PHYSIOLOGICAL EFFECTS OF TEMPERATURE AND THERMAL STRESS ON THE SEED GERMINATION OF <em>STRYPHNODENDRON</em> <em>POLYPHYLLUM</em>

Abstract

The thermal effects brought about by temperature on the seed germination of Stryphnodendron polyphyllum were studied in relation to the germination percentage and relative frequency distribution of germination along the incubation time. Stryphnodendron polyphyllum seeds were found to be eurithermic, having the following cardinal temperatures: the minimum between 5 and 10 °C, the maximum between 40 and 45 °C, the optimum between 25 and 30 °C. The germination rate was temperature dependent. However, the distribution of relative frequency of germination did not fit the adjusted gaussian and did not give good linearity in the Arrhenius graphs of their isothermal germination rates. Hence, in these seeds the thermal communication between the environment and the seed growth effector is made through a temperature signal superimposed upon the random thermal noise at all germination isotherms. The absolute values of enthalpy activation of germination (△H*n) were less than 12 Kcal mol⁻¹ between 20 and 30 °C, 12 and 30 Kcal mol⁻¹ at 15 °C and higher than 30 Kcal mol⁻¹ above 35 °C. Therefore, the germination of the seeds was only limited by diffusion process between 2 and 30 °C. Below 15 and above 35 °C phase transitions and protein denaturation occurred. The lowest values of informational entropy occurred between 25 and 30 °C, showing a higher synchronisation of the germination process. Seeds without imbibition were resistant to exposure at 70 °C for 24 h, without showing a significant reduction in the rate and percentage of germination. Thermal stress of imbibed seeds at 50 °C for 24 h gave only 10% germination.