Root Immersion Research Articles

Influence of verticillium and fusarium wilts on the growth of melon

The susceptibility of the Greek melon cvs Kokkini Banana, Thraki, Peplos and Amynteou to Verticillium dahliae and Fusarium oxysporum f. sp. melonis was tested, by inoculating seedlings of the four cultivars by root immersion in a Verticillium and Fusarium inoculum suspension for 1 h. After 35 days, disease incidence was estimated from a disease index calculated as the product of the‘leaf symptom index’and‘vascular discoloration index’of each plant. In addition, plant height, main stem diameter, above-ground fresh and dry weight and root fresh and dry weight were measured. The disease severity of verticillium and fusarium wilts on plants was estimated by the correlation coefficient (r) between the disease index and the other characteristics. Both fungi had a significant negative effect on all the measured characteristics independently of the tested cultivar. Finally, the four melon cultivars showed different degrees of susceptibility to Verticillium and Fusarium indicating that tolerant selections can be achieved.

Effects of salinity and sulfide on the distribution of Phragmites australis and Spartina alterniflora in a tidal saltmarsh

In laboratory studies, the short-term response of Phragmites australis and Spartina alterniflora to root immersion in solutions of different salinity and sulfide concentration was measured as the rate of ammonium depletion (a proxy for root uptake) from an initial concentration of 20 μM. From 0 to 20 ppt in the absence of sulfide, ammonium uptake as a function of dry root weight decreased for both Phragmites (from 29.7 ± 3.5 s.e. to 8.2 ± 1.5 μmol N g −1 h −1) and Spartina (from 25.5 ± 3.5 to 9.0 ± 1.5 μmol N g −1 h −1). With an average sulfide concentration of 582 μM at 20 ppt, the rate of ammonium uptake for Spartina (10.9 ± 2.2 μmol N g −1 h −1) was not significantly different from the rate in the absence of sulfide. In contrast, the rate of ammonium uptake was significantly lower for Phragmites when the average sulfide concentration was increased from 0 to 375 μM (1.7 ± 1.6 μmol N g −1 h −1). In a tidal saltmarsh, the average porewater sulfide concentration in Phragmites australis stands (124 ± 206 μM) was almost an order of magnitude lower than that measured in stands of Spartina alterniflora (989 ± 166 μM). These field and laboratory results support the notion that increased sulfide in the rhizosphere reduces the ability of Phragmites to take up nutrients relative to species such as Spartina that are better-adapted to sulfidic soil conditions, thus restricting the distribution of Phragmites in tidal saltmarshes.

Root Development and Aerenchyma Formation in Two Wheat Cultivars and One Triticale Cultivar Grown in Stagnant Agar and Aerated Nutrient Solution

Stagnant nutrient solution containing 0‐1% agar and with an extremely low oxygen level (‘stagnant agar solution’) was used to simulate the gaseous composition and slow gas diusion of waterlogged soils. Comparisons were made between the growth of two wheat cultivars (Triticum aestiaum, cvs. Gamenya and Kite) and one triticale cultivar (Triticosecale, cv. Muir) grown in stagnant relative to aerated solution. For all genotypes tested, immersion of roots in stagnant agar solution resulted in the death of the entire seminal root system and led to profuse branching of the laterals of the nodal roots. In the stagnant agar solution aerenchyma, as a percentage of the total cross sectional area of nodal roots, was 18% for Muir, 14% for Kite and 12% for Gamenya; the roots of species with more aerenchyma also attained a longer maximum root length as predicted by the model of Armstrong (in: Woolhouse HW, ed. Adaances in botanical research, aol. 7. London: Academic Press, 1979). Muir also had a nodal root}shoot fresh weight ratio of 0‐5 compared with 0‐2‐0‐3 in Kite and Gamenya. The greater number and length of nodal roots of Muir did not lead to better shoot growth than in the other genotypes; one possible reason for this lack of improvement is a low eciency of aerenchymatous roots in wheat. # 1998 Annals of Botany Company

Pectic enzymes as a selective pressure tool forin vitro recovery of strawberry plants with fungal disease resistance

A novel strategy in selecting strawberry (Fragaria xananassa L.) plants with resistance toRhizoctonia fragariae andBotrytis cinerea was developed. Purified pectic enzymes produced byR. fragariae were usedin vitro to select morphogenetic calluses. Both regenerated shoots and plants were testedin vitro andin vivo withR. fragariae andB. cinerea. Thein vitro resistance of shoots regenerated under selection pressure was confirmed byin vivo tests with runner plants either by root immersion in a suspension ofR. fragariae mycelium before potting the plants in sterile soil, or by spraying the leaves with several strains ofB. cinerea spores. The increase of resistance against pathogens was correlated to the increase of phenolic compounds, particularly orthodibydroxyphenols.

The effects of azadirachtin on the acquisition and inoculation of potato leafroll virus by Myzus persicae

The roots of Nicotiana clevelandii (Gray) seedlings infected with potato leafroll virus (PLRV) were immersed in 0, 50, 100 or 150 ppm azadirachtin solutions for 84 h. Adult apterous peach-potato aphids, Myzus persicae (Sulzer), were placed onto the seedlings for an acquisition access period (AAP) of 72 h starting 12 h after root immersion or 2 days after the seedlings had been re-potted in compost. The aphids were then placed onto indicator plants to assess PLRV acquisition. Although azadirachtin did not affect aphid survival, PLRV infection of the indicator plants was recorded less frequently when inoculated by aphids which had spent the AAP on azadirachtin-treated plants. The ability to produce viable nymphs on indicator plants was severely reduced when the aphids had spent the AAP on seedlings with their roots immersed in azadirachtin. This effect was also detected after the aphids had spent the AAP on azadirachtin-treated seedlings re-potted after treatment. The concentrations required to prevent PLRV acquisition from infected seedlngs were not visibly phytotoxic, but a higher concentration of azadirachtin (500 ppm) caused short-term (wilting) and long-term (deformation) phytotoxicity. Immersing the roots of uninfected N. clevelandii seedlings in 500 ppm azadirachtin solution did not prevent them becoming infected with PLRV after exposure to viruliferous aphids in ‘choice’ and ‘nochoice’ experiments.

Effect of abscisic acid on the cell cycle in the growing maize root

The mechanism by which the rate of cell proliferation is regulated in different regions of the root apical meristem is unknown. The cell populations comprising the root cap and meristem cycle at different rates, proliferation being particularly slow in the quiescent centre. In an attempt to detect the control points in the cell cycle of the root apical meristem of Zea mays L. (cv. LG 11), quiescent-centre cells were stimulated to synthesise DNA and to enter mitosis either by decapping or by immersing intact roots in an aqueous 3,3-dimethyl-glutaric acid buffer solution. From microdensitometric and flow-cytometric data, we conclude that, upon immersion, the G2 phase of the cell cycle of intact roots was shortened. However, when 50 μM abscisic acid (ABA) was added to the immersion buffer, parameters of the cell cycle were restored to those characteristic of intact roots held in a moist atmosphere. On the other hand, decapping of primary roots preferentially shortened the G1 phase of the cell cycle in the quiescent centre. When supplied to decapped roots, ABA reversed this effect. Therefore, in our model, applied ABA retarded the completion of the cell cycle and acted upon the exit from either the G1 or the G2 phase. Immersion of roots in buffer alone seems to trigger cells to more rapid cycling and may do so by depleting the root of some ABA-like factor.

The Effects of Heavy Metals and Root Immersion on Isoflavonoid Metabolism in Alfalfa (Medicago sativa L.).

Modest increases in the concentration of medicarpin, 6-fold in leaves and 4-fold in roots, were observed in alfalfa (Medicago sativa L.) seedlings treated with 1 mM metal salts for 72 h. However, medicarpin-3-O-glucoside-6"-O-malonate (MGM) and formononetin-7-O-glucoside-6"-O-malonate (FGM) levels were up to 50-fold lower in metal-treated compared to control roots. Approximately 10% of the "missing" conjugates could be accounted for in the root treatment solution, where FGM and MGM transiently accumulated prior to their hydrolysis. Time-course studies revealed that total isoflavonoid content (roots plus solution) increased slightly after CuCl2 treatment, whereas the levels of FGM and MGM increased rapidly in alfalfa roots immersed in water. This increase was reduced by aeration. The phenylalanine ammonia-lyase inhibitor L-[alpha]-aminooxy-[beta]-phenylpropionic acid was used to show that immersion of the roots reduced conjugate rates of degradation, which explains their accumulation. In contrast, conjugate rates of degradation were elevated in CuCl2-treated roots, with 50% of the increase being due to hydrolysis. Up to 90% of formononetin and medicarpin produced in response to CuCl2 treatment arose via conjugate hydrolysis. Our results demonstrate that both immersion/anaerobiosis and abiotic elicitation modify isoflavonoid metabolism in alfalfa, and that metal-stimulated accumulation of phytoalexins may arise through the release from preformed stores rather than de novo synthesis.

Xyloglucan Endotransglycosylase Activity, Microfibril Orientation and the Profiles of Cell Wall Properties Along Growing Regions of Maize Roots

A series of physical and chemical analyses were made on the expanding zone of maize seedling roots grown in hydroponics. Comparison of longitudinal profiles of local relative elemental growth rate and turgor pressure indicated that cell walls become looser in the apical 5 mm and then tighten 5-10 mm from the root tip. Immersion of roots in 200 mol m-3 mannitol (an osmotic stress of 0-48 MPa) rapidly and evenly reduced turgor pressure along the whole growing region. Growth was reduced to a greater extent in the region 5-10 mm from the root tip than in the apical region. This indicated rapid wall-loosening in the root tip, but not in the more basal regions. Following 24 h immersion in 400 mol m-3 mannitol (an osmotic stress of 0-96 MPa) turgor had recovered to pre-stressed values. Under this stress treatment, growth was reduced in the region 4-10 mm from the root tip, despite the recovery of turgor, indicating a tightening of the wall. In the root apex, local relative elemental growth rate was unchanged in comparison to control tissue, showing that wall properties here were similar to the control values. Cellulose microfibrils on the inner face of cortical cell walls became increasingly more parallel to the root axis along the growth profile of both unstressed and stressed roots. Orientation did not correlate with the wall loosening in the apical region of unstressed roots, or with the tightening in the region 5-10 mm from the root tip following 24 h of osmotic stress. Longitudinal profiles of the possible wall-loosening enzyme xyloglucan endotransglycosylase (XET) had good correspondence with an increase in wall loosening during development. In the zone of wall tightening following osmotic stress, XET activity was decreased per unit dry weight (compared with the unstressed control), but not per unit fresh weight.

The Effect of Colchicine as a Chromosome Doubling Agent for Wheat-Rye Hybrids as Influenced by pH, Method of Application, and Post-Treatment Environment

Hybrids of wheat (Triticum durum) × rye (Secale montanum) (2n = 21) were treated with a 0.06 % solution of colchicine. In the induction of fertile plants, fertile spikes, and seed-set per spike, the root immersion technique was 21.7 %, 14.1 %, and 4.4 % respectively more effective than the use of the inverted vial. Colchicine solutions ranging in pH from 3.5 to 7.5 with the root immersion technique reached the highest frequencies of fertile (or partially fertile) hybrids (77.7 %), and fertile spikes (68.9 %) at a pH 5.5 used for the treatment, although the highest overall percentage of large Q seeds resulted from treatments at low pH (3.5). The overall mean frequency of induced fertile plants was six-fold higher when treated in a growth chamber (19/15 °C day/night temperature and 18 h photoperiod) compared to treatments conducted in a greenhouse. The frequency of euploidy (2n = 42) was found to be highest in the large seed class and lowest, i.e. just about 50 %, in the class of small seeds.

Short-duration Presprouting, Ethephon, and Cutting Increase Plant Production by Sweetpotato Roots

Sweetpotato [Ipomoea batatas (L.)] plants were harvested earlier following immersion of roots in 1500 mg ethephon/liter for 10 minutes or cut transversely 1 to 2 cm from the proximal end before bedding than when roots were not treated. Combined ethephon and cutting treatments did not promote earlier harvests than either applied separately. Presprouting for 10 days reduced the time to first plant harvest from whole or cut roots of `Georgia Red', but not from roots of `Georgia Jet'. Immersion in ethephon increased the number of early and total plants produced by both cultivars. Short-duration presprouting and cutting of roots increased the number of early and total plants produced by `Georgia Red', but not by `Georgia Jet'. Total plant production was increased by cutting non-presprouted roots that had been immersed in ethephon. Cutting did not significantly increase total plant production from presprouted roots, but immersion in ethephon increased total number of plants produced from presprouted whole roots. Plant weight and deterioration of the bedded roots during plant propagation were not influenced by treatments. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

Elicitor-induced accumulation of glyceollin and callose in soybean roots and localized resistance against Phytophthora megasperma f.sp. glycinea

Immersion of roots of 2-day-old soybean seedlings ( Glycine max cv. Harosoy 63) into solutions of several glucan elicitors caused the accumulation to various degrees of the soybean phytoalexin glyceollin. Laminarin and polytran proved to be more effective elicitors in this system than the glucan elicitor from Phytophthora megasperma f.sp. glycinea (Pmg). Digitonin and tomatin caused, in addition to glyceollin accumulation, the deposition of callose in the rhizodermis. Pretreatment of the soybean roots with laminarin effected an increase in resistance of the seedlings against a compatible race of Pmg.

Rapid Oscillations in Fructose 2,6-Bisphosphate Levels in Plant Tissues

The fructose 2,6-bisphosphate (Fru 2,6-P(2)) content of pea, Pisum sativum, roots and leaves were measured following flooding with water and found to change in times of minutes and to exhibit oscillatory-type changes. Each organ changes its Fru 2,6-P(2) content in a unique pattern in response to environmental disturbances such as flooding or light. For example, when roots of intact illuminated pea plants are flooded, roots decrease their Fru 2,6-P(2) content while simultaneously leaves increase their Fru 2,6-P(2) content; but both organs exhibit oscillatory-type patterns within flooding time of about 30 minutes. Half-change times can be as rapid as 2 to 3 minutes. The endogenous extractable activity of the root pyrophosphate-dependent phosphofructokinase also exhibits an oscillatory pattern upon root immersion slightly after Fru 2,6-P(2) changes occur. We postulate from these results that Fru 2,6-P(2) is a primary signal molecule which enables plants to regulate their metabolism to cope with changing environments.

Phyllosphere of Cotton as a Habitat for Diazotrophic Microorganisms

Positive nitrogenase activities ranging from 0.18 to 0.78 nmol of C(2)H(4) cm h were detected on the leaf surfaces of different varieties of cotton (Gossypium hirsutum L. and G. herbaceum L.) plants. Beijerinckia sp. was observed to be the predominant nitrogen-fixing microorganism in the phyllosphere of these varieties. A higher level of phyllosphere nitrogen-fixing activity was recorded in the variety Varalaxmi despite a low C/N ratio in the leaf leachates. Leaf surfaces of the above variety possessed the largest number of hairy outgrowths (trichomes) which entrapped a majority of microbes. Immersion of plant roots in nutrient medium containing P(i) led to the accumulation of label in the trichome-borne microorganisms, thereby indicating a possible transfer of nutrients from leaf to microbes via trichomes. Extrapolation of acetylene reduction values suggested that 1.6 to 3.2 kg of N ha might be contributed by diazotrophs in the phyllosphere of the variety Varalaxmi during the entire growth period.

The Effect of Warm Water Treatment ofPinus radiataSeedlings on Mycorrhizae Survival, Root Growth Capacity andPhytophthoraEradication

SYNOPSIS Immersion of roots of Pinus radiata D. Don seedlings in water at 48 and 50° C for five, 10 and 15 minutes eradicated Phytophthora but caused a significant decrease in biomass production two years after field planting. Wheat grains infected with Phytophthora cinnamomi were immersed in water at temperatures from 38 to 50° C at 1°C intervals for periods from one to 30 minutes. The temperature/time relationship was negatively linear, requiring 25 minutes at 41°C and 5 minutes at 45°C for the complete elimination of the fungus. The roots of Phytophthora-infected Pinus radiata seedlings were treated with the minimum time/temperature combinations which eradicated the fungus from wheat grains. Root growth capacity (RGC) and mycorrhizal initiation of seedlings treated at 41°C for 25 minutes did not differ significantly from the control, but the higher temperature treatments reduced it significantly. Phytophthora was completely eliminated at 41°C for 25 minutes.

Rates of emission of H2S from plants and patterns of stable sulphur isotope fractionation

In all green plants both HSO−3 and SO42− are reduced during photosynthesis, and many species can emit the product as H2S gas. Plants will emit H2S after fumigation with acute doses of SO2 gas1,2, irrigation with 5% K2SO4 solutions3, or immersion of roots in HSO−3 and SO42− solutions4. If such emissions of H2S by plants occur in nature, then this process adds sulphur to the atmosphere and contributes to the global sulphur budget. Oxidation of biogenic H2S in the atmosphere may also contribute to the formation of acid rain. We report here that irradiated plants with roots immersed in HSO−3 and SO42− solutions at concentrations found in nature emit H2S from their leaves, and that the fractionation of stable isotopes of sulphur during H2S emission may be useful for identifying atmospheric sulphur that has been generated by photosynthetic reduction of sulphur.

Biosynthesis of triterpenoid sapogenols in soybean and alfalfa seedlings

By incubation of germinating soybeans with mevalonate-[2- 14C] (MVA), radioactivity was incorporated into four sapogenols which were identified by TLC. Unequivocal evidence for the identity of three of the four sapogenols was provided by co-crystallization to constant specific radioactivity. The partition of incorporated radioactivity into lipid- and water-soluble fractions and the pattern of radioactivity of individual sapogenols varied with the mode of administering labeled substrates to soybean seedlings, such as incubation of germinating soybeans with MVA-[2- 14C], immersion of roots into MVA-[2- 14C] or foliar application of squalene-[ 14C]. When alfalfa seedlings were incubated with MVA-[2- 14C], about two-thirds of the radioactivity incorporated into the sapogenols was associated with medicagenic acid.

Transmission of Soil-borne Barley Yellow Mosaic Virus

Two-rowed barley plants grown on autoclaved soil showed infection when mechanically inoculated on leaves with soil-borne barley yellow mosaic virus. Test seedlings grown on this soil or autoclaved soil containing the roots of these infected plants failed to produce infection.A drench of Dexon** at a concentration of 70-140ppm on drill furrows of infected fields immediately before sowing brought about a considerable decrease in the disease incidence. On the other hand, the infectivity of diseased leaf juice was not affected by the addition of Dexon to the juice at concentrations of 50-200ppm in mechanical inoculations.Naturally infected roots were homogenized and filtered through 325 mesh screen. The filtrate was found to contain a high concentration of resting spores of Polymyxa graminis Led., and showed infectivity when inoculated to soil. The infectivity was lost at a dilution of 1:102.Naturally infected roots stored in refrigerator (4°C) for 4 months were immersed in tap water in petri dishes at 13-15°C. The water was changed daily. Infectivity of this water was tested by soaking germinated barley seeds in it, and was found to be infective from the 4th day after root immersion. A considerably high infectivity persisted until the 15th day. The infectivity of the water became higher when infected roots were kept in wet soil at 23°C for more than two weeks before immersion.The number of zoospores mostly of P. graminis released on successive days after the roots were immersed was found to be closely correlated with the infectivity of the water.From these results, P. graminis is suspected to be a vector of this virus.

Transmission of Soil-borne Barley Yellow Mosaic Virus

Two-rowed barley plants grown on autoclaved soil showed infection when mechanically inoculated on leaves with soil-borne barley yellow mosaic virus. Test seedlings grown on this soil or autoclaved soil containing the roots of these infected plants failed to produce infection.A drench of Dexon** at a concentration of 70-140ppm on drill furrows of infected fields immediately before sowing brought about a considerable decrease in the disease incidence. On the other hand, the infectivity of diseased leaf juice was not affected by the addition of Dexon to the juice at concentrations of 50-200ppm in mechanical inoculations.Naturally infected roots were homogenized and filtered through 325 mesh screen. The filtrate was found to contain a high concentration of resting spores of Polymyxa graminis Led., and showed infectivity when inoculated to soil. The infectivity was lost at a dilution of 1:102.Naturally infected roots stored in refrigerator (4°C) for 4 months were immersed in tap water in petri dishes at 13-15°C. The water was changed daily. Infectivity of this water was tested by soaking germinated barley seeds in it, and was found to be infective from the 4th day after root immersion. A considerably high infectivity persisted until the 15th day. The infectivity of the water became higher when infected roots were kept in wet soil at 23°C for more than two weeks before immersion.The number of zoospores mostly of P. graminis released on successive days after the roots were immersed was found to be closely correlated with the infectivity of the water.From these results, P. graminis is suspected to be a vector of this virus.

Chromosome Endoreduplication (Endopolyploidy) in Pea Root Meristems Induced by 8-Azaguanine

SUMMARYThe effect of 8-azaguanine (5 × 10−4M) on the root meristems of Pisum sativum has been studied.The immediate effect of 8-azaguanine is an inhibition of interphase (G2) nuclei to enter mitosis ending in the absence of mitosis after a 12-hour treatment. Inhibition of DNA synthesis (H3-thymidine incorporation) starts to appear after 6 hours: 8-azaguanine does not interfere with DNA synthesis once it is initiated, but it inhibits the initiation of DNA synthesis (passage from G1 to S) at least in the majority of cells (data of the DNA cyto-photoinetry).When roots treated with 8-azaguanine for 17 hours recover in water for 24 hours, both diploid (14 monochromosomes) and endotetraploid (14 diplochromosomes = 4-chromatid chromosomes) mitoses are found in the meristem. The proportion of diplochromosome mitoses is still higher when the 24-hour water recovery follows two 8-azaguanine treatments, 17-hours each, separated by a 6-hour root immersion in 5 x 10—4M guanine. A treatment has also been found which ind...

Incorporation of C14-labeled maleic hydrazide into the root-tip cells of Allium cernuum, Vicia faba, and Tradescantia paludosa.

Allium cernuum, Vicia faba, and Tradescantia paludosa were treated by root immersion in maleic hydrazide (1 mM/liter) labeled with C(14) (C(14)-MH) for 1 hour to determine the location within the cell to which MH moves during various periods of time after treatment. Root tips were fixed 24 hours, 48 hours, 72 hours, and 3 weeks after treatment. Autoradiographs of root tips squashed 24 to 72 hours after fixation showed that C(14)-MH was distributed throughout the nuclei and was particularly concentrated in the nucleoli. The nucleolar localization of the chemical was transitory, fixations made 3 weeks after treatment showing well labeled nuclei many of which completely lacked label in the nucleoli. The chromosomes seen in mitotic divisions of all three species had the same amount of label in euchromatic as heterochromatic areas. Since the chemical was not accumulated preferentially in heterochromatic areas, it seems likely that the reported specificity of MH for the breakage of heterochromatin can not be due to preferential heterochromatic incorporation.