Temporal and Spatial Regulation of 1-Aminocyclopropane-1-Carboxylate Oxidase in the Pollination-Induced Senescence of Orchid Flowers

Abstract

Pollination of many flowers initiates a sequence of precisely regulated developmental events that include senescence of the perianth and development of the ovary. The plant hormone ethylene is known to play a key role in regulating the biochemical and anatomical changes that constitute the postpollination syndrome. For this reason, we have studied the pollination syndrome in Phalaenopsis orchids by examining the spatial and temporal location of ethylene biosynthesis within the orchid flower, and how this biosynthesis is regulated by factors that influence expression of genes that encode key enzymes in the ethylene biosynthetic pathway. In particular, we examined the role in the postpollination syndrome of the expression of the gene for l-aminocyclopropane-1-carboxylate (ACC) oxidase, which catalyzes the conversion of ACC to ethylene. In vivo incubation of tissues with the ethylene precursor ACC demonstrated that ACC oxidase activity increases after pollination in the stigma, contrary to the observation that activity is constitutive in petunia and carnation gynoecia. RNA blot hybridization of floral tissues indicates that the increase in ACC oxidase activity is due to de novo synthesis of mRNA and presumably protein, which is induced after pollination. Furthermore, the pattern of induction is consistent with a model of coordinate regulation of gene expression in which the pollination signal travels to other organs of the flower to induce their ethylene production. We have also used in situ hybridization to define further the temporal and spatial expression of ACC oxidase within the floral organs, showing that expression, and, by inference, the capability to oxidize ACC to ethylene, is induced in all living cells of the tissues examined after pollination. These findings contrast with work in petunia that suggests that ACC oxidase is localized to the stigmatic surface.It has been recognized for many years that pollination of flowers greatly accelerates senescence of nonessential floral organs such as the petals and sepals (Borochov and Woodson, 1989). Pollination of the flower results in an increase in ethylene production, which is thought to coordinate the senescence process and which may play a role in other aspects '

1-Aminocyclopropane-1-Carboxylate Oxidase Activity Limits Ethylene Biosynthesis in Rumex palustrisduring Submergence

“…In many species, ACC oxidase gene activity is positively regulated at the transcriptional level by ethylene (Drory et al, 1993;Nadeau et al, 1993;Kim and Yang, 1994;Tang et al, 1994;Peck and Kende, 1995;Barry et al, 1996;Mekhedov and Kende, 1996). RP-ACO transcript levels were also strongly induced in R. palustris by ethylene treatment (Fig.…”

Expression of 1-Aminocyclopropane-1-Carboxylate Oxidase during Leaf Ontogeny in White Clover1

“…Of particular significance is the view that the expression of the ACC oxidase gene family, like that of ACC synthase genes, is highly regulated in plants and constitutes an extra tier of control of ethylene biosynthesis. Differential expression of ACC oxidase genes has been observed in orchid flowers (Nadeau et al, 1993), mung bean epicotyls (Kim and Yang, 1994), petunia floral tissues (Tang et al, 1994;Tang and Woodson, 1996), broccoli floral tissue (Pogson et al, 1995), tomato (Barry et al, 1996) …”

“…Of particular significance is the view that the expression of the ACC oxidase gene family, like that of ACC synthase genes, is highly regulated in plants and constitutes an extra tier of control of ethylene biosynthesis. Differential expression of ACC oxidase genes has been observed in orchid flowers (Nadeau et al, 1993), mung bean epicotyls (Kim and Yang, 1994), petunia floral tissues (Tang et al, 1994;Tang and Woodson, 1996), broccoli floral tissue (Pogson et al, 1995), tomato (Barry et al, 1996) and melon leaf tissues (Lasserre et al, 1996(Lasserre et al, , 1997, carnation floral tissues (ten Have and Woltering, 1997), sunflower seedling tissue (Liu et al, 1997), geranium floral tissue (Clark et al, 1997), and leaf tissue of Nicotiana glutinosa (Kim et al, 1998). However, compared with fruit and floral tissue, fewer studies have been undertaken of the regulation of ACC oxidase gene expression during leaf development (John et al, 1995;Barry et al, 1996;Lasserre et al, 1996;Bouquin et al, 1997;Kim et al, 1998), even though ethylene is considered an important regulator of leaf ontogeny in higher plants (Osborne, 1991).…”

Nucleotide Sequence of a cDNA Encoding 1-Aminocyclopropane-1-Carboxylate Oxidase from Senescing Orchid Petals

“…This cDNA was used to demonstrate that ACC oxidase is regulated at the leve1 of transcript abundance in both the stigma and petals following pollination (Nadeau et al, 1993). Here we present the sequence of a second ACC oxidase cDNA (D-AC02), which was isolated from a library containing transcripts from the senescing perianth of Doritaenopsis orchids (Table I).…”