Electron microscopy as a powerful tool for detection and identification of plant viruses.

摘要

Electron microscopy (EM) has advantages in the initial stages of detection or identification of a plant viruses because of 4 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 prior information (such as a sequence) is not needed in order to detect them. It also means, quite often, that these viruses can be overlooked when checking on something else, i.e. the discoveries of cryptoviruses and ophioviruses. This is something that can never occur as the result of an ELISA or PCR test, which tells 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, 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, well-known viruses can be picked up by serological or molecular methods, and no-one will fund researchers to look for new pathogens or to pursue the unexpected; and (3) although the EM can image biological structures and resolve them with separations of one or 2 nanometres, the application of specific probes (serological and 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, but it is so much more versatile in probing the cell biologically (and in colour). 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 micro m..