Variations in assimilation rate, photoassimilate translocation, and cellular fine structure of potato cultivars (Solanum Tuberosum L.) exposed to elevated CO₂

Rising atmospheric CO₂ concentrations are expected to impact the productivity of plants. Cultivars demonstrate different responses to CO₂ levels, hence, screening and recognizing the cultivars with a higher capacity for translocation of photoassimilates would certainly be beneficiary. To investigate the interactive impact of enhancing CO₂ on physiology, cellular fine structure and photoassimilate translocation of micro-propagated potato plantlets, plantlets (cvs. Agria and Fontane) were grown under ambient (400 ppm) or elevated (800 ppm) CO₂ concentrations in controlled environments. These high-yielding cultivars are widely cultivated in Iran and have a wide range of consumption as fresh marketing, French fries, and chips industry. Transmission electron micrographs showed an increase in the length, width, and area of chloroplasts. The number of chloroplasts per cell area was significantly increased in Agria at elevated CO₂. Also, there was an increase in mitochondria number in Agria and Fontane. Chloroplast number and Np were increased by a similar magnitude at doubled CO₂, while, mitochondria number was increased greater than the leaf Rd enhancement at elevated CO₂. Elevated CO₂ increased net photosynthesis, dark respiration (Rd), and starch concentration in leaves. However, there was no dramatic change in the leaf soluble carbohydrate content in the plants grown at elevated CO₂, apart from at 75 days after transplant (DAT) in Agria. Net photosynthesis remained relatively unchanged for each cultivar throughout the growing season at elevated CO₂, which demonstrated more efficient CO₂ assimilation to ambient CO₂. The greatest starch content was measured at 55 DAT that was accompanied by lower Np and higher Rd. The diminished starch content of leaves was contributed to a lower leaf dry matter as well as a greater tuber dry matter in Fontane. Our results highlighted a variation in photoassimilate translocation between these cultivars, in which Fontane demonstrated a more efficient photoassimilate translocation system at the elevated CO₂.