caa a22 4500 445841826 CHVBK 20180317145347.0 cr unu---uuuuu 170323e20111101xx s 000 0 eng 10.1007/s10725-011-9596-8 doi (NATIONALLICENCE)springer-10.1007/s10725-011-9596-8 The interaction of light irradiance with auxin in regulating growth of Helianthus annuus shoots [Elektronische Daten] [Leonid Kurepin, Linda Walton, Edward Yeung, David Reid] Plants growing under canopy shade or in near-neighboring proximity of taller vegetation are the receivers of shade light conditions. The effect of light irradiance (photosynthetically active radiation [PAR]), one of the main components of shade light, on the growth of various tissues of sunflower seedlings and the possible role of auxin were investigated. Gradual reductions in PAR irradiance level from near-normal to low and very low result in significant and gradual increases in sunflower hypocotyl growth and endogenous auxin content. Similar reductions in PAR level resulted in significant and gradual decreases in sunflower cotyledon and leaf growth, and endogenous auxin content. Exogenously applied auxin increased hypocotyl elongation under near-normal PAR, where IAA levels are below optimum, but decreased elongation under very low PAR, where IAA levels are already at optimum. These results suggests that auxin acts as positive growth regulator of sunflower hypocotyls subjected to low light irradiance stress. This is further supported by the transfer experiments where seedlings transferred, for example, from near-normal PAR to very low PAR showed increased elongation associated with increased IAA levels. Therefore, it is reasonable to conclude that light irradiance-mediated changes in hypocotyl elongation of young sunflower seedlings are regulated by endogenous auxin levels. Springer Science+Business Media B.V., 2011 PAR nationallicence Light irradiance nationallicence Growth nationallicence Auxin nationallicence Sunflower nationallicence Kurepin Leonid Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut Walton Linda Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut Yeung Edward Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut Reid David Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut Plant Growth Regulation Springer Netherlands 65/2(2011-11-01), 255-262 0167-6903 65:2<255 2011 65 10725 https://doi.org/10.1007/s10725-011-9596-8 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10725-011-9596-8 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Kurepin Leonid Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut NATIONALLICENCE 700 1- Walton Linda Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut NATIONALLICENCE 700 1- Yeung Edward Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut NATIONALLICENCE 700 1- Reid David Department of Biological Sciences, University of Calgary, Calgary, AB, Canada aut NATIONALLICENCE 773 0- Plant Growth Regulation Springer Netherlands 65/2(2011-11-01), 255-262 0167-6903 65:2<255 2011 65 10725 Metadata rights reserved Springer special CC-BY-NC licence nationallicence SWISSBIB 445841826 BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer