Fig. 9

a Auxin model shows how auxin concentration affects sepal development in spinach 1. Auxin transport inhibitor (NPA) treatment to pollinated flower (red dotted line) resulted in polar auxin flow weakening that might drop the auxin concentration to level resulted in sepal wilting 2. Increase in auxin concentration under auxin analogs (2, 4D, IAA) application to unpollinated flower (purple dotted line) resulted in sepal development in unpollinated flower sepal at certain concentration, further increase in auxin resulted in sepal wilting indicate auxin level is critical for sepal development. b Auxin regulatory metabolic changes for sepal size modulation in spinach. It shows the influence of Trp-dependent auxin biosynthesis and auxin signaling pathway on cell division, expansion, and cell wall biogenesis to modify sepal size in spinach female flower following pollination 1. Pollination resulted in pollen factor activation which biosynthesizes auxin and 2. activates auxin signaling pathway 3. auxin regulate gene responsible for cell wall loosening/expansion 4. and cell division pathway for sepal cell proliferation for development 5–6. Auxin also indirectly (through photosynthesis) or directly regulate cell wall synthesis pathway for biomass accumulation for sepal development