Slow imbibition of Annona emarginata (Annonaceae) seeds: Metabolic and ultrastructural evaluations

Abstract

Germination pattern may be affected when seeds are dispersed under flooded conditions or subjected to pre-germination treatments such as immersion in plant growth regulators and priming. We evaluated the metabolic and ultrastructural changes in the seeds of Annona emarginata (Schltdl.) H. Rainer seeds caused by immersion in water (0 MPa) during the imbibition phase (phase I). The immersion time necessary for initially dry seeds (10% water content) to reach a water content of 15%, 20%, and 35% was recorded. The seeds were also immersed in a polyethylene glycol 6000 solution (-1.2 MPa) to decrease the rate of water uptake and increase the immersion times required for the seeds to reach the selected water contents. With shorter immersion times, seed damage did not decrease germinability. Seeds immersed for 122 h sustained damage to the cell membrane system and organelles, resulting in a decreased percentage and rate of germination. Decreasing the rate of water uptake increased the time required to finish imbibition phase to 317 h and resulted in more ultrastructural damages and a decreased germination index. We conclude that in seeds with slower imbibition, longer immersion times may cause severe metabolic damage if the seeds are immersed until the end of the imbibition phase, resulting in reduced germination.