Figure 1.
An antagonistic pair of feedback loops governs hormone levels in Arabidopsis. (a) Synthesis and degradation of the hormone ABA (species A) are modulated by two pathways (involving S and D, respectively) that themselves respond to ABA levels. Throughout this work, we will use parameters βi to correspond to the strengths of these responses, and Λi to correspond to the sensitivity of ABA to these signals. (b) A, S and D are produced and degraded, with levels modulating the rates of these processes. (c) Fluorescence microscopy following Topham et al. [37] identifies cellular localization of members of the S and D pathways in Arabidopsis embryos, showing that they are both present (scaled reflectance >0) in a range of cells (highlighted) at the same developmental stage. The antagonistic feedback loops thus together modulate ABA levels in these cells.