Wind-dispersed plants have evolved ingenious ways to lift their seeds 1,2. The common dandelion uses a bundle of drag-enhancing bristles (pappus) to help keep their seeds aloft. This passive flight mechanism is highly effective, enabling seed dispersal over formidable distances 3,4 ; however, the engineering underpinning pappus-mediated flight remains unresolved. Here, we have visualized the flow around dandelion seeds, uncovering an extraordinary type of vortex. This vortex is a ring of recirculating fluid, which is detached due to the flow passing through the pappus. We hypothesized that the circular disk-like geometry and the porosity of the pappus are the key design features that enable the formation of the separated vortex ring. The porosity gradient was surveyed using microfabricated disks, and a disk with a similar porosity was found able to recapitulate the flow behaviour of the real pappus. The porosity of the dandelion's pappus appears to be tuned precisely to stabilize the vortex, while maximizing the aerodynamic loading and minimizing the material requirement. The discovery of the separated vortex ring signals the existence of a new class of fluid behaviour around fluid-immersed bodies that may underlie locomotion, weight reduction, and particle retention of biological and manmade structures. Dandelions (Taraxacum officinale agg.) are highly successful perennial herbs, which can be found in temperate zones all over the world 5. Dandelions, like many other members of the Asteraceae family, disperse their bristly seeds using the wind and convective updrafts 6,7. Most dandelion seeds likely land within 2 m 8,9 ; however, in warmer, drier and windier conditions, some may fly further (up to 20,000 seeds per hectare travelling more than 1 km by one estimate) 6,10. Asteraceae seeds routinely disperse over 30 km and occasionally even 150 km 3,4. Plumed seeds comprise a major class of dispersal strategies used by numerous and diverse groups of flowering plants, of which the common dandelion is a representative example. Plumed seeds contain a bundle of bristly filaments, called a pappus, which are presumed to function in drag enhancement (Fig. 1a-c). The pappus prolongs the descent of the seed, so that it may be carried farther by horizontal winds 11 , and it may also serve to orientate the seed as it falls 7,12. Dandelion seeds fall stably at a constant speed in quiescent conditions 2,13-15. For wind-dispersed seeds, maintaining stability while maximizing descent time in turbulent winds may be useful for long-distance dispersal 16,17. It is not clear, however, why plumed seeds have opted for a bristly pappus rather than a wing-like membrane, which is known to enhance lift in some other species (e.g., maples 1). Here, we uncover the flight mechanism of the dandelion, characterizing the fluid dynamics of the pappus and identifying the key structural features enabling its stable flight. To examine the flow behaviour around the pappus, we built a vertical wind tunnel (Fig. 1d, and M1), designed so that the seed ca...
The degree of shoot branching in Arabidopsis is determined by the activation of axillary buds. Bud activity is regulated by diverse environmental and developmental signals, often mediated via plant hormones, including auxin, strigolactone and cytokinin. The transcription factor BRANCHED1 (BRC1) has been proposed to integrate these regulatory signals. This idea is based on increased branching in brc1 mutants, the effects of bud-regulating hormones on BRC1 expression, and a general correlation between BRC1 expression and bud growth inhibition. These data demonstrate the important role of BRC1 in shoot branching, but here we show that in Arabidopsis this correlation can be broken. Buds lacking BRC1 expression can remain inhibited and sensitive to inhibition by strigolactone. Furthermore, buds with high BRC1 transcript levels can be active. Based on these data, we propose that BRC1 regulates bud activation potential in concert with an auxin transport-based mechanism underpinning bud activity. In the context of strigolactone-mediated bud regulation, our data suggest a coherent feed-forward loop in which strigolactone treatment reduces the probability of bud activation by parallel effects on BRC1 transcription and the shoot auxin transport network.
Strigolactones are a recently identified class of hormone that regulate multiple aspects of plant development. The DWARF14 (D14) α/β fold protein has been identified as a strigolactone receptor, which can act through the SCFMAX2 ubiquitin ligase, but the universality of this mechanism is not clear. Multiple proteins have been suggested as targets for strigolactone signalling, including both direct proteolytic targets of SCFMAX2, and downstream targets. However, the relevance and importance of these proteins to strigolactone signalling in many cases has not been fully established. Here we assess the contribution of these targets to strigolactone signalling in adult shoot developmental responses. We find that all examined strigolactone responses are regulated by SCFMAX2 and D14, and not by other D14-like proteins. We further show that all examined strigolactone responses likely depend on degradation of SMXL proteins in the SMXL6 clade, and not on the other proposed proteolytic targets BES1 or DELLAs. Taken together, our results suggest that in the adult shoot, the dominant mode of strigolactone signalling is D14-initiated, MAX2-mediated degradation of SMXL6-related proteins. We confirm that the BRANCHED1 transcription factor and the PIN-FORMED1 auxin efflux carrier are plausible downstream targets of this pathway in the regulation of shoot branching, and show that BRC1 likely acts in parallel to PIN1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.