Flowering In Chenopodium Rubrum Research Articles

Effect of Darkness on Growth and Flowering of Chenopodium rubrum and C. murale Plants in vitro

Chenopodium rubrum, a short-day plant, and C. murale, a long-day plant, were grown in vitro in continuous darkness. Control C. rubrum plants exposed to continuous darkness for 15 d at cotyledonary phase, did not flower, while 80 % of plants flowered on the medium with 5 % glucose and 10 mg dm-3 GA3. Control C. murale plants exposed to continuous darkness for 10 d at the age of 4th pair of leaves, did not flower, while GA3 (1 - 5 mg dm-3) stimulated flowering up to 65 %.

Benzyladenine-induced inhibition of flowering in Chenopodium rubrum in vitro is not related to the levels of isoprenoid cytokinins

The effect of 6-benzylaminopurine (BAP) on floweringand on endogenous levels of isoprenoid cytokinins wasinvestigated in explanted terminal shoots of Chenopodium rubrum cultivated in vitro. Themother plants were grown under continuous light andexplants were cut off when the 6th leaf primordiumoriginated at the shoot apex. The explants wereexposed to one dark period of 13 hours inductive forflowering or to continuous light on medium with orwithout BAP (0.05;0.2;0.4 mg.l-1). Undernon-inductive conditions no flowering was observedeither in the control or after BAP treatment. Afterreceiving one inductive dark period, the controlexplants flowered. However, BAP application either atthe beginning of the inductive dark period and/orduring the following light cultivation inhibitedflowering and stimulated initiation and growth of leafprimordia. In the case of the most efficient BAPconcentration (0.05 mg.l-1) flowering wasinhibited by 80% and the number of leaf primordia wasincreased by 3. Explantation caused a significantincrease in the total amount of endogenous cytokininsin the explants within first 13 h, provided they werekept in light. When explants were kept in darkness,only a slight increase in cytokinin levels wasobserved. BAP treatment had no influence on the levelsof endogenous cytokinins either in light or indarkness. We may thus conclude, that BAP applicationinhibited flowering of photoperiodically inducedterminal shoot explants and stimulated leaf primordiaformation with no significant effect on changes inlevels of endogenous isoprenoid cytokinins. This maysuggest the direct ability of BAP to regulate morphogenesis.

Photoperiodic induction of flowering in Chenopodium rubrum L. might be controlled by an oscillatory mechanism

Summary Long-term recordings of bioelectric potential difference across intact Chenopodium rubrum L. plants have been performed by subjecting them to different conditions for flowering during 10 days. Switching the light-on/off caused transient changes of the potential difference and the photosynthetic process was the major generator of those transients. Besides these transients, with average amplitude of 32 mV and duration of 22 min, self-sustained oscillations of the potential difference were also observed predominantly in the light-on period. The form of the individual spontaneous transients was usually similar to the light-induced transients, lasting 10–15 min, with an average amplitude of 6–7 mV. As the age of the plant increases, the frequency of the oscillations increased to more than four spikes per hour for some induced plants. With induced plants the oscillations were more ordered and of higher frequency. The results obtained point to the possibility that a frequency-controlled oscillatory bioelectric mechanism might be one of the initial steps in flowering control.

Methyl jasmonate inhibits growth and flowering inChenopodium rubrum

C. rubrum plants of different age were treated with methyl jasmonate (JA-Me), in some cases in combination with photoperiodic flower induction. Plants treated with JA-Me (3×10−4, 3×10−5 and 5×10−7M) showed inhibition of growth and flowering. No effect of JA-Me application on ethylene formation was observed.

The Interaction of Direct Electric Current with Endogenous Rhythms of Flowering in Chenopodium rubrum

Summary Chenopodium rubrum is known to have an endogenous rhythm of flowering with two maxima at about the 12th and 44th h of darkness. Consecutive applications of direct electric current (DC) (6 μA · plant -1 , cathode being connected with leaf tips, anode with the roots) within the last 4 h of darkness, i.e. in intervals 0–4, 4–8, .....48–52 h, respectively, after which period the plants were transferred to light, was inhibitory to flowering only within 4–8, 8–12 and 12–16 h, respectively. The second peak of flowering was inhibited moderately in some experiments and not at all in the other ones. Use of very sensitive plants showed that DC starts losing its effectiveness already in the interval 16–20 h of darkness. Consecutive DC treatments, each 4h of darkness (0–4, 4–8, ....40–44h), after which period the plants remained in darkness and were transferred to light together at the 44th h, resulted in some fluctuations of apex growth and branching. As these fluctuations could be connected with a rhythm in cell division in the apex described by King (1975) , the same experiment was repeated with plants raised under constant conditions, which should not display this type of rhythm. Indeed, the fluctuations in apex growth and branching almost disappeared. It is concluded that DC does not interfere with the timing mechanism of endogenous rhythm (the phase remains unchanged). The inability of DC to abolish the second peak of flowering suggests that endogenous rhythm of flowering cannot be explained by rhythmic production of floral stimulus.

Organ correlations and flowering in chenopodium rubrum L.

Correlations within a shoot ofChenopodium rubrum L. ecotype 374 grown under continuous light or photoperiodic flower induction were studied using surgical treatments. Removal of a single pair of shoot organs had a variety of effects depending on position: significant changes in the number of leaf pair on the main axis or in axillary buds and in the height of shoot apices; or no effect on the parameters scored. Flowering was not affected by any of the treatments carried out. Decapitation brought about a significant increase in the number of leaf pairs in axillary buds and flowering was inhibited in 8- and 9-d old plants. Flowering was not affected in 21-d old plants. The role of shoot organ correlations, especially that of apical dominance, in regulation of flowering inC.rubrum is discussed.

The effect of IAA application on endogenous rhythm of flowering inChenopodium rubrum L.

The study deals with the effect of indol-3-ylacetic acid (IAA) on endogenous rhythm of flowering inChenopodium rubrum L. ecotype 374. Phase setting of the rhythm and length of its period were not affected, its amplitude decreased or changed insignificantly depending on the time and the site of IAA application. The intervals of significant inhibitory effect of IAA applied to apical buds terminated later than after IAA application to photoreceptive organs. The inhibitory effect did not correlate with the level of IAA uptake. Results obtained support the hypothesis that both photoreceptive organs and apical buds are the sites of inhibitory effect of applied IAA.

Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 × 10 -4 M or 3 × 10 -4 M was applied to the apical buds of Chenopodium rubrum plants exposed to different photoperiodic treatments and showing different patterns of floral differentiation. Stimulation of growth in width of the apical meristem of the shoot and/or inhibition of growth in length was obtained under all photoperiodic treatments. This change of growth pattern was followed by different effects on flowering. In non-induced plants grown under continuous light ABA stimulated periclinal divisions in the peripheral zone and the initiation of leaves as well as the growth in width of bud primordia. In plants induced by two short days reduced growth of the meristem coincided with ABA application. Longitudinal growth of the meristem was inhibited in this case and only a temporary stimulation of inflorescence formation took place. In plants induced at a very early stage, ABA exerted a strong inhibitory effect on flowering. A permanent and reproducible stimulatory effect on flowering was obtained in plants induced by three sub-critical photoperiodic cycles if ABA was applied to apices released from apical dominance. In this case formation of lateral organs and internodes was promoted by ABA and was followed by stimulated inflorescence formation. Gibberellic acid (GA2) at 1× 10 -4 M or 3 × 10 -4 M brought about a similar effect on flowering as ABA, although the primary growth effect was different, i.e. GA 2 stimulated longitudinal growth. The effects of ABA and GA 2 on floral differentiation have been compared with earlier results obtained from auxin and kinetin applications. These growth hormones are believed to regulate flowering by changing cellular growth within the shoot apex. Depending on the actual state of the meristem identical growth responses may result in different patterns of organogenesis and even in opposite effects on flowering.

Promotive effect of abscisic acid in flowering ofChenopodium rubrum as the result of decreasing apical dominance

Abscisic acid (ABA) was applied in a concentration of 1. 10−3 M and 1. 10−4 M to the quantitative SD plantChenopodium rubrum under various light regimes. ABA did not influence flowering in plants under continuous illumination, enhanced flowering in plants subjected to long days and inhibited it in plants induced by short days. It was concluded that ABA can not substitute for inductive treatment but its action may be additive to initial stages of reproductive morphogenesis (enhanced growth rate and branching of the apical meristem) as evoked by long days.

Photoperiodic Time Measurement and Effects of Temperature on Flowering in Chenopodium rubrum L

The critical dark period length (c. 8 h darkness) required for induction of flowering of C. rubrum is insensitive to temperature (Q10 c. 1.0) over the temperature range 10-25°C. However, the period of a rhythm controlling floral induction is shown to be temperature sensitive (Q10 c. 1.4) over the temperature range 9-22°C. The discrepancy in temperature dependence of these two parameters of photoperiodic time-measurement could reflect differences in their rates of adjustment after a temperature shift. By contrast, at least two other species (Pharbitis nil and Hyoscyamus niger) show marked temperature sensitivity of their critical daylength. Thus, there may be more than one time- keeper in the photoperiodic control of flowering.

Change of growth correlations in the shoot meristem as the cause of age dependence of flowering in Chenopodium rubrum

Summary Three, six and nine days old seedlings of the short-day plant Chenopodium rubrum show marked differences in the number of inductive cycles they need to evoke floral differentiation. The older the plants, the more inductive cycles and the longer the time required for flowering. We have compared the changes in the anatomical structure of the shoot apex and in the growth of leaf and bud primordia in the age groups mentioned. The speed of floral differentiation does not correlate with the zonal pattern of the shoot apex before induction. Floral differentiation is, however, influenced by the amount of meristematic tissue and the number of leaves initiated. Photoperiodic treatment causes an immediate inhibition of leaf growth in all age groups and, soon after, a release from apical dominance in the apex. Consequently, branching of the shoot apex occurs and the growth of leaf primordia is inhibited. Finally, formation of new leaves in the peripheral zone ceases and differentiation of the terminal flower takes place. If the number of inductive cycles is insufficient, restored leaf organogenesis and a correlated inhibition of bud primordia resume, and a reversal to the vegetative state sets in. The manner of initiation of the lateral organs — leaves and buds — is similar in plants of various age. There are, however, quantitative differences in the number and growth of the lateral organs at the onset of photoperiodic induction as well as during induction and during postinductive changes. These differences in growth cause differences in the number of inductive short-day cycles required for inhibition of vegetative growth and the changes leading to flowering. In younger plants having less well-developed vegetative growth, a single photoperiodic cycle is sufficient to induce flower formation. In older plants a single cycle results in an initial change of the growth correlations between leaf and bud primorida, i.e. in branching, while further floral differentiation requires repeated photoperiodic cycles. Thus, with Chenopodium rubrum the importance of the suppression of leaf growth during the transition from the vegetative to the reproductive state may be demonstrated.

Effects of various alcohols on the induction of flowering in Chenopodium rubrum L.

Summary Seedlings of Chenopodium rubrum were treated with several alcohols during the 13 h dark period that induces flowering. The primary alcohols (C2-C5) inhibited the induction strongly. Secondary (C3, C4) and tertiary (C4) alcohols had no significant effect. Alcohol dehydrogenase in C. rubrum seedling extracts was acting on the primary alcohols only, its kinetic properties being comparable to those of the yeast enzyme (E.C. 1.1.1.1.). The profiles for ethanol sensitivity and for alcohol dehydrogenase activity in the seedlings were not identical, although both showed a slight increase at the end of the dark period. It was concluded that the inhibition of flowering is not by interference with a membrane system but via metabolic effects on the primary inductive process. On the basis of their relative turnover velocities with alcohol dehydrogenase, n-butanol and n-pentanol are the most effective inhibitors of the compounds tested.

Nature of light requirement for the flowering of Chenopodium rubrum L. (Ecotype 60� 47?N)

It has been shown that induction of flowering in Chenopodium rubrum L. (ecotype 60° 47' N) seedlings in BCJ light conditions is intensity dependent (Cumming, 1969, Canad. J. Bot. 47, 1247-1250) and that, this intensity dependence is not based on photosynthesis (Sawhney and Cumming, 1971, Can. J. Bot. 49, 2133-2137). Since BCJ light emits a high proportion of energy in the far-red, and the High Energy Reaction (HER) has its action maxima in the far-red and blue regions of the spectrum, we tested the involvement of HER in the light induction of flowering in C. rubrum. Our results show that optimum intensities of blue light are effective in inducing flowering in C. rubrum. Red light exposure does not lead to flower induction. We suggest the HER may be involved in the flower induction of C. rubrum in light. However, when high energy in blue and/or farred is provided in presence of energy between 500-700 nm wavebands, there is no flowering in C. rubrum. We suggest that flower inducing activity of HER may be counteracted by flower inhibitory action of red wavebands.

Nature of light requirement for the flowering of Chenopodium rubrum L. (Ecotype 60� 47? N)

Seedlings of the short-day plant, Chenopodium rubrum L. (Ecotype 60° 47' N) were irradiated with different intensities and qualities of light for 24 h preceding a single inductive dark period (12 h). Our data shows that a relatively low intensity incandescent light (35-100 ft. c.) is not effective as the photoperiod for flowering. The above effect is not due to a requirement for a relatively high level of photosynthesis. Our results suggest a definite promotory role of a blue High Energy Reaction (HER). We could not demonstrate the involvement of a far-red HER. We suggest that ineffectiveness of far-red may have been due to establishment of rather low Phytochrome, P FR , levels, suboptimal for flowering. A certain critical level of P FR (30-40%, that presumably established by blue light) seems to be necessary for photoreactions involved in flowering of C. rubrum. There are indications in our experiments of the operation of a red radiation mediated flower inhibitory photoreaction.

Nature of light requirement for the flowering of Chenopodium rubrum L. (Ecotype 60� 47? N)

Seedlings of C. rubrum were irradiated with different light qualities and intensities following a single inductive dark period. Our results show that relatively low intensity white light (35–100 ft. c.) does not support flower development while high intensity white light (650–800 ft. c.) permits 100% flowering. We have shown that the low intensity light inhibiton of flower development is not due to suboptimal photosynthesis. Relatively low intensities of light rich in far-red or blue wavebands sustains optimum flower development, whereas red light is totally ineffective in this respect. Considering that the intensity dependent High Energy Reaction (HER) has its action maxima in the blue and far-red we propose that HER may be positively involved in the flower development of C. rubrum. Our study further suggests that there may be some flower inhibitory component at play in relatively low intensity white light conditions and HER may be required to counteract this flower inhibitory effect.

Effect of different sugars on flowering ofChenopodium rubrum L. in dependence on the conditions of germination and initial growth

Flowering ofChenopodium rubrum seedlings fed different sugars at a concentration of 0.6 and 0.4 M, reap, during a single inductive cycle was stimulated or inhibited in dependence on the conditions of germination and initial growth. Plants allowed to germinate at alternating temperatures of 28 °C and 5 °C showed a slower initial growth and their development was stimulated by some sugars as compared to controls induced in the absence of sugars. Plants germinated at alternating temperatures of 32 °C and 5 °C exhibited a rapid initial growth and flowering was inhibited after induction in the presence of sugars. On the other hand, development proceeded more rapidly in control plants induced in the absence of sugars after germination at the higher temperature than after germination at the lower one. The differences between the two variants quoted above could be observed also after induction by two 16 h dark cycles. Glucose and sucrose were most effective in stimulating flowering under appropriate conditions of germination. Fructose was less effective and the action of maltose was very weak. Xylose, ribose and galactose were innocuous, while arabinose, glucoso-6-phosphate and mannitol were toxic to the plants. The sugars inhibited root growth in all cases and led to an increase in starch accumulation in the underground and overground plant organs. At a concentration of 0.6 M they mostly inhibited the length of the cotyledons and, especially, of the first leaf; at a concentration of 0.4 M growth of the overground organs was stimulated. The results are discussed with respect to the possible ohanges in photoperiodic sensitivity brought about by the rate of initial growth.

Investigation of the endogenous rhythm of flowering inChenopodium rubrum L.

Under the conditions applied in our laboratory 4 1/2 days old plants ofChenopodium rubrum require 2–3 photoperiodic cycles for maximal flowering response, whereas 2 1/2 days old plants are able to flower after having obtained a single inductive cycle. The period length of the free-running rhythm of flowering observed in 2 1/2 days old plants after a single transfer from light to darkness is 30h and the first peak of flowering occurs at about hour 12 in darkness. When a cycle consisting of 16h darkness and 8h light or of 8h darkness and 8h light precedes the long dark period the rhythm is rephased. Rephasing is greater when the light commenced to act on the positive slope of the first peak of the free running rhythm than when it impinged on the negative slope. With an 8h interruption of darkness by light rhythm phase is controlled by the light-on, as well as by the light-off signal. Feeding 0.4 M glucose during the long period of darkness enhanced the amplitude of the flowering response and, moreover, substituted for one photoperiodic cycle.

Time-dependence of auxin and ethrel effects on flowering in chenopodium rubrum L.

IAA, NAA and ethrel (1 × 10-4M and 3 × 10-4M) was applied to the plumula of Chenopodium plants at different time after the start of photoperiodic treatment and the flowering response was investigated. The inhibitory effect was found with all the applications during the first two days, whereas a stimulatory one on the third and fourth day. We assume this dual effect reflects the differences attained in developmental phase and in the degree of shoot apex differentiation.

The Effects of CCC, Ethrel, Abscisic Acid, Abscisic Aldehyde, and Abscisic Hydrocarbon on the Development and Flowering of Chenopodium rubrum L.

Ethrel, CCC, abscisic acid, and two chemically similar compounds were tested at various concentrations on seedlings and excised stem tips exposed to one of two photoperiodic regimes, one inductive, the other noninductive relative to flowering. None of the substances tested was able to induce or promote flowering of specimens exposed to photoperiodically noninductive conditions. All of the tested substances inhibited or delayed flowering of excised stem tips, and all, with the exception of abscisic hydrocarbon, delayed flowering of seedlings. In most experiments the effects of a test substance on flowering appeared to have been indirect through the substance's inhibitory effect on leaf development. In contrast, the inhibition of flowering of excised stem tips by Ethrel appeared to have been at least partly a direct, rather than mainly a leaf-mediated, process.

The Effect of Defoliation, and Hypocotyl and Root Removal, on the Development and Flowering of Chenopodium rubrum L.

Seedlings of Chenopodium rubrum flowered earliest when they had intact cotyledons, and incremental cotyledon pruning delayed flowering. Seedlings with roots removed prior to photoperiodic induction regenerated roots quickly and, although this treatment delayed flowering slightly, the pattern of flowering of such seedlings with incremental cotyledon pruning was similar to that of seedlings with root and cotyledon pruning. Seedlings with hypocotyls and roots removed prior to photoperiodic induction took longest to flower compared with the other two types of seedlings, and time to flower was not linearly correlated with amount of cotyledon pruning. Presence of cotyledons on seedlings without hypocotyls and roots, that is, on excised stem tips, appeared to inhibit epicotyl development in culture. Gibberellic acid (GA3) overcame this inhibition, and earliest flowering was associated with 10-7M GA3. However, GA3 (10-8-10-6M) did not affect the flowering of cultured excised stem tips devoid of cotyledons.