Purification and properties of β-xylosidase isozymes from cucumber seeds

Transformed tissues can be efficiently selected with the help of selectable markers. We studied the influence of genotype, culture medium, and chemical nature of selectable markers on the callus formation of sunflower ( Helianthus annuus L.) hypocotyl explants during the selection process. Kanamycin was found not to be a suitable marker for sunflower transformation, while paromomycin and phosphinotri-cin are both useful. Because the mechanism of action of these inhibitors is intimately connected with the physiological reactions of the cultured tissues, we investigated the influence of key media components on the efficiency of selection of transformed callus on phosphinotricin. Auxin, cytokinin, and gibberellic acid, as well as nitrate concentration, all had a strong influence on the spontaneous resistance of untrans-formed sunflower hypocotyl explants against this herbicide. The number of transformed cells varied in function of the growth regulator balance. Possible reasons for this media dependence are discussed.