Agriculture Reference
In-Depth Information
sexual progeny, and transgenerational inheritance is favored in cells in
the corpus layer. This layer normally produces germ cells in sexual
reproduction, demonstrating that some, if not strict, lineage is main-
tained in plant germ lines. Although plant species have a propensity for
multiple stem cell lines (meristems) at many physical locations
capable of leading to gametogenesis, sexual reproduction in many plants
(especially monocots) is con
ned to a stricter germ cell lineage (Johri and
Coe 1983; Hunter et al. 2006). Also, despite frequent adventitious
reproduction at many stages of the life cycle, gametogenic cell lines
often form very early and continuously after fertilization, similar to
many animals. Totipotency or pluripotency of cell clusters rather than of
single cells may re
ect also the requirement of a small population of cells
to produce critical threshold levels of epigenetic control factors, as was
also realized in animal cultures (Blau et al. 1983). This may also allow
coordinated enhancement of control factor production (Yamanaka and
Blau 2010).
Plants display indeterminate somatic development and continue to
produce or maintain totipotent germ cells or pluripotent meristem cells
adventitiously very late into their development at many physical loca-
tions in the plant body. In an extreme example, the Kalenchoe plant is
able to form complete plantlets on the leaf margin meristems and these
plantlets often form a second or third set of plantlets on their successive
margins (Walbot and Evans 2003). Plants also appear to be capable
of arising easily from multiple lineages or perhaps even by
dedifferentiation (Avivi et al. 2004; Komarova et al. 2004). Even though
it is possible that plant totipotent somatic cells may be observed long
after fertilization, most cells in the plant body are not totipotent. The
classical experiments of Takebe appeared to demonstrate that highly
differentiated leaf cells and their intrinsic cytoplasm and nuclei are able
to dedifferentiate and regenerate the entire plant somatic structure
(Nagata and Takebe 1971; Takebe et al. 1971). This is in contrast to
animals where the egg cytoplasm had always been required. However, a
dif
cult question has been whether or not somatic cell totipotency is
always the result of dedifferentiation, or also occurs from cryptic latent
niche germ or pluripotent cells that are not easily recognized in the
somatic structure (Sugimoto et al. 2011). Considering that totipotency
that has been demonstrated from terminal somatic cells has always
utilized a population and not a single isolated cell, it could not be
concluded that totipotent or pluripotent cytoplasm in cryptic plant or
animal (Gurdon 1962; Sugimoto et al. 2011) stem cells is not required,
until nuclear reprogramming experiments were achieved in animals
(Takahashi and Yamanaka 2006).
