Taxonomic significance of macro and micro-morphology of Geranium L. species Using Scanning Electron Microscopy.

Macro and micromorphology of different parts that is, sepals, petals, flowers, indumentum, and leaf shape of 22 Geranium L. taxa from Iran were studied. These taxa representing the eight sections of the genus as sect. Dissecta, sect. Geranium, and sect. Tuberosa (of subgen. Geranium); sect. Batrachioidea, sect. Divaricata, sect. Lucida, sect. Ruberta and sect. Trilopha (of subgen. Robertium), that were collected from different geographical habitats of Iran. The biometric study involved 27 quantitative and 33 qualitative characters which were studied by use of stereomicroscopy and scanning electron microscopy (SEM). Statistical analyses were done by use of PAST software. Principal Component Analysis defined the most variable characters. Results showed that the diagnostic features were; length, width, apex of sepals, petals, trichomes type in pedicles and sepals along with their density, the shape length and width of leaves. In general, the present study revealed that the species could be differentiated by macro and micro-morphological characters. Taxa of two subgenera were clearly separated based on selected characters. These characters were found useful for the taxonomic identification and species delimitation in almost all taxa studied at the sub generic level, although some species of section Geranium and section Dissecta are mixed and nested in both subgenea.

Quantitative analysis of the thermal requirements for stepwise physical dormancy-break in seeds of the winter annual Geranium carolinianum (Geraniaceae).

BACKGROUND AND AIMS: Physical dormancy (PY)-break in some annual plant species is a two-step process controlled by two different temperature and/or moisture regimes. The thermal time model has been used to quantify PY-break in several species of Fabaceae, but not to describe stepwise PY-break. The primary aims of this study were to quantify the thermal requirement for sensitivity induction by developing a thermal time model and to propose a mechanism for stepwise PY-breaking in the winter annual Geranium carolinianum. METHODS: Seeds of G. carolinianum were stored under dry conditions at different constant and alternating temperatures to induce sensitivity (step I). Sensitivity induction was analysed based on the thermal time approach using the Gompertz function. The effect of temperature on step II was studied by incubating sensitive seeds at low temperatures. Scanning electron microscopy, penetrometer techniques, and different humidity levels and temperatures were used to explain the mechanism of stepwise PY-break. KEY RESULTS: The base temperature (Tb) for sensitivity induction was 17·2 °C and constant for all seed fractions of the population. Thermal time for sensitivity induction during step I in the PY-breaking process agreed with the three-parameter Gompertz model. Step II (PY-break) did not agree with the thermal time concept. Q10 values for the rate of sensitivity induction and PY-break were between 2·0 and 3·5 and between 0·02 and 0·1, respectively. The force required to separate the water gap palisade layer from the sub-palisade layer was significantly reduced after sensitivity induction. CONCLUSIONS: Step I and step II in PY-breaking of G. carolinianum are controlled by chemical and physical processes, respectively. This study indicates the feasibility of applying the developed thermal time model to predict or manipulate sensitivity induction in seeds with two-step PY-breaking processes. The model is the first and most detailed one yet developed for sensitivity induction in PY-break.

Subsurface examination of a foliar biofilm using scanning electron- and focused-ion-beam microscopy.

The dual beam scanning electron microscope, equipped with both a focused ion- and scanning electron-beam (FIB SEM) is a novel tool for the exploration of the subsurface structure of biological tissues. The FIB can remove a predetermined amount of material from a selected site to allow for subsurface exploration and when coupled with SEM or scanning ion-beam microscopy (SIM) could be suitable to examine the subsurface structure of bacterial biofilms on the leaf surface. The suitability of chemical and cryofixation was examined for use with the FIB SEM to examine bacterial biofilms on leaf surfaces. The biological control agent, Burkholderia pyroccinia FP62, that rapidly colonizes the leaf surface and forms biofilms, was inoculated onto geranium leaves and incubated in a greenhouse for 7 or 14 days. Cryofixation was not suitable for examination of leaf biofilms because it created a frozen layer over the leaf surface that cracked when exposed to the electron beam and the protective cap required for FIB milling could not be accurately deposited. With chemically fixed samples, it was possible to precisely FIB mill a single cross section (5µm) or sequential cross sections from a single site without any damage to the surrounding surface. Biofilms, 7 days post-inoculation (DPI), were composed of 2-5 bacterial cell layers while biofilms 14 DPI ranged from 5 to greater than 30 cell layers. Empty spaces between bacteria cells in the subsurface structure were observed in biofilms 7- and 14-DPI. Sequential cross sections inferred that the empty spaces were often continuous between FP62 cells and could possibly make up a network of channels throughout the biofilm. FIB SEM was a useful tool to observe the subsurface composition of a foliar biofilm.

[Study on morphology of the pollen of 4 species from Geranium in Heilongjiang Province].

Morphology of the pollen of 4 species from Geranium in Heilongjiang province which are G. wilfordii Maxim., G. sibiricum L., G. platyanthum Duthie. and G. dahuricum DC. were observed with optical microscope and scanning electron microscope. The results showed pollen grains of the four species were nearly spherical, with short clavate-shaped, net-shaped and cave-shaped veins on the outer walls and three short-furrow germ pores. Both the clava size and number of clava per unit surface area were different. This paper provided evidences for palynology classification of Geranium.