Changes Induced by Magnesium Ions in the Morphology of Some Plant Viruses with Filamentous Particles

Abstract

SUMMARYParticles of henbane mosaic virus in extracted plant sap were usually straight and 9oo nm. long but occasionally flexuous and 8oo rim. long. The length and flexuousness of the particles depended on the composition of the extracting medium. When exposed to magnesium ions (o'o5 M), the particles were long and straight but when exposed to o'o5 M-EDTA they were shorter and flexuous. Similar morphological differences were found when pepper veinal mottle virus or bean yellow mosaic virus was extracted in the two solutions. With pepper veinal mottle virus, each form of particle could be converted to the other by changing the medium.

The general properties of potyviruses

“…The particle lengths of some viruses, as noted previously, are markedly affected by divalent metallic ions [26], The particles of most fungal-transmitted potyviruses are of two predominant lengths of c. 275 and 550nm [49].…”

“…Filamentous viruses transmitted by mites, whiteflies (Bemisia tabaci) or the fungus Polymyxa graminis (Plasmodiophoromycetes) also were shown to induce pinwheel formation, and thus to be possible members of the group [43]. The qualifying range of particle lengths for group membership was extended (680-900nm) to permit the inclusion of aphid-borne viruses which, in the presence of divalent metallic ions such as Mg++ [11,26], or the sap of some plant species [13], are mostly straight and c. 850nm long [22]. Reduction of the qualifying length to 680 nm also permitted the inclusion of mite-transmitted viruses (particles mostly c. 700 nm) and its increase to 900 nm the inclusion of the whitefly-transmitted sweet potato mild mottle virus (particles mostly 850-900 nm long); the viruses transmitted by non-aphid vectors were thereafter included in the potyvirus group, but placed in subgroups as possible members [45].…”

“…have provided accessory and supportive criteria [26,44,45]. More recently, however, modem analytical procedures have permitted the molecular properties of the component proteins and nucleic acids to be determined and used taxonomically [14,37,38,53,75].…”

Taxonomy of Potyviruses: Current Problems and Some Solutions

“…Most potyviruses have slightly flexuous, filamentous particles, 720-770 nm long [75], and 11-12 nm wide, made up of approximately 2,000 copies of a single CP subunit arranged in a helical man ner around a single copy of the viral RNA [2,3,9], The basic pitch of the potyvirus nucleocapsid helix is 3.3-3.5 nm, with 7-8 CP subunits per ring [76] and no obvious central cavity visible except on rare occasions [3]. While most potyviruses have filamentous particles that fall within these size limits, some, for example those infecting flower bulbs [77], have straighter filamentous parti cles of 850-950 nm in lengh, and others are known to become straighter and longer if exposed to magnesium ions [78,79], Most potyviruses are more flexuous than potex and carlavirus particles, but less flexuous than closteroviruses, and generally ap pear narrower in diameter than members of the other filamentous plant virus groups. However, considerable care is required when making size estimations [3], and variations in stain distribution and penetration may ex plain some of the reported variations in di ameter measurements [5].…”

Three strains of bean yellow mosaic virus: symptoms and accumulation in eight pea cultivars (Pisum sativum L.)

“…The symptoms in pea plants and the slightly longer particles of the BYMV-Ps isolate were similar to those of the pea mosaic strains of BYMV previously described, and the symptoms caused by BYMV-Vf in the test plants resembled those described for the bean strain ofBYMV (BOS 1970a,b, Tapio 1970. As with other potyviruses, the length of BYMV particles in plant extracts is affected by the concentration of magnesium ions in the extraction buffer (Govier and Woods 1971). On the other hand, BYMV-G differed from the other two BYMV isolates by its milder symptoms in most of the test plant species, and also serologically, as has been reported previously for other BYMV isolates (JONES and Diachun 1977).…”