Mesophyll conductance, photoprotective process and optimal N partitioning are essential to the maintenance of photosynthesis at N deficient condition in a wheat yellow-green mutant (Triticum aestivum L.).

The major effect of nitrogen (N) deficiency is the inhibition on CO ₂ assimilation regulated by light energy absorption, transport and conversion, as well as N allocation. In this study, a yellow-green wheat mutant (Jimai5265yg) and its wild type (Jimai5265, WT) were compared between 0 mM N (N ₀ ) and 14 mM N (N ₁₄ ) treatments using hydroponic experiments. The mutant exhibited higher photosynthetic efficiency (A _n ) than WT despite low chlorophyll (Chl) content in non-stressed conditions. The photosynthetic advantages of the mutant were maintained under N deficient condition. The quantitative analysis of limitations to photosynthesis revealed that CO ₂ diffusion associated with mesophyll conductance (g _m ) was the dominant limitation. Relative easiness to gain CO ₂ in the chloroplast contributed to the higher A _n of Jimai5265yg. N deficiency induced the photoinhibition of PSII, but the cyclic electron transport and photochemical activity of PSI was higher in Jimai5265yg compared to Jimai5265, which was a protective mechanism to avoid photodamage. Because of the sharp drop of A _n , N deficient seedlings had much lower photosynthetic N use efficiency (PNUE). However, N deficiency increased the relative content of photosynthetic N (N _psn ) and decreased the relative content of storage N (N _store ). The range of change in N partitioning induced by N deficiency was smaller for Jimai5265yg compared to WT. The less insensitive to N deficiency for the mutant in terms of photosynthetic property and N partitioning suggested that g _m , cyclic electron transport around PSI and more optimal N partitioning pattern is necessary to sustain photosynthesis under N deficient condition.
(Copyright © 2021. Published by Elsevier GmbH.)