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

Abstract

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.

Structure-Guided Engineering of Plant Phytochrome B with Altered Photochemistry and Light Signaling

“…Given the central importance of phys in regulating plant photomorphogenesis, it has long been proposed that their rational redesign could offer new strategies to better tailor crops to fit specific agricultural environments, including, for example, the improvement of seed germination, attenuation of the SAR, modification of flowering time, and delayed senescence (Ballaré et al, 1994;Izaguirre et al, 2006). While sufficiently resolved three-dimensional structures of plant phys await, we demonstrate here that the bacterial models provide reasonable surrogates with which to predictably modify the photobehavioral properties of the plant versions via structure-guided mutagenesis.…”

Evidence for competition and cooperation among climbing plants

“…To measure the degree of height inequality, I used the coefficient of variation (CV; s.d./mean), which is commonly used for this purpose (e.g. [31,32]). When testing for treatment effects on the CV in height, I used the mean height of plants in a group as a covariate, and all models also included the blocking factor 'table'.…”

Shade avoidance inTrifolium repens: costs and benefits of plasticity in petiole length and leaf size

“…Increased petiole elongation in a vertical light gradient (as compared with elongation under homogeneous shading) improves leaf placement and should result in enhanced light harvesting and higher carbohydrate production (Ballare et al, 1994;Leeflang et al, 1998). However, this extra supply may be directly used by the petiole carrying the leaf laminas for further elongation.…”

“…Shade-avoidance responses are induced by lower amounts of photosynthetically active radiation (PAR), a decreased red to far-red ratio (R:FR) of the incident light, and the perception of ethylene produced by neighbouring plants (Schmitt & Wulff, 1993;Ballare et al ., 1994;Pierik et al ., 2003;Schmitt et al ., 2003). The induced responses enable plants to reduce the negative fitness consequences caused by competition for light (Aphalo & Ballare, 1995;de Kroon & Hutchings, 1995;Sultan, 1995;Huber & Hutchings, 1997;van Hinsberg, 1997;Geber & Griffen, 2003).…”

“…Plasticity enables plants to alter morphological, physiological and developmental traits to match their phenotypes to the environment they are growing in (Ballare et al ., 1994;Sultan, 2005), thereby buffering the potentially negative effects of environmental variation on growth and reproduction.…”