Ripening or maturation is a process in
fruit that causes them to become more edible. In general, fruits get
sweeter, less acidic, less green and
softer as they ripen.
After a process known as
pollination the petals of the
flower fall off , the
ovary begins to expand and the
ovule begins to develops into a
seed. The ovary eventually comes to
form, along with other parts of the flower in many cases, a
structure surrounding the seed or
seeds that is the fruit.
Stages of ripening/maturation are regulated by
phytoregulators (hormones).
At first the developing seeds inside the ovary wall start to produce cytokinins which are
hormones that are secrete by the seed and cause cell
division in the
ovary wall that begins to
expand.
Next, the growing seeds produce gibberellic acid which
is exported to the wall of the ovary
and causes rapid expansion of each of the
cells. The combination of more cells and expanding cells leads to
tremendous increase in the size of the ovary. As this is happening, the
mother plant is producing another hormone, abscisic acid, which
causes the embryo in the
developing seeds to become
dormant. This is adaptive because it prevents the seed from
sprouting inside the warm, moist fruit. Fruit development continues
until the seeds have achieved a complete ripening.
An other important plant hormone involved with ripening is the chemical
ethylene. Ethylene is a gas
created by plants at the final stage of maturation. Ethylene causes
increased levels of certain enzymes
in the fruit. These enzymes include:
• amylase, which breaks down starch
to produce simple sugars.
• pectinase breaks down pectin, the substance that keeps fruit hard.
• Other enzymes break down the green pigment
chlorophyll, which is replaced
by other coloured pigments such as
blue, yellow or red.
This sequence of events is diagrammed below:
With some multi-seeded fruits the extent of development of the
pulp of the fruit is proportional to
the number of fertilized ovules. The wall
of the fruit, developed from the
ovary wall of the flower, is called the
pericarp or
fruit wall.
Some species of climbing
plants develop holdfast roots which help to support the vines on
trees, walls, and rocks. By forcing their way into minute pores and
crevices, they hold the plant firmly in place.
Climbing plants, like the poison ivy (Toxicodendron
radicans), Boston ivy (Parthenocissus
tricuspidata), and trumpet creeper (Campsis
radicans), develop holdfast roots which help to
support the vines on trees, walls, and rocks. By forcing their
way into minute pores and crevices, they hold the plant firmly
in place. Usually the Holdfast roots die at the end of the first
season, but in some species they are perennial. In the tropics
some of the large climbing plants have hold-fast roots by which
they attach themselves, and long, cord-like roots that extend
downward through the air and may lengthen and branch for several
years until they strike the soil and become absorbent roots.
Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House,
1994
