Elemental Analysis of Silicon in Plant Material with Variable-Pressure SEM

Abstract

Introduction The cellular structure of biological plant material has been well characterized by light and electron microscopy [1]. Scanning electron microscopy (SEM) uses an electron beam to scan the surface of a sample to study the external morphology of plant cells, tissues, and organs [2]. Analytical SEM beam conditions are typically tailored to the requirements of the sample being investigated, and in the case of biological plant specimens, a low-kV electron beam (1 to 5 kV) is routinely employed for sample surface imaging to reduce beam damage to the tissue. For certain analyses, as in this work, it is necessary to work at non-conventional operating conditions in order to fully characterize the materials being studied by energy dispersive X-ray spectrometry (EDS). By varying the SEM beam conditions, inorganic phases can be located either at the top surface or in the sub-surface regions of plant tissue. Microscopic investigations of primary plant structures reveal details about plant structural morphology that helps the analyst better understand the functionality of each of the organelles. For example, SEM studies of onion root tips with freeze etching preparation show the location and morphology of the cell wall, nucleus, and nuclear pores [3]. More detailed studies of the double membrane, inner membrane space, and other metabolic compartments are used to understand the processes of photorespiration and amino acid synthesis [4]. Chloroplasts play a very important role in plant tissues for primary life-sustaining functions such as photosynthesis. Studies with SEM and transmission electron microscopy (TEM) show the morphology of chloroplasts and other sub-micron components, such as the inner and outer membranes and the individual thylakoids [4]. The cytoskeleton of the plant cell consists of a network of fibrous actin filaments and microtubules that provide important functions such as cytoplasmic organization, cell division, cell growth, and cell differentiation.