The temporal and species dynamics of photosynthetic acclimation in flag leaves of rice (Oryza sativa) and wheat (Triticum aestivum) under elevated carbon dioxide

Chunwu Zhu Lewis Ziska Jianguo Zhu Qing Zeng Zubing Xie Haoyan Tang Xiaodong Jia Toshihiro Hasegawa. The temporal and species dynamics of photosynthetic acclimation in flag leaves of rice (Oryza sativa) and wheat (Triticum aestivum) under elevated carbon dioxide. Physiologia Plantarum 2012 145: 395–405.

Abstract

In this study we tested for the temporal occurrence of photosynthetic acclimation to elevated [CO₂] in the flag leaf of two important cereal crops rice and wheat. In order to characterize the temporal onset of acclimation and the basis for any observed decline in photosynthetic rate we characterized net photosynthesis g_s g_m C_i-C_a C_i-C_c V_cmax J_max cell wall thickness content of Rubisco cytochrome (Cyt) f N chlorophyll and carbohydrate mRNA expression for rbcL and petA activity for Rubisco sucrose phosphate synthase (SPS) and sucrose synthase (SS) at full flag expansion mid-anthesis and the late grain-filling stage. No acclimation was observed for either crop at full flag leaf expansion. However at the mid-anthesis stage photosynthetic acclimation in rice was associated with RuBP carboxylation and regeneration limitations while wheat only had the carboxylation limitation. By grain maturation the decline of Rubisco content and activity had contributed to RuBP carboxylation limitation of photosynthesis in both crops at elevated [CO₂]; however the sharp decrease of Rubisco enzyme activity played a more important role in wheat. Although an increase in non-structural carbohydrates did occur during these later stages it was not consistently associated with changes in SPS and SS or photosynthetic acclimation. Rather over time elevated [CO₂] appeared to enhance the rate of N degradation and senescence so that by late-grain fill photosynthetic acclimation to elevated [CO₂] in the flag leaf of either species was complete. These data suggest that the basis for photosynthetic acclimation with elevated [CO₂] may be more closely associated with enhanced rates of senescence and as a consequence may be temporally dynamic with significant species variation.