Differentiation, development and plasticity · Biology… | StemPy Lab
Course 11.1·Lesson 3 of 3
Differentiation, development and plasticity
Differentiation is the maturation of cells made by the meristems, as they take up the shape and job of a permanent tissue. Living cells that have lost the power to divide can start to divide again (dedifferentiation), and the new cells can mature again (redifferentiation). Development is the sum of growth and differentiation. Plants show plasticity: one plant can make different forms, as in heterophylly. Development is controlled by factors inside the plant and by factors outside it.
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From a dividing cell to a working cell
A new cell made by a meristem does not yet have a job. It is like a student who has just joined school. In time the cell takes up a shape and a job. A cell of the root tip may become a root hair. A cell of the stem may become a pipe for water.
This change is called differentiation. The cells made by the root apical meristem, the shoot apical meristem and the cambium mature to perform specific functions. This act of maturation is differentiation.
What differentiation does
Differentiation changes the cell so that it is best made for its work. Think of the pipes of the xylem, the tracheary elements.
The cell loses its protoplasm. It becomes dead and empty.
It builds a strong, elastic wall made of lignin and cellulose.
The wall is thick, so the pipe does not collapse when water is pulled up through it.
The cell gives up many things, and in exchange it does one job very well.
The place decides the fate
Cells that come from the same meristem do not all end up alike. This kind of differentiation is called open differentiation. The final form of a cell depends on where it lies.
Take the root tip. The cells that are pushed away from the apical meristem on the outer side become root cap cells. Those pushed to the edge of the root mature as the epidermis. Cells pushed inwards become other tissues. They came from the same group, but their place made the difference.
Dedifferentiation and redifferentiation
A cell that has matured has usually lost the power to divide. But it is not always a closed door. Under certain conditions, living differentiated cells can start to divide again. This is dedifferentiation.
Two familiar cases are in a dicot stem.
The interfascicular cambium forms from cells of the medullary rays, which are parenchyma cells that had stopped dividing.
The cork cambium forms from living cells of the cortex.
The new meristem makes new cells. These new cells may again stop dividing and mature to do a specific job. This is redifferentiation. For example, the cambium makes secondary xylem and secondary phloem, and the cork cambium makes cork.
A cycle of three boxes joined by arrows. At the top left, a box of meristem cells: two small square cells, each with a big purple nucleus, labelled small cells that divide. A green arrow called differentiation runs to a box at the top right with permanent cells: one cell with a big pale vacuole and one tall cell with a thick brown wall. From there a red arrow called dedifferentiation runs down to a box at the bottom called meristem again, with three small dividing cells and the words interfascicular cambium, cork cambium. A blue arrow called redifferentiation runs from that box back up to the top left, with the note that new cells mature again into secondary xylem, phloem and cork.
Put the three words in order.
Differentiation: a dividing cell matures into a permanent cell.
Dedifferentiation: a living permanent cell begins to divide again.
Redifferentiation: the cells made by the new meristem mature again.
Development
Development is the sum of all the changes that a plant goes through in its life, from the germination of the seed to old age, called senescence. It includes growth, and it includes differentiation.
Development = growth + differentiation.
Seeds germinate, roots and shoots grow, leaves open, flowers form, fruits ripen, and in the end the plant ages. These are all stages of development.
Plasticity
Plants follow different paths in their development in response to their surroundings or to the stage of their life. They can make different kinds of structures. This ability is called plasticity.
The best known example is heterophylly, which means that one plant bears leaves of different shapes. It has two kinds of cause.
Because of the stage of life. In cotton, coriander and larkspur, the leaves of the young plant, the juvenile leaves, differ in shape from the leaves of the mature plant.
Because of the surroundings. In buttercup, the leaves that grow in air are different from the leaves that grow in water. The leaves in air are broad. The leaves in water are narrow and thread-like.
Two drawings. On the left, a coriander plant: two broad, lightly lobed leaves low on the stem, marked juvenile leaves, and, higher up, leaves made of several thin segments, marked mature leaves, finely divided. On the right, a buttercup plant standing in water: above the water line two broad lobed leaves, marked leaves in air, and below the line three narrow, thread-like divided leaves, marked leaves in water.
You should find that the new leaf is broad before the week of the change and finely cut after it.
What controls development?
Growth, differentiation and development are very closely related. Development is controlled by two kinds of factor.
Intrinsic factors work from inside the plant. They include intracellular factors, the genes in the cell, and intercellular factors, the chemicals that move between cells, such as the plant growth regulators.
Extrinsic factors work from outside the plant. They are light, temperature, water, oxygen and nutrition.
The next course takes up the plant growth regulators.
Try it in Python
The program says which kind of leaf a coriander plant makes in each week of its life.
Practise with new numbers
Common mistakes
Saying that dedifferentiation is the same as differentiation. In dedifferentiation, a mature living cell begins to divide again.
Giving the wrong cells. The interfascicular cambium and the cork cambium arise from living permanent cells, not from dead ones.
Mixing up development and growth. Development is growth plus differentiation.
Putting buttercup with the stage of life. The leaves of buttercup change with water and air. The leaves of cotton, coriander and larkspur change with age.
Mixing up plasticity with a change of genes. Plasticity is the ability of one plant to make different forms.
Remember these
Differentiation: cells made by the meristems mature to do specific jobs.
Dedifferentiation: living permanent cells divide again, as in the interfascicular cambium and the cork cambium.
Redifferentiation: the cells of the new meristem mature again, for example into secondary xylem.
Development = growth + differentiation, from seed germination to senescence.
Plasticity: heterophylly in cotton, coriander and larkspur by age, and in buttercup by surroundings.
Intrinsic factors: genes and plant growth regulators. Extrinsic factors: light, temperature, water, oxygen and nutrition.
Check yourself
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
What is differentiation? Give one change that a cell undergoes when it becomes a tracheary element.
Give one example of dedifferentiation in a dicot stem.
What is redifferentiation?
What is plasticity? Name two plants that show heterophylly because of age.
Name the two kinds of factor that control development, and one example of each.
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