Morfometria, germinação e armazenamento de sementes de Colubrina glandulosa Perkins

Abstract

Colubrina glandulosa Perkins, popularly known as colubrina, is a tree species native to Brazil, belonging to the Rhamnaceae family, with potential for use in the recovery of degraded areas. The objective of this work was to characterize the seeds from a physical and morphological point of view, to study the post-seminal development, to indicate the best treatment to overcome dormancy of colubrina seeds, to determine the cardinal temperatures for germination, to verify the isothermal velocity variation based on the transition state model, calculate the variation of ΔH≠ as a function of temperature, and evaluate different storage conditions on the physiological potential of the seeds. For the physical characterization, eight replicates of 100 seeds were weighed and the length, width and thickness of each seed were measured. For the morphological description, the shape, color and location of the hilum and the micropyle were analyzed, besides the tissue reserve, type and location of the embryo. In the post-seminal study, the germination process was recorded until 19 days after sowing. Seven treatments of dormancy were used: intact seeds (T1); immersion in sulfuric acid for 60 minutes (T2); immersion in sulfuric acid for 90 minutes (T3); splitting of the integument in the region opposite the hilum (T4); immersion in distilled water at 80 °C, followed by standing in the same water for 24 hours at room temperature (T5); immersion in distilled water for 24 hours at room temperature (T6); and immersion in distilled water for 48 hours at room temperature (T7). The isothermal incubation was carried out at constant temperatures of 5, 10, 15, 20, 25, 30, 35 and 40 ºC and alternating at 20-30 ºC, with eight-hour photoperiod. The Arrhenius equation was linearized by logarithmic transformation, by constructing the graph with coordinates y = –RlnV and x = A(1/T), from the variations of the germination velocity along the entire thermal range. The net change in enthalpy (ΔH≠) as a function of temperature was represented by the expression ΔH≠ = [RT(θ – T).(Tm + TM)]/[(T – Tm).(TM – T)]. Seeds were stored in a paper bag and glass bottle and stored in a laboratory and dry chamber environment for 15 months, with the evaluation being performed quarterly. The seeds of colubrina presented irregular size with a maximum length of 5.09 mm and a minimum of 1.91 mm; maximum width of 4.92 mm and minimum of 1.82 mm; and a maximum thickness of 2.75 mm and a minimum thickness of 1.22 mm. The seed is testal, presenting embryo of the invaginated type. Seed germination is epigene and seedlings are phanerocotonares. The splitting of the integument in the region opposite the hilum is the indicated method for overcoming dormancy of seeds of C. glandulosa. The seeds germinated in the range of 10 °C ≤ T ≤ 35 °C, with the optimal temperature in the range of 25 °C <T <30 °C, the minimum at 5 °C <T <10 °C, and the maximum at 35 °C <T <40 °C. Based on the model of the activated complex, the speed of germination depends curvilineamente of the temperature. Applying the laws of thermodynamics, the graph of the temperature dependent variation of ΔH≠, whose curve has two asymptotes close to Tm and TM, showed that the energy (enthalpy) of activation of the germination is negative as the temperature tends to TM, being the processes that occur in the supra-optimal range of nature different from those occurring in the infra-optimal region. The physiological potential of the seeds was maintained at least 15 months when packed in a porous or impermeable package and stored in a dry chamber.