Abstract

Nitrogen deficiency (N) influences plant growth and metabolism at both physiological and transcriptional levels. However, the early responses of mulberry (Morus alba L.) to N limitation have not been clearly described. In this study, 2.5-month-old cuttings of the ‘Sakon Nakhon’ cultivar were grown in an aeroponic system and exposed to full nitrogen (FN), nitrogen-free (–N), or deionized water (DI) treatments for 14 days in a completely randomized design with four replicates per treatment. Nitrogen deprivation led to a significant reduction in SPAD green index, reflecting decreased chlorophyll content. In contrast, specific leaf weight (SLW) and specific root length (SRL) were not significantly affected, indicating that leaf and root structure remained stable during the short experimental period. Transcriptome data showed that genes involved in nitrogen uptake and transport, particularly members of the NRT1/PTR family, together with chloroplastic chaperone protein DnaJ 20, were downregulated under –N conditions. At the same time, genes associated with stress responses and secondary metabolism, including nerolidol synthases, MLO-like protein 6, and basic helix–loop–helix transcription factors (bHLH18 and bHLH36), were upregulated. These results suggest that, under nitrogen-free aeroponic conditions, mulberry primarily responds through early transcriptional adjustment before visible morphological changes occur.