Exogenous gibberellins inhibit coffee (Coffea arabica cv. Rubi) seed germination and cause cell death in the embryo

The mechanism of inhibition of coffee (Coffea arabica cv. Rubi) seed germination by exogenous gibberellins (GAs) and the requirement of germination for endogen-ous GA were studied. Exogenous GA417 inhibited coffee seed germination. The response to GA417 showed two sensitivity thresholds: a lower one be-tween 0 and 1 lM and a higher one between 10 and 100 lM. However, radicle protrusion in coffee seed depen-ded on the de novo synthesis of GAs. Endogenous GAs were required for embryo cell elongation and endosperm cap weakening. Incubation of coffee seed in exogenous GA417 led to loss of embryo viability and dead cells were observed by low temperature scanning microscopy only when the endosperm was surround-ing the embryo. The results described here indicate that the inhibition of germination by exogenous GAs is caused by factors that are released from the endo-sperm during or after its weakening, causing cell death in the embryo and leading to inhibition of radicle protrusion