Thin Walled Oil Cells In Cinnamomum Bark

1t

t

Source: Bakker et al, 1992. Notes

Oil = oil cells; muc = mucilage cells; p = palisade parenchyma; s = spongy parenchyma; — = absent; 1 = S0.1 cell/mm leaf width; 2 = 0.1—1 cell/mm; 3 = 1—2 cells/mm; 4 = 2—5 cells/mm; 5 = 5—10 cells/mm; p — present. t = lamina thickness; 1 = 100—200 |xm; 2 = 200—300 |xm; 3 = >300 |xm; cu = adaxial cuticle thickness; 1 = <3 fxm; 2 = 3—8 fxm; cp = adaxial epidermis thickness; — = not sclerified; ± = slightly sclerified; + = moderately, distinctly sclerified; ++ = strongly sclerified.

p = palisade parenchyma; 1 = unilayered; — = not sclerified; c = upper layer with sclerified outer periclinal wall; c* = (upper layer) with thickened outer periclinal and anticlinal walls, sclerified; t = (upper layer) totally sclerified. s = spongy parenchyma; — = not sclerified; ± = weakly sclerified; + = sclerified; pa = papillate abaxial epidermis; — = flat; ± = lowly domed outer periclinal walls; + = dome shaped papillae.

ad.ha = adaxial hairs; ab.ha = abaxial hairs; f = frequency; — = absent; 1 = S 0.1 hair/mm leaf width; 2 = 0.1—1 hair/mm; 3 = 1-2 hairs/mm; 4 = 2-5 hairs/mm; 1 = length; 1 = S 50 ^m; 2 = 50-100 ^m; 3 = 100-200 ^m; s = thick walled (solid); t = thin walled; i = intermediate wall thickness. v = venation; p = penninerved; 1 = main vein distinct; t = triplinerved.

Source: Bakker et al, 1992. Notes

Oil = oil cells; muc = mucilage cells; p = palisade parenchyma; s = spongy parenchyma; — = absent; 1 = S0.1 cell/mm leaf width; 2 = 0.1—1 cell/mm; 3 = 1—2 cells/mm; 4 = 2—5 cells/mm; 5 = 5—10 cells/mm; p — present. t = lamina thickness; 1 = 100—200 |xm; 2 = 200—300 |xm; 3 = >300 |xm; cu = adaxial cuticle thickness; 1 = <3 fxm; 2 = 3—8 fxm; cp = adaxial epidermis thickness; — = not sclerified; ± = slightly sclerified; + = moderately, distinctly sclerified; ++ = strongly sclerified.

p = palisade parenchyma; 1 = unilayered; — = not sclerified; c = upper layer with sclerified outer periclinal wall; c* = (upper layer) with thickened outer periclinal and anticlinal walls, sclerified; t = (upper layer) totally sclerified. s = spongy parenchyma; — = not sclerified; ± = weakly sclerified; + = sclerified; pa = papillate abaxial epidermis; — = flat; ± = lowly domed outer periclinal walls; + = dome shaped papillae.

ad.ha = adaxial hairs; ab.ha = abaxial hairs; f = frequency; — = absent; 1 = S 0.1 hair/mm leaf width; 2 = 0.1—1 hair/mm; 3 = 1-2 hairs/mm; 4 = 2-5 hairs/mm; 1 = length; 1 = S 50 ^m; 2 = 50-100 ^m; 3 = 100-200 ^m; s = thick walled (solid); t = thin walled; i = intermediate wall thickness. v = venation; p = penninerved; 1 = main vein distinct; t = triplinerved.

while in C. verum (Sri Lanka) spongy tissue is thicker. A collection of wild C. verum has the highest spongy tissue thickness (0.111 mm) (Shylaja, 1984).

Bakker et al. (1992) carried out a detailed study on the comparative anatomical features of a large number of Cinnamomum spp. (Table 2.2). The palisade is typically one layered. Sclerification of palisade cells is noted in certain species including C. verum, in which the outer periclinal and anticlinal walls are thickened and sclerified. C. verum (and other species) possess lysigenous cavities in the leaf tissue. In C. verum, C. cassia and C. camphor a they are numerous, while in other species they are much less. Lysigenous cavities occur in both palisade and spongy tissues, though in C. verum they are found mostly in spongy tissue and rarely in palisade.

Oil and mucilage containing idioblasts are always present in palisade and spongy parenchyma (Bakker et al, 1992). Among species they vary in size, shape, stainability and number. Most of the species show minor anatomical variations among them. The above workers carried out a cluster analysis based on leaf anatomical characteristics and showed that oil and mucilage cells played a significant role in the grouping of the species. Bakker and Gerritsen (1989) studied the ultrastructure of developing and mature mucilage cells in the leaves and shoot apices of C. verum and C. burmannii. In all mucilage cells a suberised layer is formed in the outer cellulosic cell wall at a very early stage in development. Oil cells are also known to have suberised cell walls. Many features can distinguish these two types of secretory cells. A typical oil cell has a three-layered cell wall — an outer cellulosic layer, a middle suberised layer and an inner cellulosic layer. An oil drop is often attached to a protuberance of the wall, called the cupule, and is enveloped by the plasmalemma (Maron and Fahn, 1979). Oil is usually synthesised in the plastids (Cheniclet and Carde, 1985). Mucilage cells usually lack a suberised layer, C. verum is an exception to this. Mucilage is produced in the Golgi apparatus, from which vesicles filled with polysaccharides move towards the plasmalemma and fuse with it. Mucilage accumulates between the plasmalemma and cell wall (Trachtenbeg and Fahn, 1981). The two types of secretory cells can be distinguished by the staining reaction with Sudan IV, Chrysoidin and Alcian Blue (Bakker et al, 1992).

Development of oil and mucilage cells

Bakker et al. (1991) reported the development of oil and mucilage cells in the young leaf and shoot apex of Cinnamomum burmannii, on which the following discussion is based. Oil and mucilage cells occur in relatively large numbers in a zone underlying epidermis, i.e. in the outer cortex of the shoot and in the mesophyll of developing leaves. Three arbitrary developmental stages can be distinguished in both types of idioblasts; the first two are the same for both oil and mucilage cells (Fig. 2.3).

Stage 1: The young idioblast, possessing a large central vacuole, is recognisable by the absence of osmiophilic deposits in vacuoles (which occur in the vacuoles in the adjoining cells in plenty). There is a parietal layer of cytoplasm that is slightly more electron dense than that of the surrounding cells. The plastids are distinctly small with reduced thylakoids.

Stage 2: At this stage a suberised cell wall is deposited in the cells. This layer consists mostly of two to three discontinuous lamellae and sometimes up to six lamellae. Subsequently, additional wall material gets deposited. The cytoplasm at this stage contains many mitochondria, small plastids, and a slightly increased amount of dictyosomes.

Stage 3 (Oil cells): Development during this stage differs in oil cells and mucilage cells. In the oil forming idioblasts a distinct layer of inner-wall material gets deposited against the suberised layer. Thickness of this inner wall layer increases significantly as development progresses from 44 nm to 162 nm. Based on thickness of the inner cell-wall layer and the composition of the cytoplasm, stage 3 can be subdivided into three intergrading developmental stages — a, b and c. In 3a, the cell contains a suberised cell wall and an inner wall layer. The large central vacuole disappears and is replaced with a few smaller ones having wavy outlines. The cytoplasm is more compact and contains a small oil cavity. In stage 3b, the inner wall thickness increases and the oil cavity increases in size. A cup-shaped cupule that is attached to a thickened part of the inner wall layer (cupule base) is formed. At first the oil cavity is distinctly enclosed by plasmalemma, which later disintegrates. Plastids disintegrate, paving the way to the formation of many small vacuoles, and they later fuse with the oil cavity. In stage 3c, the cell reaches maturity, the suberised layer is about 36 ± 10 nm thick and appears as a translucent layer. The inner-wall layer (about 162 ± 69 nm

Cinnamomum Tamala Microscopic Structure

Figure 2.3 Schematic representation showing the developmental stages of oil and mucilage cells in Cinnamomum burmannii. Stage 1: Young cells with typical plastids and a central vacuole devoid of deposits. Stage 2: Idioblasts with a suberised layer. Oil cell: Stage 3a: An inner wall layer is present, a small oil cavity is attached to a cupule, oil droplets and bundles of tubular ER appear in the cytoplasm. Stage 3b: An enlarged oil cavity, enveloped by a partly disintegrated plasmolemma is in contact with the vacuoles. Stage 3c: Near mature cells with a large cavity filled with oil and no longer enclosed by the plasmolemma. Mucilage cell: Stage 3a: Collapsed cell with mucilage deposited against the suberised layer. Stage 3b: Cytoplasm moves inward due to mucilage deposition, the central vacuole disappears. Stage 3c: Near mature cells filled with mucilage surrounding degenerating cytoplasm. c — cytoplasm; cb — cupule base; cv — central vacuole; d — dictyosome; g — starch granule; iw — inner wall layer; m — mucilage; mi — mitochondrion; n — nucleus; o — oil droplet; oc — oil cavity; p — plastid; r — ribosomes; s — suberised layer; t — tubular endoplasmic reticulum; v — vacuole; ve — vesicle; w — initial cell wall. (Source: Bakker et al., 1991.)

Figure 2.3 Schematic representation showing the developmental stages of oil and mucilage cells in Cinnamomum burmannii. Stage 1: Young cells with typical plastids and a central vacuole devoid of deposits. Stage 2: Idioblasts with a suberised layer. Oil cell: Stage 3a: An inner wall layer is present, a small oil cavity is attached to a cupule, oil droplets and bundles of tubular ER appear in the cytoplasm. Stage 3b: An enlarged oil cavity, enveloped by a partly disintegrated plasmolemma is in contact with the vacuoles. Stage 3c: Near mature cells with a large cavity filled with oil and no longer enclosed by the plasmolemma. Mucilage cell: Stage 3a: Collapsed cell with mucilage deposited against the suberised layer. Stage 3b: Cytoplasm moves inward due to mucilage deposition, the central vacuole disappears. Stage 3c: Near mature cells filled with mucilage surrounding degenerating cytoplasm. c — cytoplasm; cb — cupule base; cv — central vacuole; d — dictyosome; g — starch granule; iw — inner wall layer; m — mucilage; mi — mitochondrion; n — nucleus; o — oil droplet; oc — oil cavity; p — plastid; r — ribosomes; s — suberised layer; t — tubular endoplasmic reticulum; v — vacuole; ve — vesicle; w — initial cell wall. (Source: Bakker et al., 1991.)

thick) is very electron dense. Cytoplasm degenerates completely and oil fills the entire vacuole.

Stage 3 (Mucilage cells): At stage 3 the mucilage idioblasts develop through three stages — a, b, c. In 3a, the cell has a collapsed appearance, and there is an abundance of hypertrophied dictyosomes budding off the vesicles. Mucilage has just started to be deposited as a layer between the suberised layer and the cytoplasm. The cell membrane is pushed inside hard the inner vacuole is still intact. In stage 3b, the cytoplasm consists mainly of dictyosome vesicles full of mucilage and they finally fuse with plasmalemma. The cytoplasm has been forced to move inward by the accumulated mucilage and the central vacuole gets reduced considerably. In stage 3c, the cell is mostly round, the suberised layer is 37 — 7 nm thick, and the cell is completely filled with mucilage. Cytoplasm gets degenerated and the vacuole disappears completely. Main similarities and differences between the developmental stages of oil and mucilage idioblasts are given in Table 2.3.

Foliar epidermal characters

Ravindran et al. (1993) and Baruah and Nath (1997) studied the foliar epidermal characteristics in several species of Cinnamomum, including C. verum, C. cassia, C. camphora and C. tamala.

Epidermis

Epidermis consists of a single layer of cells covered by smooth cuticle. Cuticle is thick on the upper surface, thin on the lower. Epidermal cells are of two types: (i) In C. camphora (and also in species such as C. parthenoxylon, C. cecidodaphne and C. glanduliferum) cell walls are straight or only slightly curved; (ii) In C. verum, C. cassia, C. malabatrum, C. tamala, etc. cell walls are sinuous (Fig. 2.4). Epidermal walls of different species show varying degrees of birefringence and autofluorescence of cell walls, which indicate sclerification (Bakker et al., 1992).

The epidermis in many species possesses trichomes. Often (as in C. verum, C. cassia) trichomes are microscopic and occur only on the lower surface, but in species like C. perrottettii both leaf surfaces are hirsute and trichomes are visible to the unaided eye. Trichome distribution is sparse in C. verum, in certain C. malabatrum collections, moderately dense in C. cassia and dense in C. perrottettii (Ravindran et al, 1993). Trichomes are short (less than 0.1 mm), medium (0.1—0.2 mm) or long (above 0.2 mm). Structurally trichomes are identical. They are unicellular, unbranched and nonglandular, thick walled, and enclose a narrow lumen in the centre. In C. bejolghota the trichomes are papillate (Baruah and Nath, 1997).

Christophel et al. (1996) used leaf cuticular features in relation to taxonomic delimitation in Lauraceae. They found that South American species of Cinnamomum have distinctive cuticular signatures and that they are clearly different from the species occurring in Australia. Interestingly the American species of Cinnamomum studied by the above authors had been earlier placed in the genus Phoebe. Asian species of the genus, including the type species, form a third distinctive group. Further study may well lead to the conclusion that the group is not natural (and is perhaps polyphyletic) as it is currently defined (Christophel et al., 1996).

Venation pattern

Kim and Kim (1984) studied the venation pattern in some Lauraceae using soft X-ray analysis and reported acrodromous venation in C. camphora, C. japonicum and C. loureirii.

Table 2.3 Main similarities and differences in the developmental stages 3a—c of oil cells and mucilage cells in the shoot apex of Cinnamomum burmannii. For comparison, the characteristics of ground tissue cells are included

Cell size at maturity Cell wall at maturity

Central vacuole Plastids

Accumulation

Main organelles involved in secretion

Cytoplasm

Oil cells

Spherical 25 X 18 (xm

Typically 3-layered with suberised layer and inner-wall layer Cupule present Few specific plasmodesmata Local breakdown

Absent at stage 3a; small vacuoles, devoid of deposits, disappear at stage 3c

Typical small plastids with reduced thylakoids, disappear at stage 3b

Oil is stored in the oil cavity between cupule and plasmalemma

Oil-formation in the plastids, migration guided by tubular ER Final fusion with oil cavity membrane: the plasmalemma Formation of a parietal layer at stage 3c and final degeneration

Mucilage cells

Spherical 21 X 20 (xm

Typically 2-layered with suberised layer

First deposited mucilage resembles inner wall layer

Sometimes a cupule present

Few specific plasmodesmata

Local breakdown

Present at stage 3a; devoid of deposits. Disappear at stage 3b

Typical small plastids with reduced thylakoids, lose their definition at stage 3 c

Mucilage is deposited between the wall and the plamalemma

Mucilage secretion by hypertrophied dictyosomes Vesicles finally fuse with the plasmalemma

The parietal layer is forced inward during development and finally degenerates

Ground tissue cells

Variable shapes, mostly smaller No additional wall layers

Many normal plasmodesmata

Present with deposits

Larger plastids with distinct thylakoids.

Osmiophilic granules in the central vacuole

Not applicable

Includes distinct organelles and groundplasm

Source: Bakker etat., 1991-

Brachidodromous

Figure 2.4 Sketches showing two types of venation patterns. 1. A representative leaf of cinnamon showing the typical acrodromous venation pattern. 2. A leaf of camphor tree showing the acrodromous and pinnate-brochydodromous type of venation.

Shylaja (1984) also reported acrodromous venation pattern in south Indian species of Cinnamomum. Baruah and Nath (1998) recognised three venation patterns in the Cinnamomum species they have studied. In the majority of taxa venation pattern is acrodromous. Here leaves are triplinerved, running in a convergent arch along with two or rarely four lateral nerves. The lateral nerves in most taxa do not reach the apex. In certain species (C. glanduliferum and C. glaucacens) venation is pinnate-camptodromous (brachidodromous). In C. camphor a and C. parthenoxylon venation is intermediate between the above two patterns (Fig. 2.4).

The 1° veins are moderately stout and straight in C. malabatrum, C. cassia and C. tamala. Lateral 1° veins are generally basal or supra basal. In the case of C. camphora and C. parthenoxylon 1° veins are anastomosing with the secondaries. In most cases the 2° veins arise from both sides of the 1° veins in an opposite or sub-opposite manner and they are upturned and gradually disappear at apical and basal margins. In C. camphora, C. glanduliferum and C. parthenoxylon 2° veins arise on both sides of 1° veins in an alternate or sub-opposite manner and extend towards the margins and join to form a series of prominent arches (Baruah and Nath, 1998).

The number of 2° veins varies from leaves to leaves in a single taxon, as does the angle between 1° and 2° veins. In C. cassia, C. glanduliferum, C. glaucacens, and C. parthenoxylon the sub-adjacent 2° arches are enclosed by 3°—4° arches, while these 2° arches are simple in other taxa studied by Baruah and Nath (1998).

Minor veins of the 4° and 5° order, which originate from 3° veins, constitute the areoles or vein islets. The areoles are generally tetragonal or polygonal in shape. The size and number of areoles are variable in apical, middle and basal portions of lamina. Veinlet endings are generally simple (linear or curved).

Cassia Trichome

Figure 2.5 Foliar epidermal characteristics of some Cinnamomum spp. 1. C. tamala; 2. C. verum; 3. C. cassia;

4. C. camphora; 5. C. panthenxylon. a-lower epidermis; b-upper epidermis. In 1, 2 and 3 the cell walls are sinuous and stomata anomocytic; in 4 and 5 the cells are straight and stomata paracytic.

Stomata

Cinnamon leaves are hypostomatic, with stomata confined to the lower surface of leaves. Stomata are anomocytic, surrounded by a variable number of cells that are indistinguishable in size or form from the rest of the epidermal cells (Fig. 2.5). In C. camphora, stomata are of paracytic type, i.e. they are accompanied on either side by one or more subsidiary cells parallel to the long axis of the pore and guard cells. The guard cells may be equal or unequal in size and are attached to each other at the margins of the concave side with the aperture lying in between the walls. Rare occurrence of other types of stomata was also reported (Baruah and Nath, 1997) (Fig. 2.6).

Guard cells are unevenly thickened, and thickening is heavy along the aperture. Stomatal characters are given in Table 2.4. Stomatal frequency is found to be lower in

Tipe Daun Brachidodromous

Figure 2.6 Rare stomatal types observed in Cinnamomum spp. 1. Paracytic (amphibrachial) stoma in C. cassia. 2. Sunken stoma in C. bejolghota, flanked by eight subsidiary cells. 3. Paracytic stoma in C. sulphuratum. 4, 5. Adjoining paracytic stoma with three or four subsidiary cells in C. cecidodaphne. (Source: Baruah and Nath, 1997.)

Figure 2.6 Rare stomatal types observed in Cinnamomum spp. 1. Paracytic (amphibrachial) stoma in C. cassia. 2. Sunken stoma in C. bejolghota, flanked by eight subsidiary cells. 3. Paracytic stoma in C. sulphuratum. 4, 5. Adjoining paracytic stoma with three or four subsidiary cells in C. cecidodaphne. (Source: Baruah and Nath, 1997.)

Table 2.4 Stomatal characteristics of four species of Cinnamomum

Species

Frequency/mm2

Guard cell length

Guard cell breadth

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