Thermal-Biological Aspects of Seed Germination of Colubrina glandulosa Perkins Under Different Temperatures

The aim of this study was to determine the cardinal temperatures for germinating colubrina seeds, verify isothermal velocity variation based on the transition state model and calculate the ΔH≠ variation as a function of temperature. Seeds were incubated at constant temperatures of 5, 10, 15, 20, 25, 30, 35 and 40 oC and alternating temperature from 20-30 oC in an 8-hour photoperiod. The variables analyzed were: G, PC, IVG, TMG, VMG, Fi, U, Z, CR, CPA, MSR and MSP. Arrhenius equation was linearized by logarithmic transformation, producing the graph of -RlnV × 1/T from the experimental values of velocity. A net enthalpy change (Delta H≠) in relation to temperature was represented by the expression: Delta H≠ = [RT(Theta – T) × (Tm + TM)]/[(T – Tm) × (TM – T)]. The logarithm regression of the reaction rate on the reciprocal of the temperature fit best to the quadratic model. The distribution of Delta H≠ with asymptotes close to Tm and TM indicated that the processes that occurred in the supra-optimal temperature range were of a different nature from those that occurred in the infra-optimal temperature range. The data showed |Delta H≠| < 12 Kcal/mol in the optimal range and |Delta H≠| > 30 Kcal/mol for temperatures of 10, 15 and 35 oC. The minimum and maximum temperature limits were 10 and 35 oC, respectively. Germination speed was related to temperature in a curvilinear manner. The germination process was endergonic and only occurred when energy was ≥ -38.35 Kcal/mol and ≤ 32.42 Kcal/mol.