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Polarity of the components present in the plant

The document discusses the concept of polarity in plants and animals, highlighting its morphological and anatomical expressions. It outlines the differences between shoot and root ends during regeneration and emphasizes the role of polarity in embryonic development and tissue organization. Polarity is crucial for various cellular functions, including growth and differentiation, and is influenced by factors such as auxin distribution and call signaling.

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POLARITY
Polarity expression Morphologically – Stem ,Root & Leaf Cuttings. Anatomically – Embryo development & Tissue organisation.
POLARITY • The term polarity was first used by ALLAM in 1864 in connection with phenomenon of animal regeneration • Now being used to describe this phenomenon in both PLANTS and ANIMALS. • Polarity means establishment of differences @ the 2 ends of a structure (Shoot & root tip). INTRODUCTION
Polarity Expressd in EXTERNAL STRUCTURE • The most conspicuous expression of polarity is in EXTRENAL MORPHOLOGY • In Higher Plants • Difference between root end & shoot end are determined very rarely @ first division of fertilized egg. • The differentiation is not irreversible however for roots often appear on stems under favourable conditions & less commonly, buds & shoots appear on roots.
In 1878 Vochting grew cuttings of willow kept under moist conditions . These are grown in both upright and inverted conditions. 1) Roots grow morphologically @ the basal end 2) Shoot from buds @ the original apical end 3) If such shoot cut into 2 or more parts transversely each part regenerated & roots and shoots in the same polar fashion. 4) This is consider as polar character.
Polarity in willow shoots 1) Dia -1 shows A PORTION OF STEM SUSPENDED IN MOIST AIR IN ITS NORMAL POSITION & PRODUCING ROOTS & SHOOTS 2) Dia- 2 shows A PORTION OF STEM SIMILARLY EXCEPT IN AN INVERTED POSITION This is consider as polar character.
Polarity expressed in EXTERNAL STRUCTURE •3 Types • Stem cutting • Root cutting • Leaf cutting
STEM CUTTINGS
STEM CUTTINGS • In stem cuttings polar regeneration of shoots & roots are clearly obvious in most higher plants, but there are considerable difference between sps.,
 Reversal of the position of cuttings with respect to gravity does not alter the polarity  Small pieces of stem tissues still exhibit polarity effect
ROOT CUTTINGS
ROOT CUTTINGS • Root cuttings behave in polar fashion. The shoots are regenerated at the basal or proximal pole ( the end next to shoot ) & roots from the apical (distal) pole. • This polarity is maintained even if the root cutting is grown in a inverted condition .
LEAF CUTTINGS
LEAF CUTTINGS • Leaf cuttings behave quite differently from stems & roots then show somewhat different type of polar behaviour • In most cases, regeneration of both roots & shoots occurs @ the leaf base near the cut end of the petiole.
Polarity as Expressed in INTERNAL STRUCTURE • Polar phenomena are manifested not only in external form but in internal structure. • 2 types • Embryonic development • Tissue reorganisation
Embryonic Development • In vascular plants polarity is first seen during the division of the fertilized egg. • In seeded plants, the embryo has a definite orientation in the ovule, the tip of the young radicle always being directed toward micropyle & the plumular end toward the chalaza. • The embryo sac always shows polar character in the presence of egg apparatus being located at the micropylar end.
The embryo shows polarity with distinction between root and the shoot that begins early during the development Once established this polar behaviour persists and is apparently irreversible
Tissue Reorganisation • Vochting (1918) observd that root will fuse with a shoot pole but 2 similar poles when brought together will not fuse • Bloch (1957) on the other hand , observed that the fruits of lagenaria will knit the tissues in any orientation after being cut & replaced. • Colquhoun (1929) removed bud & pieces of bark in casuarina & reapplied them in inverted position. • Wood fibres & vessels, however , show the characteristic turns & twists.
Continues……… • This suggest unpolarised or unstable polarity of the cambial cells & that wood elements differentiate , polarity is gradually impressed upon them. • The polar behaviour is also shown by the aggregation of the protoplasm at one end or position of the chromatophor in the cells.
Cell polarity, referring to the asymmetric distribution of cellular components, structure and function within a cell, is a fundamental feature of all living organisms play critical roles in almost all aspects of cellular function, for example, expansion, division, differentiation, growth, and morphogenesis For example, the pollen tube and root hair are formed by extremely polarized tip growth The puzzle shaped pavement cells require diffused polar growth for ‐ morphogenesis Specialized cell function, including directional movement of nutrient or phytohormones, can be achieved by directional enrichment and/or activity of the transporters
plays important roles in the regulation of asymmetric cell division- generates two daughter cells that differ in cell fates and is essential for the development of multicellularity while maintaining the stem cell population in plants. cell walls, that function to assist in the establishment of cellular asymmetry proteins or lipids, to one side of the cell and this process often requires highly coordinated activities of cell signaling, membrane trafficking, and cytoskeleton reorganization With regard to polarly localized proteins, they can be integral to the plasma membrane (PM) or associated with the PM
The asymmetric distribution of proteins at the PM is an important feature of cell polarity in plants Auxin is unique among all phytohormones because it regulates numerous aspects of plant growth and development via its polar transport tightly controlled auxin flow and distribution control the embryonic axes, the formation of primary and lateral roots, shoot derived organ ‐ generation and fruit development Initiation of stomatal cell lineage begins with the asymmetric division both auxin signaling and protein expression showed asymmetries that regulate stomatal division and cell fate determination.
Calcium, a second messenger, is an organizer of cell polarity in plants. Polarity originates early in development apical basal polarity is evident even before the first zygotic division ‐ within the egg cell itself embryo sac itself exhibits polar organization, with the egg cell and synergids adjacent to the micropyle, while the antipodal cells are found at the opposite chalazal end. Polarity in the egg cell is seen anatomically as the location of a large vacuole at its micropylar end, while the chalazal end is relatively cytoplasmic  In some species, polarity in the egg cell and, subsequently, the zygote is exaggerated by a reorganization of cytoplasmic components
Polarity of the components present in the plant