Tomato root development and N assimilation depend on C and ABA content under different N sources
González-Hernández, Ana Isabel | Scalschi, Loredana | García-Agustín, Pilar | Camañes, Gemma
Root plasticity is controlled by hormonal homeostasis and nutrient availability. In this work, we have determined the influence of different N regimens on growth parameters and on the expression of genes involved in auxin transport and N-assimilation in tomato seedlings. NH₄⁺ nutrition led to an inhibitory effect on root fresh weight (FW), lateral root (LR) number and root density, while an increase in the primary root (PR) length was observed. The expression of N assimilation genes GS2 and ASN1, is affected by NH₄⁺ nutrition. Moreover, in order to relieve the toxic effect of NH₄⁺ on root development, glucose or 2-oxoglutarate was supplied as a C source during NH₄⁺ treatment. The addition of 2-oxoglutarate improved root parameters compared to the NH₄⁺ regimen. N-assimilation gene analysis showed that NH₄⁺-fed tomato plants try to alleviate the toxic effect by concurrently upregulating ASN1 and anaplerotic PEPC2 expression, whereas when 2-oxoglutarate is supplied, ASN1 induction was not observed. The addition of both C skeletons induced the expression of the ROS-scavenging genes GSH and SOD. In addition, since ABA plays a role in root development, the ABA-synthesis-defective mutant flacca was studied under NO₃⁻ and NH₄⁺ regimens. It displayed a decrease in LR number under NO₃⁻ conditions, whereas, the NH₄⁺-fed seedlings showed a decrease solely in PR length that was reverted when ABA was exogenously supplied. Moreover, flacca seedlings displayed a reprogramming of the N/C assimilation genes. Altogether, these results reflect the importance of N and C sources and ABA homeostasis in root development of tomato seedlings.
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