Endogenous abscisic Acid levels in germinating and nongerminating lettuce seed

The concentrations of abscisic acid in Grand Rapids lettuce (Lactuca sativa L.) seeds imbibed under conditions which promote or inhibit germination were determined by electron capture-gas chromatography. The concentration of abscisic acid in dry seeds was 12 to 14 nanograms per 100 milligrams. During 24-hour imbibition, the abscisic acid content diminished more rapidly during conditions which allow germination (25 C in light) than in conditions which inhibited germination (35 C in light or darkness at 25 C). A decrease in endogenous levels of abscisic acid was not always correlated with germination.     

Endogenous levels of abscisic acid in aging carnation flower parts

Aging carnation flower parts were used to determine whether or not any correlation existed between the concentration of abscisic acid (ABA) and a predisposition of the tissue for ethylene synthesis. Levels of ABA were measured using an enzyme-linked immunosorbent assay (ELISA) following purification steps including prepacked silica gel columns. Increased ABA levels paralleled the increase of ethylene and the onset of irreversible wilting in the carnation petals. Neither the green tissue nor the receptacle showed any sign of wilting with the remainder of the flower parts, but increased ABA was detected in both tissues subsequent to, or coincident with, the ethylene climacteric peak in the senescing petals. An increase of ABA in both the styles and the ovary was detected in the preclimacteric flower, and did not appear to be triggered by the production of ethylene. Increased ABA in the gynoecium also did not result in the onset of ethylene production in the preclimacteric flower.     

Endogenous abscisic acid content in cucumber leaves under the influence of unfavourable temperatures and salinity

Endogenous abscisic acid (ABA) content was measured in leavesof Cucumis sativus L. under the influence of hardening (lowand high) temperatures and salinity. The rise in cold and heatresistance of the seedlings was accompanied by a considerableincrease in the ABA level in the leaves. Chloride salinity alsobrought about a rise in the ABA content. The data indicate thatABA may induce resistance when the plants are exposed to severalstresses. Key words: Cucumis sativus, ABA, cold and heat hardening, salinity     

Drought-induced increases in abscisic Acid levels in the root apex of sunflower

Abscisic acid (ABA) levels in 3-mm apical root segments of slowly droughted sunflower plants (Helianthus annuus L. cv Russian Giant) were analyzed as the methyl ester by selected ion monitoring gas chromatography-mass spectrometry using characteristic ions. An internal standard, hexadeuterated ABA (d6ABA) was used for quantitative analysis. Sunflower seedlings, grown in aeroponic chambers, were slowly droughted over a 7-day period. Drought stress increased ABA levels in the root tips at 24, 72, and 168 hour sample times. Control plants had 57 to 106 nanograms per gram ABA dry weight in the root tips (leaf water potential, −0.35 to −0.42 megapascals). The greatest increase in ABA, about 20-fold, was found after 72 hours of drought (leaf water potential, −1.34 to −1.47 megapascals). Levels of ABA also increased (about 7− to 54-fold) in 3-mm apical root segments which were excised and then allowed to dessicate for 1 hour at room temperature.     

Endogenous levels of abscisic acid and indole-3-acetic acid during in vitro rooting of Wild Cherry explants produced by micropropagation

Levels of endogenous ABA and IAA were quantified during the first week of in vitro rooting of Wild Cherry (Prunus avium L.) using IBA in the culture medium. Hormones were measured in the apical, median and basal parts of the explants using an avidin-biotin based enzyme linked immunosorbent assay (ELISA), after a purification of the methanolic extracts by high-performance liquid chromatography (HPLC).Root primordia started to differentiate from day 5 at the basal part of the explants. ABA and IAA showed considerable changes and high levels were detected during the first week of culture. ABA levels increased transiently mainly in the apical part during root formation. Exogenous IBA was possibly transformed into IAA mainly in the basal part of the explants.     

Effects of anaerobiosis on ethylene production, respiration and flowering in iris bulbs

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30°C, production was 12–20 pmol C₂H₄ (kg fresh weight)^?1 h^?1. Higher temperatures (35°C, 40°C) enhanced the ethylene production; a treatment with 40°C for ca 7 days caused a 3 times higher ethylene production than at 30°. During anaerobic storage (in 100% N₂) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N₂ was replaced by air, a burstlike ethylene production was observed. Twenty-four h after the replacement, ethylene production was equal to control values again. The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5-norbornadiene (NBD), an ethylene antagonist. Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity. Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst-like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering.     

Multiplication and distribution of iris severe mosaic virus in secondarily-infected iris bulbs after stress induced by heat and wounding

In freshly-lifted iris bulbs infected with iris severe mosaic virus (ISMV), virus was not always detected in the basal plate and rarely in bulb scale tissue. After exposing the bulbs to stress (wounding or high-temperature treatment) the sensitivity of virus detection was enhanced. The improved detection of viral antigen after local stress (wounding) coincided with an increase of viral RNA synthesis. When general stress (high-temperature treatment) was applied, the virus could be reliably detected in the basal plate, and usually in vascular bundles and surrounding tissue. Virus was detected in the upper part of the bulb scale when such tissues were detached from the basal plate. Thus, virus must have been present in the scales in localised spots, albeit at a very low concentration, and multiplication is likely to be the main factor involved in the improved sensitivity of viral detection. The distribution of ISMV in the bulb after local or general stress treatment is discussed.     

Role of abscisic acid in chilling tolerance of rice (Oryza sativa L.) seedlings. I. Endogenous abscisic acid levels

Changes of ABA levels in chilled rice (Oryza sativa L.) seedlings of two varieties were determined. On exposure to chilling, ABA concentration rapidly increased in the chilling-tolerant cultivar (cv. Tainung 67, TNG.67) but not in the chilling-sensitive cultivar (cv. Taichung Native 1, TN.1). Both detached shoots and roots of TNG.67 seedlings showed a significant ABA increase after exposure to chilling. TN.1 seedlings could not accumulate ABA under low temperature but well-watered status. Exogenous application of the ABA biosynthetic inhibitor, fluridone, reduced ABA accumulation, as well as survival ratio of chilled TNG.67 seedlings. Electrolyte leakage and leaf conductance were also increased by the inhibitor and the effects could be reversed by exogenously applied ABA. ABA concentrations in xylem sap of TNG.67 seedlings increased within 4 h after chilling, and this was temporally coincident with the reduction of leaf conductance. The roles of endogenous ABA in the tolerance of rice seedlings to chilling on a whole plant basis are discussed and suggested.     

The effect of methyl jasmonate and abscisic acid on differentiation of benzyladenine-induced bulblets inMuscari bulbs

Methyl jasmonate (JA-Me) at a concentration of 0.5% in lanolin paste totally inhibited bulblets formation induced by benzyladenine in intactMuscari bulbs. Lower concentrations of JA-Me delayed development and growth of bulblets induced by benzyladenine. It seems that methyl jasmonate acts as a powerful inhibitor of cell division induced by cytokinin in used test. In comparison with methyl jasmonate, abscisic acid did not show an inhibitory effect on bulblets formation induced by benzyladenine, even in a higher concentration.     

Effect of abscisic Acid on the linoleic Acid metabolism in developing maize embryos

Partially purified protein extracts from maize (Zea mays L.) embryos, whether treated or not with abscisic acid (ABA), were incubated with linoleic acid (LA) and 1-[¹⁴C]LA. The resulting LA metabolites were monitored by high performance liquid chromatography with a radioactivity detector and identified by gas chromatography-mass spectrometry. α- and γ-ketol metabolites arising from 9-lipoxygenase activity were the more abundant compounds detected in the incubates, although the corresponding metabolites produced by 13-lipoxygenase were also present in the samples. In addition, a group of stereoisomers originating from two isomeric trihydroxy acids (9, 12, 13-trihydroxy-10-octadecenoic and 9, 10, 13-trihydroxy-11-octadecenoic acids) are described. Important variations in the relative proportions of the LA metabolites were observed depending on the embryo developmental stage and on ABA treatment. Two new ABA-induced compounds have been detected. These compounds are present in embryos at all developmental stages, being more abundant in old (60 days) embryos. Furthermore, ABA induction of these compounds is maximum at very young developmental stages, decreasing as maturation progresses. A tentative structure for these compounds (10-oxo-9, 13-dihydroxy-11-octadecenoic acid and 12-oxo-9, 13-dihydroxy-10-octadecenoic acid) is also provided. This study revealed an early stage in maize embryogenesis characterized by a higher relative sensitivity to ABA. The physiological importance of ABA on LA metabolism is discussed.     

Endogenous levels of abscisic acid,indole-3-acetic acid and benzyladenine during in vitro bud growth induction of Wild cherry (Prunus avium L.)

Levels of endogenous growth substances (abscisic acid: ABA; indole-3-acetic acid: IAA) and applied benzyladenine (BA) were quantified during the eight first days of in vitro propagation of Wild Cherry (Prunus avium L.). Axillary buds from the middle part of the explants started to grow at day 2, thus were released from apical dominance. Hormone levels were measured in the apical, median and basal parts of the explants using an avidin-biotin based enzyme-linked immunosorbent assay (ELISA) after a purification of the extracts by high performance liquid chromatography (HPLC). All hormones showed rapid and considerable changes during the first eight days of growth. Exogenous IBA was probably transformed into IAA mainly in the basal part of the explant, and BA penetrated quickly. ABA levels were transiently enhanced in the apical part of the explants bearing young leaves. These phenomena are discussed in connection with the axillary bud reactivation.     

Endogenous levels of abscisic acid and gibberellins in leaf protoplasts competent for plant regeneration in Betula platyphylla and Populus alba

Differences in endogenous levels of abscisic acid and gibberellinsbetween Betula platyphylla and Populusalba leaf protoplasts were determined using micro-scale extractionand purification steps, including thin layer chromatography ormicro-high-performance-liquid-chromatography and quantification by enzymelinkedimmunosorbent assay or micro-bioassay. The content of abscisic acid was tentimes higher in B. platyphylla than in P.alba on the basis of both cell number and dry weight; in contrast,levels of gibberellins were lower in the former. Leaf protoplasts of bothspecies are competent for plant regeneration through the exogenous supply ofauxins and cytokinins. The function of abscisic acid in these protoplastcultures is discussed in relation to the need for a strong cytokinin,N-(2-chloro-4-pyridyl)-N-phenylurea (4-CPPU) for colony proliferation inB. platyphylla, in contrast to a weak cytokininrequirementin P. alba.     

Endogenous levels of free and conjugated forms of auxin, cytokinins and abscisic acid during seed development in Douglas fir

Endogenous levels of free and conjugated forms of three classes of planthormones were quantified at various stages of megagametophyte development inDouglas fir. Megagametophytes were excised weekly from 8–16 weeks pastpollination (WPP), a period encompassing the central cell to the earlymaturation stage of seed development. The hormones indole-3 acetic acid (IAA),indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine(iP), isopentenyladenosine (iPA), abscisic acid (ABA) and abscisic acid glucoseester (ABA-GE) were extracted, purified, fractionated by high- performanceliquid chromatography (HPLC), and then quantified using an enzyme-linkedimmunosorbent assay (ELISA) method. Z levels ranged from 0–25ng/g dry weight (DW) and were highest in megagametophytes at thecentral cell stage (8 WPP). During embryogenesis, Z levels peakedduring week 13. In contrast, the ZR conjugate was not detected over the periodstudied. The iP content of megagametophytes increased at 10 and 13WPP, while the iPA concentration increased at 13 WPP.Prior to fertilisation, IAA was highest in megagametophytes at 9WPP. During embryogenesis, the major IAA accumulations occurred at11, 13 and 15 WPP, the concentration ranging from 0–0.43g/g DW. IAAsp concentrations reached their highest level duringembryogenesis at 14 WPP. ABA content increased at 11 and 13WPP, with a concentration range of 0.1–13 g/gDW. In contrast, ABA-GE levels were relatively constant over the 9-weekperiod analyzed. The endogenous levels of plant hormones varied withmegagametophyte development and were associated with morphological changes.     

Determination of endogenous abscisic acid levels in immature cereal embryos during in vitro culture

Levels of endogenous abscisic acid (ABA) in immature wheat (Triticum aestivum cv. Timmo) and barley (Hordeum vulgare cv. Golden Promise) embryos have been determined by enzyme-linked immunosorbent assay. Embryos of both cereal species showed an increase in ABA content during development on the parent plant. Immature embryos were excised and cultured in vitro on nutrient media that led to precocious germination or on media containing 9% (w/v) mannitol that maintained their developmental arrest. Barley and wheat embryos responded to these culture conditions in an identical manner with respect to changes in morphology, fresh weight, protein and lectin content. However, in complete contrast, the ABA content of barley embryos increased by an order of magnitude during culture on mannitol, whereas that of wheat embryos showed no significant change. The results are discussed within the context of the role of ABA in the regulation of embryo development.Abbreviations ABA abscisic acid - BGA barley-germ agglutinin - dpa days post anthesis - ELISA enzyme-linked immunosorbent assay - GC-MS gas chromatography-mass spectrometry - WGA wheat-germ agglutinin     

Jasmonic Acid induces tuberization of potato stolons cultured in vitro

The aim of the study was to assess the potential in vitro effects of jasmonic acid and kinetin on tuberization of potato (Solanum tuberosum). Of the two, the former was by far the stronger in vitro promoter of stolon tuberization. Number of tubers induced per stolon, tuberization rate, and final tuber weight were higher by factors of 2.8, 2.3, and 6.4, respectively. Bioassay sensitivity of jasmonic acid, measured in terms of the point at which the concentration for inducing tuberization was saturating, was more than 20 times greater than that of kinetin. Tuberization in both cases was associated with a decrease in rooting ability. Jasmonic acid also triggered a general state of induction throughout the stolon.     

Wild-type levels of abscisic Acid are not required for heat shock protein accumulation in tomato

Levels of endogenous abscisic acid (ABA) in wild type were not required for the synthesis of heat shock proteins in detached leaves of tomato (Lycopersicon esculentum Mill., cv Ailsa Craig). Heat-induced alterations in gene expression were the same in the ABA-deficient mutant of tomato, flacca, and the wild type. Heat tolerance of the mutant was marginally less that the wild type, and in contrast, ABA applications significantly reduced the heat tolerance of wild-type leaves. It was concluded that elevated levels of endogenous ABA are not involved in the tomato heat shock response.     

Endogenous abscisic acid levels in stems and axillary buds of intact or decapitated broad-bean plants (Vicia faba L.)

Endogenous levels of abscisic acid (ABA) were measured by gas-liquid chromatography (electron capture) in stems and axillary buds of intact or decapitated broad-bean plants ( Vicia faba L. cv. Aguadulce). Endogenous ABA was distributed in the main axis according to a concentration gradient from the apical part of the stem towards the base. Axillary buds contained ABA levels which were from 4 to 9 times higher than those in the corresponding nodes and internodes. Decapitation of the plant was followed within 6 h by a large decrease of ABA levels in all the parts of the main axis. The diminution of ABA content was the most important in axillary buds released from apical dominance. Twenty-four hours after the decapitation, the ABA concentration further decreased in the upper parts of the stem, while no modification was observed in the basal parts of the stem containing the smallest levels of ABA.     

Dependence of vitamin B12 levels on the growth rate of cells cultured in vitro

Vitamin B12 content has been determined in different kinds of cells grown in vitro and in the culture media. The results indicate a dependence of the vitamin levels on the growth rate and growth characteristics.