PHYTOCHROME CONTROL OF PHOTOTROPISM AND CHLOROPHYLL ACCUMULATION IN THE APICAL CELLS OF PROTONEMAL FILAMENTS OF WILDTYPE AND AN APHOTOTROPIC MUTANT OF THE MOSS CERATODON PURPUREUS
T. Lamparter et al., PHYTOCHROME CONTROL OF PHOTOTROPISM AND CHLOROPHYLL ACCUMULATION IN THE APICAL CELLS OF PROTONEMAL FILAMENTS OF WILDTYPE AND AN APHOTOTROPIC MUTANT OF THE MOSS CERATODON PURPUREUS, Plant and Cell Physiology, 38(1), 1997, pp. 51-58
The aphototropic mutant line ptr116 of the moss Ceratodon purpureus sh
ows characteristics of a deficiency in the phytochrome chromophore. Ph
otoreversibility measurements indicate an approximately 20 time lower
concentration of spectrally active phytochrome compared to wildtype, w
hereas normal phytochrome apoprotein levels are found on immunoblots.
Feeding with the tetrapyrroles biliverdin, the proposed precursor of t
he phytochrome chromophore, or phycocyanobilin, which may replace the
phytochrome chromophore, resulted in the rescue of ptr116 phototropism
. The ptr116 mutant and the phenotypically-related mutant ptr1 contain
lower chlorophyll levels than the wildtype, Chlorophyll content of wi
ldtype and mutant tissue grown under different light conditions was es
timated using conventional spectrophotometry of extracts and fluorimet
rically, on single apical cells, Dark-grown tissue contained about 100
times less chlorophyll than tissue grown under standard white light c
onditions, Red light given for 24 h to dark adapted filaments induced
an increase in the chlorophyll content in the wildtype, but not in ptr
116, Blue light induced an increase in chlorophyll both in wildtype an
d in ptr116, The red light effect on the wildtype was partially revers
ible with far-red. If ptr116 was grown on phycocyanobilin, an increase
in chlorophyll was also found when cells were irradiated with red lig
ht. The results indicate that phytochrome as well as a blue light phot
oreceptor regulate chlorophyll accumulation in C.purpureus protonemata
, It can be assumed that in ptr116, the synthesis of the phytochrome c
hromophore is blocked specifically beyond the synthesis common to chlo
rophyll and the phytochrome chromophore and affects an enzymatic step
between protoporphyrin and biliverdin.