The influence of meristematic tissue and injuries on the transport of tobacco mosaic virus in Nicotiana tabacum L. cultivar Samsun

Brants, D.H.

Acta Bot Neerlandica 10(2): 113-163


DOI: 10.1111/j.1438-8677.1961.tb00044.x
Accession: 014253837

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The rate of transport of the virus in the plant was estimated by determining the rapidity with which it appeared in uninoculated leaves. For this purpose the leaves of a plant were cut at different times after inoculation and placed in water. Under this condition, virus-material present in the leaves at the moment of cutting was allowed to multiply for 3 days. After this period each leaf was pressed out and tested for the presence of virus by means of the local lesion test on leaves of Nicotiana glutinosa. From experiments in which either the lowest, the middle or the topmost leaf was inoculated, it became evident that inoculation of the middle leaf caused the most rapid virus-transportation. The influence of meristematic tissue on virus-transportation was studied in different ways. One of the most obvious methods was to eliminate the meristematic tissue by removing it. Removal of the stem tip did not influence either the direction or the rate of virus-transportation out of the inoculated leaf. Removal of the axillary buds or both axillary buds and stem tip caused an increased rate of spreading of the virus. When the stem was slightly wounded without removal of plant-parts the same result was obtained and apparently it was the injury that influenced virus-transportation. Microscopical examination of the wound-reactions in N. tabacum revealed a suberin-coating of cells during the 1st 48 hours after wounding. It became evident that wounding of the stem of a plant exercised an influence on the rate of virus-transport only when the wound was inflicted 24 hours before, simultaneously with or up to 48 hours after inoculation of a middle leaf. When the injury was made more than 24 hours before or more than 48 hours after inoculation, no influence was perceptible. Probably in the former case wound-reactions had already stopped and, in the latter, the virus-material had already extended too far. The influence of wounding was also studied in leaves. One part of a leaf was inoculated, another part was wounded slightly at different times in relation to the moment of inoculation. The leaves were cut into sections 20, 22 or 24 hours after inoculation and these strips were kept on a fluid medium for 4 days in order to allow the virus-material present at the moment of cutting to multiply. Virus-material was transported quickly to the wounded region only when the injuries were made during a period from 48 hours before to simultaneously with the moment of inoculation. Within 18 hours after inoculation, virus-material began to move from the inoculated region of the leaf. All effects of wounding of leaves seemed to support the conclusion drawn from the results of experiments with wounded stems. Another method of investigating the influence of meristems on the rate of virus-transport was elimination of meristem-activity without inflicting a wound. The stem tips and the axillary buds of a tobacco plant were dusted with fusarex (2, 3, 5, 6-tetra-chloro-nitrobenzene), whereupon the plants remained in the original stage of development until 10 days after treatment. The action of the meristems was inhibited. When the middle leaf of such a plant was inoculated with TMV a very limited virus-multiplication took place but no virus-transport from that leaf occurred. Inhibition of meristem-activity and cell-growth greatly diminished virus-multiplication and the spread of virus through the plant. After 10 days the inhibiting action of fusarex ceased and the plants resumed growth. After 5 weeks, treated plants showed virus-symptoms; many leaves were somewhat deformed or discolored. A 3rd series of experiments was performed with tobacco callus-tissue into which a prepared meristem or a stem tip was introduced without provoking injuries. The advantages of this method were: a) virus-transport could be studied in homogenous callus-tissue after lateral inoculation with TMV; b) only 1 meristem could influence the rate of virus-transport in the callus, which is impossible in a plant in possession of many axillary buds; c) no injuries were inflicted upon the callus-tissue by introduction of a meristem or a stem tip. Though the meristems and stem tips developed into small stems with leaves, no histological connection was found between the callus-tissue and the "grafts". Thirty days after "grafting" the callus-tissue had formed rootlets and the rate of virus-transport was suddenly increased in comparison with the controls without meristem or stem tip. Anatomical observations demonstrated that the stem tip had induced a differentiation in the callus-tissue, consisting of formation of vascular elements. The callus-tissue was no longer homogeneous. Microscopical observations of homogeneous tissue without stem tip revealed thin places in the cell-walls. Probably these places are responsible for the virus-transport from cell to cell in homogeneous tissue in which virus spreads slowly, about 1 mm a week. Apparently an introduced meriste m did not influence the rate of transport in callus-tissue directly, but indirectly by inducing a differentiation of the tissue. The homogeneous callus-mass was changed into a potential plant with a stemtip, vascular tissue and roots allowing transport of material, including virus, in a way, comparable with that of a normal plant. It could not be demonstrated by the experiments that primary meristematic tissue itself attracts virus-material. The directing action mentioned in the literature that has been attributed to top meristems apparently does not derive from the meristems themselves but from the active young tissues formed by the primary meristematic tissues, such as leaf-primordia, which attract virus. Also mature cells reversed into a juvenile state by wounding exercise an attractive action on virus material reaching the attraction-sphere of the wound during the "conditioning phase," i.e. during the 1st 72 hours after injuring.