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Die Sonnenblume - eine Sonnenuhr: Pflanzenphysiologie
Abstract
Sonnenblumen (Helianthus annuus) nutzen ihre innere Uhr, um sich morgens dem Sonnenaufgang zuzuwenden. Dies beschleunigt bei jungen Sonnenblumen das Wachstum und erwärmt bei voll erblühten Pflanzen die Blüten, was wiederum die Bestäubung durch Insekten fördert.
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Searching for the Sun
The growth of immature sunflower plants tracks the Sun's movement. The young plants lean westward as the day progresses but reorient to the east each night. As the flowers mature and open, they settle into a stable east-facing orientation. Atamian et al. show how circadian rhythms regulate the east-west elongation of cells in the young plants' stems (see the Perspective by Briggs). They show that eastward-oriented flowers are warmer than westward-oriented flowers, and this warmth attracts pollinators. Auxin signaling pathways in the stem coordinate to fix the eastward orientation of the mature plant.
Science , this issue p. 587 ; see also p. 541
Plants are exposed to periodic changes of light and darkness in their habitats through the Earth’s rotation around its axis. Accordingly, plants have evolved an endogenous system to schedule their day in synchrony with their surroundings. Here, we review the blueprint of the core clockwork in plants and how the core clockwork orchestrates time-of-day-specific gene expression programmes.
Written in collaboration with his son Francis, a notable botanist, this 1880 book builds on Darwin's earlier investigations into climbing plants, orchids, insectivorous plants, flower variety, and the processes of fertilisation. This detailed study of many species from seed to mature plant further develops Darwin's work on adaptation and evolution, with the aim of collating the results of individual studies into common factors applicable to plants in general. Particular emphasis is given to analysis and investigation of the process here termed circumnutation, the movement of the stem of the plant in order to direct the head in certain directions. This is seen as of paramount importance, with the conclusion that it is modification of this feature that has enabled plants to adapt and evolve so diversely. The authors also note similarities between plants and animals, such as sensitivity to touch and habit of action at certain times.
Plants are photoautotrophic sessile organisms that use environmental cues to optimize multiple facets of growth and development. A classic example is phototropism - in shoots this is typically positive, leading to growth towards the light, while roots frequently show negative phototropism triggering growth away from the light. Shoot phototropism optimizes light capture of leaves in low light environments and hence increases photosynthetic productivity. Phototropins are plasma-membrane-associated UV-A/blue-light activated kinases that trigger phototropic growth. Light perception liberates their protein kinase domain from the inhibitory action of the amino-terminal photosensory portion of the photoreceptor. Following a series of still poorly understood events, phototropin activation leads to the formation of a gradient of the growth hormone auxin across the photo-stimulated stem. The greater auxin concentration on the shaded compared with the lit side of the stem enables growth reorientation towards the light. In this Minireview, we briefly summarize the signaling steps starting from photoreceptor activation until the establishment of a lateral auxin gradient, ultimately leading to phototropic growth in shoots.
Copyright © 2015 Elsevier Ltd. All rights reserved.
- H S Atamian
H. S. Atamian et al., Science, 2016, 353,
587-590.
- C Fankhauser
- J M Christie
C. Fankhauser, J. M. Christie, Current
Biology, 2015, 25, R384-389.
Staiger In: Rhythms in Plants
- S Danisman
- J L Mateos
S. Danisman, J. L. Mateos, D. Staiger
In: Rhythms in Plants, 2015, S. Mancuso
(Hrsg.) Springer Verlag, 257–278.
- S Danisman
- J L Mateos
- D Staiger In
S. Danisman, J. L. Mateos, D. Staiger
In: Rhythms in Plants, 2015, S. Mancuso
(Hrsg.) Springer Verlag, 257-278.
Francis Darwin The power of movement in plants 1880
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- Staiger