Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

Size of the Chrysanthemum Shoot Apex in Relation to Inflorescence Initiation and Development

The size of the apical dome of Chrysanthemum morifolium Ramat.at the transition to inflorescence initiation in continuouslight (long days) was not systematically influenced by eitherthe temperature or the irradiance under which the plants weregrown. It was generally 0.26 mm in diameter and c. 3.6 x 10^–3mm³ in volume when the first bract was initiated. The dimensionsof the apical dome of plants in short days were only slightlysmaller at this stage. Similarly, each step in the further developmentof the chrysanthemum inflorescence was associated with a narrowrange of apex sizes, indicating that inflorescence initiationand development are closely related to apex size. Chrysanthemum morifolium Ramat, shoot apex, inflorescence initiation     

Further Effects of Light Intensity, Carbon Dioxide Concentration, and Day Temperature on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne in Controlled Environments

In earlier work the effects of light intensity over the range31 to 250 J cm^–2 day^–1 and carbon dioxide concentrationfrom 325 to 900 ppm with 8-h days at 18.3 °C and 16-h nightsat 15.6 °C were described. The present paper is concernedwith three further experiments with light levels up to 375 Jcm^–2 day^–1 (which corresponds to the daily totalin a glasshouse in southern England in early May or August andthe intensity is approximately that of mid-winter sunshine),carbon dioxide concentration up to 1500 ppm, and day temperaturesof 18.3 to 29.4 °C. Final plant weight was increased by light over the range 125–375J cm^–2 day^–1 and by carbon dioxide over the range325–900 ppm, with positive interaction between them; thisinteraction was increased by raising the temperature to 23.9°C and somewhat more at 29.4 °C day temperature. Leaf-arearatio and specific leaf area were reduced by increasing eitherlight or carbon dioxide but there was little effect of temperature.Leaf-weight ratios were uniform within experiments but therewere small consistent differences between one experiment andthe other two which also affected leaf-area ratios. Mean unit leaf rate was scarcely affected by day temperatureover the range investigated. There were the usual increasesdue to increased light and carbon dioxide concentration anda consistent difference in absolute value between one experimentand the other two. These differences in mean unit leaf rateare illustrated in detail in the ontogenetic trend of unit leafrate and plant size. Lower unit leaf rates were to a considerableextent compensated for by increased leaf-area ratios in theusual way. Despite the substantial differences in day temperature the specificwater contents (g water g dry weight^–1) differed little,showing in the majority of cases higher values in the highertemperature for otherwise similar treatment combinations. Flower development was somewhat delayed at 23.9 °C day temperature,and substantially so at 29.4 °C. Lateral branch length wasincreased at 23.9 °C and excessively so at 29.4 °C.This reveals quite clearly that a temperature optimum for vegetativegrowth may not be the optimum for flowering performance norproduce a desirable plant shape. Despite the marked effects of temperature on rate of flowerdevelopment, the relationship between flower development andthe ratio of flower to total weight was the same for all treatmentcombinations in all three experiments and coincident with thatreported earlier. Gasometric determinations indicated that respiratory loss bythe whole plant was a smaller proportion of net photosyntheticgain at a temperature of 29.4 °C than at 18.3 °C andwas likewise a smaller proportion at 1500 ppm carbon dioxidethan at 325 ppm. If photorespiration of leaves is assumed tobe as great as their dark respiration, the respiratory lossesare in the range of 31–50 per cent of the gross gain.Greater rates of photorespiration would increase the proportionaterespiratory loss.     

A Catastrophe Model for the Switch from Vegetative to Reproductive Growth in the Shoot Apex

A mathematical model is constructed to describe the morphopneticswitch that occurs when a vegetative plant apex becomes reproductive.The cusp equation from catastrophe theory is modified, and isused to relate primordial size at initiation to apex size. Theresulting equation may be viewed as an equation of state definingthe allowed organizational modes of the shoot apex. The modelsimulates the growth of the apex from the vetative stage toearly reproductive growth, and makes reasonable predictionsabout apex size and growth rate, primordial sizes, and the lengthsof the plastochron. flowering, mathematical model, catastrophe theory, shoot apex     

The Effects of Foliar Applications of (2-Chloroethyl)-trimethylammonium Chloride on Leaf Area and Dry Matter Production by the Brussels Sprout Plant

When CCC was applied as a spray to the leaves of Brassica oleraceaL. (Brussels sprout) grown in pots, plant height and mean internodelength were reduced. The effects appeared more slowly and wereless pronounced than those previously observed when CCC hadbeen applied to the soil; other differences were that root growthwas not inhibited, stem weight was only significantly reducedat the highest rate of application (2 per cent), and stomatalnumber per unit area of lower leaf epidermis was not affected.In common with soil applications, leaf thickness, stem diameter,and the percentage moisture contents of the leaves were allincreased by foliar applications.In a further experiment theprogress of wilting was observed in untreated plants and inplants treated with CCC applied either to the leaves or to thesoil. The rates of water loss and the moisture contents of theleaf laminae of the treated plants, after a period of wilting,were not significantly different from the controls. The treatedplants, however, looked less ‘wilted‘ for the changein angle of the leaf lamina to the stem was less and their leaveswere therefore held more upright.     

Leaf Area and Absolute Leaf Water Content

Leaf area was found to be an almost linear function of absoluteleaf water content (that is fresh weight—dry weight) forseveral dicotyledonous genotypes. A closely similar relationshipheld for a given genotype in the same rooting medium despiteincreasing plant size and different treatments which resultedin leaves which were sometimes morphologically dissimilar andoften substantially different in specific leaf water contents(water/dry matter). The usefulness of the linear relationshipfor estimating leaf area in growth studies is noted.     

Inflorescence Development in Chrysanthemum morifolium as a Function of Light on the Inflorescence

Covered, developing flower buds of Chrysanthemum morifoliumcv. Bright Golden Anne did not atrophy, although their dry weightwas lower than that of uncovered buds at 21, 28, 35 and 42 dafter the start of short days. This reduced dry weight was primarilydue to a reduction in the dry weight of the bracts, which arephotosynthetically active. The reduction in dry weight was notdue to a decrease in the number of bracts or florets or to alag in development of the covered buds. At 49 d the weight ofboth covered and uncovered buds was not significantly different,although the weight of the covered bracts was still reducedcompared with uncovered bracts. At 28 d uncovered buds fixedabout 40 times more ¹⁴CO₂ than covered buds. Both covered anduncovered buds had the same sink intensity and relative specificactivity, but the first bract had a greater sink intensity andrelative specific activity when covered than when uncovered,owing to photosynthesis by the bract itself. Chrysanthemum morifolium, flower development, assimilate partitioning, light, bract photosynthesis     

The Effects of Light Intensity at Different Stages in Flower Initiation and Development of Chrysanthemum morifolium

Rooted chrysanthemum cuttings were raised in growth cabinetsat a ‘standard’, constant light level of 125 J cm^–2day^–1 and were induced to flower by giving daily cyclesof 8 h light followed by 16 h of uninterrupted darkness. Sampleswere transferred at weekly intervals to either a higher lightlevel of 375 J cm^–2 day^–1 or a lower light levelof 31 J cm^–2 day^–1 where they remained for 2 weeksbefore they were returned. It was shown that receptacle formationnormally began in the second week of inductive short-days (short-days8–14) and floret initiation in the third week (short-days15–21) when plants were grown throughout in the standardenvironment Receptacle formation was delayed and significantlymore leaves were formed below the flower if short-days 8–14were spent in low light. Transfer to high light for this periodhad no apparent effect Transfer to low light at the onset offloret formation retarded their further development and reducedthe total number of florets formed Transfer to high light atthis stage slightly increased the number of florets formed butdid not appear to affect their development. The data for stageof flower development after 11 weeks of growth reflected theseeffects of light level on the early development of the apex The total and flower dry weights of plants transferred to lowlight for 2 weeks were generally smaller than those of plantswhich had remained throughout in the standard condition Highlight only produced lasting increases in weight when the transferswere made during the later stages of growth. Most of the additionaldry matter formed at this time was accounted for in increasedflower weight The correlation between flower development andflower weight ratio previously found under constant environmentsalso applied to transferred plants except when the light levelwas changed for the last 2 weeks of growth; relatively highvalues of flower weight ratio were then obtained by transferto high light and relatively low values by transfer to low light.     

Carbon Dioxide Effects on Auxin Responses of Coleoptile Sections

In the wheat cylinder bioassay technique as previously usedhere 5 sections have been enclosed in a 2 x 38 in, assay tubetogether with 0.5 ml. of the test solution. A method developedfor estimating the amount of carbon dioxide which accumulatesin these tubes through the respiration of the enclosed sectionshas shown that the level can rise to 20 per cent. after 24 hrs.at 25°C. In the presence of a 100 p.p.m. IAA(6x10^-4M.) testsolution, growth of 5 enclosed sections is depressed from 8hrs. onwardas and they eventually shrink, releasing their accumulatedIAA back into the solution. The growth of sections under various gas mixtures of carbondioxide in air has also been followed and these experimentsshow that section length is reduced approximately lineraly withrespect to increasing carbon dioxide concentration up to 20per cent. in air, both in the presence and absence of a 100p.p.m. IAA solution. The slope of the fitted regression line,however, is much steeper when the test solution contains IAA—i.e.there is a large interaction. In the presence of IAA, growth-time data show that a reductionin the growth rate, as compared with that in normal air, canbe detected after only 4 hrs, at the highest carbon dioxideconcentration. In the absence of IAA, high concentrations ofcarbon dioxide accelerate growth during the first 8 hrs. ofthe assay but depress it later. The mechanism of action of this interaction is unknown but itis not shown at very high concentrations of IAA, e.g. 1,000p.p.m. (6x10^-3M.).     

Effects of Carbon Dioxide Concentration on the Growth of Callistephus chinensis cultivar Johannistag

Carbon dioxide enrichment to 600 ppm increased the amount ofdry matter produced by Callistephus chinensis plants in growthcabinets with negligible mutual shading over a period of 18weeks. Further enrichment to 900 ppm showed smaller and morevariable increases. These effects were the result of a higherunit leaf rate of the treated plants. The direct effect on unitleaf rate was partly offset by a reduction in leaf-area ratio,and this was due almost entirely to the effect on specific leafarea with hardly any effect on leaf-weight ratio. Carbon dioxideaccelerated flower development by about a week at 600 ppm andsomewhat less at 900 ppm. The proportion of the total plantweight in the form of flowers showed a similar trend with timein all treatments and the relationship between flower-weightratio and dry-matter content of flowers was likewise similarfor all treatments, with the highest dry-matter contents ofabout 19 per cent associated with the highest flower-weightratios of about 0.44 for mature flowers. Carbon dioxide enrichmentsignificantly increased the dry-matter content of leaves. Theefficiency of energy conversion based on incident light anda twenty-four-hour cycle of 8 h light and 16 h dark for smallplants of 140–300 mg total dry weight (leaf areas of 50–120cm²) was about 4.7 per cent for the 325 ppm treatment, 6.3 percent for 600 ppm, and 5.5 per cent for 900 ppm. By referenceto some further experiments on the growth of C. chinensis cultivarJohannistag in glasshouse conditions, considerable adaptiveresponse to high and low light intensity was also demonstrated.