All chemicals were obtained from SigmaeAldrich (St Louis, MO,
USA) unless stated otherwise. Naphthalene acetic acid (NAA) was
used at 100 nM. N-1-naphthylphthalamic acid (NPA), from Chem
Service,was used as an inhibitor of basipetal auxin efflux at 200 nM
(Casimiro et al., 2001). Sodium hydrosulfide (NaHS)was used as the
H2S donor. Hypotaurine (HT) was regarded as an H2S scavenger at
200 mM. The concentrations of the above-mentioned chemicals
were determined in pilot experiments from which the significant
responses were obtained.