Phytopath. Z., 90, 27—30 (1977)© 1977 Verlag Paul Parey, Berlin und HamburgISSN 0031-9481 / ASTM-Coden: PHYZA3

Faculty of AgricultHral Sciences of the University of Zagreband Riidjer Boskovic Institute, 2agreh, Yugoslavia

The Effect of Lettuce Mosaic Virus on Plant Cells

j By

ANA SARIC and MERCEDES WRISCHER

With 3 figures

Received December 13, 1976

Lettuce mosaic virus like all members of Poty virus group induces cyto-plasmic inclusions of distinctive configuration known as pinwheels in the leafcells of its host plants. The presence of laminated aggregates in the cytoplasmof mfected plants is considered as an additional feature in the subdivision IIof Poty virus group (EDWARDSON 1971), to which subdivision Lettuce mosaicvirus (LMV) belongs. However, besides these inclusion bodies we have alsonoticed an abnormality in mitochondria which is the subject of the presentpaper.

Material and Methods

LMV was isolated from crisphead lettuce {Lactuca sativa) showing obvious mosaicsymptoms early in the season. Using phosphate buffer containing 1 '%: thioglycolic acid thevirus was easily transmitted from lettuce to Chenopodium amaranticolor and C. quinoa inwhich local symptoms appeared 10—14 days after inoculation followed soon by systemicsymptoms. On the other hand, the infection in C. amaranticolor always remained local.Faint symptoms appeared in inoculated Pisum sativum. The identity of virus was confirmedby serologica!') tests, microprecipitin and immunodiffusion in gel containing SDS (GOODINGand BiNG 1970) as well as by reactions in indicator plants (TOMLISON 1970, PURCIFULL,CHRISTIE and ZITTER 1976). Samples were collected trom Chertopodium quinoa immediately.ifter the appearance of systemic symptoms, from locally infected C. amaranticolor, fromnaturally and from manually infected lettuce with systemic symptoms.

') We are indebted to Dr. D. Z. MAAT, Institute for Phytopathological R.eseardi,Wagcningen, for the antiserum to LMV.

28 SARIC and WRISCHER

Small pieces of leaves of infected and healthy plants {Chenopodium quinoa, C.ama-runtkolor and Lactuca sativa) were fixed for 1 hour in 1 Vf glutaraldchyde (in cacodylatcbuffer, pH 7.2 at 2 ^C). After washing in buffer they were postfixed in 1 '/,• OsO_, (in caco-dylate buffer) for 2 hours, and after dehydration, they were embedded in Araldite. Ultra-thin sections were stained with uranyl acetate and lead citrate, and examined in a SiemensElmiskop I.

Results

The most striking structures in mesophyll cells of the chlorotic leaf partsof infected C. quinoa are single, considerably enlarged mitochondria, oftenseveral fim in diameter (up to 5/mi). In sections they usually appear oval orroundish, although they sometimes have small amoeboid extensions. Many in-vaginations of the inner membrane protrude in the form of long tubules intothe very dense matrix. Some of these tubules are sometimes dilated, thus form-ing vacuoles inside the mitochondrion {Fig. 1). There are also mitodiondria ofnormal size and ultrastructure, which sometimes tightly aggregate into largeclusters. In C. amaranticolor mitochondria are mostly normal, but frequentlyform clusters (of 10—20 mitochondria in the section).

In the cytoplasm of all examined Chenopodium leaves pinwheel structuresand laminated aggregates are very frequent (Figs. 1 and 2). Among these in-clusions small aggregates of thin tlexuous filaments of undetermined lengthsometimes appear (Fig. 2). They may be taken to represent virus particles. Inaddition to those, there are also some large lipid globules in these cytoplasmicregions.

In the cytoplasm of naturally infected lettuce leaves only pinwheels andlaminated inclusions were found, but never enlarged mitochondria. In lettuce,which was experimentally infected with LMV from C. quinoa, however,enlarged mitochondria also appeared. These were mostly elongated, reachinga length of 5—6/fm (Fig. 3).

In infected leaves of all investigated plants the chloroplasts are usuallysmaller than in the control. They contain some large plastoglobules, althoughtheir thylakold system is still normal. All other cell structures appearedunchanged.

I

Discussion

Giant mitochondria have already been found in plants infected with somefilamentous viruses. KITAJIMA and LOVISOLO (1972) observed large mito-chondria In Datura stramonium infected with Poty virus Henbane mosaicvirus. They suggested that this phenomenon might be connected with a certainhost/virus combination. WEINTRAUB and RAGETLI (1971 a and b) noticedhypertrophied mitochondria as well as pinwheels in Chenopodium quinoainfected with a virus isolated from Virginia crab apple showing stem groovingsymptoms. According to WEINTRAUB and RAGETLI (1971 b) the hypertrophiedmitochondria are the results of proliferation of single mitochondria, whichopinion is well in accordance with our results. More recently TANNE (1976)

The Effect of Lettuce Mosaic Virus on Plant Cells 29

3Fig. 1. C.quinou systemically infected with LMV. Portion of a chloronc leaf cell. Anenlarged mitodiondrion and laminated aggregates arc present in the cytoplasm. X 30,000

Fig. 2. Tbe same material as in Figure I.Cytoplasm with laminated aggregates and filamentous inclusions (arrows). X 48,000

Fig. 3. Lettuce systemically infected with LMV from C. qmnoa.An elongated mitochondrion in a leaf cell, X 25,000

30 SARIC and WRISCHER, The Effect of Lettuce Mosaic Virus on Plant Cells

has reported that a filamentous virus associated with leaf roil of grapevinealso induced giant mitodiondria in Nicotiana glntinosa in addition to pin-wheels.

It seems that the ability to induce hypertrophy of mitochondria isdiaracteristic of some Poty viruses and this property may also be of somevalue in the classification of viruses within the Poty virus group.

Summary

The electron microscopy of plants infected with Lettuce mosaic virus(LMV) showed that apart from the already reported inclusion bodies — pin-wheels and laminated aggregates — this virus also induced a hypertrophy otmitodiondria reaching several /(m in diameter.

Zusammenfassung

Der Einflufi des Salatmosaik-Virus auf pflanzHche Zellen

Bei einer elektronenmikroskopisdien Untersudiung von Pflanzen die mitSalatmosaik-Virus infiziert waren, wurde festgestellt, dafi neben den sdionbekannten EinschlufSkorpern in Form von ,,pinwheels" und lamellenartigenAggregaten, auch eine Hypertrophie von Mitochondrien auftrat. Diese ver-grof^erten Mitodiondrien konnen mehrere /mi im Durdimesser erreidien.

Literature

EDWARDSON, J. R., 1971: Some properties of the potato Y group. Florida Monograph. Ser.Fla. agric. Exp. Sta. No. 4.

GOODING, G. V., Jr., and N. W. BING, 1970: Serological identification of potato virus Yand tobacco etch virus using itiimunodiffusion plates containing sodium dodecyl sul-fate. Phytopathology 60, 1293.

KITAJIMA, E. W., and O. LOVISOLO, 1972: Mitodiondriat aggregates in Datura leaf cellsinfected with henbane mosaic virus. J. Gen. Virol. 16, 265—271.

PURCIFULL, D . E., S. R. CRISTIE, and T. A. ZITTER, 1976; Bidens mottle virus, C.M.I./A.A.B.Description of plant viruses. No. 161

TANNE, E., 1976: 6tb intern, conf. virus and viruslike diseases of the grapevine, Cordoba—Madrid.

TOMLISON. |. A., 1970: Lettuce mosaic virus. C.MJ./A.A.B. Description of plant viruses.No. 9.

WECNBRAUB, M., and H. W. J. RAGETLI, 1971a: Some characteristics of a virus from Vir-ginia crab apple. Phytopathology 61, 431—432.

T and , !971b: A mitodiondria! disease of leaf cells infected with an apple virus.J. Ulcrastruct. Res. 36, 669—693.

Authors' addresses: Prof. Dr. ANA SARIC, Faculty of Agricultural Sciences of theUniversity, Simunska 25, Yu-4I000 Zagreb (Yugoslavia). Dr. MERCEDES WRISCHER, RudjerBoikovic Institute, Bijcnicka 54, Yu-41000 Zagreb (Yugoslavia).