The pattern of CN-sensitive and CN-insensitive respiration was studied in young, mature and old leaves of sunflower. Leaves were infiltrated with 5mM KCN or SHAM or a combination of two to assess the presence of CN-sensitive and resistant respiration in the leaf during its ontogeny. The leaves were also treated with BA and ABA and their effect on CN-sensitive and CN-resistant respiration was recorded. Highest respiration rate was observed in young leaves followed by old and mature leaves. CN had no effect on young leaves but it inhanced respiration in mature and old leaves. SHAM reduced respiration in young leaves while in mature leaves the effect was very drastic, indicating that major portion of respiration is alternate respiration at this stage. BA increased respiration in old leaves whereas no response was noted in young leaves. ABA and SHAM decreased respiration in young leaves drastically.
