Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Auxins are important regulators of growth and development in higherplants. They mediate a plethora of effects in very low concentrations viadirected movement inside and between plant tissues. These propertiesdesignate them as plant hormones. Systematic quantification of auxins havegiven important insights into its roles in various developmental processes.The levels of the main auxin, indole-3-acetic acid (IAA), have previouslybeen shown to be highly dynamic in both spatial and temporal sense. In themature leaves of Arabidopsis thaliana and Nicotiana tabacum, a daily peakof IAA, which takes place during the light period, has been established.These fluctuations have been reported to persist in continuous conditions,suggesting that an internal oscillator plays a role in the regulation, andexcluding the possibility that IAA levels would mirror the light-dependentdiurnal metabolism. Furthermore, high-throughput analysis of geneexpression imply that IAA-related metabolism include genes that are underthe control of the internal oscillator.Physiological and molecular events that show persistent patterns undercontinuous light conditions are regulated, directly or indirectly, via aninternal molecular oscillator. This mechanism, which is based on temporallyseparated reciprocal regulation of transcription factors, generates dailyrhythms that are believed to allow organisms to anticipate the transitionsbetween the light and dark periods. Successful anticipation of the transitionsis thought to bring about a significant competitive advantage.In this work, IAA levels were quantified from seelings of A. thaliana withrespect to the dark-to-light transition and to the time of day. Upon the darkto-light transition, different responses were seen between three ecotypes ofA. thaliana, proving that light-induction of IAA levels is an ecotype-specificphenomenon. Light-induction likely reflects different growth strategiesbetween the ecotypes. A time-series experiment, which followed the levelsof IAA though the day, revealed no daytime peak in A. thaliana seedlings,but did suggest a light-to-dark transition-related pulse of IAA, synthetizedin the cotyledons and flushed to the roots. Under continuous conditions, theregulation of IAA levels were found to follow the logic of hypocotylelongation: both light and an internal oscillator seemed to play a role.