Variation of mesophyll conductance mediated by nitrogen form is related to changes in cell wall property and chloroplast number

Abstract

Plants primarily incorporate nitrate (NO₃⁻) and ammonium (NH₄⁺) as the primary source of inorganic nitrogen (N); the physiological mechanisms of photosynthesis (A) dropdown under NH₄⁺ nutrition has been investigated in many studies. Leaf anatomy is a major determinant to mesophyll conductance (g_m) and photosynthesis; however, it remains unclear whether the photosynthesis variations of plants exposed to different N forms is related to leaf anatomical variation. In this work, a common shrub, Lonicera japonica was hydroponically grown under NH₄⁺, NO₃⁻ and 50% NH₄⁺/NO₃⁻. We found that leaf N significantly accumulated under NH₄⁺, whereas the photosynthesis was significantly decreased, which was mainly caused by a reduced g_m. The reduced g_m under NH₄⁺ was related to the decreased intercellular air space, the reduced chloroplast number and especially the thicker cell walls. Among the cell wall components, lignin and hemicellulose contents under NH₄⁺ nutrition were significantly higher than those in the other two N forms and were scaled negatively correlated with g_m; while pectin content was independent from N forms. Pathway analysis further revealed that the cell wall components might indirectly regulate g_m by influencing the thickness of the cell wall. These results highlight the importance of leaf anatomical variation characterized by modifications of chloroplasts number and cell wall thickness and compositions, in the regulation of photosynthesis in response to varied N sources.

Author contributions

S.G. and Y.C. conceived the idea and designed the experiment; Y.C., Y.P., Y.Y., and T.L. completed the experiments; Y.C. analysed the data and wrote the manuscript; Y.L. and Y.P. helped in manuscript revising; S.G. and M.W. provided funding support. All the authors contributed critically to the drafts and gave final approval for publication.

Data availability statement

The data underlying this article are available in the article and in its online supplementary material.

Conflict of interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Supplementary information

Supplementary data is available at Horticulture Research online.

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