Growth,graviresponsiveness and abscisic-acid content of Zea mays seedlings treated with Fluridone

Ten-d-old seedlings of Zea mays L. cv. Tx 5855 treated with 1-methyl-3-phenyl-5-(3-[trifluoromethyl]phenyl)-4-(1H)-pyridinone (Fluridone) were analyzed for abscisic acid (ABA) content using high-performance liquid chromatography with an analysis sensitivity of 2.5 ng ABA g^-1 fresh weight (FW). Seedlings were divided into three portions: leaves, detipped roots, and root tips (terminal 1.5 mm). Control plants (water treatment only; no Fluridone) were characterized by the following amounts of ABA: leaves, 0.114±0.024 (standard deviation) g ABA g^-1 FW; detipped roots, 0.260±0.039±g ABA g^-1 FW; root tips, no ABA detected. We did not detect any ABA in tissues of Fluridone-treated plants. Primary roots of treated and untreated seedlings were strongly graviresponsive, with no significant differences between the curvatures or the growth rates of primary roots of Fluridone-treated and control seedlings. These results indicate that 1) Fluridone completely inhibits ABA synthesis, and 2) ABA is not necessary for positive gravitropism by primary roots of Zea mays.Abbreviations ABA abscisic acid - Fluridone 1-methyl-3-phenyl-5-(3-[trifluoromethyl]phenyl)-4-(1H)-pyridinone - FW fresh weight - SD standard deviation     

The carotenoid and abscisic acid content of viviparous kernels and seedlings ofZea mays L.

Carotenoid and abscisic acid (ABA) levels were determined in endosperm, embryos and seedlings of wild-type and viviparous (vp) mutants ofZea mays L. Carotenoid concentrations were determined by absorption spectrometry following purification by high-performance liquid chromatography and ABA concentrations by combined gas chromatography-mass spectrometry. Lutein and zeaxanthin were the terminal carotenoids in wild-type tissue. The carotenoid profiles ofvp-1 andvp-8 tissue were similar to that of the wild type; invp-2, vp-5, vp-7 andvp-9 carotenogenesis was blocked at early stages so that xanthophylls were absent. Except forvp-1, where the ABA content was similar to the wild type, the ABA content ofvp embryos was substantially reduced, to 6–16% of the corresponding wild type. Thus, the absence of xanthophylls was associated with reduced ABA content, which was in turn correlated with vivipary. Kernels ofvp-8 had a reduced ABA content although xanthophylls were present. Seedlings of carotenoid-deficient mutants rescued from viviparous kernels contained less ABA than did wild-type seedlings grown in the same way. Furthermore, the ABA concentration of such seedlings did not increase in response to water deficit. Conversely,vp-1 seedlings contained normal levels of carotenoids and ABA. Carotenoid-deficient seedlings did not contain appreciable amounts of chlorophyll so that chloroplast development was not normal. Thus ABA-deficiency could be associated with abnormal plastid development rather than the absence of carotenoids per se.Abbreviations ABA abscisic acid - DAP days after pollination - i.d. internal diameter - FW fresh weight - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - MS mass spectrometry - vp viviparous     

Root Growth, Secondary Root Formation and Root Gravitropism in Carotenoid-deficient Seedlings of Zea mays L.

The effect of ABA on root growth, secondary-root formation androot gravitropism in seedlings of Zea mays was investigatedby using Fluridone-treated seedlings and a viviparous mutant,both of which lack carotenoids and ABA. Primary roots of seedlingsgrown in the presence of Fluridone grew significantly slowerthan those of control (i.e. untreated) roots. Elongation ofFluridone-treated roots was inhibited significantly by the exogenousapplication of 1 mM ABA. Exogenous application of 1 µMand 1 nM ABA had either no effect or only a slight stimulatoryeffect on root elongation, depending on the method of application.The absence of ABA in Fluridone-treated plants was not an importantfactor in secondary-root formation in seedlings less than 9–10d old. However, ABA may suppress secondary-root formation inolder seedlings, since 11-d-old control seedlings had significantlyfewer secondary roots than Fluridone-treated seedlings. Rootsof Fluridone-treated and control seedlings were graviresponsive.Similar data were obtained for vp-9 mutants of Z. mays, whichare phenotypically identical to Fluridone-treated seedlings.These results indicate that ABA is necessary for neither secondary-rootformation nor for positive gravitropism by primary roots. Zea mays, gravitropism, carotenoid-deficient, Fluridone, root growth, vp-9 mutant     

Abscisic acid,xanthoxin and violaxanthin in the caps of gravistimulated maize roots

The occurrence and distribution of abscisic acid (ABA), xanthoxin (Xa) and the carotenoid violaxanthin (Va) were investigated in root tips of maize (Zea mays L. cv. Merit). In roots grown in the dark, Va and ABA were present in relatively high amounts in the root cap and in low amounts in the adjacent terminal 1.5 mm of the root. Xanthoxin was present in equal concentrations in both regions. In roots exposed to light, the ABA distribution was reversed, with relatively low levels in the root cap and high levels in the adjacent 1.5-mm segment. Light also caused a decrease in Va in both regions of the root and an increase in Xa, especially in the cap. In the maize cultivar used for this work, light is necessary for gravitropic curving. This response occurs within the same time frame as the light-induced ABA redistribution as well as the changes in the levels of Va and Xa. These data are consistent with a role for ABA in root gravitropism and support the proposal that Xa may arise from the turnover of Va.Abbreviations ABA abscisic acid - GC gas chromatography - HPLC high-performance liquid chromatography - GC-MS gas chromatography-mass spectroscopy - V_a violaxanthin - Xa xanthoxin     

Distribution of IAA and ABA in gravistimulated primary roots ofZea mays. L.

The transport of¹⁴C-IAA and¹⁴C-ABA applied exogenously to root cap toward the elongation zone was investigated in gravi- and light-stimulated primary roots ofZea mays L. cv. Golden Cross Bantam 70. No significant difference of either IAA or ABA in radioactivities was observed between upper and lower halves of elongation zones during the latent period (0–60 min after the stimulation) of gravitropic response. When quantitative analysis of endogenous IAA and ABA by an internal standard method was carried out 60 min after gravi- and/or light-stimulation, no asymmetric redistribution of either IAA or ABA was observed between upper and lower halves of elongation zones. Light irradiation increased by 20% the contents of ABA in elongation zones. These results suggest that although both IAA and ABA are basipetally transportable and can transmit their information to the elongation zone during a latent period we cannot explain the gravitropic curvature by their redistributions between the two (upper and lower) halves of primary roots ofZea. On the basis of results from the present work and previous papers, the distribution of IAA and ABA in gravistimulatedZea roots is discussed. A part of this study was reported at the Eighth Annual Meeting of the IUPS Commission on Gravitational Physiology at Tokyo 1986.     

Seed development and vivipary in Zea mays L.

Seed development was investigated in kernels of developing wild-type and viviparous (vp-1) Zea mays L. Embryos and endosperm of wild-type kernels began to dehydrate at approx. 35 d after pollination (DAP); viviparous embryos did not desiccate but accumulated fresh weight via coleoptile growth in the caryopses. Concentrations of endogenous abscisic acid (ABA) in the embryo were relatively high early in development, being approx. 150 ng·g^-1 fresh weight at 20 DAP. The ABA content declined thereafter, falling to approx. 50 ng·g^-1 at 30 DAP. Endosperm ABA content was always low, being less than 20 ng·g^-1. There were no differences between wild-type and vp-1 tissues. Immature kernels did not germinate when removed from the ear until late in development. The ability to germinate was correlated with decreasing moisture content in the endosperm at the time of removal; premature drying of immature kernels resulted in greatly increased germination following imbibition. Excised embryos germinated precociously when removed from the endosperm as early as 25 DAP. Such germination could be prevented by treatment with 10^-5 M ABA or by lowering the solute potential (_s) of the medium with 0.3 M mannitol. Treatment of excised embryos with ABA led to internal ABA concentrations comparable to those in embryos in which germination was inhibited in situ. Mannitol treatment did not have this effect, although water-deficit stress of excised embryos resulted in substantial ABA production. Germinated vp-1 embryos were less sensitive to growth inhibition by ABA or mannitol than germinating wild-type embryos. The vp-1 seedlings were not wilty and their transpiration rates were reduced in response to ABA or water shortage.Abbreviations and symbols ABA abscisic acid - DAP days after pollination - FW fresh weight - vp-1 viviparous genotype - _s solute potential     

GRAVITROPISM IN ABSCISIC-ACID DEFICIENT SEEDLINGS OF ZEA MAYS

We did not detect any abscisic acid (ABA) in roots or leaves of carotenoid-deficient mutants of Zea mays. Similarly, we did not detect any ABA in roots or leaves of seedlings treated with Fluridone (an inhibitor of carotenogenesis) even after subjecting them to polyethylene glycol (PEG)-induced moisture stress. Primary roots of untreated, Fluridone-treated, and mutant seedlings were strongly graviresponsive. These results suggest that 1) ABA is not necessary for positive gravitropism by primary roots of these cultivars of Z. mays, and 2) ABA is synthesized via the carotenoid pathway.     

Gravitropism in a starchless mutant of Arabidopsis

The starch-statolith theory of gravity reception has been tested with a mutant of Arabidopsis thaliana (L.) Heynh. which, lacking plastid phosphoglucomutase (EC 2.7.5.1) activity, does not synthesize starch. The hypocotyls and seedling roots of the mutant were examined by light and electron microscopy to confirm that they did not contain starch. In upright wild-type (WT) seedlings, starch-filled plastids in the starch sheath of the hypocotyl and in three of the five columellar layers of the root cap were piled on the cell floors, and sedimented to the ceilings when the plants were inverted. However, starchless plastids of the mutant were not significantly sedimented in these cells in either upright or inverted seedlings. Gravitropism of light-grown seedling roots was vigorous: e.g., 10^o curvature developed in mutants rotated on a clinostat following a 5 min induction at 1 · g, compared with 14^o in the WT. Curvatures induced during intervals from 2.5 to 30 min were 70% as great in the mutant as the WT. Thus under these conditions the presence of starch and the sedimentation of plastids are unnecessary for reception of gravity by Arabidopsis roots. Gravitropism by hypocotyls of light-grown seedlings was less vigorous than that by roots, but the mutant hypocotyls exhibited an average of 70–80% as much curvature as the WT. Roots and hypocotyls of etiolated seedlings and flower stalks of mature plants were also gravitropic, although in these cases the mutant was generally less closely comparable to the WT. Thus, starch is also unnecessary for gravity reception in these tissues.Abbreviations PAR photosynthetically active radiation - PAS periodic acid-Schiff's reagent - PGM phosphoglucomutase - WT wild-type     

Growth and Graviresponsiveness of Primary Roots of Zea mays Seedlings Deficient in Abscisic Acid and Gibberellic Acid

Moore, R. and Dickey, K. 1985. Growth and graviresponsivenessof primary roots of Zea mays seedlings deficient in abscisicacid and gibberellic acid.—J. exp. Bot. 36: 1793–1798. The objective of this research was to determine if gibberellicacid (GA) and/or abscisic acid (ABA) are necessary for graviresponsivenessby primary roots of Zea mays. To accomplish this objective wemeasured the growth and graviresponsiveness of primary rootsof seedlings in which the synthesis of ABA and GA was inhibitedcollectively and individually by genetic and chemical means.Roots of seedlings treated with Fluridone (an inhibitor of ABAbiosynthesis) and Ancymidol (an inhibitor of GA biosynthesis)were characterized by slower growth rates but not significantlydifferent gravicurvatures as compared to untreated controls.Gravicurvatures of primary roots of d-5 mutants (having undetectablelevels of GA) and vp-9 mutants (having undetectable levels ofABA) were not significantly different from those of wild-typeseedlings. Roots of seedlings in which the biosynthesis of ABAand GA was collectively inhibited were characterized by gravicurvaturesnot significantly different from those of controls. These results(1) indicate that drastic reductions in the amount of ABA andGA in Z. mays seedlings do not significantly alter root graviresponsiveness,(2) suggest that neither ABA nor GA is necessary for root gravicurvature,and (3) indicate that root gravicurvature is not necessarilyproportional to root elongation. Key words: Abscisic acid, Ancymidol, Fluridone, gibberellic acid, root gravitropism, Zea mays     

The role of the epidermis and cortex in gravitropic curvature of maize roots

In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53° in 5 h) than in intact roots (82°), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h^-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.Abbreviations df degrees of freedom - IAA indole-3-acetic acid     

Immunological assay of phytochrome in small sections of roots and other organs of maize (Zea mays L.) seedlings

Phytochrome was determined in small sections of maize (Zea mays L.) seedlings by means of a highly specific double sandwich enzyme immunoassay which uses a monoclonal anti-phytochrome antibody for binding phytochrome and anti-phytochrome serum to detect the bound phytochrome. The distribution of phytochrome in maize seedlings was followed from germination to the 7th d after soaking the caryopses. Regions of high phytochrome accumulation were found in the coleoptile tip, the root cap and the shoot apex: the values for 5-d-old seedlings were 120, 80 and 70 g phytochrome per g fresh weight (or 0.91, 0.61 and 0.53 nmol·g^-1), respectively. The mesocotyl and the leaves contained relatively low amounts of phytochrome (less than 10 g·g^-1FW), which were almost uniformly distributed throughout these organs. As might be expected, regions of these organs adjacent to the shoot apex showed higher levels. The root, other than root tip, was almost devoid of phytochrome (0.2 to 0.5 g·g^-1). The general distribution of phytochrome in organs did not change during the development of seedlings. The amount of phytochrome, however, did fluctuate: up to the 5th or 6th d after soaking the caryopses, the levels increased in the regions of high phytochrome accumulation but thereafter decreased. After the 6th d the roots were 15 cm or longer and the coleoptiles became prone to penetration by primary leaves. The tips of adventitious roots, emerging after the 6th d, were also found to contain phytochrome. When the root cap was illuminated (4.3 W·m^-1), phytochrome was degraded as in illuminated shoots. Degradation of phytochrome in coleoptile, mesocotyl and shoot apex started with a lag phase but phytochrome degradation in the root cap and the leaves started without a lag. In contrast to shoot phytochrome, which was almost completely degraded under continuous illumination, about 3% of initial phytochrome was measured in root caps after 24 h continuous illumination. Some of the data, obtained by immunological measurements, may indicate differences between phytochrome, or its synthesis or degradation, in the root cap and shoots. The results are discussed with a view to different red-light-mediated responses of grass seedlings.Abbreviations ABTS 2,2-azino-bis(3-ethylbenz-thiazoline)-sulfonic acid - EIA enzyme immunoassay - PBS phosphatebuffered saline - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Variations in abscisic acid, indole-3-acetic acid and zeatin riboside concentrations in two Mediterranean shrubs subjected to water stress

Water stress induced an increase in endogenous concentrations of ABA in Lavandula stoechas L. plants to 13100 pmol ABA g^–1 FW, which may contribute to the maintenance of water relations between the second and the third day of water stress treatment. After the third day, a sharp decrease in ABA levels was observed to 2630 pmol ABA g^–1 FW, together with a decrease in water content and water potential and a loss of plant response to water stress. Water deficit did not induce an increase in endogenous ABA concentration, which remained at 514 pmol ABA g^–1 FW in Rosmarinus officinalis L., which is more sclerophyllous than L. stoechas. Nevertheless, the relative water content of Rosmarinus officinalis L. after seven days of water stress decreased more than 40% and reached values of –3.2 MPa. R. officinalis showed lower levels of ABA, but significantly higher levels of IAA and ZR than L. stoechas (4 times and 6 times respectively in well watered-plants). The increase in ABA levels is not a common mechanism in these two Mediterranean shrubs which survive under water stress conditions.Abbreviations ABA abscisic acid - d days of water stress treatment - DW dry weight - FW fresh weight - IAA indole-3-acetic acid - RP Reversed Phase - RWC relative water content - TW turgid weight - WC water content - ZR zeatin riboside - water potential     

Dormancy in somatic embryos and seeds ofVitis: changes in endogenous abscisic acid during embryogeny and germination

Abscisic acid (ABA) in extracts of somatic embryos and seeds of Gloryvine (Vitis vinifera L.xV. rupestris Scheele) was measured by gas chromatography-mass spectrometry-selected ion monitoring using deuterated ABA, (±)-[C-3Me-²H₃]ABA, ([²H₃]ABA) as internal standard. The ABA content increased rapidly during embryogeny (0.035 ng/embryo at the globular stage to 0.22 ng/embryo at the mature stage). The level of ABA in the tissues of somatic embryos, expressed in ng/mg dry weight, decreased from the globular stage (0.76 ng/mg) to the mature stage (0.25 ng/mg). Chilling (4° C) induced normal germination of seeds and mature somatic embryos and precocious germination of globular, heart-shaped and torpedoshaped somatic embryos. In all cases chilling led to a marked reduction in endogenous ABA. Exogenous (±)-ABA inhibited the germination of chilled somatic embryos.Abbreviations ABA abscisic acid - [²H₃]ABA (±)-[C-3Me-²H₃]-abscisic acid - BHT 2,6-di-t-butyl-4-methylphenol - GC-MS gas chromatography-mass spectrometry - Me-ABA and Me-[²H₃]ABA methyl esters of ABA and [²H₃]ABA, respectively - SIM selected ion monitoring     

Inversion of gravitropism by symmetric blue light on the clinostat

Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceeded by symmetric preirradiation with blue light (12.7 mol photons·m^–2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 mol·m^–2, and could be separated into two parts: fluences exceeding 5 mol·m^–2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 mol·m^–2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. Thistonic blue-light influence appears to be transient, which is in contrast to the stability observed fortropistic blue-light effects.This work was supported by the Deutsche Forschungsgemeinschaft.     

Variation for Root Aerenchyma Formation in Flooded and Non-Flooded Maize and Teosinte Seedlings

Morphological and anatomical factors such as aerenchyma formation in roots and the development of adventitious roots are considered to be amongst the most important developmental characteristics affecting flooding tolerance. In this study we investigated the lengths of adventitious roots and their capacity to form aerenchyma in three- and four-week-old seedlings of two maize (Zea mays ssp. mays, Linn.) inbred accessions, B64 and Na4, and one teosinte, Z. nicaraguensis Iltis & Benz (Poaceae), with and without a flooding treatment. Three weeks after sowing and following a seven day flooding treatment, both maize and teosinte seedlings formed aerenchyma in the cortex of the adventitious roots of the first three nodes. The degree of aerenchyma formation in the three genotypes increased with a second week of flooding treatment. In drained soil, the two maize accessions failed to form aerenchyma. In Z. nicaraguensis, aerenchyma developed in roots located at the first two nodes three weeks after sowing. In the fourth week, aerenchyma developed in roots of the third node, with a subsequent increase in aerenchyma in the second node roots. In a second experiment, we investigated the capacity of aerenchyma to develop in drained soil. An additional three teosinte species and 15 maize inbred lines, among them a set of flooding-tolerant maize lines, were evaluated. Evaluations indicate that accessions of Z. luxurians (Durieu & Asch. Bird) and two maize inbreds, B55 and Mo20W, form aerenchyma when not flooded. These materials may be useful genetic resources for the development of flooding-tolerant maize accessions.     

Transport and metabolism of [3H]iso-pentenyladenine following application to the tips of intact and decapitated tap roots of Pinus pinea

[³H]iso-Pentenyladenine ([³H]iP) was fed for 24 h to the tips of intact and root tip-decapitated Pinus pinea seedlings. Twelve and 24 h after application to the roots of intact plants most of the applied radioactivity (±60%) was transported to the shoot. Root tip removal increased transport of the applied radioactivity to the shoot, but the overall pattern of distribution of radioactivity in the seedling did not change. Large amounts of radioactivity were recovered from the elongation zone of the root. Some radioactivity also accumulated in the older part of the root with well-developed lateral roots. When [³H]iP was applied one day after decapitation, no significant changes in the pattern of radioactivity distribution were found between the intact and decapitated root systems. However, when applied 7 days after decapitation there was a significant increase of radioactivity in the region of the root where lateral roots were emerging. HPLC separation of extracts from the different root sections showed that [³H]iP was extensively metabolized in the root. Six peaks of radioactivity, which co-chromatographed with authentic cytokinin standards, were detected.Abbreviations ABA abscisic acid - ADE adenine - IAA indole-acetic acid - iP iso-pentenyladenine - HPLC high performance liquid chromatography - [OG]DHZ O-glycosyldihydrozeatin - [9R-MP]DHZ ribosyldihydrozeatin monophosphate - [9G]iP iso-pentenyladenine-9-glucoside - [9R]Z ribosylzeatin - [9R]iP iso-pentenyladenosine - TLC thin layer chromatography     

The role of extracellular free-calcium gradients in gravitropic signalling in maize roots

Gravitropism in roots has been proposed to depend on a downward redistribution of calcium across the root cap. However, because of the many calcium-binding sites in the apoplast, redistribution might not result in a physiologically effective change in the apoplasmic calcium activity. To test whether there is such a change, we measured the effect of gravistimulation on the calcium activity of statocyte cell walls with calcium-specific microelectrodes. Such a measurement must be made on a tissue with gravity sensing cells at the surface. To obtain such a tissue, decapped maize roots (Zea mays L. cv. Golden Cross Bantam) were grown for 31 h to regenerate gravitropic sensitivity, but not root caps. The calcium activity in the apoplasm surrounding the gravity-sensing cells could then be measured. The initial pCa was 2.60 ± 0.28 (approx 2.5 mM). The calcium activity on the upper side of the root tip remained constant for 10 min after gravistimulation, then decreased 1.7-fold. On the lower side, after a similar lag the calcium activity increased 1.6-fold. Control roots, which were decapped but measured before recovering gravisensitivity (19 h), showed no change in calcium activity. To test whether this gradient is necessary for gravitropic curvature, we eliminated the calcium activity gradient during gravitropism by applying a mobile calcium-binding site (di-nitro-BAPTA; 1,2-bis(2-amino-5-nitro-phenoxy)ethane-N,N,N,N-tetraacetic acid) to the root cap; this treatment eliminated gravicurvature. A calcium gradient may be formed by proton-induced calcium desorption if there is a proton gradient. Preventing the formation of apoplastic pH gradients, using 10 and 50 mM 2-(N-morpholino)ethanesulfonic acid (Mes) buffer or 10 mM fusicoccin to stimulate proton excretion maximally, did not inhibit curvature; therefore the calcium gradient is not a secondary effect of a proton gradient. We have found a distinct and rapid differential in the apoplasmic calcium activity between the upper and lower sides of gravistimulated maize root tips which is necessary for gravitropism.Abbreviations BAPTA 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid - FC fusicoccin - Mes 2-(N-morpholino)ethanesulfonic acid The authors thank Phyllis Woolwine for drawing Fig. 1, Dr. Sarbjit Virk for assistance with total calcium measurements, Dr. Paul Sampson for statistical advice, and Michael Newton for developing the EM algorithm to analyze the time-series data. This work was supported by NASA grant NAGW-1394 and by a NASA Research Associateship to T.B. through NASA grant NAGW-70.     

Distribution of growth and proton efflux in gravireactive roots of maize (Zea mays L.)

Roots of Zea mays were maintained in a vertical orhorizontal position and the local elongation rate and H⁺ fluxes were measured using Sephadex beads containing a pH indicator. When the roots were kept horizontally, the growth of the lower side was strongly inhibited and that of the upper side slightly stimulated as compared with vertical roots. The H⁺ extrusion, which was greatest in the elongation zone, was strongly inhibited on the lower side and slightly stimulated on the upper side as compared with vertical roots.     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

Abscisic acid (ABA) inhibition of lateral root formation involves endogenous ABA biosynthesis in Arachis hypogaea L.

ABA has been found to play a significant role in post-embryonic developmental in peanut seedlings. The results from the current study indicate that in the presence of exogenous 10 μmol l⁻¹ ABA, lateral roots (LRs) number decreased and seedling development was delayed. This effect was eliminated by 25 μmol l⁻¹ naproxen, an inhibitor of ABA biosynthesis. The Arabidopsis mutant deficient in ABA biosynthesis, nced3, displays a phenotype with more and longer LRs. We found that ABA decreased root-branching in peanut in a dose-dependent way. ABA-treated seedlings showed higher endogenous ABA levels than the control and naproxen-treated seedlings. RT-PCR results indicated that the expression of AhNCED1, a key gene in the ABA biosynthetic pathway, was significantly up-regulated by exogenous ABA in peanut. The mRNA levels of AhNCED1 began to increase 2 days after ABA treatment. The results from the current study show that ABA inhibits peanut LR development by increasing endogenous ABA contents.