Trends in overweight and obesity by socioeconomic status in Year 6 school children, Australian Capital Territory, 2006-2018.

BACKGROUND: Due to the high prevalence and adverse consequences, overweight and obesity in children continues to be a major public health concern worldwide. Socioeconomic background and health-related behaviours (such as diet, physical activity and sedentary behaviors) are important factors associated with weight status in children. Using a series of height and weight assessments from the Australian Capital Territory Physical Activity and Nutrition Survey (ACTPANS), trends in prevalence of overweight and obesity by socioeconomic status were examined in ACT Year 6 school children between 2006 and 2018. METHODS: The ACTPANS has been conducted every 3 years since 2006. A total of 6729 children were surveyed. Complete data on height and weight were available for 6384 (94.9%) participants. Trends in the prevalence of overweight and obesity and associations between weight status and risk factors (such as socioeconomic status, physical activity, screen time and consumption of sugar-sweetened soft drinks (SSD)) were examined using logistic regression. RESULTS: The prevalence of overweight and obesity remained stable in girls (from 22.5% in 2006 to 21.6% in 2018) but declined in boys (from 27.8 to 17.9%). During the same period, levels of physical activity increased slightly, while screen time and the consumption of fast food and SSD decreased. Socioeconomic gradient, based on the school-level Index of Community Socio-Educational Advantage (ICSEA), was highly associated with prevalence of overweight and obesity. Since 2006, the estimated prevalence of overweight and obesity has remained high in the lowest SES groups, but a concurrent downward trend was observed in the highest SES group, leading to increasing disparity between SES groups. Children in the lowest ICSEA quintile were more likely to be overweight or obese compared to those in the moderate and highest ICSEA quintiles. Children in lower ICSEA quintiles also reported lower levels of physical activity, higher levels of screen time, and higher levels of fast food and SSD consumption compared to those in higher ICSEA quintiles. CONCLUSIONS: While recent trends in overweight and obesity in ACT children are encouraging, the prevalence remains unacceptably high, especially in those from low socioeconomic backgrounds. Additional prevention efforts are required to address the socioeconomic disparity.

Contribution of maternal overweight and obesity to the occurrence of adverse pregnancy outcomes.

AIMS: Maternal overweight and obesity in pregnancy are known to increase the risk of a range of complications and adverse pregnancy outcomes. This study estimates the population-level contribution of maternal overweight and obesity to adverse pregnancy outcomes. METHODS: Data derived from the Australian Capital Territory (ACT) Maternal and Perinatal Data Collection were analysed. A total of 24 161 women who had a singleton birth in 2009-2015, with maternal weight and height information available, were included. In this study, the association between risk factors and outcomes was investigated using multilevel regression modelling. Based on model predictions under various hypothetical maternal weight scenarios, the number and proportion of adverse perinatal outcomes that could be potentially prevented were estimated. RESULTS: Maternal overweight and obesity were associated with increased risks of gestational diabetes mellitus (GDM), pre-eclampsia, caesarean delivery, preterm birth (PTB), large for gestational age (LGA) and admission to the special care nursery or neonatal intensive care unit (SCN/NICU). The estimated proportions of adverse pregnancy outcomes attributable to overweight and obesity in pregnancy are 29.3% for GDM, 36.2% for pre-eclampsia, 15.5% for caesarean delivery, 21.6% for longer antenatal stay in hospital (≥2 days), 16.3% for extreme PTB, 25.2% for LGA and 6.5% for SCN/NICU admission. CONCLUSIONS: Maternal overweight and obesity contribute to a large proportion of obstetric complications and adverse outcomes in the ACT. Effective intervention strategies to reduce the prevalence of overweight and obesity in pregnant women could have significant beneficial effects on pregnancy outcomes.

Hybrid variation for root system efficiency in maize: potential links to drought adaptation.

Water availability can limit maize (Zea mays L.) yields, and root traits may enhance drought adaptation if they can moderate temporal patterns of soil water extraction to favour grain filling. Root system efficiency (RSE), defined as transpiration per unit leaf area per unit of root mass, represents the functional mass allocation to roots to support water capture relative to the allocation to aerial mass that determines water demand. The aims of this study were to identify the presence of hybrid variation for RSE in maize, determine plant attributes that drive these differences and illustrate possible links of RSE to drought adaptation via associations with water extraction patterns. Individual plants for a range of maize hybrids were grown in large containers in shadehouses in Queensland, Australia. Leaf area, shoot and root mass, transpiration, root distribution and soil water were measured in all or selected experiments. Significant hybrid differences in RSE existed. High RSE was associated with reduced dry mass allocation to roots and more efficient water capture per unit of root mass. It was also weakly negatively associated with total plant dry mass, reducing preanthesis water use. This could increase grain yield under drought. RSE provides a conceptual physiological framework to identify traits for high-throughput phenotyping in breeding programs.

Root morphological traits that determine phosphorus-acquisition efficiency and critical external phosphorus requirement in pasture species.

Annual pasture legume species can vary more than 3-fold in their critical external phosphorus (P) requirement (i.e. P required for 90% of maximum yield). In this work we investigated the link between root morphology, P acquisition and critical external P requirement among pasture species. The root morphology acclimation of five annual pasture legumes and one grass species to low soil P availability was assessed in a controlled-environment study. The critical external P requirement of the species was low (Dactylis glomerata L., Ornithopus compressus L., Ornithopus sativus Brot.), intermediate (Biserrula pelecinus L., Trifolium hirtum All.) or high (Trifolium subterraneum L.). Root hair cylinder volumes (a function of root length, root hair length and average root diameter) were estimated in order to assess soil exploration and its impact on P uptake. Most species increased soil exploration in response to rates of P supply near or below their critical external P requirement. The legumes differed in how they achieved their maximum root hair cylinder volume. The main variables were high root length density, long root hairs and/or high specific root length. However, total P uptake per unit surface area of the root hair cylinder was similar for all species at rates of P supply below critical P. Species that maximised soil exploration by root morphology acclimation were able to prolong access to P in moderately P-deficient soil. However, among the species studied, it was those with an intrinsic capacity for a high root-hair-cylinder surface area (i.e. long roots and long root hairs) that achieved the lowest critical P requirement.

Pre-anthesis ovary development determines genotypic differences in potential kernel weight in sorghum.

Kernel weight is an important factor determining grain yield and nutritional quality in sorghum, yet the developmental processes underlying the genotypic differences in potential kernel weight remain unclear. The aim of this study was to determine the stage in development at which genetic effects on potential kernel weight were realized, and to investigate the developmental mechanisms by which potential kernel weight is controlled in sorghum. Kernel development was studied in two field experiments with five genotypes known to differ in kernel weight at maturity. Pre-fertilization floret and ovary development was examined and post-fertilization kernel-filling characteristics were analysed. Large kernels had a higher rate of kernel filling and contained more endosperm cells and starch granules than normal-sized kernels. Genotypic differences in kernel development appeared before stamen primordia initiation in the developing florets, with sessile spikelets of large-seeded genotypes having larger floret apical meristems than normal-seeded genotypes. At anthesis, the ovaries for large-sized kernels were larger in volume, with more cells per layer and more vascular bundles in the ovary wall. Across experiments and genotypes, there was a significant positive correlation between kernel dry weight at maturity and ovary volume at anthesis. Genotypic effects on meristem size, ovary volume, and kernel weight were all consistent with additive genetic control, suggesting that they were causally related. The pre-fertilization genetic control of kernel weight probably operated through the developing pericarp, which is derived from the ovary wall and potentially constrains kernel expansion.

Self-organisation at the whole-plant level: a modelling study.

Within-plant light and nutrient environments are spatially and temporally heterogeneous. The development of different parts of a plant is highly coordinated, which enables the efficient capture and use of resources in such heterogeneous environments. The physiological mechanisms underlying the correlative control of distantly located plant tissues and organs are still not fully understood. In this study, a mathematical model based on a self-organisation mechanism for resource allocation mediated by polar auxin transport is proposed to explain the origin of correlative effects among shoot branches. In the model, the shoot system of an individual plant is treated as a collection of relatively independent modular subunits competing for root-derived resources. The allocation of root-derived resources to different parts of the shoot is determined by their relative vascular contacts with the root system. The development of the vascular network is specified by the polar transport of auxin produced by various parts of the shoot in response to their immediate internal and external environments. The simulation results show that, by altering the amount of auxin they release individually in response to the local environment and modifying their relative vascular contact with the root system, subunits of a shoot are able to coordinate without a central controller and self-organise into functional and structural patterns such as light foraging and correlative dominance. This modelling study suggests that morphological dynamics at the whole-plant level can be understood as the sum of all modular responses to their local environments. The concept of self-organisation holds great promise for an in-depth understanding of the organisational laws that generate overall plant structure and functions.

A model for the circadian oscillations in expression and activity of nitrate reductase in higher plants.

BACKGROUND AND AIMS: Nitrate is the major nitrogen source for many plants. The first step of the nitrate assimilation pathway is the reduction of nitrate to nitrite, catalysed by nitrate reductase (NR). Circadian oscillations in expression and activity of NR have been demonstrated in many plant species. The pathway by which this circadian behaviour is regulated remains to be elucidated. In this study, based on recent experimental observations, a mathematical model is proposed to explain the origin of diurnal and circadian oscillations in NR gene expression and enzyme activity. METHODS: The dynamic model is based on the feedback interconnections between NR and its substrate, nitrate. In the model, NR activity is regulated at the transcriptional level, in response to the balance between nitrate influx and reduction, and at the post-translational levels in response to signals from carbon assimilation. Conditions for the model system to generate self-sustained circadian oscillations are investigated by numerical simulations. KEY RESULTS AND CONCLUSIONS: Under light/dark cycles, the simulation results are in agreement with the observed diurnal pattern of changes in leaf nitrate concentration, NR transcript level and NR activity. Within a range of kinetic parameter values, circadian oscillation behaviour persists even under constant light, with periods of approx. 24 h. These simulation results suggest that sustained circadian oscillations can originate from the feedback interactions between NR and its substrate, nitrate, without the need to postulate the existence of an endogenous 'circadian clock'.