ROLE OF TEMPERATURE AS A TRIGGERING SIGNAL FOR ORGANOGENESIS OR SOMATIC EMBRYOGENESIS IN WOUNDED LEAVES OF CHICORY CULTURED IN-VITRO

Static liquid half-strength Murashige and Skoog medium, containing 10.1 mM KCl instead of KNO3, 1.7 mM glutamine, microelements, vitamins, 60 mM sucrose, 0.1 mu M alpha-naphthaleneacetic acid and 2.5 mu M 2-isopentenyladenine allows either somatic embryogenesis or shoot organogenesis along the borders of leaf incisions of a Cichorium hybrid (Cichorium intybus L. x Cichorium endivia L.). These phenomena are temperature-dependent and the latter promotes the development of callus and shoots at 20 degrees C and 25 degrees C instead of direct somatic embryogenesis at 35 degrees C. At 30 degrees C all types of morphogenesis are observed. After 5 d of culture, cells grown at each temperature exhibit enlarged nuclei with prominent nuclleoli, fragmented vacuoles and dense cytoplasm. However, at 25 degrees C, callose is restricted to wounded cells whereas at 35 degrees C some nearby mesophyll cells show a more or less complete callose sheath. On the 7th day, proembryos at 35 degrees C show a superficial network which is absent at 25 degrees C on shoot primordia which are covered with a smooth precocious protoderm. Why do activated cells undergo segmentation and somatic embryogenesis at 35 degrees C instead of ordinary mitosis with callus and shoot formation at 20 degrees C and 25 degrees C?