Modification of apparent phytochrome synthesis in pisum by inhibitors and growth regulators

Phytochrome in cultured wild carrot tissue. I. Synthesis

Stable levels of P(FR) occur in light-grown suspension cultures of wild carrot. Upon darkening such tissue, P(R) accumulates until the high P(R) level characteristics of dark-grown tissue is reached. Data are compatible with the idea of an equilibrium between processes of synthesis and destruction in tissue grown in the light. Reappearance of phytochrome also follows light-induced pigment destruction in dark-grown tissue. The rate of P(R) appearance is similar in both cases. The rate of disappearance of P(FR), however, is slower in light-grown tissue than in dark-grown tissue.

The in vivo properties of Amaranthus phytochrome

Phytochrome has been measured in etiolated seedling of Amaranthus caudatus. The phytochrome content increases from the time of germination until 72 hr from sowing, after which it remains constant at 27.5x10(-3) Δ (ΔOD) units per 200 seedlings. After a saturating dose of red light P fr decays in the dark to a form not detectable photometrically. There is no evidence for the process of dark reversion of P fr to P fr found in other dicotyledons. Even in the presence of azide, a selective inhibitor of decay, the process of dark reversion is not observed. The decay of P fr has been investigated at different temperatures and follows first order decay kinetics throughout. Over the temperature range 15-30° the Q 10 of decay remained constant at 4.3.The photostationary states of phytochrome (P fr /P total )maintained by mixed red/far-red light have been measured in both seedlings and partially purified protein extracts, with good agreement. The rate of phytochrome decay can be manipulated by changing the P fr /P total ratio. The lag period before a decay curve becomes exponential is characteristic of a particular P fr /P total ratio and represents the time for attainment of the photostationary state. The effect of energy on decay has been investigated under red and blue light. The rate of phytochrome decay is dependent on the P fr /P total ratio and only becomes energy dependent when the light intensity is so low that the photostationary state is never attained.The process of apparent phytochrome synthesis has been found in Amaranthus. After reducing the phytochrome to a low level by red light treatment a rate of apparent synthesis of 1.35×10(-4) Δ (δOD) units per hr per 200 seedlings was observed, levelling off at 29% of the original phytochrome level.Under white tungsten lights of high intensity there is a deviation from the expected first order decay kinetics. The nature of this low rate of decay cannot be explained at the present time.

Growth and anthocyanin synthesis in excised Sorghum internodes : I. Effects of growth regulating substances

Ligh-induced anthocyanin synthesis in excised dark-grown internodes of Sorghum was depressed by the addition of auxin to the incubating medium at physiological concentrations. Both IAA and the synthetic auxin, 2,4-D, reduced anthocyanin yield. Similar results were obtained with isolated internode segments and in internodes incubated with coleoptiles (the major source of endogenous auxins) attached. Auxin increased the duration of the lag phase before anthocyanin synthesis began and reduced the rate during the subsequent linear phase. Elongation continued longer with IAA than without it and anthocyanin formation did not begin until extension growth had ceased or was slowing down in both cases; the rate of anthocyanin synthesis in the IAA solution remained depressed compared with that in buffer even after extension growth had ceased in both.At low concentrations IAA stimulated elongation growth without reducing anthocyanin yield and it is unlikely that the effect of IAA on anthocyanin synthesis results from the increased utilisation in growth of substrates needed for anthocyanin formation. The results of reciprocal transfer experiments from dark to light, and vice versa, showed that the action of IAA was associated with its presence in the incubating medium during the irradiation period. If present only in darkness, before or after transfer to light, IAA did not reduce anthocyanin formation; in the former case total yield was increased by IAA as a result of the stimulation of elongation growth, the concentration of anthocyanin remaining unchanged.GA3 also decreased anthocyanin content; the effect was greater in sections incubated with coleoptiles attached and it is possible that GA3 acts by increasing the concentration of endogenous auxins. However, CCC, which has been reported to decrease endogenous auxin levels, also reduced anthocyanin yield.The effect of IAA was not influenced by the presence of ascorbate in the incubating medium, nor did added ascorbate result in the formation of any acylated cyanidin derivative in internodes maintained in darkness.Possible relationships between light-induced anthocyanin formation and the photo-inhibition of elongation are discussed.

Stability of phytochrome concentration in dicotyledonous tissues under continuous far-red light

The phytochrome concentration in dark-grown seedlings of Pisum sativum, Phaseolus aureus and Sinapis alba remained constant under continuous far-red illumination for periods of up to 6 hours. Similar treatment of Zea mays seedlings reduced the phytochrome concentration by more than 60 percent. The results in the dicotyledonous seedlings may be due to the reversion of Pfr to Pr at a rate sufficient to prevent Pfr destruction; no evidence for reversion has been detected in Zea. Typical photomorphogenic responses were observed in the dicotyledonous seedlings in the absence of Pfr destruction.