No abstract

Removal of stamens, or even of only the anthers, at an early stage of corolla development, before the start of main anthocyanin production, inhibited both growth and pigmentation of attached corollas of Petunia. When only one or two stamens were removed from one side, the inhibition was restricted to the corolla side adjacent to the detached stamens. Application of gibberellic acid (GA3) substituted for the stamens in its effect on both growth and pigmentation. In detached corollas, isolated at the early-green stage and grown in vitro in sucrose medium, GA3 promoted growth and was essential for anthocyanin synthesis. A marked enhancement of anthocyanin production was observed 48 h before the increase in corolla growth rate. Corollas detached at later stages were able to continue their growth and pigmentation in sucrose without GA3. When Paclobutrazol (β-[(4-chlorophenyl)-ethyl]-α(1,1-dimethylethyl)-H-1,2,4-triazol-1-ethanol), an inhibitor of gibberellin biosynthesis, was added to the growth medium of in-vitro-grown corollas, pigmentation was inhibited but there was no effect on corolla growth. Low levels of GA3 counteracted the Paclobutrazol effect on pigmentation but did not affect growth. The above results indicate that the effect of GA3 (and probably that of the stamens) on corolla growth is independent of its effect on pigmentation. Gibberellic acid and paclobutrazol had no effect on [(14)C]sucrose uptake by in-vitro-grown corollas. The activity of phenylalanine ammonialyase was correlated with the effect of stamens and GA3 on pigmentation in corollas grown in vivo and in vitro.

Pollination initiates a syndrome of developmental events that contribute to successful reproduction, including perianth senescence, changes in pigmentation, and ovule differentiation in preparation for impending fertilization. In orchid flowers, initiation of each of these processes in distinct floral organs is strictly and coordinately controlled by pollination, thus providing a unique opportunity to study the signals that coordinate interorgan postpollination development. Because ethylene has been implicated in contributing to regulation of severa1 aspects of postpollination development, we focused on determining the expression of its biosynthetic genes and their possible role in regulation. The abundance of mRNA encoding both 1-aminocyclopropane-l-carboxylic acid (ACC) synthase and ACC oxidase in the stigma, ovary, and labellum was found to be coordinately regulated by emasculation, auxin, and ethylene. Although petals contribute up to 26% of total flower ethylene and accumulate high levels of ACC oxidase mRNA and activity following pollination, no ACC synthase mRNA or activity was detected in this tissue. Together, these results support a model of interorgan regulation of postpollination development that depends on pollination-stimulated accumulation of mRNA encoding ethylene biosynthetic enzymes in a developmentally regulated and tissue-specific manner. This model relies on the translocation of a soluble hormone precursor, ACC, rather than on the translocation of the hormone itself. In this way, ACC serves to actuate the response already initiated by ethylene perceived by other parts of the flower. Thus, ACC may function as a secondary transmissible signal that coordinates postpollination development in diverse floral organs.

No abstract

The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporaDly with petal-inroDling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or amino- is disruption of membrane integrity and loss of intracellular compartmentation. Kende et al. (3,28) have noted a strong correlation between membrane leakiness and phospholipid breakdown in senescing flowers. Moreover, treatment of Tradescantia with ethylene accelerates the onset of membrane leakiness and phospholipid deterioration in petals, but the ethylene effect is dependent upon synthesis of new protein (28). Borochov et al. (6,7) have reported that the microviscosity of plasma membranes from rose petals rises with advancing senescence in a manner that correlates with an increase in sterol:phospholipid ratio reflecting phospholipid breakdown.Senescing carnation flowers exhibit a climacteric-like rise in ethylene production (5,17,20). In addition, exposure of carnation flowers to exogenous ethylene induces inrolling of the petals and results in increased ethylene synthesis (10, 24, 26). In the present study, we have used cut carnation flowers to examine the ability of ethylene to induce chemical and physical changes in microsomal membrane lipids of senescing petals. MATERIALS AND METHODSPlant Material. Carnation flowers (Dianthus caryophyllus L. cv. White Sim) were grown in raised beds in a greenhouse according to established culturing procedures. Mature flowers were cut at the commercial stage of development (fully open with a yellowish tinted center) and either used directly for membrane isolation or trimmed to an 8 cm stem length and placed individually in 20-ml vials containing either deionized water or test solutions. Flowers held in water or test solutions were maintained at 22°C, and the levels of water or test solutions were adjusted as necessary to 1 cm below the calyx.Treatments. For treatment with ethylene, flowers were placed in deionized H20 in specially constructed Plexiglas chambers (135 L capacity) equipped with an internal fan to promote circulation, two ports for gas flow, and a removeable front panel. Exposure to ethylene was achieved by injecting ethylene into the chambers to a final concentration of 1 ,pl/l. Throughout the exposure, the chambers were connected to an air stream containing 1 ,ld/l ethylene that was flowing at 20 ml/min. Chambers containing control flowers were flushed at the same rate with air that had been rendered ethylene-free by passage through potassium permanganate coated with aluminum silicate (Purafil, Chamblee, GA). Ethylene treatments were terminated by removing the flowers from the chambers t...