Abstract:
Phytohormones play important roles in plant acclimation to changes in environmental conditions. However, their
role in whole-plant regulation of growth and secondary metabolite production under increasing atmospheric CO2
concentrations ([CO2]) is uncertain but crucially important for understanding plant responses to abiotic stresses. We
grew winter wheat (Triticum aestivum) under three [CO2] (170, 390, and 680 ppm) over 10 weeks, and measured gas
exchange, relative growth rate (RGR), soluble sugars, secondary metabolites, and phytohormones including abscisic
acid (ABA), auxin (IAA), jasmonic acid (JA), and salicylic acid (SA) at the whole-plant level. Our results show that, at the
whole-plant level, RGR positively correlated with IAA but not ABA, and secondary metabolites positively correlated
with JA and JA-Ile but not SA. Moreover, soluble sugars positively correlated with IAA and JA but not ABA and SA.
We conclude that increasing carbon availability stimulates growth and production of secondary metabolites via upregulation
of auxin and jasmonate levels, probably in response to sugar-mediated signalling. Future low [CO2] studies
should address the role of reactive oxygen species (ROS) in leaf ABA and SA biosynthesis, and at the transcriptional
level should focus on biosynthetic and, in particular, on responsive genes involved in [CO2]-induced hormonal signalling
pathways.
