4.4 Root tissue metabolites
A total of 14 annotated metabolic pathways were found in this study, and
the most differentially expressed (upregulated) metabolite was
S-adenosylmethionine (SAM) (in eight of the 14 metabolic pathways). SAM
is second only to ATP in biological utilization and is involved in
numerous intracellular metabolic reactions (Fontecave et al., 2004).
Studies have shown that SAM has an important role in regulating plant
adaptations to various abiotic stresses, such as iron deficiency (Lan et
al., 2011), drought (Mayne et al., 1996) and salinity (Gong et al.,
2016; Fujimoto et al., 2011) as well as biotic stresses (e.g. resistance
to pathogenic bacteria) (Fujimoto et al., 2011) and has a complex
time-dependent role in the senescence processes (Owiti et al., 2011).
However, the effect of planting density on the abundance of SAM in roots
has not been reported previously. In cucumber, soaking broken-root
seedlings in SAM-containing solution significantly promoted root
development, chlorophyll accumulation, enhanced photosynthetic rate, and
improved plant uptake of N, P, and K (Liu et al., 2018). In the study
presented here, the average abundance of SAM in quinoa roots in
low-density planting was twice that in high-density planting. It is
suggested that SAM can improve the adaptation of quinoa to coastal
saline soils and may have some growth-promoting effects. Further
research is needed to shed some light on the mechanism underpinning
SAM-related promotion of quinoa growth.