THE POSSIBLE INVOLVEMENT OF THE HEAT SHOCK ELEMENT EXISTING ON THE PROMOTER OF CYTOSOLIC APX GENE IN HEAT-SHOCK-MEDIATED PROTECTION OF RICE SEEDLINGS AGAINST CHILLING INJURY

¹ Hokkaido National Agricultural Experiment Station, Hitsujigaoka 1, Toyohira-ku, Sapporo 062-8555, Japan

² Hokkaido Green-Bio Institute, Naganuma, Hokkaido 069-1301, Japan

Rice (Oryza sativa L.) seedlings, when kept at 42 ūC for 24 h before being kept at 5 ūC for 7 d, did not develop chilling injury. Levels of APX activity were higher in heated seedlings. The elevated activity of APX was sustained after 7 d of chilling. The cytosolic APX gene expression in response to high and low temperature was analyzed with APXa gene probe. APXa mRNA levels increased within 1 h after seedlings were exposed to 42 ūC. Elevated APXa mRNA levels could also be detected after 3 h of heating. APXa mRNA level reduced after 2 d of chilling at 5 ūC.The promoter of APXa gene was cloned from rice genomic DNA by TAIL-PCR, and characterized by DNA sequencing. The promoter had a minimal heat shock factor-binding motif, 5'-nGAAnnTTCn-3', located 81-bp upstream to TATA box. Heat shock induction of APXa gene could be a possible cause of reduced chilling injury in rice seedlings.