A causal role for ethylene and endo‐β‐1,4‐glucanase in the abscission of red‐raspberry (Rubus idaeus) drupelets

During raspberry ( Rubus ideaus L. cv Glen Clova) fruit ripening, endo‐ β ‐1,4‐glucanase (EGase; EC 3.2.1.4) specific activity (per g fresh weight) increases approximately 15‐fold. Highest activity was associated with the surfaces of the receptacles where the weakening abscission zones are located. Immunoblotting using antibodies raised against a bean abscission‐EGase (ab.‐EGase) identified a single protein of Mr 52 kDa that was present only in ripe fruit and was most prominent in the receptacle. Using reverse transcription‐polymerase chain reaction (RT‐PCR), two 497‐bp partial putative EGase clones were obtained from ripe receptacle mRNA (termed RI‐EGL1 and 2 ) which share 53% amino acid identity. The more abundant RI‐EGL1 was used to obtain its full length clone from a ripe receptacle cDNA library. The deduced amino acid sequence of RI‐EGL1 was similar to other ab.‐EGase sequences (ca 67%) and contained the conserved motifs present in all E2‐class EGases. Northern analysis revealed that RI‐EGL1 expression was limited to ripe‐fruit receptacles. Application of the ethylene antagonist 1‐methylcyclopropene (1‐MCP) to green fruits indicated that endogenous ethylene accelerates raspberry abscission and increases both EGase activity and RI‐EGL1 expression.