Influence of thidiazuron, ethylene, abscisic acid and dark storage on the expression levels of ethylene receptors (ETR) and ACC synthase (ACS) genes in Pelargonium

Expression of ACC synthase and ethylene receptor (ETR) genes were evaluated in different organs of Pelargonium and in response to treatment of leaves with TDZ, ethylene, ABA or exposure to darkness. To isolate unknown ACS genes, a degenerate primer pair was used to amplify three DNA fragments using genomic DNA from Pelargonium leaves. Sequence analysis of two novel partial putative ACC synthases led to their designation as PzACS3 and PzACS4. Gene-specific primers were constructed and synthesized commercially using already published ACC synthase genes, ethylene receptor genes and the two novel putative ACC synthase genes. Expression studies were done using semi-quantitative RT-PCR. The previously isolated ACC synthase genes (pGAC-1 and GACS2) were expressed in most of tissues examined in cultivar 'Katinka' except in roots and petals, respectively. PzACS3 and PzACS4 genes were expressed and undetectable in roots, respectively whereas ethylene receptor gene (PhETR1) was strongly expressed in roots and buds. PhETR2 was constitutively expressed. Transcripts of pGAC-1, GACS2, PzACS3, PzACS4, PhETR1 and PhETR2 genes were expressed in a treatment-specific fashion and correlated positively with ethylene production after treatments except, 2 mu l l(-1) ethylene, which had inhibitory effect. Ethylene had no effect on expression of all investigated genes whereas ABA and dark storage increased pGAC-1 and GACS2 transcripts, respectively. TDZ treatment resulted in a higher expression of the negative acting ethylene receptor, PhETR1, thus it could have reduced sensitivity of Pelargonium leaves to ethylene with concomitant beneficial effect of delaying the onset of leaf yellowing.