The influence of light quality on the phytochrome content of light grown Sinapis alba L. and Phaseolus aureus Roxb

Persistent effects of changes in phytochrome status on internode growth in light-grown mustard: Occurrence, kinetics and locus of perception

Extension growth of the first internode in fully de-etiolated mustard (Sinapis alba L.) seedlings (11-12.5 d old) is under the control of both the current phytochrome photoequilibrium (Pfr/P, ratio of the far-red-absorbing form of phytochrome to total phytochrome) and that established by short (<12 h) pretreatments. Plants were pretreated with either light pulses providing different calculated Pfr/P followed by dark incubations of different durations (a), or with a 12-h period of white light establishing different Pfr/P (b). After the pretreatments, the plants received either light pulses providing different Pfr/P, followed by dark incubations (c), or continuous white light with or without addtional far-red light (d). Thus, four experimental approaches were followed: (a)→(c); (a)→(d); (b)→(c) and (b)→(d). Extension growth during the second period (c or d) was not only affected by the current phytochrome status, but also by that established during the pretreatment period (a or b). The results show the existence of a long-term promotion of stem growth which persists after the end of the low Pfr/P pretreatment. This effect is different from the previously reported rapid effect of far-red light added to background white light as follows: (i) the duration of low Pfr/P required to effect a full response is longer (2.5 h); (ii) the duration of the promotion after returning to high Pfr/P is longer (approx. 24 h) and (iii) the locus of perception is mainly in the leaves, rather than the growing internode.

Phytochrome quantitation in crude extracts of Avena by enzyme-linked immunosorbent assay with monoclonal antibodies

An enzyme-linked immunosorbent assay (ELISA), which uses both rabbit polyclonal and mouse monoclonal antibodies to phytochrome, has been adapted for quantitation of phytochrome in crude plant extracts. The assay has a detection limit of about 100 pg phytochrome (<1 fmol of monomer) and can be completed within 10 h. Nonspecific interference by crude plant extracts was detected and corrected for. Quantitation of phytochrome in crude extracts of etiolated oat (Avena sativa L.) seedlings by ELISA gave values that agreed well with those obtained by spectrophotometric assay. When etiolated oat seedlings were irradiated continuously for 24 h, the amount of phytochrome detected by ELISA and by spectrophotometric assay in crude extracts of these seedlings decreased by more than 1000-fold and about 100-fold, respectively. This discrepancy indicates that phytochrome in light-treated plants may be antigenically distinct from that found in fully etiolated plants. Both a decrease in the light and an increase in the dark of phytochrome content was observed in crude extracts of light-grown oat shoots, both green and Norflurazon-bleached, in response to a 12:12-h light-dark cycle. When these light-grown oat seedlings were kept in darkness for 48 h, phytochrome content detected by ELISA increased by 50-fold in crude extracts of green oat shoots, but only about 12-fold in extracts of herbicide-treated oat shoots. Phytochrome reaccumulation in green oat shoots was initially more rapid in the more mature cells of the primary leaf tip than near the basal part of the shoot. The inhibitory effect of Norflurazon on phytochrome accumulation was much more evident near the leaf tip than the shoot base. A 5-min red irradiation of oat seedlings at the end of a 48-h dark period resulted in a subsequent, massive decrease in phytochrome content in crude extracts from both green and Norflurazon-bleached oat shoots. These observations eliminate the possibility that substantial accumulation of chromophore-free phytochrome was being detected and indicate that Norflurazon has a substantial effect on phytochrome accumulation during a prolonged dark period.