Phytochrome-Mediated Phototropism in De-Etiolated Seedlings

Ballaré, Carlos L.; Scopel, Ana L.; Radosevich, Steven R.; Kendrick, Richard E.

doi:10.1104/pp.100.1.170

Cited by 75 publications

(62 citation statements)

References 32 publications

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“…mosses; Esch et al, 1999), but there are few reports of a direct phytochrome-regulated phototropism in flowering plants (Iino et al, 1984;Parker et al, 1989). In addition, Ballare et al (1992) reported a phytochrome-dependent phototropism in cucumber (Cucumis sativus) shoots by showing that a far-red-dependent negative phototropic response was at least partly mediated by phyB. The data presented in this paper show that both phyA and phyB are required for the red-lightdependent positive phototropic response in Arabidopsis roots.…”

Section: Discussionmentioning

confidence: 64%

Phytochromes A and B Mediate Red-Light-Induced Positive Phototropism in Roots

et al. 2003

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(J.L.M., R.P.H.)The interaction of tropisms is important in determining the final growth form of the plant body. In roots, gravitropism is the predominant tropistic response, but phototropism also plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism that is mediated by the phototropin family of photoreceptors. In contrast, red light induces a positive phototropism in Arabidopsis roots. Because this red-light-induced response is weak relative to both gravitropism and negative phototropism, we used a novel device to study phototropism without the complications of a counteracting gravitational stimulus. This device is based on a computer-controlled system using real-time image analysis of root growth and a feedback-regulated rotatable stage. Our data show that this system is useful to study root phototropism in response to red light, because in wild-type roots, the maximal curvature detected with this apparatus is 30°to 40°, compared with 5°to 10°without the feedback system. In positive root phototropism, sensing of red light occurs in the root itself and is not dependent on shoot-derived signals resulting from light perception. Phytochrome (Phy)A and phyB were severely impaired in red-light-induced phototropism, whereas the phyD and phyE mutants were normal in this response. Thus, PHYA and PHYB play a key role in mediating red-light-dependent positive phototropism in roots. Although phytochrome has been shown to mediate phototropism in some lower plant groups, this is one of the few reports indicating a phytochrome-dependent phototropism in flowering plants.Plants have evolved selective and sensitive mechanisms to deal with the constant sensory input they receive from the environment. In roots, gravity is the most critical signal for growth and development, and, thus, gravitropism has been well-characterized in this organ (Sack, 1991;Kiss, 2000). However, it has become increasingly clear that gravitropism interacts with a number of other tropistic responses including phototropism, thigmotropism, and hydrotropism in determining the final growth form of the primary root and the entire root system (Hangarter, 1997;Correll and Kiss, 2002).Phototropism in roots was extensively reviewed in a classical paper by Hubert and Funke (1937) but has received increased attention since the report by Okada and Shimura (1992), who isolated mutants in root phototropism that were later shown to be deficient in the blue-light receptor PHOT1 (Briggs and Christie, 2002). Roots are typically negatively phototropic in response to white and blue light (Okada and Shimura, 1992;Vitha et al., 2000) and use the same photoreceptors that are involved in phototropism in stems and stem-like organs (Sakai et al., 2000). Furthermore, similar to root gravisensing (Blancaflor et al., 1998), sensing of blue light for phototropism occurs in the root cap .We have recently identified a red-light-induced positive phototropism in primary roots of Arabidopsis ). This tropistic response ...

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Section: Discussionmentioning

confidence: 64%

Phytochromes A and B Mediate Red-Light-Induced Positive Phototropism in Roots

et al. 2003

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“…This is suggested by physiological studies showing that in phyB-deficient Arabidopsis mutants {jjhyB), as well as in the putative phyB-deficient mutants of cucumber {Hi) and Brassica {ein), elongation responses to changes in R:FR ratio are highly attenuated or absent (Robson, Whitelam & Smith 1993, and references therein). Phototropic responses to FR are also absent in /// (Ballare et al 1992), whereas other responses to FR are conserved in phyB-deficient mutants. These include, for example, the acceleration of flowering and changes in leaf area and specific stem length in Arabidopsis (e.g.…”

Section: Photoreceptorsmentioning

confidence: 91%

Foraging for light: photosensory ecology and agricultural implications

Ballaré

Scopel

Sánchez

1997

Plant Cell & Environment

121

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This mini-review is concerned with one of the facets of the sensory physiology of plants that, in the last decade, has heen intensively studied using genetically altered plants and eco-physiological techniques -the perception of the proximity of neighhouring piants through specific informational photoreceptors. We focus on the signalling mechanisms that allow individual shoots to 'forage' for light in patchy and highly dynamic canopy environments. We present evidence from recent experiments suggesting that the fitness of each individual plant in the population, the growth of the population as a whole, and the degree of growth inequality among neighbours are all strongly dependent on the timing and precision of foraging mechanisms controlled, at least partially, hy phytochrome-B-like phytochromes. This evidence is discussed in the context of potential impacts on yield of agricultural crops resulting from the artificial alteration of plant sensitivity to proximity photo-signals. Directed overexpression of phytochrome genes appears to he an interesting avenue to explore in order to alter the photomorphogenesis of specific organs (or developmental stages) without affecting the overall ahility of the plants to forage for light.

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“…By perceiving R/FR changes in the spectral composition of reflected (back-scattered) light via phytochrome, plants can remotely detect the proximity of other plants and respond with morphological changes before being shaded by their neighbors (2,6,7). Early proximity responses include: changes in branching rate (8), accelerated stem elongation (9,10), stem bending away from neighbors, and other phototropic phenomena (11,12). Because some of these responses would increase the ability ofindividual plants to capture photosynthetic light in a patchy canopy, R/FRlight signals are thought to convey critical information to plants that are competing with each other for colonizing the aerial environment (2,5,6).…”

mentioning

confidence: 99%

Signaling among neighboring plants and the development of size inequalities in plant populations.

Ballaré

Scopel

Jordan

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

105

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Transgenic tobacco plants that express an oat phytochrome gene (phyA) under control of the cauliflower mosaic virus (CaMV) 35S promoter and display altered photophysiology were used to test the role of light as a vehicle of information in dominance relationships between neighboring plants. Compared with the isogenic wild type, phyAoverexpressing plants showed dramatically reduced morphological responsivity to changes in the red/far red ratio of the incident light and to the proximity of neighboring plants in spacing experiments. In transgenic canopies an increase in stand density caused the small plants of the population to be rapidly suppressed by their neighbors. In wild-type canopies, plants responded to increased density with large morphological changes, and there appeared to be an inverse relationship between the magnitude of this morphological response and the ranking of the individual plant in the population size hierarchy. In these wild-type populations, size inequality increased only moderately with density within the time frame of the experiments. Our results suggest that, in crowded stands, the ability of individual plants to acquire information about their light environment via phytochrome plays a central role in driving architectural changes that, at the population level, delay the development of size differences between neighbors.Higher plants respond to the proximity of other plants with plastic morphological and physiological changes. Some of these responses are simple changes in growth rate caused by variation in the supply of environmental resources (e.g., light, nutrients) imposed by neighboring individuals (1). Others are triggered by systems that appear to have evolved specifically to acquire information about the nearness of other plants (2). One such system is driven by phytochrome, a family of photochromic plant photoreceptors (3) that are sensitive to the red (R)-to-far red (FR) ratio (R/FR) of the incident light (4,5 (23,24). The lack of information on the role of light signaling in the genesis of population structure may have far reaching consequences, as the idea of engineering photomorphogenically "blind" genotypes to "improve" crop plants is currently being actively debated (25).Abbreviations: CV, coefficient of variation; FR, far-red radiation; LAI, leaf area index; PPFD, photosynthetic photon flux density; R, red radiation; wt, wild type.tTo whom reprint requests should be addressed at the * address. 10094The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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Phytochrome-Mediated Phototropism in De-Etiolated Seedlings

Cited by 75 publications

References 32 publications

Phytochromes A and B Mediate Red-Light-Induced Positive Phototropism in Roots

Phytochromes A and B Mediate Red-Light-Induced Positive Phototropism in Roots

Foraging for light: photosensory ecology and agricultural implications

Signaling among neighboring plants and the development of size inequalities in plant populations.

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