Pistil-Specific and Ethylene-Regulated Expression of 1-Aminocyclopropane-1-Carboxylate Oxidase Genes in Petunia Flowers.

Abstract

The differential expression of the petunia l-aminocyclopropane-l-carboxylate (ACC) oxidase gene family during flower development and senescence was investigated. ACC oxidase catalyzes the conversion of ACC to ethylene. The increase in ethylene production by petunia corollas during senescence was preceded by increased ACC oxidase mRNA and enzyme activity. Treatment of flowers with ethylene led to an increase in ethylene production, ACC oxidase mRNA, and ACC oxidase activity in corollas. In contrast, leaves did not exhibit increased ethylene production or ACC oxidase expression in response to ethylene. Gene-specific probes revealed that the ACOl gene was expressed specifically in senescing corollas and in other floral organs following exposure to ethylene. The AC03 and AC04 genes were specifically expressed in developing pistil tissue. In situ hybridization experiments revealed that ACC oxidase mRNAs were specifically localized to the secretory cells of the stigma and the connective tissue of the receptacle, including the nectaries. Treatment of flower buds with ethylene led to patterns of ACC oxidase gene expression spatially distinct from the patterns observed during development. The timing and tissue specifieity of ACC oxidase expression during pistil development were paralleled by physiological processes associated with wproduction, including nectar secretion, accumulation of stigmatic exudate, and development of the self-incompatible response.

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

“…Developmental stages of flowers were previously described (Tang et al, 1994) with stage 5 representing anthesis. Flowers at stages 4 and 5 were emasculated prior to anther dehiscence.…”

“…The fulllength ACC oxidase cDNA pACOl (Wang and Woodson, 1992) was used as a hybridization probe following labeling with [ 32 P]dATP by random priming. Prehybridization, hybridization, and washing conditions were carried out as previously described (Tang et al, 1994). The hybridized membranes were exposed to XAR-5 film (Kodak) with an intensifying screen at -70°C.…”

“…Pollinated styles were fixed in 2% glutaraldehyde in 0.05 M KPO 4 buffer (pH 7.0) at room temperature for 3 h. Tissues were dehydrated and embedded as previously de- scribed (Cox and Goldberg, 1988), and the sections were hybridized to digoxigenin-11-UTP-labeled pACOl sense and antisense probes as previously described (Tang et al, 1994).…”

“…Ethylene is synthesized from S-adenosylmethione by the enzymes ACC synthase and ACC oxidase (Kende, 1993). The development of petunia styles is associated with an increase in the activity of ACC oxidase (Pech et al, 1987) and the expression of ACC oxidase mRNAs (Tang et al, 1994) in the stigmatic tissue. At anthesis, the petunia stigma is capable of converting applied ACC to ethylene but does not produce significant ethylene until pollinated (Pech et al, 1987).…”

“…We are interested in the regulation of ethylene biosynthesis in flowers, particularly following pollination and during senescence. In this regard we have initiated a study of the ACC oxidase gene family from petunia and its regulation (Wang and Woodson, 1992;Tang et al, 1993Tang et al, ,1994. The petunia ACC oxidase gene family consists of four members, three of which are actively transcribed.…”