Ultrastructural observations on foliar glandular trichomes of Stevia rebaudiana

Foliar glandular trichomes of Stevia rebaudiana (Bert.) Bert. were examined by transmission electron microscopy in order to detect changes occurring in their cells in association with the secretory process. In the foliar, 10-celled lipophilic glandular trichome of Stevia rebaudiana (Bert.) Bert., the six secretory cells forming three pairs of head cells are vacuolated, possess large nuclei and are rich in ribosomes, mitochondria, plastids and ER elements. Dictyosomes are relatively frequent in these cells. The plastids, which form starch grains, are leucoplasts in cells of the apical pair and chloroplasts in cells of the two subapical pairs. The basal cells and stalk cells possess some degree of vacuolation and are rich in ribosomes. Also in these cells, the nuclei are relatively large; ER elements, chloroplasts and dictyosomes are present in moderate number, and mitochondria are frequent. Wall ingrowths are found in head cells as well as in the stalk and basal cells. Plasmodesmata, in moderate number, occur more frequently in transverse walls of head cells, as well as in those between cells of the second subapical pair and stalk cells and between the latter and basal cells. Plasmodesmata connect mesophyll cells and basal cells. To form the secretory sheath, the cuticular membrane detaches from the outer walls of the apical secretory cells, along a line that appears to be the pectin layer

Infrared spectra of complex organic molecules in astronomically relevant ice mixtures. V.: Methyl cyanide (acetonitrile)

Laboratory astrophysics and astrochemistr

Mapping the evolution of pure CO2 ices irradiated by ions, UV, and electrons using the upgraded PROCODA code (employing an effective rate constant ordering by thermochemistry data)

Laboratory astrophysics and astrochemistr

D* Production in Deep Inelastic Scattering at HERA

This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+$ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.Comment: 17 pages including 4 figure

Observation of Scaling Violations in Scaled Momentum Distributions at HERA

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of $x$ and $Q^2$ using the ZEUS detector. The evolution of the scaled momentum, $x_p$, with $Q^2,$ in the range 10 to 1280 $GeV^2$, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of $Q^2$.Comment: 21 pages including 4 figures, to be published in Physics Letters B. Two references adde