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

Abstract

In Cymbidium flowers, emasculation by removal of the pollinia and the anther cap leads within 24 hours to red coloration of the labellum (lip). Lip coloration, being the first sign of senescence in these flowers, has been ascribed to the action of ethylene in the lip. When a small incision in the base of the lip is made prior to emasculation, or when the lip is excised and placed in water within 10 to 15 hours after emasculation, coloration is considerably delayed. This indicates that a coloration-associated factor is moving in or out of the lip. Measurements of ethylene production of excised flower parts, isolated at different times after emasculation, showed an increase only in the central column; the other flower parts, including the lip, did not show a measurable change. In contrast, in situ measurements of the ethylene production of the central column and the remaining portion of the flower revealed a simultaneous increase in all the flower parts following emasculation. Similarly, application of radiolabeled 1-aminocyclopropane-1-carboxylic acid (ACC) to the top of the central column in situ leads to the production of radiolabeled ethylene by all the flower parts. In addition, the ethylene production of isolated lips, measured immediately after excision, was initially high but ceased within 10 to 15 minutes. Treatment of the central column in situ with ethylene or ethephon did not stimulate ACC production but did stimulate lip coloration and this was accompanied by an increased internal ethylene concentration in the lip. The data indicate that endogenously produced as well as applied ACC is rapidly translocated from the site of production or application to all the other flower parts where it is immediately converted into ethylene. By excision of a flower organ, the influx of ACC is prevented, causing a rapid decrease in ethylene production. In addition, it was found that ethylene may also be translocated in physiologically significant amounts within the flower. The roles of ACC and ethylene as mobile senescence or wilting factors in emasculation-and pollination-induced senescence is discussed.

1‐methylcyclopropene extendsCymbidiumorchid vaselife and prevents damaged pollinia from accelerating senescence

“…The beneficial effect of MCP on flowers with damaged pollinia is highly significant, as this form of damage occurs readily during packing and transport. There has been some debate about the nature of the transmitted signal from wounded flower parts (Woltering 1990a;Woltering et al 1995). Kwack et al (1996) showed that an inhibitor of ethylene production (aminovinylglycine) protected Cymbidium orchids from the effects of damaged pollinia.…”

“…The signal which causes accelerated senescence after pollen release is believed to be gaseous ethylene (Burg & Dijkman 1967;Woltering & Somhorst 1990;Woltering et al 1995), but other factors such as 1-aminocyclopropane-l-carboxylic acid (ACC) have been implicated (Woltering 1990a). We describe here the effect of MCP treatment of intact or damaged flowers in the presence or absence of added ethylene.…”

Interorgan regulation of ethylene biosynthetic genes by pollination.

“…ACC synthase activity has been reported to be induced in response to emasculation in the gynoecium, but not the perianth, of Cymbidium flowers (Woltering, 1989;Woltering and Somhorst, 1990). Based on results with orchids and other flowers, it has been demonstrated that ACC, synthesized in the gynoecium, is translocated to the perianth where it is converted to ethylene by ACC oxidase (Whitehead et al, 1983Woltering, 1990). Such a spatial separation of ethylene biosynthetic enzyme activities could provide the basis for interorgan coordination of the postpollination syndrome of developmental events.…”

“…Emasculation constitutes a physical perturbation that accompanies pollination, whereas ACC and auxin are two substances reported to be a component of orchid pollen (Fitting, 1909;Müller, 1953;Arditti, 1979;Stead, 1992). The role of emasculation as an important signal in the postpollination syndrome was investigated because it has been previously reported that emasculation leads to pigmentation changes, perianth senescence, and the induction of ACC synthase activity in the column, but not the perianth, of Cymbidium orchid flowers (Arditti, 1979;Woltering, 1989Woltering, , 1990Woltering and Harren, 1989;Woltering and Somhorst, 1990). In our experiments, emasculation of flowers detached from the plant resulted in both ethylene production and changes in ACC synthase and ACC oxidase mRNA abundance in most organs.…”

Aquaporin structure–function relationships: Water flow through plant living cells

“…Ethylene significantly increased stomatal conductance, root hydraulic conductivity (L p ), and root oxygen uptake in hypoxic seedlings. Ethylene can increase plasma membrane permeability permitting more water to cross the cells [106]. At the whole plant level, increased water transport in hypoxic aspen seedlings exposed to ethylene was explained in terms of enhanced aquaporin activity, probably due to a direct effect of ethylene on the phosphorylation of aquaporins [107].…”