الصدمة الحرارية تحفز محتوى الاحماض النووية والبروتينات والفعالية النوعية لانزيمات بناء نيوكليوتيد الثايمين في كالس سيقان السمسم Sesamum indicum L.

The present study revealed that exposure of stem derived callus of Sesamum indicum L. that grown on initiation medium Murashige and Skoog (MS) supplemented with naphthalene acetic acid (NAA 1.0 mg L-1) + benzyl adenine BA 2.0 mg L-1 to 25, 30, 35, 40, 45 or 50◦ C as short term heat shock stHS 5,10 min. and long term heat shock ltHS 15, 20min. enhanced a desirable changes of callus growth. Moreover, the amounts of nucleic acids DNA, RNA, proteins and the specific activity of thymidylate synthase (TS), dihydrofolate reductase (DHFR) and serine hydroxy methyl transeferase (SHMT) enzymes were also increased. The heat shock treatment 40◦ C/15 min. gave the best effect in amount of both DNA and RNA that increased to 95 and 949 µg/g compared to control 58 and 550µg/g callus fresh weight respectively. Total protein was also increased to2.85 mg/g compared to control 1.47 mg/g. Maximum specific activities of TS, DHFR and SHMT enzymes were recorded 3.41, 0.97, 0.31µmol/min/mg protein respectively compared with control 1.70, 0.43, 0.13µmol/min/mg protein. Whereas, heat shock treatments 45 and 50◦ C of both tearms reduced each of callus fresh weight, DNA, RNA amount, and decreased the specific activities of the above enzymes.