The Dual Role of Auxin in Flowering.

Self Cite

Since the demonstration bv Hamner and Bonner (7) of the importance of the dark period for photoperiodic induction in the short-day plant Xanthium, there have been many attempts to elucidate the reactions which take place within the plant during this period (2,11,13,18). The dark period reactions appear to be concerned directly with the act of induetion-the persistent change of the plant from the vegetative to the flowering condition. In Xanthium the flowering condition persists after a single completed act of induction even though the photoperiod during floral development is too long for induction to occur in vegetative plants. The condition of the plant after induction has taken place will be termed the induced state to distinguish it from the act of induction.The induced state in Xanthium is a quantitative one. Rate of development of the floral bud is dependent upon the intensity of the original act of induction. A measure of the rate of development based upon a series of floral stages has been previously described (21). By the application of this system the quantitative nature of induction can be demonstrated by? the relationship between length of the inductive dark period and subsequent rate of floral development, as measured by floral stage a number of days after induction (this is illustrated by the control points of the experiment shown in fig 4). The longer the dark period, the more rapidly the buds develop. This may be interpreted on the supposition that the rate of bud development is dependent upon the amount of flowering hormone produced, and that longer dark periods result in the production of more flowering hormone. This view is supported by the fact that buds develop at different rates when the leaves are removed from Xanthium plants at different times after the beginning of induction (9,21,22,23 fig 5). These results are in accord with the hypothesis that rate of floral development is determined by the amount of flowering hormone which reaches the growing point. The longer the leaves remain on the plant, the more hormone is translocated from them to the growing point.The experiments below concern kinetic studies on the reactions of the dark period. Xanthium pensylvanicum Wall.4 plants were treated at various times by red light interruption of the dark period and/or the application of auxin (whieh inhibits the act of induction, 21). The effects of these treatments on floral induction were measured in terms of rate of subsequent floral development, which is assumed to measure the amount of flowering hormone exported from the leaf. METHODSPlants were grown as previously described (3, 20, 21) from seed and maintained in a vegetative condition by daylight supplemented with incandescent irradiation of approximately 100 fe to make up a total day length of approximately 20 hours. To facilitate auxin treatment and to insure controlled light intensity during interruption of the dark period, plants were defoliated to a single leaf after first being classified according to the size of the most rapidly expandi...

supporting

confidence: 48%

The Reactions of the Photoinductive Dark Period

Bonner

1956

Self Cite

“…Nine days after exposure to the single inductive dark period, plants were examined with a dissecting microscope to classify their apical meristems according to a series of floral stages previously described (19,20). Each point in the figures represents the average floral state of 10 plants that were given the same treatment.…”

mentioning

confidence: 99%

Twilight Effect: Initiating Dark Measurement in Photoperiodism of Xanthium

Salisbury

1981

Self Cite

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

“…They were grown and handled as earlier described (4). The temperature during an inductive 16-hour night was kept at 23 to 25 C. After 9 days the apical buds were dissected and classified according to Salisbury's floral system (14). With this method the standard deviation of the stage based on a group of 15 untreated plants is of the order of 15 % of a floral stage unit (table I).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Suppression of Floral Induction by Inhibitors of Steroid Biosynthesis

Bonner¹,

Heftmanń²,

Zeevaart³

1963

This paper concerns a class of metabolic inhibitors which possess the ability to suppress the flowering of short-day plants and which appear to do so by interfering with generation of the flowering stimulus by the leaf. The inhibition of flowering with which we are here concerned is thus different from that elicited by 5-fluorouracil and 5-fluorodeoxyuridine. These two substances act by preventing successful receipt by the bud of the leaf-produced floral stimulus (4,17). The substances here reported as active in inhibition of the generation of flowering stimulus by the leaf are of further interest in that they are inhibitors of the biogenesis of steroids. Materials & MethodsPlant Material. The cocklebur (Xanthiumn pensylvanicum Wall) plants used were of our inbred strain. They were grown and handled as earlier described (4). The temperature during an inductive 16-hour night was kept at 23 to 25 C. After 9 days the apical buds were dissected and classified according to Salisbury's floral system (14)