HETEROBLASTIC DEVELOPMENT IN PLANTS
161
5-lobed leaves (Fig. 1), formed only 3-lobed juvenile leaves after grafting. Conversely the number of juvenile leaves formed by seedling apices
was reduced in the grafts of the latter on adult plants. The authors
reject the view that the results must be explained by a rejuvenation of
the meristem caused by young tissues, since reversion also occurred in
some mature apices grafted at apical parts of adult plants. It was
considered that the progressive changes in leaf form are determined by
a substance synthesized in the leaves and accumulating in the basal part
of the stem and/or root. The author would again interpret these results
in terms of apical strengthening. The reversion in adult apices grafted
on adult plants could be explained on the basis of a temporary check
resulting from the grafting process.
c. Some Metabolic and Physiological Changes. In his investigations on
"ontogeny and senility in plants," Trippi (1963d) studied the activity
of the enzymes catalase, p-phenol oxidoreductase, amylase, and peroxidase in stem tissues of Robinia pseudoacacia. Comparisons were made
between plants of different ages, namely 1-year-old vegetative plants,
10-year-old vegetative plants, and 50-year-old plants in the reproductive
phase. The differences in activity obtained were interpreted as supporting
the concept that the variation in the quality of the meristems with age
is accompanied by structural changes in the cells. These changes were
considered to be substantially stable, since vegetative propagation from
juvenile and adult zones produced individuals which retained differential
enzyme activity, although some measure of rejuvenation had ensued in
the adult clone.
In later work Trippi et al. (1965) investigated amylase activity,
capacity for indoleacetic acid destruction, nitrogen level, and substances
stimulating fungal development, in tomato plant tissues at different
stages of ontogeny. There were again differences between apical and
basal parts and as in Robinia there was a partial rejuvenation on vegetative reproduction. Trippi (1965) also studied similar properties, including seed-germination inhibitors in 3-, 10-, and 30-year-old plants of
grapevine. It was concluded that a combination of deficiencies of water,
nutrients, and cell division substances would account for aging and
death in plants. This interpretation would imply that the aging of the
apical meristem mentioned by Trippi (1963d) is not inherent, but is
induced by the condition of the rest of the plant.
d. Rejuvenation in Adventitious Shoots and Lateral Branches. The
morphological reversion to primary leaf forms so frequently observed
during the sprouting of lateral or adventitious buds was explained in
Section III,B,2, in terms of apical strengthening. As postulated by
Krenke (1940), there is also evidence of some physiological rejuvenation
during the sprouting of such buds. The greater rooting capacity of
161
5-lobed leaves (Fig. 1), formed only 3-lobed juvenile leaves after grafting. Conversely the number of juvenile leaves formed by seedling apices
was reduced in the grafts of the latter on adult plants. The authors
reject the view that the results must be explained by a rejuvenation of
the meristem caused by young tissues, since reversion also occurred in
some mature apices grafted at apical parts of adult plants. It was
considered that the progressive changes in leaf form are determined by
a substance synthesized in the leaves and accumulating in the basal part
of the stem and/or root. The author would again interpret these results
in terms of apical strengthening. The reversion in adult apices grafted
on adult plants could be explained on the basis of a temporary check
resulting from the grafting process.
c. Some Metabolic and Physiological Changes. In his investigations on
"ontogeny and senility in plants," Trippi (1963d) studied the activity
of the enzymes catalase, p-phenol oxidoreductase, amylase, and peroxidase in stem tissues of Robinia pseudoacacia. Comparisons were made
between plants of different ages, namely 1-year-old vegetative plants,
10-year-old vegetative plants, and 50-year-old plants in the reproductive
phase. The differences in activity obtained were interpreted as supporting
the concept that the variation in the quality of the meristems with age
is accompanied by structural changes in the cells. These changes were
considered to be substantially stable, since vegetative propagation from
juvenile and adult zones produced individuals which retained differential
enzyme activity, although some measure of rejuvenation had ensued in
the adult clone.
In later work Trippi et al. (1965) investigated amylase activity,
capacity for indoleacetic acid destruction, nitrogen level, and substances
stimulating fungal development, in tomato plant tissues at different
stages of ontogeny. There were again differences between apical and
basal parts and as in Robinia there was a partial rejuvenation on vegetative reproduction. Trippi (1965) also studied similar properties, including seed-germination inhibitors in 3-, 10-, and 30-year-old plants of
grapevine. It was concluded that a combination of deficiencies of water,
nutrients, and cell division substances would account for aging and
death in plants. This interpretation would imply that the aging of the
apical meristem mentioned by Trippi (1963d) is not inherent, but is
induced by the condition of the rest of the plant.
d. Rejuvenation in Adventitious Shoots and Lateral Branches. The
morphological reversion to primary leaf forms so frequently observed
during the sprouting of lateral or adventitious buds was explained in
Section III,B,2, in terms of apical strengthening. As postulated by
Krenke (1940), there is also evidence of some physiological rejuvenation
during the sprouting of such buds. The greater rooting capacity of