Title : Wheat (Triticum aestivum L.) photosynthesis is site specifically and temporally varied between genotypes
Abstract:
Wheat is one of the most important cereals for global food security and has been targeted for yield improvement for decades. Understanding the underlying physiological and molecular processes of crop plants is critical to improving photosynthetic efficiency. In our study, we investigated the comparative physiological and molecular mechanisms of photosynthesis, the biological capacity of carbon assimilation (Vcmax and Jmax) and the sucrose metabolism between wheat spikes and flag leaves using three wheat genotypes grown under glasshouse conditions. Spike dry weight, spike and flag leaf photosynthetic area and nitrogen (N) concentrations of the photosynthetic organs were measured at
different growth stages. Furthermore, Vcmax and Jmax were calculated in flag leaves and wheat spikes using carbon dioxide response (A-Ci) curves at four different growth stages. Molecular level changes in photosynthesis and sucrose metabolism were assessed using gene expression analysis from real-time, quantitative-PCR using key genes related to photosynthesis (rbcL and rbcS) and sucrose metabolism (SPS1, SUS1 and SPP1). We observed a significant genotypic, site-specific and temporal variation in Vcmax and Jmax. Interestingly, the Vcmax and Jmax between wheat spikes and flag leaves at late-grain filling across all genotypes was not statistically significant. Further, a significant difference was
observed in the expression of photosynthetic genes between wheat spikes and flag leaves showing much higher expression in flag leaves across all growth stages. However, both the organ types (pericarps and flag leaves) displayed a similar expression pattern across considered growth stages. The N content of the photosynthetic organs revealed that the highest Rubisco content in wheat pericarps may be present at the grain enlargement phase although the photosynthetic gene expression indicated the contrary. The expression of key genes related to sucrose metabolism (SPS1, SUS1, and SPP1) in wheat pericarps revealed that there were strong positive correlations between the biological capacity of carbon assimilation and SPS1, SUS1 and SPP1 expression during the heading to grain enlargement phase. Moreover, our results suggested that metabolic processes of wheat spikes may perform a major role in grain filling and thus total yield.
