LITERATURE REVIEW

Cattleya

Cattleyas were among the first tropical orchids to come into cultivation. Their culture is often used as the basis for comparison with other types of orchids, being highly prized for their large blooms. They have well-adaptation to their habitat organs include thickened stems for food storage called pseudo-bulbs, roots that cling to the substrate to hold the plant in place, and thick, leathery leaves that transpire little water (Rittershausen, 1999; Ombrello, no date).

1. Origin Most of the Cattleyas have been developed from plants native of the America’s,

especially Central and South America. The species range through tropical across the Panama Isthmus as far north as the rainforests of Mexico, but the best are found in the steamy Brazilian rainforests. The epiphytic or air plants grow on the trunks and stout branches of the forest trees, in their wild state existing for hundreds of years, growing into huge clump several metres across (Rittershausen, 1999). The flower was introduced to England, when in 1818; William Cattleya imported some tropical plants from Brazil. In 1821, the genus was named Cattleya by the plant taxonomist, John Lindley (Bechtel et. al, 1992; Papp, 2004).

While the number of Cattleya species is comparatively small, they are so closely related to other genera in the alliance that much interbreeding has taken place, resulting in many intergeneric hybrids. The first Cattleya cross, Cattleya hybrida, appeared in 1857. It was the first tropical hybrid to be recognized by the Royal Horticultural Society, who awarded it a first class certificate. During the first half of the twentieth century cattleyas were in great demand as cut flowers and today they are cultivated by a growing band of devotees. Due to their size and irregular flowering habits, they have not

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entered the pot-plant trade in large number, but will be found in specialist nurseries (Rittershausen, 1999).

The Cattleya has ventured a long way since it was first seen and the beginning of hybridization to produce some of the most flamboyant, largest, best scented, and colorful flowers amongst the Cattleya family. Eventually it became the “florists orchid” or more commonly known as the “Corsage orchid” (Papp, 2004).

Cattleyas have been the most hybridized, and has resulted in a treasure of beautifully colored flowers available in almost any color except blue and black; there are no blue or black orchids of any kind. The intermarriages between Cattleya and other genera such as Laelia, Brassavola, Sorphronitis and many more has produced plants far removed from the original Cattleya species of decades ago (Papp, 2004).

2. Classification Cattleya is classified Kingdom Plantae, Division: Magnoliophyta, Class:

Liliopsida, SubClass: Liliidae, Order: Asparagales, Family: Orchidaceae, Subfamily: Epidendroideae, Tribe: Epidendreae, Subtrip: Laeliinae and Genus: Cattleya (Bechtel et. al, 1992; http://en.wikipedia.org/wiki/Cattleya).

There are approximately 53 species of Cattleya from Mexico to South America (see Appendix). The genus is divided into two groups; bifoliate and monofoliate cattleyas. The first group, such as Cattleya trianae, is found in Mexico and Brazil while the latter one, such as Cattleya bicolor, is found in Brazil, Columbia, Panama, Peru and Venezuela. Bifoliate Cattleya contains two broad leaves growing from each pseudobulb. Monofoliate Cattleya, on the other hand, contains only one, narrower and more erect leaf originating from each pseudobulb.

The typical flower has three rather narrow petals: two are fringed; the third is the conspicuous lip with a fringed margin and various markings and specks. At the base, the fringed margins are folded into a tube. Each flower stalk originates from a pseudobulb. (http://en.wikipedia.org/wiki/Cattleya)

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3. Botanical The Cattleya is either epiphytic or lithophytic. The stems are thickened called

pseudobulb and have one or two leaves at apex of each. The Leaves are usually thick and coriaceous or fleshy. The Inflorescence occurs at terminal (one flower) or racemose as peduncle usually subtended by a large spathaceous sheath. The Sepals are free or more or less equal and fleshy. The Petals are mostly much broader than sepals and less fleshy. The Lip is sessile, erect, free or rarely to column-base and enfold column. The Column is usually long, wingless, semiterete, arcuate as anther terminal, and has somewhat compressed to four pollinia. The Capsule is ellipsoidal (Bechtel et. al, 1992). Disection of Cattleya flower (Appendix figure1.)

4. The culture

The Cattleyas are epiphytes and called “tree dwellers” as they inhabit the branches of trees and sometimes barren rocks. Their nutrition is derived from the atmosphere or from decaying organic matter that accumulates on branches or in crotches between limbs so they are not parasites of trees. Cattleyas thrive in this nutrient poor and freely draining medium (Ombrello, no date). Cattleya orchids are slow-growing, taking 5-7 years or more to flower from seed since most produce relatively few and large flowers at maturity (Ombrello, no date). There are long-lived perennials and will usually flower annually. Commercial growers maintain plants for 8-10 years before replacing them (http://en.wikipedia.org/wiki/ Cattleya). The Culture is relatively straightforward for orchids, and they are considered by many to be the archetypical epiphytic "orchid" in that they require very well-drained media, frequent wet/dry cycles, good air circulation, moderate light and temperature, judicious watering and an occasional dose of fertilizer (Ombrello, no date; http://en. wikipedia.org/wiki/Cattleya).

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In nature, Cattleyas start off life as tiny seeds within a seedpod or capsule on the mother plant. When the seedpod matures and splits open, Cattleya seeds are released and dispersed by the wind. The germination is occurred when seeds fall on a suitable medium and contact with a microscopic fungus. The fungus converts complex starches to simple sugars that seeds can use for energy. Cataleyas could be growth with artifical mediums that supply the necessary nutrients in a small flask.

In recently, Cattleyas are propagated by tissue culture technique. Tissue from growing point of single shoot can yield hundreds of identical plants. Conventional methods, asexual propagation, would take many years to accomplish and will probably lead to an almost unimaginable variety of types in the future (Ombrello, no date).

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Ethylene

1. Introduction

Ethylene (C2H4) is a simple organic molecule gas with biological activity. This molecule gas, regulates various plant physiological processes, the growth and development of plants initial germination to senescence, including seed germination, root hair development, root nodulation, flower and leaf senescence, responsiveness to stress and pathogen attacks, abscission and fruit ripening (Johnson and Ecker, 1998). The ethylene molecule isn’t direct in effect to plant physiological processes but it result from action together of ethylene, receptor protein and some metal ions to stimulate gene expression into other responsive aspect many physiological process (Brady and Speirs, 1991). In general, plant tissues produce few amounts ethylene. The production of ethylene is induced by internal signal during development and in response to environmental stimulant from biotic stress, such as pathogen attack or insect attack and abiotic stress, such as wounding, flooding, drought, chilling injury, auxin and auxin inhibitor treatment (Theologis, 1992). These factors activate to ethylene production in normal state of plant.

2. Ethylene Biosynthetic Pathway

The pathway for ethylene biosynthesis was elucidated by Yang and Hoffman (1984). The precursor of ethylene is methionine, which plants produce itself. Methionine is converted to S-adenosyl-L-methionine (SAM or AdoMet) by the enzyme methionine-s-adenosyl transferase with adenosine triphosphate (ATP). Then SAM is converted to 1-aminocyclopropane-1-carboxylic acid (ACC) and 5-methylthioadenosine (MTA) is recycled through the pathway by converting to methionine (Figure 1.). ACC is converted to ethylene, CO2 and HCN by ethylene forming enzyme (EFE) or ACC oxidase. In oxygen state use cofactor, Fe2+ ion and ascorbic acid (John, 1997). The CO2 and HCN are converted to β-cyanoalanine for protection to toxic substance, HCN, accumulator. In

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addition, ACC is also converted to 1-(malonylamino) cyclopropane-1-carboxylic acid (MACC) (Kende, 1993).

Figure 1. The ethylene biosynthetic pathway of higher plants. Source : Arshad et al., 2002

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3. Ethylene forming enzyme (EFE) or ACC oxidase The last step in ethylene pathway is the conversion of ACC to ethylene. Since this

step requires O2, the enzyme is also called ACC oxidase which is a bisubstrate enzyme. It requires both O2 and ACC as substrates (Abeles et al, 1992; Hooykass et al., 1999; Arshad and Frakenberger, 2002). In addition, ascorbic acid, bicarbonate, ferrous ion and dioxygen were required for activity of this enzyme. The ACC oxidase is classified as a nonheme Fe (II) enzyme (Rocklin et al., 1999). The production of ethylene in vivo was inhibited by several types of chemicals including analogs of ACC, uncouplers of oxidative phosphorylation, free-radical scavengers, metal chelators sulfhydryl reagents and heavy metal ions action on the conversion of ACC to ethylene (Yang and Hoffman, 1984). The metal ions, Co2+, Cu2+ and Zn2+, are more effective in inhibiting ACC oxidase activity. They might replace Fe2+ and forming inactive enzyme-metal complexes (Arshad and Frakenberger, 2002).

4. Regulation of Ethylene Production

In ethylene synthesis pathway, ACC oxidase and ACC synthase, are highly regulated. Two systems of ethylene regulation in higher plants, system I and system II, have been proposed. In system I, ethylene is an auto-inhibitor controlling the basal levels of ethylene production in non-ripening climacteric fruits and vegetative tissues of both climacteric and non-climacteric fruits. In system II, ethylene acts as auto-stimulator. It operates during ripening of climacteric fruits and petal senescence. The mechanisms of regulation in system II require the induction of ACC synthase and ACC oxidase (Yang and Hoffman, 1984; Nakatsuka et al., 1998; Alexander and Grierson, 2002).

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Senescence 1. Introduction

Senescence is a pervasive developmental process operating at many stages

and levels during the life cycle of an organism. It has an important function in cell differentiation, not only in the most obvious example of xylem differentiation, but also in other cases such as the development of leaf lobing patterns and the breakdown of specialized cells in the embryo and the female gametophyte. Its function at the organ level is illustrated by senescence of leaves, flower parts, and fruits. Perhaps, the most remarkable senescence is the post reproductive senescence of the whole organism (Noodén, 1988).

Alteration of plastid structure and function in senescence are often reversible and it is argued that such changes represent a process of transdifferentiation or metaplasia rather than deterioration. It may be that the irreversible senescence of many flowers and some leaves represents the loss of ancestral plasticity during evolution. Reversibility serves to distinguish senescence fundamentally from programmed cell death (PCD), as does the fact that viability is essential for the initiation and progress of cell senescence. Senescence, particularly its timing and location, requires new gene transcription, but the syndrome is also subject to significant post-transcriptional and post-translational regulation. The reversibility of senescence must relate to the plastic, facultative nature of underlying molecular controls. Senescence appears to be cell-autonomous, though definitive evidence is required to substantiate this. The vacuole plays at least three key roles in the development of senescing cells : it defends the cell against biotic and abiotic damage, thus preserving viability, it accumulates metabolites with other function, such as animal attractants, and it terminates senescence by becoming autolytic and facilitating true cell death (Thomas et al., 2003).

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2. Flower senescence Flowering, which is one of the most dramatic and spectacular events in plant

development, is often associated with senescence and death. The process is sudden and comprehensive in monocarpic plants, such as Agave Americana and Phyllostachys edulis, where the entire plant dies after flowering or fruiting. In polycarpic plants, such as Dianthus superbus and Cattleya spp., senescence and death are restricted to some parts of the flower itself-mainly the corolla and stamens, which normally abscise or wither soon after flowering. The flower is a more complex organ and the interrelationship between the various flower parts may determine their rate of senescence. Since senescence of the whole flower is so complex, the present discussion will deal primarily with processes occurring during senescence of the corolla (Leshem et al., 1986).

The first change in cells during senescence (Matile and Winkenbach, 1971) was observed in the vacuole membrane-the tonoplast showing invagination, that is, formation of enclosed vesicle containing cytoplasmic components. This may indicate autophagic activity of the vacuole and the loss of compartmentation, which in young cells maintains separation of the cytoplasm and organelles from vacuoles containing hydrolytic enzymes. The breakdown of compartmentation is expressed by increased hydrolytic activity of the cellular macromolecules-mainly proteins and nucleic acids. The autolysis of the cell components leads to complete disintegration and death (Leshem et al., 1986) These changes are schematically illustrated in Figure 2.

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Figure 2. Schematic illustration of morphological changes in mesophyll cells

of senescing corollas of morning glory. (A) Autophagical (digestive) activity of the vacuole. Invagination of the tonoplast results in incorporation of cytoplasmic material into the vacuole. (B) Shrinkage of the vacuole, dilution of the cytoplasm and swelling of the cytoplasmic membrane systems. (C) Autolysis of the cell components is initiated by the breakdown of the tonoplast.

Source : Leshem et al. (1986)

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3. Ethylene action and flower senescence A hypothetical model for the action of ethylene in flower senescence is shown in

Figure 3. This scheme suggests a membrane-based binding site that is activated or repressed by a “sensitivity factor”. The ethylene molecule binds to a site where the inhibitors of ethylene action, Ag+ and 2, 5-norbornadiene (NBD), can also bind. When the binding site is sensitized and ethylene binds to it, a second message is generated which interacts with the 5’ (promoter) region of genes involved in ethylene-regulated senescence, inducing transcription of the genes, and synthesis of the proteins encoded by these genes. (Reid and Wu, 1991)

Figure 3. Hypothetical scheme for the action of ethylene in inducing

flower senescence. Source : Reid and Wu (1991)

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4. Ethylene in the control of flower senescence Ethylene, a group of plant hormones, influences the rate of ageing of various

flowers and has been implicated to participate in the regulation of flower senescence. The symptoms of ethylene effects vary in various flowers. It can cause in-rolling of petals, as in carnation or morning glory, loss of turgor, as in petunia and some orchids, change in pigmentation or it can induce abscission of flower buds or corollas, as in snapdragon, geranium and sweet pea (Leshem, 1986).

Petal and other floral organs are derived from leave and share common biochemical processes during senescence. Both leaves and flowers exhibit a combination of mobilizatin, wilting, and abscission during senescence. One difference between these organs is the ability of pollination a similar rapid deterioration and abscission of the leaf (Abeles et al., 1992).

Not all flowers use an increase in ethylene production as the signal indicating the end of their functional life. In some cases, externally supplied ethylene does not induce floral senescence. Orchids exhibited a range of responses to applied ethylene. Vanda spp. is the most sensitive. It showed accelerated senescence after a day of 0.3 µl /liter ethylene. Cattleya spp., Cymbidium spp., and Paphiopedilum spp., are intermediately sensitive. These plants showed a response to ethylene within 3 to 7 days after ethylene treatment. Orchids that almost insensitive to externally applied ethylene are Dendrobium spp., and Oncidium spp., (Abeles et al., 1992).

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