BIOLOGIA PLANTARUM 49 (3): 347-354, 2005 347 Changes in protein profiles associated with somatic embryogenesis in peanut A. ROJA RANI*, V.D. REDDY**, P. PRAKASH BABU* and G. PADMAJA* 1 School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India* Department of Genetics, Osmania University, Hyderabad 500 007, India** Abstract The somatic embryogenesis potential of zygotic embryo axes of peanut (Arachis hypogaea L. cv. DRG-12) at different stages of development was evaluated by culturing on MS medium with 18.1 μM 2,4-dichlorophenoxyacetic acid (2,4-D). A 100 % frequency with 18.3 somatic embryos per explant was observed from 4 mm long immature zygotic embryo axes collected 31 - 40 d after pollination. Medium supplemented with 16.6 μM picloram resulted in slow development of somatic embryos whereas in the presence of 21.5 μM α-naphthaleneacetic acid (NAA), the explants underwent maturation with induction of roots after 30 d. The changes in protein profiles in zygotic embryo axes at different stages of development correlated with their potential to form somatic embryos. Immature zygotic embryo axes exhibited high frequency somatic embryogenesis in the stage preceding abundant accumulation of 22 and 65 kDa proteins. The content of 22 and 65 kDa proteins decreased immediately after culture on medium fortified with 18.1 μM 2,4-D and increased again after 12 d of culture coinciding with the development of somatic embryos on the explants. The content of 22 and 65 kDa proteins was low at 15 d of culture on medium supplemented with 16.6 μM picloram possibly due to slow development of the somatic embryos on the explant. On maturation medium containing 21.5 μM NAA, a marked increase in the content of 22 and 65 kDa proteins in 15 d-old cultures was observed. Additional key words: protein analysis, sodium dodecyl sulphate-polyacrylamide gel electrophoresis, zygotic embryo axes. Introduction Peanut or groundnut (Arachis hypogaea L.) is one of the principal oil seed legumes rich in protein and is grown in tropical and sub-tropical regions of the world. Plant regeneration via organogenesis (Mroginski et al. 1981, Chengalrayan et al. 1995, Victor et al. 1999) and somatic embryogenesis (Sellars et al. 1990, Baker and Wetzstein 1994, Chengalrayan et al. 1998, Little et al. 2000, Radhakrishnan et al. 2002, Joshi et al. 2003) has been reported from different explants of peanut. Regeneration of plants via somatic embryogenesis is of special significance as it yields genetically more stable regenerants owing to single cell origin. Somatic embryogenesis also holds considerable potential for enhancing the understanding of various aspects related to embryo development and provides the most efficient regeneration method suitable for gene transfer. In peanut, immature zygotic embryos, cotyledons and developing leaves have been reported to be the most responsive explants for the induction of somatic embryogenesis compared to the differentiated plant tissues (Hazra et al. 1989, George and Eapen 1993, Reddy and Reddy 1993). Many other factors including genotype, photoperiod, nitrogen formulation, type and concentration of auxin, carbon source supplied in the medium are also known to affect the embryogenesis response from somatic tissues of peanut (Chengalrayan et al. 1998, Ozias-Akins et al. ⎯⎯⎯⎯ Received 6 January 2004, accepted 29 November 2004. Abbreviations: 2,4-D - 2,4-dichlorophenoxyacetic acid; MS - Murashige and Skoog (1962) medium; Mr - molecular mass; NAA - α-naphthaleneacetic acid; PAGE - polyacrylamide gel electrophoresis; SDS - sodium dodecyl sulphate; Tris - Tris hydroxymethyl aminomethane. Acknowledgements: ARJ acknowledges the UGC, New Delhi for the award of JRF and SRF. The financial assistance rendered to GP by unassigned grant scheme of UGC, and the support received from the UGC-SAP and DST-FIST programmes of the School/Department are gratefully acknowledged. The authors wish to thank Mr. N. Prabhakar Rao, Farm Manager, DOR, Hyderabad, for providing the experimental material. We would like to express our grateful thanks to Dr. P. Suprasanna, Scientist, Bhabha Atomic Research Centre, Mumbai for his valuable suggestions in the preparation of manuscript. 1 Corresponding author; fax: (+91) 040 23010120, e-mail: gprsl@uohyd.ernet.in