Phototropism in seedlings of sunflower, Helianthus annuus L.

In this thesis the phototropic bending of hypocotyls of sunflower seedlings, Helianthus annuus L., is investigated.Chapter 1 gives the reasons for this project. Although phototropism has been studied extensively over the past 100 years, the understanding of the mechanism is far from clear. During this century two main hypotheses were developed, namely the theory of BLAAUW (1915), explaining phototropism as an effect of growth inhibition by light, and the CHOLODNY-WENT theory (1927, 1928), in which the lateral distribution and basipetal transport of the growth-promoting substance, auxin, are involved. Especially the latter received the attention of many investigators, probably because it deals with the first phytohormone discovered. The research on this subject has been mainly concentrated on the properties of auxin and the way in which it influences the pattern of curvature in etiolated coleoptiles. Much experimentation has been done with the exogenous application of diffusate from coleoptile tips or IAA, the auxin, to etiolated monocotyledonous seedlings, without measuring the endogenous levels of this growth substance in the plants themselves. In 1975 BRUINSMA et al., investigating the levels of IAA, in illuminated and shaded halves of phototropically stimulated, green sunflower seedlings, showed that this hormone is equally distributed between both halves. This discovery, and the fact that the evidence for both hypotheses mentioned above is still inconclusive, led to the present investigation.As experimental material sunflower seedlings, Helianthus annuus L., were chosen. Chapter 2 lists the material and methods used for the experiments described in the subsequent Chapters.Chapter 3 describes the influence of other processes on phototropism. It is shown that geotropism acts strongly on the deflected hypocotyl. Only the first hour after the beginning of the phototropic response can be considered to show pure phototropism. Because the delay in the onset of the response, the maximal degree of curvature is determined for each individual seedling during the first 2 hours of phototropic stimulation. The influences of the age of the seedling and length of the hypocotyl were studied as well. Seedlings of 4 to 5 days old and 40 to 60 mm long bend as uniformly as possible, and were used in the experiments described in this thesis. Careful manipulation of the seedlings did not influence the response.Chapter 4 deals with the influence of the other organs of the green seedling on the bending of the hypocotyl. It is concluded that neither the cotyledons and the shoot tip, nor the roots are essential for the response, although a stress effect due to the removal of these organs may cause a delay. The epidermis of the hypocotyl is indirectly involved; the peripheral layers are not necessary for the perception of the unilateral light, but probably control the growth, without which curvature cannot occur.In Chapter 5 the results of treatments with different wavelengths are shown. Unilateral blue light is the main active region, although the response caused by blue light is always slightly less than when caused by unilateral white light. In contrast to seedlings grown in white light, etiolated ones are not phototropically sensitive. Pretreatment of dark-grown seedlings with white or blue light renders them able to curve, and only illumination of the hypocotyl is necessary. The role of the cotyledons, that cannot be removed during this treatment without decreasing the bending, is probably to supply the substrates essential for the growth of the hypocotyl. Pretreatment with darkness of seedlings grown in white light makes them phototropically unresponsive. Again, only the hypocotyl needs this treatment and this indicates that the mechanism for phototropism is located within the hypocotyl. Green seedlings pretreated with red light only show poor curvature, but the growth rate of the seedlings is not related to the bending capacity.Chapter 6 presents the results of the effect of pretreatment with far-red irradiation on the phototropic response. It is shown that far red, more than a treatment in darkness, decreases the curvature in seedlings grown in white light and that the response is a low-energy reaction (L.E.R.). Red light did not affect the lack of bending of etiolated plants, but prolonged red illumination could reverse the effect of far-red irradiance in green seedlings. It is concluded that the perception of the far-red irradiance is located in both the hypocotyl and the cotyledons. Again, no correlation between the growth rate and the curvature of plants pretreated with far red can be detected.The involvement of hormones in the phototropic response is studied in Chapter 7. IAA is not unilaterally distributed in curving parts of the seedlings that were 30 to 45 min phototropically stimulated. No IAA could be detected in diffusates from the seedlings, and this absence is not due to destruction of IAA at the cut surface. However, a growth-inhibiting activity was found in the diffusates, both from hypocotyls and from cotyledons, and this activity was not asymmetrically distributed in bending plants.The role of the growth inhibitor, xanthoxin, was investigated. Experiments are described to show that xanthoxin is not contaminated with ABA after the extraction procedure, and that a bioassay can be properly used for the determination of xanthoxin. In straight hypocotyls xanthoxin is equally distributed, but in curving and curved ones more inhibitor can be extracted from the illuminated side than from the shaded one. From seedlings pretreated with white or blue light, which are phototropically sensitive, a higher amount of xanthoxin can be extracted than from etiolated, phototropically unresponsive, plants. In seedlings pretreated with red light, which show only a poor bending, a variable amount of xanthoxin was detected. The results of experiments in which xanthoxin was exogenously applied to seedlings were inconclusive.Gibberellic acid, GA 3 , applied to the seedlings pretreated with red light 1 hour before the onset of the phototropic experiment, increases the curvature, whereas GA 3 applied to plants grown in white light has no effect. The growth rate of the treated plants does not differ from that of the control group. Seedlings treated daily with various concentrations of the growth retardant CCC show different lengths after four days. Their phototropic curvature, however, is the same, again demonstrating that the extent of curvature is not related to the elongation growth.In the General Discussion (Chapter 8) the CHOLODNY-WENT theory is rejected as an explanation of phototropism in the sunflower seedling. Instead the theory of BLAAUW is modified by ascribing the phototropic reaction to a growth inhibition at the irradiated side, caused by light-induced relative accumulation of xanthoxin at that side. This may account for a curvature independent of the growth rate regulated by auxin and gibberellin

Nephrotoxicity of continuous amphotericin B in critically ill patients with abdominal sepsis:a retrospective analysis with propensity score matching

BACKGROUND: Continuous infusion of conventional amphotericin B (CCAB) is used in ICUs for pre-emptive treatment of invasive fungal infections. Amphotericin B has previously been associated with nephrotoxicity. OBJECTIVES: To investigate if CCAB with therapeutic drug monitoring (TDM) results in renal impairment over time in critically ill patients with abdominal sepsis. PATIENTS AND METHODS: The study was conducted at mixed medical-surgical ICUs of two large teaching hospitals in the Netherlands. Consecutive patients who were treated on the ICUs between 2006 and 2019 for abdominal sepsis, with or without CCAB, were included. CCAB dosing was guided by TDM. Serum creatinine concentrations and renal failure scores of patients with CCAB treatment were compared with those without CCAB treatment. Excluded were: (i) patients treated with CCAB for less than 72 h; and (ii) patients with renal replacement therapy. RESULTS: A total of 319 patients were included (185 treated with CCAB and 134 controls). A multiple linear regression model showed that the serum creatinine concentration was independent of CCAB treatment (β = -0.023; 95% CI = -12.2 to 7.2; P = 0.615). Propensity score matching resulted in 134 pairs of CCAB-treated and non-treated patients. Again, the analysis of these pairs showed that the cumulative CCAB dose was not associated with serum creatinine concentration during intensive care treatment (β = 0.299; 95% CI = -0.38 to 0.98; P = 0.388). CONCLUSIONS: CCAB with TDM did not result in renal impairment over time in critically ill patients with abdominal sepsis

Low dose aspirin in the prevention of recurrent spontaneous preterm labour - the APRIL study: A multicenter randomized placebo controlled trial

Background: Preterm birth (birth before 37 weeks of gestation) is a major problem in obstetrics and affects an estimated 15 million pregnancies worldwide annually. A history of previous preterm birth is the strongest risk factor for preterm birth, and recurrent spontaneous preterm birth affects more than 2.5 million pregnancies each year. A recent meta-analysis showed possible benefits of the use of low dose aspirin in the prevention of recurrent spontaneous preterm birth. We will assess the (cost-)effectiveness of low dose aspirin in comparison with placebo in the prevention of recurrent spontaneous preterm birth in a randomized clinical trial. Methods/design: Women with a singleton pregnancy and a history of spontaneous preterm birth in a singleton pregnancy (22-37 weeks of gestation) will be asked to participate in a multicenter, randomized, double blinded, placebo controlled trial. Women will be randomized to low dose aspirin (80 mg once daily) or placebo, initiated from 8 to 16 weeks up to maximal 36 weeks of gestation. The primary outcome measure will be preterm birth, defined as birth at a gestational age (GA) < 37 weeks. Secondary outcomes will be a composite of adverse neonatal outcome and maternal outcomes, including subgroups of prematurity, as well as intrauterine growth restriction (IUGR) and costs from a healthcare perspective. Preterm birth will be analyzed as a group, as well as separately for spontaneous or indicated onset. Analysis will be performed by intention to treat. In total, 406 pregnant women have to be randomized to show a reduction of 35% in preterm birth from 36 to 23%. If aspirin is effective in preventing preterm birth, we expect that there will be cost savings, because of the low costs of aspirin. To evaluate this, a cost-effectiveness analysis will be performed comparing preventive treatment with aspirin with placebo. Discussion: This trial will provide evidence as to whether or not low dose aspirin is (cost-) effective in reducing recurrence of spontaneous preterm birth. Trial registration: Clinical trial registration number of the Dutch Trial Register: NTR 5675. EudraCT-registration number: 2015-003220-31

Construct validity of the post-COVID-19 functional status scale in adult subjects with COVID-19

Background An increasing number of subjects are recovering from COVID-19, raising the need for tools to adequately assess the course of the disease and its impact on functional status. We aimed to assess the construct validity of the Post-COVID-19 Functional Status (PCFS) Scale among adult subjects with confirmed and presumed COVID-19. Methods Adult subjects with confirmed and presumed COVID-19, who were members of an online panel and two Facebook groups for subjects with COVID-19 with persistent symptoms, completed an online survey after the onset of infection-related symptoms. The number and intensity of symptoms were evaluated with the Utrecht Symptom Diary, health-related quality of life (HrQoL) with the 5-level EQ-5D questionnaire, impairment in work and activities with the Work Productivity and Activity Impairment questionnaire and functional status with the PCFS Scale. Results 1939 subjects were included in the analyses (85% women, 95% non-hospitalized during infection) about 3 months after the onset of infection-related symptoms. Subjects classified as experiencing 'slight', 'moderate' and 'severe' functional limitations presented a gradual increase in the number/intensity of symptoms, reduction of HrQoL and impairment in work and usual activities. No differences were found regarding the number and intensity of symptoms, HrQoL and impairment in work and usual activities between subjects classified as experiencing 'negligible' and 'no' functional limitations. We found weak-to-strong statistical associations between functional status and all domains of HrQoL (r: 0.233-0.661). Notably, the strongest association found was with the 'usual activities' domain of the 5-level EQ-5D questionnaire. Conclusion We demonstrated the construct validity of the PCFS Scale in highly-symptomatic adult subjects with confirmed and presumed COVID-19, 3 months after the onset of symptoms.Clinical epidemiolog

Clinical characteristics of women captured by extending the definition of severe postpartum haemorrhage with 'refractoriness to treatment': a cohort study

Background: The absence of a uniform and clinically relevant definition of severe postpartum haemorrhage hampers comparative studies and optimization of clinical management. The concept of persistent postpartum haemorrhage, based on refractoriness to initial first-line treatment, was proposed as an alternative to common definitions that are either based on estimations of blood loss or transfused units of packed red blood cells (RBC). We compared characteristics and outcomes of women with severe postpartum haemorrhage captured by these three types of definitions. Methods: In this large retrospective cohort study in 61 hospitals in the Netherlands we included 1391 consecutive women with postpartum haemorrhage who received either ≥4 units of RBC or a multicomponent transfusion. Clinical characteristics and outcomes of women with severe postpartum haemorrhage defined as persistent postpartum haemorrhage were compared to definitions based on estimated blood loss or transfused units of RBC within 24 h following birth. Adverse maternal outcome was a composite of maternal mortality, hysterectomy, arterial embolisation and intensive care unit admission. Results: One thousand two hundred sixty out of 1391 women (90.6%) with postpartum haemorrhage fulfilled the definition of persistent postpartum haemorrhage. The majority, 820/1260 (65.1%), fulfilled this definition within 1 h following birth, compared to 819/1391 (58.7%) applying the definition of ≥1 L blood loss and 37/845 (4.4%) applying the definition of ≥4 units of RBC. The definition persistent postpartum haemorrhage captured 430/471 adverse maternal outcomes (91.3%), compared to 471/471 (100%) for ≥1 L blood loss and 383/471 (81.3%) for ≥4 units of RBC. Persistent postpartum haemorrhage did not capture all adverse outcomes because of missing data on timing of initial, first-line treatment. Conclusion: The definition persistent postpartum haemo

ABA levels in the different organs of dry-stored tulip bulbs (cv. apeldoorn) during 5°C cold- or 17°C control-treatment

ABA levels in the sprout, the basal plate, the two inner and the two outer bulb scales were determined, both at 5°C (special precooling) as at 17°C (controls). ABA levels, expressed as nmol.g-1 DW, declined slowly but continuously in the basal plate and the two inner and two outer bulb scales. In the sprout an initial decrease in ABA was observed, whereafter the level remained similar. No differences between 5°C and 17°C were observed, until the end of November. From that moment on, a sharp increase in the scales of bulbs stored at 5°C was found. As both bulbs of which the precooling had already been completed before that time, and bulbs of which the precooling was only completed around January showed proper growth and flowering, it was concluded that the ABA levels in these organs had no relation to growth or flowering