Production of emetic alkaloid by in vitro culture of cephaelis ipecacuanha A. Richard

Callus and adventitious roots were induced on leaf segments from shoot culture of Cephaelis ipecacuanha A. Richard on Murashige-Skoog medium containing 2,4-dichlorophenoxyacetic acid, indole-3-acetic acid, 1-naphthaleneacetic acid and kinetin. The contents of emetic alkaloids in calli, roots and root suspension cultures were quantified by HPLC. Roots cultured in solid and liquid Murashige-Skoog media yielded emetine and cephaeline. The amount of the two alkaloids in the root suspension culture was very similar to that of roots from ipecac mother plant grown in a greenhouse. In contrast, calli subcultured on Murashige-Skoog media containing combinations of 2,4-dichlorophenoxyacetic acid and kinetin produced only trace amounts of emetic alkaloids.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - NAA l-naphthaleneacetic acid - Kin kinetin - MS Murashige-Skoog - EM emetine - CP cephaeline - DW dry weight.     

Hormones in the grains and roots in relation to post-anthesis development of inferior and superior spikelets in japonica/indica hybrid rice

Grain filling is usually not adequate in later-flowering inferior spikelets in japonica/indica (J/I) hybrid rice (Oryza sativa) although it shows stronger hybrid vigor than indica/indica (I/I) hybrid. This study investigated the potential causes by examining changes in zeatin (Z) + zeatin riboside (ZR), indole-3-acetic acid (IAA), gibberellins (GAs, GA₁ + GA₄), and abscisic acid (ABA) in spikelets and roots during the grain filling period. The inferior spikelets of J/I hybrid exhibited low rate of endosperm cell division and slow grain filling. During the early grain filing period, they had less Z + ZR, IAA, and ABA, but more GAs, than the earlier-flowering superior spikelets. If compared to the inferior spikelets of the I/I hybrid, the J/I inferior spikelets also had less Z + ZR, IAA, and ABA. Rates of endosperm cell division and grain filling were positively and significantly correlated with Z + ZR and ABA contents in both grains and roots or IAA in grains, whereas not significantly correlated with GAs either in grains or roots or IAA in roots. Applications of kinetin, IAA, or ABA to spikelets, or kinetin and ABA to roots, enhanced cell division and grain filling in the inferior spikelets. Results suggest that low contents of cytokinins and ABA in both grains and roots and low contents of IAA in grains may result in the poor filling of inferior spikelets in the J/I hybrid.     

Cadmium distribution and its effects on molybdate-containing hydroxylases in Phragmites australis

The influence of cadmium (Cd) on physiological and biochemical parameters was studied to elucidate the mechanism of Cd resistance in Phragmites australis. Cadmium concentrations in roots, stems and leaves increased with exogenous Cd concentration, but Cd content in roots was much higher than in shoots. X-ray microanalysis was used to reveal compartments in which Cd accumulated in root cortex. Cadmium concentrations followed a gradient with the sequence: intercellular space > cell wall > vacuole > cytoplasm, indicating that most Cd was immobilized in the apoplast or sequestered into the vacuolar lumen. Sequential extraction of various Cd chelates revealed that more than half of extractable Cd was bound to proteins, whereas 26% was bound to organic acids. Cd-binding protein fractions were found in the roots after gel filtration chromatography, among which a polypeptide with an apparent molecular mass of 14 kDa bound Cd most avidly. One newly synthesized polypeptide of low molecular mass (1 kDa) appeared under Cd pollution, whereas a prominent fraction of 72 kDa disappeared. Four aldehyde oxidase (AO) isoenzyme activities increased significantly in roots under Cd pollution. Cd stress also enhanced xanthine dehydrogenase (XDH) activities in roots. Two AO polypeptides of different molecular sizes were detected in the roots by Western blot assay. The abundance of the 160 kDa subunit correlated with Cd stress, but the amount of the 90 kDa polypeptide did not change under Cd treatment. Enhanced abscisic acid (ABA) contents were observed in roots of P. australis exposed to Cd. The involvement of Cd distribution in plant tissues and subcellular compartments and of AO and XDH enzymatic activities in the acclimation mechanism of P. australis to Cd pollution is discussed herein.     

Traditional and non-traditional plant growth regulators alters phytochemical constituents in Catharanthus roseus

The effect of different plant growth regulators (PGR) and elicitor treatments on the alkaloid profile variation of Catharanthus roseus was investigated in the present study. The PGR used were paclobutrazol (PBZ), gibberellic acid (GA₃) and Pseudomonas fluorescens elicitors (PF Elicitors). The estimated alkaloids were ajmalicine, catharanthine, tabersonine, serpentine and vindoline. In roots, the ajmalicine content increased significantly under all the treatments on all sampling days. In roots, the catharanthine contents increased with the age in control and growth regulator treatments, but the increase was not prominent and significant in PGR treatments when compared to controls. The serpentine contents of the plant increased with PGR treatments, but the increase was more prominent in PBZ treatments when compared to other treatments. The increase was in the order PBZ > PF Elicitors > GA₃. C. roseus never showed any significant increase in tabersonine contents in the roots under GA₃ treatments, but it increased significantly under PBZ and PF Elicitors when compared to control plants. The root vindoline contents increased with PBZ and PF Elicitors treatments but the decreased under GA₃ treatments when compared to control plants. Our results have good significance, as these increases the secondary metabolites of this traditional medicinal plant.     

The impact of heavy metals on the activity of some enzymes along the barley root

Barley seedlings 48 h after the onset of germination on filter paper treated for 24 h by 1 mM cadmium (Cd), 3 mM nickel (Ni) or 0.5 mM mercury (Hg) showed similar approximately 45% root growth inhibition. Although root growth inhibition was similar, loss of cell viability evaluated, as Evans blue uptake was distinct among Cd, Ni and Hg treated roots. While Cd and Hg caused cell death along the whole barley root (0–8 mm), Ni induced significant loss of cell viability only in root cells 6–8 mm distance from the root tip. Our results suggest that different metabolic processes are activated in different parts of barley root in relation to distance from the root tip during heavy metal (HM) treatment. Some of them are characteristic for several HMs such as inhibition of ascorbic acid oxidase or glutathione-S-transferase stimulation, while others are specific for individual HMs, e.g. activation of acid phosphatase and lipoxygenase by Cd and Hg, or inhibition of ascorbate peroxidase by Ni and Hg treatment.     

Chemical characterization,in vitro dry matter and ruminal crude protein degradability and microbial protein synthesis of some cowpea (Vigna unguiculata L. Walp) haulm varieties

A study was carried out to evaluate the chemical composition, in vitro apparently and truly degraded dry matter (DM), utilizable crude protein at the duodenum (uCP) (total CP at the duodenum minus endogenous CP), methane production, and short chain fatty acid production of haulms of six cowpea varieties. The study was arranged in a 2 × 2 × 2 factorial design, with three replicates. Three improved (ITA2, ITA6 and ITA8) and three commercial (Oloyin, Peu and Sokoto) cowpea varieties harvested during wet and dry seasons were used for the study. After an initial gas test to evaluate 96 h gas production profiles of haulms with and without polyethylene glycol (PEG), the time to half maximal gas production was calculated and a second incubation conducted with fermentation stopped at substrate specific half time (t_1/2) and 24 h for each substrate. True DM degradability was measured from incubated residues and combined with gas volume to estimate the partitioning factor. Crude protein flow to the duodenum was estimated by combining gas volume with the measured ammonia nitrogen in the incubated fluid. Addition of PEG did not have any effect (P>0.05) on all the variables determined. Interaction between group (improved vs. commercial) and season was observed for CP (P=0.002), lignin (P=0.003) and hemicellulose (P=0.030) contents of the haulms. A group × season interaction was also observed for some of the variables at both substrate specific t_1/2 and 24 h. Commercial cowpea haulms had greater (P=0.002) microbial mass and produced less (P<0.05) methane than the improved cowpea haulms. The improved cowpea haulms were less (P<0.001) degraded in the rumen and as a result ensured greater (P<0.001) amount of uCP. The results validated that cowpea haulm is an important agro-based by-product that is adequate in protein and energy to sustain ruminant animal production in Nigeria and other Sub-Saharan African countries during the extended dry season.     

Salicylic acid alleviates mercury toxicity by preventing oxidative stress in roots of Medicago sativa

Salicylic acid (SA) as a signal molecule mediates many biotic and environmental stress-induced physiological responses in plants. In this study, we investigated the role of SA in regulating Hg-induced oxidative stress in the roots of alfalfa (Medicago sativa). Plants pretreated with 0.2 mM SA for 12 h and subsequently exposed to 10 μM Hg²⁺ for 24 h displayed attenuated toxicity to the root. The SA-promoted root growth was correlated with decreased lipid peroxidation in root cells. The ameliorating effect of SA was confirmed by the histochemical staining for the detection of loss of membrane integrity in Hg-treated roots. We show that treatment with 0.2 mM SA increased the activity of NADH oxidase, ascorbate peroxidase (APX) and peroxidase (POD) in the roots exposed Hg. However, a slightly decreased superoxide dismutase (SOD) activity was observed in SA + Hg-treated roots when compared to those of Hg treatment alone. We also measured accumulation of ascorbate (ASC), glutathione (GSH) and proline in the roots of alfalfa and found that roots treated with SA in the presence of Hg accumulated more ASC, GSH and proline than those treated with Hg only. These results suggest that exogenous SA may improve the tolerance of the plant to the Hg toxicity.     

Influence of slope on root system anchorage of Pinus yunnanensis

In southwestern China, Yunnan pines (Pinus yunnanensis) have been extensively cultivated on barren hills for reforestation and ecological engineering. The objective of this work is to study the influences of slope gradient on anchorage of root systems of P. yunnanensis. Pulling experiments were carried out at low (5–6°), moderate (25–26°) and high gradient (42–43°) by using selected 15-year-old P. yunnanensis. The results showed that the anchorage resistances induced by the slope gradient were significantly (P < 0.01) different from each other and followed in the order of high slope > moderate slope > low slope. Anchorage strength of upslope-grown roots increased with size and length of first-order lateral roots as well as the number of second-order lateral roots. Contributions of upslope-grown roots for preventing plants from overturning varied considerably between those from different slopes. The contribution of roots growing on upslope side on high slope to the anchorage of root system reached 50%, whereas those on moderate and low slopes were about 44% and 37%, respectively. It was concluded that the anchorage resistance was closely related to slope gradient and root distribution, while upslope-grown roots were positively related to anchorage resistance.     

Growth and root distribution of Vallisneria natans in heterogeneous sediment environments

Plant growth, biomass allocation and root distribution were investigated in the submerged macrophyte Vallisneria natans growing in heterogeneous sediments. Experimentally heterogeneous sediment environments were constructed by randomly placing 4 cm of clay or sandy loam into the top (0–4 cm) or bottom (4–8 cm) layer within an experimental tray, providing two homogeneous and two heterogeneous treatments. Biomass accumulation was significantly affected by the experimental treatments: higher in the homogeneous sediment of clay (32 mg per plant) and the two heterogeneous treatments (about 27 mg per plant), but lower in the homogeneous sediment of sandy loam (15 mg per plant). Root: shoot ratio was also different among the four treatments. Compared with the treatments of clay in the top layer, plants allocated more biomass to roots at the treatments of sandy loam in the top layer. Heterogeneous sediments significantly affected root distribution pattern. Compared with the treatments of sandy loam in the bottom layer, root number (7–8 versus 13–14) and total root length (3.6–4.0 cm versus 29.5–40.0 cm) in the bottom layer were significantly higher in the treatments with clay in the bottom layer. These results indicate that both sediment structure and nutrient availability influence growth and root system distribution of V. natans.     

Proanthocyanidin diversity in the EU ‘HealthyHay’ sainfoin (Onobrychis viciifolia) germplasm collection

This study investigated 37 diverse sainfoin (Onobrychis viciifolia Scop.) accessions from the EU ‘HealthyHay’ germplasm collection for proanthocyanidin (PA) content and composition. Accessions displayed a wide range of differences: PA contents varied from 0.57 to 2.80 g/100 g sainfoin; the mean degree of polymerisation from 12 to 84; the proportion of prodelphinidin tannins from 53% to 95%, and the proportion of trans-flavanol units from 12% to 34%. A positive correlation was found between PA contents (thiolytic versus acid–butanol degradation; P < 0.001; R² = 0.49). A negative correlation existed between PA content (thiolysis) and mDP (P < 0.05; R² = −0.30), which suggested that accessions with high PA contents had smaller PA polymers. Cluster analysis revealed that European accessions clustered into two main groups: Western Europe and Eastern Europe/Asia. In addition, accessions from USA, Canada and Armenia tended to cluster together. Overall, there was broad agreement between tannin clusters and clusters that were based on morphological and agronomic characteristics.     

Promotion of Salvia miltiorrhiza hairy root growth and tanshinone production by polysaccharide–protein fractions of plant growth-promoting rhizobacterium Bacillus cereus

This study was to examine the effects of polysaccharides from a plant growth-promoting rhizobacterium (PGPR) Bacillus cereus on the growth and tanshinone production of Salvia miltiorrhiza hairy roots. A polysaccharide fraction designated BPS was isolated from the hot water extract of B. cereus cells by ethanol precipitation. BPS applied to the root culture at 100–400 mg l⁻¹ a few days before the stationary growth phase stimulated the tanshinone accumulation of roots by about 7-fold (1.59 mg g⁻¹ versus 0.19 mg g⁻¹) and also notably promoted the root growth (15% increase in biomass). BPS was a polysaccharide–protein complex containing about 27% protein, which is essential for root growth promotion. BPS was separated by ultrafiltration into two molecular weight (MW) fractions, of which the high MW fraction (∼35.8 kDa) with higher protein content (∼31%) promoted the root growth while the lower MW fraction with lower protein content (∼17%) suppressed the growth. The results suggest that the polysaccharide portion of BPS was responsible for stimulating the tanshinone accumulation while the protein portion was responsible for promoting the hairy root growth. Polysaccharides from PGPR are potential sources of active elicitors and growth-promoting agents for plant roots in culture.     

Short-time response in root morphology of Vallisneria natans to sediment type and water-column nutrient

Rooted submerged macrophytes can absorb significant amounts of nutrients from both sediment and water. We investigated root morphology of Vallisneria natans in mesocosm plastic bins, in response to three types of sediment (sandy loam, clay, and a 50:50 (v/v) mixture of the two sediments) and two levels of water-column nutrient (well water and nutrient medium). Compared to the plants grown in the clay or mixed sediments, root diameter decreased (0.39–0.41 versus 0.36–0.37 mm) but total root length per plant increased (0.87–1.27 versus 1.14–1.62 m) when grown in sandy loam. Increase of nutrient availability in water column led to decreased specific root length (306–339 versus 258–281 m g⁻¹). However, both sediment type and water-column nutrient had no impacts on root number (ranged from 19 to 24 number of roots per plant). Root weight ratio, root:leaf mass ratio and root:leaf length ratio generally decreased with enhanced nutrient availability in sediment or water. Plant growth was affected by sediment type alone (P < 0.05), rather than water-column nutrient (P > 0.05). However, plant N and P contents were significantly impacted by both sediment type (P ≤ 0.001) and water-column nutrient (P < 0.05). Increase of nutrient availability in sediment or water led to increased plant N (ranged from 2.47 to 4.77 mg g⁻¹) and P concentrations (ranged from 42.8 to 62.0 mg g⁻¹). These results indicate that considerable variation in root morphology of V. natans exists in response to the fertility of the sediment it is rooted in.     

Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.     

Water status and water diffusion transport in lupine roots exposed to lead

Water status and diffusion transport were studied in the roots of yellow lupine (Lupinus luteus L., cv. Juno) treated for 48 h with two selected concentrations of Pb(NO₃)₂: 150 mg l⁻¹, which inhibited root growth by about 50% (medium stress intensity), as well as 350 mg l⁻¹, which almost entirely suppressed root elongation (severe stress intensity). Relative water content (RWC), which characterizes the degree of root water saturation, slightly increased at the lower lead concentration and remained unchanged at the higher lead dose. Ultrastructure analyses under a transmission electron microscope revealed that plasmolysis was not evoked by lead in the apical part of the meristem. Moreover, direct observation of meristem cells using Nomarsky optics indicated enhanced vacuolization in the presence of both lead concentrations. These data suggest that the water status of the roots was not affected by the metal. Due to the fact that proline is involved in the maintenance of turgor in the cells, the metabolism of this amino acid was investigated. In the roots, the activity of enzymes involved in proline synthesis, such as pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), increased at 150 mg l⁻¹ Pb²⁺; nevertheless, proline content was diminished at the lower lead concentration. This effect is likely the result of proline degradation by proline dehydrogenase (PDH), since the activity of this enzyme increased at the lower lead dose. On the other hand, in the presence of 350 mg l⁻¹ Pb²⁺, a low level of proline was correlated with a decrease in the activity of P5CS and OAT, as well as unchanged PDH activity in lupine roots. These data may imply that enzymatic synthesis of proline was strongly damaged by the metal ions. The low level of proline in both experimental variants suggests that proline accumulation is inessential to maintaining the osmotic uptake of water into root cells. NMR spectroscopy showed that exposition of lupine seedlings to lead caused a deceleration in water transport in the roots due to a reduction in the water transfer rate across the membranes (transmembrane transfer) and vacuoles continuum, as well as water diffusion along the root apoplast. Fluorescence staining and immunogold labeling showed the presence of callose strands in cell walls and/or in the vicinity of them. In lead-treated lupine roots, callose was mainly localized in the parenchyma cortex placed lengthwise to the vascular cylinder. Callose deposits in the cell walls may reduce vacuolar transport, as well as increase cell wall resistance to water flow. Deceleration of diffusional water movement to the vascular system, may in turn, influence the rate of long-distance water transport to aerial parts of the plant.     

Saikosaponin accumulation and antioxidative protection in drought-stressed Bupleurum chinense DC. plants

Dried root of Bupleurum spp. is one of the most popular ingredients in many oriental medicinal preparations. Potted Bupleurum chinense DC. seedlings were subjected to progressive drought stress by withholding irrigation followed by a rewatering phase. The changes in antioxidant system, hydrogen peroxide (H₂O₂), superoxide radicals (O₂^?), and malondialdehyde (MDA) contents as well as saikosaponin a (SSa) and saikosaponin d (SSd) content in B. chinense roots were investigated. Additionally, the antioxidant activity of the roots extract was evaluated. The results showed that B. chinense root appeared highly resistant to water deficit. Both SSa and SSd content increased with the progressive water deficit, however, decreased under severe drought conditions or after water recovery. Moderate drought treatment resulted in 83% increase in SSa content and 22% increase in SSd content compared to the well-hydrated treatment. And increased SSa and SSd content during drought were accompanied by enhanced O₂^? content and superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) activity until severe drought stress. Notably, in vitra antioxidant tests demonstrated that the lipid peroxidation inhibition capacity was positively correlated with the content of SSa and SSd, particularly significant at p = 0.05 with SSd content. These results suggest that B. chinense roots exhibit effective antioxidative protection mechanism to withstand drought stress. And it could be speculated that drought-induced SSa and SSd accumulation in B. chinense roots may be stimulated via active oxygen species, and consequently involve in mitigating the oxidative damage due to its high anti-lipid peroxidation capacity.     

Root health evaluation of three alfalfa varieties in Kerquin sandy land

Without a robust and healthy root system, establishment, productivity, and persistence are compromised. Consequently, research on alfalfa root morphology and health is very important in development of technology for efficient improvement and production of alfalfa. The objectives of this study were to evaluate the root morphology and health of three alfalfa varieties, Algonquin, Golden Queen, and Yellow Flower and to determine relationships among root morphology traits and root health. Yields from these varieties ranged from 5.83 to 43.93 t/ha, total root length ranged from 215.17 to 708.89 mm, root surface area from 124.95 to 468.37 cm², volume from 3.24 to 57.72 cm³, and forks from 1.25 × 10³ to 10.54 × 10³, and tips from 0.65 × 10³ to 3.17 × 10³. Root infestation score was negatively correlated with yield (r = ?0.997, P < 0.01), and was positively correlated with all root morphology traits (r = 0.466–0.997, P < 0.01), and yield was negatively associated with root morphology traits (r = ?0.755 to ?0.998, p < 0.01) with the exception of root tips (r = 0.448, P < 0.01). Results from these analyses indicated that root infestation score was the lowest averaged over age of alfalfa stand in Algonquin. Yield in 2-year old stands was greater in Golden Queen compared to the other two cultivars.     

Production of emetine and cephaeline from cell suspension and excised root cultures of Cephaelis ipecacuanha

Production of the ipecac alkaloids, emetine and cephaeline was studied in cell suspension and excised root cultures of Cephaelis ipecacuanha. A two-stage cell suspension culture was developed for enhanced accumulation of the alkaloids. In the first-stage, suspension cultures were established in Murashige and Skoog's (MS) medium containing 2,4-D and NAA which was suitable for cell growth and the second-stage culture system was composed of MS medium containing IBA, IAA and 6% sucrose which favoured alkaloid production. The production of emetine and cephaeline was greatly increased in the two-stage culture method compared to the single-stage culture. Optimal alkaloid synthesis was obtained in excised root culture of the plant in medium composed of half-strength MS salts, IBA (0.25 mgl⁻¹) and 2% sucrose. A discernible higher accumulation of cephaeline in two-stage cell suspension culture as well as in excised root culture in comparison to that of the three-year-old roots was a     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

Nitric oxide protects sour pummelo (Citrus grandis) seedlings against aluminum-induced inhibition of growth and photosynthesis

Limited data are available on the amelioration of nitric oxide (NO) on aluminum (Al)-toxicity. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 0 and 1.2 mM AlCl₃·6H₂O × 0 and 10 μM sodium nitroprusside (SNP, an NO donor). Under Al stress, SNP increased root phosphorus (P) and Al, but decreased shoot Al. Al decreased photosynthesis, maximum quantum yield of primary photochemistry (F_v/F_m) and total performance index (PI_tot,sbs), but increased inactivation of oxygen-evolving complex (OEC), K-band and relative variable fluorescence at I-steps (V_I). SNP alleviated Al-induced changes for all these parameters. SNP stimulated Al-induced secretion of malate and citrate by excised roots from Al-treated seedlings, while Al did not increase their contents in roots. Antioxidant system in leaves and roots was up- and down-regulated by Al, respectively. SNP prevented Al-induced accumulation of malondialdehyde (MDA) in roots and leaves. In conclusion, SNP alleviates Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain. This occurs through increasing Al-immobilization and P level in roots and Al-induced secretion of malate and citrate from roots, and decreasing Al accumulation in shoots. Thus, the decrease of photosynthesis is prevented. Increased P level and Al-immobilization in roots through SNP may be effected through enhanced secretion of malate and citrate.     

Quantifying the effects of root reinforcement of Persian Ironwood (Parrotia persica) on slope stability; a case study: Hillslope of Hyrcanian forests,northern Iran

Forest vegetation is known to enhance the stability of slopes by reinforcing soil and increasing its shear resistance through root system. The effects of root reinforcement depend on the morphological characteristics of the root system, the tensile strength of single roots, and the spatial distribution of the roots in soil. In the present study the results of research carried out in order to evaluate the biotechnical characteristics of the root system of Persian Ironwood (Parrotia persica), in northern Iran are presented. Profile trenching method was used to obtain root area ratio (RAR) values for uphill and downhill sides of the individual trees. For each species, single root specimens were sampled and tested for their tensile strength. It was found that root density generally decreases with depth according to an exponential law. Maximum RAR values were located within the first 0.1 m, with maximum rooting depth at about 0.65 m. RAR values ranged from 0.001% at lower depths to 1.39% near the surface, at upper 0.1 m depth. Significant differences of RAR values, rooting depth and root cohesion between uphill and downhill were observed, however, the differences were not significant for number of roots (ANCOVA). Downhill profiles had higher RAR values, rooting depth and root cohesion. In general, root tensile strength tends to decrease with diameter according to a power law, as observed by other researchers. Downhill roots were significantly stronger in tensile strength than uphill ones. Inter-species variation of tensile strength in downhill roots was also observed. The resulting data were used to evaluate the reinforcing effects in terms of increased shear strength of the soil, using Wu/Waldron Model. The root reinforcement provided by Persian Ironwood is about 46.0 kPa in the upper layers and 0.3 kPa in the deeper horizons. The results of Spearman test revealed a significant correlation between RAR and c_r and that best followed by a power law. The results presented in this paper contribute to expanding the knowledge on biotechnical characteristics of Persian Ironwood on slope reinforcement.