The Reaction Controlling Floral Initiation

Six experiments studied the effects of low levels of red and far-red light upon the initiation of measurement of the dark period in the photoperiodic induction of flowering in Xanthium stunarium L. (cocklebur), a short-day plant, and compared effects with those of comparable light treatments applied for 2 hours during the middle of a 16-hour inductive dark period. Red Ught, or red plus far-red, at levels that inhibit flowering when applied during the middle of the inductive dark period, either had no effect on the initiation of dark measurement (ie., were perceived as darkness), or they delayed the initiation of dark measurement by various times up to the full interval of exposure (2 hours). Far-red Ught alone had virtually no effect either at the bnning or in the middle of the dark period. These results confirm that time measurement in the photoperiodic response of short-day Xanthium plants is not simply the time required for metabolic dark conversion of phytochrome. Results also suggest that the pigment system

mentioning

confidence: 99%

Twilight Effect: Initiating Dark Measurement in Photoperiodism of Xanthium

Salisbury

1981

“…favorable condition for floral initiation (1,2). Since this is not the case for Cestrum there may be a basic difference between long day induction in it and in simple long day plants.…”

mentioning

confidence: 99%

“…SHORT DAY (1), discussed previously; namely, the nyctotemperature should have the greatest effect upon SD induction, for it is during the nyetoperiod that the pigment should be in the proper state (absorbing red radiation) for coupling with thermochemical reactions involved in the svnthesis of the floral stimulus or its precursors.…”

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confidence: 99%

Floral Initiation in Cestrum nocturnum, a Long-Short Day Plant. III. The Effect of Temperature upon Long Day and Short Day Induction.

Sachs

1956

favorable condition for floral initiation (1, 2). Since this is not the case for Cestrum there may be a basic difference between long day induction in it and in simple long day plants. On the other hand perhaps this behavior is due to the requirement for subsequent short day induction. Harder and Buinsow (4) reported that floral initiation in Kalanchoe Blossfeldiana, a short day plant, was inhibited if plants were exposed to long days prior to short day induction; as the length of the photoperiod of the preceding long days was increased the effectiveness of short day induction was decreased. The authors suggested that an inhibitory substance was formed in the long photoperiods. In a previous paper concerning Cestrum (5) it was shown that the effect of long day induction was confined to the treated leaves and it was concluded that the hypothetical product of long day induction was not translocated from the leaves. In addition evidence was presented showing that this product was a precursor of the floral stimulus. If along with the floral stimulus precursor an inhibiting substance were formed, as suggested for K. Blossfeldiana, perhaps the explanation for the reduced effectiveness of a 24-hour photoperiod is that the ratio of inhibitor to precursor is highest in this daylength. The precursor accumulates in the leaves and, if the inhibitor were dissipated by translocation or destruction, the ratio of inhibitor to precursor would decrease with prolonged long day induction. This would explain why the difference between a 24-and 16-hour photoperiod decreased as the number of long days increased. SUMMARY It has been shown that a 16-hour photoperiod is superior to a 24-hour photoperiod for long day induction in Cestrum nocturnum, a long-short day plant. It was suggested that, along with a promoting substance, an inhibitor is formed during the photoperiod. which require long day (LD) followed by short day (SD) induction for floral initiation (6). The purpose of this paper is to present the results of investigations on the effect of temperature upon LD and SD induction in Cestrum nocturnum, a long-short day plant (7).METHODS AND MATERIALS All experiments were performed in the Earhart Laboratory (9). The temperatures in the greenhouses and artificial light rooms were controlled to 430 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from

“…In recent years it has become clear, primarily through the determination of .action spectra, that several of these apparently unrelated processes may have a common photoreceptor. For exanmple, the action spectra for the inhibition of stern growth of albino barley and promotion of leaf growth of etiolated peas (1,12), the photoperiodic control of floral initiation of cocklebur and other photoperiodically sensitive plants (2,13,14), and the photoreaction controlling lettuce seed germination (3,6), appear to be similar, if not identical. Since light, to be photochemically effective, must first be absorbed, it follows that there must exist in all these tissues a pigment whose absorption spectrum should resemble the action spectrum obtained in vivo.…”

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confidence: 99%

“…Recently, however, evidence has accumulated that alcohol and CO2 may be formed during bacterial dissimilation of glucose by pathways (7,10) other than the classical glycolysis, and, moreover, enzymes responsible for the reactions of one of these alternate pathways (the hexose monophosphate shunt or oxidative pathway) have been characterized in higher plant tissues (1,2,9). It was thus of interest to reexamine glucose breakdown in a plant tissue using methods which would reveal whether a mechanism other than the E.M.P.…”

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confidence: 99%

A Porphyrin Pigment from Photosensitive Non-chlorophyllous Plant Tissues.

Todd¹,

Galston²

1954

It has long been known that visible radiations exert direct control over the growth and development of plants by photoreactions other than those involved in photosynthesis. In recent years it has become clear, primarily through the determination of .action spectra, that several of these apparently unrelated processes may have a common photoreceptor. For exanmple, the action spectra for the inhibition of stern growth of albino barley and promotion of leaf growth of etiolated peas (1,12), the photoperiodic control of floral initiation of cocklebur and other photoperiodically sensitive plants (2,13,14), and the photoreaction controlling lettuce seed germination (3, 6), appear to be similar, if not identical. Since light, to be photochemically effective, must first be absorbed, it follows that there must exist in all these tissues a pigment whose absorption spectrum should resemble the action spectrum obtained in vivo.In all of the processes mentioned above, red light of wave length approximately 660 m,u is most effective, blue light is much less effective, and yellow and green light aIre almost completely ineffective. These facts led to the suggestion that the receptor pigment is an open-chain tetrapyrrole such as phycocyanin (1). However, such a pigment, though intensively sought after in higher plants, has never been found outside of the blue-green algae.Recently, with the discovery that the red-light reaction controlling lettuce seed germination is immediately reversible by subsequently applied far-red irradiation at about 730 m/i (3), attention has been given to the possibility that the photoreceptor is actuallv a reversibly-reduced porphyrin. According to this interpretation, the relatively low promotive activity in the blue region of the spectrum would be due not to low absorption in this region, but rather to the low differential absorption between the promotive (660 m,u-absorbing) of interfering pigments such as chlorophyll. The present work involves the isolation and characterization of a porphyrin, widely distributed in nonchlorophyllous photosensitive tissues, and of possible importaince as the photoreceptor in several light sensitive processes.-MATERIALS AND METHODS In most of the experiments reported here, the initial extraction of pigment from the tissues was with peroxide-free diethyl ether (hereafter referred to as "ether"), petroleum ether, or acetone. The crude extracts were thoroughly washed with water (acetone extracts were first. t.ransferred to another solvent such as ether), followed by further solvent fractionation or by purification on sucrose or cellulose columns. Where seeds were to be extracted, they were usually ground in the dry state in a Wiley mill (20 to 40 mesh) and extracted with organic solvents. Tissues suchi as pea stems were usually lxyophilizedI and then extracted, although some extracts were made of fresh tissue ground in a mortar. Although the pigment here described was present in all plant materials examined, the richest source was found to be the seeds of various Poa (b...