Pollination and stigma wounding: same response, different signal?

In Petunia hybrida flowers, both pollination and stigma wounding induced a transient increase in ethylene pro­ duction and hastened corolla senescence. Ethylene production by different flower parts was measured in situ using laser photoacoustic (LPA) spectroscopy. In pollinated flowers, ethylene was exclusively produced by the stigma/style region whereas wounding of the stigma induced ethylene production both by the stigma/style region and by the remaining flower parts. In aminoethoxyvinylglycine (AVG)-treated flowers, sub­ sequent treatment of the unwounded stigma with 1«aminocyclopropane-1-carboxylic acid (ACC) induced ethylene production exclusively by the stigma/style region whereas treatment of a previously wounded stigma with ACC induced a simultaneous increase in ethylene production by the stigma/style region and the remaining flower parts. These results suggest that following stigma wounding, either ACC or ethylene is involved in inter-organ communication. Following pol­ lination, the signal is apparently not directly related to ethylene. In vivo ACC oxidase activity of most flower parts, including the gynoecium, was higher in light than in dark. Light or dark did not influence the relative contri­ butions of stigma/style and remaining flower parts to the total pollination, wounding or ACC-induced ethy­ lene production, indicating that ACC is not transloc­ ated. Both in excised styles and intact flowers, radiolabelled ACC and its analogue a-amino/sobutyric acid (AIB), applied either to an intact or wounded stigma, were largely immobile confirming that ACC is not likely to play a role in inter-organ signalling. The results collectively suggest that following stigma wounding, translocation of ethylene may be the signal responsible for initiation of corolla senescence; following pollination the signal is not directly related to ethylene.