Plant Science, 67 (1990) 203-209 203 Elsevier Scientific Publishers Ireland Ltd. SELECTION OF S-{2-AMINOETHYL)-L-CYSTEINE TOLERANCE IN EMBRYOGENIC CALLI AND REGENERATED PLANTS OF PENNISETUM PURPUREUM SCHUM. FLONA A. REDWAY and INDRA K. VASIL Department of Vegetable Crops, Laboratory of Plant Cell and Molecular Biology, University of Florida, Gainesville, FL 3~611 fU.S.A.J (Received June 5th, 1989) (Revision received October 2nd, 1989) (Accepted October 31st, 1989) Embryogenic callus tissues of Pennisetum purpureum were selected for tolerance to S-(2-Aminoethyl~L-cysteine (AEC), Calli were selected after 18 weeks on media containing 0.125, 0.25 and 0.50 mM of AEC. AEC tolerant calli readily regenerated green shoots on regeneration medium both with and without the AEC. Leaves from tolerant mature regenerants formed embryogenic calli at high frequencies on AEC containing medium. The tolerant ealli as well as the regenerants contained 21 to 470]0 more free lysine than that of the controls as determined by amino acid analysis. Key words: S-(2-aminoethyl~L-cysteine; Pennisetum purpureum; embryogenic callus Introduction Lysine is an essential amino acid for humans as well as animals. Pennisetum purpureum (Napier or Elephant grass) is economically important as a forage crop and biomass species but is nutritionally deficient in lysine. Increas- ing the lysine content of the vegetative tissues of P. purpureum could partially correct lysine deficiency and make it a valuable source of animal nutrition. S-(2-Aminoethyl~L-cysteine (AEC) is an ana- logue of lysine and has been shown to act as a feedback inhibitor in the aspartate biosynthetic pathway in Nicotiana sylvestris [1] and in some members of the Gramineae as well, namely bar- ley [2,3], maize [4] and oats [5]. By selecting for feedback insensitive mutants which are toler- ant to different levels of AEC it is possible to increase lysine content of plant tissues [5--7]. AEC resistant lines have been obtained in bar- ley [2], rice [7], oats [5] and pearl millet [8]. Recently an AEC resistant wheat cell suspen- sion culture has alse been characterized [9]. This paper describes the selection of AEC tolerant embryogenic calli and regeneration of plants from the tolerant calli of Pennisetum purpureum. Materials and Methods CaUus formation The basal portions of young leaves from mature field grown plants of P. purpureum Schum. (Selection pp. 12) were used for the ini- tiation of embryogenic callus. Shoots were surface sterilized and leaves dissected as described by Haydu and Vasil [10], and then cultured on pp medium: Murashige and Skoog's basal medium [ll] supplemented with 1.0 mg 1-1 naphthaleneacetic acid (NAA), 0.5 mg 1-1 2,4- dichlorophenoxyacetic acid (2,4-D), 0.5 mg 1-1 6- benzylaminopurine (BAP) and 5% coconut milk, Gelrite 0.2%, (pH 5.8). Cultures were main- tained at 27 °C in the dark. Leaf segments (approximately 1000 pieces) were cultured for three weeks after which the white, compact embryogenic calli were subcul- tured to pp medium containing different concentrations of AEC (0.125, 0.25, 0.50, 1.0 and 1.5 raM); pp medium free of AEC was used as the control. Cultures were maintained at 27 °C 0168-9452/90/$03.50 © 1990 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland