The Molecular Biology Of Aluminium Resistance In Rice (Oryza Sativa L.)

To identify genes for rice tissue tolerance for aluminium iron (A13+) toxicity, an indica variety IR1552, sensitive to Al toxicity, and a japonica variety Azucena, tolerant to Al toxicity were used.Phosphoenolpyruvate carboxylase (PEPC) cDNA fragment obtained from RT-PCR based on the sequence in wheat, soybean and maize was used to detect the polymorphism between the two varieties and the gene expression pattern under A13+ stress. The results showed that the transcription of PEPC was not induced by Al3"1" stress. By using the molecular map of a DH population derived from a cross between Azucena and IR64, the PEPC cDNA fragment was mapped on chromosome 5.Mitochondrial malate dehydrogenase (MDH) cDNA clone (AJ131205) from professor Ocheretina, mitochondrial citrate synthase (CS) cDNA clone (C10531) from MAFF Gene Bank in Japan and glyoxysomal citrate synthase cDNA clone (AW033758) from Clemson University were used to investigate their roles in the tolerance. The transcription of the three-cDNA clones was induced by A13+ stress.The transcription of MDH reached the highest level after 24 hours of A13+ stress in both the tolerant and the sensitive variety, then decreased. The transcription decreaced remarkably in IR1552 but not in Azucena.In tolerant variety Azucena, the transcription of mitochondrial CS reached the highest level after 2 hours of A13+ stress, then decreased, while after 8 hours, the transcription increased again, and came to stabilization. In sensitive variety IR1552, the transcription of mitochondrial CS increased after 12 hours of A13+ stress and reached the highest level after 24 hours of A13+ stress. After 48 hours of A13+ exposure, the transcription of mitochondrial CS of both varieties was similar. The transcription of glyoxysomal CS decreased at initial stress and then increased in both the tolerant and the sensitive variety. In tolerant variety Azucena, the transcription of glyoxysomal CS reached the lowest level after 2 hours of A13+ stress, then increased remarkably, while after 12 hours, reached the highest level. In sensitive variety IR1552, the transcription of glyoxysomal CS reached the lowest level after 8 hours of A13+ stress, then increased, while after 24 hours reached the level of CK.Based on the results, we proposed that the transcription of key enzymes including mitochondrial MDH, mitochondrial CS and glyoxysomal CS involved in organic acid metabolism increased with A13+ exposure in the root tip. The capacity for organic acid synthesis was relatively increased. But the transcription of PEPC was relatively unaffected by A13+ exposure.It was noted that the transcription of mitochondrial MDH and mitochondrial CS increased by A13+ exposure in both the tolerant and the sensitive variety, hi the tolerant variety, however, the transcription of mitochondrial CS and glyoxysomal CS increased by A13+ exposure was more rapidly, and the transcription of mitochondrial MDH after stressed for 24 hours in Azucena reduced slower.