Light irradiance differentially regulates endogenous levels of cytokinins and auxin in alpine and prairie genotypes of Stellaria longipes.

The growth patterns of plants from alpine (sun) and prairie (shade) ecotypes of Stellaria longipes in response to change in light irradiance was investigated and involvement of cytokinins (CKs), auxin (IAA) and abscisic acid (ABA) was studied to examine the mechanism behind phenotypic plasticity of these plants in response to light signalling. Low light irradiance induced shoot growth in plants of both ecotypes, but IAA levels were higher in plants from alpine, but not prairie ecotype. Dynamics of CK profiles in response to changing photosynthetically active radiation were quite different between ecotypes and changes were more pronounced in the plants of alpine ecotype, where opposite patterns in CK accumulation between low and normal light irradiances were observed. The plants of both ecotypes showed similar trends in ABA levels under low light irradiance. Thus, the highly plastic plants of prairie ecotype may have evolved mechanisms to control the growth in response to reduced light irradiance without major alterations in the levels of CKs or IAA. These results demonstrate that within species, plants from open habitats show less growth response to reduced light irradiance than plants from shaded habitats.