Effect of Rice Straw Incorporation on Phytotoxicity of Isoxaflutole to an Exotic Weed Phalaris minor Retz.

Phalaris minorRetz. is a major exotic annual weed in the wheat (Triticum aestivum L.) crop. Unharvested rice (Oryza sativa L.) straw, unburned and burned, is often incorporated in the field prior to cultivating wheat. Isoxaflutole (Balance), a pre-emergent systemic soil applied herbicide, has potential to control P. minor. Glasshouse experiments were conducted to determine the phytotoxicity of isoxaflutole defined by reductions in relation to shoot length of P. minor when grown in unamended soil or soil amended with unburned or burned rice straw. A 120 g soil was amended with 0, 1, 2 and 4 g of unburned or burned rice straw, and placed in 150 mL styrofoam pots. Appropriate amount of isoxaflutole (75% active ingredient, ai) was added to pots to get final concentration of 0, 7.5, 30, 60 and 120 μg ai/pot. Unamended soil and soil amended with unburned or burned rice straw were analyzed for pH and organic matter; two important determinants of isoxaflutole activity. Results indicate a significant reduction in shoot length of P. minor when grown in soil treated with isoxaflutole at 30, 60 or 120 μg ai/pot. Inhibition in the shoot length of P. minor was observed when soil amended with unburned straw was treated with isoxaflutole at 7.5 and 30 μg ai/pot compared with unamended soil treated with similar amounts of isoxaflutole. No significant change in isoxaflutole toxicity was observed when soil amended with unburned straw was treated with isoxaflutole at 60 and 120 lg ai/pot compared with unamended soil treated with similar amounts of isoxaflutole. Isoxaflutole phytotoxicity to P. minor shoot length was eliminated when soil amended with burned straw was treated with isoxaflutole at 7.5 and 30 μg ai/pot. P. minor shoot length was greater when soil amended with burned straw was treated with isoxaflutole at 60 and 120 μg ai/pot relative to herbicide-treated unamended soils. We conclude that incorporation of burned rice straw greatly reduces the phytotoxicity of isoxaflutole toP. minor.     

Phytotoxicity of selected herbicides to mung bean (Phaseolus aureus Roxb.)

Mung bean (Phaseolus aureus Roxb.) is grown after harvest of wheat during the fallow period. Herbicides such as metsulfuron, atrazine and isoxaflutole are recommended to control weeds in wheat–rice cropping system including weeds of fallow crop. The effects of three herbicides with different modes of action—atrazine, photosystem II inhibitor; metsulfuron, acetolactate synthase inhibitor; and isoxaflutole, 4-hydroxyphenylpyruvatedioxygenase inhibitor—on shoot height, chlorophyll concentrations and cellular damage in herbicide-treated mung bean were studied. While isoxaflutole inhibited shoot growth and chlorophyll concentration of mung bean, atrazine and metsulfuron did not cause reduction in the shoot growth of mung bean. Metsulfuron (226, 452, 1356 and 2260 μg/kg soil) and isoxaflutole (452, 1356 and 2260 μg/kg soil) in soil reduced the concentration of leaf chlorophyll of mung bean compared to the control. Atrazine in soil did not affect the total chlorophyll concentration of mung bean leaves. Electron micrographs showed that untreated mung bean had elongated chloroplasts, thylakoids organized as intact grana, distinct starch grains and a small number of plastoglubuli. Mesophyll cells of atrazine-treated mung bean leaves had swollen chloroplasts and thylakoids with disorganized grana. Leaves of metsulfuron-treated mung bean had swollen chloroplasts with a large number of starch grains. Starch grains were not observed in leaves of mung bean treated with either atrazine or isoxaflutole. Complete disruption of thylakoids was observed in isoxaflutole-treated mung bean leaves. Leaves of atrazine-treated mung bean showed detached microfibrils along with distorted and degenerated secondary walls. Metsulfuron-treated mung bean leaves showed aggregated microfibrils with completely dissolved secondary walls, while isoxaflutole-treated leaves had completely degenerated secondary walls with complete loss of microfibrils. We conclude that isoxaflutole at higher doses, influence mung bean at the morphological, physiological and cellular levels.     

Phosphorus deficiency-induced reduction in root hydraulic conductivity in Medicago falcata is associated with ethylene production

Plants grown in phosphorus-deficient solutions often exhibit disruption of water transport due to reduction in root hydraulic conductivity (Lpr) and enhanced ethylene production. To uncover the relationship between the reduction in Lpr and increase in ethylene production, we investigated effect of phosphorus (P) deficiency on ethylene production and Lpr in legume plants of Medicago falcata L. There was an increase in ethylene production and a reduction of Lpr of M. falcata roots when M. falcata seedlings grown in P sufficient solutions (0.5 mM H₂PO₄^2?) were transferred to P-deficient solutions (5 μM H₂PO₄^2?). Antagonists of ethylene biosynthesis, CoCl₂ and aminoethoxyvinylglycine (AVG), abolished the P deficiency-induced ethylene production. Root hydraulic conductivity of M. falcata seedlings grown in P-sufficient solutions was insensitive to CoCl₂ and AVG, while the two chemicals enhanced Lpr for those grown in P-deficient solutions, suggesting that P deficiency-induced decrease in Lpr can be reversed by inhibiting ethylene production. Ethylene precursor 1-amino cyclopropane-1-carboxylic acid (ACC) and ethylene donor ethephon had greater inhibitory effect on Lpr of P-sufficient seedlings than that of P-deficient seedlings. Root hydraulic conductivity of P-sufficient seedlings was more sensitive to HgCl₂ than that of P-deficient seedlings. Taken together, these findings suggest that ethylene induced by P deficiency may play an important role in modulation of root hydraulic conductivity by affecting aquaporins in plants.     

Role of iron plaque in Cd uptake by and translocation within rice (Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L⁻¹) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L⁻¹) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L⁻¹ Fe were exposed to ¹⁰⁹Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe₀ at Cd_0.1, and at Cd_1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of ¹⁰⁹Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to ¹⁰⁹Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.     

Effect of salinisation of soil on growth, water status and general nutrient accumulation in seedlings .of Delonix regia (Fabaceae)

Greenhouse experiments were conducted to assess the effect of salinisation of soil on emergence, growth, water content, proline content and mineral accumulation of seedlings of Delonix regia (Hook.) Raf. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 1.9, 3.9, 6.0 and 7.9 dS m^?1. A negative relationship between seedling emergence and salt concentration was obtained. Salinity caused reduction in water content and water potential of tissues (leaves, stems, tap roots and lateral roots) that resulted in internal water deficit to plants. Consequently, shoot and root elongation, leaf expansion and dry matter accumulation in leaves, stems, tap roots and lateral root tissues of seedlings significantly decreased in response to increasing concentration of salt. Proline content in tissues was very low. There were no effective mechanisms to control net uptake of Na on root plasma membrane and subsequently its transport to shoot tissues. Potassium content significantly decreased in tissues in response to salinisation of soil. This tree species is a moderate salt-tolerant glycophytic plant. Nitrogen and calcium content in tissues significantly decreased as soil salinity increased. Phosphors content in tissues exhibited a declining trend with increase in soil salinity. Changes in tissues and whole-plant accumulation pattern of other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species in response to salinisation, are discussed.     

Salt tolerant Methylobacterium mesophilicum showed viable colonization abilities in the plant rhizosphere

The source of infection has always been considered as an important factor in epidemiology and mostly linked to environmental source such as surface water, soil, plants and also animals. The activity of the opportunistic pathogens associated with plant root, their adaptation and survival under hostile environmental condition is poorly understood. In this study the salt tolerance ability of Methylobacterium mesophilicum and its colonization in the root and shoot of plants under severe drought and salt stress conditions were investigated. The colonization of plant by M. mesophilicum was investigated in a gnotobiotic sand system, and their survival in pots with saline soil. Bacterial strain was found to colonize rhizosphere of cucumber, tomato and paprika grown under normal and salt stress condition and reached up to 6.4 × 10⁴ and 2.6 × 10⁴ CFU/g root. The strain was resistant to Gentamicin, Ampicillin, Amoxicillin plus Clavulanic acid, Cefotaxime, neomycin, penicillin and was also tolerant to salinity stress (up to 6% NaCl). These abilities play important roles in enabling persistent colonization of the plant surface by M. mesophilicum strains. In conclusion, this study provides background information on the behaviour of opportunistic pathogen M. mesophilicum on plants and their survival in harsh environmental conditions.     

Nature of the Interference Mechanism of Sugarcane (Saccharum officinarum L.) Straw

Sugarcane (Saccharum officinarum L.) straw left in the field after harvest interferes with the growth of winter and summer weeds. In the last years, there was a progressive move away from burning sugarcane straw to retaining it on the soil surface after harvest to prevent soil degradation and environmental pollution. Water-soluble phenolics leachated from straw into soil may suppress weed growth. A study was carried out to investigate (1) the effect of biotic (unautoclaved) soil treated with burned and unburned sugarcane straw leachates on seedling growth and foliar proline content of beggarticks (Bidens subalternans L.) and wild mustard (Brassica campestris L.), (2) the modification of sugarcane straw phytotoxicity in abiotic (autoclaved) soil and biotic (unautoclaved) soil plus activated charcoal, and (3) changes of inorganic ions and phenolic contents in biotic soil after treatment with burned and unburned sugarcane straw leachate. Unburned straw leachate significantly inhibited root elongation of 7-d-old beggarticks and wild mustard seedlings. Burned straw leachate did not affect seedling growth of the assayed weeds suggesting that organic straw phytotoxins were involved. Experiments with activated charcoal, however, did not provide clear evidence supporting the involve of organic molecules in straw phytotoxicity. Unburned straw leachate incorporated in biotic soil was more inhibitory than in abiotic soil on root growth suggesting that microbial activity is involved in sugarcane straw interference. There was no evidence of nutrient microbial immobilization. Unburned sugarcane straw leachate increased total phenolic content in biotic soil more than in abiotic soil or biotic soil plus charcoal. Burned sugarcane straw leachate did not increase phenolic compounds levels in biotic soil. Linear regression analysis indicated a strong correlation between levels of soil phenolic contents and root growth inhibition. Soil characteristics evaluated in soil treated with burned and unburned sugarcane straw leachate suggest that straw phytotoxicity is related with organic molecules, such as phenolic compounds, rather than to variations in inorganic nutrients. Unburned straw leachate induced proline accumulation in seedling leaves of both beggarticks and wild mustard. Proline foliar content was higher in seedlings grown in biotic soil than in seedlings grown in biotic soil plus charcoal suggesting that straw organic constituents induced proline accumulation. Proline foliar content of seedlings grown in biotic soil treated with burned straw leachate was not significantly different from water control. The present study showed that sugarcane straw leachate interferes with seedling growth of beggarticks and wild mustard and that water-soluble phenolics can play a role in the seedling growth inhibition of the assayed weeds.     

Auxin-cytokinin synergism in vitro for producing genetically stable plants of Ruta graveolens using shoot tip meristems

An efficient micropropagation protocol was developed for Ruta graveolens Linn. using shoot tip meristems derived from a 4-month-old field grown plant. In vitro shoot regeneration and proliferation was accomplished on Murashige and Skoogs (MS) semi-solid medium in addition to different doses of cytokinins viz.6- benzyl adenine (BA), Kinetin (Kn) or 2-isopetynyl adenine (2iP), singly or in combination with auxins viz. indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) or α-naphthalene acetic acid (NAA). Highest regeneration frequency (27.6%) was obtained on (MS) medium composed of BA (10 µM) with maximum number (9.4) of shoots and 4.3 cm shoot length after 4 weeks of incubation. Among various combinations tried best regeneration frequency (71%) of multiple shoot formation with highest number (12.6) of shoots per shoot tip explants were achieved in MS medium augmented with a combination BA (10.0 µM) and NAA (2.5 µM) after 4 weeks of incubation. The optimum frequency (97%) of rhizogenesis was achieved on half-strength MS medium having 0.5 µM IBA after 4 weeks of incubation. Tissue culture raised plantlets with 5–7 fully opened leaves with healthy root system were successfully acclimatized off in Soilrite? with 80% survival rate followed by transportation to normal soil under natural light. Genetic stability among in vitro raised progeny was evaluated by ISSR and RAPD markers. The entire banding pattern revealed from in vitro regenerated plants was monomorphic to the donor. The present protocol provides an alternative option for commercial propagation and fruitful setting up of genetically uniform progeny for sustainable utilization and germplasm preservation.     

Impact of rock materials and biofertilizations on P and K availability for maize (Zea Maize) under calcareous soil conditions

The present work evaluated the synergistic effects of soil fertilization with rock P and K materials and co-inoculation with P and K-dissolving bacteria [PDB (Bacillus megaterium var. phosphaticum) and KDB (Bacillus mucilaginosus and B. subtilis)] on the improvement of P and K uptake, P and K availability and growth of maize plant grown under limited P and K soil conditions (calcareous soil). The experiment was establishment with eight treatments: without rock P and K materials or bacteria inoculation (control), rock P (RP), rock K (RK), RP + PDB, RK + KDB and R(P + K)+(P + K)DB. Under the same conditions of this study, co-inoculation of PDB and KDB in conjunction with direct application of rock P and K materials (R(P + K)) into the soil increased P and K availability and uptake, and the plant growth (shoot and root growth) of maize plants grown on P and K limited soils.     

Effect of arsenic on visible symptom and arsenic concentration in hydroponic Japanese mustard spinach

Responses of Japanese mustard spinach (JM-spinach; Brassica rapa L. var. pervirdis) were investigated at elevated levels of arsenic (As). Plants were grown hydroponically in the greenhouse under 0, 6.7, 33.5 and 67 μM As (equal to 0, 0.5, 2.5 and 5 mg L^?1 As, respectively) for 14 days. Arsenic was used as sodium meta-arsenite (NaAsO₂). Toxicity symptom was solely shown as shoot growth repression at 33.5 and 67 μM As exposures. Dry weight (DW) enhanced by 19.4% in shoot and 38.9% in root in the 6.7 μM As level as compared to control but decreased by 48.1% and 72.1% DW in shoot and 24.1% and 61.1% DW in root in the 33.5 and 67 μM As levels, respectively. This result indicated that As at lower concentration might have slight stimulating effect on JM-spinach growth, but toxicity increased with increasing As. Based on the regression lines between growth and As concentration in the plant tissues, the critical toxicity level (CTL) of As in JM-spinach shoot was 7.85 μg g^?1 DW considering 10% DW reduction. The CTL for the root was almost 2110 μg As g^?1 DW, indicating that shoot of JM-spinach was more sensitive to As-toxicity than that of root. Arsenic concentrations increased in plant parts with increasing As in the medium. Arsenic concentrations were also compared in DW and fresh weight (FW) basis. The JM-spinach concentrated unaccepted level of As in shoots for human consumption in the higher As levels without showing visible toxicity symptom. In spite of decreasing iron (Fe) concentration in shoot in the highest As level, chlorophyll index did not decrease accordingly. Phosphorus (P) concentration also decreased. Phosphorus concentration decreased much more than Fe concentration. Low P might help to mobilize Fe in shoots, resulting in higher chlorophyll index at 67 μM As level. Phosphorus might compete with Fe in shoot tissues of As-stressed JM-spinach.     

Cellular evidence of allelopathic interference of benzoic acid to mustard (Brassica juncea L.) seedling growth.

Cellular changes in the roots of mustard (Brassica juncea L.) grown in soil treated with 1.09, 1.46 and 1.83 mg benzoic acid per g soil, a known allelochemical, were analyzed after 7 days. The recoverable concentration of 1.09, 1.46 and 1.8 mg benzoic acid per g soil (measured by high performance liquid chromatography) was 68, 150 and 250 microg benzoic acid per g soil, respectively. The benzoic acid treatments suppressed root growth by 30.5%, 58.8% and 81.1% with increasing concentrations. Transmission electron microscopy studies of roots showed irregular shaped cells arranged in disorganized manner and disruption of cell organelles at cellular level. Root cells showed dissolution of middle lamella (at 68 and 150 microg benzoic acid per g soil) but intact middle lamella with increased wall deposits was observed with 250 microg benzoic acid per g soil. Damage to the mustard root at cellular level was evidenced by changes in cell morphology and internal organization.     

Salt stress response in tomato beyond the salinity tolerance threshold

Crop salt tolerance is generally assessed as the relative yield response to increasing root zone salinity, expressed as soil (EC_e) or irrigation water (EC_w) electrical conductivity. Alternatively, the dynamic process of salt accumulation into the shoot relative to the shoot biomass has also been considered as a tolerance index. These relationships are graphically represented by two intersecting linear regions, which identify (1) a specific threshold tolerance, at which yield begins to decrease, and (2) a declining region, which defines the yield reduction rate. Although the salinity threshold is intuitively a critical parameter for establishing plant salt tolerance, we focused our interest on physiological modifications that may occur in the plant at salinity higher than the so-called tolerance threshold. For this purpose, we exposed hydroponically grown tomato plants to eight different salinity levels (EC = 2.5 (non-salinized control); 4.2; 6.0; 7.8; 9.6; 11.4; 13.2; 15.0 dS m⁻¹). Based on biomass production, water relations, leaf ions accumulation, leaf and root abscisic acid and stomatal conductance measurements, we were able to identify a specific EC value (approximately 9.6 dS m⁻¹) at which a sharp increase of the shoot and root ABA levels coincided with (1) a decreased sensitivity of stomatal response to ABA; (2) a different partitioning of Na⁺ ions between young and mature leaves; (3) a remarkable increase of the root-to-shoot ratio. The specificity and functional significance of this response in salt stress adaptation is discussed.     

Characterization of calnexin in soybean roots and hypocotyls under osmotic stress

Calnexin is an endoplasmic reticulum-localized molecular chaperone protein which is involved in folding and quality control of proteins. To evaluate the expression of calnexin in soybean seedlings under osmotic stress, immunoblot analysis was performed using a total membrane protein fraction. Calnexin constantly accumulated at an early growth stage of soybean under normal growth conditions. Expression of this protein decreased in 14-day-old soybean roots when treated with 10% polyethylene glycol for 2 days. Other abiotic stresses such as drought, salinity, cold as well as abscisic acid treatment, similarly reduced accumulation of calnexin and this reduction was correlated with reduction in root length in soybean seedlings under abiotic stresses. When compared between soybean and rice, calnexin expression was not changed in rice under abiotic stresses. Using Flag-tagged calnexin, a 70 kDa heat shock cognate protein was identified as an interacting protein. These results suggest that osmotic or other abiotic stresses highly reduce accumulation of the calnexin protein in developing soybean roots. It is also suggested that calnexin interacts with a 70 kDa heat shock cognate protein and probably functions as molecular chaperone in soybean.     

Influence of inoculation with plant growth promoting rhizobacteria (PGPR) on tomato plant growth and nematode reproduction under greenhouse conditions

Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J₂/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.     

Ectomycorrhiza affect architecture and nitrogen partitioning of beech (Fagus sylvatica L.) seedlings under shade and drought

The aim of this study was to investigate the influence of ectomycorrhizal fungi (EMF) on the architecture of and nitrogen (N) partitioning in young beech (Fagus sylvatica) plants in response to different light regimes and water deprivation. We hypothesized that EMF modify biomass partitioning and architecture of young beech plants by increased N uptake in comparison with non-mycorrhizal (NM) plants and that therefore, the drought responses of EM and NM plants diverge. We anticipated that full light-exposed plants were more drought tolerant due to improved water status and nutrition, whereas shade-acclimated EM plants were more drought susceptible because of decreased mycorrhizal colonization. To test these hypotheses seedlings were grown in native or sterilized forest soil. To avoid effects of soil pretreatment NM and EM plants were transplanted into sand-peat culture systems and exposed to shade, drought or the combination of both factors. Shade resulted in reduced root biomass production decreasing the root-to-shoot ratio. Mild drought stress (pre-dawn water potential [Ψ_pd] = −1.3 MPa) did not affect biomass partitioning. EMF colonization did not increase plant biomass, but had strong effects on root architecture: the numbers of root tips as well as the absolute and specific root lengths were increased because of formation of thin roots, especially in the diameter classes from 0.2 to 0.8 mm. In contrast to our expectation N uptake of well irrigated EM plants was not increased despite their larger potential for soil exploitation. Overall, EM plants exhibited higher amounts of carbon fixed per unit of N taken up than NM plants and shifted N partitioning towards the roots. Beneficial effects of EMFs were apparent under mild drought but the responses differed depending on the light availability: shaded EM plants showed a delay in the decrease of Ψ_pd; light exposed EM plants showed increased N uptake compared with NM beeches. These results indicate that EMFs are involved in mediating divergent responses of beech to drought depending on the light availability.     

Influence of phosphorus nutrition on growth and metabolism of Duo grass (Duo festulolium)

Use of suitable plants that can extract and concentrate excess P from contaminated soil serves as an attractive method of phytoremediation. Plants vary in their potential to assimilate different organic and inorganic P-substrates. In this study, the response of Duo grass (Duo festulolium) to variable rates of soil-applied potassium dihydrogen phosphate (KH₂PO₄) on biomass yield and P uptake were studied. Duo grown for 5 weeks in soil with 2.5, 5 and 7.5 g KH₂PO₄ kg^?1 soil showed a significantly higher biomass and shoot P content of 8.3, 11.4 and 12.3 g P kg^?1 dry weight respectively compared to plants that received no soil added P. Also, the ability of Duo to metabolize different forms of P-substrates was determined by growing them in sterile Hoagland's agar media with different organic and inorganic P-substrates, viz. KH₂PO₄, glucose-1-phosphate (G1P), inositiol hexaphosphate (IHP), adenosine triphosphate (ATP) and adenosine monophosphate (AMP) for 2 weeks. Plants on agar media with different P-substrates also showed enhanced biomass yield and shoot P relative to no P control and the P uptake was in the order of ATP > KH₂PO₄ > G1P > IHP = AMP > no P control. The activities of both phytase (E.C.3.1.3.26) and acid phosphatases (E.C.3.1.3.2) were higher in all the P received plants than the control. Duo grass is capable of extracting P from the soil and also from the agar media and thus it can serve as possible candidate for phytoextraction of high P-soil.     

Changes of phenylethanoid and iridoid glycoside distribution in various tissues of shoot cultures and regenerated plants of Harpagophytum procumbens (Burch.) DC. ex Meisn

Harpagophytum procumbens is a medicinal plant containing several compounds with pharmaceutical activity. Previously, we established shoot culture and in vitro regenerated plants of H. procumbens. In this study, HPLC and LC-ESI-MS were used to identify harpagoside, harpagide, verbascoside and isoverbascoside in various tissues (stems, leaves and callus) of shoots multiplied on Schenk and Hildebrandt (SH) solid medium supplemented with 0.57 μM indole-3-acetic acid (IAA) and 8 μM 6-benzylaminopurine (BAP), as well as in stems, leaves and root tubers of in vitro propagated plants grown in the greenhouse for 3, 6 and 12 months. The content of the compounds was also determined by HPLC. For comparison, control H. procumbens plants initiated from seeds were analyzed. H. procumbens shoots grown under in vitro conditions accumulated lower amounts of iridoids and phenylethanoids than the plants derived from them. The levels of analyzed compounds were higher in the organs of 3- or 6-month-old plants than in those of 12-month-old plants. Differences in the distribution of secondary metabolites were also observed between organs. The aerial parts (stems, leaves) of 3-month-old in vitro regenerated plants were characterized by the highest amounts of phenylethanoids, which significantly exceeded those detected in control plants. Total iridoid content, calculated as the sum of harpagoside and harpagide, was highest in the root tubers of 6-month-old plants. In these organs the level of harpagoside was comparable to that in root tubers of 6-month-old seed-propagated plants, but the level of harpagide was much lower.     

Production of rhoifolin and tiliroside from callus cultures of Chorisia chodatii and Chorisia speciosa

The current work aims to stimulate the production of rhoifolin and tiliroside as two valuable phytochemicals from Chorisia chodatii Hassl. and Chorisia speciosa A. St.-Hil. callus cultures. A comparison between three explants from the in vitro germinated seedlings of both species for callus induction and accumulation of both flavonoids was carried out. Highly efficient calluses were induced from the leaves, stems and roots of C. chodatii seedlings on Gamborg’s B5 (B5) and Murashige and Skoog (MS) media containing 2.0 mg/l β-naphthalene acetic acid (NAA) and 0.5 mg/l 6-benzyladenin (BA) or kinetin (Kn), while those of C. speciosa seedlings efficiently produced calluses on both media supplemented with 0.5 or 1.0 mg/l NAA and 0.5 mg/l BA. Besides, the highest contents of rhoifolin (1.927 mg/g DW) and tiliroside (1.776 mg/g DW) from C. speciosa cultures were obtained from the calluses of seedlings’ roots and stems maintained on B5 medium containing 1.0 mg/l NAA and 0.5 mg/l BA, respectively. On the other hand, the maximum rhoifolin content (0.555 mg/g DW) from C. chodatii cultures was obtained from the calluses of seedlings’ stems grown on B5 medium supplemented with 2.0 mg/l NAA and 0.5 mg/l BA, whereas the highest tiliroside content (0.547 mg/g DW) was provided by the root explants on B5 medium containing 2.0 mg/l NAA and 0.5 mg/l Kn. Both flavonoids were bioaccumulated in greater amounts than the wild and cultivated intact plants, which provides a promising tool for their future commercial production under a controlled environment, independent of climate and soil conditions.     

Uptake of intact amino acids by plants depends on soil amino acid concentrations

Studies in different ecosystems have shown that plants take up intact amino acids directly but little is known about the influence of free amino acid concentrations in the soil on this process. We investigated the effect of three different soil amino acid N concentrations (0.025, 0.13 and 2.5 μg N g^?1 soil) on direct uptake of four dual labelled (¹⁵N, ¹³C) amino acids (glycine, tyrosine, lysine, valine) in a greenhouse experiment using Anthoxantum odoratum as a model plant.Our results revealed that 8–45% of applied ¹⁵N was incorporated into plant root and shoot tissue 48 h after labelling. Additional ¹³C enrichment showed that 2–70% of this incorporated ¹⁵N was taken up as intact amino acid. Total ¹⁵N uptake and ¹⁵N uptake as intact amino acids were significantly affected by soil amino acid N concentrations and significantly differed between the four amino acids tested.We found a positive effect of soil amino acid concentrations on uptake of mineralized ¹⁵N relative to amino acid concentrations for all amino acids which was presumably due to higher diffusion rates of mineralized tracer to the root surface. However, intact amino acid uptake relative to amino acid concentrations as well as the proportion of total ¹⁵N taken up directly decreased with increasing soil amino acid N concentrations for all amino acids, irrespective of their microbial degradability. This effect is most likely controlled by the mineral N concentration in soil and perhaps in plants which inhibits direct amino acids uptake.Overall, we conclude that plant internal regulation of amino acid uptake controlled by mineral N is the main mechanism determining direct uptake of amino acids and thus a lower contribution of intact amino acid uptake to the plants N nutrition has to be expected for higher amino acid concentrations accompanied by mineralization in soil.     

Phytotoxicity of isoxaflutole to Phalaris minor Retz.

Littleseed canarygrass (Phalaris minor Retz.) is a major weed in wheat fields, and has developed resistance to the commonly used herbicide isoproturon. This study explores the potential use of isoxaflutole, a pre-emergence herbicide, to control littleseed canarygrass. Greenhouse studies were carried out to determine the phytotoxicity of isoxaflutole in relation to shoot height, fresh shoot biomass and leaf chlorophyll concentration of wheat and littleseed canarygrass. Electron microscopy was used to examine any damage to leaf chloroplast at ultrastructural level. Results indicate that isoxaflutole (0.5 mg/L) significantly reduced the shoot height of littleseed canarygrass (39.6%), but no significant reduction in the shoot height of wheat was observed (9.6%) when compared to control. None of the concentrations (0.05, 0.1, 0.5 and 1 mg/L) of isoxaflutole altered soil chemistry in relation to pH, organic matter, macro or micro inorganic ions. While untreated littleseed canarygrass leaves had elongated chloroplast, starch grains and small number of plastoglobuli; treated littleseed canarygrass leaves had swollen chloroplast, large number of plastoglobuli, and a lack of starch grains. We conclude that isoxaflutole can be an effective herbicide for controlling littleseed canarygrass.