EFFECTS OF GROWTH SUBSTANCES ON FROND AND FLOWER PRODUCTION IN LEMNA GIBBA G3

Frond and flower production in a long-day duckweed, Lemna gibbaG3, growing under different photoperiodic conditions in presenceand absence of varied concentrations of applied IAA, KIN andGA was investigated. The predominant actions of IAA, KIN and GA were revealed tobe respectively the depression of flowering, the promotion offrond multiplication and the enhancement of flowering. The rateof increase in FL % as an index of the concentration of floralstimulus in the tissues was curtailed greatly by IAA, to a lesserextent by KIN and little by GA. GA at 10^–5 M apparentlyreduced the critical day length (12 hr) and the induction period(48 hr) by 2 and 4 hr, respectively. No vegetative growth waspromoted by KIN in the light. On the basis of these and relevant findings the sites of actionof the growth substances examined in the flowering process ofthe duckweed were suggested. (Received May 30, 1965; )     

Frond and flower production in Lemna gibba G 3 in presence of respiratory inhibitors

Effects of respiratory inhibitors on frond and flower productionin light culture of a long-day duckweed, Lemna gibba G 3, wereinvestigated. The inhibitors examined could be divided into3 groups based on their specific actions: (A) 2,4-Dinitrophenol(10^–6M), arsenate (10^–4M), malonate (10^–2M),o-phenanthroline (10^–6M), ,'-dipyridyl (10^–5M) andazide (10^–6M) inhibited flower production by suppressingthe rate of flower production without affecting the inductionperiod. Frond production, however, was promoted by these reagents.Effective time of application came one day after the end ofthe induction period. (B) Iodoacetate (10^–6M) and fluoride(10^–4M) inhibited both flower production and, less significantly,frond production. Reduced rate of flower production was responsiblefor the inhibition of flowering. Effective time of applicationpreceded by one day that of A group inhibitors. (C) Salicylaldoxime(10^–6M), diethyldithiocarbamate (10^–6M) and 8-hydroxyquinoline(10^–7M) enhanced flower production by reducing the lengthof the induction period, and simultaneously slightly inhibitedfrond production. Effective time of application was the latterhalf of the induction period. The implications of these findingsare discussed with special reference to the component processesinvolved in photoperiodic induction of flowering in duckweed. (Received March 27, 1969; )     

LIGHT- AND DARK-GROWTH IN LONG-DAY DUCKWEED, LEMNA GIBBA G3, AS AFFECTED BY KINETIN

Under short-day conditions the growth or the production of fronds in Lemna gibba G3 was stimulated by KIN (10^–5 M);the longer the nyctoperiod, the greater the stimulation was.Under long-day conditions KIN was slightly inhibitory for thefirst 2 days, but promotive thereafter. IAA (10^–5 M) reversedthe growth inhibition by KIN in long-days, and DCA (10^–4to 10^–6 M) and also CA (10^–4 to 10^–6 M), althoughless effectively, cancelled the growth promotion by KIN in short-days.DCA (10^–5 M) little altered the KIN inhibition in thefirst 2 days of light culture, nevertheless it alleviated strikinglythe KIN promotion in the subsequent illuminated days. These and relevant findings explained the above-described promotionand inhibition by KIN of the duckweed growth in terms of invivo level of a cofactor (probably auxin) which may be underthe regulative influence of photoperiodic conditions given.Moreover, some bearing of the above conclusion on floweringmechanism in this long-day duck-weed was suggested. (Received September 12, 1966; )     

Resemblance of growth substances to metal chelators with respect to their actions on duckweed growth

Action patterns of IAA, KIN and GA on the growth of Lemna gibbaG3 are similar to those reported for agents chelating both cupricand ferric ions. Relatively high doses of growth substances,e.g.10^–6 M IAA or KIN and ^–4 M GA, inhibit developmentof photoperiodically induced flower buds and antagonisticallypromote frond multiplication; whereas, at relatively low doses,e.g. 10^–9 M IAA or KIN and ^–5 M GA, they acceleratethe process occurring in the latter half of the induction periodto enhance flower induction. Complex forming abilities of IAA,KIN and GA with cupric and ferric ions are demonstrated spectrophotometrically.Moreover, the ferrous ion-dependent oscillatory change in reproductiveand vegetative photophilies of duckweed is eliminated by KINbut not by IAA and GA. Of the three growth substances tried,KIN alone shows an affinity for ferrous ions. (Received April 5, 1971; )     

Periodical growth response of Lemna gibba G3 to light-break

Brief exposure to light promotes frond multiplication in Lemnagibba G3 in darkness. Extent of promotion changes periodicallywith the time of the light-break. Response curves are interpretedin terms of a superposition of two modes of growth responseto light-break, which are, respectively, under the control ofdifferent physiological timing devices; circadian oscillationand the hourglass-type clock. Circadian oscillation, which consistsof a half-cycle of increasing photophily followed by anotherhalf-cycle of declining photophily, starts at a light-on signaland continues for a few days with rapid damping. The 24-hr periodof oscillation is the same at temperatures ranging from 16 to26°C. The hourglass is released by a light-off signal to‘accumulate sand’ or to increase photophily in asigmoidal way with time and is temperature-sensitive; the tempoof‘sand accumulation’ being quicker at 21°Cthan at 16 or 26°C. Oscillation is hastened to fade-outat 21°C, most likely due to the accelerated pace of thehourglass. Red and far-red reversibility is disclosed in bothmodes of growth response. (Received December 31, 1969; )     

Disappearance of rhythmicity in growth response to dark- and light-breaks in Lemna gibba G3 due to iron deficiency

Inhibition of flower initiation in light culture of a long-dayduckweed, Lemna gibba G3 by an inserted period of brief darknesschanges its magnitude with the application time of the dark-break.‘Response vs. time of the dark-break’ curve consistsof superimposed thermo-insensitive oscillatory and thermo-sensitivehourglass components. Oscillation is diurnal and damps in afew days. The situation is very similar to what has previouslybeen revealed concerning the non-photosynthetic light-requirementof the same strain of duckweed for frond multiplication. Increasingphotophily for flower production is likely accompanied by decreasingphotophily for frond production, and vice versa. The presenceof iron chelators such as o-phenanthroline and ,'-dipyridylor reduced iron concentration in culture medium abolishes theoscillatory change, without modifying the hourglass change,in either vegetative or reproductive photophily. Ferrous, butnot ferric, ions likely mediate between the basic clock andthe photophily. Critical daylength for flower induction is notaffected by exogenous chelators. (Received November 17, 1970; )     

RIBONUCLEIC ACIDS IN SOLUBLE CYTOPLASM OF GERMINATING BEAN

From 1.5 day-old bean germ-axes and cotyledons were preparedmicrosomal (Ms) and 78,400 /g supernatant (Sp) RNA's by phenolextraction. Sp-RNA from germ-axes differed considerably fromMs.RNA from either tissue with respect of quantitative nucleotidecomposition; the former being very similar to yeast s.RNA. Sp-RNAfrom cotyledons gave an intermediate nucleotide pattern betweenthose of Ms-RNA's and of Sp.RNA of germ-axes. Accepting abilityfor ¹⁴C-leucine in the presnece of added ATP, MgCl₂ and "activatingenzyme" was the highest in Sp-RNA from germ-axes, followed bySp-RNA from cotyledons. Ms.RNA's could hardly function as acceptorfor activated leucine. The capacity of leucine incorporationof cotyledonous Sp-RNA agreed well with that predicted fromits s-RNA level evaluated from the observed nucleotide compositionon the assumption that the Sp.RNA consisted of active RNA ofyeast s-RNA type and inactive RNA of Ms.RNA type. The resultswere discussed along the line of a hypothesis on the presenceof "transportable RNA" in germinating bean seed tissues. (Received July 19, 1960; )     

EFFECTS OF NUCLEIC ACID- AND PROTEIN-ANTIMETABOLITES ON FROND AND FLOWER PRODUCTION IN LEMNA GIBBA G3

Frond and flower production in a long-day duckweed, Lemna gibbaG3, grown under continuous illumination in the presence or absenceof varied concentrations of 5-fluorodeoxyuridine, 5-fluorouracill,2- thiouracil, 8-azaguanine or ethionine and/or correspondingmetabolite, i.e., thymidine, orotic acid, uracil, guanine ormethionine, have been investigated. From the results obtained,the presumptive flows of vegetative and reproductive informationfrom gene DNA to protein have been associated with frond andflower initiation in the duckweed meristem, respectively. (Received September 3, 1964; )