ORIGINAL PAPER Shade light interaction with salicylic acid in regulating growth of sun (alpine) and shade (prairie) ecotypes of Stellaria longipes Leonid V. Kurepin • Linda J. Walton • Allison Hayward • R. J. Neil Emery • David M. Reid • C. C. Chinnappa Received: 15 January 2012 / Accepted: 28 March 2012 Ó Springer Science+Business Media B.V. 2012 Abstract The possible involvement of salicylic acid (SA) in a typical growth response of plants to shade light was investigated using the model system Stellaria longipes L. Goldie. The prairie (shade) ecotype of S. longipes is from foothills grassland habitat where it grows under shrubs or among taller grasses. The plants of this ecotype responded, as expected, with increased growth under lower red to far- red (R/FR) ratio and reduced photosynthetically active radiation (PAR). By contrast, the alpine (sun) ecotype is from an open sunny habitat, where canopy shade is a non- factor. The plants of this ecotype failed to respond with increased growth under a lower R/FR ratio, but had increased growth under a reduced PAR level. To examine the possible role of SA in shade light-mediated growth, the two main components of shade light, R/FR ratio and PAR, were uncoupled, and a series of experiments were per- formed by measuring the endogenous SA content and the plant response to exogenous SA concentrations. Contrary to the alpine plants, the prairie plants had increased endogenous SA content and higher shoot biomass accu- mulation under a low R/FR ratio treatment compared with normal or high R/FR ratios. Both alpine and prairie plants responded to a low PAR treatment with a decrease in endogenous SA content and an increase in shoot biomass accumulation, but the magnitude of this response was higher in prairie plants. Based on the results of this study, we conclude that shoot SA content is differentially regu- lated by both R/FR ratio and PAR signals, and SA may contribute, in ecotype specific manner, to growth changes in plants subjected to changing light environments. Keywords R/FR ratio Light quality PAR Light intensity Salicylic acid Shoot growth Introduction Plant growth and developmental processes can be altered by light quality and quantity. For example, plants growing in canopy shade or in the shade of neighbouring taller vegetation are usually receiving altered light quality (measured as red to far-red [R/FR] ratio) and reduced light quantity (measured as photosynthetically active radiation [PAR]) (reviewed in Ballare 1999; Smith 2000). Plants grown under lower R/FR ratios and lower PAR irradiance conditions normally exhibit increased stem elongation, whereas leaf growth can increase or decrease depending on species (Smith 2000; Vandenbussche et al. 2005; Kurepin et al. 2007d). The changes in plant growth in response to these light signals are regulated by multiple plant hor- mones: mainly by gibberellins, but there are also reports of the involvement of ethylene, auxins and cytokinins (Beall et al. 1996; Vandenbussche et al. 2005; Kurepin et al. 2006a, b; 2007a, b, c, d; 2008), whereas the role of abscisic acid is not clear (Kurepin et al. 2007b, c). Salicylic acid (SA) is a plant hormone primarily known for its involvement in the induction of Systemic Acquired Resistance (SAR) as a result of pathogen infection; but SA L. V. Kurepin L. J. Walton D. M. Reid C. C. Chinnappa Department of Biological Sciences, University of Calgary, Calgary, AB, Canada L. V. Kurepin A. Hayward R. J. N. Emery Biology Department, Trent University, Peterborough, ON, Canada Present Address: L. V. Kurepin (&) Department of Biology, University of Western Ontario, London, ON, Canada e-mail: lkurepin@uwo.ca 123 Plant Growth Regul DOI 10.1007/s10725-012-9686-2