Anatomy Embryology Cytology 21 Anatomy

Tomlinson (1969) and Mercy et al. (1977) carried out preliminary anatomical studies on aerial stem, rhizome, leaf sheath and root of cardamom plants. Aerial stems of leafy shoot has the typical monocot structure with numerous closed collateral endarch vascular bundles scattered in the ground parenchyma (Fig. 2.3). The stem is solid. There is a thin sub-epidermal layer of sclerenchymatous cells separating the inner vascular bundles from the outer ones. Each vascular bundle is surrounded by a prominent bundle sheath of sclerenchyma cells. There are two-three large metaxylem vessels and a few protoxylem vessels. A protoxylem lacuna is present in some bundles. In the parenchyma cells, rhomboidal crystals of calcium oxalate are found occasionally.

Rhizome is sharply differentiated into an outer cortex and a central core by a plexus of irregular, congested vascular bundles (Fig. 2.4). Root traces are inserted in this plexus. In the peripheral cortex, there are only a few vascular bundles while numerous bundles are seen in the subcortical and central core regions, where they are irregularly distributed. They are closed, collateral and endarch as in the aerial stem. In each bundle, there are several protoxylem and metaxylem vessels. The bundles are supported with sclerenchymatous bundle caps. The outermost cell layers of the cortex have developed into a kind of periderm, which is a common feature in the underground rhizomes of Zingiberaceae.

The sheathing base of the leaf has single layered upper and lower epidermis. Patches of hypodermal sclerenchyma occur associated with both upper and lower epidermal regions, but they are more prominent below the upper epidermis. Vascular bundles are arranged in a single row alternating with large schizogenous airspaces. Each bundle has a bundle sheath of sclerenchyma, a large patch of phloem and xylem below the phloem (Fig. 2.5).

Three Anatomical Airspaces
(a) (b)

Figure 2.3 Anatomical features of cardamom stem: (a) TS of aerial stem-diagrammatic; (b) TS of aerial stem — a portion enlarged. See text for details (Source: Mercy et al., 1977).

Figure 2.3 Anatomical features of cardamom stem: (a) TS of aerial stem-diagrammatic; (b) TS of aerial stem — a portion enlarged. See text for details (Source: Mercy et al., 1977).

Rhizome Anatomy

Figure 2.4 Anatomical features of cardamom rhizome: (a) TS of the rhizome diagrammatic; (b) TS of rhizome — a portion enlarged. See text for details (Source: Mercy et al., 1977).

Anatomy Aerial Stem
Figure 2.5 Anatomical features of cardamom leaf sheath: (a) TS of leaf sheath-diagrammatic view through the tip portion of the aerial shoot showing the cyclic layers of leaf sheath; (b) a portion enlarged. ph — phloem, xy — xylem, vb — vascular bundle (Source: Mercy et al., 1977).

Cardamom plant has the characteristic fibrous root system of monocots. The root consists of epidermis that is single layered with a large number of epidermal hairs. Cortex and pith regions are large and parenchymatous. The endodermis shows well developed casparian strips (Fig. 2.6).

Cardamom leaf has the structure of a typical monocot leaf, bound by upper epidermis, hypodermis, single layered palisade tissue, spongy parenchyma and lower epidermis (Fig. 2.7). Stomata are distributed mostly on the lower epidermis only. Stomata are para-cytic, having the guard cells flanked by some what elongated, conical shaped subsidiary cells (Fig. 2.7). The stomatal frequency (SF) showed variations (Krishnamurthy, 1989). The values for a few clones are given below (Value for 1 mm2 and mean of 10 replications).

Clone P1 P2 P3 P5 P6 P8 CL 258 CL 664 CL 668 CL 676 CL 757 V 179 SF 627 535 685 484 633 597 600 553 644 557 627 680

Pillai et al. (1961) studied the root apical organization in many Zingiberaceae members including cardamom. They found that the root apical organization of cardamom is similar to that in Alpinia, Hedychium etc. and consists of three sets of structural initials, one each for the root cap and plerome and a common zone for dermatogen and periblem (Fig. 2.9). The root cap has two distinct regions, the columella in the middle and a peripheral region around it, distinguishable by the different types of cell complexes. In the root body two histogens could be distinguished: (1) The plerome concerned with the formation of the stele and (2) the protoderm—periblem complex concerned with the formation of the outer shell to the stele including the periblem and the dermatogen. The protoderm—periblem complex is located outside the plerome and is composed of a single tier of cells. The cells of this zone located at the flanks exhibit T-divisions, which enables the tissue to widen out.

Dermatogen separates out as a distinct layer from the products of divisions of the protoderm—periblem complex at some distance on the flanks. This tier divides anti-clinally, later forming the epidermis.

Portion Enlarged
Figure 2.6 Anatomical features of cardamom root: (a) TS of root-diagrammatic view; (b) a portion enlarged: xy - exarch xylem; ph - phloem; ed - endodermis (Source: Mercy et al., 1977).

Hypodermis arises from the inner of the twin daughter cells of the T-divisions of the protoderm-periblem initials. The cells composing this tissue vacuolated earlier than the other cells of the cortex. Endodermis differentiates from the periblem cells. After a few T-divisions, the innermost layer switches over to anticlinal divisions, ultimately leading to the endodermis.

Plerome has at its tip a quiescent center, made of more or less isodiametric cells (Fig. 2.8). On the sides of the plerome dome is the uniseriate pericycle. The metaxylem vessel elements get differentiated near the plerome dome vacuolating earlier. The isodiametric cells at the very center of the plerome divides like a rib-meristem to give rise to the pith. Pillai et al. (1961) could distinguish at the root tip

Cardamom Images

Figure 2.7 (a) TS of a cardamom leaf through the midrib: a — epidermis; b — hypodermis; c — single layered palisade; d — spongy parenchyma cells; e — vascular bundle; f — lower epidermis. (b) a portion of epidermis showing stoma: a — guard cell; b — subsidiary cell.

Figure 2.7 (a) TS of a cardamom leaf through the midrib: a — epidermis; b — hypodermis; c — single layered palisade; d — spongy parenchyma cells; e — vascular bundle; f — lower epidermis. (b) a portion of epidermis showing stoma: a — guard cell; b — subsidiary cell.

2 zones on cytophysiological grounds. The quiescent center found at the tip of the root body in characterized by:

(a) cyloplasm lightly stained with pyronin-methyl green and haematoxylin;

(b) smaller nuclei and nucleoli;

(c) cell divisions less frequent;

(d) vacuolation in most cells.

In median longisections this group of cells is in the shape of a cup with the brim forwards. This zone embraces and includes cells belonging to all the structural histogens of the root body and it is not structurally delimitable and gradually merges with the zone outside, the meristematic zone.

The meristematic zone is shaped like an arch surrounding the quiescent center. This zone is composed of cells:

(a) with cytoplasm more deeply stained with pyronin-methyl green and haematoxylin;

(b) showing divisions more frequently;

Periblem Are Situated
Figure 2.8 Root apical organization of cardamom. Median LS of root tip with independent plerome and root cap, and protoderm-periblem complex. a - the quiescent centre; b - meristem-atic zone; c - region where the Kooper and Kappe type divisions occur; d - dermatogen (Source: Pillai et al, 1961).

(c) showing larger nucleoli and nuclei;

(d) where vacuolation is not prominent.

The root apical organization of cardamom falls under the category Type 2 of Easu (1953), which is the most prevalent type among the monocots.

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