Influence of external zinc and phosphorus supply on Cd uptake by rice (Oryza sativa L.) seedlings with root surface iron plaque

Rice seedlings were grown in hydroponic culture to determine the effects of external Zn and P supply on plant uptake of Cd in the presence or absence of iron plaque on the root surfaces. Iron plaque was induced by supplying 50 mg l⁻¹ Fe²⁺ in the nutrient solution for 2 day. Then 43-day-old seedlings were exposed to 10 μmol l⁻¹ Cd together with 10 μmol l⁻¹ Zn or without Zn (Zn–Cd experiment), or to 10 μmol l⁻¹ Cd with 1.0 mmol l⁻¹ P or without P (P–Cd experiment) for another 2 day. The seedlings were then harvested and the concentrations of Fe, Zn, P and Cd in dithionite–citrate–bicarbonate (DCB) extracts and in roots and shoots were determined. The dry weights of roots and shoots of seedlings treated with 50 mg l⁻¹ Fe were significantly lower than when no Fe was supplied. Adsorption of Cd, Zn and P on the iron plaque increased when Fe was supplied but Cd concentrations in DCB extracts were unaffected by external Zn or P supply levels. Cd concentrations in shoots and roots were lower when Fe was supplied. Zn additions decreased Cd concentrations in roots but increased Cd concentrations in shoots, whereas P additions significantly increased shoot and root Cd concentrations and this effect diminished when Fe was supplied. The percentage of Cd in DCB extracts was significantly lower than in roots or shoots, accounting for up to 1.8–3.8% of the plant total Cd, while root and shoot Cd were within the ranges 57–76% and 21–40% respectively in the two experiments. Thus, the main barrier to Cd uptake seemed to be the root tissue and the contribution of iron plaque on root surfaces to plant Cd uptake was minor. The changes in plant Cd uptake were not due to Zn or P additions altering Cd adsorption on iron plaque, but more likely because Zn or P interfered with Cd uptake by the roots and translocation to the shoots.     

Copper uptake and translocation in chicory ( Cichorium intybus L. cv. Grasslands Puna) and tomato (Lycopersicon esculentum Mill. cv. Rondy) plants grown in NFT system. I. Copper uptake and distribution in plants

The uptake and distribution of copper was examined in chicory (Cichorium intybus L. cv. Grasslands Puna) and tomato (Lycopersicon esculentumMill. cv. Rondy) plants grown in a Nutrient Film Technique System (NFT) with addition of 0.05, 5, 10 and 20 mg Cu L^-1. Biomass production of shoots and roots of both chicory and tomato was strongly depressed by Cu concentrations higher than 5 mg Cu L^-1 in the rooting media. Although Cu concentrations in both shoots and roots of both species increased with increasing Cu concentrations in the rooting media, the increase in roots was very much greater than that in shoots, in which the range of concentrations was small. A large proportion of total Cu uptake was retained by roots except when plants were grown in solution Cu concentrations of 0.05 mg Cu L^-1. Copper retention by roots limited Cu translocation to xylem and shoots. Copper adsorption by the root appears to buffer against increases of Cu in the rooting media. A cupric-sensitive electrode used in conjunction with total Cu analysis by graphite furnace atomic absorption spectrophotometry (GFAAS) indicated that more than 99.6% of total Cu in xylem sap was in a complexed form. Large differences between measured and predicted Cu accumulation by shoots of tomato (0.134–0.243 mg Cu plant^-1, 0.660–4.274 mg Cu plant^-1, respectively) and chicory (0.095–0.203 mg Cu plant^-1, 0.626–1.620 mg Cu plant^-1, respectively) suggest that some xylem transported Cu is recirculated to roots via the phloem. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of jasmonic acid on in vitro explant growth and microtuberization in potato

The shoot fresh mass, root length and root numbers of two potato (Solanum tuberosum L.) cultivars Favorita and Helanwuhua were increased significantly by the application of 0.2 – 2 mg dm⁻³ jasmonic acid (JA) in the Murashige and Skoog medium. However, the growth of potato explants was inhibited by JA at high concentrations (20 – 50 mg dm⁻³). Chlorophyll content in explant leaves decreased with an increase in the concentration of JA. In leaves treated with 0.2 mg dm⁻³ JA acid peroxidase activity increased, while in the leaves treated with more than 2 mg dm⁻³ JA peroxidase activity decreased. Under the dark, the microtuber numbers, fresh mass and percentage of big microtubers of two potato cultivars were not promoted by the application of 0.2 – 50 mg dm⁻³ JA.     

Salicylic acid can regulate phloem unloading in the root tip

In three-day-old maize (Zea mays L.) seedlings, we removed the endosperm, coleoptile with leaflets, and adventitious roots. Primary roots were exposed to 0–10⁻³ M salicylic acid (SA) for 1–5 h; scutellum, to 10⁻² M 2-desoxy-D-glucose (2dG). 2dG-sucrose synthesized from 2dG was transported from scutella to the roots along the phloem. Its accumulation in 5-mm-long root tips was the measure of phloem unloading. At the concentrations higher than 10⁻⁴ M, SA suppressed unloading. Simultaneously, the uptake of ¹⁴C-5,5-dimethyloxazolidinedione (DMO) by root segments was inhibited, indicating cytoplasm acidification. 10⁻³ M SA also inhibited root respiration and growth. The lower SA concentrations (10⁻⁵ and 10⁻⁶ M) activated unloading under conditions of weak sucrose phloem transport to the root. They did not affect DMO uptake, respiration, and growth. 10⁻⁴ M SA stimulated unloading during 1- or 2-h exposure but did not affect it at longer treatments. A dependence of SA action on its concentration and exposure duration implies its involvement in the control of phloem unloading in the root tip.     

Cell division activation in the quiescent center of excised maize root tip

The phenomenon of activating cell proliferation in the quiescent center of excised maize roots is described. The root tips were grown on wet filter paper in Petri dishes. This phenomenon was observed in 8 to 14 maize cultivars and was absent in excised Arabidopsis root tips. The distribution of mitoses in meristems greatly varied in individual seedlings roots from the same seed lot and seedlings of different cultivars. Meristem opening was observed after the removal of small root tips not longer than 3 mm and intact seminal roots. Sucrose (2%) and 10⁻⁶–10⁻⁸ M indole-3-acetic acid did not prevent meristem opening. These findings indicate that the state of quiescent center is maintained by a system of intercellular and interorgan relations, which are to be clarified.     

Root regeneration as an indicator of aluminium toxicity in loblolly pine

Loblolly pine (Pinus taeda L.) seedlings were grown in sand culture and exposed to solution Al concentrations of 0, 5, 10, 20, 40, and 80 mg.l⁻¹ in two separate studies. Root regeneration potential (RRP) of loblolly pine was found to be very sensitive to Al. Both the total number and total length of new white roots produced during a 24-day period declined with as little as 5 mg Al.l⁻¹ in solution.     

Impact of phosphorus mineral source (Al–P or Fe–P) and pH on cluster-root formation and carboxylate exudation in Lupinus albus L.

Lupinus albus L. were grown in rhizoboxes containing a soil amended with sparingly available Fe–P or Al–P (100 μg P g⁻¹ soil/resin mixture). Root halves of individual plants were supplied with nutrient solution (minus P) buffered at either pH 5.5 or 7.5, to assess whether the source of mineral-bound P and/or pH influence cluster-root growth and carboxylate exudation. The P-amended soil was mixed 3:1 (w/w) with anion-exchange resins to allow rapid fixation of carboxylates. Treatments lasted 10 weeks. Forty percent and 30% of the root mass developed as cluster roots in plants grown on Fe–P and Al–P respectively, but cluster-root growth was the same on root-halves grown at pH 5.5 or 7.5. Mineral-bound P source (Al– or Fe–P) had no influence on the types of carboxylates measured in soil associated with cluster roots—citrate (and trace amounts of malate and fumarate) was the only major carboxylate detected. The [citrate] in the rhizosphere of cluster roots decreased with increased shoot P status (suggesting a systemic effect) and also, only for plants grown on Al–P, with decreased pH in the root environment (suggesting a local effect). In a separate experiment using anion exchange resins pre-loaded with malate or citrate, we measured malate (50%) and citrate (79%) recovery after 30 days in soil. We therefore, also conclude that measurements of [citrate] and [malate] at the root surface may be underestimated and would be greater than the 40- and 1.6-μmol g⁻¹ root DM, respectively estimated by us and others because of decomposition of carboxylates around roots prior to sampling.     

Root growth responses to lead in young maize seedlings

This work was undertaken to follow the appearance and development of symptoms of lead toxicity in growing roots of seedlings. The effects of lead nitrate (10^-2–10⁵ M) were studied on the roots of maize (Zea mays) seedlings, cvs. Diamant and Sterling. The roots were grown on filter paper either on glass in trays or in large Petri dishes. The following characteristics of root growth were studied: seed germination, length of primary and seminal roots, number of seminal and lateral roots, length of branching zone, length of meristem and fully-elongated cells and the number of fully-elongated cells along the daily length increment. 10^-2 M lead nitrate exerted a clear toxic effect on root elongation just after radicle emergence; its influence on shoot growth was weak. However 10^-2 M Pb solution did not affect either radicle emergence itself or seminal root emergence, which can be explained by the impermeability of seed testa to lead salt. The inhibitory effect of 10^-3 M lead nitrate appeared a day later and was not as toxic: the growth of primary and seminal roots proceeded at lower rate due to a partial inhibition of cell division and cell elongation in them. 10^-3 M lead nitrate modified the root system morphology: it exerted no effect on the emergence of lateral roots and their number, but induced a more compact distribution of lateral roots along a shorter branching zone due to a reduced length of mature cells in the primary root. As a result of the more prominent inhibition of primary root growth, a shorter branching zone with more compactly located lateral roots occupied a position much closer to the root tip than in roots grown without the influence of lead.     

The role of sucrose and nitrogen in adventitious root formation on cultured rose shoots

Cultured shoots ofRosa ‘Improved Blaze’ were used to determine the effects of sucrose and inorganic nitrogen on adventitious root formation. Shoots grown in media containing high sucrose concentrations (146.07–262.93 mM) produced more and longer roots than those grown in media containing 0–87.64 mM sucrose. This response to sucrose was related to the metabolism of sucrose rather than its osmotic properties since the use of mannitol and 3-O-methyl-α-D-glucopyranoside as osmotic substitutes did not reproduce the effect on rooting. The number and length of roots increased when the shoots were grown in media with the nitrogen concentration of the Murashige-Skoog (MS) salt formulation reduced from 60 to 7.5 mM. Neither nitrate (NO ₃ ⁻ ) nor ammonium (NH ₄ ⁺ ) alone at any of the concentrations tested had the effect on rooting that both had together in the ratio of the MS salt formulation. When the sucrose and nitrogen concentrations were both varied, the greatest rate of root initiation occurred on shoots grown in media with a high sucrose to nitrogen concentration ratio.     

Chloramphenicol effects on adventitious root production by radish hypocotyls

Abstract

The excision of the root accelerates greatly the formation of adventitious roots in the hypocotyl of etiolated radish seedlings, but if the seedlings develop in CAP 1×10^?4M, no adventitious root are induced after cutting. IAA either alone or associated with CAP, significantly increases the number of primordia in normal hypocotyls if given at the moment of cutting, while it has not stimulatory effect on the hypocotyls of seedlings grown in CAP. IAA has significant effect on both elongation and tickening of hypocotyl segments prepared from seedlings grown in CAP, and this could indicate a specific action of the inhibitor either on a particular process or on particular cells.

The endodermis and the pericycle, which are the two cell layers implicated in the formation of the adventitious roots, could be the mediators of this particular effect of CAP in rooting.     

Root growth of potato crops on a marine-clay soil

Summary In 1982 and 1983 root samples were taken by auger from potato crops grown on marine clay in the Flevo-Polder. The roots increased their penetration depth throughout the periods of measurement, and ultimately reached depths between 80 cm and 100 cm below the hills. Between 50 and 60 days after emergence, decay of roots commenced, starting in the upper horizons. In the hill mean root length densities varied between 1 and 2 cm cm⁻³. Below the hills root density rarely exceeded 1 cm cm⁻³. The random variation in root density was equivalent to a coefficient of variation of 50%. There were significant effects of the position of sampling (relative to the centre of the plant) on root density; densities were usually lowest beneath the furrow. Depending on season and sampling date, total root length varied between 3.4 and 7.1 km m⁻², and root dry mass varied between 33 and 77 g m⁻². Representative figures for specific root length were 100–120 m g⁻¹ dry weight. About 90% of the root diameters were smaller than 0.44 mm; the most frequent class (35%) were roots with diameters between 0.12 and 0.20 mm.     

Micropropagation ofTribulus terrestris L., an important medicinal plant

Direct regeneration of shoots and roots through juvenile expiants has been achieved inTribulus terrestris. Cotyledonary leaves along with epicotyl segment from young seedlings were cultured on MS medium containing various concentrations of auxin with cytokinin and glutamine. A combination of 0.2 mgL⁻¹ NAA, 0.5 mgL⁻¹ BAP and 50 mgL⁻¹ glutamine induced high frequency of shoot and root differentiation in 10 weeks. The callus also could be induced on the above medium from the cut end of radical segments. Morphogenic response such as per cent shoot and root differentiation was recorded at regular intervals.     

Root growth and calcium uptake in relation to calcium concentration

Summary The purpose of the present work has been to investigate the influence of calcium supply on root growth in barley. The plants were grown in pots, in which the upper part was a sand-perlite mixture and the lower part a test solution with varying calcium concentration (10⁻⁶–10⁻² M CaCl₂). The two parts were separated by a peat layer impeding a calcium transport from the upper to the lower part. The growth of the roots in the test media was examined daily by counting the total number of roots and the number of roots with laterals. The development of the number of roots had an exponential course at all calcium concentrations and was enhanced by increased calcium concentration. At harvest it was found that the size of the roots (length and dry weight) decreased with decreasing calcium concentration to a certain extent.     

Influence of inoculum morphology on growth of Atropa belladonna hairy roots and production of tropane alkaloids

Summary The specific growth rate of Atropa belladonna hairy roots measured in terms of root length increased by about 25% to 0.49 d^-1 when the inoculum consisted of a root with the primary root tip excised. The biomass dry weight produced after 14 d increased by 28%. In contrast, presence of laterals in the inoculum with or without lateral tips excised did not influence the growth rate. Although hyoscyamine was found to accumulate at higher concentrations in the more mature root tissues (2.1 ± 0.2 mg g^-1) than in the tips (1.1 ± 0.3 mg g^-1), hyoscyamine content in the harvested roots was independent of inoculum morphology.     

Effect of Chilling on DNA Endoreplication in Root Cortex Cells and Root Hairs of Soybean Seedlings

Relative nuclear DNA contents in cortex parenchyma cells in root segments of 3- and 7-d-old soybean seedlings grown at 25 °C and in plants grown for 3 d at 25 °C, and then for 4 d at 10 °C, were determined with cytophotometry. Measurements revealed that in each variant the cortex cell nuclei with DNA content between 2C and 8C were in all the examined segments and nuclei with 8C – 16C DNA appeared in higher parts of roots. However, in chilled plant cells the number of 8C – 16C DNA nuclei was very low. Therefore, chilling inhibited endoreplication in comparison with plants grown at 25 °C for 7 d, and even reduced endopolyploidy level as compared to the initial seedlings, i.e. 3-d-old plants. DNA contents in root hairs grown at 25 °C (control) and in root hairs emerged at 10 °C were also determined. In controls 4C – 8C DNA nuclei predominated while in chilled plants an additional population of 2C – 4C DNA appeared. Thus a reduction of DNA synthesis was brought about by low temperature. The occurrence of an intermediate DNA contents besides those with full endoreplication cycles suggests the possibility of differential DNA replication. This suggestion seems to be supported by the lack of ³H-thymidine incorporation into root hair nuclei at the examined developmental stage both in control and chilled root hairs. The same number, but larger, chromocentric lumps in polyploid cortex cell nuclei of higher root zones, in comparison to meristematic nuclei, suggests that endoreduplication process occurred. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of VA-mycorrhiza in growth and mineral nutrition of apple (Malus pumila var.domestica) rootstock cuttings

One-year-old apple cuttings (Malus pumila var.domestica cv. M26) were grown for 6 months in pot culture with and without inoculum of the VA-mycorrhizal fungus (VAMF)Glomus macrocarpum in soil from a long-term fertilizer field experiment with different P availability (20, 210, and 280 mg CAL-extractable P kg⁻¹). The indigenous VAMF propagule density was reduced by 0.5 Mrad X-irradiation. At harvest, non-inoculated and inoculated plants had similar proportions of root length bearing vesicles. Net dry weight of tree cuttings was significantly increased by inoculation only at 20 mg P kg⁻¹ (+62%). Increasing P availability from 210 to 280 mg P kg⁻¹ led to a 4-week depression of shoot elongation rate only in the inoculated plants. Uptake of P was significantly enhanced by inoculation at 20 and 210 mg P kg⁻¹ (+64 and +12%, respectively). On average, inoculated plants had significantly higher concentrations of Zn in leaves and in roots (+16 and +14%, respectively) and of copper in stems and in roots (+13 and +126%, respectively). Proportion of vesicle bearing root length was significantly correlated with root caloric content. A lipid content of 0.9–4.5% in the root dry matter was attributed to the presence of vesicles corresponding to 1.6–8.2% of total root caloric content. As the control plants were also infected, the beneficial effect of VA-mycorrhiza on nutrient uptake and growth of apple cuttings was underestimated at all P levels. Furthermore, VAM-potential at the lowest P level was not fully exploited as onset of infection was most certainly delayed because of a decreased photosynthetic rate due to P deficiency. Energy drain by VAMF-infection was most probably underestimated considerably, due to, among others, loss of infected root cortex during root growth, sampling and staining. It is concluded that apple cuttings rely on VA-mycorrhizal P-uptake at least in low P soils. In high P soils, apple cuttings may profit predominantly from the uptake of Zn and Cu by the fungal symbionts.     

In vitro PPFD and media composition affect both in and ex vitro performance of Alstroemeria Butterfly-hybrids

The objective was to reduce in vitro production costs while retaining or improving plant quality, in particular the suitability for pot plant production. Plants were grown at photosynthetic photon flux densities (PPFD) of 0–40 μmol m^-2 s^-1 and sucrose concentrations of 3–7% during the multiplication phase and the effects of sucrose, BA, and NAA during root formation were investigated. Ex vitro growth were tested in both experiments. A small reduction in the rhizome multiplication rate was found with increasing PPFD and sucrose concentration. Increasing sucrose concentration reduced the number of aerial shoots. Aerial shoots were etiolated when cultured in darkness and their number increased with increasing PPFD at 3% sucrose, whereas PPFD did not affect the number of aerial shoots at 5 or 7% sucrose. During the multiplication phase a synergistic promoting effect of PPFD and sucrose was observed on root formation. Root formation after transfer to rooting medium was affected by sucrose and PPFD during the multiplication phase. PPFD did not influence root formation after propagation on 7% sucrose, whereas on 3 or 5 % sucrose root formation was gradually inhibited when PPFD was decreased below 17 μmol m^-2 s^-1. The formation of thick roots was promoted by propagation in light, and not influenced by sucrose concentration. Ex vitro growth was not affected by in vitro conditions, except for 7% sucrose during the multiplication phase that reduced flowering. Root formation on rooting medium was reduced by BA and promoted both by NAA and high levels of sucrose. The root inhibiting effect of BA could not completely be overcome by simultaneous application of NAA and high sucrose concentrations. Thick roots were only produced in the presence of NAA, and not affected by sucrose treatment. Ex vitro flowering was negatively influenced by the presence of BA during root formation and by high levels of sucrose if BA was absent in the rooting medium. High sucrose levels and NAA could partially compensate for the negative effect of BA on flowering. This revised version was published online in June 2006 with corrections to the Cover Date.     

Very fine roots respond to soil depth: biomass allocation,morphology, and physiology in a broad-leaved temperate forest

Very fine roots (<0.5 mm in diameter) of forest trees may serve as better indicators of root function than the traditional category of <2 mm, but how these roots will exhibit the plasticity of species-specific traits in response to heterogeneous soil nutrients is unknown. Here, we examined the vertical distribution of biomass and morphological and physiological traits of fine roots across three narrow diameter classes (<0.5, 0.5–1.0, and 1.0–2.0 mm) of Quercus serrata and Ilex pedunculosa at five soil depths down to 50 cm in a broad-leaved temperate forest. In both species, biomass and the allocation of very fine roots were higher in the surface soil but lower below 10-cm soil depth compared to values for larger roots (0.5–2.0 mm). When we applied these diameter classes, only very fine roots of Q. serrata exhibited significant changes in specific root length (SRL; m g⁻¹) and root nitrogen (N) concentrations with soil depth, whereas the N concentrations only changed significantly in I. pedunculosa. The SRL and root N concentrations of larger roots in the two species did not significantly differ among soil depths. Thus, very fine roots may exhibit species-specific traits and change their potential for nutrient and water uptake in response to soil depth by plasticity in root biomass, the length, and the N in response to available resources.     

Micropropagation of bromeliad <Emphasis Type="Italic">Aechmea fasciata</Emphasis> via floral organ segments and effects of acclimatization on plantlet growth

Although suckers and seedlings can be used for the propagation of bromeliads, the low number of propagules and cross-variation limit their uniformity and mass cultivation. In this study, high-efficiency shoot organogenesis and plant regeneration were achieved on callus derived from petal and ovary explants of Aechmea fasciata (Bromeliaceae). Calluses were induced on half-strength Murashige and Skoog inorganic salts (1/2MS) supplemented with 1.0–1.5 mg l⁻¹ 2,4-dichlorophenoxyacetic acid in combination with 1.0 or 0.5 mg l⁻¹ α-naphthaleneacetic acid (NAA), and shoots regenerated after transfer to 1/2MS basal medium containing the combination of 1.0 mg l⁻¹ NAA + 0.5 mg l⁻¹ 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea. Those plantlets grown under a middle light intensity (50 μmol m⁻² s⁻¹) showed a dramatic increase in survival percentage (up to 95%) and the maximum number of newly developing roots. The plantlets that were transplanted onto pots were successfully grown in the greenhouse.     

Effects of humic acid-herbicide interactions on the growth of Pisum sativum in nutrient solution

Slight increases in root length and dry matter production were measured in roots and shoots of Pisum sativum seedlings, when germinated seeds were grown for eight days in a controlled environment chamber, on Nitch nutrient solution to which 10 mg L^-1 soil humic acid (HA) had been added. A concentration of 100 mg L^-1 of HA produced a small reduction in dry matter production of shoots. In the presence of herbicides, 10 mg L^-1 cycluron or 100 mg L^-1 prometone, root elongation and shoot growth was reduced by varying degrees with respect to the control. Nutrient solutions containing 100 mg L^-1 cycluron, 10 or 100 mg L^-1 alachlor, or as little as 0.1 mg L^-1 of 2,4-D resulted in an almost complete suppression of the growth of pea seedlings. The addition of 10 or 100 mg L^-1 of HA to nutrient solution containing the herbicide was found to be either ineffective in enhancing growth, or even further reduced growth, compared to samples grown in the presence of the herbicide alone. The results of this preliminary study suggest that the generally accepted view that humic substances exert a positive effect on plant growth may not occur when humic substances interact with herbicides.