Recent studies indicate that global temperatures will rise substantially in the

21st century, leading to the extinction of several plant species, as plant metabolism and

germination are greatly affected by temperature. Melanoxylon brauna, a tree species native

to the Atlantic Forest that occurs from northeastern to southeastern Brazil, is one of the many

species threatened by global warming. Despite the economic and ecological importance

of M. brauna, studies investigating the influence of heat stress on seed germination and

biochemical responses are still incipient. This study aimed to evaluate enzyme activity in the

micropylar region of M. brauna seeds during germination under heat stress conditions. Endo-

β-mannanase, α-galactosidase, polygalacturonase, pectin methylesterase, pectin lyase, total

cellulase, 1,3-β-glucosidase, and 1,4-β-glucosidase activities were determined in micropyles of

seeds imbibed for 24, 48 and 72 h at 25, 35 and 45 °C. Seed germination was highest at 25 °C.

Endo-β-mannanase activity was not detected under any of the experimental conditions, but

imbibition temperature had a significant effect on the activity of all other enzymes.