78
JOHN G. TORREY
pea root segments, Torrey (1956, 1962) showed that absence from the
medium of several chemical constituents, including thiamine, nicotinic
acid, adenine, and certain micronutrient elements, prevented or limited
root initiation. Critical for the initiation process was an external supply
of auxin; this hormone was found to interact with supplied adenine sulfate and kinetin in such a way as to suggest that both auxin and a
natural kinin were active in controlling root initiation in the intact root.
This general picture of hormonal control of the initiation process with the
possibility of limitation of initiation in in vitro systems by other limiting
components of the nutrient medium appears to apply equally well to root,
stem, or callus tissue pieces cultured in vitro.
In Figs. 13-19 are illustrated examples of bud or root initiation in
cultured organs or tissues, in which the onset of specific structural
organization could be manipulated by control of the physical or chemical,
especially hormonal environment surrounding the cells or tissues. (See
p. 72.)
Gautheret has shown that light and temperature affect both callus tissue growth and root initiation in Topinambour
cultures. In the presence
of optimum concentrations of NAA at 26°C, nearly seven times as many
roots were formed in white fluorescent light as in the dark. Tissues grown
in light, then grafted to tissues grown in the dark, were capable of
inducing roots in the latter, apparently under the stimulus transmitted
from the light-grown tissue to that grown in the dark (Spanjersberg
and Gautheret, 1962). Recently, Furuya and Torrey (1964) found that
red light inhibition of auxin-induced root initiation in pea root segments
could be completely reversed by small amounts of far-red irradiation.
The involvement of hormonal stimuli in addition to auxin seems probable
in both these systems which deserve further exploration at the chemical
level.
B. Bud and Leaf Initiation
Bud initiation in callus tissue under the control of chemical and
physical aspects of the environment has been described as frequently as
root initiation. White (1939) reported that bud initiation in tobacco
callus tissue occurred under the inductive conditions of submerged
culture. Since the time when these observations were made, many studies
have been undertaken on bud initiation in callus tissue, especially in
response to particular nutrient environments. The most extensive studies
are those of Skoog and his associates, referred to earlier, in which bud
initiation under the influence of an appropriate auxin-kinin balance was
observed in Nicotiana
tabacum stem callus (summarized in Skoog and
Miller, 1957). Gautheret (1959) reviewed his own work on bud formation
JOHN G. TORREY
pea root segments, Torrey (1956, 1962) showed that absence from the
medium of several chemical constituents, including thiamine, nicotinic
acid, adenine, and certain micronutrient elements, prevented or limited
root initiation. Critical for the initiation process was an external supply
of auxin; this hormone was found to interact with supplied adenine sulfate and kinetin in such a way as to suggest that both auxin and a
natural kinin were active in controlling root initiation in the intact root.
This general picture of hormonal control of the initiation process with the
possibility of limitation of initiation in in vitro systems by other limiting
components of the nutrient medium appears to apply equally well to root,
stem, or callus tissue pieces cultured in vitro.
In Figs. 13-19 are illustrated examples of bud or root initiation in
cultured organs or tissues, in which the onset of specific structural
organization could be manipulated by control of the physical or chemical,
especially hormonal environment surrounding the cells or tissues. (See
p. 72.)
Gautheret has shown that light and temperature affect both callus tissue growth and root initiation in Topinambour
cultures. In the presence
of optimum concentrations of NAA at 26°C, nearly seven times as many
roots were formed in white fluorescent light as in the dark. Tissues grown
in light, then grafted to tissues grown in the dark, were capable of
inducing roots in the latter, apparently under the stimulus transmitted
from the light-grown tissue to that grown in the dark (Spanjersberg
and Gautheret, 1962). Recently, Furuya and Torrey (1964) found that
red light inhibition of auxin-induced root initiation in pea root segments
could be completely reversed by small amounts of far-red irradiation.
The involvement of hormonal stimuli in addition to auxin seems probable
in both these systems which deserve further exploration at the chemical
level.
B. Bud and Leaf Initiation
Bud initiation in callus tissue under the control of chemical and
physical aspects of the environment has been described as frequently as
root initiation. White (1939) reported that bud initiation in tobacco
callus tissue occurred under the inductive conditions of submerged
culture. Since the time when these observations were made, many studies
have been undertaken on bud initiation in callus tissue, especially in
response to particular nutrient environments. The most extensive studies
are those of Skoog and his associates, referred to earlier, in which bud
initiation under the influence of an appropriate auxin-kinin balance was
observed in Nicotiana
tabacum stem callus (summarized in Skoog and
Miller, 1957). Gautheret (1959) reviewed his own work on bud formation