Solució amb Slat 2D

2.1.1 Development of the Flower (Sárkány and Szalay 1964)

The first step in the development of the flower is the appearance of the two sepal initials on the base of the hemispherical apical meristem in an opposite arrangement. Triangular sepals with a wide base are positioned on the apical dome laterally surrounding the axis. The sepals overgrow the apical dome, consisting of the calyx. The initials of the four petals emerge under the calyx. They are arranged in two whorls in a decussate arrangement. The development of the petals is slower than that of the sepals.

The anthers develop from four initials of two whorls. The ‘indefinite’ number of anthers is the result of the multiplication of these initials.

Numerous carpels emerge along a ring as a plate-shaped structure at the central area of the apical meristem (Fedde, 1936).

After this early developmental state begins the parallel growth and differentiation of the floral parts. Inside the more or less oval floral bud, enveloped by the calyx, the carpels form a ‘cup’ with placentae on their inner surface. The upper margin of the carpels form the sessile, discoid stigma, its lobes growing centripetally close to the ovary. The stamens differentiate into filaments and anthers with two bilocular thecae. Following differentiation, in parallel with the processes of microsporogenesis and microgameto-genesis in the locules of anthers and in the ovules, all floral parts show an intensive increase in size.

2.1.2 Characterisation of the Slower

The flowers of P. somniferum are radially symmetric and have a heterochlamydeous perianth. The calyx has a protective function and the colour of

the corolla attracts pollinators. The number and arrangement of floral parts is described by the floral diagram (Figure 8) and the floral formula which is

(Fedde, 1936; Alexander, 1952).

At the opening of the floral bud the sepals are shed. The arrangement of petals in the vegetative bud (vernation) is crumpled (Weberling, 1992). After the sepals fall, the petals unfold as a result of intensive growth (Figure 9). The petals fall off within the next two days. The stamens persist for a short period after the abscission of the petals, then they shrink and dry out.

2.1.3 Morphology and Anatomy of Floral Parts 2.1.3.1 Perianth

The sepals are green in colour, their anatomical structure resembles that of the leaves, but the mesophyll is homogenous, composed of 4–10 isodiametric parenchyma cell layers. The venation of sepals consists of 7–10 main veins with collateral vascular bundles. In the phloem the phloem parenchyma is the dominant tissue, with the sieve tubes and companion cells being less well developed. Phloem fibres exist. The laticifers can be easily recognized, forming an arch in the phloem.

The four petals are decussate, arranged in two whorls. The petals of the outer whorl are larger and overlap the two inner ones. The petals are thin in cross section. The outer transversal wall of the epidermis is more or less convex and is covered with a cuticle. Stomata exist. The mesophyll involves 7–10 parenchymatic cell layers, with reticulate, weakly developed venation. The xylem consists of mainly tracheids; in the

phloem there are only sieve cells. Laticifers also exist (Kapoor, 1995). The colour of the petals is variable: white, pink, red, etc. in some cases with a dark basal spot. 2.1.3.2 Androecium

The numerous stamen are hypogynous and are inserted on the ring-like receptacle. The filaments are long, more or less flat and terminate at the basal area of the anthers. The anthers comprise two thecae which enclose the pollen sacs.

The filament is covered by epidermis. Stomata and cuticle are present. The vascular elements are arranged in a single concentric bundle, where in the central xylem part tracheids can be found and in the ring-like phloem sieve cells are present.

The loculamentum of the anther has a bilayered wall (exothecium and endothecium). In the loculamentum the sporogenous tissue is covered by the tapetum. The maturation of spores is followed by the longitudinal dehiscence of thecae. 2.1.3.3 Gynoecium

The ovary is globular, its situation is superior and it is connected to the pedicel by a thin gynophore. The style absent, so the sessile plate-like stigmata is on top of the ovary. Stigmatic rays are fused together at their edges. The result of this fusion are the stigma lobes. In Papaveraceae family the stigma lobes develop from a pair of rays

of two neighbouring carpels (commissural stigmas). The pollen-receptive papillate surface is situated along the united margin of the stigmatic lobes. Papaver somniferum has dry stigma. The vascular supply resembles that of the perianth.

The gynoecium of Papaver somniferum is paracarpous, i.e. the margins of fused carpels do not reach the centrum of the ovary on the ventral side, they only form centripetal projections called septa. The septa bear the placentae over their whole surface. The placentae are triangular in transversal section. Their tissue is loosely arranged parenchyma which contains a great number of amyloplasts.

The numerous ovules develop in rows on the placentae covering the surface of the septa. In the ovule, as a result of meiotic division, four haploid macrospores emerge. After disintegration of the three outer cells of the linear tetrad, the innermost haploid cell—the chalazal macrospore—develops into the embryo sac. The ovules are covered with two integuments.

2.2 Fruit

The characteristic fruit type of Papaver genus is the unilocular capsule, developing from a multicarpellate paracarp gynoecium (Figure 10). The shape of the capsule is variable: ovate, obovate, clavate, globose, etc. It is supported by a neck. At the top of the capsule is the stigmatic disc. The number of stigmatic rays is the same as that of the carpels. Under the stigmatic disc there are pores dehiscing apically (Gunn, 1980). During the development of the fruit, the ovary wall turns into the pericarp with three parts: the exocarp, mesocarp and endocarp.

The outer epidermis, covered by a thick cuticle, consists of polygonal cells with thick and frequently pitted walls (Brückner, 1982). The stomata are not sunken. The hypodermis is collenchymatous during maturation of the capsule and becomes sclerified on ripening. The epidermis and hypodermis together are called the exocarp. The cells of the parenchymatic mesocarp contain chloroplasts and a highly branched vein system (Figure 11). The number of vascular bundles in the capsule is the same as that of the carpels. They form two branches: toward the mesocarp (valve bundle) and toward the placenta (placental bundle). The valve bundles are collateral and form a rich network of bundles in the mesocarp (valve traces). The laticifers of this network (Figure 12) are the main source of latex and their density increases in parallel with the growth of the capsule. The placental bundles are marginal, situated at the fusion of the carpels near to the placentae, and may be amphicribral in structure. The lateral branches (traces) of the placental bundles supply the ovules. When the traces pass into the ovules, no laticifers are present in the vascular elements. The laticifers terminate near the chalaza (Fairbairn and Kapoor, 1960). A characteristic feature of Papaver fruit is that the dorsal bundles are absent (Kapoor, 1973). The endocarp is a unicellular layer of tangentially elongated cells.

Following intensive growth, the capsule enters the ripening period. Anatomically this means an increase of lignification in the phloem parenchyma of the placental bundle, in the endocarp and in the ground parenchyma of the capsule and pedicel.

Figure 11 Transversal section of the fruit wall: 1, placental bundle; 2, seeds; 3, endocarp 4, network of valve traces

2.3 Seed

2.3.1 Characteristics of Seed

The seeds are narrowly or broadly reniform (Figure 13), about 1mm in length and 0.6 mm wide (Röder, 1957). The colour of the seeds is very variable; they may be white, cream, yellow—brown, red—brown, red—lilac, blue, blue—grey, grey, dark blue or almost black (Swarbrick and Raymund, 1970). The colour of the seeds may even vary inside a single capsule (Schijfsma et al. 1960).

Seeds develop from subcampylotropous bitegmic, crassinucellate ovules (Corner, 1976). The seed coat consists of six cell layers (Figure 14). From the outer integument develops the outer epidermis with a waxy cuticle, a crystalline layer with calcium- oxalate crystal sand and a fibrous layer with conical cells of thick cellulosic walls (Figure 15). A parenchymatous layer with thin-walled cells, a layer with cells of reticulate cell wall thickening and pigment-rich protoplasm, and finally a very thin parenchymatic layer originate from the inner integumentum (Brückner, 1983). The anticlinal wall of the outer epidermis is more or less waxy and bold (Figure 16), forming a pattern of quadrangular or irregular fields (Gunn, 1980). The periclinal wall shows special cuticular ornamentation (Röder,1957; Fritsch, 1979; Mihalik et al., 1995) and this characteristic, together with the shape of the anticlinal walls, is of diagnostic value (Figure 17). The cuticle is inseparable from the outer seed coat.

The curved endosperm is soft and fleshy and contains aleurone grains and oil. The cell wall of the endosperm is thin.

The white linear embryo is small, basal, axile, about half the length of the seed. Cotyledons are parallel and entire (McClure, 1957). The placental traces involve

Figure 13 Seed of P. somniferum

Figure 14 Schematic drawing of seed coat layers of P. somniferum. 1, outer epidermis; 2, crystal cells; 3, fibrous layer; 4, parenchyma layer; 5, cells with reticulate cell wall thickening; 6, inner parenchymatic layer; 7, endosperm (Fedde, 1936)

Figure 15 Seed coat layers developing from the outer integument (transversal section): 1, waxy cuticle; 2, outer epidermis; 3, crystal layer; cells with calcium oxalate crystal sand; 4, fibrous layer

laticifers but they do not extend into the seed. The procambial strands of the embryo do not contain laticiferous elements—they appear only at a definite state of differentiation.

2.3.2 Germination

The opium poppy has epigeal germination. Following the appearance of the root, the epicotyl elongates, elevating the two lanceolate cotyledons, about 1 cm in length, above the soil surface (Figure 18).

3 STRUCTURE AND DEVELOPMENT OF LATICIFERS