Radiation-induced phenotypic alterations in relation to isozymes and RAPD markers in Vigna radiata (L.) Wilczek

Abstract

Purpose: The present investigation is aimed at studies on the effects of gamma rays on in vitro and in vivo damage in Vigna radiata. The parameters studied are germination frequency, seedling injury, isozyme alteration and random amplified polymorphic DNA (RAPD) markers. Results obtained are analyzed in the light of modern applications of radiation damage.Materials and methods: Seeds of Vigna radiata were subjected to gamma irradiation with a dose of 20 – 200 Gy. The percent of seedling damage and frequency of germination were determined. Callus samples were produced in vitro and exposed to gamma rays. The irradiated callus samples were processed to extract total protein, and specifically stained for superoxide dismutase (SOD) and peroxidase isozymes. Total genomic DNA was extracted from irradiated callus samples and subjected to random amplified polymorphic DNA analysis using 23 random decamer primers.Results: Gamma irradiation resulted in retardation in seedling height and decrease in germination frequency in a dose dependent manner. Inhibition assay identified variation in response between different isoforms of SOD on radiation exposure. Changes in peroxidase activity were also observed following irradiation. RAPD analysis showed that new bands appeared in the 20 Gy irradiated sample which in the case of some primers showed similarity with the control. The calli irradiated with 50 Gy and 100 Gy of gamma rays was found to have striking resemblance in banding pattern. Callus irradiated at 200 Gy showed maximum damage. DNA damage as revealed by RAPD analysis was reflected in the appearance of new bands with varying molecular weights.Conclusion: New isoforms of SOD appeared after irradiation followed by 24 h recovery. Some isoforms of peroxidase reappeared in calli after 24 h recovery. Results of RAPD analysis indicated that the DNA polymorphism was dose dependent.