Auxin plays important roles during the entire life span of a plant. This small organic acid influences cell division, cell elongation and cell differentiation, and has great impact on the final shape ...and function of cells and tissues in all higher plants. Auxin metabolism is not well understood but recent discoveries, reviewed here, have started to shed light on the processes that regulate the synthesis and degradation of this important plant hormone.
Chemicals such as phthalates, parabens, bisphenol A (BPA) and triclosan (TCS), used in a wide variety of consumer products, are suspected endocrine disrupters although their level of toxicity is ...thought to be low. Combined exposure may occur through ingestion, inhalation and dermal exposure, and their toxic as well as combined effects are poorly understood.
The objective of the study was to estimate the exposure to these chemicals in Swedish mothers and their children (6–11years old) and investigate potential predictors of the exposure. Urine samples from 98 mother–child couples living in either a rural or an urban area were analyzed for the concentrations of four metabolites of di-(2-ethylhexyl) phthalate (DEHP), three metabolites of di-iso-nonyl phthalate (DiNP), mono-ethyl phthalate (MEP), mono-benzyl phthalate (MBzP) and mono-n-butyl phthalate (MnBP), methylparaben (MetP), ethylparaben (EthP), propylparaben (ProP), butylparaben, benzylparaben, BPA, and TCS. Information on sociodemographics, food consumption habits and use of personal care products, obtained via a questionnaire, was used to investigate the associations between the urinary levels of chemicals and potential exposure factors.
There were fairly good correlations of biomarker levels between the mothers and their children. The children had generally higher levels of phthalates (geometric mean ΣDEHP 65.5μg/L; ΣDiNP 37.8μg/L; MBzP 19.9μg/L; MnBP 76.9μg/L) than the mothers (ΣDEHP 38.4μg/L; ΣDiNP 33.8μg/L; MBzP 12.8μg/L; MnBP 63.0μg/L). Conversely, the mother's levels of parabens (MetP 37.8μg/L; ProP 13.9μg/L) and MEP (43.4μg/L) were higher than the children's levels of parabens (MetP 6.8μg/L; ProP 2.1μg/L) and MEP (28.8μg/L). The urinary levels of low molecular weight phthalates were higher among mothers and children in the rural area (MBzP p=<0.001; MnBP p=0.001–0.002), which is probably due to higher presence of PVC in floorings and wall coverings in this area, whereas the levels of parabens were higher among the children in the urban area (MetP p=0.003; ProP p=0.004) than in the rural area. The levels of high molecular weight phthalates were associated with consumption of certain foods (i.e. chocolate and ice cream) whereas the levels of parabens were associated with use of cosmetics and personal care products.
•We quantified the levels of phthalates, BPA, parabens and triclosan in urine.•The levels were significantly correlated to certain foods and hygiene products.•Mothers had higher levels of parabens and a phthalate used in hygiene products.•Children had generally higher levels of phthalates present in food.
Phytohormones are physiologically important small molecules that play essential roles in intricate signaling networks that regulate diverse processes in plants. We present a method for the ...simultaneous targeted profiling of 101 phytohormone-related analytes from minute amounts of fresh plant material (less than 20 mg). Rapid and nonselective extraction, fast one-step sample purification, and extremely sensitive ultra-high-performance liquid chromatography-tandem mass spectrometry enable concurrent quantification of the main phytohormone classes: cytokinins, auxins, brassinosteroids, gibberellins, jasmonates, salicylates, and abscisates. We validated this hormonomic approach in salt-stressed and control Arabidopsis (Arabidopsis thaliana) seedlings, quantifying a total of 43 endogenous compounds in both root and shoot samples. Subsequent multivariate statistical data processing and cross-validation with transcriptomic data highlighted the main hormone metabolites involved in plant adaptation to salt stress.
Foliar shade triggers rapid growth of specific structures that facilitate access of the plant to direct sunlight. In leaves of many plant species, this growth response is complex because, although ...shade triggers the elongation of petioles, it reduces the growth of the lamina. How the same external cue leads to these contrasting growth responses in different parts of the leaf is not understood.
Using mutant analysis, pharmacological treatment and gene expression analyses, we investigated the role of PHYTOCHROME INTERACTING FACTOR7 (PIF7) and the growthpromoting hormone auxin in these contrasting leaf growth responses.
Both petiole elongation and lamina growth reduction are dependent on PIF7. The induction of auxin production is both necessary and sufficient to induce opposite growth responses in petioles vs lamina. However, these contrasting growth responses are not caused by different auxin concentrations in the two leaf parts.
Our work suggests that a transient increase in auxin levels triggers tissue-specific growth responses in different leaf parts. We provide evidence suggesting that this may be caused by the different sensitivity to auxin in the petiole vs the blade and by tissue-specific gene expression.
Plant hormones are a group of naturally occurring, low-abundance organic compounds that influence physiological processes in plants. Our knowledge of the distribution profiles of phytohormones in ...plant organs, tissues, and cells is still incomplete, but advances in mass spectrometry have enabled significant progress in tissue- and cell-type-specific analyses of phytohormones over the last decade. Mass spectrometry is able to simultaneously identify and quantify hormones and their related substances. Biosensors, on the other hand, offer continuous monitoring; can visualize local distributions and real-time quantification; and, in the case of genetically encoded biosensors, are noninvasive. Thus, biosensors offer additional, complementary technologies for determining temporal and spatial changes in phytohormone concentrations. In this review, we focus on recent advances in mass spectrometry-based quantification, describe monitoring systems based on biosensors, and discuss validations of the various methods before looking ahead at future developments for both approaches.
Abstract
The size of plant organs is highly responsive to environmental conditions. The plant’s embryonic stem, or hypocotyl, displays phenotypic plasticity, in response to light and temperature. The ...hypocotyl of shade avoiding species elongates to outcompete neighboring plants and secure access to sunlight. Similar elongation occurs in high temperature. However, it is poorly understood how environmental light and temperature cues interact to effect plant growth. We found that shade combined with warm temperature produces a synergistic hypocotyl growth response that dependent on PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) and auxin. This unique but agriculturally relevant scenario was almost totally independent on PIF4 activity. We show that warm temperature is sufficient to promote PIF7 DNA binding but not transcriptional activation and we demonstrate that additional, unknown factor/s must be working downstream of the phyB-PIF-auxin module. Our findings will improve the predictions of how plants will respond to increased ambient temperatures when grown at high density.
Soil compaction represents a major challenge for modern agriculture. Compaction is intuitively thought to reduce root growth by limiting the ability of roots to penetrate harder soils. We report that ...root growth in compacted soil is instead actively suppressed by the volatile hormone ethylene. We found that mutant
and rice roots that were insensitive to ethylene penetrated compacted soil more effectively than did wild-type roots. Our results indicate that soil compaction lowers gas diffusion through a reduction in air-filled pores, thereby causing ethylene to accumulate in root tissues and trigger hormone responses that restrict growth. We propose that ethylene acts as an early warning signal for roots to avoid compacted soils, which would be relevant to research into the breeding of crops resilient to soil compaction.
A key challenge in biology is to understand how the regional control of cell growth gives rise to final organ forms. Plant leaves must coordinate growth along both the proximodistal and mediolateral ...axes to produce their final shape. However, the cell-level mechanisms controlling this coordination remain largely unclear. Here, we show that, in A. thaliana, WOX5, one of the WUSCHEL-RELATED HOMEOBOX (WOX) family of homeobox genes, acts redundantly with WOX1 and WOX3 (PRESSED FLOWER PRS) to control leaf shape. Through genetics and hormone measurements, we find that these WOXs act in part through the regional control of YUCCA (YUC) auxin biosynthetic gene expression along the leaf margin. The requirement for WOX-mediated YUC expression in patterning of leaf shape cannot be bypassed by the epidermal expression of YUC, indicating that the precise domain of auxin biosynthesis is important for leaf form. Using time-lapse growth analysis, we demonstrate that WOX-mediated auxin biosynthesis organizes a proximodistal growth gradient that promotes lateral growth and consequently the characteristic ellipsoid A. thaliana leaf shape. We also provide evidence that WOX proteins shape the proximodistal gradient of differentiation by inhibiting differentiation proximally in the leaf blade and promoting it distally. This regulation allows sustained growth of the blade and enables a leaf to attain its final form. In conclusion, we show that the WOX/auxin regulatory module shapes leaf form by coordinating growth along the proximodistal and mediolateral leaf axes.
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•WOX1, 3, and 5 are required redundantly for lateral leaf growth and auxin biosynthesis•YUC1 expression can partially bypass the requirement for WOX genes in leaf growth•Time-lapse imaging allows quantitation of WOX effects on leaf growth•WOXes shape a growth gradient that underlies the A. thaliana ellipsoid leaf shape
Zhang et al. discover that a genetic module comprising WOX homeobox proteins and the hormone auxin shapes Arabidopsis leaf form. They find that WOXes promote auxin biosynthetic gene expression. By using time-lapse imaging, they also show that this module generates a proximodistal gradient of growth that helps leaves grow laterally.
Plant architecture is optimized for the local light environment. In response to foliar shade or neighbor proximity (low red to far-red light), some plant species exhibit shade-avoiding phenotypes, ...including increased stem and hypocotyl growth, which increases the likelihood of outgrowing competitor plants. If shade persists, early flowering and the reallocation of growth resources to stem elongation ultimately affect the yield of harvestable tissues in crop species. Previous studies have shown that hypocotyl growth in low red to far-red shade is largely dependent on the photoreceptor phytochrome B and the phytohormone auxin. However, where shade is perceived in the plant and how auxin regulates growth spatially are less well understood. Using the oilseed and vegetable crop species Brassica rapa, we show that the perception of low red to far-red shade by the cotyledons triggers hypocotyl cell elongation and auxin target gene expression. Furthermore, we find that following shade perception, elevated auxin levels occur in a basipetal gradient away from the cotyledons and that this is coincident with a gradient of auxin target gene induction. These results show that cotyledon-generated auxin regulates hypocotyl elongation. In addition, we find in mature B. rapa plants that simulated shade does not affect seed oil composition but may affect seed yield. This suggests that in field settings where mutual shading between plants may occur, a balance between plant density and seed yield per plant needs to be achieved for maximum oil yield, while oil composition might remain constant.
The plant hormone auxin is believed to influence almost every aspect of plant growth and development. Auxin transport, biosynthesis and degradation combine to form gradients of the hormone that ...influence a range of key developmental and environmental response processes. There is abundant genetic evidence for the existence of multiple pathways for auxin biosynthesis and degradation. The complexity of these pathways makes it difficult to obtain a clear picture of the relative importance of specific metabolic pathways during development. We have developed a sensitive mass spectrometry‐based method to simultaneously profile the majority of known auxin precursors and conjugates/catabolites in small amounts of Arabidopsis tissue. The method includes a new derivatization technique for quantification of the most labile of the auxin precursors. We validated the method by profiling the auxin metabolome in root and shoot tissues from various Arabidopsis thaliana ecotypes and auxin over‐producing mutant lines. Substantial differences were shown in metabolite patterns between the lines and tissues. We also found differences of several orders of magnitude in the abundance of auxin metabolites, potentially indicating the relative importance of these compounds in the maintenance of auxin levels and activity. The method that we have established will enable researchers to obtain a better understanding of the dynamics of auxin metabolism and activity during plant growth and development.
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