Poplars, apoplastic barriers, and the environment

This doctoral thesis, “Poplars, apoplastic barriers, and the environment”, is dedicated to the ecophysiological traits of poplars, especially their apoplastic barriers in roots and leaves, in the scope of environmental changes. <br> After establishing the basis by introducing poplar-specific characteristics and peculiarities, the location and function of suberized and cutinized plant-atmosphere interfaces, as well as the role of anthropogenic climate change and environment-related research, a set of nine different studies will be presented. <br> These results are non-chronologically but contentwise meaningfully arranged, and thus Chapters 1 and 2, two review-like publications, further introductorily elucidate the chemical and physiological complexity of rhizospheric suberized and atmospheric cutinized apoplastic transport barriers in roots and leaves, respectively. Their plasticity in response to abiotic stress conditions, exact functional implications, and dependence on omnipresent water potential gradients are highlighted. Chapters 3 to 6 are dedicated to the suberized transport barriers of poplar roots in particular. By establishing an experimental pipeline for hydroponic poplar cultivation (Chapter 3), the reactions of roots towards various abiotic stress (osmotic stress, salt exposure, exogenous abscisic acid supplementation, and oxygen deficiency) and additional deviating cultivation (aeroponics and soil) conditions could be investigated (Chapter 4 and Chapter 5). Adventitious root development, the variable formation of suberized apoplastic barriers in endodermal and sometimes exodermal tissue layers, and the functional consequences were explored in detail. Most of the insights generated were acquired using <em>Populus × canescens</em> wildtypes. However, the final root-specific study was able to even extend this information with four suberin-deficient poplar mutants that appear to be incapable of root suberization in various gradations (Chapter 6). Chapters 7 to 9 contrastingly focus on the cutinized apoplastic barriers of poplar leaves. By cultivating different poplar species in an identical environment (Chapter 7) and a single species in three diverse environments (Chapter 8), species-specific phenotypic variations and environmentally influenced adaptations of leaves could be compared. Differential leaf development, the customizable deposition of cutinized apoplastic barriers in the shape of leaf cuticles, and subsequent functional disparities were studied. In analogy to roots, the final leaf-specific publication expands previous wildtype-generated knowledge with the comparative analysis of poplar mutants that are affected in the biosynthesis of cuticular wax constituents (Chapter 9). <br> All of these findings are conclusively discussed by explicitly focusing on poplars in the context of environmental changes. They are also comprehensively interrelated by covering apoplastic barriers in the roots and leaves of plants more generally.