Regulation of ethylene biosynthesis in reproductive organs of damson plum (Prunus domestica L. subsp Syriaca)

In this paper, ethylene production, ACC quantification, and the determination of ACC-oxidase (ACO) activity and the transcript levels PdACS1, PdACO1, and PdACO2, have been evaluated in different parts of developing flowers (sepals, petals, stamens, and pistils) and fruits (epicarp, mesocarp, and seed) of damson plum (Prunus domestica L. subsp. Syriaca), which is a drupe. The fertilized pistil was the only floral organ to register net ethylene production. PdACS1 mRNA was detected exclusively in the stamen. Regarding PdACO1 and PdACO2 transcription, at pre-anthesis, anthesis, and post-anthesis, it was found that: (a) both genes were expressed in all studied floral organs, but accumulation of PdACO1 transcripts was consistently higher; (b) anthesis provoked a sharp accumulation of PdACO1 in sepals, petals, and stamens, while in the pistil no changes occurred; (c) an increase of PdACO2 transcription occurred in sepals concomitantly with anthesis; (d) pollination appeared to activate the transcription of PdACO1 in the pistil. The whole fruit of this plum produced ethylene only at the beginning of S1 and in S4 (climacteric), while the seed produced it at the end of the S1 and throughout S2, when a great richness in ACC and high ACO activity occurred. PdACS1 expression was detectable in the whole fruit at the beginning of development and in the epicarp and mesocarp during ripening. No expression of PdACS1 has been detected in isolated seeds. Even though the transcript for PdACO2 was temporal and spatially absent in fruit development, mRNA levels of PdACO1 notably changed. In the seed, the higher transcriptional activity of PdACO1 appeared at the end of phase S1. The greatest amounts of ACC were registered in the ripening mesocarp and epicarp. Whereas PdACO1 mRNA was detected in the mesocarp at the middle of S1, during the breaker stage (S3), and at the end of the climacteric phase (S4), in epicarp the expression occurred only in S4 stage. These results clearly demonstrate that the seed actively participates in ethylene production during the first phase of damson plum development.