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ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptx

The document discusses anomalous secondary growth in dicot roots, focusing on the characteristics and functions of primary and adventitious roots. It describes abnormal secondary growth in certain plant families such as Chenopodiaceae and Convolvulaceae, noting how cambium rings exhibit unusual activity leading to changes in xylem and phloem arrangement. The conclusion emphasizes that anomalous secondary growth increases plant girth through complex interactions of vascular and cork cambium, deviating from typical growth patterns.

Science◦
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS RASHMI M G 1st MSc. Botany MAHARANI’S SCIENCE COLLEGE WOMEN MYSORE
INTRODUCTION ROOTS- are generally divided into 2 categories, • Primary normal roots, which originate from the embryo and usually persist throughout life. • Adventitious roots, which arise secondarily from stem, leaf or other tissues and which may be either permanent or temporary.
ROOT- FUNCTION Functions- primary roots are to anchor that plant in the soil, to absorb water and soluble substances and to serve as storehouse of food materials. Functions of adventitious roots are very various. Sometimes they enter the soil and act as primary roots. In other cases they may be modified into climbing organs, stilts, props, thorns, haustoria, etc.
ABNORMAL SECONDARY GROWTH IN DICOT ROOT Abnormality of secondary growth dicot roots is to adapt for the storage function. Members like Umbelliferae, Cruciferae, Chenopodiaceae, Compositae, Convolvulaceae etc. Ex. 1. Beet root (Beta vulgaris) 2. Sweet potato (Ipomoea batatas) 3. Radish (Raphanus sativus)
Beta vulgaris root • Family- Chenopodiaceae • Root has typical dicot structure. • Shows radial and diarch condition of stele. • As it is a storage root, there occurs an increase in girth of the root to accommodate the increase in number of cells. • Secondary growth is of anomalous type due to abnormal activity as well as position of cambium.
Secondary growth initiated by formation of primary cambium ring • It is formed by joining of cells of pericycle (outside) the protoxylem and parenchyma cells (between) the xylem and phloem Abnormal activity of primary cambium ring • Forms secondary xylem and parenchyma cells in alternate groups, towards the inner side, whereas on the outer side, it forms secondary phloem opposite to secondary xylem and parenchymatous cells opposite to inner parenchymatous cells Result will be, • Formation of ring of conjoint, collateral vascular bundles embedded in parenchymatous tissue • Parenchymatous cells functions as storage tissues.
Cambium after forming the ring of vascular bundles ceases its activity Secondary ring of cambium arises outside the first cambium ring • Secondary cambium is developed from phloem parenchyma cells or sometimes from the inner cells cut off by pericycle. Abnormal behavior of secondary cambium Result will be, • Formation of another ring of conjoint, collateral vascular bundles arranges external to first ring of bundles
TS of Beta vulgaris root
Ipomoea batatas root 1. Family- Convolvulaceae 2. Young condition- cortex is . well developed with wide intercellular spaces. 3. Well developed endodermis. 4. Stele typically shows radial and pentarch or hexarch arrangement of vascular tissue.
TS of Ipomoea batatas root
Formation of cambium ring which is normal in function initially, however at later stages it begins to behave abnormally forming a separate strands of secondary xylem and phloem embedded in parenchymatous ground tissue. Strands of xylem gets surrounded by individual rings of secondary cambium which originates from the parenchymatous cells of ground tissue surrounding the xylem vessels. Secondary cambium surrounding the xylem vessel behaves abnormally Formation of elements of secondary xylem towards the centre and few sieve tubes and laticiferous elements away from the centre Cambium forms parenchymatous cells on both inner and outer side • These cells get filled with reserve foods and functions as storage tissue
Raphanus sativus root • Family- Cruciferae. • Has a typical diarch primary xylem. • At the beginning of secondary growth a normal cambium is formed which cuts off secondary xylem towards inner side and secondary phloem towards outer side. • Some of these parenchymatous cells become meristematic and develop to form secondary cambium, these cambium completely surround the strands of secondary xylem scattered in ground tissue.
Secondary cambium activity is abnormal. It forms few xylem elements but large amount of parenchyma both internal and external to the cambium ring As the root matures, numerous patches of secondary xylem surrounded by secondary cambium lie scattered in parenchymatous ground tissue These parenchyma cells accumulate reserve food and functions as storage tissue There is increase in girth of root due to formation of circular patches of secondary xylem
Anomalous secondary growth in Raphanus sativus TS of Raphanus sativus
CONCLUSION Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
REFERENCE A textbook of botany, plant anatomy and economic botany, volume III, S N Pandey, a Chadha, Vikas publications.