Medicinal and Aromatic Plants - vol 45 - Turmeric- The Genus Curcuma

28 Turmeric: The Genus Curcuma
Oil canals are present in ground parenchyma in actively growing regions along with phloem
and xylem. Oil canals are formed lysigenously by the disintegration of entire cells. The process of
formation of oil canals seems to be similar to that in ginger rhizomes described by Remashree et
al. (1999) and Ravindran et al. (2005).
Chakravarty (1939) reported the occurrence of a fugacious cambium just below the endodermoid
layer. It is a short-living cambium (meristematic cells) and may vary from two to six layers. It soon
disappears almost completely, leaving behind a ring of crowded bundles. Though a true cambial
ring does not form in monocots, however, the presence of ray and fusiform initials points to a true
cambial nature. This cambial zone produces secondary vascular bundles and parenchyma cells
centripetally to form a distinct zone of secondary thickening.
Remashree et al. (2003) reported the comparative rhizome anatomy of C. longa, C. aromatica,
C. amada, and C. zedoaria. They identified the key characters for distinguishing the four species
(Table 2.2). All the species are similar in their basic anatomical features; however, variations exist
in the number and arrangement of primary and secondary bundles, orientation of tissues, number
and shapes of curcumin cells, starch grains, and oil cells. The primary vascular bundles are abundant
and scattered in both outer and inner zones in C. longa and C. amada, less in C. zedoaria, and
least in C. aromatica. The numbers of oil and curcumin cells vary in the four species, and they are
higher in the apical and nodal region than in the internodal region. Although Curcuma is a monocot,
Remashree et al. (2003) reported the presence of cambial elements in the rhizomes of the four
Curcuma spp.
Oil cell initials are present in the meristematic region. They are more or less spherical and densely
stained with Sudan Black. Small irregular bodies, clusters of globular drop-like structures, and granular
bodies are seen inside the oil cell. Large oil cells are present in C. zedoaria; the size decreases in C.
aromatica, C. amada, and C. longa in that order. Oil cells are round-to-ovoid and more or less globular;
the oil cell index decreases in the order: C. aromatica → C. zedoaria → C. amada → C. longa.
Curcumin cells appear yellowish-red following boric acid treatment. The cell wall is thick and
filled with curcumin, which appears orange with boric acid treatment. The longisection of rhizome
shows a long canal containing curcumin deposit. The number of curcumin cells is very few in C.
amada and C. aromatica and numerous in C. longa and C. zedoaria (Remashree et al., 2003).
2.4.1 ONTOGENY OF OIL CELLS AND DUCTS
Oil cells and ducts develop in the meristematic region early in the development of rhizomes. The
development of oil cells, curcumin cells, secretary ducts, and stages of secretion were reported by
Remashree (2003) on which the following discussion is based. Both schizogenous and lysigenous
types of development are found in turmeric.
2.4.1.1 Schizogenous Type
This type of secretary duct originates in the intercalary meristem of the developing region. The
ducts are initiated by the separation of a group of densely stained meristematic cells through the
dissolution of middle lamella. Concurrent separation of the cells leads to the formation of an
intercellular space bordered by parenchymatous cells possessing dense protoplasmic content. These
ducts anastamose and appear branched. The widening of the duct is affected by the separation of
the bordering cells along the radial walls.
2.4.1.2 Lysigenous Type
This type of secretary duct formation is met with both in the meristematic regions and in the mature
part of the rhizomes. There are four stages in its development — initiation, differentiation, secretion,
and quiescence. These steps take place acropetally and are a gradual process (Figure 2.6).