Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2012
Publication Date: 9/1/2012
Citation: Zhu, C., Zhu, J., Zeng, Q., Xie, Z., Tang, H., Ziska, L.H., Haseggawa, T. 2012. The temporal and species dynamics of photosynthetic acclimation in flag leaves of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) under elevated carbon dioxide. Physiologia Plantarum. 145:395-405. Interpretive Summary: Although initial exposure to higher atmospheric carbon dioxide can result in enhanced photosynthetic rates, with time, these rates often drop. This decline is referred to as photosynthetic acclimation. Yet, if this decline could be reduced or eliminated, than plants could show a greater response to rising CO2 levels, and consequently, could increase their overall yields. In this study, we tested for the occurrence of photosynthetic acclimation in the flag leaf of two important cereal crops, rice and wheat, at elevated carbon dioxide (CO2) using a Free-Air-CO2-Enrichment (FACE) system. A number of parameters were tested. Among these parameters, elevated CO2 had the greatest effect on leaf senescence; however, the rate did vary between crops. Overall, these data suggest that the basis for photosynthetic acclimation to CO2 is temporally dynamic, and may vary as a function of species. As a result, it may be possible to breed or select for reduced senescence for crop and wheat lines in the future. This information will be of interest to plant breeders, agronomists and crop scientists.
Technical Abstract: Although initial exposure to higher atmospheric carbon dioxide can result in enhanced photosynthetic rates, temporal declines in photosynthesis associated with prolonged exposure to higher CO2 levels can also result in a down-regulation or acclimation of photosynthesis. In this study, we tested for the occurrence of photosynthetic acclimation in the flag leaf of two important cereal crops, rice and wheat, at elevated CO2 using a Free-Air-CO2-Enrichment (FACE) system in order to characterize the temporal occurrence of acclimation, and the basis for any observed decline in photosynthetic rate. Net photosynthesis, conductance, transpiration, cell wall thickness, content of Rubisco, cytochrome f content, N, chlorophyll and carbohydrate, mRNA expression for rbcL and petA, activity for Rubisco, SPS and SS were measured at full flag expansion, mid-anthesis and the late grain-filling stage. No acclimation was observed for either crop at expansion. At the mid-anthesis stage, photosynthetic acclimation in rice was associated with RuBP carboxylation and regeneration limitations, while wheat only had the carboxylation limitation. With time, the decline of Rubisco content and activity contributed to RuBP carboxylation limitation in both crops, however, the sharp decrease of Rubisco enzyme activity played a more important role in wheat. Although an increase in non-structural carbohydrates did occur, it was not always associated with photosynthetic acclimation in the flag leaf or associated changes in SPS and SS. Rather, over time elevated CO2 appeared to enhance the rate of N degradation and senescence so that by late-grain fill, no photosynthetic enhancement of elevated CO2 in the flag leaf of either species was observed. These data suggest that the basis for photosynthetic acclimation is temporally dynamic, and may vary as a function of species.