane has been undertaken. Trichomes of the multicellular filamentous cyanobacteria Phormidium uncinatum were illuminated with a very narrow light beam forming a light spot that covered only 4–5% of a 1–2 mm long cyanobacterial trichome. Such illumination was found to support motility (gliding along agar surface) of the trichome under conditions when the light was the only energy source. It was also shown that illumination with the light spot caused rotation of rings of slime (accompanying the operation of the ‘motors’ responsible for the motility of cyanobacteria) not only in the illuminated, but also in the distal, nonilluminated part of the trichome. Electric potential transmission along trichomes was revealed by means of the extracellular electrode technique. The light spot was found to induce generation of an electric potential difference between two electrodes in the dark region of the trichomes, which were placed at different distances from the illuminated end. Cutting the trichomes between the light spot and the closest ‘dark’ electrode abolished this effect. Valinomycin + K⁺ and carbonyl cyanide p-trifluoromethoxyphenylhydrazone affected the potential difference formation between two ‘dark’ electrodes much stronger than that between a light and a dark electrode. All the light spot-induced effects develop in the seconds time scale. Both the amplitudes and the kinetics of the potential difference measured with four electrodes placed along the trichome prove to be in good agreement with the theoretical curves computed on the basis of the electric cable equation. It is concluded that transcellular power transmission in the form of Δψ takes place along trichomes of cyanobacteria. This confirms the hypothesis about the biological function of Δψ as a transportable form of energy.     

Relationship between Feeding Damage by Beet armyworm,Spodoptera exigua (Lepidoptera: Noctuidae) and Leaf Trichome Density of Potato

The responses (infestation level and feeding preference) of 50 potato cultivars, including seven Korean recommended cultivars to Spodoptera exigua larvae were examined in the field and the laboratory. Based on the number of potato leaves damaged by S. exigua larvae in the field, seven cultivars (Anco, Denali, Bintje, Jidose, Sandra, Shimabara, and Spunta) were found tolerant to the insect attack, whereas Nicola and Dejima cultivars were highly susceptible. In feeding preference tests using leaflets of 10 selected cultivars (Anco, Denali, Bintje, and seven recommended cultivars), no significant differences were seen among the cultivars, indicating no involvement of chemical resistance. In trichome density per mm² leaf area, underside leaf surface contained higher trichome densities than the upper side, and the number of long trichome were distributed four times more than short trichome on average. Total leaf trichome density was the highest on cv. Dejima of 32.1, followed by cvs. Bintje and Denali, but the lowest on cv. Jopung of 6.9. From correlation analysis, infestation level in the field by S. exigua was correlated with the density of shorter trichome on upper side of leaf surface (r = 0.737^* in 1996 and 0.772^** in 1997). However, it was not correlated with the density of the longer trichome on underside.     

Studies of the site and mode of biosynthesis of tobacco trichome exudate components

Detached glandular trichome head preparations and epidermal strips with and without trichome heads were used to identify glandular trichome heads as the site of sucrose ester biosynthesis in tobacco. Carbon dioxide in solution as well as sucrose, glucose, and acetate were shown to serve as precursors to both sucrose esters and duvatrienediol diterpenes in detached trichome heads or epidermal strips, and gaseous CO2 was also efficiently utilized by epidermal strips. Thus, glandular heads can biosynthesize these principal exudate components from a molecule as simple as CO2. While formation of duvatriendiols from all precursors tested and conversion of sucrose and glucose to sucrose esters was light dependent, utilization of acetate to label the 6-O-acetyl group of the glucose moiety of sucrose esters occurred equally well in light and dark. The data suggest that CO2 and/or monosaccharides produced in trichome head cells and perhaps that supplied by other epidermal cells can act as carbon sources for sucrose ester and duvatrienediol biosynthesis which occurs in the glandular trichome head.     

Cost of trichome production and resistance to a specialist insect herbivore in <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

Theory predicts that trade-offs between resistance to herbivory and other traits positively affecting fitness can maintain genetic variation in resistance within plant populations. In the perennial herb Arabidopsis lyrata, trichome production is a resistance trait that exhibits both qualitative and quantitative variation. Using a paternal half-sib design, we conducted two greenhouse experiments to ask whether trichomes confer resistance to oviposition and leaf herbivory by the specialist moth Plutella xylostella, and to examine potential genetic constraints on evolution of increased resistance and trichome density. In addition, we examined whether trichome production is induced by insect herbivory. We found strong positive genetic and phenotypic correlations between leaf trichome density and resistance to leaf herbivory, demonstrating that the production of leaf trichomes increases resistance to leaf damage by P. xylostella. Also resistance to oviposition tended to increase with increasing leaf trichome density, but genetic and phenotypic correlations were not statistically significant. Trichome density and resistance to leaf herbivory were negatively correlated genetically with plant size in the absence of herbivores, but not in the presence of herbivores. There was no evidence of increased trichome production after leaf damage by P. xylostella. The results suggest that trichome production and resistance to leaf herbivory are associated with a cost and that the direction of selection on resistance and trichome density depends on the intensity of herbivory.     

Progress in the molecular genetic analysis of trichome initiation and morphogenesis in Arabidopsis

Arabidopsis trichomes are large unicellular structures that develop on the surface of most shoot-derived organs. In leaves, the number, spacing and shape of trichomes is tightly regulated, and this process has been used as an experimental system to study the control of cell fate and pattern formation. The control of trichome initiation is complex: both the potential of a cell to adopt the trichome cell fate and an intricate signaling pathway determine the pattern of trichome initiation events. Several important new results suggest that trichome initiation and morphogenesis are redundantly regulated by both positive and negative factors. A testable model for the control of trichome initiation is presented.     

Genetic control of trichome branch number in Arabidopsis: the roles of the FURCA loci

We are using trichome (hair) morphogenesis as a model to study how plant cell shape is controlled. During a screen for new mutations that affect trichome branch initiation in Arabidopsis, we identified seven new mutants that show a reduction in trichome branch number from three branches to two. These mutations were named furca, after the Latin word for two-pronged fork. These seven recessive mutations were placed into four complementation groups that define four new genes: FURCA1, FURCA2, FURCA3 and FURCA4. The trichome branch number phenotype indicates that the FURCA genes encode positive regulators of trichome branch initiation. Analysis of double mutants suggests that primary and secondary branch initiation events are not genetically distinct, but rely on the levels of partially redundant groups of regulators of trichome branch initiation. Based on the analysis of both epistatic and additive genetic interactions between the FURCA genes and other genes that control trichome branch number, we propose a model that explains how these genes interact to control trichome branch initiation. This model successfully predicts the phenotypes of all the single and double mutants examined and suggests points of control of the trichome branch pathway.     

Differential regulation of a MYB transcription factor is correlated with transgenerational epigenetic inheritance of trichome density in Mimulus guttatus

? Epigenetic inheritance, transgenerational transmission of traits not proximally determined by DNA sequence, has been linked to transmission of chromatin modifications and gene regulation, which are known to be sensitive to environmental factors. Mimulus guttatus increases trichome (plant hair) density in response to simulated herbivore damage. Increased density is expressed in progeny even if progeny do not experience damage. To better understand epigenetic inheritance of trichome production, we tested the hypothesis that candidate gene expression states are inherited in response to parental damage. ? Using M. guttatus recombinant inbred lines, offspring of leaf-damaged and control plants were raised without damage. Relative expression of candidate trichome development genes was measured in offspring. Line and parental damage effects on trichome density were measured. Associations between gene expression, trichome density, and response to parental damage were determined. ? We identified M. guttatus MYB MIXTA-like 8 as a possible negative regulator of trichome development. We found that parental leaf damage induces down-regulation of MYB MIXTA-like 8 in progeny, which is associated with epigenetically inherited increased trichome density. ? Our results link epigenetic transmission of an ecologically important trait with differential gene expression states - providing insight into a mechanism underlying environmentally induced 'soft inheritance'.     

γ-Radiation Induces Leaf Trichome Formation in Arabidopsis

We observed induction of additional trichome formation on the adaxial surface of mature leaves of Arabidopsis after massive doses (1-3 kilograys) of gamma-radiation from cobalt-60. A typical increase in trichome number was observed in the seventh leaf when the full expansion of the fifth leaf was irradiated. Under normal growth conditions, trichome numbers on the adaxial surface of seventh leaf of the Arabidopsis ecotypes Columbia (Col) and Landsberg erecta (Ler) were 122.5 +/- 22.7 and 57.5 +/- 14.5, respectively. However, gamma-radiation induced additional trichome formation and the numbers rose to 207.9 +/- 43.7 and 95.0 +/- 27.1 in Col and Ler, respectively. In Col the shape of new trichomes was intact and their formation was spatially maintained at equal distances from other trichomes. In Ler trichome morphology was aberrant and the formation was relatively random. Treatment with antioxidants before gamma-irradiation suppressed the increase in trichome number, and treatment with methyl viologen and light induced small trichomes. These results suggest that gamma-radiation-induced trichome formation is mediated by active oxygen species generated by water radiolysis. gamma-Radiation-induced trichome formation was blocked in the trichome mutants ttg-1, gl1-1, and gl2-1. These results suggest that gamma-radiation-induced trichome formation is mediated by the normal trichome developmental pathway.     

Analysis of the cable structure of blue-green algae

Peculiarities of electrical responses under local illumination of filamentous cyanobacteria (blue-green algae). Phormidium uncinatum were studied by means of extracellular electrodes. Recording of electrical responses at different distances from the exposure place and comparison of these data with the results obtained on physical model of Ph. uncinatum end expected response parameters computed made it possible to estimate the parameters of the cable which can serve as the object model: RC=440 c/cm2 and lambda min greater than or equal to 0.07 cm. According to these values and taking membrane capacity as C=10(-6) phi/cm2, intracellular resistance Rm=10(7) Ohm and conductivity of the surface membrane G less than or equal to 10(-6) I/Ohm cm2 were estimated.     

Propagation of electrical potential changes in filamentous cyanobacteria

Possible energy transmission along conjugating membranes was investigated. It was found by extracellular electrodes that under local illumination of blue-green algae Phormidium uncinatum the electrical current propagated along trichomes. The form and sign of the responses show that e. m. f. appears in the illumination region, which generates on the cellular membrane the potential difference with a negative charge inside the cell. The initiated transmembrane potential difference propagates along the filament of Ph, uncinatum like along a cable. The hypothesis concerning a cable structure of Ph, uncinatum was supported in the experiments with intersection of algae, and with intracellular injection of fluorescein showing the existence of direct diffusion exchange through cellular interfaces.     

ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.     

Defensive role of leaf trichomes in resistance to herbivorous insects in Datura stramonium

This study assessed the role of leaf trichome density as a component of resistance to herbivores, in six populations of Datura stramonium. Phenotypic selection on plant resistance was estimated for each population. A common garden experiment was carried out to determine if population differences in leaf trichome density are genetically based. Among population differences in leaf trichome density, relative resistance and fitness were found. Leaf trichome density was strongly positively correlated to resistance across populations. In 5 out of 6 populations, trichome density was related to resistance, and positive directional selection on resistance to herbivores was detected in three populations. Differences among populations in mean leaf trichome density in the common garden suggest genetic differentiation for this character in Datura stramonium. The results are considered in the light of the adaptive role of leaf trichomes as a component of defence to herbivores, and variable selection among populations.     

Atlas of foliar surface features in woody plants,VI. Carya (Juglandaceae) of north America

Scanning electron microscopy was used to examine foliar surface features such as trichome types and the micro-relief formed by cell contours, cuticular patterns, and epicuticular wax in the genusCarya. The fourteen taxa native to Mexico and eastern United States were sampled throughout their geographical ranges, and are represented here by specimens that include segregate taxa, interspecific hybrids, and mature and immature leaves of each. Six trichome types are recognized in this survey: acicular, fasciculate, multiradiate, solitary, capitate-glandular, and peltate scale. There are no consistent differences between representatives of either the two Sections of the genus or the two ploidy levels. Although there is significant inter- and intra-specific variation, the use of scanning electron microscopy provides few taxonomically useful characters or character-states beyond those already available through light microscopy. Foliar surfaces of the fourteen taxa and three hybrids are illustrated.     

Cell division and trichome breakage in Beggiatoa

The process ofBeggiatoa trichome division was elucidated through phase-contrast microscopy and transmission and scanning electron microscopy. Trichome breakage and dispersion is accomplished by the formation of sacrificial cells (necridia) at various points within the trichome. Upon dying, the sacrificial cells lyse, dividing the trichome into two daughter trichomes. This process is identical with that found in many oscillatorian blue-green bacteria, but differs from the mechanism of trichome division in most of the other flexuous gliding bacteria. Cellular division within the trichome occurs by septation, involving the cytoplasmic membrane and the electron-dense L2 (peptidoglycan) layer. The outer envelope layers do not take part in division.     

Trichome density of main stem is tightly linked to PepMoV resistance in chili pepper (Capsicum annuum L.)

A relationship between pepper trichome and pepper mottle virus (PepMoV) resistance was examined. In an intraspecific F(2) mapping population from the cross between Capsicum annuum CM334 (trichome-bearing and PepMoV resistant) and Chilsungcho (glabrous and PepMoV susceptible), major QTLs for both traits were identified by composite interval mapping in linkage group (LG) 24 corresponding a telomere region on pepper chromosome 10. Ptel1 of putative trichome enhancing locus was a common major QTL for trichome density on the main stem and calyx. Ptel1 apart from HpmsE031 at a 1.03?cM interval was specifically associated to the trichome density on the main stem, whereas Ptel2 near m104 marker on LG2 was specific for the calyx trichome. Epistatic analysis indicated that Ptel1 engaged in controlling the trichome density by mutual interactions with the organ-specific QTLs. For PepMoV resistance, two QTLs (Pep1 and Pep2) were identified on the LG 24. Pep1 was located with Ptel1 in the R-gene cluster (RGC) for potyvirus resistance including Pvr4 with broad spectrum resistance to potyviruses. Pep1 flanking TG420 marker seemed to be the major factors determining correlation with PepMoV resistance. These results indicate that the level of trichome density on pepper main stem can be used as a morphological marker for Pvr4 in pepper breeding.