The Effect of Restricted Germination during Vernalization on First Leaf Length of Winter Rye

Winter rye grain was vernalized, using the restricted moisturetechnique, at various temperatures and moisture levels and therelation between first-leaf blade length and the degree of vernalizationanalysed. There was an inverse relation between these two factors,but leaf length was influenced by both temperature and moisturelevel in a manner quite different from the effect on the vernalizationtemperatures and the major requirement for short-leaf productionproved to be the period of restricted germination normally imposedduring vernalization. Cell counts of the epidermis of the firstleaf blade showed that the reduction in length was due to inhibitionof the earliest phase of leaf extension growth. It is suggested that some growth-promoting substance in theembryo, possibly IAA, is broken down during the restricted germinationperiod. When grain is sown this shortage impedes early leafextension until the level is restored by synthesis or translocation.     

Temperature Response of Vernalization in Wheat: Modelling the Effect on the Final Number of Mainstem Leaves

This paper outlines a modelling approach which predicts theeffect of both continuous and intermittent low temperature regimeson the final number of leaves in winter wheat. The model takesaccount of the balance between the concurrent processes of leafprimordium initiation and rate of saturation of vernalization,and their response to temperature. The inverse of the time tosaturation of vernalization, at which stage final leaf numberis set, is modelled as a linear function of vernalizing temperature,between 0 and 17 °C. The rate of leaf primordium initiationis modelled using the established linear relationship betweenrate and temperature above 0 °C. Final leaf number is hencethe product of the number of leaf primordia initiated once vernalizationis saturated. In the model, genotypes are characterized by (1)the slope and intercept of the linear response of the rate ofsaturation of vernalization to temperature in the vernalizingrange, and (2) by a development rate towards floral transitionat on-vernalizing temperatures (above 17 °C). The modelis tested against data from experiments where six cultivarsof winter wheat plants of different ages were exposed to a rangeof low temperature regimes, including continuous and intermittentvernalizing temperatures. Overall, the model predicted, withr ²values of 70–90%, the final leaf number across a rangeof six to 21 leaves. Prediction of final leaf number for somecultivars was better in continuous than in intermittent vernalizingregimes. This modelling approach can explain the often-conflictingreports of the effectiveness of different temperatures for vernalization,and the interaction of plant age and vernalization effectiveness. Triticum aestivum L.; wheat; vernalization; rate; temperature; leaf number; modelling; phenology; flowering     

Effect on the Progeny of Applying Different Day Length and Hormone Treatments to Parent Plants of Lactuca scariola

Seedlings of the self-fertilizing species Lactuca scariola L. grown continuously in 8 h days did not flower even one year from sowing. Seedlings grown in 16 h days uatil flower buds appeared 96 days after germination were either transferred to 8 h days or treated weekly with gibberellic acid (GA₃), abscisic acid (ABA) or chlormequat (CCC) and retained, together with untreated control plants, in 16 h days. Each growth regulator caused characteristic morphological changes in the treated plants. All these plants flowered and produced seeds but the seeds showed distinct differences in weight, in their time to germination and in the seedlings which they produced. Germination and seedling characters depended on the light regime during germination as well as on the chemical applied to the parent plant and the rate of application. The parental treatment also affected the shape and size of the seedlings on a given day after germination, and certain treatments of the parent plant (transfer from long to short days and treatment with CCC in long days) advanced the flowering date of the seedlings. The gibberellin level in the seeds was raised, in increasing order, by treatment of the parent plant with 100 mg/1 GA₃, transfer from long to short days, 10 mg/1 GA₃, and 5000 mg/l CCC. It is suggested that the effect of day length on plant performance is mediated by the level of growth regelating substances within the plant and that the behaviour of seeds can be modified by the parental environment via the accumulation of different levels of certain growth factors in the seeds. A rise of one growth substance in the parent plant can result in the accumulation of a different one in the seeds.     

The Influence of Genes for Vernalization Response on Development and Growth in Wheat

Studies were made of the influence of genes for vernalizationresponse on the growth and development of four near-isogeniclines of bread wheat (Triticum aestivum L.). The duration from sowing of flower initiation, terminal spikeletformation and ear emergence all increased with increasing vernalizationresponse. There was a close positive relationship between thedays from sowing to flower initiation and from sowing to earemergence, indicating that the duration of either phase of developmentis a useful measure of relative vernalization when daylengthdoes not limit the rate of development. Total spikelet number per ear and the duration of spikelet initationincreased with increasing vernalization response and there wasa correspondingly higher rate of spikelet initiation in thetwo lines with stronger vernalization response. Most of the differences in growth between the lines were associatedwith diferences in development caused by the vrn genes. Maximumtotal above-ground dry matter and total leaf area per plantincreased with increasing vernalization repsonse but relativegrowth rate and leaf area per plant were not significantly differentbetween the lines. There were no differences in net assimilationrate between the four lines until 40 d from sowing; thereafterit decreased, with the greatest decrease in the line with thestrongest vernalization response. Flower initiation, terminal spikelet formation, spikelet initiation, ear emergence, growth rate     

Effect of Day Length and Night Temperature on Starch Accumulation and Degradation in Soybean

The effect of the day length on the accumulation and the degradationof the starch in leaf, stem and root tissues of prefloweringsoybean plants was determined by growing plants under a 7 or14 h light regime. As has been reported previously, the rateof starch accumulation by leaves was inversely related to daylength. High sucrose content was associated with a high rateof starch accumulation. Stem tissue showed diurnal fluctuationsin starch content and the rate of accumulation was also inverselyrelated to day length. This starch resulted from photosynthesiswithin the stem itself. A negligible amount of starch was foundin root tissue of both sets of plants. The rate of starch breakdown in leaves of 7 h plants was significantlyless than that in 14 h plants. Nevertheless, leaf starch inshort day length plants was depleted at least 4 h prior to theend of the dark period. In both sets of plants, degradationof stem starch started simultaneously with that in the leavesand continued throughout the dark period, although at a muchlower rate than that of leaves. Thus, stem starch acted as abuffer once leaf starch was depleted, providing carbohydratesto the plant, although in small quantities. To determine if soybean leaves adjust their rate of starch accumulationduring the light period to different dark period temperatures,plants were grown under temperature regimes of 30/20 ^°Cand 30/30 ^°C. Plants did not differ in rate of starch accumulationor CO₂ exchange rate, but did show large differences in growthcharacteristics. High temperature plants had significantly greaterleaf area and tended to have greater leaf area ratio. Thus,despite similar rates of starch accumulation on a leaf areabasis, high temperature plants accumulated greater amounts ofstarch on a per plant basis. Glycine max(L.)Merr., soybean reserve carbohydrates, remobilization, source-sink realtionships     

The Nature and Duration of Gene Action for Vernalization Response in Wheat

Four near-isogenic lines of wheat were studied to determinethe nature and duration of gene action for vernalization responseunder 2 weekly vernalization periods from 0 to 10 weeks. With time to floral initiation the Vrn 1 Vrn 2 and Vrn 1 vrn2 genotypes showed a cumulative response whereby days to floralinitiation decreased as the period of vernalization increased.The vrn 1 Vrn 2 and the vrn 1 vrn 2 genotypes also showed acumulative response for periods of vernalization less than 6weeks for the former and 8 weeks for the latter. Days to earemergence was closely related to days to floral initiation dueto the constancy of the period from floral initiation to earemergence across all lines and treatments and, consequently,they gave similar measures of the relative strength of vernalizationresponse. It appears that genes for vernalization response ceaseto act after floral initiation. The implications of these findings to breeding for increasedadaptability and yield in wheat are discussed. Triticum aestivum, wheat isogenic lines, vernalization, floral initiation, ear emergence, gene action     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

The Effect of Gibberellic Acid on Fibre-cell Length

Measurements were made of fibre-cells from plants of Corchorusolitorius L., Hibiscus cannabinus L., and Cannabis sativa L.Which had been sprayed with gibberellic-acid solution. Fibre-cellsfrom treated plants showed a highly significant increase inlength, 20–130 per cent, for the whole stem and as muchas 400 per cent. for a single intermode. Gibberellic acid increased the variation in cell-length andthe positive skewness of the distribution of the variate. Differences in cell-length can be related to the developmentalsequence of the shoot and the variation in internode-length.     

The Effect of Light Intensity, Day Length, and Temperature on Fatty Acid Synthesis and Desaturation in Vicia faba L.

Some effects of light intensity, day length, and temperatureon the fatty acid composition of the major glycerolipids ofleaves of Vicia faba L. (cv. Giant Windsor) were observed. Increasinglight intensity caused an increase in the relative concentrationsof 16 : 1 in PG and 18 : 3 in MGDG and DGDG. Increasing daylength during growth (and continuous illumination of leaf tissue)had no effect on 16 : 1 in PG but caused a decrease in the 18: 3 content of PG, PC, MGDG, and DGDG. Since the quantitiesof these lipids increased under these conditions, the decreasewas not due to photodestruction but to the differences in therelative rates of biosynthesis and desaturation of fatty acids.Incubation of leaf tissue in the dark for 4 d had little effecton the fatty acid composition of MGDG, DGDG, and PG. Temperaturealso controls fatty acid synthesis and desaturation. Above theoptimum growth temperature (20 °C), the 18 : 3 content ofMGDG, DGDG, PG, and PC decreased. In mature leaf tissue, thedegree of unsaturation of MGDG may be modified upward in responseto temperature changes. When plants were grown at 30 °Cand transferred to 20 °C the level of 18 : 3 in MGDG ofthe leaf tissue increased to levels found in plants grown onlyat 20 °C. The level of 18 : 3 in MGDG does not decreaseas rapidly when plants grown at 20 °C were transferred to30 °C. This suggests that the lower temperature induceddesaturation of 18 : 2 to 18 : 3.     

The Response to Gibberellin in Pisum sativum Grown under Alternating Day and Night Temperature

The application of gibberellins (GA) reduces the difference in stem elongation observed under a low day (DT) and high night temperature (NT) combination (negative DIF) compared with the opposite regime, a high DT/low NT (positive DIF). The aim of this work was to investigate possible thermoperiodic effects on GA metabolism and tissue sensitivity to GA by comparing the response to exogenously applied GA (in particular, GA₁ and GA₃) in pea plants (Pisum sativum cv. Torsdag) grown under contrasting DIF. Control plants not treated with growth inhibitors or additional GA were 38% shorter under negative (DT/NT 13/21°C) than positive DIF (DT/NT 21/13°C) because of shorter internodes. Additional GA₁ or GA₃ decreased the difference between positive and negative DIF. In pea plants dwarfed with paclobutrazol, which inhibits GA biosynthesis at an early step, the response to GA₁ was reduced more strongly by negative compared with positive DIF than the response to GA₃. The induced stem elongation by GA₁₉ and GA₂₀ did not deviate significantly from the response to GA₁. Plants treated with prohexadione-calcium, an inhibitor of both the production and the inactivation of GA₁, grew equally tall under the two temperature regimes in response to both GA₁ and GA₃. We hypothesize that the reduced response to GA₁ compared with GA₃ in paclobutrazol-treated plants grown under negative DIF is caused by a higher rate of 2β-hydroxylation of GA₁ into GA₈ under negative than positive DIF. This contributes to lower levels of GA₁ and consequently shorter stems and internodes in pea plants grown under negative than positive DIF. Differences in tissue sensitivity to GA alone cannot account for this specific thermoperiodic effect on stem elongation. Received May 28, 1998; accepted May 29, 1998     

The Effects of Vernalization on the Growth of the Wheat Shoot Apex

he effect of vernalization on the growth of the wheat shootapex was examined by comparing three genetic lines of ChineseSpring (CS) wheat having strong [CS (Hope 5D)], medium (CS Euploid),or no [CS (Hope 5A)] vernalization requirement. The mean volumeof the apical dome increased gradually in all lines, and thenthe apical dome enlarged rapidly as its relative growth rate(RGR) increased prior to double ridge formation. Phytomer volumeat initiation remained constant, so that the ratio of phytomerto apical dome at primordium initiation decreased in successiveplastochrons. In CS Euploid and in unvernalized CS (Hope 5D),the RGR of the apical dome tended to decrease at least untilinitiation of the collar primordium. The rate of primordiuminitiation at double ridge formation increased in proportionto the RGR of the apex at that time; i.e. it increased greatlyin CS (Hope 5A) and vernalized CS (Hope 5D), less so in CS Euploid,but no increase was observed in unvernalized CS (Hope 5D). Thetime of formation of double ridges seemed to be independentof the growth rate or size of the apical dome. The number oftillers present at ear emergence was inversely proportionalto vernalization requirement and was reduced by vernalization.Vernalization resulted in a decrease in the RGR of the newly-initiatedleaf primordia in relation to the RGR of the apical dome andthe axial part of the phytomer. Transfer of plants from longto short days at various times during growth showed that vernalizationincreased the number of labile primordia which could developinto either leaf, collar or spikelet. Vernalization thereforeseems to alter the ability of the apex to respond to subsequentphotoperiod rather than to affect its growth directly. Triticum aeslivum, wheat, chromosome substitution lines, shoot apex growth, vernalization     

Glycemic Response to Exercise in the Subarctic Depends on Time of Day,Season and Sex

Between December 1992 and September 1996, a total of 62 healthy athletes (32 males and 30 females) exercised for 30 minutes, with an intensity of 60% VO 2, in one or more morning and afternoon sessions in the months December, February, April, June and September. Blood samples obtained for determinations of glucose were drawn at 0, 1, 5, 10 and 30 minutes of each exercise span. The total area under the glucose-time curves was calculated both in original units (mmol/l) and after normalization to percent of starting value for 263 exercise spans. These calculated areas, representing the glucose “response” during exercise, were tested for the effect of sex, time of day and season by ANOVA and by the least-squares fit of a 1-year cosine. During exercise a significant effect was found by ANOVA for sex (p < 0.001), time of exercise (p =0.006) and month (p =0.007). No significant interactions were found. Exercise in the morning beginning at 11:30h produced a smaller glucose response for both sexes, when compared with exercise in the afternoon beginning at 16:30h. With regard to sex, a smaller integrated glucose response to exercise occurred in females. The response was lowest for both sexes in Dec (winter) compared to other months, while the response was greatest for females in September, and for males in April and June. A circannual rhythm was found both for baseline glucose (p =0.005, acrophase= Feb 20) and glucose–time response areas in mmol/l (p <0.001, acrophase=Feb 4), and normalized values (p =0.05, acrophase=Dec 19). This finding is in accordance with previous reports that, at least in the subarctic area, the glycemic response to a standardized exercise is influenced by season and timing of exercise. This observation may be of importance for athletes involved in vigorous training and patients with Diabetes Mellitus, among others.     

The Effect of Mechanically Induced Stress on the Growth of Cauliflower, Lettuce and Celery Seedlings

Brushing cauliflower, lettuce and celery seedlings with paperfor 1.5 min each day for 11–13 d, 10–12 d or 21–28d, respectively resulted in smaller, more compact, plants thanthe unbrushed controls. In all three species shoot fresh anddry weights and leaf area were reduced following brushing. Incauliflower and celery the largest growth reduction was in petiolelength. In lettuce, which has no discernible petioles, the reductionin leaf length caused by brushing was proportionally greaterthan the reduction in leaf width. Brushing reduced hypocotyllength in cauliflowers and to a lesser extent in lettuce. Petioleand hypocotyl thickness was reduced in cauliflower, whereashypocotyl thickness was increased in lettuce following brushing.Brushing increased leaf thickness in cauliflower, celery andto a lesser extent in lettuce and increased the percentage drymatter content of lettuce shoots. The weight of chlorophyllper fresh weight of leaf tissue increased following brushingin celery and lettuce and declined in cauliflowers. Root length and the number of branches per root system werereduced in all three species following brushing. Root dry weightwas reduced and the root:shoot dry weight ratio was increasedin lettuce, reduced in celery and unaffected in cauliflowers. There were different patterns of response to brushing, the reductionin leaf weight being greatest in the youngest leaf of cauliflowerand least in the youngest leaf of lettuce and celery. Growthresponses to brushing were seen several days after brushinghad ceased, noticeably in leaves which were barely visible atthe time of brushing. It is suggested that growth retardation of cauliflowers, lettuceand celery, induced by mechanical stress such as brushing mayprove valuable as a means of ‘conditioning’ theseedlings to withstand both the physical and physiological stresseswhich occur at and during transplanting. Brassica oleracea, cauliflower, Lactuca sativa L., lettuce, Apium graveolens L., celery, mechanical stress, shoot growth, root growth, chlorophyll     

Effect of Light Quality and Vernalization on Late-Flowering Mutants of Arabidopsis thaliana

We have analyzed the response to vernalization and light quality of six classes of late-flowering mutants (fb, fca, fe, fg, ft, and fy) previously isolated following mutagenesis of the early Landsberg race of Arabidopsis thaliana (L.) Heynh. When grown in continuous fluorescent illumination, four mutants (fca, fe, ft, and fy) and the Landsberg wild type exhibited a reduction in both flowering time and leaf number following 6 weeks of vernalization. A significant decrease in flowering time was also observed for all the mutants and the wild type when constant fluorescent illumination was supplemented with irradiation enriched in the red and far red regions of the spectrum. In the most extreme case, the late-flowering phenotype of the fca mutant was completely suppressed by vernalization, suggesting that this mutation has a direct effect on flowering. The fe and fy mutants also showed a more pronounced response than wild type to both vernalization and incandescent supplementation. The ft mutant showed a similar response to that of the wild type. The fb and fg mutants were substantially less sensitive to these treatments. These results are interpreted in the context of a multifactorial pathway for induction of flowering, in which the various mutations affect different steps of the pathway.