New organs such as shoots, roots or embryos can
be induced to form on plant tissues lacking pre-
Such freshly originated organs
are said to be adventive or adventitious.
of new form and organisation, where previously it
was absent, is termed adventitious organogenesis, or,
Adventitious formation of shoots is referred to as
and of roots as
From explants, structures may be formed that are
similar to the embryos found in true seeds. Such
embryos often develop a region equivalent to the
suspensor of zygotic embryos and, unlike shoot or
root buds, come to have both a shoot and a root pole.
To distinguish them from zygotic or seed embryos,
embryos produced from cells or tissues of the plant
body are called somatic embryos and the process
leading to their inception is termed
(see Chapter 9).
‘embryoid’ has been especially used when it has been
unclear whether the embryo-like structures seen in
cultures were truly the somatic equivalent of zygotic
Somatic embryogenesis is now such a
widely observed and documented event that somatic
embryo has become the preferred term.
formation of leaves adventitiously
denotes the presence of a shoot meristem.
leaves appear without apparent shoot formation:
opinions are divided on whether such leaves can have
, or whether a shoot
meristem must have been present first of all and
subsequently failed to develop. An example is
regeneration from flower-stem explants in tulip
(Kuipers and Langens-Gerrits, 1997).
of flowers or floral parts is rare, occurring only under
special circumstances. They are formed from, e.g.,
flower stem tissues (Van Den Ende
This type of regeneration is not relevant to plant
embryogenesis are essential for plant multiplication
New plants are seldom obtained in culture
by the union of shoots and roots independently
formed in callus.
The production of complete
plantlets by adventitious regeneration is achieved
from adventitious shoots, which are subsequently
rooted, or from somatic embryos.
Shoots, roots and
somatic embryos arise from single cells, or groups of
cells, which become induced by the cultural
conditions to become centres of active cell division
(adventitious meristems), each capable of producing
an organ of the one kind.
Regeneration has now been observed
numerous plants of many genera, but it cannot yet be
Even within a single species,
varieties can be found, which are recalcitrant.
Moreover, the capacity for regeneration can be lost