Requirement for far-red light to maintain secondary needle extension growth in northern but not southern populations of Pinus sylvestris (Scots pine).

Extension growth of secondary needles is under photoperiodic control in Pinus sylvestris. To test for the effects of far-red light on maintaining this extension growth, seedlings of six populations originating from latitudes between 57 degrees and 67 degrees N were raised for 11 weeks in continuous incandescent (metal halogen) light at 300 &mgr;mol m-2 s-1 and 20 degrees C and then transferred at the same temperature to a daily regime of 8 h incandescent light (230 &mgr;mol m-2 s-1) followed by a 16 h day extension with cool white fluorescent light (40 &mgr;mol m-2 s-1, R/FR ratio 7.5) or with incandescent lamps (20 &mgr;mol m-2 s-1, R/FR ratio 2.

Latitudinal cline of requirement for far-red light for the photoperiodic control of budset and extension growth in Picea abies (Norway spruce).

To test for the effects of far-red light on preventing budset in Picea abies, seedlings of six populations originating from latitudes between 67°N and 47°N were grown for 4-8 weeks in continuous incandescent (metal halogen) light at 300 µmol m s and 20°C and then transferred, at the same temperature, to a daily regime of 8 h incandescent light (300 µmol m s ) followed by 16 h cool white fluorescent light (40 µmol m s ). (Cool white lamps are deficient in far-red light, with a R/FR ratio of 7.5 compared with 2.

Regulation of swelling of etiolated-wheat-leaf protoplasts by phytochrome and gibberellic acid.

The effect of light on the size of intact protoplasts isolated from the primary leaves of etiolated Triticum aestivum was studied. A 2-min red-light irradiation in the presence of 1 mM KCl was sufficient to cause a swelling of protoplasts compared with those maintained in darkness. The effect was photoreversible by far-red light over two light cycles, indicating the involvement of phytochrome.

Photoperiodic Control of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy : The Effect of Skeleton and Continuous Light Photoperiods.

The control of night-break timing was studied in dark-grown seedlings of Pharbitis nil (Choisy cv. Violet) following a single continuous or skeleton photoperiod. There was a rhythmic response to a red (R) interruption of an inductive dark period, and the phasing of the rhythm was influenced by the preceding light treatment.

Light requirement, phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois : III. A comparison of spectrophotometric and physiological assay of phytochrome transformation during induction.

During an inductive dark period for flowering, changes in phytochrome have been followed in cotyledons of Pharbitis nil seedlings using a spectrophotometric and a physiological technique. There was agreement between the two techniques, both indicating a rapid lowering of the levels of the far-red-absorbing form of the pigment (Pfr) during the first 30-90 min of darkness. Thus, Pfr could provide the cue which signals the beginning of darkness and the length of the critical dark period was, in some instances, correlated with the time of Pfr disappearance.