Nitrogen supply affects root and shoot amino acid composition in Eucalyptus clones

Abstract

Changes in amino acid composition are frequently observed in plants under various conditions of stress, such as nutrient deficiencies. Hence, amino acids have been proposed as more sensitive indicators of N status than total N concentration. The goal of this study was to evaluate alterations in amino acid composition of young eucalyptus clones as a result of variable N supply. An experiment was carried out in a greenhouse with two Eucalyptus clones (VM-01 and I-144) and six N application rates (0, 0.74, 2.93, 4.39, 5.85, and 8 mmol L-1 of NH 4 NO 3) grown in a nutrient solution in a randomized block design. Amino acid concentrations varied greatly as a function of N supply and depended on the organ (root or leaf) and the genotype evaluated. Roots showed greater number of amino acids than leaves (17 and 14, respectively), probably because of a higher amino acids synthesis or translocation to the roots. For both clones, N deficiency induced a significant decrease in proline, arginine, and methionine concentration in roots and a decrease in tyrosine, alanine, threonine, and methionine in leaves. These decreases were also associated with lower total N concentration and total dry matter of the eucalyptus clones. In conclusion, N supply affects amino acid composition, and the amino acids listed above are likely to be more sensitive indicators of N status than total N in eucalyptus clones.

Co-occurrence of organic and inorganic N sources influences asparagine uptake and internal amino acid profiles in white clover

“…At the same time, the total N content remained unchanged (S7 Table). This is in line with observations made by Ferreira, Novais (18), who concluded that free-amino acids show a greater promise than total N in understanding the effect of external N on the plant N status, in that amino acid content can respectively increase or decrease in stress conditions without any changes in the total N. Although no studies could be found on the effect of external N on amino acid profile in legumes, (31) reported a decrease in the content of non-essential amino acids in response to high N for maize (Zea mays L.). They hypothesized that decline of the non-essential amino acids was due to deficiency of carbon skeletons for the assimilation of NH 4 + .…”

“…In that context our findings support that not only the amount of amino acids, but also information on the composition of amino acids is needed to determine to what extent the plant is N stressed and how the plant signals N demand between root and shoot. Thus, our findings demonstrate that the external organic and inorganic N affects the accumulation of certain amino acids in clover, which could help in further understanding how the plant senses various N stress conditions and circulates amino acids between roots and shoots (18, 32). Soil inorganic and organic N status could therefore be used as an indicator for nutritional quality of protein content in forage legumes.…”

“…In retrospect, it would have been very useful if we had sampled nodules separately to measure nodule Asn concentration, because the present findings on the relation between external N doses and internal Asn concentrations does not seem to be directly in line with the hypothesis of Asn being the key in internal regulation of N 2 -fixation in legumes. Alternatively, other pathways in which Asn is utilized for synthesis of other amino acids could be a reason for a declining Asn content (18, 30), as we observed an increasing tendency in the concentration of Phe, Thr, and Tyr alongside increasing total N (S4 Fig). However, more research would be needed to establish this link.…”

“…N uptake is thought to be strongly regulated by the N demand of the plant, specifically by the pool of amino compounds circulating between shoot and roots (7). Correspondingly, changes in amino acid composition can be affected by the N supply (18). This was observed by Cambui et al (2011) who reported that in Arabidopsis thaliana grown on a mixture with NO 3 and glutamine, a greater fraction of root N was derived from organic than inorganic N. Some studies also reported that plants supplied with organic N show different root morphology and higher root:shoot ratio than those supplied with inorganic N (8).…”

Silicon fertigation and salicylic acid foliar spraying mitigate ammonium deficiency and toxicity in Eucalyptus spp. clonal seedlings

“…As a result, NH 4 + toxicity decreases shoot and root dry mass production ( Fig 3 ). On the other hand, N supply at low levels decreases dry mass production ( Fig 3 ), due to the important function of this nutrient in plant metabolism, which also occurs in eucalyptus seedlings [ 3 ].…”