Adaptation to ultraviolet radiation in marine green macroalgae : screening and tolerance
For plants and algae UVB radiation represents an important stress factor associated with sunlight. This radiation has the potential to inhibit physiological processes like photosynthesis as well as to damage molecules like the DNA. In plants adaptation to UVB radiation is based on two main resistance mechanisms: physical screening or cellular tolerance. The main goal of this thesis was to investigate to which extent and how precisely these strategies are present in different representatives of green macroalgae. For the first time UV screening was discovered in the order Cladophorales and the connected photoprotective function could be demonstrated in UVB challenge experiments. In contrast the majority of the remaining orders did not exhibit UV screening and was analyzed for the alternative resistance mechanisms like photosystem II (PS II) repair and DNA repair capacities. Especially species from the very abundant and often highlight exposed genus Ulva had an outstandingly high UVB tolerance of PS II. Field experiments corroborated the high potential of cellular UVB tolerance mechanisms in Ulva intestinalis.