The gibberellins (GAs) are a group of endogenous compounds that promote the growth of most plant organs, including stem internodes. We show that in tobacco (Nicotiana tabacum) the presence of leaves is essential for the accumulation of bioactive GAs and their immediate precursors in the stem and consequently for normal stem elongation, cambial proliferation, and xylem fiber differentiation. These processes do not occur in the absence of maturing leaves but can be restored by application of C19-GAs, identifying the presence of leaves as a requirement for GA signaling in stems and revealing the fundamental role of GAs in secondary growth regulation. The use of reporter genes for GA activity and GA-directed DELLA protein degradation in Arabidopsis thaliana confirms the presence of a mobile signal from leaves to the stem that induces GA signaling.

SummaryEnhancing plant height and growth rates is a principal objective of the fiber, pulp, wood and biomass product industries. Many biotechnological systems have been established to advance that task with emphasis on increasing the concentration of the plant hormone gibberellin, or on its signalling. In this respect, the most studied gibberellin biosynthesis enzyme is the GA 20-oxidase which catalyses the rate limiting step of the pathway. Overexpression of the gene resulted in an excessively high activity of the gibberellin deactivating enzyme, GA 2-oxidase. Consequently, this feedback regulation limits the intended outcome. We assume that silencing GA 2-oxidase transcription would abolish this antithetical effect, thereby allowing greater gibberellin accumulation. Here, we show that silencing the gibberellin deactivating enzyme in tobacco model plants results in a dramatic improvement of their growth characteristics, compared with the wild type and GA 20-oxidase over-expressing plants. Moreover, the number of xylem fiber cells in the silenced lines exceeded that of GA 20-oxidase over-expressing plants, potentially, making GA 2-oxidase silencing more profitable for the wood and fiber industries. Interestingly, crossing GA 20-oxidase over-expressing plants with GA 2-oxidase silenced plants did not yield consequential additive effects. Our findings unveil the benefits of silencing GA 2-oxidase to substantially increase tobacco growth and fiber production, which suggest using this approach in cultivated forest plantations and industrial herbaceous plants, worldwide.

Introduction We conducted an open‐label study to examine the effects of the flavonoid (−)‐epicatechin in seven ambulatory adult patients with Becker muscular dystrophy (BMD). Methods Seven participants received (−)‐epicatechin 50 mg twice per day for 8 weeks. Pre‐ and postprocedures included biceps brachii biopsy to assess muscle structure and growth‐relevant endpoints by western blotting, mitochondria volume measurement, and cristae abundance by electron microscopy, graded exercise testing, and muscle strength and function tests. Results Western blotting showed significantly increased levels of enzymes modulating cellular bioenergetics (liver kinase B1 and 5′‐adenosine monophosphate–activated protein kinase). Peroxisome proliferator‐activated receptor gamma coactivator‐1alpha, a transcriptional coactivator of genes involved in mitochondrial biogenesis and cristae‐associated mitofilin levels, increased as did cristae abundance. Muscle and plasma follistatin increased significantly while myostatin decreased. Markers of skeletal muscle regeneration myogenin, myogenic regulatory factor‐5, myoblast determination protein 1, myocyte enhancer factor‐2, and structure‐associated proteins, including dysferlin, utrophin, and intracellular creatine kinase, also increased. Exercise testing demonstrated decreased heart rate, maximal oxygen consumption per kilogram, and plasma lactate levels at defined workloads. Tissue saturation index improved in resting and postexercise states. Discussion (−)‐Epicatechin, an exercise mimetic, appears to have short‐term positive effects on tissue biomarkers indicative of mitochondrial biogenesis and muscle regeneration, and produced improvements in graded exercise testing parameters in patients with BMD.

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