IMPROVEMENT OF COLD RESISTANCE IN RICE SEEDLINGS BY 5-AMINOLEVULINIC ACID

5-Aminolevulinic acid (ALA) at low concentrations increased cold resis tance in rice seedlings. The pretreatment of rice seedlings by root-so aking with ALA solution at 0.1-1 ppm reduced the ratio of leaf rolling and electrolyte leakage from leaf tissue after cold treatment. Thirty days after cold treatment at 5 degrees C for 5 days, the plants treat ed with 1 ppm ALA resulted in 85% survival ratio, 6.1 leaves per plant and 111.8 mg dry weight per aerial part of seedling, while 65%, 5.9 a nd 65.0 mg respectively in the control plants. The dry weight of seedl ings treated with ALA increased 1.7 folds as compared to the control p lants. These results are the first evidence that ALA has protective ef fects against cold stress in rice seedlings. Abscisic acid (ABA) and b rassinolide (BR) also increased the cold resistance in our bioassay sy stem. Protective effect of BR at 0.001 ppm against cold stress was sim ilar to that of ALA, However, protective effect of ABA was different f rom that of ALA in terms of the ratio of leaf rolling after cold stres s. ABA protected young leaves rather than old ones, while ALA and BR w ere more effective on the protection of old leaves.