Embryo responses to extreme water events provide insights into the behavior of Butia capitata (Arecaceae) seed banks during hydration cycles

Dormant seed embryos in seed banks can experience hydration cycles that subject them to water stress (WS) and then fast hydration (FH). Physiological and cytological aspects of embryos of the Cerrado (neotropical savanna) palm Butia capitata were evaluated when subjected to osmotically induced WS and FH. The water potential (psi(w)), viability, and vigor of dehydrated or hydrated embryos were determined after immersion in osmotic solutions. Embryos were submitted to FH (psi(w) =0 MPa), moderate WS (psi(w) = -1 and -2 MPa), and severe WS (psi(w) = -2 and -4 MPa). Indicators of oxidative stress (H2O2, O-2(-), MDA, and CAT, SOD, and APX activities), membrane functionality (electrical conductivity and leaching of K+, Mg2+, and Ca2+), and ABA content were evaluated. The ultrastructures of dehydrated embryos and hydrated embryos submitted to psi(w) = 0, - 1, and - 2 MPa were evaluated. Dehydrated embryos (psi(w) = - 8.5 MPa) showed high tolerance to WS that was related to their abundant protein reserves, SOD activities, and high ABA contents. Embryos tolerate FH and hydration makes psi(w) = -0.2 MPa. Hydrated embryos also show high tolerance to WS, which is related to their control of oxidative stress and increases in their ABA contents. Loss of viability under severe WS occurs associated with the blockage of protein mobilization, loss of membrane functionality, and the collapse of cellular structure. Embryo tolerance to WS and FH is crucial to the resilience of B. capitata seed banks exposed to hydration cycles in the seasonal Cerrado biome environment.