Figure 1.

Elevated root-zone CO₂ concentration on cellular ultrastructure of oriental melon seedling roots (A). Ultrastructure changes in root tips after treatment of high root-zone CO₂. The magnification is 2.0 K. Scale bar: 5.0 µm. The white arrows in CK-3d, T1-3d and T2-3d indicated that the start of the formation of starch grains within the cells. The white arrows in CK-6d, T1-6d and T2-6d indicated that the content of starch grains under T2 treatment was significantly higher than that of CK and T1. The white arrows in T1-9d and T2-9d indicated that the number of organelles began to dissolve and disappear. The white arrows in T1-12d and T2-12d indicated that there were fewer organelles in T2 than in T1 on the 12th day. The white arrows in T1-15d and T2-15d indicated that the organelles in T2 were completely dissolved compared with T1. Day 0 means no treatment. On the 3rd day, it was observed that the number of mitochondria was significantly increased, and the number of starch grains under T1 was larger than that of the T2 treatment. On the 6th day, it was observed that the starch grains under the CK group (control check, elevated root-zone CO₂ concentration 0.2%) began to accumulate, accompanied by the increase in mitochondria, while the amyloid membrane of T2 began to rupture and dissolve, then the starch grains were released. On the 9th day, starch grains treated with the increase in root-zone CO₂ concentration began to accumulate in the inner cells of the roots, the number of mitochondria was significantly reduced and cavities appeared, while the starch grains under T2 treatment of the amyloplasts were mostly released. On the 12th day of treatment, the mitochondria in the apical cells were deformed, the number of inner cristae decreased and the edges were blurred. On the 15th day, only a small number of recognizable organelles remained in the apical cells under T1 treatment, the starch grains of T2 root tip cells were released, and starch grains of the CK group began to be released but mitochondria could still be found. (B) Ultrastructure changes in root tips after elevated root-zone CO₂ treatment for 3, 6, 9, 12 and 15 days. The magnification is 1.0 K. Scale bar: 1.0 µm.