Regulation of the subunit composition of plastidic glutamine synthetase of the wild-type and of the phytochrome-deficient aurea mutant of tomato by blue/UV-A- or by UV-B-light.
The photomorphogenetic aurea mutant of tomato severely deficient in spectrophotometrically active phytochromes was used to study the light-regulation of the single-copy nuclear gene encoding plastidic glutamine synthetase (GS-2; EC 6.1.3.2). The de-etiolation of dark-grown aurea mutant seedling cotyledons showed an obligatory dependency on blue light. A limited red light-responsiveness of etiolated aurea cotyledons is, however, retained as seen by the stimulation of both the GS-2 transcript and protein level in the cotyledons of aurea seedlings during growth in red light. The subunits of the octameric GS-2 enzyme were represented by polypeptides with similar electrophoretic mobilities (polypeptides a) in etiolated wild-type or aurea mutant cotyledons. GS-2 proteins with similar apparent molecular masses were also seen in the cotyledons of red light-grown aurea mutant seedlings. In contrast, GS-2 polypeptides with different apparent molecular masses (polypeptides a and b) were detected in the cotyledons of wild-type seedlings grown in red light. This difference indicates that the (post-translational) modification of tomato GS-2 subunit composition is mediated by the photoreceptor phytochrome. The illumination of etiolated wild-type or aurea cotyledons with UV-A- or UV-B-light light resulted in an increase in both the GS-2 transcript and protein level. Following illumination of etiolated wild-type seedlings with UV-A-light, the relative proportion of the GS-2 polypeptides a and b was similar than upon irradiation with blue light but different than after exposure to UV-B- or red light. This result suggests the involvement of a blue/ UV-A-light-specific photoreceptor in the regulation of tomato GS-2 subunit composition.
Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Germany.
A
A
Migge
E
E
Carrayol
B
B
Hirel
M
M
Lohmann
G
G
Meya
T W
TW
Becker
D015870:Gene Expression / Q000528:radiation effects; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D008027:Light; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics* / Q000528:radiation effects; D009154:Mutation; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000201:enzymology; D011487:Protein Conformation / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays
D012333:RNA, Messenger; D018749:RNA, Plant; D010834:Phytochrome; D005974:Glutamate-Ammonia Ligase