Root Systems Of Intact Plants Research Articles

Biohybrid plants with electronic roots via in vivo polymerization of conjugated oligomers

Plant processes, ranging from photosynthesis through production of biomaterials to environmental sensing and adaptation, can be used in technology via integration of functional materials and devices. Previously, plants with integrated organic electronic devices and circuits distributed in their vascular tissue and organs have been demonstrated. To circumvent biological barriers, and thereby access the internal tissue, plant cuttings were used, which resulted in biohybrids with limited lifetime and use. Here, we report intact plants with electronic functionality that continue to grow and develop enabling plant-biohybrid systems that fully maintain their biological processes. The biocatalytic machinery of the plant cell wall was leveraged to seamlessly integrate conductors with mixed ionic-electronic conductivity along the root system of the plants. Cell wall peroxidases catalyzed ETE-S polymerization while the plant tissue served as the template, organizing the polymer in a favorable manner. The conductivity of the resulting p(ETE-S) roots reached the order of 10 S cm-1 and remained stable over the course of 4 weeks while the roots continued to grow. The p(ETE-S) roots were used to build supercapacitors that outperform previous plant-biohybrid charge storage demonstrations. Plants were not affected by the electronic functionalization but adapted to this new hybrid state by developing a more complex root system. Biohybrid plants with electronic roots pave the way for autonomous systems with potential applications in energy, sensing and robotics.

Reducing Strength Prevailing at Root Surface of Plants Promotes Reduction of Ag+ and Generation of Ag0/Ag2O Nanoparticles Exogenously in Aqueous Phase

Potential of root system of plants from wide range of families to effectively reduce membrane impermeable ferricyanide to ferrocyanide and blue coloured 2,6-dichlorophenol indophenol (DCPIP) to colourless DCPIPH2 both under non-sterile and sterile conditions, revealed prevalence of immense reducing strength at root surface. As generation of silver nanoparticles (NPs) from Ag+ involves reduction, present investigations were carried to evaluate if reducing strength prevailing at surface of root system can be exploited for reduction of Ag+ and exogenous generation of silver-NPs. Root system of intact plants of 16 species from 11 diverse families of angiosperms turned clear colorless AgNO3 solutions, turbid brown. Absorption spectra of these turbid brown solutions showed silver-NPs specific surface plasmon resonance peak. Transmission electron microscope coupled with energy dispersive X-ray confirmed the presence of distinct NPs in the range of 5–50 nm containing Ag. Selected area electron diffraction and powder X-ray diffraction patterns of the silver NPs showed Bragg reflections, characteristic of crystalline face-centered cubic structure of Ag0 and cubic structure of Ag2O. Root system of intact plants raised under sterile conditions also generated Ag0/Ag2O-NPs under strict sterile conditions in a manner similar to that recorded under non-sterile conditions. This revealed the inbuilt potential of root system to generate Ag0/Ag2O-NPs independent of any microorganism. Roots of intact plants reduced triphenyltetrazolium to triphenylformazon and impermeable ferricyanide to ferrocyanide, suggesting involvement of plasma membrane bound dehydrogenases in reduction of Ag+ and formation of Ag0/Ag2O-NPs. Root enzyme extract reduced triphenyltetrazolium to triphenylformazon and Ag+ to Ag0 in presence of NADH, clearly establishing potential of dehydrogenases to reduce Ag+ to Ag0, which generate Ag0/Ag2O-NPs. Findings presented in this manuscript put forth a novel, simple, economically viable and green protocol for synthesis of silver-NPs under ambient conditions in aqueous phase, using root system of intact plants.

Chemical Screen for Limited-Transpiration-Rate Trait Among Sorghum Genotypes

A limited-transpiration trait has been proposed for sorghum (Sorghum bicolor L.) as a desirable trait for water-deficit environments so that water conservation early in the growing season allows greater water availability during the latter stages of crop growth. This study was undertaken to explore if chemical inhibitors—mercury, silver, gold, zinc, cylcoheximide—could be used to screen for the limited-transpiration trait. Inhibitors were fed either to detached leaves or to the root systems of intact plants, and changes in transpiration rates were recorded. Only treatment with silver resulted in discrimination among genotypes. Those genotypes that most strongly expressed the limited-transpiration trait were less sensitive to being fed silver than those that either had weaker expressions of the limited-transpiration trait or did not express the trait. The results with leaves indicated the silver test could be effective as a negative screen for sorghum genotypes that potentially express the limited-transpiration trait.

Plants fabricate Fe-nanocomplexes at root surface to counter and phytostabilize excess ionic Fe

While evaluating the impact of iron nanoparticles (NPs) on terrestrial plants we realized potential of root system of intact plants to form orange-brown complexes constituted of NPs around their roots and at bottom/side of tubes when exposed to FeCl3. These orange-brown complexes/plaques seen around roots were similar to that reported in wetland plants under iron toxicity. Transmission electron microscopy coupled with energy dispersive X-ray analysis revealed that orange-brown complexes/plaques, formed by root system of all 16 plant species from 11 distinct families tested, were constituted of NPs containing Fe. Selected area electron diffraction and powder X-ray diffraction spectra showed their amorphous nature. Thermogravimetric and fourier transform infra-red analysis showed that these Fe-NPs/nanocomplexes were composed of iron-oxyhydroxide. These plant species generated orange-brown Fe-NPs/nanocomplexes even under strict sterile conditions establishing inbuilt and independent potential of their root system to generate Fe-NPs. Root system of intact plants showed ferric chelate reductase activity responsible for reduction of Fe(3+) to Fe(2+). Reduction of potassium ferricyanide by root system of intact plants confirmed that root surface possess strong reducing strength, which could have played critical role in reduction of Fe(3+) and formation of Fe-NPs/nanocomplexes. Atomic absorption spectrophotometric analysis revealed that majority of iron was retained in Fe-nanocomplexes/plaques, while only 2-3% was transferred to shoots, indicating formation of nanocomplexes is a phytostabilization mechanism evolved by plants to restrict uptake of iron above threshold levels. We believe that formation of Fe-NPs/nanocomplexes is an ideal homeostasis mechanism evolved by plants to modulate uptake of desired levels of ionic Fe.

Root system of live plants is a powerful resource for the green synthesis of Au-nanoparticles

Sixteen plant species from 11 distinct families were evaluated for their potential to exogenously fabricate Au-nanoparticles (NPs) at the root surface. The root system of intact plants of all species turned clear pale yellow colloidal salt solutions of Au purple/golden. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy revealed the presence of Au-NPs in the range of 5–100 nm in these colloidal solutions. PXRD showed the crystalline nature of Au-NPs. Reduction of 2,6-dichlorophenol-indophenol (DCPIP) by the root system of intact plants confirmed that the root surface possesses the strong reducing strength necessary for the reduction of Au3+ to Au0 and to generate Au-NPs. Our findings unequivocally demonstrated for the first time that roots of intact plants of certain species can be exploited for the bulk synthesis of Au-NPs exogenously under ambient conditions in an aqueous phase. These findings highlight a novel, simple, economically feasible and green/eco-friendly scheme for the exogenous production of Au-NPs in an aqueous phase under ambient conditions.

In vivo staining of reduced iron by 2,2′ bipyridine in rice exposed to iron toxicity

AbstractA protocol for a novel method to visualize Fe(II) in rice tissues is proposed. The method is based on the selective formation of a purple‐red color complex of 2,2′ bipyridine and Fe(II). Rice genotypes were exposed to 18 mM Fe(II) in nutrient solution for 2 d. Root systems of intact plants were subsequently placed in 2,2′ bipyridine solutions. The formation of the [Fe(bipy)<$>_3^{2+}<$>] color complex was visualized using bifocal microscopy. The method may improve the selection of genotypes during breeding for Fe‐toxicity resistance of rice.

Root system hydraulic conductivity in species with contrasting root anatomy

Previous research suggested that the hydraulic properties of root systems of intact plants could be described by two parameters: the hydraulic conductivity (Lpr) or the slope of the flow-density/water potential gradient relationship, and the offset or minimum water potential gradient required to induce flow. In this study, Lpr and offset were correlated with anatomical features of the root radial path in plants with contrasting root anatomy. Two woody and three herbaceous species were examined which exhibit a range of root anatomical features: Asparagus densiflorus (Kunth) Jessop (asparagus), Dendrobium superbum Rchb. f. (dendrobium), Glycine max (L.) Merr. (soybean), Prunus persica (L.) Batsch. (peach), Citrus aurantium L. (sour orange). Lpr varied about 8-fold, and the offset varied about 6-fold among the five species. Lpr was inversely related to root diameter (r2=0.39) and cortex width (r2=0.55), suggesting that species with thinner roots or roots with a thin cortex had the highest Lpr. Further observations suggested that the cortex width was a stronger determinant of Lpr than root diameter. However, the offset was not correlated with root diameter, stele diameter or cortex width, but was >2-fold higher in species having an exodermis in the root radial path (sour orange, asparagus, and dendrobium) compared to those lacking an exodermis (peach and soybean). The data of root Lpr obtained were similar to those given in the literature for both intact plants and excised roots which have been measured with different techniques. It is concluded that Lpr and offset, which describe the flow-water potential relationship for intact root systems, are related to differences in the root cortex; specifically, its thickness and the presence/absence of a suberized exodermis. Hence, these anatomical differences may, in part, cause the variability in root hydraulic properties that exists among plant species.

Nitrate effects on nodulation and nitrogenase activity of actinorhizal Casuarina studied in split-root systems

Nodulation and nitrogenase activity of inoculated Casuarina cunninghamiana Miq. were evaluated after exposing parts of root systems of intact plants to varied concentrations of potassium nitrate using split-root, solution culture systems. In a first experiment, plants were supplied with either: low concentrations of nitrate (0.05 m m) on both sides of the root system (L: L), high concentrations of nitrate (3.00 m m) on both sides of the root system (H:H), or low concentrations of nitrate on one side and high concentrations on the other side of the root system (L:H). In a second experiment, L:L and H:H treatments were retested using an apparatus which continuously supplied nutrient solutions to each side of the split-root system. In this experiment, the L:H treatment was substituted by a L:VH (6.00m m) treatment to evaluate the effects of very high nitrate concentrations. In both experiments, all plants were exposed to nitrate treatments 2 weeks prior to inoculation with Frankia strain CcI3 (HFP 020203). In the first experiment, root hair development was suppressed and no nodules formed on root systems directly exposed to 3.00 m m nitrate, but root hairs and nodules were observed on all root systems exposed to 0.05 m m nitrate. The number of nodules and nodule biomass on the low side of L:H plants were not significantly different from those observed on either side of L:L plants. In the second experiment, root hair development was not suppressed by any of the nitrate treatments (6.00, 3.00 and 0.05 m m), however, the number of nodules formed per side and their biomass were generally inversely related to the nitrate concentration on that side. Specific nitrogenase activities measured on the low side of L:VH plants were significantly lower than those measured on either side of L:L plants. The results of both experiments showed that: (1) nitrate inhibited nodule initiation strictly locally, (2) nodule development appeared to be inhibited locally, and (3) specific nitrogenase activity was inhibited systemically.

Proline Fed to Intact Soybean Plants Influences Acetylene Reducing Activity and Content and Metabolism of Proline in Bacteroids

Supplying l-proline to the root system of intact soybean (Glycine max [L.] Merr.) plants stimulated acetylene reducing activity to the same extent as did supplying succinate. Feeding l-proline also caused an increase in bacteroid proline dehydrogenase activity that was highly correlated with the increase in acetylene-reducing activity. Twenty-four hours after irrigating with l-proline, endogenous proline content had increased in host cell cytoplasm and bacteroids, about three- and eightfold, respectively. In bacteroids, proline concentration was calculated to be at least 3.5 millimolar. In experiments in which [U-(14)C]l-proline was supplied to uprooted, intact plants incubated in aerated solution, (14)C-labeled products of proline metabolism, as well as [(14)C]proline itself, accumulated in both host cells and bacteroids. When plants were incubated in aerated solutions containing [5-(3)H]l-proline, (3)H-labeled proline was found in host cells and bacteroids. [(3)H] Pyrroline-5-carboxylate was found in bacteroids, but not host cells, after a 2-hour incubation in [5-(3)H]l-proline. When [U-(14)C]l-proline was supplied for 24 hours, a significant amount of [(14)C] pyrroline-5-carboxylate was found in the host cells, in contrast with the results from the shorter incubation in [5-(3)H]proline, although the amount in the host cells was only about half the quantity found in the bacteroids. Taken as a whole, these results indicate that proline crosses both plant and bacterial membranes under the in vivo experimental conditions utilized and are consistent with a significant role for proline as an energy source in support of bacteroid functioning. In spite of the increase in acetylene-reducing activity when proline was supplied to the root system of intact plants, proline application did not rescue stemgirdled plants from loss of acetylene-reducing activity, although succinate application did. This suggests a nonphloem route for succinate, but not proline, from roots to nodules.

Effects of shoot removal on N2fixation and assimilation in modulation mutant and wild-type soybean

Abstract The effects of a decapitation (shoot removal) treatment on soybean (Glycine max L. Merr.) N2 fixation, transport and assimilation were determined in a partially nitrate-tolerant nodulation mutant line (N0D1-3) and the parent (Williams) using a 15N tracer technique. The root systems of intact plants were exposed to 15N2 and the shoots from half of the plants were removed 1 h after the onset of 15N2 exposure. Decapitated and intact plants were harvested at 2 h after decapitation. N2 fixation activity was markedly depressed by the decapitation treatment and the amount of fixed 15N in soluble and insoluble N in the nodules was decreased. Simultaneously, the concentration of amino-N, ureide-N, and soluble carbohydrate in the nodules also declined following shoot removal. Although the NOD1-3 line fixed N2 more actively than Williams, the response to decapitation was very similar in the two lines. From the results obtained it is suggested that the rapid decline in N2 fixation following decapitation was ...

IAA Distribution in the Hypocotyls and Primary Leaves of Phaseolus vulgaris L. Treated with Paclobutrazol in Relation to Their Rooting Capacity

The IAA content and its distribution were investigated in hypocotyls and primary leaves of bean plants treated with paclobutrazol in connection with the root formation of intact plants, stem and leaf cuttings. The amount of IAA in paclobutrazol-treated hypocotyls is higher than that of the control but more IAA accumulated in the basal part of the treated hypocotyls. Accumulation of IAA in the basal region correlates well with the increased root system of intact plants and with the more intensive rooting of stem cuttings. Although the IAA level in treated primary leaves was also higher than in the control, distribution of the hormone between the petiole and leaf blade was not favourable for the rooting process.

Nitrogenase Activity and Nodule Gas Permeability Response to Rhizospheric NH3 in Soybean

This study was conducted on soybean (Glycine max L. Merr.) nodules to determine if exogenous NH(3) exerts a controlling influence over nitrogenase activity through changes in nodule gas permeability (P), and if decreasing carbohydrate availability, as a result of low-light treatment, increases the sensitivity of root nodules to NH(3). Nodulated root systems of intact plants were exposed to one of several NH(3) concentrations ranging from 0 to 821 microliters per liter for an 8-hour period. Treatments were conducted under high-light (2300 micromoles per square meter per second) or low-light (800 micromoles per square meter per second) conditions. Increasing the NH(3) concentration and length of exposure of NH(3) caused a progressive decline in acetylene reduction activity (ARA). There was generally a greater reduction in ARA under the low-light treatment compared to the high-light treatment at a particular NH(3) concentration. The NH(3) concentration necessary to decrease P was greater than that needed to decrease ARA, and there was no evidence of a causal relationship between P and ARA in response to NH(3).

Nodule structure and nitrogenase activity ofCoriaria arborea in response to varying pO2

When excised root nodules ofCoriaria arborea are assayed for nitrogenase activity at various pO2 they show a broad optimum between 20 and 40 kPa O2, with some evidence for adaptation. Continuous flow assays of nodulated root systems of intact plants indicate that Coriaria shows an acetylene induced decline in nitrogenase activity. When root systems were subject to step changes in pO2 nitrogenase activity responded with a steep decline followed by a slower rise in activity both at lower and higher than ambient pO2. Thus Coriaria nodules are able to adapt rapidly to oxygen levels well above and well below ambient. Measurement of nodule diffusion resistance showed that the adaptation is accompanied by rapid increase in resistance at above ambient pO2 and decrease in resistance at below ambient pO2. Plants grown with root systems at pO2 from 5–40 kPa O2 did not differ in growth or nodulation. The anatomy of Coriaria nodules shows they have a dense periderm which encircles the nodule and also closely invests the infected zone. The periderm is both thicker and more heavily suberised in nodules grown at high pO2 than at low pO2. Vacuum infiltration of India ink indicates that oxygen diffusion is entirely through the lenticel and via a small gap adjacent to the stele.

Sites of synthesis, translocation and accumulation of pyrrolizidine alkaloid N-oxides in Senecio vulgaris L.

(14)C-Labelled alkaloid precursors (arginine, putrescine, spermidine) fed to Senecio vulgaris plants via the root system were rapidly taken up and efficiently incorporated into the pyrrolizidine alkaloid senecionine N-oxide (sen-Nox) with total incorporations of 3-6%. Considerable amounts of labelled sen-Nox were translocated into the shoot and were directed mainly into the inflorescences, the major sites of pyrrolizidine-alkaloid accumulation. Detached shoots of S. vulgaris were unable to synthesize pyrrolizidine alkaloids, indicating that the roots are the site of their biosynthesis. Further evidence was obtained from studies with in-vitro systems established from S. vulgaris: root cultures were found to synthesize pyrrolizidine alkaloids but not cell-suspension cultures, tumor cultures or shoot-like teratomas obtained by transformation with Agrobacterium tumefaciens. Studies on transport of [(14)C]sen-Nox, which was fed either to detached shoots or to the root system of intact plants, indicate that the alkaloid N-oxide does not simply follow the transpiration stream but is specifically channelled to the target tissues such as epidermal stem tissue and flower heads. Exogenously applied [(14)C]senecionine is rapidly N-oxidized. If the phloem path along the stem is blocked by a "steam girdle" translocation of labelled sen-Nox is blocked as well. Root-derived sen-Nox accumulated below the girdle and only trace amounts were found in the tissues above. It is most likely that the root-to-shoot transport of sen-Nox occurs mainly if not exclusively via the phloem. In accordance with previous studies the polar, salt-like N-oxides, which are often considered to be artifacts, were found to be the real products of pyrrolizidine-alkaloid biosynthesis as well as the physiological forms for long-distance transport, tissue-specific distribution and cellular accumulation.

Effects of hypoxia and elevated carbon dioxide concentration on water flux through Populus roots.

Restricted gas exchange between the rhizosphere and aerial environment reduces the concentration of oxygen (O(2)) and elevates the concentration of carbon dioxide (CO(2)) in the root zone, thereby leading to increased resistance to root water uptake. In this study, the effects of hypoxia and 20% CO(2) on water flux (J(v)) through roots of hybrid poplar (Populus trichocarpa Torr. & A. Gray x P. deltoides Bartr. ex Marsh) were measured in detached root systems under pressure in solution culture. Because stomata closed and there was no change in foliar water potential in hypoxic plants, root resistance was measured in detached systems as opposed to using whole plant measurements. However, under aerated conditions root resistance values were similar in intact plants and excised roots. Water fluxes through pressurized root systems treated with nitrogen and low oxygen (< 2% O(2)), elevated CO(2) (20% CO(2)), and low O(2) with elevated CO(2) concentrations were reduced to 40, 51 and 58%, respectively, of J(v) of plants aerated with ambient air. Reductions in J(v) occurred more rapidly in response to elevated CO(2) than to low O(2) concentrations. The effects of low O(2) and elevated CO(2) were not additive. Changes in pH that resulted from elevated CO(2) concentrations did not account for the reduction in J(v). When root systems of intact plants were pretreated for 24 or 48 h with low O(2) concentration, J(v) measured on pressurization was reduced by 33 and 48%, respectively, compared to aerated roots. Stomatal conductance was also reduced, however, so leaf water potential of plants with hypoxic roots were similar to those of aerated controls.

Acetylene reduction, H2 evolution and 15N2 fixation in the Alnus incana-Frankia symbiosis

Acetylene reduction, (15)N2 reduction and H2 evolution were measured in root systems of intact plants of grey alder (Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C2H2: (15)N2 were compared with C2H2:N2 ratios calculated from C2H2 reduction and H2 evolution, and with C2H2:N2 ratios calculated from accumulated C2H4 production and nitrogen content. It was possible to calculate C2H2:N2 ratios from C2H2 reduction and H2 evolution because this source of Frankia did not show any hydrogenase activity. The ratios obtained using the different methods ranged from 2.72 to 4.42, but these values were not significantly different. It was also shown that enriched (15)N could be detected in the shoot after a 1-h incubation of the root-system. It is concluded that the measurement of H2 evolution in combination with C2H2 reduction represents a nondestructive assay for nitrogen fixation in a Frankia symbiosis which shows no detectable hydrogenase activity.

Evidence for a Purine Pathway of Ureide Synthesis in N2-fixing Nodules of cowpea [Vigna unguiculata (L.) WALP.

The principal nitrogenous solutes produced from N 2 -fixation and exported from the nodules of cowpea [ Vigna unguiculata (L.) WALP.] were allantoin and allantoic acid. The following evidence suggests that these ureides were derived from purines. 1. Nodules were particularly active in enzymes of purine oxidation (xanthine dehydrogenase, uricase, allantoinase). 2. These enzymes were found largely restricted to the cytosol of the bacteroid containing cells (ie in close proximity to the sites of N 2 fixation) an-d increased in activity with nodule development. 3. Allopurinol (4-hydroxypyrazolo [3,4-d] pyrimidine) was an effective inhibitor of the xanthine dehydrogenase extracted from cowpea nodules and low concentrations (0.08-0.31 mM) applied to the root systems of intact plants in liquid culture rapidly (within 1 hr) inhibited ureide export, reduced the nodule pools of ureides and caused a concomitant accumulation of xanthine in nodules. 4. Glycine-2, 14 C supplied to slices of nodule tissue was more readily incorporated into allantoin and allantoic acid than glucose-U, 14 C or acetate-1,2, 14 C.

Alternating Perturbation Response of the Water Regulatory System in Arena Leaves

AbstractThe transpiration response of excised primary Avena leaves was studied when pulse perturbations were given to the water regulatory system. Repeated light pulses given to the leaf caused regularly alternating transpiration responses, i.e. the magnitude alternated regularly between a high and a low value. This effect, denoted alternating pulse response, could be recorded under quite different light pulse conditions but was not found when the pulse interval was too long or too short (longer than about 60 min. shorter than about 15 min). Sodium chloride given to the transpiration stream induced and increased the effect. Alternating pulse response could also be recorded when mannitol pulses were given to the root system of intact plants.

Biological dinitrogen fixation (acetylene reduction) associated with Florida mangroves.

Biological dinitrogen fixation in mangrove communities of the Tampa Bay region of South Florida was investigated using the acetylene reduction technique. Low rates of acetylene reduction (0.01 to 1.84 nmol of C(2)H(4)/g [wet weight] per h) were associated with plant-free sediments, while plant-associated sediments gave rise to slightly higher rates. Activity in sediments increased greatly upon the addition of various carbon sources, indicating an energy limitation for nitrogenase (C(2)H(2)) activity. In situ determinations of dinitrogen fixation in sediments also indicated low rates and exhibited a similar response to glucose amendment. Litter from the green macroalga, Ulva spp., mangrove leaves, and sea grass also gave rise to significant rates of acetylene reduction. Higher rates of nitrogenase activity (15 to 53 nmol of C(2)H(4)/g [wet weight] per h were associated with washed excised roots of three Florida mangrove species [Rhizophora mangle L., Avicennia germinans (L) Stern, and Laguncularia racemosa Gaertn.] as well as with isolated root systems of intact plants (11 to 58 mug of N/g [dry weight] per h). Following a short lag period, root-associated activity was linear and did not exhibit a marked response to glucose amendment. It appears that dinitrogen-fixing bacteria in the mangrove rhizoplane are able to use root exudates and/or sloughed cell debris as energy sources for dinitrogen fixation.