Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed through growth, maturation, flowering, seed formation and senescence. The term is also applied to formation of cells/tissues/organs.
It can also applied for change in phases of life, e.g., from vegetative to flowering, and from leaf initiation to leaf expansion. It is also used at sub-cellular level, e.g., appearance of chloroplasts in cells exposed to light. The last phase of the development process in plants is senescence during which, events leading to ageing and death take place.
Diagrammatic representations of the sequence of processes of development of a cell are summarized as follows:
The plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity, e.g., heterophylly in cotton, coriander and larkspur.
In such plants the leaves of the juvenile plant are different in shape than those in mature plants. On other hand, difference in shapes of leaves produced in air and while in water in buttercup (Ranunculus) also represent heterophyllous development due to environment. This phenomenon of heterophylly is an example of plasticity.
Thus, growth differentiation and development are very closely related events in the life of a plant. However, development in considered as sum of growth and differentiation.
The development in plants (i.e., both growth and differentiation) is under control of intrinsic and extrinsic factors. The former includes both intracellular (genetic) or intercellular factors (chemicals such as plant growth regulators) while extrinsic factors include light, temperature, water, oxygen, nutrition, etc..
However, the role(s) of PGRs are only one kind of intrinsic control. Along with genomic control and extrinsic factors, they play an important role in plant growth and development. The extrinsic factors, such as temperature and light control plant growth and development via PGR. Such events are vernalisation, flowering, dormancy, seed germination, plant movements, etc.