CHANGING PATTERNS IN THE RESPONSE TO CYANIDE OF ARUM MITOCHONDRIA OXIDIZING MALATE AND OTHER SUBSTRATES.

Over a flowering season of 7 weeks, mitochondria from the spadices of Arum maculatum showed a progressive increase in the rate at which added malate was oxidized from less than 20 nmoles mic[sup-1] mg protein[sup-1] to more than 700 nmoles min[sup-1] mg protein[sup-1]. In the oxidation of succinate, α-ketoglutarate and other substrates, much smaller differences in rate were found. Mitochondria oxidizing malate responded to the addition of high (3.8 mM) concentrations of cyanide by stimulation when their initial rate of malate oxidation was low and by inhibition when it was high. Stimulation by KCN even with high concentrations did not increase the O[sub2] uptake rate of young spadices to the level of mature ones. Associated with this alteration in response to cyanide was a reverse response to ADP. The early, slowly respiring mitochondria which were stimulated by KCN were often inhibited by ADP while the mitochondria from later spadices which were inhibited by KCN were usually stimulated by ADP. Similar variations in the relative rate of malate oxidation, response to cyanide and to ADP were observed in mitochondria prepared on the same day from spadices at different stages of development from the same location. In this case the change from young (β) to fully matured (∊) spadices approximately paralleled those from the early season to the end of the flowering period. The changes in malate metabolism of the spadix mitochondria were not solely related to stage of spadix development, however, since those from spadices at the same apparent developmental stage gathered over a 5-week period also showed an increase in the rate of malate oxidation and a change in response to cyanide and ADP. [ABSTRACT FROM AUTHOR]