Understanding Maize Response to Nitrogen Limitation in Different Light Conditions for the Improvement of Photosynthesis

Abstract

The photosynthetic capacity of leaves is determined by their content of nitrogen (N). Nitrogen involved in photosynthesis is divided between soluble proteins and thylakoid membrane proteins. In C4 plants, the photosynthetic apparatus is partitioned between two cell types: mesophyll cells and bundle sheath. The enzymes involved in the C4 carbon cycle and assimilation of nitrogen are localized in a cell-specific manner. Although intracellular distribution of enzymes of N and carbon assimilation is variable, little is known about the physiological consequences of this distribution caused by light changes. Light intensity and nitrogen concentration influence content of nitrates in leaves and can induce activity of the main enzymes involved in N metabolism, and changes that reduce the photosynthesis rate also reduce photosynthetic N use efficiency. In this review, we wish to highlight and discuss how/whether light intensity can improve photosynthesis in maize during nitrogen limitation. We described the general regulation of changes in the main photosynthetic and nitrogen metabolism enzymes, their quantity and localization, thylakoid protein abundance, intracellular transport of organic acids as well as specific features connected with C4 photosynthesis, and addressed the major open questions related to N metabolism and effects of light on photosynthesis in C4 plants.

Keywords: bundle sheath and mesophyll chloroplasts of C4 plant maize; enzymes and regulation; nitrogen and light intensity; photosynthesis.

Figure 1

Schematic representation of plant nitrate assimilation. Reactions take place in mitochondrium (mit), chloroplast (chl), and cytoplasm (cyt). Enzymes and transporters are symbolized by numbers: 1—nitrate transporter, 2—ammonium transporter, 3—nitrate reductase, 4—nitrite transporter, 5—nitrite reductase, 6—glutamine synthetase, 7—glutamate synthase, 8—plastidic glutamate–malate translocator, 9—plastidic 2-oxoglutarate–malate translocator, and 10—mitochondrial glutamate–glutamine translocator. The major pathway of nitrate assimilation is shown in bold. Modified from [10].

Figure 2

Nitrogen allocation on the percentage of different N components within the leaf in C3 (A) and NADP-ME C4 (B) plants. Modified by Mu and Chen [17].

Figure 3

Schematic representation of the distribution of major steps in assimilation of carbon and nitrogen between mesophyll (M) and bundle sheath (BS) cells of maize. Dark-shaded rectangles represent chloroplasts; transport steps of C compounds are marked by solid arrows; dashed lines indicate the transport of N compounds. Gln: glutamine; Glu: glutamate. Modified by Kopriva and Kopriva [88].