INCORPORATION OF TRITIUM (3H1)LABELLED THYMIDINE IN Oryza sativa UNDER HEALTHY AND INFECTED (BY Rhizoctonia solani) CONDITIONS JANUARY - MARCH 1998

GUIDE: Dr. ANNAPURANI S

AVINASHILINGAM DEEMED UNIVERSITY , COIMBATORE

Project Work as a requirement for UnderGraduation

A comparison was made of the ability of rice (Oryza sativa) saplings to incorporate tritium labelled thymidine under normal and infected growth conditions. Rice saplings were infected with Rhizoctonia solani, a paddy sheath blight causing fungal pathogen at the active tillering stage and controls were also set up simultaneously. 3H1 thymidine was prepared as an aqueous label and applied to the soil. After an absorption period of 30 days the crop was harvested into different tissues namely leaf, stem and root. DNA was violated from each of the samples and activity in each sample was counted using a Beckman Liquid Scintillation counter. A quench curve was plotted with percentage efficiency of standards on X axis and the H number of standards on Y axis. The percentage efficiency of the samples was obtained by extrapolation and used to calculate dpm. Chlorophyll content was estimated in fresh leaves from control and infected plants. The estimation of total chlorophyll content (Sadasivam and Manikkam, 1992) did not show any significant difference in the control and diseased rice leaves.

One reason of increased incorporation of labelled thymidine in infected saplings could be due to a high rate of DNA replication and activation of repair mechanisms to counteract DNA damage by the pathogen. Another reason might have been that the pathogen R.solani also used tritiated thymidine as a precursor for DNA synthesis. This study was done with the aim of extending it in the direction of unraveling the molecular basis of disease and resistance pathways in plants. Part of the work was done at the Tamilnadu Agricultural University under the guidance of Dr.Rajarajan