High irradiance increases NH sub(4[super]+ tolerance in Pisum sativum: Higher carbon and energy availability improve ion balance but not N assimilation)

• Published in: Journal of plant physiology Vol. 168; no. 10; pp. 1009 - 1015
• Main Authors: Ariz, Idoia, Artola, Ekhine, Asensio, Aaron Cabrera, Cruchaga, Saioa, Aparicio-Tejo, Pedro Maria, Moran, Jose Fernando
• Format: Journal Article
• Language: English
• Published: 01.07.2011
• Subjects: Assimilation; Availability; Carbon; Efflux; Irradiance; Physiology; Roots; Tolerances
• ISSN: 0176-1617
• DOI: 10.1016/j.jplph.2010.11.022

The widespread use of NO sub(3[super]- fertilization has had a major ecological impact. NH) sub(4)[super]+ nutrition may help to reduce this impact, although high NH sub(4[super]+ concentrations are toxic for most plants. The underlying tolerance mechanisms are not yet fully understood, although they are thought to include the limitation of C, the disruption of ion homeostasis, and a wasteful NH) sub(4)[super]+ influx/efflux cycle that carries an extra energetic cost for root cells. In this study, high irradiance (HI) was found to induce a notable tolerance to NH sub(4[super]+ in the range 2.5-10 mM in pea plants by inducing higher C availability, as shown by carbohydrate content. This capacity was accompanied by a general lower relative N content, indicating that tolerance is not achieved through higher net N assimilation on C-skeletons, and it was also not attributable to increased GS content or activity in roots or leaves. Moreover, HI plants showed higher ATP content and respiration rates. This extra energy availability is related to the internal NH) sub(4)[super]+ content regulation (probably NH sub(4[super]+ influx/efflux) and to an improvement of the cell ionic balance. The limited C availability at lower irradiance (LI) and high NH) sub(4)[super]+ resulted in a series of metabolic imbalances, as reflected in a much higher organic acid content, thereby suggesting that the origin of the toxicity in plants cultured at high NH sub(4[super]+ and LI is related to their inability to avoid large-scale accumulation of the NH) sub(4)[super]+ ion.