Alterações fisiológicas e citológicas em resposta ao estresse hídrico em embriões de Butia Capitata (Arecaceae)

Abstract

Butia capitata, popularly known as coquinho-azedo, is a palm tree that occurs in the Cerrado biome. Its fruits are used in the manufacture of juices, ice cream, liqueurs and beer, as well as a source of food for the native fauna. Its exuberance gives it potential for use in landscape projects. Because it is a species that tolerates desiccation, it can form seed banks in the soil. However, irregular rains and the occurrence of fires in their habitat may subject the seeds to severe water stress, and thus impair their germination and establishment of the seedlings. Adjustment of embryo metabolism to hydration and drying cycles is crucial for the persistence of seed banks. The objective of this work was to evaluate physiological and cytological aspects in embryos of B. capitata, palm adapted to semi-arid environments, under osmotically induced water stress. The variation of the mass, water potential, viability and vigor of dehydrated or hydrated embryos were measured after immersion in osmotic solutions with different water potentials (ψ) (0; -2; -4; -6; -8 and -10 MPa for dehydrated embryos and 0; -0.5; -1; -2; -3 and -4 MPa for hydrated embryos) at times 0, 12, 24 and 36 hours (change in mass and ψ) and at time 12 hours (viability and vigor). Based on the results, ψ that simulated a non-stressing condition (0 MPa), moderate water stress (-1 and -2 MPa) and severe water stress (-2 and -4 MPa) were selected. Under these conditions, oxidative stress (H2O2, O2-, MDA and CAT, SOD and APX), membrane functionality (electrical conductivity and leaching of K+ ions, Mg2+ and Ca2+) and ABA quantification were evaluated. The ultrastructure of dehydrated embryos and hydrated embryos submitted to ψ = 0, -1 and -2 MPa was evaluated. Dehydrated embryos (-8.5 MPa) present high tolerance to water stress, which is related to the abundance of lipid and protein reserves, SOD activity and high ABA content. Embryos tolerate rapid hydration and hydration does ψ = -0.2 MPa. Hydrated embryos also present high tolerance to water stress, which is related to the control of oxidative stress and increase of ABA content. Loss of viability, under severe water stress, is associated with blockade of protein mobilization, loss of membrane functionality and cellular destruction. The resistance of the embryos to water stress favors the maintenance of seed banks of B. capitata in environments with a seasonal climate of the Cerrado biome.