Indian Journal of Experimental Biology Vol. 47, March 2009, pp. 198-203 Role of PGRs and inhibitors in induction and control of somatic embryogenesis in Themeda quadrivalvis N Habibi, R K Suthar & S D Purohit* Plant Biotechnology Laboratory, Department of Botany, University College of Science, Mohanlal Sukhadia University, Udaipur 313 001, India Received 27 August 2008; revised 5 January 2009 Somatic embryogenesis could be achieved in Themeda quadrivalvis (Linn.) O. Ktze -fodder grass species on MS medium supplemented with 2,4-D. Incorporation of putrescine in the medium stimulated embryogenesis, however its lower concentration stimulated production of non-regenerative callus. Other polyamines such as spermine and spermidine could not evoke similar response. Ascorbic acid used as antioxidant could not prevent browning in embryogenic cultures, however it stimulated embryogenesis. Inhibition of auxin polar transport by use of TIBA and HFCA reduced the embryogenic response significantly and produced distorted or abnormal embryos. Antiethylene substances such as AgNO 3 and CoCl 2 added in the medium adversely affected the process of embryogenesis and counteracting the stimulatory role of ethylene. Keywords: Plant growth regulators, Plant inhibitors, Somatic embryogenesis, Themeda quadrivalvis Monocots have always offered challenges towards in vitro culture and plantlet regeneration largely on account of lack of sufficient areas of meristematic activity in them. Consequently, a large number of workers have used immature zygotic embryos or other embryogenic/meristematic tissues to achieve regeneration through somatic embryogenesis in economically important plants including cereals and grass species 1-3 . The onset and progression of embryogeny in monocot cultures are determined by a variety of factors that have been studied widely in a number of plants such as, the type and developmental stage of the explant 4-6 and the explant genotype 7-9 . Further, the exogenously supplied auxin is essential for the process of somatic embryogenesis. Generally, auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), is critical for the production of regenerable callus in grasses 7 . In addition to the classical auxins, few natural growth substances such as polyamines with regulatory roles in somatic embryogenesis have been discovered in the last few years 10-12 . A number of other chemical factors have been found to affect the disposition of a particular tissue to undergo somatic embryogenesis. Such chemicals include auxin polar transport inhibitors 13-15 , anti-ethylene substances 16, 17 and antioxidants such as ascorbic acid 14 . The present paper reports the role of auxin and other growth regulatory substances and their inhibitors in induction, control and regulation of somatic embryogenesis in Themeda quadrivalvis (Linn.) O. Ktze (commonly known as godli ghas), an important fodder grass. Materials and Methods Plant material⎯For the present investigation the plants of T. quadrivalvis were collected from the fields of Mohanlal Sukhadia University, Udaipur, India. Husk was removed and seeds were dissected under stereoscopic microscope. The seeds were then surface sterilized in a laminar airflow bench (Yorco, India) with HgCl 2 (0.2%) for 10 min. After washing several times with double distilled water, seeds (ca 3 per tube) were placed axenically on auxin supplemented Murashige and Skoog’s medium. Induction of embryogenic callus⎯Murashige and Skoog’s medium containing 2,4-D (0.5-5.0 mg l -1 ) served as callus induction medium. pH of the medium was adjusted to 5.8 prior to autoclaving at 1.06 kg cm 3 . Inoculated cultures were maintained in dark under controlled culture room conditions at 28±2°C using air-conditioners (Amtrex). RH (50-60%) was maintained through a humidifier (Yorco, India). ____________________ *Correspondent author Telephone: +91 294 2410300 E-mail: sdp_1956@live.in Somatic embryogenesis-influence of chemical factors⎯Embryogenic potential of the callus was