Image analysis in the electron microscopy of cellulose protofibrils

Abstract

Electron microscope images of parallel arrays of Ramie cellulose protofibrils, obtained at various levels of defocus, are discussed in terms of phase contrast. The optical diffraction pattern of appropriately &focused images shows discrete maxima in the resolution range of 2-5 nm. The pattern is dominated by strong equatorial reflections arising from the lateral spacing of the protofibrils which is about 5 nm. From the observed reciprocal lattice net, it is concluded that the protofibrils are characterized by some form of axial texture that repeats with a periodicity of about 6 nm. The lattice reflections in the optical diffraction pattern are shown to be essentially invariant over a wide range of defocusing conditions. From this it is inferred that the pattern arises from real object order. It is emphasized that the optical diffraction pattern derives from gross structural features related to the morphology of the protofibrils and not from their internal structure.

Image analysis in the electron microscopy of cellulose protofibrils II. Digital correlation methods

“…From the through focal series, three negatives were selected for digital image analysis: r 1 corresponds to figure l-h, 2 to figure l-e, and ~ 3 to figure 1-a of our previous paper [1]. The amount of defocus (underfocus denoted by positive values) is 1300 nm for r 1; 100 nm for r 2; and -1500 nm for r 3.…”

“…The micrographs were taken using a Philips EM400T with a pointed filament at 100 kV and at a calibrated magnification of 47,700 [1]. From the through focal series, three negatives were selected for digital image analysis: r 1 corresponds to figure l-h, 2 to figure l-e, and ~ 3 to figure 1-a of our previous paper [1].…”

“…Details of the specimen prepara-tion have been described in the previous paper [1]. The sample was dispersed in distilled water by ukrasonification.…”

“…In a recent paper [1], the application of the optical diffraction technique for image analysis of electron micrographs of negatively stained ramie cellulose protofibrils was reported. Electron microscope images of parallel arrays of protofibrils, obtained at various levels of defocus, were explained in terms of phase contrast.…”

“…The optical method, however, has a poorer quantitative performance than the digital method used here [6]. In this paper, the procedure for digital image analysis of cellulose protofibrils will be outlined and some preliminary results using the two-dimensional digital ACF will be discussed in comparison with the results reported previously [1].…”