Heat-resistance response of Ceiba aesculifolia seedlings induced by thermopriming

Ceiba aesculifolia (ceiba) is a tropical plant species with high resistance to environmental stresses and assigns biomass and reserves to belowground tissues to cope with hydric stress. We determined if thermotolerance can be induced in ceiba seedlings by implementing a heat stress and heat priming protocol to germinating seeds. Assessment of seedling survival and development was done at two developmental stages, fully expanded cotyledon and three true leaves seedlings under controlled conditions, as well as saplings under field conditions. Heat stress was induced by subjecting germinated seeds to different supra-optimal temperatures for 45 min. A 100 % of seedlings subjected to heat below 42 °C survived. Seedling survival decreased at 48 °C and 50 °C, the latter also accumulated starch as a result of the treatment. The priming temperature was set at 37 °C since germinating seeds did not present any injury in the radicle and all seedlings survived. Thermopriming treatment at 37 °C for 90 min promoted 50 % of seedling survival to the lethal temperature (51 °C) and an increase in starch accumulation. No significant change on plant height and coverage in field conditions were detected in thermo-primed plants. Seedling survival and further development at 51 °C after thermopriming indicates the induction of thermotolerance mechanisms in ceiba by the presence of two or three tubers in 50 % of the treated seedlings and a 27 % increase in tuber starch content. These early developmental / functional responses in ceiba could allow them to develop and establish in heat-stressed soil environments.