ORGANIZED DEVELOPMENT IN PLANTS
81
described by Skoog and Miller (1957) ; the callus cultured on the surface
of a liquid medium of the same composition failed to produce organized
structures. This observation is rather reminiscent of Skoog's earlier report (1944) of a change in capacity to organize as being dependent on
change in physical substrate. Kehr and Smith (1954) raised the question
whether callus tissue in continued subculture lost the capacity to form
organized structures as a result of prolonged culture in vitro. This change
might be equated to the phenomenon of anergy noted by Gautheret
(1948) in which callus tissue changes its physiological state and no
longer requires an external supply of auxin, but synthesizes enough auxin
for its own requirements. Such tissue changes its morphology, becoming
more friable and hydrated, and apparently also loses its capacity to
form organs. One is faced here with the question of whether these
changes involve basic changes in the genome of the cell or whether,
under a given set of conditions used for culturing the cells, the actual
expression of the genetic information is substantially reduced or modified. No clear evidence for a decision in this matter is currently available. Clearly, there is a substantial gap in our information between a
tissue such as anergized carrot callus parenchyma in culture described
by Gautheret, which behaves in a remarkably restricted manner, and the
carrot callus cells studied by Steward, which show the potentiality of
whole-plant formation.
C. Bud Initiation and Apical Meristem Culture
In 1946, Ball demonstrated that isolated shoot apices of Lupinus and
Tropaeolum, only 400 μ
3 in volume and excised so as to include the three
youngest leaf primordia, could be successfully grown into whole plants
when cultured in a relatively simple nutrient medium containing sucrose
and inorganic salts. This result has been achieved by other investigators
with a number of species of angiosperms, with certain ferns, and with
members of other lower vascular plants (cf., Wetmore and Wardlaw,
1951). Using this procedure, Morel and Martin (1955) reported the
culture of isolated shoot apices of potato {Solanum tuberosum)
possessing young leaf primordia. Apices isolated from virus-infected plants and
grown in culture could be shown to be free of virus infection, and, thus,
whole plants grown from such apices could be used to provide virus-free
stocks for vegetative propagation. This method of isolated shoot apex
culture has been used in horticulture for producing virus-free plants of
a number of important commercial species.
In all successful cases of apical meristem culture in the angiosperms,
the apical meristem must have at least one attached leaf primordium as
81
described by Skoog and Miller (1957) ; the callus cultured on the surface
of a liquid medium of the same composition failed to produce organized
structures. This observation is rather reminiscent of Skoog's earlier report (1944) of a change in capacity to organize as being dependent on
change in physical substrate. Kehr and Smith (1954) raised the question
whether callus tissue in continued subculture lost the capacity to form
organized structures as a result of prolonged culture in vitro. This change
might be equated to the phenomenon of anergy noted by Gautheret
(1948) in which callus tissue changes its physiological state and no
longer requires an external supply of auxin, but synthesizes enough auxin
for its own requirements. Such tissue changes its morphology, becoming
more friable and hydrated, and apparently also loses its capacity to
form organs. One is faced here with the question of whether these
changes involve basic changes in the genome of the cell or whether,
under a given set of conditions used for culturing the cells, the actual
expression of the genetic information is substantially reduced or modified. No clear evidence for a decision in this matter is currently available. Clearly, there is a substantial gap in our information between a
tissue such as anergized carrot callus parenchyma in culture described
by Gautheret, which behaves in a remarkably restricted manner, and the
carrot callus cells studied by Steward, which show the potentiality of
whole-plant formation.
C. Bud Initiation and Apical Meristem Culture
In 1946, Ball demonstrated that isolated shoot apices of Lupinus and
Tropaeolum, only 400 μ
3 in volume and excised so as to include the three
youngest leaf primordia, could be successfully grown into whole plants
when cultured in a relatively simple nutrient medium containing sucrose
and inorganic salts. This result has been achieved by other investigators
with a number of species of angiosperms, with certain ferns, and with
members of other lower vascular plants (cf., Wetmore and Wardlaw,
1951). Using this procedure, Morel and Martin (1955) reported the
culture of isolated shoot apices of potato {Solanum tuberosum)
possessing young leaf primordia. Apices isolated from virus-infected plants and
grown in culture could be shown to be free of virus infection, and, thus,
whole plants grown from such apices could be used to provide virus-free
stocks for vegetative propagation. This method of isolated shoot apex
culture has been used in horticulture for producing virus-free plants of
a number of important commercial species.
In all successful cases of apical meristem culture in the angiosperms,
the apical meristem must have at least one attached leaf primordium as