Abstract
Ajaponica X indica rice variety "Tongil" was treated with various low temperatures in phytotrons under natural light to investigate the discoloration processes of leaves experimentally. The results obtained are summarized as follows: 1. Leaf number did not increase at 15°/10°C (day/night), but increased gradually with increase of temperature, while, the length of leaf blades and sheaths which were at grand growth period was markedly shortened under low temperature. The increase in plant height of seedling was inhibited under low temperature over 6 days. 2. Leaf color changed to light green, yellow or brown when treated below 20°/15°C, and brown color spread over whole leaf blade at 15°/10°C. 3. Chlorophyll content of leaf blades began to decrease at the 3rd day under low temperature (17°/12°C), and markedly decreased at the 9th day. 4. Chloroplasts treated by low temperatures contained larger starch grains in size and amount and more lipid globules, and also thylakoid membranes were some-what distended and disordered. 5. Under normal temperatures the mean sectional areas of chloroplasts in meso-phyll cells were about 2.4 times greater than in bundle sheath cells, but under lower temperatures they decreased to 1.7 times mostly due to a grcat expanding of the chloro-plasts in bundle sheath, resulting from a much deposition of starch grains. 6. Under normal temperatures the chloroplasts of the mesophyll cells close to both the adaxial and abaxial epidermis contained less starch grains compared to those at the central portion, but under lower temperatures the chloroplasts at the abaxial side contained more starch grains than those of the adaxial side.
