Trimester-specific diagnostic accuracy of ultrasound for detection of placenta accreta spectrum: systematic review and meta-analysis

BACKGROUND

This study aimed to assess the diagnostic accuracy of ultrasound for detecting placenta accreta spectrum (PAS) during the first trimester of pregnancy and compare it with the accuracy of second and third trimester ultrasound in pregnancies at risk for PAS.

METHODS

PubMed, Embase, and Web of Science, databases were searched to identify relevant studies published from inception until March 10th, 2023. Inclusion criteria were all studies, including cohort, case-control, or cross-sectional studies, that evaluated the diagnostic accuracy of first trimester ultrasound performed prior to 14 weeks (first trimester) or after 14 weeks of gestation (second/third trimester) for diagnosis of PAS in pregnancies with clinical risk factors. The primary outcome was to assess the diagnostic accuracy of ultrasound in detecting PAS in the first trimester, and to compare it with the accuracy of ultrasound in the second and third trimesters. The secondary outcome was to evaluate the diagnostic accuracy of each ultrasonographic marker individually across the trimesters of pregnancy. Reference standard was PAS confirmed at pathological or surgical examination. The potential of ultrasound and different ultrasound signs to detect PAS was assessed by computing summary estimates of sensitivity, specificity, diagnostic odds ratio (DOR) and positive (LR+) and negative (LR-) likelihood ratios.

RESULTS

A total of 37 studies including 5,764 pregnancies at risk of PAS, with 1,348 cases of confirmed PAS, were included in our analysis. The meta-analysis yielded a sensitivity of 86% (95% CI: 78%, 92%) and specificity of 63% (95% CI: 55%, 70%) during the 1st trimester, while the sensitivity was 88% (95% CI: 84%, 91%) and specificity was 92% (95% CI: 85%, 96%) during the 2nd/3rd trimester. Regarding ultrasonographic markers examined in the 1st trimester, lower uterine hypervascularity exhibited the highest sensitivity of 97% (95% CI: 19%, 100%), and uterovesical interface irregularity demonstrated the highest specificity of 99% (95% CI: 96%, 100%). However, in the 2nd/3rd trimester, loss of clear zone had the highest sensitivity of 80% (95% CI: 72%, 86%), while uterovesical interface irregularity exhibited the highest specificity of 99% (95% CI: 97%, 100%).

CONCLUSION

First trimester ultrasound has similar accuracy to second and third trimester ultrasound for the diagnosis of PAS. Routine first trimester ultrasound screening for patients at high risk of PAS may improve detection rates and allow earlier referral to tertiary care centers for pregnancy management. This article is protected by copyright. All rights reserved.

Longitudinal assessment of spiral and uterine arteries in normal pregnancy using novel ultrasound tool

OBJECTIVES

To use superb microvascular imaging (SMI) to evaluate longitudinally spiral artery (SA) and uterine artery (UtA) vascular adaptation in normal human pregnancy, and to develop reference ranges for use at various gestational ages throughout pregnancy.

METHODS

The data for this study were obtained from the National Institutes of Health (NIH)-funded Human Placenta Project. Women aged 18-35 years, with a body mass index < 30 kg/m2 , without comorbidities, with a singleton gestation conceived spontaneously, and gestational age at or less than 13 + 6 weeks were eligible for inclusion. The current analysis was restricted to uncomplicated pregnancies carried to term. Exclusion criteria included maternal or neonatal complications, fetal or umbilical cord anomalies, abnormal placental implantation or delivery < 37 weeks. Women who fulfilled the inclusion criteria formed the reference population of the Human Placenta Project study. Each participant underwent eight ultrasound examinations during pregnancy. The pulsatility index (PI) of both the left and right UtA were obtained twice for each artery and the presence or absence of a notch was noted. Using SMI technology, the total number of SA imaged was recorded in a sagittal placental section at the level of cord insertion. The PI and peak systolic velocity (PSV) were also measured in a total of six SA, including two in the central portion of the placenta, two peripherally towards the uterine fundal portion, and two peripherally towards the lower uterine segment.

RESULTS

A total of 90 women fulfilled the study criteria. Maternal UtA-PI decreased throughout the first half of pregnancy from a mean ± SD of 1.39 ± 0.50 at 12-13 weeks' gestation to 0.88 ± 0.24 at 20-21 weeks' gestation. The mean number of SA visualized in a sagittal plane of the placenta increased from 8.83 ± 2.37 in the first trimester to 16.99 ± 3.31 in the late-third trimester. The mean SA-PI was 0.57 ± 0.12 in the first trimester and decreased progressively during the second trimester, reaching a nadir of 0.40 ± 0.10 at 24-25 weeks, and remaining constant until the end of pregnancy. SA-PSV was highest in early pregnancy with a mean of 57.16 ± 14.84 cm/s at 12-13 weeks' gestation, declined to a mean of 49.38 ± 17.88 cm/s at 20-21 weeks' gestation and continued to trend downward for the remainder of pregnancy, reaching a nadir of 34.50 ± 15.08 cm/s at 36-37 weeks' gestation. A statistically significant correlation was noted between SA-PI and UtA-PI (r = 0.5633; P < 0.001). Multilevel regression models with natural cubic splines were used to create reference ranges of SA-PSV and SA-PI for given gestational ages.

CONCLUSION

From early gestation, we have demonstrated the ability to image and quantify SA blood flow in normal pregnancy, and have developed reference ranges for use at various gestational ages throughout pregnancy. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Unplanned Cesarean delivery is associated with risk for postpartum depressive symptoms in the immediate postpartum period

PURPOSE

Postpartum depression (PPD) is a common pregnancy complication. The association between cesarean delivery (CD) and PPD has shown conflicting results in prior studies, although emergent CD appears to be a clear risk factor. Establishing PPD risk is critical and may, however, be related to the unplanned nature of the CD, rather than the surgery itself. Our objective was to determine whether women who underwent unplanned CD were more likely than those with vaginal delivery to have higher depressive symptoms and thus screen positive for PPD risk in the immediate postpartum period.

MATERIALS AND METHODS

This cohort study was conducted at a community medical center using data for deliveries between 8/2015-1/2016. Women were screened in the hospital for depressive symptoms (PPD risk) using the Edinburgh Postnatal Depression Scale (EPDS) within 4 days post-delivery. Logistic regression, adjusting for maternal race/ethnicity and parity, was performed to evaluate the association between delivery route (vaginal vs planned vs unplanned CD) and PPD risk (EPDS ≥ 10).

RESULTS

A total of 2094 women had complete data for analysis. Overall, 44 women (2.1%) screened positive for PPD risk. Logistic regression results showed that unplanned CD was significantly associated with PPD risk (OR = 2.28, 95% CI 1.13-4.57, p = .022), after adjusting for parity and race/ethnicity. Planned CD was not associated with PPD risk.

CONCLUSION

Unplanned CD may be an independent risk factor for PPD risk in the immediate postpartum period. This finding might explain why some previous studies have demonstrated different results with regards to risk of CD where the unplanned nature of the delivery was not accounted for.

Precise charm to strange mass ratio and light quark masses from full lattice QCD

By using a single formalism to handle charm, strange, and light valence quarks in full lattice QCD for the first time, we are able to determine ratios of quark masses to 1%. For m(c)/m(s) we obtain 11.85(16), an order of magnitude more precise than the current PDG average. Combined with 1% determinations of the charm quark mass now possible this gives m(s)(2 GeV)=92.4(1.5) MeV. The MILC result for m(s)/m(l)=27.2(3) yields m(l)(2 GeV)=3.40(7) MeV for the average of u and d quark masses.

Changes in the metabolic footprint of placental explant-conditioned culture medium identifies metabolic disturbances related to hypoxia and pre-eclampsia

Pre-eclampsia (PE) is a multi-system disorder thought to be mediated by circulating factors released from damaged placental villous trophoblast. There is extensive evidence of changes in the villous tissue in PE, some of which may be replicated by culturing villous tissue in hypoxic conditions. Metabolic footprinting offers a hypothesis-generating strategy to investigate factors released from this tissue in vitro. This study investigated differences in the factors released from villous trophoblast from uncomplicated pregnancies (n=6) and those with PE (n=6). In both cases, explanted placental villous fragments were cultured for 96 h in 1% O(2) (hypoxia) or 6% O(2) (placental normoxia). Metabolites consumed from and released into serum-conditioned culture medium were analysed by Ultra Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS). The relative concentration of 154 features of the metabolic footprint were observed to change in culture medium from uncomplicated pregnancies cultured in normoxic and hypoxic conditions (p<0.00005). 21 and 80 features were also different in culture medium from PE versus uncomplicated pregnancies cultured in hypoxic and normoxic conditions, respectively (p<0.00005). When comparing all 4 groups, 47 metabolic features showed a similar relative concentration in PE-derived media cultured in normoxic conditions to conditioned media from normal villous tissue cultured in hypoxic conditions. These data suggest that hypoxia may have a role in the placental pathogenesis of PE. Three areas of metabolism were highlighted for systems biology investigation; glutamate and glutamine, tryptophan metabolism and leukotriene or prostaglandin metabolism.

The decline of laparoscopic sterilisation

Female sterilisation is an extensively used method of contraception all over the world but there appears to be a decline in the performance of this procedure in Ireland. There also appears to be an increased uptake of safe, long-acting contraceptive alternatives. We set out to establish the extent of the decline of laparoscopic sterilisation and to explore possible explanations. Data for female sterilisation from Ireland was obtained from the Hospital In-Patient Enquiry Scheme (HIPE) section of the Economic and Social Research Institute for the years 1999 to 2004. Recent sales figures for long acting reversible contraceptives, specifically the levo-norgestrel-loaded intrauterine system (LNG-IUS) (Mirena) and the etonogestrel implant (Implanon) were also obtained. Laparoscopic tubal ligations reduced from 2,566(1999) to 910 (2004). In the corresponding period the use of Mirena coils increased from 4,840 (1999) to 17,077 (2004).

Ascertaining women's preferred mode of address and preferred choice of title during pregnancy and childbirth

To determine how women in pregnancy would like to be addressed and to ascertain their preferred choice of title during pregnancy. A questionnaire was administered to 925 antenatal women. Midwifery and medical staff (183) were invited to respond to a similar questionnaire. The response rate was 71.2% from the survey of pregnant women. The vast majority (82.1%) preferred to be addressed by their first name. Women were in favour of being called 'patient' (32.8%) as their first choice. The staff survey yielded a response rate of 77%. The majority (81.8%) of health professionals preferred to address women by their first name. 'Mother' (28.7%) was the most popular first choice. We conclude that women in pregnancy do have a preference on how they would like to be addressed and this is predominantly by first name. Health professionals also prefer to call pregnant women by their first name. The term 'patient' was the most popular first choice of title of women in pregnancy but the term 'mother' was the preferred choice of the health professionals. Medical staff were more likely to choose 'patient' than midwives.

The anthropometric assessment of dysmorphic features in schizophrenia as an index of its developmental origins

BACKGROUND

Evidence suggests that schizophrenia may be a disorder with origins in early intrauterine mal-development. We have constructed a comprehensive anthropometric scale for the evaluation of dysmorphic features as an index of the nature and timing of developmental disturbance.

METHOD

A detailed set of craniofacial and bodily measures was compiled and applied to 174 patients with schizophrenia and 80 matched control subjects.

RESULTS

Patients had significantly higher scores on this scale and displayed multiple anomalies of the craniofacial region with an overall narrowing and elongation of the mid-face and lower face. Twelve craniofacial anomalies independently distinguished patients from controls and these variables correctly classified 95% of patients and 80% of control subjects.

CONCLUSIONS

This new scale, while procedurally more exacting than the Waldrop scale, more clearly defines the topography of anomalies previously suspected in individuals with schizophrenia. These findings constitute direct evidence for disturbed craniofacial development in schizophrenia and indicate origins in the foetal period during which the characteristic human facial pattern evolves in close association with brain differentiation.

Prevalence and correlates of mixed-handedness in schizophrenia

Increased rates of nonright-handedness have been reported in schizophrenia, but a clear distinction has not been made between left- and mixed-handedness. Handedness preferences in 96 patients fulfilling DSM-III criteria for schizophrenia and 43 normal comparison subjects were assessed with the Edinburgh Handedness Inventory. A 100% criterion was used to establish left- and right-handedness. Results were analyzed with mantel-Haenszel odds ratios adjusted for age and sex. The schizophrenic group showed a significant increase in the proportion of mixed-handers compared with the normal group. There was no increase in pure left-handedness in the schizophrenic relative to the normal group. Mixed-handedness in the schizophrenic patients was significantly associated with chronicity of illness. Mixed-handed patients were less likely to have a family history of psychotic illness than patients with strong right- or left-handedness. The results indicate a neurodevelopmental rather than a genetic origin for anomalous lateralization in schizophrenia.

Abscisic acid biosynthesis in roots : I. The identification of potential abscisic acid precursors, and other carotenoids

The pathway of water-stress-induced abscisic acid (ABA) biosynthesis in etiolated and light-grown leaves has been elucidated (see A.D. Parry and R. Horgan, 1991, Physiol. Plant. 82, 320-326). Roots also have the ability to synthesise ABA in response to stress and it was therefore of interest to examine root extracts for the presence of carotenoids, including those known to be ABA precursors in leaves. All-trans- and 9'-cis-neoxanthin, all-trans- and 9-cis-violaxanthin, antheraxanthin (all potential ABA precursors), lutein and β-carotene were identified on the basis of absorbance spectra, reactions with dilute acid, retention times upon high-performance liquid chromatography and by comparison with leaf carotenoids that had been analysed by mass spectrometry. The source of the extracted carotenoids was proved to be root tissue, and not contaminating compost or leaf material. The levels of total carotenoids in roots varied between 0.03-0.07% of the levels in light-grown leaves (Arabidopsis thaliana (L.) Heynh, Nicotiana plumbaginifolia Viv., Phaseolus vulgaris L. and Pisum sativum L.) up to 0.27% (Lycopersicon esculentum Mill.). The relative carotenoid composition was very different from that found in leaves, and varied much more between species. All-trans-neoxanthin and violaxanthin were the major carotenoids present (64-91 % of the total), but while Lycopersicon contained 67-80% all trans-neoxanthin, Phaseolus, Pisum and Zea mays L. contained 61-79% all-trans-violaxanthin. Carotenoid metabolism also varied between species, with most of the carotenoids in older roots of Phaseolus being esterified. Roots and leaves of the ABA-deficient aba mutant of Arabidopsis had reduced epoxy-xanthophyll levels compared to the wild-type.

Abscisic acid biosynthesis in roots : II. The effects of water-stress in wild-type and abscisic-acid-deficient mutant (notabilis) plants of Lycopersicon esculentum Mill

The ubiquity of the apo-carotenoid abscisic acid (ABA) biosynthetic pathway elucidated in water-stressed, etiolated leaves of Phaseolus vulgaris (see A.D. Parry and R. Horgan, 1991, Physiol. Plant. 82, 320-326), has been difficult to establish. Light-grown leaves contain very high carotenoid: ABA ratios, preventing correlative studies, and no etiolated leaves so far studied, other than those of Phaseolus, have been found capable of synthesising significant amounts of ABA in response to stress. Roots are known to synthesise ABA and contain low carotenoid levels; therefore ABA biosynthesis was investigated in soil- and hydroponically grown roots of Lycopersicon esculentum Mill. Hydroponically grown roots were stressed by immersion in 100 mM mannitol and soil-grown roots by withholding water. In both cases stress led to an increase in ABA levels and a decrease in the levels of specific xanthophylls, namely all-trans- and 9'-cis-neoxanthin and all-trans-violaxanthin. In hydroponically grown roots, and soil-grown roots stressed after removal of the shoot, ratios of xanthophyll cleaved:ABA synthesised of approx. 1∶1 were obtained. These findings are consistent with the operation of an apo-carotenoid pathway in roots, involving the conversion of all-trans-violaxanthin via all-trans-neoxanthin, to 9'-cis-neoxanthin, and the specific cleavage of 9'-cis-neoxanthin to yield the C15 ABA precursor xanthosin. Similar experiments with roots of the "leaky", ABA-deficient mutant of Lycopersicon, notabilis, indicate that the mutation does not affect the perception or transduction of stress, or the ability of the plant to cleave carotenoids. Rather, it appears that notabilis possesses an enzyme with reduced substrate specificity which cleaves more all-trans-than 9'-cis-neoxanthin.

A novel strategy for production of a highly expressed recombinant protein in an active form

Under standard growth conditions, E. coli transformed with the high-level expression vector pMON5525 produces recombinant DMAPP/AMP transferase in inactive, insoluble complexes. We have produced large amounts of active, soluble protein by growing and inducing the cells under osmotic stress in the presence of sorbitol and glycyl betaine. This caused an increase of up to 427-fold in the active yield, and the disappearance of the protein from the pelletable fraction of cell extracts. This treatment may have wide applicability.

A cytokinin-resistant mutant of Nicotiana plumbaginifolia is wilty

Selection for cytokinin resistance by incubating M2 seed of Nicotiana plumbaginifolia, after ethylmethanesulphonate mutagenesis, on 20 μM 6-benzylami-nopurine resulted in the isolation of a monogenic, recessive mutant, CKR1. Germination of the mutant is less sensitive to cytokinin inhibition than the wild type, and leaf development of the mutant occurs at cytokinin concentrations inhibitory to the wild type. Germination of the mutant is also resistant to auxin but not to abscisic acid. Three other traits jointly inherited with cytokinin resistance in the F2 are lack of root branching, precocious germination and wiltiness. The wilty phenotype is the consequence of the failure of stomatal closure during water stress.

Abscisic-acid metabolism in a wilty mutant of Nicotiana plumbaginifolia

A mutant of Nicotiana plumbaginifolia, CKR1, isolated on the basis of its enhanced resistance to cytokinins was found to have a greater tendency to wilt than the wild type (Blonstein et al., 1991, Planta 183, 244-250). Further characterisation has shown that the wiltiness in the mutant is not caused by an insensitivity to abscisic acid (ABA) because the external application of ABA leads to stomatal closure and phenotypic reversion. The basal ABA level in the mutant is < 20% of that in the wild type. Following stress, the ABA level in wild-type leaves increases by approx 9-to 10-fold while the mutant shows only a slight increase. This deficiency in ABA is unlikely to be the consequence of accelerated catabolism as the levels of two major metabolites of ABA, phaseic and dihydrophaseic acid, are also much reduced in the mutant. The qualitative and quantitative distributions of carotenoids, the presumed presursors of ABA, are the same for the leaves of both wild type and mutant. Biosynthesis of ABA at the C15 level was investigated by feeding xanthoxin (Xan) to detached leaves. Wild-type leaves convert between 9-19% of applied Xan to ABA while the mutant converts less than 1%. The basal level of trans-ABA-alcohol (t-ABA-alc) is 3-to 10-fold greater in the mutant and increases by a further 2.5-to 6.0-fold after stress. This indicates that the lesion in the wilty mutant of N. plumbaginifolia affects the conversion of ABA-aldehyde to ABA, as in the flacca and sitiens mutants of tomato and the droopy mutant of potato (Taylor et al., 1988, Plant Cell Environ. 11, 739-745; Duckham et al., 1989, J. Exp. Bot. 217, 901-905). Wild-type tomato and N. plumbaginifolia leaves can convert trans-Xan into t-ABA-alc, and Xan into ABA, while those of flacca and the wilty N. plumbaginifolia mutant convert both Xan and t-Xan to t-ABA-alc.

The role of cis-carotenoids in abscisic acid biosynthesis

Evidence has been obtained which is consistent with 9'-cis-neoxanthin being a major precursor of abscisic acid (ABA) in higher plants. A mild, rapid procedure was developed for the extraction and analysis of carotenoids from a range of tissues. Once purified the carotenoids were identified from their light-absorbance properties, reactions with dilute acid, high-performance liquid chromatography Rts, mass spectra and the quasiequilibria resulting from iodine-catalysed or chlorophyllsensitised photoisomerisation. Two possible ABA precursors, 9'-cis-neoxanthin and 9-cis-violaxanthin, were identified in extracts of light-grown and etiolated leaves (of Lycopersicon esculentum, Phaseolus vulgaris, Vicia faba, Pisum sativum, Cicer arietinum, Zea mays, Nicotiana plumbaginifolia, Plantago lanceolata and Digitalis purpurea), and roots of light-grown and etiolated plants (Lycopersicon, Phaseolus and Zea). The 9,9'-di-cisisomer of violaxanthin was synthesised but its presence was not detected in any extracts. Levels of 9'-cis-neoxanthin and all-trans-violaxanthin were between 20- to 100-fold greater than those of ABA in light-grown leaves. The levels of 9-cis-violaxanthin were similar to those of ABA but unaffected by water stress. Etiolated Phaseolus leaves contained reduced amounts of carotenoids (15-20% compared with light-grown leaves) but retained the ability to synthesise large amounts of ABA. The amounts of ABA synthesised, measured as increases in ABA and its metabolites phaseic acid and dihydrophaseic acid, were closely matched by decreases in the levels of 9'-cis-neoxanthin and all-trans-violaxanthin. In etiolated seedlings grown on 50% D2O, deuterium incorporation into ABA was similar to that into the xanthophylls. Relative levels of carotenoids in roots and light-grown and etiolated leaves of the ABA-deficient mutants, notabilis, flacca and sitiens were the same as those found in wild-type tomato tissues.

Alterations of Endogenous Cytokinins in Transgenic Plants Using a Chimeric Isopentenyl Transferase Gene

Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels.

Alterations of Endogenous Cytokinins in Transgenic Plants Using a Chimeric Isopentenyl Transferase Gene

Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels.

Mass-spectrometric quantitation of cytokinins in tobacco crown-gall tumours induced by mutated octopine Ti plasmids of Agrobacterium tumefaciens

The levels of the major cytokinins, zeatin, zeatin riboside, zeatin riboside-5'-monophosphate and zeatin-7-glucoside were measured in tobacco (Nicotiana tabacum L.) crown-gall tissues carrying insertion and deletion mutations in the T-DNA. Measurements were made by combined gas chromatography-mass spectrometry using selected ion monitoring with (15)N- and (2)H-labelled internal standards. The results demonstrate that, relative to wild-type tumour tissue, cytokinin levels are considerably elevated in tissues lacking functional T-DNA auxin-biosynthetic genes. From a detailed analysis of the major cytokinin metabolites it is concluded that a reduction in the extent of cytokinin degradation via N(6)-side-chain cleavage is an important factor leading to increased cytokinin levels in these tissues.

The effect of auxin concentration on cytokinin stability and metabolism

The stability of [(3)H]zeatin riboside supplied to freshly excised tobacco pith explants was found to be inversely related to α-naphthaleneacetic acid concentration in the incubation medium. At higher concentrations of α-naphthaleneacetic acid greater breakdown of [(3)H]zeatin riboside was indicated by higher levels of degradative metabolites (adenine, adenosine and adenosine nucleotides) formed. This auxin effect on cytokinin metabolism appears to be mediated, at least in part, through cytokinin oxidase. The results of in-vitro assays carried out with partially purified enzyme from corn kernels substantiale this conclusion. These findings are discussed in relation to recent observations of auxin and cytokinin levels in crown-gall tumours with altered morphology.

Apical localization of 1-aminocyclopropane-1-carboxylic acid and its conversion to ethylene in etiolated pea seedlings

The biosynthetic basis for the high rates of ethylene production by the apical region of etiolated pea (Pisum sativum L.) seedlings was investigated. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) was quantified in extracts of various regions of seedlings by measuring isotopic dilution of a (2)H-labelled internal standard using selected-ion-monitoring gas chromatography/mass spectrometry. The ACC levels in the apical hook and leaves were much higher than in the expanded internodes of the epicotyl. The capacity of excised tissue sections to convert exogenous ACC to ethylene was also much greater in the apical region, reflecting the distribution of soluble protein in the epicotyl.

Xanthoxin levels and metabolism in the wild-type and wilty mutants of tomato

Using (13)C-labelled internal standards and gas chromatography-mass spectrometry/multiple-ion monitoring the levels of xanthoxin (Xan) and 2-trans-xanthoxin (t-Xan) have been determined in stressed and non-stressed leaves of wildtype tomato (Lycopersicon esculentum Mill cv. Ailsa Craig), and the wilty mutants, notabilis (not), flacca (flc) and sitiens (sit). Levels of Xan were very low in all tissues. Ratios of t-Xan: Xan ranged from 10:1 to <500:1. In the wild-type and flc, t-Xan levels increased following stress. The results from feeding experiments using [(13)C]Xan and t-Xan demonstrated that whilst wild-type and not plants readily converted Xan into abscisic acid (ABA), flc and sit plants converted only a small amount of applied Xan into ABA. In all plants t-Xan was not converted into ABA. These results indicate that the flc and sit mutants are impaired in ABA biosynthesis because they are unable to convert Xan into ABA, whereas the not mutant is blocked at a metabolic step prior to Xan. Another possible ABA precursor, ABA-1',4'-trans-diol (ABA-t-diol) was found to occur in wild-type and mutant tissue. All four tissues could convert [(2)H]ABA-t-diol to ABA. Incubation of stressed leaves in the presence of (18)O2 provided evidence consistent with Xan and ABA originating via oxidative cleavage of a xanthophyll such as violaxanthin.

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 (Ψs) 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.

Partial isotope fractionation during high-performance liquid chromatography of deuterium-labelled internal standards in plant hormone analysis: A cautionary note

Deuterium-labelled indole-3-acetic acid, abscisic acid and phthalimido-1-aminocyclopropane-1-carboxylic acid were found to separate from the unlabelled compounds on reverse-phase high-performance liquid chromatography (HPLC). A similar separation was found for the methyl esters of these compounds on normal-phase HPLC. Such separations may lead to substantial errors when these compounds are used as internal standards for quantitation by gas chromatography-mass spectrometry/selective ion detection, unless the complete chromatographic peaks are collected.

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.

Selected ion monitoring/isotope dilution mass spectrometric determination of 1-aminocyclopropane-1-carboxylic acid levels in ripening tomato fruit

A new method is described for the quantitation of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene in plants. [2,2,3,3,-2H4]ACC has been synthesized and used as an internal standard for selected ion monitoring/isotope dilution quantitation of this compound in ripening tomato fruit. These data are compared with those derived from the widely used indirect oxidative ACC assay (which underestimated the ACC levels by between two- and fourfold). The greater accuracy, sensitivity (100X), and specificity of the mass spectrometric method will be of considerable benefit to those interested in factors which control ACC and ultimately ethylene levels since it is believed that ACC synthesis and its oxidative metabolism to ethylene are the key points at which ethylene biosynthesis is regulated.

Mass-spectrometric quantification of cytokinin nucleotides and glycosides in tobacco crown-gall tissue

the cytokinins of tobacco crown-gall tissue have been analysed by quantitative mass spectrometry using (2)H2-labelled cytokinin riboside 5'-monophosphates and (15)N4-labelled cytokinin glycosides as internal standards. The principal endogenous cytokinin of this tissue is zeatin riboside 5'-monophosphate. The biologically inactive 7-glucoside of zeatin is the most abundant basic cytokinin in the tissue. These findings expose the limitations of previously reported analyses of similar tissues, which were restricted to biologically active basic cytokinins. The present study demonstrates that the endogenous cytokinins of tobacco crowngall tissue show a clear correspondence to the range of metabolites formed when exogenous cytokinins are supplied to nontumorous tobacco cells.

Biosynthesis of abscissic acid

The fungus Cercospora rosicola has been studied as a model system for abscissic acid biosynthesis. 1'-dDeoxyabscissic acid and 4'-hydroxy-a-ionylidene acetic acid have been identified as endogenous compounds in this fungus. The results of feeding these and other putative intermediates suggest that abscissic acid biosynthesis proceeds via the successive oxidations of a 3-methyl-5-(2',6',6'-trimethylcyclohex-2'-en-1'-yl)-2,4-pentadienyl intermediate. Preliminary results suggest that a similar pathway may operate in plants.

Cytokinins in transfer RNA of normal and crown-gall tissue of Vinca rosea

cis-Zeatin riboside was identified in transfer-RNA hydrolysates from both normal and crown-gall tissue of Vinca rosea L. The trans-isomer was associated exclusively with the crowngall transfer-RNA. The importance of these observations is discussed in relation to biosynthesis of free cytokinins.

Determination of the levels of abscisic acid-glucose ester in plants

Abscisic acid-β-D-glucopyranosyl ester (ABAGE) has been measured in several plant species using (2)H-labelled ABAGE as an internal standard. The effects of water stress on the levels of ABAGE and its possible physiological role are discussed. Some chemical properties of ABAGE are described.

Cytokinin oxidase fromZea mays kernels andVinca rosea crown-gall tissue

Cytokinin oxidase has been partially purified from matureZea mays kernels and fromVinca rosea corwn-gall tissue. The molecular weights of the two enzymes, determined by gel filtration, are very different: 94,400 (±10%) forZ. mays and 25,100 (±10%) forV. rosea. Specificity studies have been performed using a large number of synthetic and naturally occurring cytokinins. Only a small number of these compounds serve as substrates and both enzymes exhibit similar substrate specificity. In agreement with other workers, a Δ(2) double bond in the N(6) side chain is essential for activity. The presence of glucosyl or ribosyl groups in the 7-or 9-position or an alanyl group in the 9-position of the purine moiety have little effect on their susceptibility to cytokinin oxidase, but O-glucosyl derivatives are resistant to oxidation. The relevance of these enzyme systems to studies on cytokinin metabolism and to the endogenous cytokinins is discussed.

Cytokinin biosynthesis in crown-gall tissue ofVinca rosea : The significance of nucleotides

When care was taken to minimise the effects of phosphatase activity during extraction ofVinca rosea crown-gall tumour tissue, a large proportion of extractable cytolinin activity was present in the nucleotide fraction. Analysis using ion-exchange chromatography followed by enzymic or chemical degradation and subsequent identification of the biologically active material indicated that this activity was due to zeatin riboside 5'-monophosphate. This was also the major radiolabelled cytokinin formed when this tissue was supplied with [(14)C]adenine. The incorporation of radioactivity from [(14)C]adenosine into free cytokinins was also shown, but no incorporation of radioactivity was found when [(3)H]mevalonic acid lactone was supplied to this tissue under the same conditions. In parallel experiments using normal stem callus tissue ofV. rosea, no incorporation of [(14)C]adenine into free cytokinins was observed. The significance of these results is discussed in relation to a possible transfer-RNA-independent pathway of cytokinin biosynthesis, operating primarily at the mononucleotide level.

Mass spectrometric measurement of zeatin glycoside levels in Vinca rosea L. crown gall tissue

The range of zeatin glycosides found in crown gall tissue of Vinca rosea L. has been quantified using a mass spectrometric isotope dilution procedure. Problems in the quantitative analysis of cytokinins in plant extracts are discussed.

Cytokinin metabolism in Phaseolus vulgaris L. : Identification of endogenous cytokinins and metabolism of [8-(14)C]dihydrozeatin in stems of decapitated plants

The major cytokinins in stems of decapitated, disbudded bean plants have been identified by enzymic degradation, Sephadex LH20 and reversed phase high performance liquid chromatography, and by combined gas chromatography-mass spectrometry as 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9-β-D-ribofuranosylpurine (zeatin riboside), 6-(4-hydroxy-3-methylbutylamino)-9-β-D-ribofuranosylpurine (dihydrozeatin riboside), and the 5'-phosphates of these compounds (zeatin ribotide and dihydrozeatin ribotide). Minor cytokinins in this tissue were tentatively identified as dihydrozeatin-O-β-D-glucoside and zeatin ribotide-O-β-D-glucoside. [8-(14)C-]Dihydrozeatin appeared to be rapidly metabolized to dihydrozeatin ribotide when supplied to segments of stems from decapitated plants. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.

Dihydroconiferyl alcohol - A cell division factor from Acer species

A compound that stimulated growth of soybean callus was isolated from spring sap of sycamore (Acer pseudoplatanus L.). Insufficient compound was isolated to permit it to be characterised. A compound with identical properties was isolated from commercial maple syrup, the concentrated spring sap of Acer saccharum L. The compound was identified as 3-(3-methoxy-4-hydroxyphenyl)-propan-1-ol (dihydroconiferyl alcohol, DCA). DCA was also active in the tobacco callus and radish leaf senescence assays, but was inactive in four other tests for cytokinin activity. DCA acted synergistically with kinetin to promote soybean callus growth. It is concluded that DCA has properties distinct from those of purine cytokinins.

Cytokinins from the Moss Physcomitrella patens

Gametophore-over-producing mutants of the moss, Physcomitrella patens, when grown in liquid culture export high levels of cytokinin into their culture medium. The cytokinin produced by these mutants is postulated to account for their peculiar phenotype, that of mosses treated with exogenous cytokinin. N(6)-(Delta(2)-isopentenyl)adenine, the major cytokinin, has been identified previously in two of these mutants (Wang, Cove, Beutelmann, Hartmann 1980 Phytochemistry 19: 1103-1105) and now in additional representatives. A second cytokinin, zeatin, has been identified by its chromatographic behavior and mass spectrum including chemical ionization mass spectrometry of its permethyl derivative.

Zeatin-9-glucoside, a major endogenous cytokinin of Vinca rosea L. crown gall tissue

Cultured crown gall tissue of Vinca rosea L. was found to contain, in addition to the previously reported cytokinins zeatin, zeatin riboside, and the 0-glucosides of these two compounds, relatively high levels of zeatin-9-D-glucopyranoside. This is the first conclusive identification of an endogenous cytokinin 9-glucoside.

The biosynthesis of cytokinins in crown-gall tissue of Vinca rosea

The crown-gall tissue of Vinca rosea converts labelled adenine into cytokinins. The principal initial products appear to be ribosylzeatin phosphates; zeatin and ribosylzeatin are also produced in appreciable quantities. The efficiency of conversion of adenine into cytokinins suggests a pathway of synthesis independent of turnover of tRNA. Isopentenyl adenine or its derivatives do not appear to be intermediates in the conversion of adenine to zeatin compounds. Cytokinins in V. rosea turnover rapidly and further metabolism of zeatin derivatives seems to result in their conversion into glucosides which are the main cytokinin active compounds in the tissue.

Dihydrozeatin riboside, a minor cytokinin from the leaves of Phaseolus vulgaris L

Dihydrozeatin riboside has been identified in the leaves of decapitated bean plants by Sephadex LH20 chromatography and combined gas chromatography-mass spectrometry. The relationship between the cytokinins isolated and identified from this system and those previously reported in Phaseolus is discussed.