74
G.
REVERBERI
mitochondrial enzyme. As Bell (1955) first described and Minganti
confirmed, the tadpoles which develop from eggs thus treated (DECA;
phenylthiourea, etc.) are defective not only in the melanic pigmentation
of the sensory spots, but also in showing marked tail abnormalities.
The tyrosinase cannot be blamed, as no tyrosinase at all is to be found
in the cells which give rise to the tail. Minganti at first supposed
that the inhibitors used could produce a 'secondary' action on cytochrome oxidase or on succinic dehydrogenase but this assumption had
to be discarded when it was observed that the Nadi-reaction or
the tetrazolium-reaction were always positive after treatment with the
inhibitors. This led to consideration of the possibility that in the cells
of the muscular line another respiratory system exists, different from the
usual one, which is blocked by the action of the inhibitors of the tyrosinase. According to this hypothesis, two respiratory systems would be
present in the same cell and would work together or alternatively.
Experiments with substances which inhibit the two supposed systems
at the same time are much needed.
4. Action of Hydroxylamine and Lithium Chloride
The last mentioned results obtained by using the inhibitors of
tyrosinase raised the doubt that any kind of chemical or physical
treatment might have the same effect. This supposition, however, when
checked with other chemicals, proved to be incorrect. Hydroxylamine
is a substance which blocks the activity of many enzymes (peroxidases,
catalases, decarboxylases, dehydrogenases, amino-oxidases, transferases
etc.) and generally produces diffuse abnormalities in many embryonic
structures. It has, however, been possible (Patricolo, in press) to obtain,
with a proper concentration (10~
4
M), development to the larval stage.
The tadpoles obtained after this treatment looked very interesting, in
fact, their tails were completely normal, morphologically and functionally, but the 'heads' were spectacularly abnormal (Fig. 22). They
did not possess palps, had a much reduced intestine, and an 'external'
brain with pigmented spots. We do not know where the hydroxylamine
reacted, certainly not with the usual mitochondrial enzymes, since the
specific cytochemical reactions proved to be positive and in any case,
the tadpoles' tails were normal this time.
Another no less illustrative example, is offered by the results which
were obtained using LiCl (Farinella-Ferruzza, 1952, 1955). The action
of this chemical on Ascidian development was also investigated by
Ranzi and Ferreri (1944), Colwin (1949) and Nieuwkoop (1953). The
treatment of Phallusia eggs with LiCl produced (Farinella-Ferruzza,
1955) tadpoles 'without heads'; the anterior part of the tadpole, in fact,
had no palps, and above all no brain or sensory spots; it was elongated
G.
REVERBERI
mitochondrial enzyme. As Bell (1955) first described and Minganti
confirmed, the tadpoles which develop from eggs thus treated (DECA;
phenylthiourea, etc.) are defective not only in the melanic pigmentation
of the sensory spots, but also in showing marked tail abnormalities.
The tyrosinase cannot be blamed, as no tyrosinase at all is to be found
in the cells which give rise to the tail. Minganti at first supposed
that the inhibitors used could produce a 'secondary' action on cytochrome oxidase or on succinic dehydrogenase but this assumption had
to be discarded when it was observed that the Nadi-reaction or
the tetrazolium-reaction were always positive after treatment with the
inhibitors. This led to consideration of the possibility that in the cells
of the muscular line another respiratory system exists, different from the
usual one, which is blocked by the action of the inhibitors of the tyrosinase. According to this hypothesis, two respiratory systems would be
present in the same cell and would work together or alternatively.
Experiments with substances which inhibit the two supposed systems
at the same time are much needed.
4. Action of Hydroxylamine and Lithium Chloride
The last mentioned results obtained by using the inhibitors of
tyrosinase raised the doubt that any kind of chemical or physical
treatment might have the same effect. This supposition, however, when
checked with other chemicals, proved to be incorrect. Hydroxylamine
is a substance which blocks the activity of many enzymes (peroxidases,
catalases, decarboxylases, dehydrogenases, amino-oxidases, transferases
etc.) and generally produces diffuse abnormalities in many embryonic
structures. It has, however, been possible (Patricolo, in press) to obtain,
with a proper concentration (10~
4
M), development to the larval stage.
The tadpoles obtained after this treatment looked very interesting, in
fact, their tails were completely normal, morphologically and functionally, but the 'heads' were spectacularly abnormal (Fig. 22). They
did not possess palps, had a much reduced intestine, and an 'external'
brain with pigmented spots. We do not know where the hydroxylamine
reacted, certainly not with the usual mitochondrial enzymes, since the
specific cytochemical reactions proved to be positive and in any case,
the tadpoles' tails were normal this time.
Another no less illustrative example, is offered by the results which
were obtained using LiCl (Farinella-Ferruzza, 1952, 1955). The action
of this chemical on Ascidian development was also investigated by
Ranzi and Ferreri (1944), Colwin (1949) and Nieuwkoop (1953). The
treatment of Phallusia eggs with LiCl produced (Farinella-Ferruzza,
1955) tadpoles 'without heads'; the anterior part of the tadpole, in fact,
had no palps, and above all no brain or sensory spots; it was elongated