Unbranched Roots Research Articles

Mycorrhizal associations change root functionality: a 3D modelling study on competitive interactions between plants for light and nutrients.

Summary Recent studies show that the variation in root functional traits can be explained by a two‐dimensional trait framework, containing a ‘collaboration’ axis in addition to the classical fast–slow ‘conservation’ axis. This collaboration axis spans from thin and highly branched roots that employ a ‘do‐it‐yourself’ strategy to thick and sparsely branched roots that ‘outsource’ nutrient uptake to symbiotic arbuscular mycorrhizal fungi (AMF).Here, we explore the functionality of this collaboration axis by quantifying how interactions with AMF change the impact of root traits on plant performance. To this end, we developed a novel functional–structural plant (FSP) modelling approach that simulates plants competing for light and nutrients in the presence or absence of AMF.Our simulation results support the notion that in the absence of AMF, plants rely on thin, highly branched roots for their nutrient uptake. The presence of AMF, however, promotes thick, unbranched roots as an alternative strategy for uptake of immobile phosphorus, but not for mobile nitrogen.This provides further support for a root trait framework that accommodates for the interactive effect of roots and AMF. Our modelling study offers unique opportunities to incorporate soil microbial interactions into root functionality as it integrates consequences of belowground trait expression.

Pregled botaničkih karakteristika, hemijskog sastava, farmakološke aktivnosti i primene peršuna

Parsley is a biennial aromatic plant from the Apiaceae family, which is characterized by an unbranched root, pinnately divided leaves, umbels and schizocarp. It contains essential oil in all parts, with phenylpropane and terpene compounds as main components. It is rich in flavonoids and other polyphenolic compounds, containing furanocoumarins, carotenoids, polyacetylenes, and its leaves are a source of vitamins and minerals. The chemical composition of parsley depends on a number of factors, so it differs not only in different parts and varieties of the plant but also in different samples of the same parts of one variety. The most important parsley compounds are myristicin, apiol, 1-allyl-2,3,4,5-tetramethoxybenzene, b-phellandrene, 1,3,8-p-menthatriene, b-pinene, terpinolene, apiin, oxypeucedanin and falcarinol. Parsley has a long tradition of use in the treatment of urinary tract disorders, and modern in vitro and in vivo studies reveal numerous effects of various parsley preparations such as diuretic, antiurolithiasis, hypouricemic, hypolipidemic, hypoglycemic, hypotensive, antioxidant, anti-inflammatory and antiplatelet effect. Today, apart from its medical application, parsley is one of the most commonly used culinary herbs.

Acclimatization of micropropagated mature avocado

The morphology, anatomy and physiology of in vitro cultured plants do not facilitate survival when transferred to dynamic ex vitro environments. The benefits of a micropropagation system completely depend on successful transfer of in vitro plants to septic ex vitro conditions. Avocado (Persea americana Mill.) is a luxurious tropical fruit becoming very popular with increasing consumption around the globe due to its high nutritional value. It is a “micropropagation worthy” plant species, to meet the high industry demand for clonal propagules. Being a woody perennial, in the category of recalcitrant species for micropropagation, avocado has consistently proven to be very difficult to induce roots in vitro. Even if rooted, plant survival during acclimatization is very poor due to few, mostly unbranched roots produced at the rooting stage. The current study focused on optimising the last stage of the micropropagation process; acclimatization of in vitro regenerated avocado plantlets to achieve higher survival rates. The methods tested included mist spray application, root soaking treatments and a new method where plants were acclimatized in the tissue culture jar itself. The mist spray durations tested (1, 2 and 3 days) produced similar results. Highest survival rate was 74% with 3 days mist spray. Root soaking treatments and the duration of humidity dome-cover positively influenced plant survival. Root soaking for 2-3 days followed by a 4-week dome-cover period gave very high survival of 97%. The method of acclimatizing plantlets in the tissue culture jar with lids open (under a dome cover for 2 weeks followed by no dome cover for 2 weeks) also resulted in 96% survival of plantlets even after 24 weeks under glasshouse conditions. The optimised acclimatization methods are convenient and expected to be effective on large scale. The methods will likely be transferrable to other woody species encountering similar problems as avocado during acclimatization.

Hydraulic conductivity of soil-grown lupine and maize unbranched roots and maize root-shoot junctions

Improving or maintaining crop productivity under conditions of long term change of soil water availability and atmosphere demand for water is one the big challenges of this century. It requires a deep understanding of crop water acquisition properties, i.e. root system architecture and root hydraulic properties among other characteristics of the soil-plant-atmosphere continuum. A root pressure probe technique was used to measure the root hydraulic conductances of seven-week old maize and lupine plants grown in sandy soil. Unbranched root segments were excised in lateral, seminal, crown and brace roots of maize, and in lateral roots of lupine. Their total hydraulic conductance was quantified under steady-state hydrostatic gradient for progressively shorter segments. Furthermore, the axial conductance of proximal root regions removed at each step of root shortening was measured as well. Analytical solutions of the water flow equations in unbranched roots developed recently and relating root total conductance profiles to axial and radial conductivities were used to retrieve the root radial hydraulic conductivity profile along each root type, and quantify its uncertainty. Interestingly, the optimized root radial conductivities and measured axial conductances displayed significant differences across root types and species. However, the measured root total conductances did not differ significantly. As compared to measurements reported in the literature, our axial and radial conductivities concentrate in the lower range of herbaceous species hydraulic properties. In a final experiment, the hydraulic conductances of root junctions to maize stem were observed to highly depend on root type. Surprisingly maize brace root junctions were an order of magnitude more conductive than the other crown and seminal roots, suggesting potential regulation mechanism for root water uptake location and a potential role of the maize brace roots for water uptake more important than reported in the literature.

Characterization of RAM to SAM transitions in Selaginella microphylla grown in vitro

In vitro morphogenetic ability of plant cells has been demonstrated in diverse species of angiosperms and gymnosperms but no such report is available in the genus Selaginella till date. We have established an in vitro morphogenic root culture where indole butyric acid (IBA) induced profuse branched and unbranched roots in Selaginella microphylla. We observed inter-convertibility of root apical meristem (RAM) to shoot apical meristem (SAM) in presence of IBA and showed that intact roots are also capable of transformation. Friable callus was obtained from roots on prolonged (∼50 weeks) root cultures. By isolating total RNA from each of the developmental stages, we performed cDNA synthesis followed by random amplification, sequencing, and BLAST analysis of differentially expressed transcripts to correlate morphological events with the changes on molecular level. The results revealed sequence matches to genes involved in diverse cellular processes such as transcription, translation, photosynthesis, replication, secondary metabolism, stress response, and plant defense suggesting ancient origins of such proteins and the evolutionary conservation of biological function.

Mechanical interactions between neighbouring roots during pullout tests

The quantification of root reinforcement function is important for landscape managers and engineers. The estimation of root mechanical reinforcement is often based on models that do not consider the potential interaction between neighbouring roots. Root-soil mechanical interactions related to the root spacing and bundle geometry remain unclear including potential effects on the reliability of the current models. The objective of this study is to quantify the mechanical interactions among neighbouring roots or roots networks using modelling approaches and pullout laboratory experiments. Based on simple geometrical characterization of individual root geometry, we calculated dissipation patterns of frictional root-soil interfacial stresses in radial and longitudinal directions. Considering simple superposition of shear stresses within the soil matrix, we quantified characteristic root densities at which the radial mechanical interactions influence global pullout behaviour of the root bundle both for branched and unbranched roots. Laboratory pullout tests on root bundles were carried out at root spacings of 15, 35 and 105 mm. In addition, we tested effects of non-parallel (crossing) root bundle geometry. We found no significant statistical differences in root pullout force for the different root spacing in parallel alignment of roots. Branches increase pullout force by 1.5 times. Moreover, the mean displacement at the pullout peak-force was 7.2 % of length for unbranched roots and about 4.1 % of length for branched roots. The model shows its potential comparing it with empirical results concerning the holes leaved by roots, according with the branch pattern. The study quantifies the influence of root spacing and arrangement geometry within a root bundle on its mechanical behaviour. The assumption of “non-interacting” neighbouring roots in root reinforcement methods is no longer valid for root spacing less than 15 mm and root reinforcement methods. Moreover crossing roots shown a statistical difference. This information is important for improved understanding root reinforcement mechanisms in steep hill slope and the interplay between anchoring /failure and root bundle pullout vs root breakage.

Contribution of Mycorrhizae to Early Growth and Phosphorus Uptake by a Neotropical Palm

ABSTRACT Arbuscular mycorrhizal fungi (AMF) can act as an extension of the root system of their host plants. In Desmoncus orthacanthos Martius (Arecaceae), which has thick and unbranched roots (i.e., magnolioid roots) and low densities of root hairs, this association may be essential to reach a maximum growth with minimum fertilizers. This is important because of the potential in the south of Mexico to use D. orthacanthos' shoots as a raw material to build handcrafts. To evaluate the effect of arbuscular mycorrhizae on phosphorus (P) uptake and initial growth of D. orthacanthos seedlings, a 160-day bi-factorial experiment was carried out in which plants were subject to one of two levels of mycorrhizal colonization (with or without) and one of three levels of P substrate addition (4, 12, and 24 ppm). Our results show that total dry weight (DW) and leaf area (LA) responded significantly to P addition but not to mycorrhizal colonization. Phosphorus concentration in plant tissues (Pt) was increased by both factors (mycorrhizae and P addition). Mycorrhizae increased relative growth rate (RGR) at low P level. Our results indicate that AMF play an important role in early growth and P uptake by D. orthacanthos seedlings; therefore, the AMF must be considered in plantations of this potentially economically important palm.

Root architecture of six tropical seagrass species, growing in three contrasting habitats in Indonesian waters

Although several recent studies point at the importance of seagrass roots for nutrient acquisition in oligotrophic tropical ecosystems, remarkably little is known about the root architecture of tropical seagrasses. The present study provides a detailed description of the root architecture of six seagrass species that were extracted from three sites differing in sediment type and nutrient availability (i.e., except for one species that was not present at one of the sites). Number of roots per node, order of root branching, length and diameter per root order, root hair density and length were determined and used to calculate a topological index for the different species and habitats. Root architecture differed strongly between species. The relatively long-lived and slowly-growing species Thalassia hemprichii and Enhalus acoroides were characterised by short internodes with relatively few unbranched roots per node and a high root hair density. More fast growing species such as Cymodocea rotundata, Cymodocea serrulata and Syringodium isoetifolium had many roots per node, the majority of which were branched. Surprisingly, differences in sediment type and nutrient availability, as present between locations, had little effect on root architecture. We expect this to be due to a relatively homogeneous nutrient distribution at the small scale within water saturated sediments. Overall, all seagrass species had relatively simple branching (topological index > 0.7), comparable to angiosperms of the low temperate salt marsh. We speculate that relatively simple root architecture of plants in flooded systems reflects the need for a minimal path length for oxygen transport from shoots to roots.

The Influence of Nitrogen Nutrition on the Carbohydrate and Nitrogen Status of Emergent Macrophyte Acorus calamus L.

Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6 mM) and/or forms of N (NH 4 + versus NO 3 – ) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH 4 + –N nutrition described in our previous study [Vojtiskova et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure NH 4 + –N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH 4 + –N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates (TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and negatively affected by high N availability (P = 0.001), as well as by NH 4 + –N nutrition (P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to 33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%, Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH 4 + received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH 4 + nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could explain the reduced growth of Acorus plants under high N and sole NH 4 + –N nutrition described previously.

Expression of the ipt Gene with the AGPase S1 Promoter in Tomato Results in Unbranched Roots and Delayed Leaf Senescence

Transgenic tomato plants were produced with the isopentenyl transferase gene (ipt) ligated to a promoter that is active exclusively in sink tissue. Initially, transgenic plants had smaller, round-scale leaves, swollen stems, and exhibited early development of lateral shoots compared to wild type. Expression of the ipt gene resulted in the formation of unbranched roots on cuttings and delayed senescence in excised leaves. Callus and root formation occurred on excised leaves and leaf discs during dark incubation. The retention percentage of chlorophyll, as well as cytokinin in excised leaves or discs was significantly greater than wild type. Transgenic tomato fruit had elevated levels of cytokinins in the first days after fruit set and these levels were maintained longer during fruit development.

Agrobacterium rhizogenes induced rooting of in vitro regenerated shoots of the hybrid [formula omitted

Difficulty in rooting of in vitro regenerated shoots of the hybrid Helianthus annuus×Helianthus tuberosus was overcome by transformation with an Agrobacterium rhizogenes strain carrying an Ri plasmid with functional T-DNA. Whereas rooting of control shoots (in vitro regenerated hybrid shoots) could not be induced on MS basal medium, only sparse, and unbranched roots were produced on the MS medium supplemented with indole-3-butyric acid (IBA). However, the bacterial inoculated shoots produced sparse, and unbranched roots on MS basal medium and extensively branched hairy roots on the MS medium supplemented with IBA. Paper electrophoresis of crude tissue extracts of the putatively transformed roots confirmed the transformation by A. rhizogenes. The results of the present study therefore confirm that the T-DNA of the Ri plasmid of A. rhizogenes strain AR 532 is able to elicit the transformed root phenotype thus facilitating efficient rooting of the in vitro regenerated hybrid shoots. This also indicates that transformation with A. rhizogenes can help in the establishment of a well-developed root system in difficult-to-root genotypes of sunflower hybrids.

Longevity of mycorrhizal roots depends on branching order and nutrient availability

Summary The effects are reported of branching order and nitrogen fertilization on the longevity of mycorrhizal short roots at a Norway spruce (Picea abies) stand in south‐west Sweden. A 4‐yr qualitative analysis was made, using minirhizotrons, of the emergence frequency and life span of individual mycorrhizal roots of three root orders (unbranched, main axes of branched and side branches of branched short roots, orders 1, 2 and 3, respectively). Longevity of mycorrhizal roots varied with branching order and soil depth, being greatest in unbranched (order 1) roots and those at the greatest soil depth (40–85 cm). Nitrogen addition decreased the proportion of higher mycorrhizal root orders (a fivefold reduction in order 3 compared with controls), while increasing the median longevity. Seasonal effects were recorded; mycorrhizal roots produced in spring and summer remained unsuberized during the winter. Mycorrhizal root longevity depends on the branching order of mycorrhizal roots and nitrogen addition decreases branching density while increasing longevity. The survival of mycorrhizal roots, which remain vital and unsuberized over winter, enhances water and nutrient efficiency of Norway spruce.

Ectomycorrhizal Roots Collected from the Bases of the four Edible Basidiocarps Around Mt. Wol Ak

The ectomycorrhizal roots were collected from the soils around the bases of basidiocarps of the four edible mushrooms in the stands of Pinus densiflora or Querns acutissima communities (Mt. Wol-Ak in Eastern Chung-Puk): The basidiocarps of Tricholoma matsutake (TM), Sarcodon asparatus (SA), S. imbricatum (SI), and Polyozellus multiplex (PM) are usually collected. The ectomycorrhizal roots of TM, PM and SI were related to the roots of P. densiflora, but the other to the roots of Q. acutissima in Korea. Particularly, the basidiocarps of PM were collected in the mixed stand of both P. densiflora and Q. acutissima. The morphologies of the ectomycorrhizal roots were observed to be the yellowish brown coral (dichromatous) or pyramid types in the roots of the pine, but dark brown un-branched sticks (roots) in the ends of ectomycorrhizal roots of Querus plants. The un-branched roots were covered with the dark mycelia (rhizomorph) around them. Therefore, the ectomyorrhizal roots of PM were observed to have two kinds of types; The single blackish un-branched roots were observed to be attached to the yellowish coral type roots. The bundles of TM mycelia were filled with cortical cells (in the roots of P densiflora), hut the mycelia of the other fungi (Aphylloporales) were massed between the cortical cells of P densiflora or Q. acutissima. Their anatomical and gross features were considered to be simailar but very important in the ectomycorrhizal roots for these edible mushrooms.

Root response to above-ground light quality – Differences between rhizomatous and non-rhizomatous clones of Festuca rubra

Root response to reduced red/far red ratio above ground was studied in an experiment with 12 vegetatively propagated clones of Festuca rubra, a rhizomatous grass species. A new method suitable for describing the node position within rhizome systems was developed. It uses a combination of developmental and functional directions of ordering, adopting methods of topology. At each node the root structure was defined as consisting of three root types: unbranched, long branched and fine branched. Root system size was expressed as the number and length of roots of these individual types. Rhizomatous and non-rhizomatous clones of Festuca rubra differed in the size and structure of their root systems and in the response to lowered red/far red light ratio. This response was caused more by the behaviour of the rhizomes than of the roots alone. In rhizomatous clones, the largest differences in root system structure were between the mother-nodes and the nodes on the rhizomes. The size of the root system also depended on the node position. Response to the red/far red ratio was clone specific only in some of the root parameters, especially in traits of unbranched roots at young nodes. The role of the three root morphotypes in the plant's ontogeny, nutrient uptake and ability to cope with environmental heterogeneity both above- and below ground, is discussed.

Root system growth and nodule establishment on pea (Pisum sativumL.)

Development of the root system, appearance of nodules, and relationships between these two processes were studied on pea (Pisum sativum L., cv. Solara). Plants were grown in growth cabinets for 4 weeks on a nitrogen-free nutrient solution inoculated with Rhizobium leguminosarum. Plant stages, primary root length, distance from the primary root base to the most distal first-order lateral root, and distance from the root base to the most distal nodule, were recorded daily. Distribution of nodules along the primary root and distribution of laterals were recorded by sampling root systems at two plant stages. Primary root elongation rate was variable, and declined roughly in conjunction with the exhaustion of seed reserves. First-order laterals appeared acropetally on the primary root. A linear relationship was found between the length of the apical unbranched zone and root elongation rate, supporting the hypothesis of a constant time lag between the differentiation of first-order lateral's primordia and their emergence. Decline of the primary root elongation rate was preceded by a reduction in density and length of first-order laterals. Nodules appeared not strictly but roughly acropetally on the primary root. A linear relationship was found between the length of the apical zone without nodule and root elongation rate, supporting the hypothesis of a constant time lag between infection and appearance of a visible nodule. A relationship was found between the presence/absence of nodules on a root segment and the root elongation rate between infection and appearance of nodules on the considered root segment. Regulation of both processes by carbohydrate availability, as a causal mechanism, is proposed.

Micropropagation of White Flowering Eastern Redbud (Cercis canadensis var. alba L.)

Abstract A white flowering Eastern redbud (Cercis canadensis var. alba L.) has been successfully micropropagated. Two node explants collected from the initial flush of spring growth were cultured on woody plant medium (WPM). Increased shoot multiplication occurred at 10,15 and 20 μM (2.3, 3.4 and 4.5 ppm) benzyladenine (BA). Microshoots were rooted in vitro on half strength WPM with a 15-day treatment of 100 and 300 μM (18.6 and 55.9 ppm) α-naphthaleneacetic acid (NAA) or 100 and 300 μM (20.3 and 60.9 ppm) indolebutyric acid (IBA) prior to being moved to full strength WPM without growth regulators. Percentage rooting and the mean number of roots per cutting were comparable between NAA and IBA treated microcuttings, however, the subsequent root morphology differed between the two treatments. NAA treated plants developed a coarse, unbranched root system, while IBA treated cuttings developed a more desireable fine, branched root system. Rooted microshoots were successfully acclimated to greenhouse conditions.

An Improved Method for Non-destructive Measurements of the pH at the Root-Soil Interface (Rhizosphere)

A simple and non-destructive method is described which allows the measurement of the rhizosphere pH of soil-grown plants simultaneously, by optical methods (pH indicator) and by microelectrodes. The surface of the root-soil interface is covered by a prefixed thin sheet ( ~3 mm) of agar mixed with a pH indicator (e.g. bromocresol green). Following observations of the pH changes in the agar, detailed measurements of the pH can be made by pushing antimony microelectrodes through the agar into the rhizosphere. Examples are presented of the pH gradients along the roots of both, 4 year old Norway Spruce trees supplied with NH(4)-N or NO(3)-N (pot experiment) and 60 year old Norway Spruce trees grown on acid mineral soil. In long unbranched roots a distinct pH gradient occurs in the rhizosphere with high values in basal and apical zones and low values in the zone 2 - 5 em behind the root apex. The rhizosphere pH can therefore be considerably higher or lower compared to the bulk soil. This method can be used to accurately measure the pH gradient across the rhizosphere, even by distances less than 1 mm from the root surface. These root-induced pH changes could considerably affect microbial activity and solubility of mineral elements in the rhizosphere and thus also mineral element uptake particularly on acid soils.

Nutritional and root development factors affecting growth of tissue culture plantlets of loblolly pine

Tissue culture plantlets of loblolly pine (Pinus taeda L.) were compared to seedlings to quantify growth and developmental differences. The two plant types were grown in containers in a greenhouse and sampled periodically for twenty weeks. Dry weights and nitrogen and phosphorus concentrations of the shoots and roots were determined every two weeks.During the twenty weeks in the greenhouse, seedlings grew to a greater size than the plantlets, but the relative rates of growth were approximately equal. Plantlets had significantly lower concentrations of nitrogen and phosphorus per g of shoot dry weight. Seedlings were much more efficient at nutrient uptake per g of dry weight of root. Plantlets had thick, unbranched roots, which were inefficient at nitrogen and phosphorus uptake. Nutrient uptake based on an index of root surface area was equal in the plantlets and seedlings.The main differences between plantlets and seedlings apparently were related to root system morphology rather than physiological processes. The uptake of nutrients showed the greatest difference between the plant types.

An Electrical Analogue to Simulate the Oxygen Relations of Roots in Anaerobic Media

AbstractThe paper describes the construction and the theory underlying a simple electrical analogue which may be used to simulate the internal oxygen relations of roots in the wetland condition. The model represents an unbranched root lying within an oxygen sink and consists of twenty circuit units linked in series. Each unit which can be programmed independently, represents the major oxygen diffusion paths, impedances and sinks recognizable in a centimetre‐long segment of root/wet soil system. Simplicity has been achieved by specifying constant radius for the root (0.05 cm), constant potential activity for the external sink, by expressing respiration and radial oxygen loss as a function of root surface area, and by the non‐inclusion of oxygen storage capacity.

The uptake of zinc-65 by oats in relation to soil water content and root growth

Effects of water content of the topsoil on root growth and 65Zn absorption by oats were measured. Seminal roots of oats grew through a labelled uptake layer that had been initially wetted to various water contents. The uptake layer was separated from adjacent layers of wet sand or soil by a thin layer of wax. When the uptake layer was wetted initially and allowed to dry during the uptake period, water content affected root growth and 65Zn uptake similarly. 65Zn absorption by unbranched seminal roots decreased linearly as soil water suction increased from 0.3 to 5 bar. Nevertheless significant amounts of 65Zn were absorbed (40% of that from wet soil) even when the soil water suction exceeded 15 bar, with negligible concomitant uptake of water. Provided the roots had access to water in a subjacent layer, rates of 65Zn absorption from dry soil increased with the age of the plants. The exudation of mucilage from the root was enhanced locally where the soil was dry. The mucilage may facilitate the transfer of zinc to the root in dry soil.