SOME EFFECTS OF HOST-PLANT NUTRITION ON THE MULTIPLICATION OF VIRUSES

The amounts of tobacco mosaic virus present in systemically infected tobacco plants varied greatly with the mineral nutrition of the plants and were related to the effects on plant growth. With plants in soil, supplements of phosphorus produced the greatest increases in plant size, in virus concentration of expressed sap, and in total virus per plant; nitrogen increased plant size only when phosphorus was also added, and only then increased virus concentration and total virus per plant. Combined supplements of phosphorus and nitrogen doubled the virus concentration of sap and increased the total virus per plant by factors up to forty. Potassium slightly reduced the virus concentration of sap, though it usually increased plant size and total virus per plant. From all plants, only about one-third of the virus contained in leaves was present in sap. Virus production seemed to occur at the expense of normal plant proteins, and the ratio of virus to other nitrogenous materials was highest in plants receiving a supplement of phosphorus but not of nitrogen.
The effects of host nutrition on the production of virus in inoculated leaves resembled those in systemically infected leaves, but were more variable.
No evidence was obtained, with plants grown in soil or sand, that host nutrition had any consistent effect on the intrinsic infectivity of tobacco mosaic virus.
The concentration of virus in sap from potato plants systemically infected with two strains of potato virus X was not consistently affected by fertilizers; the chief effect of host nutrition on virus production was indirect by altering plant size.     

THE INFLUENCE OF LIGHT INTENSITY ON THE SUSCEPTIBILITY OF PLANTS TO CERTAIN VIRUSES

Reducing the light intensity under which plants were grown in summer to one-third increased their susceptibility to infection with tobacco necrosis, tomato bushy stunt, tobacco mosaic and tomato aucuba mosaic viruses. With the first two viruses shading increased the average number of local lesions per leaf by more than ten times and by more than five times with the second two.
Reducing the light intensity increased the virus content of sap from leaves inoculated with Rothamsted tobacco necrosis virus by as much as twenty times. As it also reduced the total solid content of sap by about one-half, purification was greatly facilitated; crystalline preparations of the virus were readily made from shaded plants but not from unshaded controls.
Reducing the light intensity also increased the virus content of systemically infected leaves; the greatest effect was with tomato bushy stunt virus with which increases of up to ten times were obtained, but with tobacco mosaic and aucuba mosaic viruses there were also significant increases.
The importance of controlled illumination in raising plants for virus work and the possible mechanisms responsible for the variations in susceptibility are discussed.     

Photosynthesis and predisposition of plants to infection with certain viruses

The effects on susceptibility to infection with certain viruses of subjecting plants to various periods of darkness or reduced illumination before and after inoculation were tested. The viruses and hosts used were a tobacco necrosis virus in French bean and tobacco; tomato aucuba mosaic virus in tobacco; and tobacco mosaic and tomato bushy stunt viruses in Nicotiana glutinosa . All the virus-host combinations give necrotic local lesions, and susceptibility was measured by local lesion counts. Susceptibility was consistently increased by pre-inoculation treatments of host plants, whereas post-inoculation treatments had relatively little effect, but most often decreased susceptibility.
Short periods in the dark produced similar responses to longer periods in shade, but the different plants varied in their response to, and tolerance of, darkness. The maximum number of lesions was usually obtained with bean plants kept for only 24 hr. in the dark before inoculation, but with tobacco plants susceptibility increased with increasing time in the dark up to 5 days.
It is suggested that the successful establishment of infection occurs in two stages, the first of which is affected by. the accumulation of photosynthetic products. Whether these products confer resistance by increasing cell turgor or by reacting specifically with virus particles is unknown, but sap from plants in the light possesses no greater virus-inhibiting power than sap from plants kept in the dark.     

Canopy development of a determinate and an indeterminate cultivar of Vicia faba L. under contrasting plant distributions and densities

Field experiments were conducted in 1987 and 1988 to quantify differences in canopy formation between an indeterminate and a determinate genotype of Vicia faba L., grown at two plant densities and three spatial distributions. The number of stems per unit area produced by determinate plants was related to the growth rate before flowering. Leaf production per stem per unit of thermal time was similar in both plant types, but twice as many leaves per stem were produced by the indeterminate cultivar. The indeterminate cultivar produced fewer and smaller leaves in the warmer and drier weather of 1988 than in 1987. The determinate genotype produced similar sizes and numbers of leaves in both years, but fewer tillers developed in 1988 than in 1987. Accordingly, leaf mass per unit ground area was greater in 1987 than in 1988 in both genotypes. Except during early flowering, relationships between leaf mass and leaf area were constant, with higher specific leaf areas in the determinate than the indeterminate genotype. Shoot dry matter partitioning into leaves was identical in both years for indeterminate plants, but differed in determinate ones.
It is concluded that canopy development is regulated through individual leaf weight and leaf number per stem in non-tillering indeterminate, and by stem numbers per unit area in tillering determinate plants.     

THE PREPARATION AND USE OF TOBACCO MOSAIC VIRUS CONTAINING RADIOACTIVE PHOSPHORUS

Normal and tobacco mosaic-diseased Turkish tobacco plants were grown in sand for a period of several weeks, during which they were fed daily a complete nutrient solution to which had been added disodium phosphate containing radioactive phosphorus. Determinations were made of the distribution of radioactive phosphorus in different fractions such as the wash from the sand and roots, the press cake obtained on pressing the juice from the plants, the protein and protein-free portions of the supernatant liquids obtained on ultracentrifugation of the juices, and the purified tobacco mosaic virus isolated from the diseased plants. Chemical analyses as well as radiographs of the normal and diseased leaves indicated that they contained the same amount of phosphorus. Approximately 30 per cent of the radioactive phosphorus absorbed by the diseased plants was found to be combined with the purified tobacco mosaic virus that was isolated from these plants. Following the inoculation of purified tobacco mosaic virus possessing high radioactivity to normal Turkish tobacco plants, most of the radioactivity was found to be associated with non-virus components of which about 40 per cent was in the inoculated and 60 per cent in the uninoculated portions of the plants. Although a small amount of radioactive virus was isolated from the uninoculated portions of the plants, it was impossible, because of a number of complicating factors which have been discussed, to draw from the results any reliable conclusions regarding the mode of reproduction of tobacco mosaic virus.     

SOME EFFECTS OF HIGH TEMPERATURE ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION WITH VIRUSES

When plants were kept at 36°C. for some time before inoculation, their susceptibility to infection by five mechanically transmissible viruses was greatly increased. When kept at 36° after inoculation, fewer local lesions were produced than at lower temperatures, but the effects of the post-inoculation treatment differed with different viruses. Tomato spotted wilt and tobacco mosaic viruses multiply in plants at 36°, and the post-inoculation treatment reduced the local lesions they caused to numbers that varied between 10 and 90% of the control; these two viruses also have large thermal coefficients of heat inactivation. By contrast, tobacco necrosis, tomato bushy stunt and cucumber mosaic viruses, were much affected by post-inoculation treatment, lesion formation being completely prevented by exposure to 36° for a day or more. These three viruses appear not to multiply in plants at 36°, and although they have high thermal inactivation points, they have small temperature coefficients of thermal inactivation.
The extent to which lesion formation was affected by pre- or post-inoculation exposure of plants to 36° depended not only on the length of the treatment, but also on the physiological condition of the plants.
The symptoms of infected plants changed considerably if kept at 36°. At 36° Nicotiana glutinosa , inoculated with tobacco mosaic virus, gave chlorotic local lesions instead of necrotic ones, and became systemically infected. When systemically infected plants were brought to ordinary glasshouse temperature, the infected tissues all collapsed and died in a day.     

EFFECTS OF SALINITY,NITROGEN, AND POPULATION DENSITY ON THE SURVIVAL,GROWTH, AND REPRODUCTION OF ATRIPLEX TRIANGULARIS (CHENOPODIACEAE)

Populations of Atriplex triangularis were grown under laboratory conditions in a growth chamber and manipulated in an inland Ohio saline pond in order to examine the relative effects of salinity, nitrogen fertilization, and population density on growth, reproduction, and survival. For laboratory plants, nitrogen fertilization was the most important variable, with biomass and reproductive effort being greatest at the high nitrogen level. As salinity increased, biomass decreased only in plants not limited by nitrogen. Increasing density caused biomass per plant to decrease at both high and low nitrogen levels. For field plants, density was the most important variable, with biomass per plant and survival both decreasing as density increased. As density increased, size inequality among individuals increased but biomass per unit area and individual reproductive effort remained relatively constant. Nitrogen fertilization slightly enhanced survival, but did not affect biomass. It is suggested that density-dependent processes may be significant even in relatively harsh physical environments.     

Polyacrylic acid-induced resistance to tobacco mosaic virus in tobacco cv. Xanthi

Polyacrylic acid (PA) of molecular weight 1700A, 1700B and 3500 caused resistance to infection with tobacco mosaic virus in tobacco cv. Xanthi-nc, when sprayed on the leaves or watered into the soil. The numbers of lesions produced in the treated plants were between 27 and 97% fewer than in the untreated plants depending on the concentration of PA, its molecular weight and the method of application. Some resistance was caused against potato virus X and potato virus Y but only at concentrations that were harmful to the plants. It appears that PA activates a mechanism responsible for localizing viruses in hypersensitive plants.     

PHOTOSYNTHESIS AND RESPIRATION RATES OF LEAVES OF NICOTIANA GLUTINOSA INFECTED WITH TOBACCO MOSAIC VIRUS AND OF N. TABACUM INFECTED WITH POTATO VIRUS X

The rates of respiration and of photosynthesis of tobacco leaves infected with potato virus X were not affected until the leaves showed symptoms; the respiration rate was then increased by more than 30% and the photosynthesis rate decreased by 20%. When local lesions appeared on the leaves of Nicotiana glutinosa infected with tobacco mosaic virus, but not before, the respiration rate was increased by an amount, up to 30%, that varied with the number of lesions. The photosynthesis rate was decreased by 20%, but there was no effect on photosynthesis or respiration until symptoms appeared. These results differ from those previously reported for tobacco leaves infected with tobacco mosaic virus, in which both respiration and photosynthesis were affected within 1 hr. of inoculation. The validity of extrapolating arguments based on the results obtained with other combinations to this commonly used combination and vice-versa is questioned.     

Effects of (2 Chloro-Ethyl) Trimethlammonium Chloride on Plant Growth, Leaf Area, and Net Assimilation Rate

Both under glasshouse conditions and in a constant environmentwith light from fluorescent tubes, mustard plants' treatmentwith (2 chloro-ethyl) trimethylammonium chloride (CCC) respondedby an increase in total leaf area. In the glasshouse the increasewas due to the production of more lateral leaves, and in thegrowth chambers to the enlargement of stem leaves, since lateralbranches did not form. Despite the increase in area, the netassimilation rate fell; this may be attributable to an effectof CCC on the photosynthetic mechanism or to an increase inthe mutual shading of leaves, but it is more probable that theinhibition of stem growth also caused by CCC decreases the demandfor photosynthate and leaves photosynthesise less. The leafarea of mustard (a long-day plant) is increased also by short-daytreatment, and here again there is a concomitant shorteningof the stem. Chlorophyll content, both per leaf and per unit area, and totaldry matter per unit area, were increased in tobacco plants grownin culture solutions containing CCC. The treatment affectedthe distribution of nitrogen, increasing the amount per leafand decreasing it per stem.     

FACTORS AFFECTING THE PRODUCTION OF LOCAL LESIONS BY PLANT VIRUSES

Under uncontrolled glasshouse conditions the number of local lesions produced by a tobacco necrosis virus in beans depended on time of day at which plants were inoculated. Inoculations in the afternoon produced most lesions and inoculations near the end of the night produced least. Tobacco mosaic virus in Nicotiana glutinosa , and lucerne mosaic and turnip mosaic viruses in tobacco showed similar but smaller effects. The variations could affect the results of quantitative experiments with local-lesion counts.     

Interaction of cucumber mosaic virus and potato virus y with tobacco mosaic virus

A study was performed on the interaction of cucumber mosaic virus (CMV) of potato virus Y (PVY) with tobacco mosaic virus (TMV). Interference was evaluated using tobacco plantsNicotiana tabacum cv. Java responding to CMV and PVY with a systemic infection and to TMV with local necrotic lesions. The decrease in TMV — induced lesion number gave evidence of a decrease in susceptibility caused by the previous infection with CMV or PVY, the decrease of lesion enlargement demonstrated a decreased TMV reproduction in the plants previously infected with CMV or PVY. The interference concerned was incomplete, as evaluated from reproduction of the challenging TMV and from the decrease in susceptibility of the host to TMV brought about by the first infection with CMV or PVY.     

THE INFECTION OF PLANTS BY VIRUSES THROUGH ROOTS

Roots of young tomato plants became infected when inoculated with tomato bushy stunt, tobacco mosaic, and potato X viruses. Root infections also occurred when these viruses were added to soil or culture solutions in which plants were growing.
The viruses were sometimes localized around their initial entry points in roots; sometimes they invaded the root system but not the shoots, and sometimes they produced full systemic infection of roots and shoots. In some experiments, but not all, systemic infections were more frequent when the upper tap root or superficial roots were inoculated than when fibrous roots were inoculated.
In both tomato and potato, virus X spread from diseased to healthy plants sharing the same culture solution, if their roots were in contact, but not otherwise. Infection of the roots of potato plants by inoculation, produced only one plant with virus-infected haulms, although several had infected tubers.     

Effect of potato seed-tuber age on plant establishment and amelioration of age-linked effects with auxin

Studies were conducted to characterize the effect of advanced potato (Solanum tuberosum L.) seed-tuber age on plant growth potential and whole-plant morphology. Plant growth from single-eye seedcores from 5- to 18-month old `Russet Burbank' seedtubers was compared. Loss in apical dominance was apparent with advanced age. On a per-core basis, the amount of plant dry weight was equal for the two ages at 30 days from planting. However, individual plants from older cores displayed reduced shoot, root and leaf dry weights, leaf area, and leaf number. These effects reflected altered dry-matter partitioning and contributed to an overall change in plant morphology with advanced age. On a total seedcore basis, relative growth rate of plants from older seedcores was greater than that from younger seedcores over the 30 day growth interval. Leaf area ratio was also greater for plants from the older seedcores; however, unit leaf rate was not affected by tuber age and plants from both young and old seedcores assimilated dry matter at the same rate. Age-induced differences in growth indices reflected differences in the degree of plant differentiation over the interval of study. Treating younger seedcores with 1-naphthaleneacetic acid (NAA) prior to planting inhibited overall plant growth. In older cores, NAA stimulated root growth, restored apical dominance, decreased leaf number per plant, and increased average leaf area per leaf. In short, NAA altered the morphology of plants growing from older seedcores to more closely resemble that of plants growing from younger seedcores. While auxin significantly altered plant form, vigor of plants from older seedcores was not fully restored by auxin treatment, indicating that age-reduced vigor of potato seed-tubers is not solely mediated by auxin.     

INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH,SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular-arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base-treated plants produced more biomass than other treatments. Base-treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base-nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus-host plant interactions.     

SOME EFFECTS OF IODINE AND OTHER REAGENTS ON THE STRUCTURE AND ACTIVITY OF TOBACCO MOSAIC VIRUS

1. Denatured tobacco mosaic virus has a number of SH groups corresponding to its total sulfur content of 0.2 per cent. The SH groups were estimated by titration with ferricyanide, tetrathionate, and p-chloromercuribenzoate in guanidine hydrochloride solution and by reduction of the uric acid reagent in urea solution. 2. The SH groups of tobacco mosaic virus or their precursors can be abolished by reaction of the native form of the virus with iodine. 3. Tobacco mosaic virus whose SH groups have been oxidized beyond the S-S stage by iodine but whose tyrosine groups have not been converted into di-iodotyrosine groups still retains its normal biological activity as shown by the number of lesions it causes on Nicotiana glutinosa plants and by the characteristic disease produced in Turkish tobacco plants. 4. The inoculation of Turkish tobacco plants with active virus whose SH groups have been abolished by iodine results in the production of virus with the normal number of SH groups. 5. If enough iodine is added to tobacco mosaic virus or if the iodine reaction is carried out at a sufficiently high temperature, then the tyrosine groups are converted into di-iodotyrosine groups and the virus is inactivated. 6. Tobacco mosaic virus can be almost completely inactivated by iodoacetamide under conditions under which iodoacetamide reacts with few if any of the protein''s SH groups. 7. Tobacco mosaic virus is not inactivated by dilute p-chloromercuribenzoate.     

EFFECTS OF DARKNESS ON THE CONSTITUTION OF TOBACCO LEAVES AND SUSCEPTIBILITY TO VIRUS INFECTION

An attempt was made to find the causes of increased susceptibility to virus infection when tobacco plants are kept in the dark before inoculation. The changes in certain nitrogen fractions, viz. insoluble-N, amino-N, amide-N, ammonia-N and nitrate-N, and in dry matter and water content were followed in tobacco plants subjected to a period of darkness before inoculation with tobacco aucuba mosaic virus. Only nitrate-N was strongly correlated with the susceptibility to infection, but the evidence suggests that the correlation is indirect and not causal.
Dry matter and water content, determined either as dry matter percentage of fresh weight or measured separately on a leaf-disk basis Ivere found to vary directly with variation in susceptibility.     

乳胶溶液电镜在检测线状和棒状植物病毒中的应用

建立了一种检测线状或棒状植物病毒的新的电镜技术。用聚苯乙烯乳胶预先包被铜网用以测定烟草花叶病毒,马铃薯X、Y病毒,玉米矮化花叶病毒表明,铜网上沾附的病毒数量与免疫电镜法相似,比直沾法多几倍至十几倍。乳胶溶液电镜法不需制备特异抗血清,方法简便快速,特别适合于植物样品的初次病毒检测工作。     

STREAK—A VIRUS DISEASE OF TOMATOES

A comparison of streak disease of tomatoes, derived from commercial glasshouses, and experimental streak produced by combined inoculation of the viruses of potato mosaic and tobacco mosaic, is given in detail.
The characters employed in comparison are the host range of each virus and its resistance to various temperatures, to different concentrations of alcohol, and to ageing in vitro .
Glasshouse streak and tobacco mosaic show an equal resistance to alcohol, heat and ageing in vitro , and have, in addition, an identical host range. Treatment for 1 hour with 90 per cent, alcohol and for 10 minutes at 85⁰ C. did not destroy the infectivity of either of these viruses.
Glasshouse streak is shown not to contain the virus of potato mosaic, but is of itself able to produce necrosis in tomatoes without the participation of potato mosaic. The factors underlying this have not been determined.
It is concluded that tobacco mosaic and the mosaic of glasshouse streak are probably identical, and that much of the streak occurring in glasshouses is due to a single virus, and not a mixed infection of this with potato mosaic.