Variations in structural, biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)

Nobuko Tsutsumi,Miyuki Tohya,Taiken Nakashima,Osamu Ueno

doi:10.1080/1343943x.2017.1320948

Abstract

C4 plants show higher photosynthetic capacity and productivity than C3 plants owing to a CO2-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C4 plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C4 dicots. Net photosynthetic rate (PN) ranged from 19.7 to 40.5 μmol m−2 s−1. PN was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. PN was also positively correlated with the activity of the C3 enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C4 enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with PN. These data suggest that some of the biochemical and physiological traits are involved in interspecific PN variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol−1 N s−1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol−1. When these data were compared with previously published data of C4 grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.

Highlights

Photosynthetic capacity is important for plant productivity and is a potential target to increase crop productivity (Evans, 2013; Zhu et al, 2010)
The regulation of C4 photosynthesis is more intricate than that of C3 photosynthesis, because C3 photosynthesis occurs in mesophyll cells, whereas C4 photosynthesis is achieved through a collaboration of mesophyll and bundle sheath (BS) cells
Atmospheric CO2 is fixed by phosphoenolpyruvate carboxylase (PEPC) of mesophyll cells and formed C4 acids are transported to BS cells, where they are decarboxylated by C4 acid decarboxylase; the released CO2 is refixed by Rubisco in the BS cells and assimilated to carbohydrate in the C3 cycle (Hatch, 1987)

Summary

Introduction

Photosynthetic capacity is important for plant productivity and is a potential target to increase crop productivity (Evans, 2013; Zhu et al, 2010). Atmospheric CO2 is fixed by phosphoenolpyruvate carboxylase (PEPC) of mesophyll cells and formed C4 acids are transported to BS cells, where they are decarboxylated by C4 acid decarboxylase; the released CO2 is refixed by Rubisco in the BS cells and assimilated to carbohydrate in the C3 cycle (Hatch, 1987). Some of these reactions are rate limiting in C4 photosynthesis (Baer & Schrader, 1985; von Caemmerer et al, 1997; Usuda et al., 1984)

Methods

Results

Conclusion