XI. THE EMBRYOLOGY OF ASCIDIANS
73
The tail is, in the tadpoles of the Ascidians, an organ of movement and
is endowed with a notochord and a strong and contractile musculature.
One can exclude the possibility that the chorda is responsible for the
tail's abnormality by the fact that the tadpoles move very poorly and
generally lie on the bottom of the culture dish. Moreover, that NaN 3
affects the musculature is shown by the fact that control tadpoles, if
plunged into an appropriate solution of NaN 3 , become immediately and
permanently paralysed in all their movements.
How can the result obtained be interpreted? As cytochrome oxidase
is, in fact, the enzyme blocked, and as cytochrome oxidase is normally
implicated in the respiratory cycle, we suggested that because of the
blocking the respiratory cycle might not work regularly any more; there
would be, as a consequence, a poor supply of utilizable energy, with
evident detriment to the construction of fibrous, contractile proteins.
It is difficult to explain why the abnormalities are limited to the tail
only when the mitochondria are present in all cells. To explain this
difficulty one can suppose either that the mitochondria in the ^onmuscular' cells are 'protected' (by other cytoplasmic constituents), or
that they are 'resistent' to the action of the NaN 3 . This last suggestion
would be equivalent to admitting that there is another sort of mitochondria.
The above mentioned effect on the tail in the tadpoles is also brought
about by the use of KCN (Patricolo, 1959), CO (De Vincentiis, 1956a, c)
and by partial anaerobiosis (De Vincentiis, 1956b); in the latter case, the
enzyme, although not chemically blocked, nevertheless does not function.
2. Inhibition of Succinic Dehydroegnase
Another enzyme which, as well as cytochrome oxidase, is concerned
with respiratory processes, is succinic dehydrogenase.
This enzyme is 'specifically' blocked by sodium malonate and by
sodium selenite. The existence of this block can be checked by the
tetrazolium cytochemical reaction. Like cytochrome oxidase, it is a
mitochondrial enzyme. In the course of development it consequently
follows the destiny of the mitochondria, which means that it is segregated
with them in the cells of the muscular line.
The treatment of eggs at different stages of development with malonate
or selenite, induces specific abnormalities in the tadpoles; these, again,
possess normal 'heads' but distorted, twisted, and always non-functional
tails (Reverberi, 1957a).
3. Inhibition of Tyrosinase
The same result (completely unexpected) has been obtained by
Minganti (1957b) with the inhibitors of tyrosinase, which is not a
73
The tail is, in the tadpoles of the Ascidians, an organ of movement and
is endowed with a notochord and a strong and contractile musculature.
One can exclude the possibility that the chorda is responsible for the
tail's abnormality by the fact that the tadpoles move very poorly and
generally lie on the bottom of the culture dish. Moreover, that NaN 3
affects the musculature is shown by the fact that control tadpoles, if
plunged into an appropriate solution of NaN 3 , become immediately and
permanently paralysed in all their movements.
How can the result obtained be interpreted? As cytochrome oxidase
is, in fact, the enzyme blocked, and as cytochrome oxidase is normally
implicated in the respiratory cycle, we suggested that because of the
blocking the respiratory cycle might not work regularly any more; there
would be, as a consequence, a poor supply of utilizable energy, with
evident detriment to the construction of fibrous, contractile proteins.
It is difficult to explain why the abnormalities are limited to the tail
only when the mitochondria are present in all cells. To explain this
difficulty one can suppose either that the mitochondria in the ^onmuscular' cells are 'protected' (by other cytoplasmic constituents), or
that they are 'resistent' to the action of the NaN 3 . This last suggestion
would be equivalent to admitting that there is another sort of mitochondria.
The above mentioned effect on the tail in the tadpoles is also brought
about by the use of KCN (Patricolo, 1959), CO (De Vincentiis, 1956a, c)
and by partial anaerobiosis (De Vincentiis, 1956b); in the latter case, the
enzyme, although not chemically blocked, nevertheless does not function.
2. Inhibition of Succinic Dehydroegnase
Another enzyme which, as well as cytochrome oxidase, is concerned
with respiratory processes, is succinic dehydrogenase.
This enzyme is 'specifically' blocked by sodium malonate and by
sodium selenite. The existence of this block can be checked by the
tetrazolium cytochemical reaction. Like cytochrome oxidase, it is a
mitochondrial enzyme. In the course of development it consequently
follows the destiny of the mitochondria, which means that it is segregated
with them in the cells of the muscular line.
The treatment of eggs at different stages of development with malonate
or selenite, induces specific abnormalities in the tadpoles; these, again,
possess normal 'heads' but distorted, twisted, and always non-functional
tails (Reverberi, 1957a).
3. Inhibition of Tyrosinase
The same result (completely unexpected) has been obtained by
Minganti (1957b) with the inhibitors of tyrosinase, which is not a