The ultrastructure of dwarf mistletoe (Arceuthobium spp.) sinker cells in the region of the host secondary vasculature

Abstract

ALOSI, M. C., and C. L. CALVIN. 1985. The ultrastructure of dwarf mistletoe (Arceuthobium spp.) sinker cells in the region of the host secondary vasculature. Can. J. Bot. 63: 889-898. Sinker cells showed ultrastructural similarities in three species of Arceuthobium on three different hosts despite differences in season of collection and fixation. All species had abundant osmiophilic lipid bodies, plastids with prolamellarlike bodies, mitochondria with large nucleoids, chromocentric nuclei, and peculiar saccules associated with plasmodesmatal fields. Xylem may not be continuous through sinkers. Apoplastic continuity between host and parasite is afforded by fused cellulosic cell walls. Pitlike wall thinnings and "half-plasmodesmata" are found between juxtaposed host and parasite cells. One-sided, imperforate sieve pores were noted between a sieve cell and a contiguous sinker cell. However, symplastic isolation of the host and parasite seems likely. Therefore, nutrients may be absorbed from the common host-parasite apoplast. Mobilization of nutrients out of the endophytic system to the aerial shoots is thought to be facilitated by differential starch storage in the parasite body. ALOSI, M. C., et C. L. CALVIN. 1985. The ultrastructure of dwarf mistletoe (Arceuthobium spp.) sinker cells in the region of the host secondary vasculature. Can. J. Bot. 63: 889-898.Les cellules de su~oirs de trois espkces du Arceuthobium sur trois h6tes diffkrents montrent des similaritks d'ultrastructure mCme si la saison d'kchantillonnage et la fixation sont diffkrentes. Chez toutes les espkces des corps lipidiques osmiophiles abondent, de mCme que des plastides avec des corps ressemblant a des prolamelles, des mitochondries avec de gros nuclko'ides, des noyaux chromocentriques et des saccules particuliers associks a des champs plasmodesmiques. Le xylkme peut ne pas Ctre continu a travers les su~oirs. La continuitk apoplastique entre I'h6te et le parasite est assurke par la fusion des parois cellulaires cellulosiques. Des amincissements pariktaux ressemblant a des ponctuations et des demi-plasmodesmes sont presents entre les cellules juxtaposees de I'h6te et du parasite. Des cribles unifaciaux imperforks ont ktk obsewks entre une cellule criblke et une cellule de su~oir contigue. Cependant, il semble probable qu'il y ait isolement symplastique de I'h6te et du parasite. Donc, les nutriments peuvent Ctre absorbks de I'apoplaste commun h6te-parasite. Nous croyons que la mobilisation de nutriments B l'extkrieur du systkme endophytique vers les pousses aCriennes est facilitke par le stockage differentiel d'amidon dans le corps du parasite.[Traduit par le journal]

Thinning and prescribed fire effects on dwarf mistletoe severity in an eastern Cascade Range dry forest, Washington

“…Due to their wide distribution in the West (Bolsinger, 1978), dwarf mistletoes are probably responsible for more tree growth and mortality losses each year than all other forest pathogens combined. These long-lived pathogens infect host trees by ballistically discharged seeds (Strand and Roth, 1976), and feed directly from the water and mineral supply of a host tree via an endophytic root system (Alosi and Calvin, 1985;Calvin and Wilson, 1996;Scharpf and Parameter, 1967). Long-standing infections result in growth reductions (Baranyay and Safranyik, 1970;Geils et al, 2002;Hawksworth and Wiens, 1996), depressed tree vigor, and tree mortality (Hadfield and Russell, 1978), either directly caused, or in concert with other pathogens (Filip, 1984;Filip et al, 1993).…”

On the macro-micro-morphology of organs of host invasion in hemiparasite Helicanthes elasticus (Desv.) Danser

“…On reaching the host the mistletoe seeds germinate to produce small radicle followed by a hold fast and an ultimate penetration plug ( Hunt et al, 1996 , Knutson, 1984 ). The radical slowly grows and penetrates into cortex of host tissue followed by the development of root-like endophytic absorptive system ( Alosi and Calvin 1985 ). Many lateral strands grow deep into the cortical region and sinkers are developed in the sapwood region.…”

An in vitro method for screening Colletotrichum gloeosporioides as a biological control agent for western hemlock dwarf mistletoe

“…However, in the case of the dwarf mistletoe, the rapid wilting and/or fragmentation of detached shoots (K uijt 1960; A losi and C alvin 1985) presents a major obstacle. Inoculation of mistletoe shoots detached from hemlock branches on moist filter paper and in rock‐wool blocks failed because these shoots deteriorated rapidly, fragmenting into segments within a week.…”