Non-structural carbohydrates of immature seeds of Caesalpinia echinata (Leguminosae) are involved in the induction of desiccation tolerance Simone Nadur Motta Leduc A , João Paulo Naldi Silva B , Marília Gaspar A , Claudio José Barbedo B and Rita de Cássia Leone Figueiredo-Ribeiro A,C A Plant Physiology and Biochemistry Department, Institute of Botany, PO Box 68041, São Paulo, 04045-972, SP, Brazil. B Seed Department, Institute of Botany, PO Box 68041, São Paulo, 04045-972, SP, Brazil. C Corresponding author. Email: rita.cassia@pq.cnpq.br 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 gH 2 O 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 gH 2 O 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 gH 2 O 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. Received 16 September 2011, accepted 3 December 2011, published 3 February 2012 Introduction Caesalpinia echinata Lam. (brazilwood) is an endangered leguminous tree used as dyestuff in the past (Rocha et al. 2007) and currently still used for the manufacturing of high- quality bows of stringer instruments (Alves et al. 2008; Rocha 2010). This species is scarcely found in its original habitat, the moist coastal Atlantic Forest, between Rio Grande do Norte and Rio de Janeiro, as well as in seasonal dry forests (Lewis 1998; Lira et al. 2003). The physiological maturity of C. echinata seeds is achieved ~60 days after anthesis (DAA), immediately before shedding, when its water content is ~0.43–0.67 gH 2 O gDW –1 (Borges et al. 2005). The development and maturation of these seeds are not uniform in the same fruit, making it difficult to obtain lots of high-quality seeds in field conditions. However, they are tolerant to desiccation and maintain high germinability even after drying at 40–50  C to 0.08 gH 2 O gDW –1 (Barbedo et al. 2002). Mature seeds of C. echinata contain more than 40% starch, 10–15% of sugars, predominantly sucrose, and traces of raffinose and stachyose and 17% lipids (Garcia et al. 2006; Mello et al. 2010). The cyclitols galacto-pinitol and ciceritol are also present and accumulated in the cotyledons later during maturation (Borges et al. 2006). The acquisition of desiccation tolerance (DT) in orthodox seeds in field conditions occurs during the later stages of maturation and it has been correlated with increased amounts of protective compounds, including proteins and sugars (Black et al. 1999), mainly sucrose and raffinose family oligosaccharides (RFO). Sucrose accumulation appears to be a general phenomenon in response to drought and to other stresses in plants and seeds, buffering the water loss and stabilising polymers during desiccation (Horbowicz et al. 1998; Hoekstra et al. 2001; Moore et al. 2008). Free cyclitols and galactosyl cyclitols accumulated in some seeds have been proposed to contribute to structural stability of organelles, membranes, enzymes and other macromolecules, and to promote the glassy state (Obendorf 1997; Peterbauer and Richter 2001). Osmotic treatments have been used in re-establishment of DT in germinated, desiccation-sensitive seeds. Bruggink and Van der Toorn (1995) reported the survival of radicle tips or hypocotyls when germinated seeds of Impatiens balsamina and cucumber were dried after incubation in polyethylene glycol (PEG) solutions. Maturation of high-quality somatic embryos of conifers in vitro can be achieved by the use of abscisic acid and increased concentrations of sucrose and/or PEG. Under these conditions, the osmotic stress induced by PEG mimics the natural CSIRO PUBLISHING Australian Journal of Botany, 2012, 60, 42–48 http://dx.doi.org/10.1071/BT11236 Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/ajb