Samanea leaflets usually open in white light and fold together when darkened, but also open and close with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K+ pumps in motor cells in the flexor region.

Several lines of experimental evidence indicate a close connection between polyamines (PAs) and reproductive development in Arabidopsis thaliana. (l) Measurement of the titers of endogenous spermidine (SPD) and putrescine (PUT), extracted from various organs of two ecotypes and a genetic line of Arabidopsis, revealed that flowers had the highest titers of both PAs, with SPD predominating. (2) In aseptic cultures of whole plants of the ecotype Columbia, the application of appropriate enzyme inhibitors lowered SPD titer while almost completely preventing bolting and flowering. When the plants were removed to an inhibitor‐free medium, bolting and flowering resumed. (3) SPD added to the medium of aseptically cultured plants of Columbia growing under short‐day (SD) conditions, where flowering is naturally delayed, increased the SPD titer and augmented the rate and extent of flowering. Under long‐day (LD) conditions, where flowering is already rapid and abundant, it did not promote flowering any further. (4) Enzyme inhibitors of SPD synthesis given shortly before the transition from SD conditions to LD conditions prevented flowering. (5) In a delayed‐flowering mutant (CS 3123), the addition of SPD significantly accelerated flowering.

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The mechanism by which spermidine induces the appearance of floral buds in thin-layer tobacco (Nicotiana tabacum) tissue culture was studied by following the fate of the radioactive compound. VHlSpermidine was taken up rapidly by the tissue, and after a brief lag, a portion was bound to trichloroacetic acid precipitable macromolecules. Such binding increased to a maximum on day 4 of culture, coinciding with the onset of bud differentiation, and declined thereafter until shortly before flowering. About 82% of the label in the trichloroacetic acid precipitate remained as spermidine, 14% was metabolized to putrescine, 3% to spermine, and 1% to 'y-aminobutyric acid. Spermidine was covalently bound to a protein with a molecular size of about 18 kilodaltons. Hydrolysis of this protein and analysis of the labeled entities revealed 81% spermidine, 16% putrescine, and 3% spermine. This post-translational modification of a unique protein by attachment of spermidine may be causally connected to the appearance of flower buds in thin-layer tobacco cultures.Polyamines are biologically ubiquitous and have been implicated in many aspects of growth and development in a wide variety of organisms (21)(22)(23) (8,9,16) and Vigna (11), the abnormal flowering habits of polyamine mutants of tobacco (13) After an 8 h period of incubation the tissue was ground in 10% TCA and the pellet washed with 5% TCA until washes were free of radioactivity. The TCA precipitate was then extracted with 0.1 M Na-phosphate (pH 6.8) containing 0.05% SDS, and the volume of the resulting solution reduced by an Amicon Centricon-10 concentrator. Aliquots were applied to a Varian TSK-2000 SW column, 60 cm x 7.5 mm. Elution with 0.1 M Na-phosphate (pH 6.8) occurred at a flow rate of 0.8 mL/ mm.Polyamines were extracted, danslyated, separated by TLC ( 11) or HPLC (3) and quantified using a spectrophotofluorimeter. The labeled TCA-soluble and -insoluble fractions were hydrolyzed in 6 N HCI at 1 10°C for at least 18 h prior to separation. Protein was determined following the method of Bradford (2).SDS-PAGE gels were run on a 5% stacking gel and a 14% separating gel of 0.5 mm thickness at 600 V for 2 h (15).

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