PHYTOCHROME-MEDIATED BRANCH FORMATION IN PROTONEMATA OF THE MOSS CERATODON PURPUREUS

We have analyzed light induction of side-branch formation and chloropl ast re-arrangement in protonemata of the moss Ceratodon purpureus, Aft er 12 hr of dark adaptation, the rate of branch formation was as low a s 5%. A red light treatment induced formation of side branches up to 7 5% of the dark-adapted protonema, The frequency of light induced branc h formation differed between cells of different ages, the highest freq uency being found in the 5th cell, the most distal cell studied from t he apex, We examined the effect of polarized light given parallel to t he direction of filament growth, The position of branching within the cell depended on the vibration plane of polarized red light, Branch fo rmation was highest when the electric vector of polarized light vibrat es parallel to the cell surface and is fluence rate dependent, The pos itional effect of polarized red light could be nullified to some exten t by simultaneous irradiation with polarized far-red light, An aphotot ropic mutant, ptr116, shows characteristics of deficiency in biosynthe sis of the phytochrome chromophore and exhibits no red-light induced b ranch formation. Biliverdin, a precursor of the phytochrome chromophor e, rescued the red-light induced branching when added to the medium, s upporting the conclusion that phytochrome acts as photoreceptor for re d light induced branch formation, The light effect on chloroplast re-a rrangement was also analyzed in this study, We found that polarized bl ue light induced chloroplast re-arrangement in wild-type cells, wherea s polarized red light was inactive, This result suggests that chloropl ast re-arrangement is only controlled by a blue light photoreceptor, n ot by phytochrome in Ceratodon.