Molecular control of ethylene production by cyanide in Arabidopsis thaliana

Although cyanide has long been recognized as a co-product of ethylene synth esis, little attention has been given to its potential physiological and mo lecular roles. in the present work, the long-term effects of cyanide on gro wth and development were observed in Arabidopsis thaliana, Two days after a single 20-min application of cyanide, plants demonstrated visible signs of stress. Long-term detrimental effects on growth and photosynthetic capabil ities were noted, including low chlorophyll accumulation and stunted growth . Because of the relationship between cyanide and ethylene production, we c hose to evaluate the results of cyanide treatment on genes encoding protein s involved in ethylene synthesis. We have found that only the 1-aminocyclop ropane-1-carboxylic acid (ACC) synthase gene, ACS6, is rapidly activated in response to cyanide treatment, while other ACS genes were unaffected. This same gene has previously been shown to be transcriptionally activated in r esponse to touch and other environmental stimuli. Cyanide was capable of ac tivating ACS6 transcription within 10 min of treatment, and the amount of t ranscript correlated positively,vith the cyanide dosage. Due to the toxic n ature of cyanide, plant in vivo concentrations are generally maintained low er than 10 mu M, but can increase under certain stresses. In the present wo rk, we observed that physiologically relevant concentrations as low as 1 mu M HCN, considered metabolically 'safe', were capable of initiating ACS6 tr anscription, ACS6 transcripts were not substantially reduced as a result of multiple cyanide treatments, which is in contrast with the effects of mech anical stimulation on transcription. Our results suggest a relationship bet ween cyanide production during ethylene synthesis and the molecular control of ethylene synthesis. This work corresponds with earlier experiments that have demonstrated that ethylene and cyanide can elicit some similar physio logical responses. It is possible that cyanide may play an active role in e thylene regulation under conditions where rapid cyanide accumulation occurs . Since cyanide can rapidly activate ethylene synthesis, it is possible tha t it is involved in the positive-feedback regulation of ethylene that occur s in some plant tissues.