Instituto de Agrobiotecnología (Universidad Pública de Navarra-CSIC), Departamento de Producción Agraria, Campus Arrosadía, Pamplona, Spain.
Research Group on Plant Biology under Mediterranean Conditions, Departament de Biologia, Universitat de les Illes Balears, Carretera de Valldemossa, Palma de Mallorca, Illes Balears, Spain.
J Exp Bot. 2018 Jun 27;69(15):3661-3673. doi: 10.1093/jxb/ery148.
The leaf mesophyll CO2 conductance and the concentration of CO2 within the chloroplast are major factors affecting photosynthetic performance. Previous studies have shown that the aquaporin NtAQP1 (which localizes to the plasma membrane and chloroplast inner envelope membrane) is involved in CO2 permeability in the chloroplast. Levels of NtAQP1 in plants genetically engineered to overexpress the protein correlated positively with leaf mesophyll CO2 conductance and photosynthetic rate. In these studies, the nuclear transformation method used led to changes in NtAQP1 levels in the plasma membrane and the chloroplast inner envelope membrane. In the present work, NtAQP1 levels were increased up to 16-fold in the chloroplast membranes alone by the overexpression of NtAQP1 from the plastid genome. Despite the high NtAQP1 levels achieved, transplastomic plants showed lower photosynthetic rates than wild-type plants. This result was associated with lower Rubisco maximum carboxylation rate and ribulose 1,5-bisphosphate regeneration. Transplastomic plants showed reduced mesophyll CO2 conductance but no changes in chloroplast CO2 concentration. The absence of differences in chloroplast CO2 concentration was associated with the lower CO2 fixation activity of the transplastomic plants. These findings suggest that non-functional pores of recombinant NtAQP1 may be produced in the chloroplast inner envelope membrane.
叶片叶肉细胞 CO2 导度和叶绿体中 CO2 的浓度是影响光合作用性能的主要因素。先前的研究表明，质体 aquaporin NtAQP1（定位于质膜和叶绿体内膜）参与叶绿体中的 CO2 通透性。在过表达该蛋白的转基因植物中，NtAQP1 的水平与叶片叶肉细胞 CO2 导度和光合速率呈正相关。在这些研究中，所使用的核转化方法导致质膜和叶绿体内膜中 NtAQP1 水平发生变化。在本工作中，通过质体基因组过表达 NtAQP1，叶绿体膜中的 NtAQP1 水平增加了 16 倍。尽管达到了较高的 NtAQP1 水平，但与野生型植物相比，转质体植物的光合速率较低。这一结果与 Rubisco 最大羧化速率和核酮糖 1,5-二磷酸再生降低有关。转质体植物的叶肉细胞 CO2 导度降低，但叶绿体 CO2 浓度没有变化。叶绿体 CO2 浓度没有差异与转质体植物较低的 CO2 固定活性有关。这些发现表明，叶绿体内膜中可能产生了非功能重组 NtAQP1 的孔。
