Photophosphorylation and oxygen evolution were measured in 8-day-old dark-grown bean leaves (Phaseolus vulgaris) after various times of greening in far red light and in white light. The sequence of development was the same for both greening regimes, but the processes were much more rapid in white light. The capacity for photophosphorylation, as assayed by the firefly luciferase assay, appeared after 12 hours in far red light. At this stage and for times up to 24 hours, photophosphorylation was not inhibited by 10-M 3-(3,4-dichlorophenyl)-1,1-dimethylurea. At 24 hours, the capacity for oxygen evolution appeared and photophosphorylation became partially inhibited by 3-(3,4-dichlorophenyl)-l,l.dimethylurea at concentrations which inhibited oxygen evolution. In white light photophosphorylation appeared after 15 minutes, and oxygen evolution at one hour. Photophosphorylation became partially sensitive to 3-(3,4-dichlorophenyl)-1 , 1-dimethylurea when oxygen evolution appeared. Carbonylcyanide m-chlorophenylhydrazone inhibited photophosphorylation and photosynthesis at low concentrations, 10' M, with immature leaves, but the leaves developed resistance to carbonylcyanide m-chlorophenyl. hydrazone as they greened.A previous study (4) capacity for oxygen evolution indicated that a high degree of synchrony was maintained in the developing plastids even though the development time was prolonged.In the previous paper (4) no attempt was made to distinguish between the onset of oxygen evolution and photophosphorylation or to differentiate between cyclic and noncyclic photophosphorylation. In the present paper we show that cyclic and noncyclic photophosphorylation can be distinguished in the intact leaves during development and that cyclic photophosphorylation appears well before noncyclic photophosphorylation. The onset of noncyclic photophosphorylation is coincident with the onset of oxygen evolution. This sequence of appearance occurs with leaves greened in white light as well but over much shorter periods of time. MATERIALS AND METHODS Primary leaves of Phaseolus vulgaris cultivar Topcrop (W.Atlee Burpee Co., Riverside, Calif.) were used for all experiments. The conditions of growth and far red light source were the same as described previously (4). The temperature in darkness was 20 C; in light, 25 C. Greening experiments were made with far red light with 12-hr light, 12-hr dark irradiation cycles (4); with continuous far red illumination; and with continuous white light. The source of white light for greening consisted of 4 cool-white lamps (General Electric F40CW) giving 4 X 10' ergs cm' sec1 at the plants.The chlorophyll a and b contents of the leaves were determined spectrophotometrically according to the method of Ogawa and Shibata (15). Extractions were carried out under green light.The phosphorylation capacity of the leaves was determined by the firefly luciferase assay (9, 16). At selected stages of greening, primary leaves were taken and cut into 10 segments (4 to 9 mm') under green safelight. Five of t...

Abstract— Apparent synthesis* of the enzyme lipoxygenase in the cotyledons of the mustard seedling (Sinapis alba L.) is controlled by phytochrome (Pfr ground state)† through a threshold (all‐or‐none) mechanism. This response was used to determine physiologically the photostationary states, Λ that is, the [Pfr]/[Ptot] ratios established by different wavelengths in the red and far‐red range of the spectrum, including the standard red and far‐red sources used in this laboratory (Mohr, 1966). Under the premises (for which justification has been given on previous occasions) that the [Pfr]/[Ptot] ratio for standard red light is 0.8, and that the decay of Pfr is a first‐order process with a half‐life of 45 min, the [Pfr]/[Ptot] ratios determined physiologically by means of the lipoxygenase response agree with the [Pfr]/[Ptot] ratios determined spectrophotometrically by Hartmann and Spruit (cf. Fig. 9 in Hanke et al., 1969) in hypocotyl hooks of mustard seedlings. In the hook the fr, that is, the [Pfr]/[Ptot] ratio for standard far‐red, is found to be 0.023. In the cotyledons, this ratio is several times higher (Schafer et al., 1972). The conclusion that apparent lipoxygenase synthesis in the cotyledons is controlled by phytochrome located in the hook has been substantiated by further spectrophotometric (Schäfer et al., 1973) and physiological experiments (H. Oelze‐Karow and H. Mohr, in preparation). The minimum steepness of the threshold was determined. An increase of the Pfr level from 118 (relative units) to 130 leads to an instantaneous and total suppression of apparent lipoxygenase synthesis; a corresponding decrease from 130 (relative units) to 118 leads to an immediate resumption of apparent LOG synthesis at full speed. It is concluded that an explanation of the experimental facts requires a cooperative effect on the level of Pfr, a high degree of synchrony on the cellular and organismic level and rapid communication between the hypocotyl hook and the cotyledons. *The term ‘apparent synthesis’ is used operationally in the present paper to denote any increase of enzyme activity, although de novo synthesis of lipoxygenase has not so far been rigorously demonstrated. The usual inhibitor experiments (cf. Oelze‐Karow et al., 1970) have led to the conclusion that intact RNA and protein synthesis is required for an increase of lipoxygenase activity.

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Hypocotyl elongation in mustard (Sinapis alba L.) seedlings is known to be controlled by phytochrome (Pfr) through a threshold response. This phytochrome-mediated threshold response was studied in detail with the following results: (i) The P, threshold value required to suppress hypocotyl growth is much lower (0.03% P,, based on total phytochrome in the hypocotyl at 36 h after sowing = 100%) than those threshold valued observed previously in threshold control by hook phytochrome of appearance of 'potential capacity for photophosphorylation' and lipoxygenase appearance in the mustard cotyledons (1.25% Pr,, based on total phytochrome in the hypocotyl at 36 h after sowing = 100%). This probably explains why hypocotyl elongation is so extremely sensitive to light. (ii) The Pf, threshold value controlling hypocotyl growth is a system constant, independent of total phytochrome content, developmental age and actual growth rate. (iii) Threshold control of hypocotyl elongation is unaffected by the removal of the cotyledons and half of the hook. However, removal of the whole hook totally eliminates any light control over the residual hypocotyl growth. (iv) After termination of the threshold control, the hypocotyl growth rate immediately returns to precisely that found in untreated dark control even though the partial growth rates of the different parts of the hypocotyl are quite different, relative to their dark controls. Obviously, the organ grows as an integrated unit.It is concluded that the all-or-none threshold control over hypocotyl growth is exerted from the plumular hook. It appears that the hook can send off phytochrome all-or-none signals in both directions, to the cotyledons and to the hypocotyl.

Abstract— It is shown that in attached mustard cotyledons graded control of chlorophyll synthesis by physiologically active phytochrome (Pfr) and threshold control by Pfr of the ‘potential capacity’ to photophosphorylate are totally different phytochrome actions even though both controls are essential for the build‐up of the same functional complex, the machinery for photophosphorylation. The essential findings are as follows: The action of Pfr (made by a 1 min red light pulse) on the capacity and efficiency of photophosphorylation is rapid—detectable after 15 min and completed after 30 min—whereas the action of Pfr on chlorophyll formation is slower—only detectable 45 min after the original red light pulse (R). Detailed escape studies (loss of full reversibility of the inductive effect of a R pulse by far‐red) show that the effect of a R pulse on chlorophyll synthesis remains fully reversible for 45 min whereas the action of Pfr on the capacity for photophosphorylation is very fast (occurring within 2 min). Control of capacity for photophosphorylation is a threshold response (whereby the threshold value is approximately 1.25% Pfr based on total phytochrome at 36 h = 100%) whereas control by Pfr of chlorophyll synthesis is graded. Control of capacity for photophosphorylation by Pfr only operates if the hypocotyl hook is connected to the cotyledons for at least 2 min after the inductive R pulse, i.e. until full escape from reversibility has occurred, whereas chlorophyll formation in the cotyledons is not affected by the separation of hook and cotyledons.