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 KCI instead of KNO3, 1.7 mM glutamine, microelements, vitamins, 60 mM sucrose, 0.1 //M a-naphthaleneacetic acid and 2.5//M 2-isopentenyladenine allows either somatic embryo-genesis 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 °C and 25 °C instead of direct somatic embryogenesis at 35 °C. At 30 °C all types of morphogenesis are observed. After 5 d of culture, cells grown at each temperature exhibit enlarged nuclei with prominent nucleoli, fragmented vacuoles and dense cytoplasm. However, at 25 °C, callose is restricted to wounded cells whereas at 35 °C some nearby mesophyll cells show a more or less complete callose sheath. On the 7th day, proembryos at 35 °C show a superficial network which is absent at 25 °C on shoot primordia which are covered with a smooth precocious proto-derm. Why do activated cells undergo segmentation and somatic embryogenesis at 35 °C instead of ordinary mitosis with callus and shoot formation at 20 °C and 25 °C?