Ammonium and nitrate impact petal color traits and amino acid profiles differently in <i>Petunia</i>

Abstract

Nitrogen (N) is vital for ornamental plants to fulfill fundamental cellular functions. Effects of inorganic N including nitrate and ammonium on ornamental traits at the biochemical level are less reported. Given that the continuously increased concentration of CO₂ in atmosphere has greater negative effects on nitrate reduction than ammonium utilization in C₃ plants, it is vital for us to dissect various effects of different inorganic N forms on flower development, which will lead to a better understanding of the metabolic regulation of ornamental traits. In this study, <italic>Petunia x hybrida</italic> cv 'Mitchell Diploid' (MD) plants at 6~8-leaf stage were treated hydroponically with the same and regular amount of inorganic N for one month but in three different forms, 1mM NH₄NO₃ as the control (NH₄NO₃), 2mM NH₄Cl alone (NH₄-N) and 2mM NaNO₃ alone (NO₃-N). Results indicated that relative to the control, effects of NH₄-N and NO₃-N treatment alone on plant growth, N utilization and distribution, petal color traits and petal amino acid profiles were different by varying degrees. We have confirmed that NH₄-N could specifically increase ¹⁵N distribution to floral tissues, change the amino acid profiles in petals which in turn bring changes to petal colors. Results with four commercially available petunia cultivars with different flower colors also validated our findings. This study has been designed to specifically investigate effects of ammonium or nitrate as the sole source of inorganic N on the developmental and chemical features of floral tissues in <italic>Petunia</italic>.