Abstract
The non-leaf photosynthetic organs have recently attracted much attention for the breeding and screening of varieties of cereal crops to achieve a high grain yield. However, the glume photosynthetic characteristics and responses to high temperature at the late stages of grain filling are not well known in winter wheat (Triticum aestivum L.). In the present study, an experiment was conducted to investigate the anatomy, chloroplast temporal changes, chlorophyll fluorescence, xanthophyll cycle and antioxidative defense system in glumes of field-grown wheat during grain filling compared with flag leaves. Observations using a light microscope revealed that the glumes developed a solid structural base for performing photosynthesis. Compared with the flag leaves, the glumes preserved a more integral ultrastructure, as observed under transmission electron microscopy, and had higher values of Fv/Fm and ΦPSII at the maturity stage. Further analysis of the chlorophyll fluorescence demonstrated that the glumes experienced high non-photochemical quenching (NPQ) at the late stages. Determination of the pool size of the xanthophyll cycle suggested that the (A+Z)/(V+A+Z) ratio was consistently higher in glumes than in flag leaves and that the V+A+Z content was considerably higher in glumes at the maturity stage. In addition, the glumes exhibited a higher antioxidant enzyme activity and a lower accumulation of reactive oxygen species. These results suggest that the glumes are photosynthetically active and senesce later than the flag leaves; the advantages may have been achieved by coordinated contributions of the structural features, higher NPQ levels, greater de-epoxidation of the xanthophyll cycle components and antioxidative defense metabolism.
Highlights
We found that the heterogeneous variability in non-photochemical quenching (NPQ) across the leaf area was in accordance with that found for maximum variable fluorescence in dark-adapted samples (Fv)/Fm: in the regions with a relatively high maximum efficiency of photosystem II (PSII) photochemistry (Fv/Fm), the NPQ was increased, whereas in the regions with a low Fv/Fm ratio, the NPQ values were low (Figures 4A,C)
It has been suggested that photosynthesis ear accounts for a high grain yield
We found that glumes had mesophyll cells containing chloroplasts and that both the ventral and dorsal sides presented stomata, indicating that the glumes may be photosynthetically active
Summary
Many non-foliar organs, including all parts of the ear and the exposed part of the peduncle, have the ability to assimilate CO2 when exposed to light (Wang et al, 2001; Kong et al, 2010).Wheat glume and flag leafRecently, an increasing body of evidence has proven that the ear has a photosynthetic capacity that is at least comparable to that of the flag leaf (Sanchez-Bragado et al, 2014) and shows a far greater increase of net photosynthesis than flag leaves under elevated CO2 (Zhu et al, 2009). The photosynthesis of glumes is characterized by recycling of the CO2 respired by the developing grains (Gebbing and Schnyder, 2001; Sanchez-Bragado et al, 2014) and by higher ribulose-1,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) activity compared with other ear elements (Aliyev, 2012) It appears that ear parts likely have the ability to assimilate CO2 through the C4 pathway of photosynthesis and to utilize phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) to recapture the respired CO2 because, compared with flag leaves, glumes assimilate the fed 14CO2 and most of the resulting 14C in malate but less 3-phosphoglyceric acid under illumination (Singal et al, 1986). These collective results indicate that the glumes actively participate in the process of CO2 assimilation during kernel filling
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