Short‐term effect of elevated CO2 concentration (0.5%) on mitochondria in diploid and tetraploid black locust (Robinia pseudoacacia L.)

Recent increases in atmospheric CO₂ concentration have affected the growth and physiology of plants. In this study, plants were grown with 0.5% CO₂ for 0, 3, and 6 days. The anatomy, fluorescence intensity of H₂O₂, respiration rate, and antioxidant activities of the mitochondria were analyzed in diploid (2×) and tetraploid (4×) black locust (Robinia pseudoacacia L.). Exposure to 0.5% CO₂ resulted in clear structural alterations and stomatal closure in the mitochondria. Reduced membrane integrity and increased structural damage were observed in 2× plants at 6 days. However, after 0.5% CO₂ treatment, little structural damage was observed in 4× plants. Under severe stress, H₂O₂ and malondialdehyde were dramatically induced in both 2× and 4× plants. Proline remains unchanged at an elevated CO₂ concentration in 4× plants. Moreover, the total respiration and alternative respiration rates decreased in both 2× and 4× plants. In contrast, the cytochrome pathway showed no decrease in 2× plants and even increased slightly in 4× plants. The antioxidant enzymes and nonenzymatic antioxidants, which are related to the ascorbate–glutathione pathway, were inhibited following CO₂ exposure. These analyses indicated that 4× and 2× plants were damaged by 0.5% CO₂ but the former were more resistant than the latter, and this may be due to increases in antioxidant enzymes and nonenzymatic antioxidants and stabilized membrane structure.