Ammonium ions affect metal toxicity in chamomile plants

• Impact of ammonium presence or absence on Cd and Ni toxicity in chamomile was studied.
• Absence of NH4+ improved basic physiology though responses differed between Cd and Ni.
• Thiols revealed various responses in shoots and roots in the absence of ammonium.
• NH4+ absence altered coumarin-related compounds but total phenols were not affected.
• Data confirmed that NH4+ presence is stressful alone or in the presence of metals.

The impact of ammonium presence (+ NH4+) or absence (− NH4+) on cadmium (Cd) and nickel (Ni) toxicity in chamomile (Matricaria chamomilla) was studied. Elimination of ammonium elevated tissue water content, amount of soluble proteins and Fv/Fm ratio though responses differed between Cd and Ni. Antioxidative enzyme activities (ascorbate- and guaiacol-peroxidase) were also more enhanced in Cd – NH4+ than in Ni – NH4+ treatments (in comparison with respective + NH4+ counterparts). Thiols rather decreased in shoots and increased in roots in the absence of ammonium. At the level of coumarin-related metabolites, NH4+ absence typically elevated amount of herniarin glycoside precursor while “stress” coumarin derivative umbelliferone decreased, indicating an additional negative impact of ammonium presence. Subsequently, total soluble phenols and PAL activity were not enhanced by ammonium absence. Mineral nutrients were not considerably affected with the exception of Fe and K that increased preferentially in the roots in the absence of ammonium. These data clearly show that NH4+ presence is stressful alone or in the presence of metals and that ammonium is not a suitable alternative source of nitrogen.