C 4 plants show higher photosynthetic capacity and resource use efficiency than C 3 plants. However, the genetic variations of these traits and their regulatory factors in C 4 plants still remain to be resolved. We investigated physiological, biochemical, and structural traits involved in photosynthesis and photosynthetic water and nitrogen use efficiencies (PWUE and PNUE) in 22 maize lines and four teosinte lines from various regions of the world. Net photosynthetic rate (P N) ranged from 32.1 to 46.5 μmol m −2 s −1. P N was positively correlated with stomatal conductance, transpiration rate, and chlorophyll, nitrogen and soluble protein contents of leaves, but not with specific leaf weight. P N was positively correlated with the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and the C 4-acid decarboxylases, NADP-malic enzyme and phosphoenolpyruvate carboxykinase, but not with the activity of phosphoenolpyruvate carboxylase. Leaf structural traits (stomatal parameters, leaf thickness, and interveinal distance) were not correlated with P N. These data suggest that physiological and biochemical traits are involved in the genetic variation of P N , but structural traits are not directly involved. PWUE is in the lower class of values reported for C 4 plants, whereas PNUE is in the highest class of values reported for C 4 plants. PNUE was negatively correlated with leaf nitrogen content but not significantly correlated with P N. PWUE was not correlated with δ 13 C values of leaves, indicating difficulty in using δ 13 C values as an indicator of PWUE of maize. In general, teosinte lines showed lower P N but higher PWUE than maize lines.

The Chenopodiaceae is one of the families including C 4 species among eudicots. In this family, the genus Chenopodium is considered to include only C 3 species. However, we report here a transition from C 3 photosynthesis to proto-Kranz to C 3-C 4 intermediate type in Chenopodium. We investigated leaf anatomical and photosynthetic traits of 15 species, of which 8 species showed non-Kranz anatomy and a CO 2 compensation point (Γ) typical of C 3 plants. However, 5 species showed proto-Kranz anatomy and a C 3-like Γ, whereas C. strictum showed leaf anatomy and a Γ typical of C 3-C 4 intermediates. Chenopodium album accessions examined included both proto-Kranz and C 3-C 4 intermediate types, depending on locality. Glycine decarboxylase, a key photorespiratory enzyme that is involved in the decarboxylation of glycine, was located predominantly in the mesophyll (M) cells of C 3 species, in both M and bundle-sheath (BS) cells in proto-Kranz species, and exclusively in BS cells in C 3-C 4 intermediate species. The M/BS tissue area ratio, number of chloroplasts and mitochondria per BS cell, distribution of these organelles to the centripetal region of BS cells, the degree of inner positioning (vacuolar side of chloroplasts) of mitochondria in M cells, and the size of BS mitochondria also changed with the change in glycine decarboxylase localization. All Chenopodium species examined were C 3-like regarding activities and amounts of C 3 and C 4 photosynthetic enzymes and δ 13 C values, suggesting that these species perform photosynthesis without contribution of the C 4 cycle. This study demonstrates that Chenopodium is not a C 3 genus and is valuable for studying evolution of C 3-C 4 intermediates. Keywords C 3-C 4 intermediate plant • Chenopodium • CO 2 compensation point • Glycine decarboxylase • Leaf anatomy • Proto-Kranz plant Electronic supplementary material The online version of this article (

No abstract

Background and Aims C4 plants have higher photosynthetic capacity than C3 plants, but this advantage comes at an energetic cost that is problematic under low light. In the crop canopy, lower leaves first develop under high light but later experience low light because of mutual shading. To explore the re-acclimation of C4 leaves to low light, we investigated the structural and physiological changes of the leaves of maize plants grown in shaded pots. Methods Plants were first grown under high light, and then some of them were shaded (20 % of sunlight) for 3 weeks. Four types of leaves were examined: new leaves that developed under low light during shading (L), new leaves that developed under high light (H), mature leaves that developed under high light before shading and were then subjected to low light (H–L) and mature leaves that always experienced high light (H–H). Key Results The leaf mass per area, nitrogen and chlorophyll contents per unit leaf area, chlorophyll a/b ratio and activities of C3 and C4 photosynthetic enzymes were lower in H–L than in H–H leaves and in L than in H leaves. Unlike L leaves, H–L leaves maintained the thickness and framework of the Kranz anatomy of H leaves, but chloroplast contents in H–L leaves were reduced. This reduction of chloroplast contents was achieved mainly by reducing the size of chloroplasts. Although grana of mesophyll chloroplasts were more developed in L leaves than in H leaves, there were no differences between H–L and H–H leaves. The light curves of photosynthesis in H–L and L leaves were very similar and showed traits of shade leaves. Conclusions Mature maize leaves that developed under high light re-acclimate to low-light environments by adjusting their biochemical traits and chloroplast contents to resemble shade leaves but maintain the anatomical framework of sun leaves.