Barley reorganizes photosynthesis during nitrogen starvation across leaf ages

Hydroponically grown barley subjected to 14 days of nitrogen starvation responded by systematically reorganizing its photosynthetic apparatus, with the same broad pattern apparent in leaves of different ages. The experimental plants experienced a marked reduction in shoot growth and biomass, while root biomass increased, raising the root-to-shoot ratio. Nitrogen was also remobilized from senescing older leaves toward developing younger leaves. These observations indicate that nitrogen scarcity triggered both a redistribution of resources within the plant and a coordinated adjustment of photosynthesis, rather than a uniform deterioration across the canopy.

The strongest changes occurred in older leaves, where photosynthetic pigments and photosystem II efficiency were severely depleted. Younger leaves retained more substantial electron-transport and carbon-fixation capacities. The difference in stress severity was considerable, but the underlying acclimation pattern was conserved: selective degradation of photosynthetic proteins occurred alongside preferential retention of components associated with light harvesting and non-photochemical quenching. The authors therefore interpret the response as an active regulatory program that becomes apparent in leaves experiencing very different degrees of nitrogen limitation.

At the molecular level, the study found reductions in the content of RuBisCO, cytochrome b6f and core proteins associated with photosystems I and II. Photosystem I components declined more strongly than photosystem II components, shifting the balance between the two photosystems. In contrast, light-harvesting complexes and the non-photochemical-quenching regulator PsbS were preferentially retained. This combination produced a relatively enlarged functional antenna and sustained the capacity for non-photochemical quenching. In practical terms for the stressed plant, the remaining photosynthetic apparatus retained a stronger emphasis on managing absorbed light than on maximizing carbon production.

Measurements of photosynthetic function revealed a notable separation between electron transport and carbon assimilation. Electron transport remained more persistent than carbon fixation, showing that photochemical activity could continue even when the capacity to assimilate carbon was more strongly impaired. Older leaves displayed severe reductions in pigments and photosystem II efficiency, whereas younger leaves maintained a larger fraction of their electron-transport and carbon-fixation capacity. Together with nitrogen transfer from older to younger leaves, the results support a prioritization of photoprotection and continued photochemistry over carbon gain during the 14-day starvation treatment.

This was a controlled plant-acclimation study using hydroponically grown barley, with photosynthetic properties assessed across leaf ages and durations of nitrogen starvation. Its scope is limited to the measured physiological and molecular responses of barley over a 14-day experimental treatment. The findings do not establish that the same pattern occurs across field canopies or other cereal species, and the experiment does not show how long the acclimation strategy can be maintained or whether it improves crop yield. Even within those limits, the evidence of targeted protein loss, preserved quenching capacity, continued electron transport and active nitrogen remobilization provides a mechanistic basis for the conclusion that the photosynthetic reorganization is an acclimation response rather than simply progressive starvation damage. The results identify photosynthetic regulation as a potential target for further work on nitrogen-use efficiency, but no agricultural intervention was tested in the reported experiment.

Subject of Research: How barley reorganizes photosynthesis during nitrogen-starvation acclimation across different leaf ages.

Article Title: Systemic reorganization of the photosynthetic apparatus underlies acclimation to nitrogen starvation across leaf ages in barley

Article References: Tan, S.-L., Huang, X., Zhang, X.-D., Li, W.-Q., Alboresi, A., & Morosinotto, T. (2026). Systemic reorganization of the photosynthetic apparatus underlies acclimation to nitrogen starvation across leaf ages in barley. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09730-0

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09730-0

Keywords: barley, nitrogen starvation, photosynthesis, leaf age, photosystem I, photosystem II, carbon fixation, photoprotection, nitrogen remobilization, RuBisCO, Systemic, reorganization