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Depletion of the heaviest stable N isotope is associated with NH4 plants
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Orientador(es)
Resumo(s)
Background: In plants, nitrate (NO3
-) nutrition gives rise to a natural N isotopic signature (δ15N), which correlates
with the δ15N of the N source. However, little is known about the relationship between the δ15N of the N source
and the 14N/15N fractionation in plants under ammonium (NH4
+) nutrition. When NH4
+ is the major N source, the
two forms, NH4
+ and NH3, are present in the nutrient solution. There is a 1.025 thermodynamic isotope effect
between NH3 (g) and NH4
+ (aq) which drives to a different δ15N. Nine plant species with different NH4
+-sensitivities
were cultured hydroponically with NO3
- or NH4
+ as the sole N sources, and plant growth and δ15N were
determined. Short-term NH4
+/NH3 uptake experiments at pH 6.0 and 9.0 (which favours NH3 form) were carried out
in order to support and substantiate our hypothesis. N source fractionation throughout the whole plant was
interpreted on the basis of the relative transport of NH4
+ and NH3.
Results: Several NO3
--fed plants were consistently enriched in 15N, whereas plants under NH4
+ nutrition were
depleted of 15N. It was shown that more sensitive plants to NH4
+ toxicity were the most depleted in 15N. In
parallel, N-deficient pea and spinach plants fed with 15NH4
+ showed an increased level of NH3 uptake at alkaline
pH that was related to the 15N depletion of the plant. Tolerant to NH4
+ pea plants or sensitive spinach plants
showed similar trend on 15N depletion while slight differences in the time kinetics were observed during the initial
stages. The use of RbNO3 as control discarded that the differences observed arise from pH detrimental effects.
Conclusions: This article proposes that the negative values of δ15N in NH4
+-fed plants are originated from NH3
uptake by plants. Moreover, this depletion of the heavier N isotope is proportional to the NH4
+/NH3 toxicity in
plants species. Therefore, we hypothesise that the low affinity transport system for NH4
+ may have two
components: one that transports N in the molecular form and is associated with fractionation and another that
transports N in the ionic form and is not associated with fractionation
Descrição
Open Access article - can be viewed online without a subscription at: http://dx.doi.org/doi:10.1186/1471-2229-11-83
Palavras-chave
Low affinity ammonium transporters Nitrogen isotopic signature Ammonium/ammonia Ammonium dissociation isotope factor Ammonia uptake
Contexto Educativo
Citação
Ariz et al. BMC Plant Biology 2011