Studies of Long-day Inhibition in Short-day Plants

Previous experiments which the short-day plant Kalanchoe blossfeldianahave shown that long days interspersed in a period of short-dayinduction exert an active inhibition on flowering, each long-dayannulling the effect of approximately two short-day. The presentexperiments establish that three other short-day species-Biloxisoybean, Perilla ocymoides, and Chenopodium amaranticolor-aresimilarly inhibited. It is also shown that the inhibition appearsto act by making the short-days immediately succeeding the long-dayineffective, rather than by destroying previous induction. The other experiments with Kalanchoelarge temperature effectsin light or darkness on the promotive and inhibitory reactionsare demonstrated. A repetition of Harder and GÜmmer's experimentwas successful and confirmed that as little as one second oflight per day is sufficient for flowering in Kalanchoe; no floweringoccurs in complete darkness. Explaining earlier results in Kalanchoe a hypothetical schemewas postulated according to which induction of short-day plantsleads to the formation of an adaptive enzyme, which is subjectto inhibition by a substance formed in long-day conditions.From this scheme a change of critical daylength could be predictedas the result of partial induction. Two experiments set up totest this point indicated that there is in fact such a shift,thus supporting the hypothesis.     

Effects of Natural and Artificial Light in Arctic Latitudes on Long- and Short-day Plants as Revealed by Growth Analysis

The effects on growth and flowering of two short-day and twolong-day plants when grown under different conditions of illuminationare described. The plants fully investigated were Kalanchoeblossfeldiana and Xanthium pennsylvanicum and the annual varietiesof Hyoscyamus niger and Beta vulgaris. Wintex barley, Iberisumbellata, and tomato were also grown in some selected treatments.The conditions investigated comprised continuous full daylight(24 hours), full daylight for the whole of the daily photoperiodand full daylight for half the photoperiods, the other halfconsisting of either daylight reduced by shading or light fromincandescent lamps or fluorescent tubes (daylight-matching type),all of the same low intensity. Two lengths of photoperiod wereused for each species, one nearly optimal for flowering, theother closer to the critical day-length; and the order of thelow and high light treatments was varied. These factors werecombined factorially. Data were collected (or derived) for the following characteristics,though not always for all the species grown: dry weights, leafareas, heights, water contents, epidermal cell sizes, net assimilationrates, times to flowering, leaf-number increments until flowering,numbers of inflorescences, stomatal apertures, and leaf postures. Among other effects, the data revealed that in all four speciesinvestigated the adverse effects on over-all growth to be expectedfrom reduction of the daily photoperiod or of the intensityof illumination are in fact minimized. This compensation waseffected mainly by large increases in leaf areas, even thoughin all cases half the daily photoperiod consisted of full daylight.There are indications that increased efficiencies (net assimilationrates) may also have been involved. The leaf-area increasesappear to have been due to increased cell size rather than cellnumber and a close positive correlation with water content wasfound. The most striking among the effects on flowering was the failureof sugar-beet to bolt when half of its photoperiod (totals of20 and 14 hours) consisted of light from fluorescent lamps.The flowering of barley and Hyoscyamus was also delayed considerablyunder these conditions. The deficiency of red in the spectrumof the fluorescent light is believed to have been the cause.By contrast, the flowering of Iberis, a crucifer, was not affected.     

Light-Induced Growth Promotion by SPA1 Counteracts Phytochrome-Mediated Growth Inhibition during De-Etiolation

Previous evidence has suggested that SPA1 is a signal transduction component that appears to require phytochrome A for function in seedling photomorphogenesis. Using digital image analysis, we examined the time course of growth inhibition induced by red light in spa1 mutants to test the interpretation that SPA1 functions early in a phyA-specific signaling pathway. By comparing wild-type and mutant responses, we found that SPA1 caused an increase in hypocotyl growth rate after approximately 2 h of continuous red light, whereas the onset of phyA-mediated inhibition was detected within several minutes. Thus, SPA1-dependent growth promotion began after phyA started to inhibit growth. The action of SPA1 persisted for approximately 2 d of red light, a period well beyond the time when the phyA photoreceptor and its influence on growth have both decayed to undetectable levels. Also, SPA1 promoted growth for many hours in the complete absence of a light stimulus when red-light-grown seedlings were shifted to darkness. We propose that SPA1 functions in a light-induced mechanism that promotes growth and thereby counteracts growth inhibition mediated by phyA and phyB. Our finding that spa1 seedlings do not display growth promotion in response to end-of-day pulses of far-red light, even in a phyA-null background, supports this interpretation. Combined, these results lead us to the view that the rate of hypocotyl elongation in light is determined by at least two independent, opposing processes; an inhibition of growth by the phytochromes and a promotion of growth by light-activated SPA1.     

The Dynamics of Carbon Supply from Leaves of Barley Plants Grown in Long or Short Days

The role of the mature leaf in supplying carbon for growth inother parts of the plant was examined using a steady-rate ¹⁴CO₂labelling technique. The pattern of events occurring in theleaf during one complete 24 h cycle was compared in plants grownin, and adapted to long and short photoperiods. The rates ofleaf photosynthesis, night respiration and daytime loss of carbonfrom the growing regions of the plant Were similar in long orshort photoperiods. As a percentage of the total carbon fixedduring the photoperiod, total respiration was c. 50% for shortday plants but only 25% for long day plants. Thirty to forty per cent of the carbon fixed during the photoperiodwas retained in the leaf for export during darkness—therest was exported immediately. In leaves of short day plantssucrose and starch were the main form of the stored carbon.By the end of the dark period these compounds had been almostcompletely depleted. In leaves of long day plants there weremuch larger basal levels of sucrose and starch, upon which thediurnal variations were superimposed. These leaves also accumulatedfructosans. The delay in starch remobilization previously foundin leaves of short day plants was also evident in leaves oflong day plants even though large concentrations of sucroseand fructosans were present This suggests the presence of distinctpools of sucrose in the leaf.     

阿月浑子花序生长和花期物候学研究

以太行山区成龄(15年生)黄连木高接的阿月浑子(4年生)为材料,系统观测了10个阿月浑子雌雄品种的花序生长、花期物候以及开花节律.结果表明,阿月浑子花序生长始于3月下旬,生长期持续15~20 d;花期始于4月上旬,花期持续8~12 d;不同品种间的花期存在较大差异,雄株Peter和T491品种的花期较早,而雄株T11品种的花期较晚,其花期与雌株品种的花期基本吻合,可作为太行山地区适宜的授粉品种加以应用.     

The Inhibition of Growth in Higher Plants by a Homologous Series of Guanidines and its Reversal by Spermine

The effects of guazatine, synthalins A and B and a homologousseries of aliphatic monoguanidines on the growth of cress, barleyand oat seedlings, and apple cell suspension cultures have beenstudied. In the homologous series of aliphatic monoguanidines[NH₂C(=NH)NH(CH₂)_x–1CH₃] greatest inhibition was foundwith x = 8-10 for cress, barley and oats and x= 10–14for apple cells. Spermine partially reversed the inhibitionin the light for cress and barley but in the dark no reversalwas found. Technical guazatine inhibited growth to a greaterextent than pure guazatine, and was comparable in toxicity tosynthalin B in cress, barley and oats. Reversal by spermineof inhibition due to guazatine and synthalin B was greater inthe light than in the dark in these plants. Calcium ions didnot reverse the toxicity of guazatine, synthalin B or dodine.Reversal of the inhibition by guazatine, synthalin B and dodineof the growth of the apple cells was considerably greater withspermine than with spermidine. Lepidium sativumcress, Hordeum vulgarebarley, Avena sativaoat, Malus sylvestrisapple, guanidines, guazatine, synthalins, dodine, spermine, spermidine     

Observations on the Growth of Carnation (Dianthus caryophyllus L.) in Natural and Long Days

Observations were made on the growth and development of carnationsgrown in containers under natural or 24 h days. The number ofleaf pairs produced before flower initiation and the final lengthof each flowering stem were affected by the date at which theshoot appeared and its position on the plant. Dusk-to-dawn lighting reduced the number of axillary shootsin each generation but increased their rate of development.This resulted in similar numbers of flowers being produced inboth treatments. Dianthus caryophyllus L., Carnation, growth, flowering, day length     

Floral Induction of Xanthium strumarium in Long Days

An efficient method of inducing flowering in the normally strictshort-day plant, Xanthium strumarium L., in long days is described.Plants were grown in 16-h long days and subjected to two thermocycleswith a root application of gibberellic acid at the 8th h ofthe light period. A thermocycle was defined as follows. Forthe first 8 h of the 24-h cycle, the temperature was 4 °C;for the remaining 16 h, it was 23 °C. The light was on forthe first 16 h and off for the remaining 8 h. Xanthium strumarium L., floral induction, thermoperiod, gibberellic acid     

Inhibition of ABA-mediated Responses by Dithiothreitol in Plants

In plants, abscisic acid (ABA)-mediated responses during abiotic stress, growth, and development have been well studied. Many chemicals which modulate ABA responses have been identified. In this study, we report that dithiothreitol (DTT), an inducer of endoplasmic reticulum (ER) stress, can overcome ABA-mediated responses in plants. In rice seedlings, combined treatment of ABA and DTT increased shoot growth compared to ABA alone. The phenotype correlated with the expression pattern of ABA and ER stress-responsive genes. In finger millet, increase in root growth was observed in combined treatment, compared to ABA treatment. Experiments using dimethyl sulfoxide indicated that the phenotype observed was specific to DTT. Priming of germinated rice seeds with DTT followed by salinity stress indicated that DTT can mask the ABA effect. In ABA bioassay using cotton petioles, an increase in intact petioles in combined treatment of ABA and DTT was observed compared to ABA treatment. The expression of OsWRKY48, an ABA-responsive gene, was down-regulated in combined treatment, indicating that the target of DTT-induced ER stress is upstream of OsWRKY48 in the ABA signaling pathway. The study demonstrated that DTT-induced ER stress can be a potential mechanism to regulate ABA-mediated responses in plants.

     

Promotion of Growth and Flowering and Increase in Content of Endogenous Gibberellins in Gladiolus Plants Treated with the Growth Retardant CCC

Application of the growth retardant CCC to gladiolus plants resulted in stimulation of stem lenth, increased number of flowers per spike and a slight advancement of anthesis date. Leaves of treated plants were heavier than control and contained a higher amount of water and chlorophyll. The anthocyanin content in petals was also greatly increased. CCC had little or no effect on the content of the endogenous gibberellins in the acidic ethyl acetate fraction, but markedly increased the content of the native gibberellins in the aqueous fraction. The mode of action of CCC in plants is discussed on the basis of these results and a review of the literature.     

B-Nine Reversal of Benzimidazole-or IAA-induced Inhibition of Growth and Yield of Cowpea Plants

Growth, flowering, and yield of Cowpea (Vigna catjang) wereinhibited by Benzimidazole (10^-3M) or IAA (10^-2M). These growthinhibitions were reversed by B-Nine (2x10^-3M) which alone waswithout any effect. In combination, IAA and Benzimidazole weremutually antagonistic. A common mechanism is suggested for theB-Nine reversal of the Benzimidazole or IAA inhibition of growth.     

The Inhibition of Fungal Growth in Resistant Cotton Plants Infected by Fusarium oxysporum f. sp. vasinfectum

The vascular colonization of cotton plants by Fusarium oxysporum f. sp. vasinfectum was determined by examining growth of the fungus from free-hand cross sections taken from 0 to six days after inoculation at various distances above the points of root inoculation. Fungal spread in both longitudinal and lateral directions in the susceptible cultivar Rowden was evident four days after inoculation, whereas fungal spread in the resistant cultivar Seabrook Sea Island was restricted. The quantity of viable fungus in infected tissues was determined from macerated tissues plated on Czapek- Dox agar. The colony counts declined within six days after inoculation in resistant Seabrook Sea Island, but not in susceptible Rowden, implying that an inhibition of fungal growth in vascular tissues occurred in resistant Seabrook Sea Island. This inhibition could contribute to the restriction of fungal spread and thus be a factor in the resistance of cotton plants to F. oxysporum f. sp. vasinfectum .     

Chloramphenicol Inhibition of Salt Absorption by Intact Plants

The influence of chloramphenicol on the accumulation of calciumand rubidium by intact barley plants has been investigated.The uptake of both ions during 24 hrs. was reduced by exposureto the inhibitor for 24 hrs. before the uptake period. The maineffect was on the fractions of the ions which reached shootsand on those present in roots in non-exchangeable forms. Chloramphenicolalso reduced transpiration, but to a considerably smaller extent. The primary effect of chloramphenicol on salt uptake appearsto be on the mechanisms of active transport which convey ionsacross the root. Since chloramphenicol does not affect the uptakeof oxygen, it appears that the active accumulation of saltsis not directly mediated by the electron transfer in respiration.The results are compatible with the existence of a linkage betweensalt absorption and protein synthesis; the nature of this linkageis at present unknown.     

Non-hormonal Growth Promotion Shown by Aqueous Extracts

Bioassay of chromatograms of aqueous potato-sprout and -tuberextracts and lettuce-seed extracts, with the coleoptile, straight-growthtest, indicates the presence of a growth promoter running nearto the position of IAA and giving a spray colour reaction withEbrlich reagent similar to that of IAA. It is shown that bothpromotion and spray colour are due to sugars. It is concludedthat major nutrients may give large growth effects in this bioassayand that in certain cases ether extracts may contain quantitiesof these large enough to give rise to growth effects.     

Short-day and Low-temperature Induction in Lolium

The requirements for floral induction of several outbreedingpopulations of Lolium perenne, L. multiflorum, and L. rigidumhave been studied. Floral induction can be brought about byeither low temperature (0–30° C.) or short day (8hr.) independently, but short day is ineffective at low temperatures. The exact inductive requirement varies with the population.The summerannual Westerwolds ryegrass needs neither cold norshort day, the winter-annual Wimmera ryegrass shows a quantitativeresponse, while the perennial varieties from north-west Europehave an obligatory requirement for either cold or short daybefore floral induction. This relation between the annual orperennial habit and the inductive requirement was confirmedin a number of Mediterranean collections of L. perenne and L.rigidum. Considerable genetic variation in inductive requirement couldbe detected within each outbreeding population, and rapid responseto selection proved possible in Wimmera, Irish, and Kent ryegrass.