Accumulation and transport of abscisic Acid and its metabolites in ricinus and xanthium

When intact plants of Xanthium strumarium L. were water stressed, the youngest leaves accumulated the highest levels of abscisic acid (ABA). On the other hand, when leaves of different ages were detached and then stressed, the capacity to produce ABA was highest in the mature leaves. Radioactive ABA was transported from mature leaves to the shoot tips and young leaves, as well as to the roots, as evidenced by the presence of radioactive ABA and phaseic acid in the xylem exudate coming from the roots. Thus, ABA was recirculated in the plant, moving down the stem in the phloem and back up in the transpiration stream to the mature leaves. Phloem exudate collected by the use of the EDTA technique had a high concentration of ABA and phaseic acid which increased several-fold after water stress. The high ABA levels in immature leaves and apical buds are, therefore, mainly due to import from older leaves, rather than to in situ synthesis.     

Heat-stable proteins and abscisic Acid action in barley aleurone cells

[³⁵S]Methionine labeling experiments showed that abscisic acid (ABA) induced the synthesis of at least 25 polypeptides in mature barley (Hordeum vulgare) aleurone cells. The polypeptides were not secreted. Whereas most of the proteins extracted from aleurone cells were coagulated by heating to 100°C for 10 minutes, most of the ABA-induced polypeptides remained in solution (heat-stable). ABA had little effect on the spectrum of polypeptides that were synthesized and secreted by aleurone cells, and most of these secreted polypeptides were also heatstable. Coomassie blue staining of sodium dodecyl sulfate polyacrylamide gels indicated that ABA-induced polypeptides already occurred in high amounts in mature aleurone layers having accumulated during grain development. About 60% of the total protein extracted from mature aleurone was heat stable. Amino acid analyses of total preparations of heat-stable and heat-labile proteins showed that, compared to heat-labile proteins, heat-stable intracellular proteins were characterized by higher glutamic acid/glutamine (Glx) and glycine levels and lower levels of neutral amino acids. Secreted heat-stable proteins were rich in Glx and proline. The possibilities that the accumulation of the heat-stable polypeptides during grain development is controlled by ABA and that the function of these polypeptides is related to their abundance and extraordinary heat stability are considered.     

Turnover and metabolism of chlorogenic Acid in xanthium leaves and potato tubers

The active turnover of chlorogenic acid (3-caffeoylquinic acid(3)), a major phenolic component of Xanthium leaves and potato tuber disks, has been demonstrated in these tissues. Pulse-labelling experiments with radioactive l-phenylalanine and trans-cinnamic acid as well as direct feeding experiments with chlorogenic acid-(14)C labelled in the caffeoyl moiety have been employed in the turnover studies. The rate of turnover is calculated to be on the order of 50 to 100 mmumoles per hour per gram fresh weight of tissue.In Xanthium leaves chlorogenic acid is in part converted to an isochlorogenic acid identified by silica gel chromatography as 3,5-dicaffeoylquinic acid. Radioactivity of the caffeoyl moiety of chlorogenic acid is also incorporated into lignin-like insoluble polymers in the leaf. Turnover of chlorogenic acid in tuber tissue is largely accounted for by the incorporation of the caffeoyl moiety into insoluble polymers in the tissue.The significance of chlorogenic acid turnover is discussed in relation to the perception of the photoperiodic stimulus by leaves and to the possible role of chlorogenic acid in lignin synthesis.     

Compartmentation of intracellular nucleotides in mammalian cells

The important role of nucleotides in cellular metabolism requires that serious consideration be given to the question of the homogeneity or inhomogeneity of nucleotide pools in cells. The purpose of this review is to summarize the existing evidence for compartmentation of nucleotide pools, discuss the limitations of this evidence, and to discuss the implications of compartmentation for the interpretation of nucleotide concentration measurements. Evidence for nucleotide compartmentation comes from the following types of evidence: compartmentation of RNA precursors; compartmentation of deoxynucleoside triphosphates; mitochondrial compartmentation; the existence of tightly bound nucleotides; pools derived from alternative synthetic routes; compartmentation in cyclic nucleotide metabolism; channeling in the synthesis of pyrimidine nucleotides; and others. The types of evidence adduced for compartmentation will be considered critically and in detail, and alternative explanations considered, as well. Implications of the data and hypotheses on nucleotide compartmentation for the interpretation of nucleotide pool measurements in various types of experiments will be discussed.     

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in `Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.     

The Compartmentation of Abscisic Acid and beta-d-Glucopyranosyl Abscisate in Mesophyll Cells

β-d-Glucopyranosyl abscisate (ABA-GE) is synthesized in Xanthium strumarium L. leaves during water stress. Following recovery from stress, the amount of ABA-GE does not decline. These observations led to the hypothesis that ABA-GE is sequestered in the vacuole where it is metabolically inert. The localization of abscisic acid (ABA) and ABA-GE was investigated by a dimethyl sulfoxide (DMSO) compartmentation method and by direct isolation of vacuoles.     

Compartmentation and fluxes of inorganic phosphate in photosynthetic cells

An analysis of the compartmentation and fluxes of inorganic phosphate in isolated cladophyll cells from Asparagus officinalis was made in parallel with an ultrastructural study. The elution pattern of labelled inorganic phosphate (which indicates that the asparagus cells are behaving as a system of three compartments in series) was used to quantify the fluxes between the vacuole, cytoplasm and free space. A relaxation time of 198 min was calculated for inorganic phosphate exchange between the vacuole and cytoplasm. It is, therefore, suggested that the vacuole serves to buffer the cytoplasmic inorganic phosphate concentration in the long term. However, in the short term, exchange with the vacuole will not appreciably affect the cytoplasmic inorganic phosphate concentration and thus the partitioning of photosynthetically fixed carbon.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid - P_i inorganic phosphate     

Characterization of maize lines differing in leaf abscisic Acid content in the field. 1 abscisic Acid physiology

The inbred maize lines Poljl7 and F-2 have previously been shown to differ by up to three-fold in leaf abscisic acid (ABA) concentration in the field. Lines from the cross Poljl7 × F-2 differing in leaf ABA concentrations, and the parents, were studied in the field to characterize the differences amongst the lines in ABA concentrations during the season, during the day and in different parts of the plants. The water status of the plants was measured and leaves were heat girdled to get information on possible causes for the genetic variation amongst the lines in ABA concentration. Leaf ABA concentrations of the high-AB A lines increased markedly and consistently from flowering time onwards, whereas leaf ABA concentrations of the low-ABA lines gradually fell after flowering. Leaf water potentials of high-ABA and low-ABA lines were similar during this time. Leaf ABA concentrations varied little during the day, and heat girdling caused a rise in ABA concentrations, which was similar in both high-ABA and low-ABA lines, only after girdling for at least 4 h. ABA concentrations were highest in the leaves and it was only in the leaves and developing kernels that substantial differences in ABA concentrations were found between the high-ABA and low-ABA classes. Although aerial brace roots also had high ABA concentrations, other roots and stem internodes had ABA concentrations which were consistently low and the same for both ABA classes. Differences between the ABA classes were unlikely to be due to differences in leaf water status or in ABA export from the leaves. Other possible explanations for the genotypic differences in leaf ABA concentrations are discussed.     

Acid secretion and intracellular pH in isolated oxyntic cells

Summary This study demonstrates that isolated oxyntic cells are capable of secreting hydrochloric acid. Transitory peaks of medium acidification were observed when isolated oxyntic cells were stimulated with different secretagogues. The duration of these peaks was of about 3 min and had a magnitude of about 0.5 Equiv/hr mg dry weight. These peaks were abolished by selective inhibitors of acid secretion and/or secretagogue action. Cell pH, as measured by the DMO¹⁴C technique increases 0.13 pH units upon stimulation with db-cAMP. This change was abolished by pretreatment with SCN^–. From acidification and cell pH experiments an increase of 5–10 mM in base concentration inside the cell upon stimulation is calculated. These results are interpreted on the basis of the existence of a neutral anion exchange mechanism at the serosal side that serves to control the cell acid-base balance.     

Mode of action of abscisic Acid in barley aleurone layers : induction of new proteins by abscisic Acid

As part of a continuing effort to elucidate the mode of action of abscisic acid (ABA) in barley (Hordeum vulgare L. cv Himalaya) aleurone layers, we have investigated the induction of several polypeptides by ABA in this tissue. There were nine ABA-induced polypeptides as observed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and considerably more (at least 16 spots) on a two-dimensional gel. These proteins started to show enhanced synthesis 2 to 4 hours after ABA treatment, and their synthesis continued for at least 48 hours. In vitro translation using total RNA isolated from ABA-treated aleurone layers indicated that translatable mRNA levels of these proteins essentially paralleled the levels of in vivo synthesized proteins. The most abundant of the ABA-induced proteins was a 29 kilodalton polypeptide which was also synthesized in tissue incubated without ABA. In vivo synthesis of this protein declined as ABA concentration was decreased, with 1 nanomolar ABA approaching control level. Cell fractionation experiments located the 29 kilodalton major ABA-induced protein in 1,000g and 13,000g pellets; most other induced proteins were in the 80,000g supernatant. The 29 kilodalton protein appeared to be sensitive to degradation by sulfhydryl type proteases. As expected, the induction of these proteins by ABA was suppressed by gibberellic acid. Phaseic acid, the first stable metabolite of ABA, suppressed the gibberellic acid-enhanced α-amylase synthesis but was unable to induce the ABA-induced proteins. None of the ABA-induced proteins were secreted into the incubation medium. A 36 kilodalton ABA-induced protein showed cross-reactivity with antibody against a barley lectin specific for glucosamine, galactosamine, and mannosamine.     

Abscission: role of abscisic Acid

The effect of abscisic acid on cotton (Gossypium hirsutum L. cv. Acala 4-42) and bean (Phaseolus vulgaris L. cv. Red Kidney) explants was 2-fold. It increased ethylene production from the explants, which was found to account for some of its ability to accelerate abscission. Absci is acid also increased the activity of cellulase. Increased synthesis of cellulase was not du to an increase in aging of the explants but rather was an effect of abscisic acid on the processes that lead to cellulase synthesis or activity.     

Compartmentation of high-energy phosphates in resting and beating heart cells

The subcellular distribution of ATP, ADP, creatine phosphate and creatine has been analyzed by fast detergent fractionation of isolated frog heart cells. Digitonin fractionation (0.5 mg/ml, 10 s at 2 degrees C in 20 mM 4-morpholinepropanesulfonic acid/3 mM EDTA/230 mM mannitol medium) was used to separate mitochondria and myofilaments from cytosol. To separate myofilaments from the other cellular compartments. Triton X-100 was used (2%, 15 s in the same medium as digitonin). For either resting or beating cells the total cellular contents of ATP, ADP, creatine phosphate and creatine was similar, nevertheless the O2 consumption was 6-times higher. The compartmentation of these metabolites was also identical. Myofilaments contain 1.1 nmol ADP per mg total cellular proteins. In the cytosolic compartment the metabolite concentrations, all measured in nmol per mg total cellular proteins, were: ATP, 13; ADP, 0.25-0.05; creatine phosphate, 18.5 and creatine, 14. This indicated that the reaction catalyzed by creatine kinase was in a state of (or near) equilibrium.     

Involvement of abscisic Acid in potato cold acclimation

Upon exposure to 2°C day/night (D/N), leaves of Solanum commersonii (Sc) began acclimating on the 4th day from a −5°C (killing temperature) hardy level to −12°C by the 15th day. Leaves of S. tuberosum L. (St) cv `Red Pontiac' typically failed to acclimate and were always killed at −3°C. Leaves of control (20/15°C, D/N) and treated plants (2°C, D/N) of St showed similar levels of free abscisic acid (ABA) during a 15-day sampling period. In treated Sc plants, however, free ABA contents increased 3-fold on the 4th day and then declined to their initial level thereafter. The increase was not observed in leaves of Sc control plants.

Treated St plants showed a slightly higher content of leaf soluble protein than controls. In Sc, leaves of controls maintained relatively constant soluble proteins, but leaves of treated plants showed a distinct increase. This significant increase was initiated on the 4th day, peaked on the 5th day, and remained at a high level throughout the 15-day sampling period.

Exogenously applied ABA induced frost hardiness in leaves of Sc plants whether plants were grown under a 20°C or 2°C temperature regime. When cycloheximide was added to the medium of stem-cultured plants at the beginning of 2°C acclimation, or at the beginning of the ABA treatment in the 20°C regime, it completely inhibited the development of frost hardiness. However, when cycloheximide was added to plants on the 5th day during 2°C acclimation, the induction of frost hardiness was not inhibited. The role of ABA in triggering protein synthesis needed to induce frost hardiness is discussed.

     

葡萄果肉细胞脱落酸的区隔化

以处于不同发育时期的红富士葡萄 (VitisviniferaL .×VitislabruscaL .)果实为试材 ,采用胶体金免疫电镜定位技术对果肉细胞脱落酸 (ABA)的区隔化及其动态进行了研究。结果表明 :在果实发育前期 ,ABA主要存在于细胞核和胞质溶胶中 ;随着果实的进一步发育成熟 ,ABA转为主要分布在叶绿体和细胞核中。与处于第Ⅰ期、始熟期以及第Ⅲ期果实的果肉细胞ABA含量相比 ,处于第Ⅱ期的前期果实的果肉细胞ABA含量最低。这些事实说明在果实发育成熟的任一时期 ,果肉细胞ABA均呈区隔化分布 ,其在不同区隔之间的浓度差异随着果实的发育成熟而发生变化 ,即发生了再分配     

Xanthophylls and abscisic Acid biosynthesis in water-stressed bean leaves

Experiments were designed to obtain evidence about the possible role of xanthophylls as abscisic acid (ABA) precursors in water-stressed leaves of Phaseolus vularis L. Leaves were exposed to ¹⁴CO₂ and the specific activities of several major leaf xanthophylls and stress-induced ABA were determined after a chase in ¹²CO₂ for varying periods of time. The ABA specific radioactivities were about 30 to 70% of that of lutein and violaxanthin regardless of the chase period. The specific activity of neoxanthin, however, was only about 15% of that of ABA. The effects of fluridone on xanthophyll and ABA levels and the extent of labeling of both from ¹⁴CO₂ were determined. Fluridone did not inhibit the accumulation of ABA when leaves were stressed once, although subsequent stresses in the presence of fluridone did lead to a reduced ABA accumulation. The incorporation of ¹⁴C from ¹⁴CO₂ into ABA and the xanthophylls was inhibited by fluridone and to about the same extent. The incorporation of ¹⁸O into ABA from violaxanthin which had been labeled in situ by means of the violaxanthin cycle was measured. The results indicated that a portion of the ABA accumulated during stress was formed from violaxanthin which had been labeled with ¹⁸O. The results of these experiments are consistent with a preformed xanthophyll(s) as the major ABA precursor in water-stressed bean leaves.