Variation in stomatal aperture in leaves of Avena fatua L. observed by low-temperature scanning electron microscopy

Abstract. A novel technique to record the variability of stomatal aperture over the leaf surface is described. This combines observations of leaf surfaces using low-temperature scanning electron microscopy (LTSEM), with digital image analysis to produce the most accurate aperture measurements obtained to date. Leaf samples are rapidly immobilized by cryo-fixation in liquid nitrogen and stored in a purpose-built cryo-storage system. Specimens can be collected in the field, remote from the cryopreparation system, and stored for up to several weeks before being examined on the LTSEM. The advantages of this method are that the time frame of the measurements is accurately known, and is identical for all stomatal apertures in a sample, and the precision of the measurements is not limited by the resolving power of the microscope. Measurements of stomatal aperture were obtained from leaves of field grown Avena fatua using the above procedure. Leaf surface conductance (g_sur) was determined by porometry immediately before cryo-fixation of the same region of the leaf. Measurements of aperture size showed a high degree of variability within each specimen, with coefficients of variation similar to those found in previous studies. Stomatal conductance (g_s) was calculated from stomatal dimensions using formulae derived elsewhere. A linear regression between the computed values of g_s and porometric estimates of g_sur showed good agreement with the regression line passing through the origin with a slope of 1.0 (R²=0.96). Applications of the experimental system are discussed.     

Recent developments in electron microscopical techniques for studying ion localization in plant cells

This paper reviews recent technical approaches to the study of element localization in plant cells. It is concerned with sample preparation; with the use of electron probe microanalysis in the low temperature scanning electron microscope; with the use of electron energy loss spectrocopy and electron spectroscopic imaging in the transmission electron microscope. Basic principles of instrumentation, special problems during cryopreparation of plant tissues, and the application of these techniques within selected fields of botanical interests are briefly discussed.Abbreviations EDXA Energy Dispersive X-Ray Analysis - EELS Electron Energy Loss Spectrometry - EPMA Electron Probe Microanalysis - ESEM Environmental Scanning Electron Microscope - ESI Electron Spectroscopic Imaging - HPF High Pressure Freezing - LTSEM Low Temperature Scanning Electron Microscope - SEM Scanning Electron Micrsocope - TEM Transmission Electron Microscope Botanisches Institut der Tierärztlichen Hochschule HannoverDedicated to Professor André Läuchli on the occasion of his 60th birthday     

Water Storage in the Lichen Family Umbilicariaceae

Quantitative relationships between thallus structure and water storage and retention capacities In 12 species of the lichen family Umbilicariaceae were explored using three recent techniques for plant structure analysis: stereology (3D quantification of microscopic Images), mercury Intrusion porosimetry (determination of pore size distribution of tissues) and low-temperature scanning electron microscopy (LTSEM). Water storage capacity of the thallus was related neither to thallus density nor surface area of the thallus; It was directly related to the total porosity of the thallus and inversely related to the proportion of thallus volume occupied by cell walls and gelatinous substances. Water retention capacity increased with increasing thallus density and was decreased by slight increases in the surface area of the upper side of the thallus. Water storage and retention capacities exhibited a positive correlation only when the storage capacity was expressed on a surface area basis. LTSEM study of fully hydrated specimens revealed that many intercellular spaces of the upper cortex and upper parts of the algal layer contained liquid water. Intercellular spaces of the lower part of the algal layer and medulla were in general either airfilled or partially occupied by gelatinous substances. Species with rhizinomorphs and substrate-hygrophytic (water uptake from surface run-offs) stored more water and retained it longer than aerohygrophytic species (water uptake from the atmosphere) lacking rhizinomorphs. Thallus structure of aerohygrophytic species seems to facilitate rapid gas exchange with the environment, improving water uptake and carbon gain when atmospheric moisture is available but accelerating dehydration when the atmosphere becomes dry.     

Abrasive damage by wind to the needle surfaces of Picea sitchensis (Bong.) Carr. and Pinus sylvestris L.

Abstract. After a period of one week at 11m s⁻¹ in a wind tunnel, the leaf surface of Picea sitchensis and Pinus sylvestris had undergone structural modification. Low-temperature scanning electron microscopy was used to examine these changes. Picea showed flattening and smearing of wax crystals, as well as cracks in some of the wax structures filling the stomatal antechambers. In Pinus , most damage was on the cells surrounding the stomatal antechamber or on needle ridges. Artificially abraded surfaces were of similar appearance. Minimum epidermal conductance to water vapour ( g _e^MIN) was determined gravimetrically. In Picea g _c^MIN was more than doubled by wind treatment and increased eightfold by rubbing. Similar but less extreme increases occurred in Pinus. Neither species showed recovery of g _e^MIN after 1 week at low windspeed.