Fisiologia da superação de dormência em sementes de macaúba (Acrocomia aculeata), Arecaceae

Abstract

Macaw palm (Acrocomia aculeata) is a Neotropical palm specie, whose seeds have primary dormancy and show slow germination. We aimed to study physiological components during the process of overcoming dormancy and germination of macaw palm seeds. In the first chapter, we studied the role of phytormones abscisic acid (ABA), gibberellins (GA), auxin (IAA), citokinins (CK), jasmonic acid (JA), salicylic acid (SA)and the ethylene precursor 1-aminocyclopropane-1-carboxilic acid (ACC), also vitamin E and lipid peroxidation (MDA, malondialdeide) in dry, imbibed, germinated and nongerminated seeds treated or not (control) with GA3. In this chapter we concluded that germination in macaw palm involve reduction in ABA content and consequently increase in GA/ABA ratio, and vitamin E and MDA indicate oxidative signaling to germination. In the second chapter, we analyzed the levels of ABA, GA, JA, SA and vitamin E in embryos from seeds (in dry, imbibed, germinated and non-germinated phases) of recently harvested fruits and stored in nursery (simulating natural conditions) and laboratory (with and without GA3 treatment). In seeds from nursery, the levels of GA and vitamin E increased during imbibition without diminished ABA levels. These results suggest that vitamin E may be involved in repair mechanism during natural hydration/dehydration cycles and ABA is an important dormancy maintainer in soil seed banks of macaw palm. In the third chapter, we used embryos from fruits developed in two consecutive years to quantifyhydrogen peroxide (H2O2) and MDA levels, from seeds of control and after dormancy overcome treatments (GA3 application and removal of the operculum). Seeds developed in the first year showed lower germinability, higher dormancy level and less sensibility to exogenous GA. The increase in H2O2 levels in seeds from treatments with highergerminability suggest involvement of H2O2 in germination signaling in macaw palm. We conclude that environmental factors influence the physiology of A. aculeata seeds in preand post-dispersion phases signaling the control of overcoming dormancy and germinationby dynamics of phytormones, ROS and antioxidant molecules.