Effects of fluridone and abscisic acid on lateral root initiation and root elongation of excised tomato roots cultured in vitro

Roots of tomato (Lycopersicon esculentum Mill. cv. Bonny Best) were excised and cultured in the presence of the abscisic acid synthesis inhibitor fluridone, and with concentrations of exogenous abscisic acid ranging from 10⁻¹⁰to 10⁻⁴M to determine the effects of abscisic acid and its synthesis inhibition on the development of lateral roots in in vitro cultured tomato roots. Exogenous abscisic acid inhibited lateral root initiation and emergence at concentrations of 10⁻⁶M and greater. Fluridone (10⁻⁶M) enhanced the formation of lateral roots even in the presence of abscisic acid, at all concentrations tested except 10⁻⁴M. Abscisic acid increased apical distance, and fluridone reduced it up to 10⁻⁵M abscisic acid. Both fluridone and abscisic acid reduced lateral and primary root lengths. It was concluded the endogenous abscisic acid is probably involved in the regulation of lateral root initiation and root apical dominance, and that abscisic acid may affect lateral root initiation differently than lateral root emergence. This revised version was published online in June 2006 with corrections to the Cover Date.     

镉与萘复合胁迫对红树植物白骨壤幼苗萌芽及生长的影响

为探讨白骨壤(Avicennia marina)幼苗对重金属镉(Cd)和多环芳烃萘(Nap)复合胁迫的响应,采用砂基栽培,对其幼苗的萌芽和生长进行了研究。结果表明,Cd、Nap复合胁迫对白骨壤萌芽的抑制效应较单一胁迫明显,胁迫前期幼苗成活率提高,胁迫后期则降低。胁迫栽培45 d,10 mg L~(–1)的Nap在叶形态、茎高及各器官生物量上能够减轻Cd胁迫的影响,但增强对根长的抑制作用,10 mg L~(–1) Nap-25 mg L~(–1) Cd处理的叶面积、叶长、叶宽、茎高及全株生物量分别比25 mg L~(–1) Cd处理的提高9.6%、7.9%、7.4%、5.1%和20.2%,但根长则比150 mg L~(–1) Cd处理的下降11.1%。至胁迫栽培90 d,各处理间幼苗器官及全株生物量无显著影响,复合胁迫对叶形态、茎高和根长等的抑制作用要强于单一Cd胁迫。因此,随着复合胁迫时间的延长,Cd和Nap对白骨壤幼苗的生长由拮抗效应转变为协同效应。     

Root morphological and proteomic responses to growth restriction in maize plants supplied with sufficient N

The primary objective of this study was to better understand how root morphological alteration stimulates N uptake in maize plants after root growth restriction, by investigating the changes in length and number of lateral roots, ¹⁵NO₃⁻ influx, the expression level of the low-affinity Nitrate transporter ZmNrt1.1, and proteomic composition of primary roots. Maize seedlings were hydroponically cultured with three different types of root systems: an intact root system, embryonic roots only, or primary roots only. In spite of sufficient N supply, root growth restriction stimulated compensatory growth of remaining roots, as indicated by the increased lateral root number and root density. On the other hand, there was no significant difference in ¹⁵NO₃⁻ influx between control and primary root plants; neither in ZmNrt1.1 expression levels in primary roots of different treatments. Our data suggested that increased N uptake by maize seedlings experiencing root growth restriction is attributed to root morphological adaptation, rather than explained by the variation in N uptake activity. Eight proteins were differentially accumulated in embryonic and primary root plants compared to control plants. These differentially accumulated proteins were closely related to signal transduction and increased root growth.     

Auxin biosynthesis and metabolism in isolated roots of Zea mays

The synthesis and metabolism of indole-3-acetic acid (IAA) was investigated in isolated roots of corn, Zea mays L. Roots were cultured aseptically in media supplemented with either ¹⁴C-tryptophan or ¹⁴C-IAA. Exogenously supplied IAA is rapidly and completely metabolized by root tissues. The main site in the root for the synthesis of IAA is in the apex. Removal of either the root cap or the quiescent center, or the root cap and the quiescent center from the apex has no effect on the IAA-synthesizing ability of the apex. Subdividing the terminal 2.1 cm of the root into various segments and culturing them separately stimulates IAA synthesis in these isolated root tissues. Roots in culture maintain relatively constant IAA levels, reflecting the precise controls of the level of this hormone.     

Plasmodiophora brassicae-induced Cell Death and Medium Alkalization in Clubroot-resistant Cultured Roots of Brassica rapa

Plasmodiophora brassicae causes clubroot in the turnip, Brassica rapa L. We used organ cultures of adventitious roots from B. rapa seedlings to investigate the initial response of resistant and susceptible cultivars to P. brassicae infection. Primary plasmodia of P. brassicae were observed in root hairs of both susceptible and resistant cultured roots. On the other hand, secondary plasmodia were able to proliferate only in the susceptible root culture but not in the resistant one. Root cultures from the susceptible cultivar all developed clubroot 4 weeks after treatment with 10⁴, 10⁵ or 10⁶ spores/ml, but roots from the resistant cultivar did not develop clubroot under the same conditions. Cell death, as measured by Evans blue and TTC dye methods, was observed in cultured roots from the resistant cultivar but did not occur in roots from the susceptible cultivar after exposure to P. brassicae spores. Cell death was inhibited almost completely by EGTA and verapamil but not by the calmodulin antagonist W7. These results suggest the involvement of Ca²⁺ in P. brassicae‐induced cell death. Alkalization of the root culture medium of the resistant cultivar was observed 2 days after treatment with P. brassicae spores but was not observed in root culture medium from the susceptible strain. We conclude that our root culture system must be a useful tool for further studies of the molecular mechanism of clubroot resistance.     

Auxin — Calcium Interaction in Adventitious Root Formation in the Hypocotyl Explants of Sunflower (Helianthus annuus L.)

Auxin-calcium interaction has been studied to understand their involvement in adventitious root initiation from the hypocotyl explants of sunflower (Helianthus annuus L.). When hypocotyl explants were cultured on MS medium (containing calcium), 1 mg l^-1 IAA was found to be optimal for root induction. However, the hypocotyl explants washed in EGTA (10_-5M) solution for the removal of extracellular calcium, when cultured on medium containing IAA and calcium, exhibited enhanced rooting response. When EGTA-washed explants were cultured on the medium supplemented with lanthanum chloride (10^-6 and 10^-5M), it resulted in the inhibition of the rooting response and this inhibitory effect could be alleviated by the simultaneous addition of IAA. Similar observations have been made by using calcium channel blockers, verapamil and TMB-8, and also a calmodulin inhibitor, trifluoperazine. A net influx of extracellular calcium in the differentiating cells is thus presumed to accompany the auxin-induced response. These results have been discussed in light of initial lack of polarity in the decapitated hypocotyl segments subjected to auxin treatment.     

Compartmentation and Fluxes of Sugars in Roots of Phaseolus Vulgaris Under Phosphate Deficiency

The influence of phosphate deficiency on the sugar accumulation and sugar partitioning in the root cells of bean (Phaseolus vulgaris L.) was studied. Bean plants were cultured 17 - 19 d on a phosphate-sufficient and phosphate-deficient nutrient medium. Phosphate deficit in the growth medium resulted in increased sugar concentration for about 30 % in the apoplastic and cytoplasmic compartments as well as in the vacuoles of root cells. However, the distribution of sugars between apoplast and cytoplasm compartment and vacuole was not affected by decreased phosphate concentration. About 20 % of sugars were found in the apoplast and cytoplasm, about 80 % in the vacuole. Low phosphate concentration enhanced influx of exogenous ¹⁴C-sucrose into meristematic and elongation zones of root. The ¹⁴C-labelled sugar content in the root tips increased for about 60 % as compared to control plants. Phosphate deficiency increased also ¹⁴C-glucose uptake and content in the root tips. However, the amount of ¹⁴CO₂ liberated during respiration of P-deficient roots (after feeding with uniformly labelled ¹⁴C-glucose) was lower than ¹⁴CO₂ respired by control plants, thus a large part of accumulated sugars seems to be metabolically inactive. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects and Absorption of Sethoxydim in Cell Cycle Progression of Corn (Zea mays) and Pea (Pisum sativum)

The mechanisms of selective herbicidal action of sethoxydim were investigated by using cultured root tips of corn (Zea mays L. cv Goldencrossbantam) and pea (Pisum sativum L. cv Alaska). Meristematic cells in the cultured roots were arrested in G₁ and G₂ of the cell division cycle by sucrose starvation and resumed growth and cell division (proliferation) when sucrose was provided. Corn root growth after sucrose addition was inhibited by sethoxydim at concentrations of 0.01 micromolar and greater when roots were treated in the presence of sucrose but was not inhibited at 10 micromolar sethoxydim when they were treated during sucrose starvation. Greater absorption of [¹⁴C]sethoxydim into the meristematic region of corn roots was observed when cells were in proliferative condition but not when they were arrested by sucrose starvation, whereas no greater absorption of the herbicide into pea meristems was observed in either growth condition. In the cell cycle study, greater absorption of [¹⁴C]sethoxydim into the corn root meristem was observed at a certain limited time before S (DNA synthesis) stage. The physiological effects and the greater absorption of sethoxydim clearly depended on cell cycle progression of corn root meristem, whereas fatty acid synthesis, as well as its inhibition by sethoxydim, was not associated with either cell cycle progression or greater absorption of the herbicide.     

Irpexil (Methyl-acethydroxamoilacetate)-induced changes in some membrane functions and transmembrane potential in wheat seedling root segments

Abstract

A strong K⁺-dependent, fusicoccin-sensitive increase in acidic extrusion paralleled by a corresponding increase in net K⁺ uptake and hyperpolarization of transmembrane electrical potential was observed in the root segments of wheat seedlings cultured in diluite CaSO₄+0.27 mM Methyl-acethydroxamoilacetate. Moreover, K⁺-induced depolarization was also increased up to three times.     

Stimulation of in vitro root and shoot growth of potato by increasing sucrose concentration in the presence of fluridone,an inhibitor of abscisic acid synthesis

Fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, strongly stimulated rooting of nodal stem segments of potato (Solanum tuberosum L.) cultivar Arran Banner cultured in darkness on tuberisation medium. Inclusion of 10^-6 M ABA in the culture medium prevented this rooting response, indicating that root proliferation in the presence of fluridone could be due to inhibition of ABA synthesis. The rooting response to fluridone (increased total root number and root fresh weight) was obtained only at high sucrose concentrations (0.175 and 0.234 M) and was demonstrated with two potato cultivars and two culture media; one which favoured tuberisation and one which did not. Shoot numbers were also increased, but to a lesser extent than root numbers, and total fresh weight of plant material per culture was greatly increased by inclusion of both fluridone (10^-6 or 10^-5 M) and 0.234 M sucrose in the culture medium. The role of sucrose was not simply osmotic because when the osmolarity of fluridone medium was increased using mixtures of mannitol and sucrose, no root proliferation occurred unless sucrose predominated in the mixture.     

A tissue culture of the Ostrich fern Matteuccia struthiopteris (L.) Todaro

Multiple bud formation was induced from shoot apices of Matteuccia struthiopteris cultured on semi-solid Knudson's medium supplemented with 10^-5 and 10^-6 M kinetin. The effect of kinetin, naphthaleneacetic acid and gibberellic acid on shoot and root development is discussed and a three-part tissue culture system was devised for micropropagation and rooting.     

Photoautotrophic growth response of in vitro cultured coffee plantlets to ventilation methods and photosynthetic photon fluxes under carbon dioxide enriched condition

Effects of two ventilation methods (forced and natural) and two photosynthetic photon fluxes (PPF, 150 and 250 μmol m⁻² s⁻¹) on the photoautotrophic growth of in vitro cultured coffee (Coffea arabusta) plantlets were investigated. Number of air exchanges was 2.7, 5.9 and 3.9 h⁻¹ for forced low rate, forced high rate and natural ventilation, respectively. Single node cuttings of in vitro cultured coffee plantlets were cultured on Florialite, a mixture of vermiculite and cellulose fibers with high air porosity, emerged in liquid half strength basal MS medium, without sucrose, vitamins and plant growth regulators. The study included 40 days in the in vitro stage and 10 days in the ex vitro stage. Mean fresh and dry weights, leaf area, shoot and root lengths and net photosynthetic rate per plantlet were significantly greater in forced high rate treatments compared with those in natural and forced low rate treatments. PPF had a distinct effect on shoot length suppression and root elongation of coffee plantlets in forced high rate treatments. The control of carbon dioxide concentration inside the culture box according to the plant demand when growing was easy with the forced ventilation method in photoautotrophic micropropagation. This revised version was published online in June 2006 with corrections to the Cover Date.     

NO和H2O2诱导大豆根尖和边缘细胞耐铝反应的作用

 NO和H₂O₂是参与植物抗非生物胁迫反应的重要信号分子, 为了确定NO和H₂O₂在大豆(Glycine max)根尖和根边缘细胞(root border cells, RBCs)耐铝反应中的作用及其相互关系, 以‘浙春3号’大豆为材料, 研究了铝毒胁迫下大豆根尖内源NO和H₂O₂的变化, 以及外源NO和H₂O₂诱导大豆根尖和RBCs的耐铝反应。结果表明, 50 μmol·L^–1 Al处理48 h显著抑制大豆根的伸长, 提高Al在根尖的积累, 同时显著增加根尖内源NO和H₂O₂含量。施加0.25 mmol·L^–1外源NO供体亚硝基铁氰化钠(Na₂[Fe(CN)₅NO]·2H₂O, sodium nitroprusside, SNP)和0.1 mmol·L^–1H₂O₂, 能有效地缓解Al对大豆根伸长的抑制、根尖Al积累和RBCs 的死亡, 该缓解作用可以被0.05 mmol·L^–1 NO清除剂2-(4- 羧基苯)-4,4,5,5- 四甲基咪唑-1- 氧-3- 氧化物, 钾盐(C₁₄H₁₆N₂O₄·K, carboxy-PTIO, cPTIO)和150 U·mL^–1 H₂O₂清除酶(catalase, CAT)逆转。并且外源NO能够显著促进根尖H₂O₂的积累, 而外源H₂O₂对根尖NO的含量无显著影响。这表明NO和H₂O₂是诱导大豆根尖及RBCs耐铝反应的两种信号分子, NO可能通过调控H₂O₂的形成, 进而诱导大豆根尖及RBCs的耐铝反应。     

Effects of Brassinolide with Naphthalene Acetic Acid on the Formation of Adventitious Roots,Trichome-Like Roots and Calli from Cultured Tobacco Leaf Segments,and the Expression Patterns of <Emphasis Type="Italic">CNT103</Emphasis>

We treated cultured tobacco leaf segments with brassinolide (BL) and naphthalene acetic acid (NAA) and determined that optimum concentrations of NAA for adventitious root, trichome-like root, and calli formation were, respectively, 10⁻⁶, 10⁻⁵, and 10⁻⁴ M. In the adventitious root formation group, the number and length of adventitious roots were increased at lower concentrations of BL; however, they became trichome-like roots at higher levels of BL. The trichome-like root formation group showed better development when a low concentration of BL was added. However, at higher concentrations of BL, trichome-like root production was reduced, forming calli instead. In the calli formation group, more calli were formed at low BL concentrations and after persistent exposure to BL regardless of BL concentration, and the size of the leaf segments increased. The CNT103 gene, which is expressed at the root tips showed increased levels of expression at BL concentrations up to 10⁻⁹ M and decreased levels of expression at BL concentrations over 10⁻⁹ M in the adventitious roots, trichome-like roots, and calli formation groups.     

Comparison of ginsenoside composition in native roots and cultured callus cells of Panax quinquefolium L.

In order to compare the ginsenoside composition in native Panax quinquefolium and in suspension cultured cells derived from root callus, HPLC–ESI-MSⁿ analysis was performed. Under the present HPLC–ESI-MSⁿ conditions, ten ginsenosides from native root were acquired in the positive and negative ion modes, namely Rg₁, Re, Ro, malonyl-Rb₁, Rf, Rb₁, Rc, Rb₂, Rb₃ and Rd. Only four ginsenosides (Rg1, Re, Rf and Rb1) were identified from callus cells. Radical scavenging activity of P. quinquefolium callus cells with 250 mg l^?1 methanolic extract on 1,1-diphenyl-2-picrylhydrazyl (DPPH) was 55.72 %, while only 6.31 % DPPH inhibition was obtained in native root.     

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.     

Increase of Scopolamine Production by High Density Culture of Duboisia myoporoides Roots

A circulation culture system was established for the high density root culture of Duboisia roots. It consists of a vessel for root culture, an aeration tube, a medium reservoir, and a peristaltic pump. Medium saturated with pure oxygen was circulated continuously through the culture vessel and the medium reservoir, and was pumped back into the aeration tube by the pump. Duboisia roots could be cultured at densities of up to 120g dry weight (DW) dm^?3 with no decrease in scopolamine content, this density being about 20 times the amount that can be used in ordinary flask culture. The final scopolamine yield at the end of 3 weeks was 1350mgdm^?3.     

Tiba inhibition of <Emphasis Type="Italic">in vitro</Emphasis> organogenesis in excised tobacco leaf explants

Summary Triiodobenzoic acid (TIBA), an anti-auxin, was found to inhibit both shoot and root formation in cultured excised leaf explants of tobacco (Nicotiana tabacum L.). The shoot formation (SF) medium used required only exogenous cytokinin (N⁶-benzyladenine) and the root formation (RF) medium required both auxin (indole-3-butyric acid) and cytokinin (kinetin). By transferring the explants from SF or RF media to SF or RF media with TIBA (4.0×10⁻⁵ M), respectively or vice versa, at different times in culture, it was found that TIBA inhibition was at the time of meristemoid formation and after determination of organogenesis. This indicates that TIBA interfered with endogenous auxin involvement in organized cell division.     

Deoxyribonucleic Acid synthesis in root cap cells of cultured roots of convolvulus

Isolated cultured roots of Convolvulus arvensis L. were incubated in 0.2 microcurie per milliliter methyl-³H-thymidine for 14 hours, for 64 hours, or for 14 hours followed by transfer to fresh nutrient medium without tritiated thymidine. Autoradiographs of serial, longitudinal sections of roots which were continuously incubated with tritiated thymidine showed that cells of the root cap columella did not undergo DNA synthesis after their formation from the root cap initials. In roots pulse-labeled with tritiated thymidine, the movement of labeled cells through the root cap columella was followed. Labeled cells were displaced at a constant rate of 72 microns per day over a period of 6 to 9 days before they were sloughed off from the root cap. The specialized role of the root cap cells in relation to their distinctive metabolism and longevity is discussed.     

Improvement of ginsenoside production by jasmonic acid and some other elicitors in hairy root culture of ginseng (Panax ginseng C. A. Meyer)

Summary Hairy root cultures of Panax ginseng, established after the infection of root sections with Agrobacterium rhizogenes KCTC 2703, were cultured in phytohormone-free Murashige and Skoog (MS) liquid medium containing different concentrations of jasmonic acid and some other elicitors, in order to promote ginsenoside accumulation. Jasmonic acid in the range 1.0−5.0 mg l⁻¹ (4.8–23.8 μM) strongly improved total ginsenoside production in ginseng hairy roots. Peptone (300 mg l⁻¹) also showed some effect on ginsenoside improvement; however its effect was much weaker than that of jasmonic acid. Ginsenoside content and productivity were 58.65 and 504.39 mg g⁻¹, respectively. The Rb group of ginsenoside content was increased remarkably by jasmonic acid, while Rg group ginsenoside content changed only slightly compared to controls. However, jasmonic acid also strongly inhibited ginseng hairy root growth.