We have previously shown that gibberellic acid (GA) plays an important role in the regulation of anthocyanin synthesis and flavonoid gene transcription in developing petunia corollas. The aim of the present work was to examine the possible role of methyl jasmonate (JA‐Me) in the regulation of these processes. JA‐Me induces anthocyanin biosynthesis and chalcone synthase (chs) and dihydroflavonol 4‐reductase (dfr) gene expression in detached corollas. JA‐Me promoted β‐glucuronidase (GUS) activity in corollas of transgenic plants carrying the gus gene driven by a chs promoter, indicating that it acts at the level of transcription initiation. Whereas chs induction by GA3 started after 5 h and was durable. that of JA‐Me was more rapid but transient. Anthocyanin synthesis was induced by wounding and this effect was enhanced by JA‐Me. Wounding also induced an increase in jasmonate content in detached corollas. The kinetics of chs and dfr mRNA accumulation following wounding was similar to that caused by JA‐Me but not to that caused by GA3. Our results suggest that JA‐Me does not play a role in the natural developmental regulation of corolla pigmentation but that it may mediate wound‐induced changes in flavonoid gene transcription.

Ethylene is known to accelerate flower senescence, but the sequence of events that links its interaction with the tissue and the final senescence symptoms is still obscure. Recently, 1‐methylcyclopropene (1‐MCP) was found to inhibit ethylene‐induced wilting in flowers. This work was carried out in order to investigate the effects of 1‐MCP on cellular senescence symptoms in petunia flowers following expossure to ethylene. Cut petunia (Petunia hybrida) flowers that were exposed to ethylene for 12 h at concentrations of 1–12 ppm wilted sooner than their untreated counterparts. This effect was abolished by a 6‐h pre‐treatment with 1‐MCP. Immediately following the ethylene treatment, decreases in petal fresh weight and total protein content were measured, along with higher electrolyte leakage, and lower membrane lipid fluidity and protein content. When applied alone, 1‐MCP had relatively little impact on these parameters. However, when the flowers were treated with 1‐MCP prior to the ethylene treatment, ethylene had no effect. These results indicate that while ethylenes effects on wilting were obvious 3 days after the treatment, cellular parameters were affected already at the end of the treatment. Since 1‐MCP repressed these early ethylene effects, it was concluded that it interferes with ethylene action in petunia flowers at a rather early stage, long before apparent wilting.

Flowers of most plants are heterotrophic and require imported carbohydrates for their development. In most cases, Suc is transported to the flower from leaves or storage organs. The flower bud is a major sink for assimilates under favorable growth conditions, whereas a shortage of carbohydrates often leads to the arrest of flower development (Halevy, 1987). The role of sugars in flower development is multifunctional: they can act as energy sources, as osmotic regulators, and as precursors for metabolic processes (Kuiper et al., 1991).Sugars play a central role in the regulation of petunia (Petunia hybrida) flower development, which requires both SUC and GA. Normal development and pigmentation of detached, intact petunia flowers can proceed only when SUC is supplied (Weiss et al., 1995). However, when the anthers are removed from the flowers, growth and anthocyanin accumulation are inhibited. These processes are restored upon application of GA, (Weiss and Halevy,

1995. Methyl jasmonate induces pigmentation and flavonoid gene expression in petunia corollas: A possible role in wound response. -Physiol. Plant. 94: 45-50.We have previously shown that gibberellic acid (GA) plays an important role in the regulation of anthocyanin synthesis and flavonoid gene transcription in developing petunia corollas. The aim of the present work was to examine the possible role of methyl jasmonate (JA-Me) in the regulation of these processes. JA-Me induces anthocyanin hiosyrrthesis and chalcone synthase (chs) and dihydroflavonol 4-reductase (dfr) gene expression in detached corollas. JA-Me promoted /(-glucuronidase (GUS) activity in corollas of transgenic plants carrj'ing the gus gene driven by a chs promoter, indicating that it acts at the level of transcription initiation. Whereas chs induction by GA, started after 5 h and was durable, that of JA-Me was more rapid but transient. .Anthocxanin synthesis was induced by wounding and this effect was enhanced by J.A-Me. Wounding also induced an increase in jasmonate content in detached corollas. The kinetics of r/!.v and dfr mRNA accumulation following wounding was similar to that caused by JA-Me hut not to that caused by GA,. Our results suggest that JA-Me does nol pia\' a role in the natural developmental regulation of corolla pigmentation but that it may mediate wound-induced changes in flavonoid gene transcription.

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