Signaling function of NH4+ in the activation of Fe-deficiency response in cucumber (Cucumis sativus L.)

• Published in: Planta 2024-08, Vol.260 (2), p.53, Article 53
• Main Authors: Tavakoli, Fatemeh, Hajiboland, Roghieh, Bosnic, Dragana, Bosnic, Predrag, Nikolic, Miroslav, Tolra, Roser, Poschenrieder, Charlotte
• Format: Article
• Language: English
• Subjects: Agriculture; Ammonium; Ammonium chloride; Biomedical and Life Sciences; Cucumbers; Cucumis sativus; Ecology; Forestry; Gene expression; Genes; Hydroponics; Iron; Iron deficiency; Leaves; Life Sciences; Nitrates; Nitric oxide; Nitrogen; Organic acids; Original Article; Phenols; Plant Sciences
• ISSN: 0032-0935; 1432-2048; 1432-2048
• DOI: 10.1007/s00425-024-04480-5

Main conclusion NH 4 + is necessary for full functionality of reduction-based Fe deficiency response in plants. Nitrogen (N) is present in soil mainly as nitrate (NO 3 – ) or ammonium (NH 4 + ). Although the significance of a balanced supply of NO 3 – and NH 4 + for optimal growth has been generally accepted, its importance for iron (Fe) acquisition has not been sufficiently investigated. In this work, hydroponically grown cucumber ( Cucumis sativus L. cv. Maximus) plants were supplied with NO 3 – as the sole N source under –Fe conditions. Upon the appearance of chlorosis, plants were supplemented with 2 mM NH 4 Cl by roots or leaves. The NH 4 + treatment increased leaf SPAD and the HCl-extractable Fe concentration while decreased root apoplastic Fe. A concomitant increase in the root concentration of nitric oxide and activity of FRO and its abolishment by an ethylene action inhibitor, indicated activation of the components of Strategy I in NH 4 + -treated plants. Ammonium-pretreated plants showed higher utilization capacity of sparingly soluble Fe(OH) 3 and higher root release of H + , phenolics, and organic acids. The expression of the master regulator of Fe deficiency response ( FIT ) and its downstream genes ( AHA1 , FRO2 , and IRT1 ) along with EIN3 and STOP1 was increased by NH 4 + application. Temporal analyses and the employment of a split-root system enabled us to suggest that a permanent presence of NH 4 + at concentrations lower than 2 mM is adequate to produce an unknown signal and causes a sustained upregulation of Fe deficiency-related genes, thus augmenting the Fe-acquisition machinery. The results indicate that NH 4 + appears to be a widespread and previously underappreciated component of plant reduction-based Fe deficiency response.