Lemna Gibba G3 Research Articles

Uptake and Leakage of Some Ions in Relation to Potassium Uptake Rhythm in <italic>Lemna gibba</italic> G3

The time courses of the uptake of various inorganic ions from the flow medium were compared with the rhythmical potassium uptake in Lemna gibba G3. The duckweeds in the flow medium absorbed 20–40% of magnesium, 30–50% of phosphate, 40–80% potassium and 50–90% of nitrate, the percentage varying rhythmically, but they constantly absorbed about 20% of calcium. The total anion uptake was 1.5 times greater than the total cation uptake. The duckweeds absorbed cesium or rubidium as well as they did potassium. They also absorbed sodium if potassium was absent from the medium. Lithium was not absorbed even in the absence of potassium. Potassium leaked from the duckweed into the potassium-free flow medium, and the rate of leakage changed diurnally under continuous light, with maximum leakage occurring at the same circadian time as when the potassium uptake rhythm in the normal flow medium drops to the minimum point. The pattern of potassium leakage in dim light was influenced by the species of monovalent cation in the medium. In darkness, however, the leakage rhythm ran for 36 hr irrespective of cation species.

Persistence of the Potassium Uptake Rhythm in the Presence of Exogenous Sucrose in Lemna gibba G3

Persistence of the Potassium Uptake Rhythm in the Presence of Exogenous Sucrose in Lemna gibba G3

A review of chemically induced flowering in Lemna gibba G3 and Pistia stratiotes

The synthetic chelating agent EDDHA (ethylenediamine-di- o-hydroxyphenylacetic acid) and salicylic acid (SA) induce or enhance flowering in Lemna gibba L., strain G3, and Pistia stratiotes L. In L. gibba G3 these compounds also induce gibbosity, a swelling of the lower side of the fronds. EDTA (ethylenediaminetetraacetic acid) brings about similar effects in L. gibba G3. However, it is markedly less effective than EDDHA and SA and there are strong arguments in favour of a recent conclusion that it brings about its effect via a different mechanism. Ethylene induces gibbosity in L. gibba G3, however, neither in this species nor in P. stratiotes does it affect flowering. The effect of EDDHA/SA as well as ethylene on L. gibba G3 is specifically negated by autoclaved GA 3 is i.e., break-down products of GA 3 such as allogibberic acid, whereas non-autoclaved GA 3 is ineffective. On the other hand GA 3 induces profuse flowering in P. stratiotes whereas autoclaved GA 3 is less effective. In the light of the various results it could be hypothesized that a gibberellin and ethylene in combination with another factor are involved in flowering of L. gibba G3.

Participation of a membrane system in the potassium uptake rhythm in a duckweed, Lemna gibba G3

The period of the free-running potassium uptake rhythm in a long-day duckweed, Lemna gibba G3, was lengthened by Li+ and shortened by ethanol. This suggests that a membrane system participates in the circadian feed-back system. High temperature treatment (39°C) increased the motion of the rhythm when applied during periods of high potassium uptake (CT 18–06), and decreased it when applied during low potassium uptake (CT 06–18), which indicates a circadian change in the properties of the membrane. However, modification of the potassium uptake level caused by temperature change, application of valinomycin, or a change in the ambient potassium concentration caused no modification in the phase of the rhythm. Thus, the oscillator involved probably is not located in the cell membrane or the ectoplasm.

The Effects of Temperature and Dinitrophenol on the Change of the Proportion of Pfr Controlling RNA Synthesis in Lemna gibba G3 in a Prolonged Dark Period

Summary Pfr level regulating RNA synthesis in dark period was estimated by the null response method in a long-day duckweed, Lemna gibba G3. In spite of culture at different temperatures (20 to 33 °C) and of the presence of DNP, this level began to decrease at the same time (about 22nd hr after beginning of the dark period) and the lowering rate was constant. In the culture at 16 OC, however, Pfr level was high even at the 37 th or 61st hr of the dark period. The characteristics of the system holding high Pfr level, at usual temperatures, were similar to those of the physiological clock.

Spectral dependence of the critical photoperiod in the long-day duckweed, Lemna gibba G3

Spectral dependence of the light sensitive L1- and L2-phases of the critical photoperiod of Lemna gibba G3 was examined by the min-LD method for wavelengths ranging from ca. 420 to 800 nm. The L1-phase had a sharp peak of sensitivity at 650–680 nm and a gentle slope of sensitivity ascending from 500 nm toward shorter wavelengths. The L2-phase showed remarkable sensitivity around 750 nm and in the blue-violet regions (≤500 nm). Red/far-red photoreversibility was confirmed for the LI-phase, but not for the L2-phase. The properties of the light receptors involved are discussed briefly.

Maintenance of high Pfr-level in the dark period in relation to flowering in Lemna gibba G3

The relative Pfr-level in a long-day duckweed, Lemna gibba G3, was estimated by the null response method. The null % R value (% R in a R/FR-mixture that provides a null flowering response. This value was assumed to indicate the endogenous Pfr-level of the duckweed.) remained high during the initial hours of the 15 hr nyctoperiod then decreased rapidly, if a 12 or 33 hr photoperiod preceded the nyctoperiod. The null % R value dropped immediately after the start of the 15 hr nyctoperiod subsequent to a 1 or 24 hr photoperiod. Thus, the duration of the maintenance of a high Pfr-level changed rhythmically depending on the length of the preceding photoperiod. Nyctoperiods of up to 9 hr following a 12 hr photoperiod hardly affected flowering, but nyctoperiods given after a 24 hr photoperiod suppressed flowering in proportion to the length of the period. The Pfr-level in the nyctoperiod, therefore, seems to be important for flowering, and phytochrome change, as a function of the length of photoperiod, may serve as a photoperiodic timer. Although floral response to interruption with R or FR changed with the application period, the difference in response between R-treated and FR-treated plants was relatively constant during a 15 hr nyctoperiod combined with a photoperiod of any length other than 1 hr. Apparently, the floral response to the R or FR pulse was regulated by a shift in the Pfr-level caused by the light pulse.

Effect of interruption of the nyctoperiod with an R/FR-mixture of various ratios of red and far-red light on flowering in Lemna gibba G3

A brief R pulse inserted in the 15-hr nyctoperiod of the 9L 15D regime almost always promoted flower formation of a long-day duckweed, Lemna gibba G3. This R effect was partially reversed by subsequent FR, which suggests that phytochrome is involved in the floral processes occurring in the nyctoperiod. The null % R value (% of R in the R/FR-mixture that exerts no effect on flowering) was high during the initial 7.5 hr of the nyctoperiod, then rapidly decreased. The starting time of the rapid decrease in the null % R value was hardly affected by a change in temperature in the nyctoperiod. A similarly high initial level of the null % R value followed by a rapid decrease was observed when the nyctoperiod was extended to 39 hr. At hour 15 of the 39-hr nyctoperiod, flower promotion by the R puke was not reversed by subsequent FR, although the spectral dependence of the light pulse effect did not exclude the possible involvement of phytochrome. At about hour 21 of the 39-hr nyctoperiod, the null % R value began to increase rapidly, and almost reached the initial high level at hour 24 when R-FR reversibility was also restored. These results suggest that the Pfr-level remained high during the initial hours of the nyctoperiod, followed by a rapid decrease irrespective of the temperature of the nyctoperiod. This rapid decrease in the Pfr-level may play a role in the time measurement of the photoperiodic floral induction of L. gibba G3.

Comparison of the flowering behavior of the long-day plant Lemna gibba G3 from different laboratories

Comparison of the flowering behavior of the long-day plant Lemna gibba G3 from different laboratories

Modes of control by the circadian oscillator and the hourglass mechanism of the activities of cytoplasmic and chloroplast glyceraldehyde 3-phosphate dehydrogenases in Lemna gibba G3

Modes of control by the circadian oscillator and the hourglass mechanism of the activities of cytoplasmic and chloroplast glyceraldehyde 3-phosphate dehydrogenases in Lemna gibba G3

Content of Adenosine Phosphate Compounds in a Long‐Day Duckweed, Lemna gibba G3, under Different Light and Nutritional Conditions

AbstractThe levels of ATP ADP and AMP as well as the energy charge were examined in the long‐day duckweed. Lemna gibba G3, under different light and nutritional conditions. ATP and ADP content, but not AMP, decreased slightly when the plant was cultured with a medium depleted of sucrose or was exposed to continuous darkness. The energy charge was not affected either by changes in the light conditions or by the depletion of sucrose from the medium, although increase of fresh weight changed drastically under these conditions. The levels of ADP and AMP and the value of the energy charge remained nearly constant throughout a 1‐day period when the plant was exposed to short‐day, continuous light and continuous dark. ATP content decreased gradually during the light period of the short day and thereafter remained constant during the dark period. When the plant was exposed to continuous light. ATP content decreased until the 8th hour after beginning of the continuous light, only to recover rapidly to its original level during the phase coinciding with the preceding dark period of the short day. Under continuous dark conditions the ATP content remained constant throughout the day. It was concluded that the diurnal rhythm of physiological activities previously reported cannot be related to the energy charge.

Diurnal rhythm of nuclear RNA polymerase I activity in a duckweed, <italic>Lemna gibba</italic> G3, under continuous light conditions

The diurnal change of nuclear RNA polymerases I and II was examined in a longday duckweed, Lemna gibba G3, under continuous light conditions. RNA synthesis in crude nuclei was dramatically stimulated by addition of the exogenous RNA polymerase of Escherichia coli, but not by the addition of calf thymus DNA. Treatment of crude nuclei with the supernatant fractions after precipitation of the nuclei decreased the RNA synthetic activity of the nuclei irrespective of the preparation time of both fractions. RNA polymerase I activity in crude nuclei, which was determined in the presence of α-amanitin at a low concentration of KCl, exhibited a diurnal rhythm but RNA polymerase II activity, which was presumed to be a portion of RNA synthesis inhibited by α-amanitin in the presence of a high concentration of KCl, remained constant throughout the day. Identical results were obtained when both enzymes were solubilized widi ammonium sulfate and chromatographed on DEAE-Sephadex column. Both activities in the supernatant fraction obtained after precipitation of the nuclei did not change diurnally. It was concluded, therefore, that the diurnal rhythm of RNA synthetic activity in the crude nuclei is due to the RNA polymerase I activity and not the RNA polymerase II activity.

The Effects on RNA Synthesis in a Long-Day Duckweed, Lemna gibba C 3, of Irradiation with Different Ratios of Red and Far Red Light During the Prolonged Dark Period

Summary Changes in the proportion of Pfr in the long-day duckweed Lemna gibba G3 during the dark period were examined using the null response method. The dark period was interrupted for 5 minute periods at various times by lights containing different ratios of both red and far red light at an intensity of 120 µW/cm 2 . RNA synthesis was then determined at selected times following irradiation. The dark period can be divided into 3 different periods each of which has a different sensitivity to the mixed lights. The duckweed irradiated with 100 % red light showed the same or slightly stimulated RNA synthetic activity as the dark control up to the 22nd hour from the beginning of the dark period: the value of null % red was 100 % or near. The value of null % red then decreased rapidly during next 12 h period to a constant level of 40 % red and finally remained at this level until the 37th hour. We concluded that phytochrome can modulate the amplitude of RNA synthesis rhythm, but that since the Pfr level remained high until the 22nd hour from the beginning of the dark period, the diurnal change of RNA synthetic activity during the dark period is not a direct result of fluctuations in the Pfr level.

Diurnal change in leakage of electrolytes from a long-day duckweed, Lemna gibba G3, under osmotic stress induced by water treatment

Diurnal change in leakage of electrolytes from a long-day duckweed, Lemna gibba G3, under osmotic stress induced by water treatment

The occurrence of acetylcholine in Lemna gibba G3

The occurrence of acetylcholine in Lemna gibba G3

Mutually inverse rhythmic and sigmoidal changes in activity of cytoplasmic and chloroplast glyceraldehyde 3-phosphate dehydrogenases in Lemna gibba G3

Two major timing devices probably control the temporal changes in activity of cytoplasmic NAD- and chloroplast NADP-GPDs in the long-day plant Lemna gibba G3; one is an oscillator and the other an hourglass. The former is reset by a light-on signal and responsible for diurnal changes in activities of GPDs in continuous light, while the latter is reset by a light-off signal to control sigmoidal changes in activities of GPDs in continuous darkness. The activities of Cyt-NAD-GPD and Chl-NADP-GPD always change mutually inversely.

Further studies on the diurnal rhythm of uridine incorporation into RNA in the long-day duckweed, Lemna gibba G3

Using the long-day duckweed Lemna gibba G3, the changes in the activities of RNA synthesis in isolated nuclei and chloroplasts and of the reaction prerequisite for the incorporation of exogenous uridine into RNA were examined. When the duckweed was exposed to either a light-dark cycle or to continuous light, the activity of RNA synthesis in the nuclear and chloroplast fractions changed diurnally and reached its highest levels during the night phase. The changes coincided with uridine incorporation into RNA in vivo. However, the amount of radioactive uridine taken up into the acid-soluble fraction remained unchanged during the whole day. The proportion of radioactivity incorporated into phosphorylated uridine compounds as well as UTP+UDP to the radioactivity in this fraction remained constant. Thus, the diurnal rhythm of uridine incorporation into RNA was related to the diurnal rhythm of RNA synthesis in isolated nuclei and chloroplasts. The lower activity of uridine incorporation into RNA under continuous darkness may be determined by the activity of RNA synthesis in nuclei and chloroplasts as well as the uptake rate of uridine into the duckweed cells, not by the activity of its phosphorylation.

Replacement by ionophores of the photoperiodic light requirement in Lemna gibba G3

Replacement by ionophores of the photoperiodic light requirement in Lemna gibba G3

The Effects of Calcium Withdrawal on the Uridine Uptake Process in a Long-day Duckweed, Lemna gibba G3

Summary The effects of calcium withdrawal on the process of uridine uptake was examined in a long-day duckweed, Lemna gibba G3. A short term treatment in sodium citrate reduced the rate of uridine uptake. It changed the value of Vmax for uridine uptake more than that of Km. CaCl2 was the most efficient compound in offsetting the citrate reduction. Sodium citrate did not, however, change the pattern of intracellular conversion of uridine absorbed into the duckweed cells. The lowered uptake rate recovered completely after 12 h when the duckweeds were cultured in the normal culture medium. The recovery process was inhibited by compounds which normally inhibit protein synthesis, although they did not change the rate of leucine transport into the duckweed or the activity of uridine phosphorylation. We concluded from these experiments that the protein(s) necessary for the uridine transporting system were released from the duckweed by treatment with sodium citrate and that calcium may be necessary for the molecular connection of the uridine transporting protein(s) to the cell membrane.

A COMPARATIVE STUDY OF DEVELOPING AIR CHAMBERS IN FLAT AND GIBBOUS FRONDS OF LEMNA GIBBA L.

SUMMARY Cross-sections were made of developing gibbous and flat fronds of Lemna gibba G3 which were emerging from the reproductive pocket of the mother plant. In the gibbous fronds the cells of the developing air chamber walls and peripheral walls were in a more active stage of division than in the flat fronds. Consequently, it was demonstrated that gibbosity is initiated in a young developing frond mainly as a result of enhanced cell division and the subsequent increase in the number of cells.