Long-day flowering of Lemna perpusilla 6746 in Mo-deficient medium

Lemna perpusilla 6746, a short-day duckweed, flowered undercontinuous illumination if some of the SH inhibitors, such ascyanide or tungstate were added to the M-sucrose medium. Theeffect of tungstate was not overcome by simultaneous applicationof molybdate, but deletion of the Mo from the medium was enoughto induce the long-day flowering. In vivo assay of nitrate reductaseactivity suggested that nitrate reduction was not inhibitedby tungstate, CuSO₄ or AgNO₃ which induced longday flowering.The possibility was suggested that suppression of some Mo-requiringprocess other than nitrate reduction brings about the long-dayflowering in this plant. (Received November 12, 1975; )     

Effects of some SH-inhibitors and EDTA on flowering in Lemna perpusilla 6746

Lemna perpusilla 6746, a short-day duckweed, flowered undercontinuous illumination on M-sucrose medium containing CuSO₄,AgNO₃ and HgCl₂, which are SH-inhibitors. The optimum concentrationsof CuSO₄, AgNO₃ and HgCl₂ were 5, 1 and 20 µM, respectively.Other metal ions tested were ineffective, but at least two otherSHinhibitors, potassium ferricyanide and iodoacetamide, alsoinduced long-day flowering at the concentrations of 0.1-1 µM. Adding 50 µM EDTA to the medium prevented the effect ofcupric ion, but not that of other SH-inhibitors. EDTA at 200µM induced some long-day flowering when added to a mediumwith no SH-inhibitors. It also permitted some flowering whenadded together with cupric ion, and accelerated flowering inthe presence of the other SHinhibitors listed above. EDTA andSH-inhibitor effects appeared to be additive. (Received May 25, 1973; )     

Spectral dependences of flowering in Lemna perpusilla and L. gibba

Floral induction in Lemna perpusilla and L. gibba was determinedunder continuous irradiation with monochromatic light in spectralranges from 396 to 765 nm. In the former it was induced underwavelengths from about 400 to 550 nm and longer than 700 nm,while in the latter with wavelengths near 400 nm and from about550 to 650 nm. The patterns of these spectral dependences werenearly mirror images and corresponded to the P_fr level in thephotostationary states of phytochrome. (Received December 3, 1974; )     

Suppression of long-day flowering by nitrogenous compounds in Lemna perpusilla 6746

The long-day flowering of Lemna perpusilla 6746 on an SH inhibitor-containingmedium was inhibited by the application of ammonium ion to themedium. Ammonium ion not only suppressed long-day flowering,but relieved the inhibition of vegetative growth caused by theinhibitors. Nitrite, casamino acids, glutamine and asparaginehad a similar effect, suggesting that the inhibition of long-dayflowering by ammonium ion is not a direct effect of the ion.Most amino acids, with the exception of glutamate and aspartate,also prevented long-day flowering, but their effects on vegetativegrowth varied. No qualitative differences in amino acid compositionwere observed among plants cultured on media containing nitrate,nitrite or NH4₄NO₃as the sole nitrogen source. However, theamounts of free and total amino acids werehigher in plants fedwith nitrite or NH₄NO₃ than in those fed with nitrate. Thissuggests that the inhibition of long-day flowering by ammoniumand nitrite can be ascribed to increased nitrogen metabolism. Though decreased activity by SH inhibitors of nitrate reductase(SH enzyme) is assumed to result in long-day flowering by loweringthe nitrogen metabolism, lowering the nitrogen level in M mediumdid not bring about floral initiation in the absence of SH inhibitors. (Received January 7, 1975; )     

Lack of flowering responses to DGMU in a mutant of Lemna perpusilla 6746

DCMU, in a sucrose supplemented medium, promoted short and longday flowering and inhibited long day frond production of wildtype Lemna perpusilla 6746, but not of mutant strain 1073. Resultssuggest a defect in the mutant that mimics DCMU poisoning. ¹ This work was supported by National Science Foundation GrantGB-12955. (Received December 11, 1972; )     

Effects of DCMU on long-day flowering of Lemna perpusilla 6746 and photosynthetic mutant strain 1073

Long-day flowering of wild-type Lemna perpusilla (strain 6746)on ammonium-free medium with sucrose occurred in continuouslight of low intensity (25 ft-c). In higher intensities of light,frond production was increased and flowering was reduced. Thephotosynthetic inhibitor DCMU inhibited frond production andpromoted flowering in the presence or absence of exogenous sucrose.In the photosynthetic mutant strain 1073, the higher intensitiesof light inhibited frond production, but did not reduce flowering.DCMU increased mutant frond production, thus leading to increasedflowering percents. The mechanism by which DCMU affects floweringand growth appears to differ from that of other flower-promotingsupplements reported by Takimoto and Tanaka. The results suggestthat inhibition of photosynthesis enhances flowering in longdays. (Received June 25, 1977; )     

Induction of flowering in the duckweed Lemna paucicostata under non-inductive photoperiods by tannic acid

Flowering in Lemna paucicostata 6746 could be induced by tannic acid under strictly non-inductive photoperiods. This polyphenol completely abolished the photoperiodic sensitivity of strain 6746 as flowering could also be obtained under continuous light (nearly 80% flowering was recorded in the plants supplied with 10⁻⁵ tannic acid). Though its mode of action is unknown, tannic acid is unlikely to act as a gibberellin-antagonist in its effect on flowering in strain 6746.     

Morphogenesis of Asymmetry and Symmetry in Lemna perpusilla Torr

The determination of which of the two reproductive pockets ofLemna perpusilla will produce the first daughter frond undernon-flowering conditions, or the flower under inductive conditions,is related to asymmetric gradients within the mother frond whichmay be the result of the asymmetric position of the axillaryfrond. Treatments that encourage vigorous growth of axillaryfronds may overcome the normal situation of asymmetry and causea morphological symmetry which is qualitatively different fromthe symmetry induced by treatments (TIBA) which prevent thedevelopment of axillary fronds. The origin and maintenance ofasymmetry in Lemna are discussed. Lemna perpusilla Torr., morphogenesis, asymmetry of fronds, tri-iodobenzoic acid     

Flower initiation of Lemna perpusilla under continuous low-intensity light

Lemna perpusilla 6746, a short-day plant, flowered under low-intensitywhite light (10 lux)irrespective of the photoperiod. Red lightof about 20 ergs/cm²/sec also permitted flowering under continuousillumination. The effect of the low-intensity light employedwas not equivalentto that of darkness but similar to that ofblue or far-red light in photoperiodic system. (Received June 15, 1973; )     

Dark reactions in the flowering ofLemna perpusilla 6746

Summary This study concerns the effects of red and far-red light on flowering in the short day plantLemna perpusilla 6746. The critical day length for maximum flowering was found to be 10 hours. Exposure to red light near the middle of the dark period inhibited flowering, and the time of maximum sensitivity to red light occurred 9 hours after the beginning of dark periods of either 14 or 17 hours. The inhibition by red light was not reversible by far-red light, which also inhibited flowering, especially when given early in the dark period. Flowering inhibited by exposure to far-red light at the beginning of the dark period could be restored by subsequent exposure to red light. It appears that two photoperiodic partial processes in some plants may be controlled by the red, far-red reversible pigment system.With 5 Figures in the Text     

Influence of Short Term Inhibitor Treatment on the Flowering of Lemna perpusilla 6746

Short term inhibitor treatment can be used to examine the processes that occur during an inductive dark period in the short day plant Lemna perpusilla Torr., strain 6746. Several inhibitors of protein biosynthesis are most effective in reducing per cent flowering when treatment occurs over the 2-hour intervals beginning at the 12th hour or the 14th hour of a 8 (16) photoperiodic cycle. The antimetabolite, 5-fluorouracil, is most effective when treatment occurs early in the dark period. Evidence is cited suggesting that distilled water incubation inhibits flowering by interfering with protein biosynthesis.     

Flowering response of Lemna perpusilla 6746 to a single dark period

Lemna perpusilla 6746 is induced to flower by a single longdark period, but the floral buds once formed disappear afterseveral days under 5000 lux/25?C. Such regression of floralbuds is prevented by lowering the light intensity or temperature,but if the light intensity and/or temperature are lowered beyondcritical levels, new floral buds form. If the cultures are subjectedto 100 lux/20?C, neither regression nor new formation of floralbuds occurs. Under such conditions, the number of floral frondsreaches maximum about 6 days after the inductive dark periodand reamins unchanged for at least 10 days, while the percentageof floral fronds rapidly decreases thereafter, owing to thedilution by newly developed vegetative fronds. When the cultures are subjected to various lengths of a singledark period (25?C) followed by 100 lux/20?C, flowering responsesrepresented by the number of floral fronds per flask show rhythmicfluctuation with a cycle length of about 24 hr. Similar rhythmicresponse is observed when a brief light interruption is givenat different times during a single long dark period. (Received December 2, 1974; )     

Sulfur-containing Compounds in Lemna perpusilla 6746 Grown at a Range of Sulfate Concentrations

Lemna perpusilla 6746, grown photoautotrophically at a series of sulfate concentrations ranging from 0.32 to 1,000 μm, was labeled to radioisotopic equilibrium with ³⁵SO₄²⁻. Sulfur-containing compounds were isolated and purified from the colonies. Radioactivity in each compound was a measure of the amount of that compound present in the tissue. The following compounds were identified and quantitated: inorganic sulfate, glutathione, homocyst(e)ine, cyst(e)ine, methionine, S-methylmethionine sulfonium, S-adenosylmethionine, S-adenosylhomocysteine, cystathionine, chloroformsoluble (presumed to be sulfolipid), protein cyst(e)ine, and protein methionine. γ-Glutamylcyst(e)ine, erythro- and threo-thiothreonine, and S-methylcysteine were not detected. No volatile ³⁵S compounds were formed during plant growth at 1,000 μm sulfate, nor were significant amounts of ³⁵S compounds excreted into the medium.     

Influence of Temperature on the Flowering of Lemna perpusilla 6746 Grown under Skeleton Photoperiods

The flowering of Lemna perpusilla Torr. strain 6746 grown under 24-hour skeleton photoperiods consisting of 13- and 10.5-hour dark periods separated by 0.25-hr light pulses is strongly dependent on temperature. When plants are cultured in 50-ml Erlenmeyer flasks containing 20 ml of half-strength Hutner's medium supplemented with 1% (w/v) sucrose maximum, per cent, flowering occurs at 23 C. At temperatures above and below 23 C a marked decline in per cent flowering is seen.     

Effects of culture conditions on development in continuous light of floral buds in Lemna perpusilla 6746

Effects of temperature on the subsequent development in continuouslight of floral buds formed after a single short-day cycle inLemna perpusilla 6746, a short-day plant, were studied usingfronds selected in relation to the order of emergence. The floralbuds developed to stage 1 regardless of the temperature duringthe following CL. The rate of development, however, was slowerat lower temperature. The minimum number of days in CL neededfor the abortion of once formed floral buds increased with adecrease in temperature, accompanied by an increase in the frondplastochron. Furthermore, when the frond plastochron was alteredby manipulation of the environmental conditions, i.e., lightintensity or medium strength, the minimum number of days inCL required for the abortion of the floral buds also changed.These results suggest that the development pattern of floralbuds in this plant is highly correlated with the frond plastochron. (Received September 20, 1977; )