5 research outputs found

    An auxin signaling network translates low-sugar-state input into compensated cell enlargement in the fugu5 cotyledon

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    International audienceIn plants, the effective mobilization of seed nutrient reserves is crucial during germination and for seedling establishment. The Arabidopsis H + -PPase-loss-of-function fugu5 mutants exhibit a reduced number of cells in the cotyledons. This leads to enhanced post-mitotic cell expansion, also known as compensated cell enlargement (CCE). While decreased cell numbers have been ascribed to reduced gluconeogenesis from triacylglycerol, the molecular mechanisms underlying CCE remain ill-known. Given the role of indole 3-butyric acid (IBA) in cotyledon development, and because CCE in fugu5 is specifically and completely cancelled by ech2 , which shows defective IBA-to-indoleacetic acid (IAA) conversion, IBA has emerged as a potential regulator of CCE. Here, to further illuminate the regulatory role of IBA in CCE, we used a series of high-order mutants that harbored a specific defect in IBA-to-IAA conversion, IBA efflux, IAA signaling, or vacuolar type H + -ATPase (V-ATPase) activity and analyzed the genetic interaction with fugu5–1 . We found that while CCE in fugu5 was promoted by IBA, defects in IBA-to-IAA conversion, IAA response, or the V-ATPase activity alone cancelled CCE. Consistently, endogenous IAA in fugu5 reached a level 2.2-fold higher than the WT in 1-week-old seedlings. Finally, the above findings were validated in icl–2 , mls–2 , pck1–2 and ibr10 mutants, in which CCE was triggered by low sugar contents. This provides a scenario in which following seed germination, the low-sugar-state triggers IAA synthesis, leading to CCE through the activation of the V-ATPase. These findings illustrate how fine-tuning cell and organ size regulation depend on interplays between metabolism and IAA levels in plants

    Stem integrity in Arabidopsis thaliana requires a load-bearing epidermis

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    International audienceABSTRACT Because plant cells are glued to each other via their cell walls, failure to coordinate growth among adjacent cells can create cracks in tissues. Here, we find that the unbalanced growth of inner and outer tissues in the clavata3 de-etiolated3 (clv3 det3) mutant of Arabidopsis thaliana stretched epidermal cells, ultimately generating cracks in stems. Stem growth slowed before cracks appeared along clv3 det3 stems, whereas inner pith cells became drastically distorted and accelerated their growth, yielding to stress, after the appearance of cracks. This is consistent with a key role of the epidermis in restricting growth. Mechanical property measurements recorded using an atomic force microscope revealed that epidermal cell wall stiffness decreased in det3 and clv3 det3 epidermises. Thus, we hypothesized that stem integrity depends on the epidermal resistance to mechanical stress. To formally test this hypothesis, we used the DET3 gene as part of a tissue-specific strategy to complement cell expansion defects. Epidermis-driven DET3 expression restored growth and restored the frequency of stem cracking to 20% of the clv3 det3 mutant, demonstrating the DET3-dependent load-bearing role of the epidermis

    Acute neuropharmacological effects of atomoxetine on inhibitory control in ADHD children: A fNIRS study

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    The object of the current study is to explore the neural substrate for effects of atomoxetine (ATX) on inhibitory control in school-aged children with attention deficit hyperactivity disorder (ADHD) using functional near-infrared spectroscopy (fNIRS). We monitored the oxy-hemoglobin signal changes of sixteen ADHD children (6–14 years old) performing a go/no-go task before and 1.5 h after ATX or placebo administration, in a randomized, double-blind, placebo-controlled, crossover design. Sixteen age- and gender-matched normal controls without ATX administration were also monitored. In the control subjects, the go/no-go task recruited the right inferior and middle prefrontal gyri (IFG/MFG), and this activation was absent in pre-medicated ADHD children. The reduction of right IFG/MFG activation was acutely normalized after ATX administration but not placebo administration in ADHD children. These results are reminiscent of the neuropharmacological effects of methylphenidate to up-regulate reduced right IFG/MFG function in ADHD children during inhibitory tasks. As with methylphenidate, activation in the IFG/MFG could serve as an objective neuro-functional biomarker to indicate the effects of ATX on inhibitory control in ADHD children. This promising technique will enhance early clinical diagnosis and treatment of ADHD in children, especially in those with a hyperactivity/impulsivity phenotype
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