Floral Senescence Research Articles

Ethylene Synthesis and Floral Senescence following Compatible and Incompatible Pollinations in Petunia inflata

Ethylene production and floral senescence following compatible and incompatible pollinations were studied in a self-incompatible species, Petunia inflata. Both compatible and incompatible pollinations resulted in a burst of ethylene synthesis that peaked 3 hours after pollination. P. inflata pollen was found to carry large amounts of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). The amount of pollen-held ACC varied in different genetic backgrounds, and the magnitude of the peak correlated with the amount of ACC borne by the pollen. Aminooxyacetic acid (AOA), an inhibitor of ACC synthesis, had no inhibitory effect on this ethylene response, indicating that pollen-borne ACC was largely responsible for the early synthesis of ethylene. After compatible pollination, a second increase in ethylene synthesis began at 18 hours, and the first sign of senescence appeared at 36 hours. Upon treatment with AOA, the second phase of ethylene production was reduced by 95%, indicating that endogenous ACC synthesis was required for this phase of ethylene synthesis. AOA treatment also delayed senescence to 6 days after anthesis. After incompatible pollination, a second increase in ethylene production did not occur until 3 days, and the first sign of senescence occurred 12 hours later. Unpollinated flowers showed an increase in ethylene production 3 to 4 days after anthesis and displayed signs of senescence 1 day later. The significance of the early and late phases of pollination-induced ethylene synthesis is discussed.

1-Aminocyclopropane-1-carboxylate synthase in tomato is encoded by a multigene family whose transcription is induced during fruit and floral senescence

The key regulatory enzyme in the biosynthetic pathway of the plant hormone ethylene is 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.1.1.14). It catalyzes the conversion of S-adenosylmethionine to ACC, the precursor of ethylene. We isolated complementary DNA sequences, ptACC2 and ptACC4, for two distinct and differentially regulated ACC synthase mRNAs expressed in ripe tomato fruit. The authenticity of the clones has been confirmed by expression experiments in E. coli. The predicted size of the encoded polypeptides (54,690 and 53,519 Da) is similar to that of the primary in vitro translation products and to the proteins found in vivo. The sequence of the gene encoding one mRNA, LE-ACC2, has been determined and its transcription initiation site defined. Four additional genes, LE-ACC1A, LE-ACC1B, LE-ACC3 and LE-ACC4, have also been identified and the sequence of their coding regions determined. The LE-ACC1A and LE-ACC1B genes are adjacent to each other and are convergently transcribed. Their encoded polypeptides are 96% identical; the identity of the other polypeptides to each other varies between 50 and 70%. The proteins predicted to be encoded by the ACC synthase genes so far cloned from tomato and zucchini contain 11 of the 12 conserved amino acid residues found in various aminotransferases involved in the binding of the substrate and the cofactor pyridoxal-5′-phosphate. The data indicate that ACC synthase is encoded by a divergent multigene family in tomato that encodes proteins related to aminotransferases.

3-AMINO-1,2,4-TRIAZOLE, A CATALASE INHIBITOR, PROLONGS CARNATION VASE LIFE.

Sim-type carnation flowers (Dianthus caryophyllus L., cv. Elliot's White) continuously treated with 50 mM or 100 mM 3-amino-1,2,4-triazole (amitrole) and held in the dark at 18°C did not exhibit a respiratory climacteric relative to dH2O-treated controls. No morphological changes symptomatic of floral senescence appeared in treated flowers until 12-15 days post-harvest. Other triazoles were not effective in prolonging senescence. Amitrole appears to inhibit ethylene biosynthesis by blocking the enzyme-mediated conversion of S-adenosyl-L-methionine to 1-aminocyclopropane-1-carboxylate. Ethylene action appears to be progressively inhibited in that flowers held in treatment solution for 2 d or less responded to application of 10 uL/L exogenous ethylene whereas flowers held 10 d or longer exhibited no response. Electrophoretic resolution of total crude extracts evidenced protein synthesis as well as degradation. Western analysis and total activity assays showed an amitrole concentration-specific inhibition of catalase activity.

Flower Longevity and Protandry in Two Species of Gentiana (Gentianaceae)

Both Gentiana saxosa and G. serotina are protandrous. When flowers open, pollen is presented extrorsely around the closed stigma for one to six days. As the stigma opens, the stamens curve toward the corolla lobes. The length of the female phase, and therefore reproductive flower life, is determined by pollination, although in both species the corolla may remain fresh for longer than one month. Fresh female-phase flowers close at night and fail to reopen on the day following pollination. After five days in the female phase, flowers reacted less quickly to pollination and seed production was reduced; flowers pollinated on their tenth day of stigma presentation produced no seed although they appeared fresh. Senescence of unpollinated flowers differed between species: in G. saxosa the flowers remained open and gradually deteriorated, but in G. serotina the flowers eventually closed before full senescence. Pollination-induced flower senescence has been demonstrated for a number of other angiosperms, and the usual reactions to pollination are corolla abscission, color change, or wilting. In Gentiana, the closed corolla enfolds the large superior ovary and may serve to protect it from predators as well as prevent further pollinator visits. Pollination-induced flower senescence probably also minimizes flower maintenance costs by ensuring that the flower functions no longer than necessary. One correlate of this phenomenon in hermaphroditic flowers is protandry, which ensures pollen dispatch before flower closure. Floral senescence may be either time-dependent (endogenous) or exogenous (usually pollination-induced). However, there have been few detailed investigations of the factors that determine floral senescence, and hence, floral longevity (Primack, 1985). Most such studies have concentrated on corolla color changes or other physiological reactions that follow pollination and signal senescence (e.g., Arditti et al., 1973; Arditti, 1976; Gottsberger, 1971; Gori, 1983; Strauss & Arditti, 1984; Casper & La Pine, 1984; Halevy, 1984), and less attention has been afforded structural changes such as wilting, flower closure, and corolla abscission (Mayak & Halevy, 1980). Most of this research is concerned with the proximate determinants of floral longevity rather than the evolution of particular responses (but see Stead & Moore, 1979; Gori, 1983; Casper & La Pine, 1984; Devlin & Stephenson, 1984). The paucity of research on the evolutionary aspect of flower senescence is somewhat surprising, because pollination-induced senescence in particular may have important consequences for the pollination system and ultimately for the plant's overall reproductive strategy. For instance, in hermaphrodite flowers pollination-induced flower senescence will limit the duration of pollen and stigma presentation and so may influence or be influenced by the extent and nature of dichogamy (Lloyd & Webb, 1986). New Zealand species of Gentiana (in the southern group of Philipson, 1972) are protandrous (Thomson, 1881; Simpson & Webb, 1980; Webb, 1 984a). Their large, relatively simple flowers make them particularly suitable subjects for experimental studies of flower function. This paper describes the response of flowers of two species to pollination and reports the results of experiments to determine the functional duration of male and female phases in terms of pollen presentation and seed production. MATERIALS AND METHODS The two species of Gentiana selected were those that grew best in cultivation. Gentiana saxosa Forster f. grows naturally in coastal sites of southern South Island and Stewart Island, New Zealand; plants were collected from Curio Bay, Southland. Gentiana serotina Cockayne occurs in grassland in inland central South Island; plants were collected from Lake Lyndon, Canterbury. The plants were grown in clay pots in an insectproof cage in greenhouses at Lincoln, Canter1 We thank I. C. Brown and garden staff at Lincoln, Canterbury, for maintaining the plants in cultivation, J. Miles for assistance with photographs, and P. Brooke for drawing Figures 2 and 3. We are grateful to L. F. Delph-Lively, E. Edgar, and D. G. Lloyd for comments on a draft of the manuscript. 2 Botany Division, Department of Scientific and Industrial Research, Private Bag, Christchurch, New Zealand. ANN. MISSOURI BOT. GARD. 74: 51-57. 1987. This content downloaded from 157.55.39.144 on Mon, 25 Jul 2016 04:48:36 UTC All use subject to http://about.jstor.org/terms 52 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 74 TABLE 1. Results of controlled pollinations to determine self-compatibility in Gentiana saxosa and G.

Polysomal Population in Relation to Ethylene Production and the Senescence of Cut Carnation Flowers and Floral Parts

Abstract Ribosomes were isolated from styles, receptacles, and petals of cut ‘White Sim’ carnation flowers (Dianthus caryophyllus L.) during flower senescence. In all flower parts the percentage of polysomes decreased for a few days after cutting and then increased coincident with the surge of ethylene production in the final stages of floral senescence. Changes in the polysomal population in petals excised from the same flower at progressive stages of its senescence were identical with those obtained from petals excised from different flowers at similar stages of senescence. The polysomal data confirm the occurrence of increased protein synthesis coincident with ethylene production and the senescence of cut carnation flowers.

Effect of Storage Temperature on Cut Flowers of Ranunculus asiaticus L.1

Abstract Postharvest life of cut Ranunculus asiaticus flowers was substantially extended with low temperature storage; 0° and 5°C were superior to higher temperatures. Extended storage duration, however, increased the rate at which floral senescence occurred upon removal from cold storage.

Changes in the Vascular Morphology of Cut Rose Stems: A Scanning Electron Microscope Study1,2

Abstract Scanning electron microscope analysis of cut rose stems revealed several types of vascular occlusions after 5 to 10 days in either water or sucrose solutions at 18°C. The number of tracheids which exhibited “blocking” at floral senescence was less than 4%. The incidence of vascular “blocking” was equivalent at the stem base, water line and neck. Breakdown of secondary tissue in the xylem was observed more frequently than other types of occlusions, but appeared only after at least 5 days. Occasionally, “blocking” materials were found protruding through the pits and end plates of tracheids. Exudate, which occasionally clogged conducting tissue at the stem base, apparently came from the phloem at the time of harvest. Other exudates, which dried immediately during the process of cutting cross sections, formed crystals which could be misinterpreted as “blocking” materials. Some tracheids in stems held in a 2% sucrose solution developed occlusions with fungal and bacterial growth or “slime plugs”. A progressive breakdown of the secondary thickening of the tracheids was found as the rose senesced. Neither leaf removal nor placement in sucrose solutions influenced the number of occlusions. The occlusions were much larger, however, after 3 days in 2% sucrose or 5-10 days in water.

EFFECT OF FLORAL AGING ON THE GROWTH OF COMPATIBLE AND INCOMPATIBLE POLLEN TUBES IN LILIUM LONGIFLORUM

Compatible and incompatible pollen tube growth in detached styles of three Lilium longiflorum cultivare varies with the physiological age of the style. Before anthesis both compatible and incompatible pollen tubes grow, in 48 hr, only a fraction of the distance compatible tubes grow after anthesis. Incompatible pollen tubes are restricted to about half the distance of compatible tubes in the four days postanthesis, but thereafter increase up to or three‐fourths or more the length of compatible tubes at the time of floral senescence. About 10 days after anthesis, growth of both types of pollen tubes decreases. The detached style method of pollen‐tube cultivation is validated in the cultivar ‘Ace’ by seed set obtained following self‐pollination in the 6‐ to 9‐day interval and failure of seed set after either self‐ or cross‐pollination after 9 days following anthesis. Also, in agreement with detached style data, self‐pollination fails to produce seeds when attempted in bud stages or the five days following anthesis. Cross‐pollinations are successful in this period. This material and technique appear well suited for study of the nature of the self‐incompatibility reaction.