Reduced Shoot Fresh Weight Research Articles

Phytotoxic Potential and Biological Activity of Three Synthetic Coumarin Derivatives as New Natural-Like Herbicides.

Coumarin is a natural compound well known for its phytotoxic potential. In the search for new herbicidal compounds to manage weeds, three synthetic derivatives bearing the coumarin scaffold (1–3), synthesized by a carbonylative organometallic approach, were in vitro assayed on germination and root growth of two noxious weeds, Amaranthus retroflexus and Echinochloa crus-galli. Moreover, the synthetic coumarins 1–3 were also in vitro assayed on seedlings growth of the model species Arabidopsis thaliana to identify the possible physiological targets. All molecules strongly affected seed germination and root growth of both weeds. Interestingly, the effects of synthetic coumarins on weed germination were higher than template natural coumarin, pointing out ED50 values ranging from 50–115 µM. Moreover, all synthetic coumarins showed a strong phytotoxic potential on both Arabidopsis shoot and root growth, causing a strong reduction in shoot fresh weight (ED50 values ≤ 60 µM), accompanied by leaf development and a decrease in pigment content. Furthermore, they caused a strong alteration in root growth (ED50 values ≤ 170 µM) and morphology with evident alterations in root tip anatomy. Taken together, our results highlight the promising potential herbicidal activity of these compounds.

Sodium accumulation contributes to salt stress tolerance in lettuce cultivars

Increasing soil salinity of irrigated agricultural areas represents a major environmental stress factor that impairs the production of many salt-sensitive crop plants. Different lettuce cultivars were studied for identification of more tolerant ones, based on physiological properties. Five selected lettuce cultivars were grown hydroponically, salt stress was induced by 50 mM and 100 mM of NaCl. The cultivars exhibited differential reduction in shoot fresh weight. The highest sodium and free proline accumulation in the shoot of the most tolerant cultivar, associated with a moderate decrease of the root hydraulic conductance and of the leaf stomatal conductance, can be related to a better defense mechanism against osmotic stress. Salt exposure increased the potassium and calcium ion content of the xylem sap, which may be important for an efficient osmotic adjustment needed to support leaf expansion. The fact that the highest amount of Na+ was found in the shoot of the most tolerant cultivar, and the lowest in the most sensitive one, reflects that in lettuce Na+ exclusion is not a main strategy for salt tolerance. Lettuce is a good example for the case in which salinity tolerance is related not to exclusion, but to inclusion of sodium ions in the shoot system. For salt tolerant varieties the marketable yield has a higher dry biomass percentage, leaves of plants grown under high salinity are crispier, darker green and have a slight salty taste.

Alleviation Of Nacl Stress In Summer Squash ‘Eskandrani’ By Foliar Application Of Salicylic Acid

Abstract The experiment was performed to assess the possibility of overcoming NaCl salinity stress by foliar sprays of summer squash ‘Eskandrani’ with salicylic acid (SA) at the concentration of 10-6 M. NaCl treatment caused reduction of shoot fresh weight, leaf number per plant, fruit yield, concentrations of potassium in aerial parts, and the concentration of chlorophyll in leaves. Plants grown under salt stress conditions had higher shoot sodium concentrations than plants untreated with NaCl. Foliar application of SA ameliorated partly the negative effect of NaCl treatment. The beneficial effect of SA was also observed in non-stressed plants, increasing the shoot potassium accumulation and leaf photosynthetic pigments status, and decreasing sodium accumulation in shoots.

ASSESSMENT OF MORPHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF PEACH ROOTSTOCKS UNDER DROUGHT AND ALUMINUM STRESS

The challenging constrain of peach production in highlands of northern Thailand is limited irrigation water and acidic soil. These problems could be alleviated by using a suitable rootstock. Field screening for drought and acidic soil tolerant rootstocks is time consuming and costly. Therefore, any parameter related to these traits detected in a greenhouse screening would be very useful as a selection index for a breeding program. In acidic soil, aluminum toxicity is one of the major confinements on plant growth. The aim of this study was to evaluate potential morphological (shoot fresh and dry weight, leaf size and leaf burn) and physiological (photosynthesis, chlorophyll a content, leaf conductance, leaf water potential and proline content) parameters related to drought and aluminum stress. A factorial experiment with two levels of the irrigation: 1) well watered (100% of evapotranspiration, ET) and 2) drought treatment (25-50% of ET), combined with three levels of aluminum: 1) no aluminum, 2) 50 mg kg-1 of aluminum and 3) 100 mg kg-1 of aluminum was done with four-week-old ‘Flordaguard’ rootstocks. The results showed that drought and aluminum stress caused leaf burn. Drought treatment significantly reduced shoot fresh weight (50%), shoot dry weight (35%), photosynthesis rate (80%), leaf conductance (90%) and leaf water potential (75%). Conversely, drought effect increased proline content by 10%. Aluminum stress caused linear decrease in shoot fresh weight and quadratic decrease in shoot dry weight and leaf size, but leaf burn was quadratic increased. For drought stress all parameters, except leaf size, leaf burn and chlorophyll content, were potentially selection index. Meanwhile, for aluminum stress, potential selection parameters were shoot fresh and dry weight, leaf size and leaf burn.

Assessment of drought tolerance in seedlings of sugar beet (Beta vulgaris L.) cultivars using inorganic and organic solutes accumulation criteria

Drought is a major environmental factor limiting the production of crops. Drought tolerance of sugar beet (Beta vulgaris L.) cultivars in terms of growth and inorganic and organic solute accumulation was analyzed in this study. Four-week-old seedlings of three cultivars, “Gantang7”, “SD13829” and “ST21916”, differing in drought tolerance, were treated with different degrees of drought stress. Plant shoots and roots were harvested at 5 d after stress and subjected to analysis. Drought significantly reduced shoot fresh weight and water content in the three cultivars, though the least reduction was found in “ST21916”. Either decrease or no change in sodium (Na+) and potassium (K+) concentrations was observed in the three cultivars as an effect of drought, whereas a higher root Na+ and a lower root K+ concentration was noted in “Gantang7”. Root calcium (Ca2+) concentration significantly increased in “Gantang7” exposed to moderate and severe drought. Severe drought also caused a significant increase in the proline level in “SD13829” but not in “Gantang7” and “ST21916”. Under drought stress, soluble sugar concentrations significantly increased in both “Gantang7” and “SD13829” whilst remaining unchanged in “ST21916”. It is clear that Na+, K+ and soluble sugars are major contributors to osmotic adjustment (OA), while Ca2+ and proline have minor contributions to OA in all three cultivars. According to our comprehensive assessment of drought tolerance, it is shown that “ST21916” is more tolerant to drought than the other two cultivars. Therefore, our results suggest that “ST21916” may be more suitable for planting in arid and semi-arid regions.

Salicylic acid and nitric oxide alleviate osmotic stress in wheat (Triticum aestivum L.) seedlings

Salicylic acid (SA) and nitric oxide (NO) are reported to alleviate the damaging effects of stress in plants rather similarly when applied at appropriate low concentrations. An experiment was therefore conducted to study the impact of SA, sodium nitroprusside (SNP; as NO donor), and methylene blue (MB; as a guanylate cyclase inhibitor) on wheat seedling performance under osmotic stress. Osmotic stress significantly reduced shoot fresh weight (SFW), chlorophyll contents (Chla, Chlb, total Chl), and membrane stability index (MSI) and also increased malondialdehyde (MDA) level, lipoxygenase (LOX) activity, and hydrogen peroxide production. Moreover, enzymatic antioxidant activities including superoxide dismutase, guaiacol peroxidase, and glutathione reductase activity were enhanced under osmotic stress. On the contrary, SA or SNP pretreatment reduced the damaging effects of osmotic stress by further enhancing the antioxidant activities that led to increased SFW, Chl, and MSI and reduced MDA level and LOX activity. However, pretreatment of plants with MB reversed or reduced the protective effects of SA and SNP suggesting that the protective effects were likely attributed to NO signaling. Therefore, NO may act as downstream of SA signaling in reduction of induced oxidative damage in wheat seedlings.

Glyphosate Resistance in Tall Waterhemp (Amaranthus tuberculatus) from Mississippi is due to both Altered Target-Site and Nontarget-Site Mechanisms

A tall waterhemp population from Missisippi was suspected to be resistant to glyphosate. Glyphosate dose response experiments resulted in GR50(dose required to reduce plant growth by 50%) values of 1.28 and 0.28 kg ae ha−1glyphosate for the glyphosate-resistant (GR) and -susceptible (GS) populations, respectively, indicating a five-fold resistance. The absorption pattern of14C-glyphosate between the GR and GS populations was similar up to 24 h after treatment (HAT). Thereafter, the susceptible population absorbed more glyphosate (55 and 49% of applied) compared to the resistant population (41 and 40% of applied) by 48 and 72 HAT, respectively. Treatment of a single leaf in individual plants with glyphosate at 0.84 kg ha−1, in the form of 10 1-µl droplets, provided greater control (85 vs. 29%) and shoot fresh weight reduction (73 vs. 34% of nontreated control) of the GS plants compared to the GR plants, possibly indicating a reduced movement of glyphosate in the GR plants. The amount of14C-glyphosate that translocated out of the treated leaves of GR plants (20% of absorbed at 24 HAT and 23% of absorbed at 48 HAT) was significantly lower than the GS plants (31% of absorbed at 24 HAT and 32% of absorbed at 48 HAT). A potential difference in shikimate accumulation between GR and GS populations at different concentrations of glyphosate was also studied in vitro. The IC50(glyphosate concentration required to cause shikimate accumulation at 50% of peak levels measured) values for the GR and GS populations were 480 and 140 µM of glyphosate, respectively, resulting in more shikimate accumulation in the GS than the GR population. Sequence analysis of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target site of glyphosate, from GR and GS plants identified a consistent single nucleotide polymorphism (T/C, thymine/cytosine) between GR/GS plants, resulting in a proline to serine amino acid substitution at position 106 in the GR population. The GR and GS plants contained equal genomic copy number ofEPSPS, which was positively correlated withEPSPSgene expression. Thus, glyphosate resistance in the tall waterhemp population from Mississippi is due to both altered target site and nontarget site mechanisms. This is the first report of an alteredEPSPS-based resistance in a dicot weed species that has evolved resistance to glyphosate.

Neotyphodium endophyte strain and superoxide dismutase activity in perennial ryegrass plants under water deficit

The presence of Neotyphodium endophyte in forage grass tillers has been associated with increased tolerance of abiotic stresses. The effect of four endophyte treatments (plants with three different strains of Neotyphodium lolii compared with plants without endophyte) on superoxide dismutase (SOD) (EC1.15.1.1) activity in Lolium perenne cv ‘Grasslands Samson’ was measured under high and low dehydration regimes in a glasshouse experiment. SOD activity was assayed by a microplate method utilising the inhibition of reduction of a tetrazolium dye by superoxide radicals. A progressive increase in dehydration over 2 weeks reduced shoot fresh weight, dry weight and shoot water content for high, compared with low, moisture-stressed plants. Mean shoot fresh weight was significantly lower for plants with strain AR37 endophyte than for plants with strain AR1 endophyte, wild-type or endophyte-free plants, but there was no interaction between endophyte treatment and dehydration treatment. There were no differences in mean SOD activity between the dehydration treatments, and the four endophyte treatments at any of the harvests. All harvest mean SOD levels for plants in both stress groups, however, were significantly different from the preceding harvest value. Between the first and second week of moisture stress there was a significant endophyte by harvest interaction for mean percentage change in SOD activity when activity in plants with wild-type strain endophyte increased more rapidly than in AR1, AR37 or endophyte-free plants. The results are in agreement with earlier reports suggesting that Neotyphodium endophytes do not have major effects on the water stress physiology of perennial ryegrass, although water deficits applied were not extreme.

Response of plant biofuel hybrid <I>Pennisetum</I> to NaCl stress and its salinity threshold

Aims Our objectives were to examine the response of biofuel plant hybrid Pennisetum (P. americanum × P. purpureum) to NaCl stress and determine its salt tolerance mechanism and salinity threshold. Methods We cultured plants of this hybrid in plastic pots filled with sand containing 0, 0.3%, 0.5%, 0.9%, and 1.2% NaCl. After four weeks, we measured the fresh weight, dry weight, water content, plant height, tillering number and ion contents of different parts of the plants. Important findings NaCl treatment significantly reduced shoot fresh weight and dry weight by 50% at 0.568% and 0.570% NaCl, respectively. With increasing NaCl concentration, Na+ content of functional leaves did not change significantly, whereas Na+ content of old leaves and roots increased significantly. Especially when the concentration of NaCl was 0.9%, Na+ content of old leaves and roots increased two and three fold more than that of the control, meaning that Na+ content in functional leaves, old leaves and roots increased gradually. With increasing NaCl concentration, K+ content in the shoots and roots was not affected, whereas Na+/K+ in the roots increased significantly, and Na+/K+ in the shoot increased significantly only at 0.9% NaCl. These results indicated that the salt-tolerant mechanism of hybrid Pennisetum is salt exclusion, and its salinity threshold is 0.57% (about 100 mmol·L–1).

Interactive Effects of High Boron and NaCl Stresses on Subcellular Localization of Chloride and Boron in Wheat Leaves

AbstractSalinity and boron (B) toxicity often occur simultaneously and may have interactive effects on plant responses. This study aims at further investigating long‐term effects of salinity, B toxicity and their combination on wheat plants. Plants grown in hydroponics were treated with 2.5 μm H3BO3 (control), 75 mm NaCl, 200 μm H3BO3 or 75 mm NaCl + 200 μm H3BO3 and were analysed on a subcellular level 6 weeks after germination. Shoot fresh and dry weight (DW), water content, transpiration rate and osmolality were reduced, while Na+ and Cl− concentrations increased under salinity stress. However, Cl− was reduced in all compartments by an additional application of B toxicity. At adequate B supply, NaCl increased apoplastic and symplastic soluble B concentrations, whereas the total B content remained unchanged. At high B level, however, soluble and total B was reduced by additional salt stress. Despite this antagonistic effect of a combined salt and B toxicity stress on Cl− and B concentrations, an additive effect was observed regarding shoot fresh weight reduction. Our results confirm an alleviating effect of the combined stresses on toxic ion concentrations, which did not prevent additive growth reductions.

The Arabidopsis‐related halophyte Thellungiella halophila: boron tolerance via boron complexation with metabolites?

Tolerance to boron (B) is still not completely understood. We tested here the hypothesis that Thellungiella halophila, an Arabidopsis thaliana-related 'extremophile' plant, with abundance of B in its natural environment, is tolerant to B, and examined the potential mechanisms of this tolerance. With 1-10 mm B applied ([B](ext)) to Thellungiella and Arabidopsis grown in hydroponics, the steady-state accumulated B concentration ([B](int)) in the root was below [B](ext), and was similar in both, suggesting both extrude B actively. Whether grown in soil or hydroponically, the shoot [B](int) was higher in Arabidopsis than in Thellungiella, suggesting more effective net B exclusion by Thellungiella root. Arabidopsis exhibited toxicity symptoms including reduced shoot fresh weight (FW), but Thellungiella was not affected, even at similar levels of shoot-accumulated [B](int) (about 10 to 40 mm B in 'shoot water'), suggesting additional B tolerance mechanism in Thellungiella shoot. At [B](ext) = 5 mm, the summed shoot concentration of the potentially B-binding polyhydroxyl metabolites (malic acid, fructose, glucose, sucrose and citric acid) in Arabidopsis was below [B](int) , but in Thellungiella it was over twofold higher than [B](int) , and therefore likely to allow appreciable 1:2 boron-metabolite complexation in the shoot. This, we suggest, is an important component of Thellungiella B tolerance mechanism.

Effect of mixed cadmium, copper, nickel and zinc on seed germination and seedling growth of safflower

Elevated levels of heavy metals in contaminated soils are widely spread and concerns have been raised over the potential risks to humans, animals and agricultural crops. This study was conducted to evaluate the effect of mixed cadmium, copper, nickel and zinc on seed germination and seedling growth of safflower under controlled light and temperature conditions. Treatments were included 0 (control), 60, 120, and 180 mg kg-1 which were made by equal amounts of cadmium (¼), copper (¼), nickel (¼), and zinc (¼). The heavy metal mixture treatment showed toxic effects on seed germination and seedling growth of safflower. Increasing the concentration of heavy metal mixture to 180 mg kg-1 showed a significant decrease in seed germination as compared to control treatment (p<0.01). Heavy metal mixture concentration of 60 mg kg-1 reduced shoot fresh and dry weight (p<0.01). Root fresh and dry weight was diversely affected by the heavy metal treatment. However, the heavy metal mixture concentration of 180 mg kg-1 produced the lowest amount of both root fresh and dry weight. A negative response of root and shoot length of safflower to heavy metal mixture application relative to control treatment was observed at 120 mg kg-1 (p<0.01).The study suggests that cultivation of safflower in metal polluted soils should be avoided or appropriate control measures be adopted to maintain the heavy metal content of the soil below the damage threshold level. The heavy metal mixture treatment of 60 mg kg-1 exhibited the lowest percentage of tolerance in germination and seedling growth characteristics of safflower as compared to control. Key words: Germination, seedling growth, heavy metals, safflower.

Response of maize (Zea mays L.) to rimsulfuron under salt conditions

&lt;p&gt;Investigations were carried out to determine the possible interaction between salinity (60 mmol*dm&lt;sup&gt;-3&lt;/sup&gt; NaCl) and phytotoxicity of herbicide Titus 25 DF (sulfonylurea herbicide containing active ingredient rimsulfuron). The herbicide was added to the nutrient solution at two concentrations - 1 or 100 nmol*dm&lt;sup&gt;-3&lt;/sup&gt;. After 7 days of cultivation in the nutrient solution determined were the growth parameters and some biochemical compounds (photosynthetic pigments, total protein and free amino compounds content). The combined action of 1 nmol*dm&lt;sup&gt;-3&lt;/sup&gt; rimsulfuron and salt caused a reduction in plant biomass accumulation, but this reduction was due to the salt itself. In the presence of 100 nmol*dm&lt;sup&gt;-3&lt;/sup&gt; rimsulfuron, growth inhibition of maize roots was very high and salinity did not modify herbicide toxicity. However, reduction in maize shoots growth equalled the sum of the reductions caused by each particular factor applied separately (additive effect). The reduction in shoot fresh weight reached 64%.&lt;/p&gt;&lt;p&gt;The investigated stress factors induced a significant increase in amino compounds, with the exception of maize roots grown under NaCl plus 100 nmol-dm&lt;sup&gt;-3&lt;/sup&gt; rimsulfuron. The concentration of total protein in maize roots diminished under NaCl and 100 nmol*dm&lt;sup&gt;-3&lt;/sup&gt; rimsulfuron, although in the other cases, it did not change distinctly in comparison to the control. All factors, with the exception of NaCl, induced a slight increase in protein contents in maize leaves. Stress factors did not change significantly the total chlorophyll concentration, however, carotenoid content was markedly reduced. Nevertheless, the combined action of 100 nmol*dm&lt;sup&gt;-3&lt;/sup&gt; rimsulfuron and NaCl caused a 10% increase in carotenoid content as compared to the control plants.&lt;/p&gt;&lt;p&gt;In conclusion, salinity did not change the toxicity of the herbicide applied in low dose (1 nmol*dm&lt;sup&gt;-3&lt;/sup&gt;), but it did increase herbicide toxicity at high concentration (100 nmol*dm&lt;sup&gt;-3&lt;/sup&gt;) regarding the maize shoots.&lt;/p&gt;

Pitted and Hybrid Morningglory Accessions Have Variable Tolerance to Glyphosate

Two greenhouse studies were conducted to investigate the variability in tolerance to a sublethal dose of glyphosate among accessions of pitted morningglory, hybrid morningglory (a fertile hybrid between pitted and sharppod morningglory), and sharppod morningglory, collected from several states in the southern United States. The first study was conducted to evaluate the variability in tolerance to glyphosate among accessions. Glyphosate at 420 g ae/ha was applied to plants at the four- to five-leaf stage, and control (percent shoot fresh weight reduction) was determined 2 wk after treatment (WAT). Pitted morningglory response ranged from −9% (indicating no response to glyphosate) to 39% control. A similar trend was observed in hybrid morningglory. Control of two related species, cypressvine morningglory and red morningglory, averaged 40 and 29%, respectively, and was similar to control of the most susceptible pitted morningglory and hybrid morningglory accessions. Ivyleaf morningglory control was 9%. Sharppod morningglory control was highest (48%) among the morningglories studied. A second study was conducted to determine levels of tolerance to glyphosate based onGR50(dose required to cause a 50% reduction in plant growth) in 10 accessions that were least to most sensitive to glyphosate (7 pitted, 2 hybrid, and 1 sharppod morningglory). GlyphosateGR50doses ranged from 0.65 to 1.23 kg/ha, a two-fold variability in tolerance to glyphosate among the 7 pitted morningglory accessions. Increasing levels of tolerance were associated with the absence of a leaf notch. These results indicate the existence of variable tolerance to a sublethal dose of glyphosate among accessions of pitted morningglory.

Response of mycorrhizal periwinkle plants to aster yellows phytoplasma infection

The objective of our research was to assess if arbuscular mycorrhizal (AM) fungal colonization can modify the effect of infection by two aster yellows phytoplasma strains (AY1, AYSim) in Catharanthus roseus plants. Both phytoplasma strains had a negative effect on the root fresh weight, but they differed in symptoms appearance and in their influence on photosynthetic and transpiration rates of the periwinkle plants. AM plants showed significantly reduced shoot fresh weight, while the transpiration rate was significantly increased. AM fungal colonization significantly affected shoot height and fresh weight of the plants infected by each phytoplasma strains as well as the root system of plants infected with the more aggressive AYSim phytoplasma strain. Double inoculation did not reduce the negative effects induced with phytoplasma alone on the photosynthetic activity of phytoplasma-infected plants.

Glyphosate Tolerance Mechanism in Italian Ryegrass (Lolium multiflorum) from Mississippi

A threefold glyphosate tolerance was identified in two Italian ryegrass populations, T1 and T2, from Mississippi. Laboratory experiments were conducted to characterize the mechanism of glyphosate tolerance in these populations. The T1 population absorbed less14C-glyphosate (43% of applied) compared to the susceptible (S) population (59% of applied) at 48 h after treatment (HAT). The T2 population absorbed14C-glyphosate at levels (56% of applied at 48 HAT) that were similar to both T1 and S populations, but tended to be more comparable to the S population. The amount of14C-glyphosate that remained in the treated leaf was significantly higher in both T1 (67% of absorbed) and T2 (65% of absorbed) populations compared to the S population (45% of absorbed) at 48 HAT. The amount of14C-glyphosate that moved out of treated leaf to shoot and root was lower in both T1 (25% of absorbed in shoot and 9% of absorbed in root) and T2 (25% of absorbed in shoot and 11% of absorbed in root) populations compared to the S population (40% of absorbed in shoot and 16% of absorbed in root) at 48 HAT. There were no differences in epicuticular wax mass among the three populations. Treating a single leaf with glyphosate solution at the field use rate (0.84 kg ae ha−1) as 10 1-µl droplets killed the S plant but not the T1 and T2 plants (33 and 55% shoot fresh-weight reduction, respectively). Shikimic acid accumulated rapidly at higher levels in glyphosate-treated leaf segments of the S population compared to the T1 population up to 100 µM glyphosate. However, above 500 µM glyphosate, the levels of shikimate were similar in both the S and T1 populations. Furthermore, shikimic acid content was three- to sixfold more in whole plants of the S population treated with 0.22 kg ae ha−1glyphosate compared to the T1 and T2 populations. No degradation of glyphosate to aminomethylphosphonic acid was detected among the tolerant and susceptible populations. These results indicate that tolerance to glyphosate in the T1 population is partly due to reduced absorption and translocation of glyphosate and in the T2 population it is partly due to reduced translocation of glyphosate.

Colonization of root tissues and protection against Fusarium wilt of rye ( Secale cereale) by nonpathogenic rhizosphere strains of Fusarium culmorum

Colonization of rye ( Secale cereale) tissues by nonpathogenic rhizosphere Fusarium culmorum isolates DEMFc2 and DEMFc5 and a pathogenic strain DEMFc37, and their effect on plant fresh weight were studied in pot experiments. Both rhizosphere isolates colonized the epidermis and the cortex but were not found in vessels, while the pathogen colonized all three layers of root cells. The numbers of pathogen CFU isolated from plant tissues were much higher than those of the rhizosphere isolates in spite of the same number of macroconidia used as inoculum (1 × 10 5 g −1 of soil). Inoculation of seedlings with DEMFc2 resulted in a 20% increase, with DEMFc5 in more than a 20% reduction, and with DEMFc37 in a 38% reduction of shoot fresh weight of 14-day-old plants. Pre-colonization of plants with (either of) the rhizosphere isolates and subsequent inoculation with the pathogen resulted in plant weights the same as those observed in plants inoculated with the rhizosphere strain alone. The disease severity index for shoots of plants pre-colonized with DEMFc2 was reduced from class 4 (86% diseased plants) observed for plants inoculated with the pathogen alone to class 2 (average of 8% diseased plants) when pre-treated with the rhizosphere strain. The CFU number of the pathogen isolated from the interior of roots of plants pre-colonized with the rhizosphere isolates was as low as 10% of the number isolated from plants inoculated with the pathogen alone. A study of in vitro interactions between the rhizosphere isolates and the pathogen suggests that changes in plant colonization by the pathogen and its effect on fresh weight of plants pre-colonized with the rhizosphere isolates were not connected with inhibition of its growth by a direct action of the rhizosphere isolates. The results suggest that strain DEMFc2 can be considered as a potential biocontrol agent.

Glyphosate-Resistant and -Susceptible Soybean (Glycine max) and Canola (Brassica napus) Dose Response and Metabolism Relationships with Glyphosate

Experiments were conducted to determine (1) dose response of glyphosate-resistant (GR) and -susceptible (non-GR) soybean [Glycine max (L.) Merr.] and canola (Brassica napus L.) to glyphosate, (2) if differential metabolism of glyphosate to aminomethyl phosphonic acid (AMPA) is the underlying mechanism for differential resistance to glyphosate among GR soybean varieties, and (3) the extent of metabolism of glyphosate to AMPA in GR canola and to correlate metabolism to injury from AMPA. GR50 (glyphosate dose required to cause a 50% reduction in plant dry weight) values for GR (Asgrow 4603RR) and non-GR (HBKC 5025) soybean were 22.8 kg ae ha-1 and 0.47 kg ha-1, respectively, with GR soybean exhibiting a 49-fold level of resistance to glyphosate as compared to non-GR soybean. Differential reduction in chlorophyll by glyphosate was observed between GR soybean varieties, but there were no differences in shoot fresh weight reduction. No significant differences were found between GR varieties in metabolism of glyphosate to AMPA, and in shikimate levels. These results indicate that GR soybean varieties were able to outgrow the initial injury from glyphosate, which was previously caused at least in part by AMPA. GR50 values for GR (Hyola 514RR) and non-GR (Hyola 440) canola were 14.1 and 0.30 kg ha-1, respectively, with GR canola exhibiting a 47-fold level of resistance to glyphosate when compared to non-GR canola. Glyphosate did not cause reduction in chlorophyll content and shoot fresh weight in GR canola, unlike GR soybean. Less glyphosate (per unit leaf weight) was recovered in glyphosate-treated GR canola as compared to glyphosate-treated GR soybean. External application of AMPA caused similar injury in both GR and non-GR canola. The presence of a bacterial glyphosate oxidoreductase gene in GR canola contributes to breakdown of glyphosate to AMPA. However, the AMPA from glyphosate breakdown could have been metabolized to nonphytotoxic metabolites before causing injury to GR canola. Injury in GR and non-GR canola from exogenous application of AMPA was similar.

Diuron Sorption by Pine-Bark Substrate and Foliar vs. Root Absorption by Yellow Woodsorrel (Oxalis stricta)

Postemergence-applied diuron effectively controls yellow woodsorrel in nursery crops grown in pine bark–based container substrate. Whether the phytotoxicity of diuron on yellow woodsorrel is exclusively the result of foliar activity or is partially the result of root-based activity has not been determined. Application in which diuron was allowed to contact both the foliage and the pine bark–based substrate provided 84% control as determined by shoot fresh-weight reduction relative to that of a nontreated control. Foliar-only and root-only applications provided 52 and 12% shoot fresh-weight reduction, respectively. Absorption and translocation of foliar-applied diuron by yellow woodsorrel was evaluated using radiotracer techniques. After 24 h, 86% of the applied diuron had been absorbed, and 76% of the amount applied remained in the treated leaflet, indicating minimal translocation. Diuron sorption by the pine bark–based substrate was evaluated using radiotracer techniques. After 3 h, less than 6% of applied diuron remained in the aqueous phase, indicating 94% sorption. Exposing yellow woodsorrel roots to diuron concentrations as low as 0.50 mg/L resulted in injury, and concentrations equal to or greater than 10 mg/L resulted in death. Calculations described herein indicate the concentration that probably would occur within the aqueous solution held within the substrate following a 1.12-kg ai/ha application is sufficient to be phytotoxic to yellow woodsorrel. Thus, root-based absorption is a contributing factor in the overall efficacy of postemergence-applied diuron in controlling yellow woodsorrel.

Interchangeable functions of Arabidopsis PIROGI and the human WAVE complex subunit SRA1 during leaf epidermal development.

The WAVE complex is an essential regulator of actin-related protein (ARP) 2/3-dependent actin filament nucleation and cell shape change in migrating cells. Although the composition of the WAVE complex is well characterized, the cellular mechanisms that control its activity and localization are not well known. The 'distorted group' defines a set of Arabidopsis genes that are required to remodel the actin cytoskeleton and maintain the polarized elongation of branched, hair-like cells termed trichomes. Several loci within this group encode homologs of ARP2/3 subunits. In addition to trichome distortion, ARP2/3 subunit mutants have reduced shoot fresh weight and widespread defects in epidermal cell-cell adhesion. The precise cellular function of plant ARP2/3, and the means by which it is regulated, is not known. In this paper, we report that the 'distorted group' gene PIROGI encodes a homolog of the WAVE complex subunit SRA1. The similar cell shape and actin phenotypes of pir and ARP2/3 complex subunit mutants suggest that PIROGI positively regulates ARP2/3. PIROGI directly interacts with the small GTPase ATROP2 with isoform specificity and with selectivity for active forms of the protein. PIROGI shares only 30% amino acid identity with its human homolog. However, both WAVE subunit homologs are functionally interchangeable and display identical physical interactions with RHO family GTPases and the Arabidopsis homolog of the WAVE complex subunit NAP125. These results demonstrate the utility of the 'distorted group' mutants to study ARP2/3 complex functions from signaling input to cell shape output.