Non-structural carbohydrates of immature seeds of Caesalpinia echinata (Leguminosae) are involved in the induction of desiccation tolerance

Abstract

Seeds of Caesalpinia echinata fill up to physiological maturation phase ~60 days after anthesis (DAA) in the field. These seeds are desiccation tolerant to 0.08 gH2O gDW–1 and can be stored for 2 years under freezing temperatures without losing germinability. Starch (40–50%), soluble carbohydrates (10–15%, mainly sucrose and cyclitols), in addition to traces of raffinose and stachyose detected early at maturation, are supposed to be related to the acquisition of desiccation tolerance. In the present work we demonstrate that desiccation-intolerant immature seeds (45 DAA) of C. echinata can be dried until 0.14 gH2O gDW–1 when previously soaked in polyethylene glycol (PEG) solution, maintaining high germination percentage. In contrast, seeds of 55 DAA tolerated drying until 0.14 gH2O gDW–1 without previous PEG treatment, indicating that they have already reached desiccation tolerance at this developmental stage. High-performance anion exchange chromatography analysis revealed that cyclitols and sucrose increased markedly in the embryonic axes at 45 DAA after PEG treatment, reaching levels found in embryos at 55 DAA. These results suggest that PEG treatment mimics the natural maturation drying of C. echinata seeds, changing carbohydrate metabolism and triggering processes involved in desiccation tolerance.