Amino Acid Pool Sizes, Turnover, and Kinetics in Spirodela polyrhyza Grown Under Photoautotrophic, Mixotrophic, and Heterotrophic Conditions

Abstract

In this study I describe a [15N] stable isotopic labeling study of amino acids in Spirodela polyrhiza (common duckweed) grown under three light and carbon input conditions to mimic photoautotrophic, mixotrophic, and heterotrophic metabolic inputs. Labeling patterns, pool sizes, and kinetics/turnover rates were estimated for fifteen of the proteinogenic amino acids. Estimates of these parameters followed several trends. First, most amino acids showed plateaus in labeling patterns of less than 100% labeling. Second, total pool sizes appear largest in the heterotrophic condition, whereas active pool sizes appear to be largest in the mixotrophic growth condition. In contrast turnover measurements based on pool size were highest overall in the mixotrophic experiment. K-means clustering analysis also revealed more rapid turnover in the auto/mixotrophic. Emerging insights from other research were also supported, such as the prevalence of alternate pathways for serine metabolism in non-photosynthetic cells. These data provide extensive novel information on amino acid pool size and kinetics in S. polyrhiza and can serve as groundwork for future metabolic studies.