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Comment on “photomorphogenesis— a term designating photoregulation or photocontrol by plants”
380
NEWS AND VIEWS
developmental processes, as each photomorphosis is the result of a large number of physiological processes and molecular events. In plant physiology it is quite common to use the terms thermo- and hydromorphogenesis, as their results, thermo- and hygromorphoses. Low temperatures, like light, inhibit the elongation of the internodes, and the leaves of the amphibic plant Ranunculus aquutilis look different as a result of hygromorphogenesis. Accordingly, we find many xeromorphoses in desert plants. In conclusion, the term photomorphogenesis includes all formative processes modulated by light and even the biochemical and physiological processes involved, irrespective of the photoreceptor involved. Photoperiodism denotes those processes which are under the control of day length, measured with the physiological clock. Nastic movements, which are brought about by changes in turgor pressure, are either photonastic (i.e. directly caused by a change in fluence rate) or nyktinastic (i.e. governed by the physiological clock).
1 T. Tanada, Plant Phgsiol., 49 (1972)
560-562.
Comment on “Photomorphogenesis - a term designating photoregulation or photocontrol by plants” Silvia E. Braslavsky Max-Planck-Institut (F.R.G.)
fir
Strahlenchemie,
Stifstrasse 34-36,
W-4330 MidhAm
an der Ruhr
In my opinion, and also based on experience as a member and Chairperson of the Photochemistry Commission of IUPAC, in questions of terminology it is never advisable to go against the general opinion of the scientists working in a particular field. It is true that often terms are used in a general sense even if they are not as precise. This is the case with photcmwrphogenesis. We all understand by this term the control of plant development by light independent of photosynthesis, including seed germination, induction of flowering, transport of sucrose, hook opening, coleoptile elongation, anthocyanine synthesis, just to name some of the processes controlled by phytochrome and/or the blue-absorbing pigments. In fact, we use the term with a very broad meaning, i.e. for light sensing or perception [ 11. Is this wrong? Do we need to change the term to another expression? I am not sure. I think that we do understand each other when we use the term photomorphogenesis, even if we sometimes imply processes that are not morphogenie in principle. It is up to the general “photomorphogenic” community to choose
381
NEWS AND VIEWS
the proper term. More important, however, is that by keeping this rather broad and loose term, scientists working with the various pigments and analysing the various effects get together in meetings and conferences and learn from each others’ experiences. Regardless of the term used, wheat we need is to understandthe processes and discover the connection at a molecular level between the absorption of light and the signal transduction chain, still a puzzle for most of the photomorphogenic processes. 1
R. E. Kendrick and G. H. M. Kronenberg, Photom.orphogenesi.s Dordrecht, 1986.
The use of all-tram @carotene photosensitivity
in Plants, MartinusNijhoff,
to ameliorate PDT-induced skin
T. G. Truscott Department
of Chemistry,
University
of Keek,
Keele, Stc&rdshire
ST5 SBG (U.K.1
It is well known that all-trans p-carotene at doses of more than 30 mg d-l is a useful treatment for the skin photosensitivity associated with erythropoietic protoporphyria (epp). The role of B-carotene is thought to be via the quenching of the singlet oxygen (‘0,) precursor, protoporphyrin (pp) triplet and also, possibly, the quenching of ‘02 itself. 3pp+ p-carotene -
pp +3&2rotene
‘02 + p-carotene -
0, +3@2rrotene
3/3-carotene -
p-carotene + heat
However, it has been generally accepted until now that such treatment would not be useful to ameliorate the porphyrin-induced photosensitivity associated with photodynamic therapy (PDT) because of the long time needed for the skin and serum to build-up a sufficient concentration of P-carotene. Of course, the use of p-carotene prior to PDT may interfere with the cancer therapy itself. A recent paper [ 1 ] by Prince et al. suggests that a rapid serum carotene loading can be obtained with high doses of p-carotene (300 rug d-l, the maximum FDA recommended dose) and, furthermore, notes a perceptible yellow colour of the skin 10 d after treatment. Their data indicate the serum carotenoid concentration is increased six times (on average) after 10 d of carotene treatment and five times after only 1 week. Since PDT-induced skin photosensitivity persists for very much longer periods than approximately 10 d it is suggested that the use of (a high dosage) /?-caroteneafter PDT be reconsidered.
NEWS AND VIEWS
developmental processes, as each photomorphosis is the result of a large number of physiological processes and molecular events. In plant physiology it is quite common to use the terms thermo- and hydromorphogenesis, as their results, thermo- and hygromorphoses. Low temperatures, like light, inhibit the elongation of the internodes, and the leaves of the amphibic plant Ranunculus aquutilis look different as a result of hygromorphogenesis. Accordingly, we find many xeromorphoses in desert plants. In conclusion, the term photomorphogenesis includes all formative processes modulated by light and even the biochemical and physiological processes involved, irrespective of the photoreceptor involved. Photoperiodism denotes those processes which are under the control of day length, measured with the physiological clock. Nastic movements, which are brought about by changes in turgor pressure, are either photonastic (i.e. directly caused by a change in fluence rate) or nyktinastic (i.e. governed by the physiological clock).
1 T. Tanada, Plant Phgsiol., 49 (1972)
560-562.
Comment on “Photomorphogenesis - a term designating photoregulation or photocontrol by plants” Silvia E. Braslavsky Max-Planck-Institut (F.R.G.)
fir
Strahlenchemie,
Stifstrasse 34-36,
W-4330 MidhAm
an der Ruhr
In my opinion, and also based on experience as a member and Chairperson of the Photochemistry Commission of IUPAC, in questions of terminology it is never advisable to go against the general opinion of the scientists working in a particular field. It is true that often terms are used in a general sense even if they are not as precise. This is the case with photcmwrphogenesis. We all understand by this term the control of plant development by light independent of photosynthesis, including seed germination, induction of flowering, transport of sucrose, hook opening, coleoptile elongation, anthocyanine synthesis, just to name some of the processes controlled by phytochrome and/or the blue-absorbing pigments. In fact, we use the term with a very broad meaning, i.e. for light sensing or perception [ 11. Is this wrong? Do we need to change the term to another expression? I am not sure. I think that we do understand each other when we use the term photomorphogenesis, even if we sometimes imply processes that are not morphogenie in principle. It is up to the general “photomorphogenic” community to choose
381
NEWS AND VIEWS
the proper term. More important, however, is that by keeping this rather broad and loose term, scientists working with the various pigments and analysing the various effects get together in meetings and conferences and learn from each others’ experiences. Regardless of the term used, wheat we need is to understandthe processes and discover the connection at a molecular level between the absorption of light and the signal transduction chain, still a puzzle for most of the photomorphogenic processes. 1
R. E. Kendrick and G. H. M. Kronenberg, Photom.orphogenesi.s Dordrecht, 1986.
The use of all-tram @carotene photosensitivity
in Plants, MartinusNijhoff,
to ameliorate PDT-induced skin
T. G. Truscott Department
of Chemistry,
University
of Keek,
Keele, Stc&rdshire
ST5 SBG (U.K.1
It is well known that all-trans p-carotene at doses of more than 30 mg d-l is a useful treatment for the skin photosensitivity associated with erythropoietic protoporphyria (epp). The role of B-carotene is thought to be via the quenching of the singlet oxygen (‘0,) precursor, protoporphyrin (pp) triplet and also, possibly, the quenching of ‘02 itself. 3pp+ p-carotene -
pp +3&2rotene
‘02 + p-carotene -
0, +3@2rrotene
3/3-carotene -
p-carotene + heat
However, it has been generally accepted until now that such treatment would not be useful to ameliorate the porphyrin-induced photosensitivity associated with photodynamic therapy (PDT) because of the long time needed for the skin and serum to build-up a sufficient concentration of P-carotene. Of course, the use of p-carotene prior to PDT may interfere with the cancer therapy itself. A recent paper [ 1 ] by Prince et al. suggests that a rapid serum carotene loading can be obtained with high doses of p-carotene (300 rug d-l, the maximum FDA recommended dose) and, furthermore, notes a perceptible yellow colour of the skin 10 d after treatment. Their data indicate the serum carotenoid concentration is increased six times (on average) after 10 d of carotene treatment and five times after only 1 week. Since PDT-induced skin photosensitivity persists for very much longer periods than approximately 10 d it is suggested that the use of (a high dosage) /?-caroteneafter PDT be reconsidered.