ELECTRON MICROSCOPY AS A POWERFUL TOOL FOR DETECTION AND IDENTIFICATION OF PLANT VIRUSES
Electron microscopy (EM) has advantages in the initial stages of detection or identification of a plant virus because of four factors: (1) procedures are simple, rapid and inexpensive, (2) virus particles do not resemble anything occurring in a crude extract of a healthy plant, (3) their shapes and sizes are highly diagnostic, and (4) their presence is revealed without preconception-this means that you do not need to have prior information (such as a sequence) in order to detect them; it also means, quite often, that you trip over them when you were really checking on something else-the discoveries of cryptoviruses and ophioviruses are examples within my experience. This is something that can never occur as the result of an ELISA or PCR test, which can tell you nothing about the possible presence of other unrelated antigens or sequences that may be in the sample. Next to the use of test-plants and EM, serology can be the most accessible tool to apply in a new situation, and immuno-EM techniques can be powerful and quantitative, and more rapid than other methods if the number of samples is limited. However, the routine use of EM is in decline, for several reasons: (1) it is out of fashion, and lacks the stimulus of novel killer applications; (2) in an era of pre-programmed contracts and failing political interest in plant virology, the well-known viruses can be picked up by serological or molecular methods, and no-one will fund you to look for new pathogens or to pursue the unexpected; (3) Although the EM can image biological structures and resolve them with separations of one or two nanometres, the application of specific probes (serological, molecular) at this level on thin sections has been difficult and has made little progress in the last 20 years. Confocal laser microscopy has a quite poor resolution limit of around one micrometre (you can just make out a mitochondrion as a fuzzy blob) but it is so much more versatile in probing the cell biologically (and in color!). To revitalize EM studies, easier ways must be found to put biological and molecular meaning into electron images, bridging the thousand-fold gap from nm to m.
Milne, R.G. (2006). ELECTRON MICROSCOPY AS A POWERFUL TOOL FOR DETECTION AND IDENTIFICATION OF PLANT VIRUSES. Acta Hortic. 722, 37-40
diagnostics, serology, negative staining, immunogold labeling