We analyze here the impulsive phase of the 2001 August 25 eruptive flare (X5.3, S21, E38) in order to reveal the link of the time evolution of the magnetic-field reconnection rate φ ˙ (t) with the energy-release process, as quantified by electron and proton acceleration to high energies. Hard X-rays and γ -rays from 150 keV to 100 MeV were observed by the SONG (SOlar Neutrons and Gamma) detector onboard the CORONAS-F (Complex ORbital ObservatioNs of the Active Sun) mission. The soft X-ray derivative d I SXR / d t was used as a proxy for the flare energy release that revealed itself as a sequence of acceleration pulses. The reconnection rate φ ˙ (t) was calculated previously from flare-ribbon observations in EUV and coaligned magnetic-field maps. The γ -ray emission spectra were obtained from SONG data. All spectra contain both bremsstrahlung and γ -ray lines. The bremsstrahlung spectrum extends to tens of MeV. The pion-decay gamma-ray emission, being a manifestation of proton acceleration to subrelativistic energies, appeared for the first time in the time interval of the φ ˙ (t) maximum. This maximum was ahead of the maxima of d I SXR / d t as well as of all other emissions by about one minute. Proton acceleration to subrelativistic energies is confirmed by detection of solar neutrons by SONG and the Chacaltaya neutron monitor. [ABSTRACT FROM AUTHOR]