The metabolism of abscisic acid in flacca,a wilty mutant of tomato

The wilty tomato mutant flacca and the normal variety Rheinlands Ruhm were used in this research. The mutant phenotype was explained mainly by hormonal changes. One of these, the decrease in abscisic acid level, was suggested as the hormonal change closest to the mutated gene. The cause of the lower abscisic acid level in the mutant, which may be enhanced breakdown or inactivation, or inhibited biosynthesis, was investigated. The first possibility was studied by comparing mutant and normal plants treated with t-abscisic acid-2-C¹⁴ for (1) rate of production of labeled methanol-extractable metabolites and (2) radioactivity remaining in the methanol-unextractable fraction. The level of trans, trans-abscisic acid relative to that of cis,trans-abscisic acid was studied in untreated plants. Only two radioactive regions containing metabolites of abscisic acid were detected from either of the plant types, and their rates of production relative to total radioactivity was equal. The radioactivity in the methanolunextractable fraction and the level of trans,trans-abscisic acid were very low in both mutant and normal plants. The second possibility was studied partly by comparing the levels of various xanthophylls in mutant and normal plants and their effect after illumination on cress seed germination. Xanthophylls of both plant types were identical in their absorption spectra, but their levels were higher in the mutant. Of these xanthophylls, illuminated neoxanthin inhibited seed germination in both plant types, but more effectively in the mutant. The most probable explanation for the low level of cis,trans-abscisic acid in flacca is that the conversion of farnesyl PiP to abscisic acid is inhibited in this plant.     

Spatio-temporal changes in endogenous abscisic acid contents during etiolated growth and photomorphogenesis in tomato seedlings

The role of abscisic acid (ABA) during early development was investigated in tomato seedlings. The endogenous content of ABA in particular organs was analyzed in seedlings grown in the dark and under blue light. Our results showed that in dark-grown seedlings, the ABA accumulation was maximal in the cotyledons and elongation zone of hypocotyl, whereas under blue-light, the ABA content was distinctly reduced. Our data are consistent with the conclusion that ABA promotes the growth of etiolated seedlings and the results suggest that ABA plays an inhibitory role in de-etiolation and photomorphogenesis in tomato.     

Symptom hypersensitivity to acid infusion is associated with hypersensitivity of esophageal contractility

Several investigators have observed that repeated acid infusions induce stronger symptoms (symptom hypersensitivity). The goal of our study was to determine whether symptom hypersensitivity is associated with esophageal contractile hypersensitivity. Subjects with chronic heartburn symptoms underwent simultaneous pressure and ultrasound imaging of esophagus. Normal saline and 0.1 N HCl were sequentially infused into the esophagus, and subjects scored heartburn symptoms on a 1-10 scale. Saline and HCl infusions were repeated in 10 subjects with a positive Bernstein test. Esophageal contraction amplitude and duration and muscularis propria thickness were measured using a computerized method during recording. Acid infusion induced heartburn. Esophageal contractions had higher amplitudes (pressure 114.2 +/- 7.0%) and longer duration (116.8 +/- 4.4%) during acid infusion compared with saline infusion. Average muscle thickness was greater during acid infusion than saline infusion (107.0 +/- 2.0%). Sustained esophageal contractions (SECs) were identified during acid infusion. A second acid infusion (acid-2) induced heartburn with shorter latency (93.0 +/- 15.0 vs. 317.0 +/- 43.0 s) and stronger severity (8.5 +/- 0.5 vs. 5.3 +/- 0.8) than the first acid infusion (acid-1). Contraction amplitudes (140.2 +/- 13.0%), average muscle thickness (118.0 +/- 3.3%), and contraction duration (148.5 +/- 5.6 vs. 116.8 +/- 4.4%) were higher during acid-2 than acid-1. Also, numbers of SECs were greater during acid-2 than acid-1 (31 in 8 subjects vs. 11 in 6 subjects). Our data show that acid infusion into esophagus induces esophageal hypersensitivity and that a close temporal correlation exists between symptom hypersensitivity and contractility hypersensitivity.     

The 7B-1 mutant in tomato shows blue-light-specific resistance to osmotic stress and abscisic acid

Germination of wild-type (WT) tomato ( Lycopersicon esculentum Mill.) seed is inhibited by mannitol (100-140 mM) in light, but not in darkness, suggesting that light amplifies the responsiveness of the seed to osmotic stress (M. Fellner, V.K. Sawhney (2001) Theor Appl Genet 102:215-221). Here we report that white light (W) and especially blue light (B) strongly enhance the mannitol-induced inhibition of seed germination, and that the effect of red light (R) is weak or nil. The inhibitory effect of mannitol could be completely overcome by fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, indicating that mannitol inhibits seed germination via ABA accumulation in seeds. The inhibition of WT seed germination by exogenous ABA was also amplified by W or B, but not by R. In a recessive, ABA-overproducing, 7B-1 mutant of tomato, seed germination and hypocotyl growth were resistant to inhibition by mannitol or exogenous ABA, both in W or B. Experiments with fluridone suggested that inhibition of hypocotyl growth by W or B is also partially via ABA accumulation. De-etiolation in the mutant was especially less in B compared to the WT, and there was no difference in hypocotyl growth between the two genotypes in R. Our data suggest that B amplifies the responsiveness of tomato seeds and hypocotyls to mannitol and ABA, and that W- or B-specific resistance of the 7B-1 mutant to osmotic stress or ABA is a consequence of a defect in B perception or signal transduction.     

Investigations on the endogenous levels of abscisic acid in a range of parasitic phanerogams

The endogenous levels of abscisic acid in the parasitic phanerogamsArceuthobium oxycedri (DC) Bieb.,Cassytha filiformis L.,Lathraea squamaria L.,Melampyrum pratense L.,Orobanche hederae Duby., andViscum album L. were investigated. In general, the content of abscisic acid was high in parasites which deprive their hosts of both phloem- and xylem-transported substances and much lower in those that deprive their hosts of sap from the xylem only. Within the parasites studied in more depth (e.g.,Orobanche hederae, Lathraea squamaria, andMelampyrum pratense) the highest abscisic acid levels were found in their sink regions, especially in their inflorescences. It is suggested that a high concentration of abscisic acid is associated with plant tissues showing a high demand for phloem-transported substances. The possible role of abscisic acid in such tissues is discussed.     

Changes in endogenous abscisic acid and cold hardiness in Actinidia treated with triazole growth retardants

Soil drench of either paclobutrazol or uniconazole (0.4 mg/pot) was applied to plants of Actinidia arguta, Ananasnaja, to determine the effect on endogenous abscisic acid measured in November, January, and March, and the concomittant cold hardiness of the treated plants. Both paclobutrazol and uniconazole treatments significantly increased cold hardiness. Paclobutrazol was more effective in increasing ABA levels compared to uniconazole. Abscisic acid was found to be highest in January, corresponding to deep dormancy, and least in March when plants were undergoing vegetative bud break. Paclobutrazol delayed vegetative bud break by 6.3 days, while uniconazole delayed bud break by 2.9 days.     

Blue light control of hypocotyl elongation in etiolated seedlings of Lactuca sativa (L.) cv. Grand Rapids related to exogenous growth regulators and endogenous IAA, GA3 and abscisic acid

Results of studies on the interaction of blue light (B) and exogenous applied plant hormones (IAA, GA3 and ABA) as well as inhibitors of their synthesis on the control of hypocotyl elongation in etiolated seedlings of Lactuca sativa (L.) cv. Grand Rapids are presented, and compared with endogenous GA3, IAA and ABA levels measured by capillary gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM). Hypocotyl elongation of etiolated seedlings was linearly inhibited by increasing the B fluence rate between 0 and 18.3 mol m–2 s–1. Both GA3 and IAA added to the incubation medium at different concentrations were able to eliminate partially the inhibition of growth caused by 7.2 mol m–2 s–1 B. When dark (D)-grown seedlings were treated with Ca-prohexadione, a specific inhibitor of gibberellin 3-hydroxylation, they showed a growth inhibition similar to under B. Also, a suppression of growth as in B was obtained when D-grown seedlings were treated with ABA 380 M. By lowering ABA levels with fluridone (an inhibitor of ABA synthesis) a partial reversion of hypocotyl growth inhibition was obtained in B-grown seedlings. While none of the growth promoters used were able to reverse completely the growth inhibition caused by B, a proper combination of GA3, IAA and (eventually) fluridone, abolished the B effects. Correspondingly, lower levels of GA3 and IAA and a higher concentration of ABA were measured by GC-MS-SIM in B-grown hypocotyls than in D-grown ones. These results support the hypothesis that hormones are implicated in mediation of B light-dependent inhibition of hypocotyl elongation, which seems to be the result of a balance among endogenous levels of growth promoting and growth inhibiting hormones.     

Stomatal responses to jasmonic acid, linolenic acid and abscisic acid in wild-type and ABA-deficient tomato plants

Wild-type and abscisic acid (ABA) -deficient (sitiens) tomato plants were used to analyse the effects of abscisic acid (ABA), butyric acid (BA), jasmonic acid (JA) and linolenic acid (LA) on assimilation and transpiration rates in detached leaves taking up those substances into the transpiration stream. BA did not affect assimilation and transpiration rates. ABA decreased assimilation and transpiration in both wild-type and ABA-deficient mutants. JA reduced the assimilation rate in both lines but induced a significant reduction of transpiration in the wild type only. The response to LA in both lines was slower than that to JA.     

Phytochrome A, phytochrome B and HY4 are involved in hypocotyl growth responses to natural radiation in Arabidopsis: weak de-etiolation of the phyA mutant under dense canopies

The roles of phytochrome A (phyA), phytochrome B (phyB) and a putative blue-light (BL) photoreceptor (HY4) in the control of hypocotyl growth by natural radiation were investigated using phyA, phyB and hy4 mutants of Arabidopsis thaliana. Full sunlight inhibited hypocotyl growth to a larger extent in wild-type (WT) than in phyA, phyB and, particularly, hy4 seedlings. In WT seedlings, hypocotyl growth was promoted by selectively lowering BL irradiance, lowering red-light (R) plus far-red-light (FR) irradiance or lowering the R/FR ratio (which was achieved either by increasing FR or by reducing R). The effects of lowering BL were reduced in hy4 and exaggerated in phyA seedlings. The effects of lowering R+FR were reduced in phyA and exaggerated in hy4 seedlings. Neither phyB nor hy4 mutants responded to low R/FR ratios. Neighbouring plants reflecting FR without shading caused subtle reductions of the R/FR ratio. This signal promoted hypocotyl growth in WT but not in phyA, phyB or hy4 seedlings. Intermediate canopy shade produced similar effects in all genotypes. Under deep shade, de-etiolation was severely impaired in phyA seedlings, which died prematurely. Thus, the FR ‘high-irradiance reaction’ mediated by phyA could be important for seedling survival under dense canopies.     

The relation between recalcitrancy of a mangrove plant, Kandelia obovata, and high endogenous level of abscisic acid

Kandelia obovata Sheue, Liu & Yong sp. nov. is one of the cold tolerant mangrove plants. Some callus formation was obtained from the leaves of K. obovata in liquid medium containing 10 μM of 2,4-dichlorophenoxyacetic acid. However, recalcitrancy was found when subculturing them. Endogenous levels of gibberellins (GAs) and abscisic acid (ABA) in leaf protoplasts of K. obovata were determined using micro-scale extraction and purification steps, including thin layer chromatography and quantification by micro-bioassay or enzyme linked immunosorbent assays. Very high amounts of ABA and low activities of GAs were found in leaf protoplasts of K. obovata. Low concentrations of gibberellic acid and uniconazole-P were effective of enhancing cell enlargement in protoplast cultures. Exogenous application of ABA was inhibitory to protoplast culture. All cytokinins tested were inhibitory to both leaf and protoplast cultures. The high endogenous level of ABA is most likely the underlying cause of recalcitrancy of mangrove cultures.     

Reduced growth of autumn-sown wheat in a low-P soil is associated with high colonisation by arbuscular mycorrhizal fungi

Autumn-sown wheat (Triticum aestivum) was studied over two seasons in south-eastern Australia, on a low-P soil where indigenous arbuscular mycorrhizal fungi (AMF) were known to provide little nutritional benefit to crops. It was hypothesised that AMF would be parasitic under these circumstances. Shoot dry mass and water soluble carbohydrate (WSC) reserves in roots and shoots were measured for wheat grown with or without P-fertiliser, in plots where crop sequences had produced either high or low colonisation by AMF. Application of P-fertiliser greatly increased crop growth and decreased colonisation by AMF. At tillering, colonisation by AMF ranged from 24 to 66% of root length when no P was applied and from 11 to 32% when P was applied. At each P-level, high colonisation correlated with reductions of around 20% in stem and root WSC concentrations (first season) or shoot WSC content and shoot dry mass (much drier second season). Impacts on yield were not significant (first season) or largely masked by water-stress and frost (second season). While the major fungal root diseases of the region were absent, interactions between crop sequence and other unknown biotic constraints could not be discounted. The results are consistent with the parasitic impacts of colonisation by AMF being induced primarily through the winter conditions experienced by the crops until anthesis. It is concluded that wheat in south-eastern Australia may benefit from reduced colonisation by AMF, which could achieved through selected crop sequences or, perhaps, targeted wheat breeding programs.     

Signalling of abscisic acid to regulate plant growth.

Abscisic acid (ABA) mediated growth control is a fundamental response of plants to adverse environmental cues. The linkage between ABA perception and growth control is currently being unravelled by using different experimental approaches such as mutant analysis and microinjection experiments. So far, two protein phosphatases, ABI1 and ABI2, cADPR, pH, and Ca2+ have been identified as main components of the ABA signalling pathway. Here, the ABA signal transduction pathway is compared to signalling cascades from yeast and mammalian cells. A model for a bifurcated ABA signal transduction pathway exerting a positive and negative control mechanism is proposed.     

Reduced naphthylphthalamic acid binding in the tir3 mutant of Arabidopsis is associated with a reduction in polar auxin transport and diverse morphological defects.

Polar auxin transport plays a key role in the regulation of plant growth and development. To identify genes involved in this process, we have developed a genetic procedure to screen for mutants of Arabidopsis that are altered in their response to auxin transport inhibitors. We recovered a total of 16 independent mutants that defined seven genes, called TRANSPORT INHIBITOR RESPONSE (TIR) genes. Recessive mutations in one of these genes, TIR3, result in altered responses to transport inhibitors, a reduction in polar auxin transport, and a variety of morphological defects that can be ascribed to changes in indole-3-acetic acid distribution. Most dramatically, tir3 seedlings are strongly deficient in lateral root production, a process that is known to depend on polar auxin transport from the shoot into the root. In addition, tir3 plants display a reduction in apical dominance as well as decreased elongation of siliques, pedicels, roots, and the inflorescence. Biochemical studies indicate that tir3 plants have a reduced number of N-1-naphthylphthalamic (NPA) binding sites, suggesting that the TIR3 gene is required for expression, localization, or stabilization of the NPA binding protein (NBP). Alternatively, the TIR3 gene may encode the NBP. Because the tir3 mutants have a substantial defect in NPA binding, their phenotype provides genetic evidence for a role for the NBP in plant growth and development.     

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     

Photoinhibition-induced reduction in photosynthesis is alleviated by abscisic acid,cytokinin and brassinosteroid in detached tomato leaves

Detached leaves of tomato (Lycopersicon esculentum Mill.) experienced photoinhibition associated with sharp reductions in net photosynthetic rate (Pn), quantum efficiency of PSII (Φ_PSII) and photochemical quenching (qP) even though they were exposed to mild light intensity (400 μmol m⁻² s⁻¹ PPFD) at 28°C. Photoinhibition and the reduction in Pn, Φ_PSII and qP, however, were significantly alleviated by 1 mg l⁻¹ ABA, 0.1 mg l⁻¹ N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) and 0.01 mg l⁻¹ 24-epibrassinolide (EBR). Higher concentrations, however, reduced the effects or even exacerbated the occurrence of photoinhibition. Superoxide dismutase and ascorbate peroxidase activity in leaves increased with the increases in ABA concentration within 1–100 mg l⁻¹, CPPU concentration within 0.1–10 mg l⁻¹ and EBR concentration within 0.01–1.0 mg l⁻¹. Catalase and guaiacol peroxidase activity also increased with the increase in EBR concentration but CPPU and ABA treatments at higher concentrations caused a decrease. Malondialdehyde (MDA) content decreased with the increase in CPPU concentration. ABA and EBR, however, decreased MDA concentration only at 1 and 0.01 mg l⁻¹, respectively. In conclusion, detached leaves had increased sensitivity to PSII photoinhibition. Photoinhibition-induced decrease in photosynthesis, however, was significantly alleviated by EBR, CPPU and ABA at a proper concentration.     

Effects of abscisic acid on the levels of endogenous gibberellin-like substances in Solanum andigena

Summary Treatment of young, fully expanded leaves of Solanum andigena with synthetic abscisic acid resulted in marked increases in gibberellin-like substances. Abscisic acid treatment caused increases in the gibberellin content of leaves excised from both short day and long day grown plants.     

Reduced placental docosahexaenoic acid levels associated with increased levels of sFlt-1 in preeclampsia

Our earlier studies, in preeclamptic women have shown altered levels of long chain polyunsaturated fatty acids (LCPUFA), essential constituents of the cell membrane lipids responsible for membrane stability as one of the key factors contributing to the pathophysiology of preeclampsia. We have also reported elevated levels of sFlt-1 in preeclampsia. The present study examines the levels of LCPUFA and their association with sFlt-1 levels in 69 pre-eclamptic women and 40 normotensive women. DHA and omega 3 fatty acid levels were lower (p<0.001) while arachidonic acid and omega 6 fatty acid levels were higher (p<0.05) in preeclamptic women as compared to normotensive women. Maternal plasma sFlt-1 levels were higher (p<0.05) in preeclamptic women and were negatively associated with DHA (p=0.008) and omega 3 fatty acids concentrations (p=0.031). Our results suggest that altered placental LCPUFA may result in altered membrane lipid fatty acid composition leading to increased release of sFlt-1 in circulation.