Lack of Control by Early Pistillate Ethylene of the Accelerated Wilting of Petunia hybrida Flowers

Abstract

Well before pollen tube penetration, ethylene has begun to disseminate from pollinated styles of Petunia hybrida flowers. Previous stigmatic application of aminoethoxyvinylglycine (AVG) completely prevented this ethylene synthesis, indicating that the endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen is not readily converted on the stigma. Compared to other flower parts, the capacity of the ethylene forming enzyme was largest in the stigma. When applied to the stigma, ACC caused ethylene synthesis, but did not accelerate wilting, unless high concentrations (20 nanomols) were used. Upon pollination or stigma wounding, the early ethylene evolved exclusively from the gynoecium, much later followed by the synthesis of corolla ethylene. Employing wideneck Erlenmeyer flasks, the competitive inhibitor of ethylene action, norbornadiene, was applied to entire flowers in situ, with delaying effects on wound-induced wilting. In contrast, norbornadiene treatment of styles alone, using capillaries, could not postpone wilting. Pollination with foreign pollen species did not lead to accelerated corolla wilting, notwithstanding considerable synthesis of ethylene during the frst 5 hours. In situ treatment of the stigma with AVG considerably delayed wound-and pollination-induced wilting. Removal of the entire AVG-treated style 6 hours after stigma wounding still allowed for the postponement of the accelerated wilting, even at very low concentrations of AVG. It is concluded that early stylar ethylene does not play a role in the acceleration of wilting but that, much later, corolla ethylene does, induced by a mobile wilting factor from the stigma, which is ACC. levels ofthe immediate precursor, ACC' (24). The sequential rise in ACC content of carnation stigmas, ovaries, receptacles, and petals upon pollination strongly suggests that ACC might be the mobile wilting stimulus (12). Pollen itself might be the trigger in this respect as it sometimes contains large amounts of ACC (F.

Interorgan Translocation of 1-Aminocyclopropane-1-Carboxylic Acid and Ethylene Coordinates Senescence in Emasculated Cymbidium Flowers

“…It may therefore be concluded that the transported signal is not ACC but, rather, ethylene itself may be translocated or the lip may become more sensitive to ethylene following emasculation. The latter would meet our expectations as the existence of (mobile) ethylene-sensitivity factor(s) has also been suggested in cyclamen, petunia, and carnation flowers (7,9,13,19).…”

“…On the contrary, they found that AVG (applied onto the stigma) was a very effective inhibitor of pollination-induced senescence even when the entire style was removed before the AVG could have reached the corolla. This made Hoekstra and Weges (9) conclude that, although direct proof was lacking, ACC may nevertheless be the transported wilting factor in Petunia. Pollination-induced corolla abscission in Digitalis was also not accompanied by an increased ethylene production in (isolated) corollas (18).…”

Interorgan regulation of ethylene biosynthetic genes by pollination.

“…On the other hand, a model of auxin as the initia1 pollination signal has been proposed by Burg and Dijkman (1967) in which auxin from the pollen diffuses through the stigmaand stylar tissueof the column where it stimulates ethylene production as it moves, with the ethylene in turn directly triggering perianth senescence. Similarly, exogenous application of ACC results in a burst of ethylene production in many flowers, but this alone is not sufficient to elicit the full syndrome of postpollination development (Hoekstra and Weges, 1986) and instead leads to rapid cellular degradation throughout the flower (Zhang and ONeill, 1993). Although ethylene itself clearly plays an important role in coordinating interorgan postpollination development, ethylene alone is not sufficient to trigger initiation of ovary development and ovule differentiation in orchid flowers.…”

Temporal and Spatial Expression of 1-Aminocyclopropane-1-Carboxylate Oxidase mRNA following Pollination of Immature and Mature Petunia Flowers

“…It has been suggested that germination and growth of pollen tubes play a role in the elicitation of ethylene production by petunia styles (Hoekstra and Weges, 1986). We examined the germination and growth of pollen tubes on stigmas of stage 1 and stage 5 flowers to determine whether differences could account for the delay in pollination- induced ethylene production.…”

“…However, the role for pollen-held ACC in pollination-induced ethylene has been questioned. Treatment of stigmas with aminoethoxyvinylglycine, an inhibitor of ACC synthase, prevents the increase in ethylene following pollination (Hoekstra and Weges, 1986), indicating that de novo synthesis of ACC is necessary for the increase in ethylene. In addition, pollination leads to a rapid increase in ACC synthase activity in pollinated petunia styles (Pech et al, 1987).…”