86
JOHN G. TORREY
ecdysone. Here the evidence is quite clear that hormone level affects
chromosomal DNA only at specific sites (presumably certain sequences
of genes) which become active, as is seen by their puffing patterns. In
these sites RNA synthesis occurs, based on transcribed information from
the DNA of the genes. Presumably specific proteins result from such
specific gene action. Finally, specific types of cell differentiation can be
correlated with particular puffing patterns resulting from the hormone
action. In this case, hormone levels are susceptible to the particular conditions of the environment, e.g., photoperiod. Such a model suggests that
the hormone acts by causing new specific protein synthesis under particular genie control. Varner (1964) and Varner and Chandra (1964)
have evidence for an analogous system in the gibberellin-induced de
novo synthesis of proteins associated with a- and ^-amylase synthesis
in the endosperm of GA-treated seeds of barley.
It is interesting that recently Möhr (see Ohlenroth and Möhr, 1964)
has concluded from his extensive studies in plant morphogenesis under
the influence of light that irradiation absorbed by the important photomorphogenic pigment, phytochrome, acts to cause differential gene action.
According to this view, different wavelengths of light, absorbed by
specific plant pigments, effect activation of different genes, which leads
to different patterns of cellular activity and, hence, of development. In
the specific case of fern prothallus development, which remains filamentous in red light, but can be switched to a two-dimensional pattern of
cell proliferation by exposure to blue light, Möhr has shown that the
blue light leads to new protein synthesis which results in changed
orientation of cell divisions.
Hotta and his associates (see Hotta and Osawa, 1958; Hotta et al.,
1959) have shown that such two-dimensional growth in Dryoptens
fern
gametophytes can be inhibited by the base analog, 8-azaguanine. The
analog is incorporated into the RNA of the gametophyte cells; the
nucleotides then show base ratios which more closely approximate
the RNA of the one-dimensional type of fern development than that for
two-dimensional development. The inhibitor also reduces protein synthesis. The authors concluded that the switch from one-dimensional to
two-dimensional development in the fern prothallus required a specific
RNA synthesis which, in turn, led to protein synthesis specific for the
two-dimensional type of development. The intermediate steps between
pigment absorption of a specific wavelength and the synthesis of a new
protein, presumably coded more or less directly from the DNA of the
cell, have yet to be worked out. However, it would fit into our existing
knowledge reasonably well to involve hormone action somewhere between the act of pigment absorption and the gene activation necessary
for new protein synthesis. Evidence for such involvement would bring
JOHN G. TORREY
ecdysone. Here the evidence is quite clear that hormone level affects
chromosomal DNA only at specific sites (presumably certain sequences
of genes) which become active, as is seen by their puffing patterns. In
these sites RNA synthesis occurs, based on transcribed information from
the DNA of the genes. Presumably specific proteins result from such
specific gene action. Finally, specific types of cell differentiation can be
correlated with particular puffing patterns resulting from the hormone
action. In this case, hormone levels are susceptible to the particular conditions of the environment, e.g., photoperiod. Such a model suggests that
the hormone acts by causing new specific protein synthesis under particular genie control. Varner (1964) and Varner and Chandra (1964)
have evidence for an analogous system in the gibberellin-induced de
novo synthesis of proteins associated with a- and ^-amylase synthesis
in the endosperm of GA-treated seeds of barley.
It is interesting that recently Möhr (see Ohlenroth and Möhr, 1964)
has concluded from his extensive studies in plant morphogenesis under
the influence of light that irradiation absorbed by the important photomorphogenic pigment, phytochrome, acts to cause differential gene action.
According to this view, different wavelengths of light, absorbed by
specific plant pigments, effect activation of different genes, which leads
to different patterns of cellular activity and, hence, of development. In
the specific case of fern prothallus development, which remains filamentous in red light, but can be switched to a two-dimensional pattern of
cell proliferation by exposure to blue light, Möhr has shown that the
blue light leads to new protein synthesis which results in changed
orientation of cell divisions.
Hotta and his associates (see Hotta and Osawa, 1958; Hotta et al.,
1959) have shown that such two-dimensional growth in Dryoptens
fern
gametophytes can be inhibited by the base analog, 8-azaguanine. The
analog is incorporated into the RNA of the gametophyte cells; the
nucleotides then show base ratios which more closely approximate
the RNA of the one-dimensional type of fern development than that for
two-dimensional development. The inhibitor also reduces protein synthesis. The authors concluded that the switch from one-dimensional to
two-dimensional development in the fern prothallus required a specific
RNA synthesis which, in turn, led to protein synthesis specific for the
two-dimensional type of development. The intermediate steps between
pigment absorption of a specific wavelength and the synthesis of a new
protein, presumably coded more or less directly from the DNA of the
cell, have yet to be worked out. However, it would fit into our existing
knowledge reasonably well to involve hormone action somewhere between the act of pigment absorption and the gene activation necessary
for new protein synthesis. Evidence for such involvement would bring