PLANT GROWTH AND DEVELOPMENT

PLANT GROWTH AND DEVELOPMENT

Growth is one of the most conspicuous events in any living organism. It is an

irreversible increase expressed in parameters such as size, area, length, height,
volume, cell number etc. It conspicuously involves increased protoplasmic material.
In plants, meristems are the sites of growth. Root and shoot apical meristems
sometimes alongwith intercalary meristem, contribute to the elongation growth of
plant axes. Growth is indeterminate in higher plants. Following cell division in root
and shoot apical meristem cells, the growth could be arithmetic or geometrical.
Growth may not be and generally is not sustained at a high rate throughout the
life of cell/tissue/organ/organism. One can define three principle phases of growth
– the lag, the log and the senescent phase. When a cell loses the capacity to divide,
it leads to differentiation. Differentiation results in development of structures that
is commensurate with the function the cells finally has to perform. General principles
for differentiation for cell, tissues and organs are similar. A differentiated cell may

dedifferentiate and then redifferentiate. Since differentiation in plants is open, the
development could also be flexible, i.e., the development is the sum of growth and
differentiation. Plant exhibit plasticity in development.
Plant growth and development are under the control of both intrinsic and
extrinsic factors. Intercellular intrinsic factors are the chemical substances, called
(PGR). There are diverse groups of PGRs in plants,
principally belonging to five groups: auxins, gibberellins, cytokinins, abscisic acid
and ethylene. These PGRs are synthesised in various parts of the plant; they control
different differentiation and developmental events. Any PGR has diverse
physiological effects on plants. Diverse PGRs also manifest similar effects. PGRs
may act synergistically or antagonistically. Plant growth and development is also
affected by light, temperature, nutrition, oxygen status, gravity and such external
factors.
Flowering in some plants is induced only when exposed to certain duration of
photoperiod. Depending on the nature of photoperiod requirements, the plants
are called short day plants, long day plants and day-neutral plants. Certain plants
also need to be exposed to low temperature so as to hasten flowering later in life.
This treatement is known as vernalisation.

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