Agriculture Reference
In-Depth Information
environment-controlled growth rate is an important common trans-
generational phenotype that has been observed in both plants and
animals. Growth aberrations in plant somaclonal regeneration are the
most prevalent epigenetic changes observed (Larkin and Scowcroft
1981). The reduction of growth rate of plants in response to several
environmental cues has been considered a hallmark of phenotypic
adaptive response to the physical environment (Bressan et al. 1990)
and is also often linked to tolerance to biotic stress (Narsimhan et al.
2009). Plants and their cultured cells that are exposed to a challenging
environmental change readily and universally across taxa adapt to and
exhibit greatly reduced growth rates that are not due to a normal
Darwinian environmental selection process, but appear to be epige-
netically based (Hasegawa et al. 1986; Bressan et al. 1990; Maggio et al.
2006). A memory of this growth reduction and increased tolerance
persists for several mitotic generations of cultured plant cells even in
the absence of stress (Bressan et al. 1985; LaRosa et al. 1989). This
memory is further supported by observations that tolerance and the
smaller cell and slower growth phenotype are inherited by progeny
through meiosis in plants regenerated from them (Bressan et al. 1985).
Also, a common aberration of survivors resulting from mammalian
somatic nuclei transplants (cloning experiments) is the epigenetic
phenomenon of large offspring syndrome (Young et al. 1998). In the
famous case of the Dutch Hunger Winter of 1944
1945, malnourished
pregnant women carried prenatal children who exhibited decreased
birth weight, and increased insulin resistance in adulthood that
impairs somatic cell growth, as an environment (low-nutrient environ-
ment of mothers)-directed phenotype (Lumey 1992) just as in cultured
plant somatic cells. The
-
phenotype observed in the Dutch
Hungry Winter may also extend through meiotic generations (Bateson
2001; Youngson and Whitelaw 2008). These epigenetics-based reduc-
tions in growth of the progeny in both plants and humans have been
explained not on the basis of direct resource limitation but as a strategy
to conserve resources in anticipation of reduced availability in the
future, since smaller organisms require less resources from their
environment (Bressan et al. 1990; Youngson and Whitelaw 2008).
Growth reduction is not just a nutrient constraint because when
conditions are returned to normal, growth continues to be reduced.
The nutritional environment is
“
thrifty
”
somehow by plant cells or
animal somatic embryo/fetal cells, both of which being perhaps in an
easily in
“
sensed
”
uenced epigenetic state.
The importance of growth to survival, its intricate connection to the
environment, and its persistent and ubiquitous epigenetic nature in
