But the question whether nitrate/nitrite have
any specific role in upregulating their expression is not well
understood, perhaps because such experiments were conducted
in ammonium-grown cultures and the role of other
N metabolites was interpreted in terms of the presence or
absence of ammonium. In any case, there is no literature on
the expression of any of the genes of nitrate uptake, assimilation
and N metabolism in Arthrospira species, mainly due
to the lack of the gene tools needed for such studies.