Structural and photosynthetic re-acclimation to low light in C4 maize leaves that developed under high light

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.

Light reacclimatization of lower leaves in C₄maize canopies grown at two planting densities

“…The former had higher values of P2000, LCP, and RD than the latter (Table 1), as it is typical of sun and shade leaves (Björkman 1981, Givnish 1988, Sage and McKown 2006, Lambers et al 2008. Recently, some studies have reported similar results in pot-grown maize plants; leaves developed under high light and then shaded showed photosynthetic traits of shade leaves, whereas leaves developed and maintained under high light retained those of sun leaves (Bellasio and Griffiths 2014a,b;Yabiku and Ueno 2019). Therefore, our results obtained here show that the reacclimatization of photosynthetic traits to a low-light environment occurs in the lower leaves of a maize canopy as well.…”

“…4D). These results corresponded to those found in our shading experiment of pot-grown maize plants (Yabiku and Ueno 2019).…”

“…However, the lower leaves in a canopy are likely to have unique anatomical traits, because they develop under high light and are then progressively shaded. Therefore, they start with the biochemical and physiological traits of sun leaves, which change gradually to those of shade leaves, still within the anatomical structure of sun leaves, as found in our study of pot-grown maize plants (Yabiku and Ueno 2019), as well as in lower leaves of field-grown maize canopies. The lower leaves at both SPD and LPD had almost the same anatomical framework as the upper leaves had (Fig.…”

“…P1690, Pioneer Ecoscience, Tokyo, Japan) were grown in the field at Kyushu University, Fukuoka (33°35'N, 130°23'E) during late spring to mid-summer in 2016. P1690 was used in our previous pot study (Yabiku and Ueno 2019). First, the amounts of soluble N, P2O5, and K2O in soil of the field were measured by use of a test stripe (Midorikun, Fujihira Industry, Tokyo, Japan).…”

“…Recently, we have investigated the mechanism of reacclimatization to low light of maize leaves that had developed under high light in a shading experiment with pot-grown plants (Yabiku and Ueno 2019). The results showed that these leaves reacclimatize to low light by adjusting their biochemical traits and chloroplast contents to resemble shade leaves but maintain the anatomical framework of the sun leaves.…”