Rate Of Leaf Initiation Research Articles

Shoot and Root Development in Rice Related to the Phyllochron

In grasses, construction of a growing plant is determined primarily by the rate of leaf development in the shoot apex and the timing of tillering and rooting of individual phytomers relative to leaf development. Our purpose is to review shoot and root growth in relation to emergence of leaves in rice (Oryza sativa L.). Development of the leaf, tiller bud, and adventitious roots of each phytomer proceeds in order, at a rate that depends on leaf initiation rate at the shoot apex. Consequently, initiation, leaf emergence, tillering, and rooting of each tiller are closely synchronized with leaf emergence on the main stem. Leaves that emerge simultaneously are similar in size. Tillers whose leaf emergence is retarded from this synchronization will generally die before anthesis. Inflorescence development is closely correlated with development of the subtending leaves in each tiller, resulting in a highly predictable phenology in relation to leaf emergence. Because of these relationships, the leaf number concept provides researchers with an effective index for studying development of shoot and root systems in rice, including the prediction of tiller morphology, the estimation of potential tiller increase, and analysis of root system dynamics.

Effect of plant size and salinity on the growth and fruiting of glasshouse strawberry

SummaryChanges in growth and fruiting responses of strawberry cv. Rapella according to plant size (12, 26, 35 and 60 leaves per plant) and salinity (2.6, 5.8 and 8.9 mS cm–1) were evaluated under glasshouse conditions. Rates of leaf, crown and infloresccnce initiation were faster in the smaller plants but plant size had no effect on the reduction in vegetative growth and inflorescence initiation caused by salinity. Reductions in fruit number were observed only when plants with 60 leaves were exposed to the highest level of salinity (8.9 mS cm–1). Fruit fresh and dry weights from the 2.6 and 5.5 mS cm–1 treatments differed only when plants with more than 35 leaves were used. Total fruit fresh and dry weights were reduced by salinity treatment at 8.9 mS cm–1 in all but the smallest plants. The proportions of Grade ‘Extra’ and Grade I fruits were reduced as salinity and plant size increased.

Development of Leaves in Oil Palm (Elaeis Guineensis) and Determination of Leaf Opening Rate

SUMMARYOil palm rachis length was determined on primordia dissected from palms planted at four densities. It started to increase rapidly in leaf–10, that is, about ten leaves younger than the spear leaf in all density treatments. The mean number of leaf primordia at the three higher palm densities was 47.7 compared with 51.5 at the lowest density of 56 palms ha-1. Some of the palms planted at the highest density were thinned to identify the stage at which the amount of light affected the rate of leaf opening. A sudden increment of light accelerated leaf production at both the rapid expansion stage and the preceding slow expansion stage. The greatest acceleration of leaf production began 24 months after thinning, probably because of the effect of the extra light on the rate of leaf initiation. The response of leaf production to thinning may apply to other related cultural practices.Desarrollo de hojas en la palma aceitera(Elaeis guineensis)y determination de la tasa de apertura de las hojas

951 PB 446 RESPONSE OF TOMATOES GROWN IN AN AEROPONIC GROWTH CHAMBER

An aeroponic growth chamber is a system for growing plants in air with water and nutrients supplied by intermittent mist. This type of plant growth system is especially useful for experiments where root accessibility is desired. Tomatoes (Lycopersicon esculentum L. `Bonnie Best') were used to test the performance of an aeroponic growth chamber. A nutrient solution mist was applied through spray nozzles suspended below roots of supported seedlings. Mist application was regulated by electric timers, so that mist was applied for 50 sec. every 5 min. during the 16-hr light period, which was supplemented with a high-pressure sodium lamp. Root and stem lengths, leaf number and leaf lengths were measured weekly. Plastochron index (PI) was used to measure rate of leaf initiation. PI increased linearly, indicating uniform initiation of leaf primordia and absence of environmental stresses. Stem and root lengths increased consistently throughout the growing period. Each plant was harvested, separated into leaves, shoots and roots, oven dried, and dry weights measured.

Modelling cauliflower development from transplanting to curd initiation

SUMMARYA model of the development of cauliflower during the juvenile phase and the curd induction phase is set up and described. The model is based on plant growth and climate data from our own experiments and data from two previously published Dutch experiments. The duration of the juvenile phase is described by a temperature sum starting at transplanting and using a base temperature of 0°C. The temperature sum requirements (thermal time in Kelvin days) of six cultivars in our experiments ranged from 26 to 83 K d compared with about 250 K d of two other cultivars in the Dutch experiments. Possible reasons for the difference are discussed. Leaf initiation was found to be well described by temperatures above 0°C. The end of the juvenile phase can thus also be expressed as a certain number of leaves initiated. This is of practical value because leaves can easily be counted. A good description of leaf initiation data (R2 values of 0.9) was achieved when a gradual increase in the leaf initiation rate with increasing leaf number and increasing temperature was used. The end of the juvenile phase was estimated to occur on average when the plant had 12 leaves initiated in our own experiments compared with 17 to 19 leaves initiated in the Dutch experiments. The duration of the curd induction phase in the model is described by using linear responses to temperature that are symmetrical below and above an optimum temperature. A common optimum temperature for curd induction was estimated to be 12.8°C for two cultivars in the Dutch experiment, the base temperature was estimated to be 0°C, and the maximum temperature, therefore, is taken to be 25.6°C. The best fits of data in the combined model of juvenile and curd induction phase Show R2 values from 0.4 to 0.6. The model needs refinement and validation especially in modelling the duration of the curd induction phase for different cultivars. Still, the descriptive development model of cauliflower divided into distinct juvenile and curd induction phases gave a better fit than a model with no phase separation.

Some Aspects of Photoperiodism in Wheat and Its Wild Relatives

Experiments with plants grown in controlled environment conditions examine three aspects of photoperiodism in wheat. A survey of the flowering responses of 20 genotypes of diploid, tetraploid and hexaploid wheat cultivars and wild relatives to growth under three daylengths (8, 12, 16 h) after three durations of vernalisation (0, 4, 10 weeks at 20�C) showed that all were long-day plants and many responded to vernalisation. The requirement for long days was most stringent among the diploid progenitors and most relaxed among the hexaploid cultivars. However, not even the earliest flowering spring wheat cultivars (among eight) were entirely daylength-neutral. Minimum times to inflorescence initiation appeared to be determined independently of the responses to daylength. Whereas leaf initiation and appearance rates were hardly influenced by daylength, the rate of spikelet initiation responded to it from the beginning of floral induction, well before the appearance of double ridges. Comparison of the times to double ridges among near-isogenic lines of four spring wheat cultivars (Ciano 67, Yaqui 50, Rescue and April Bearded) showed that each of the three dwarfing genes Rht1, Rht2 and Rht3 advanced inflorescence initiation but without changing the response to daylength.

Amp1 ‐ a mutant with high cytokinin levels and altered embryonic pattern, faster vegetative growth, constitutive photomorphogenesis and precocious flowering

amp1, a mutant of Arabidopsis thaliana has a phenotype altered in three different aspects of plant development; spatial pattern, photomorphogenetic growth, and initiation of flowering. While fewer than 0.1% of the seedlings of wild‐type plants are non‐dicot as many as 20% of the seedlings of the amp1 mutant are tricot or tetracot. The rate of leaf initiation is faster and vegetative phyllotaxy is altered in amp1. When grown in the dark amp1 seedlings show morphogenetic properties similar to light‐grown wild‐type plants: they do not form an apical hook, have hypocotyls shorter than wild‐type plants and form etiolated true leaves. amp1 mutant flowers significantly earlier than congenic Amp1 plants. The mutant has six times more cytokinin than wild‐type suggesting that endogenous cytokinin levels might play an important role in mediating these different developmental processes. AMP1 might code for a negative regulator of cytokinin biosynthesis, or may be required for the degradation of cytokinin.

Growth and leaf life-span of a floating-leaved plant, Trapa natans L., as influenced by nitrogen flux

Trapa natans L., cultured in tanks under varying nitrogen flux, was examined with particular reference to the change in foliage structure. Leaf initiation rate, leaf loss rate and leaf life-span were independent of nitrogen flux and ranged from 140 to 250 mg N m −2 day −1. In contrast, leaf and rosette size were positively correlated with nitrogen flux. The maximum biomass was estimated to be 487 g dry weight m −2 in the most nitrogen-enriched tank. With increasing nitrogen flux, proportions of petiole and reproductive parts (fruit) in the total biomass increased, while those of stem and root decreased. Net production of T. natans was also positively correlated with nitrogen flux and ranged from 5 to 14 g dry weight m −2 day −1 for all experimental tanks, excluding a tank with algal competition.

Leaf and Spikelet Primordia Initiation in Salt‐Stressed Wheat

Salt stress is known to affect adversely shoot apex development in cereals. This study was conducted to determine rate and duration of leaf and spikelet primordia initiation as related to final leaf and spikelet numbers in salt‐stressed wheat (Triticum oestivum L.). Early shoot development of two hard red spring wheat cultivars, Yecora Rojo and Anza, was studied in both greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatments were compared with a nonsaline control treatment. The sand cultures were irrigated with complete nutrient solutions to which NaCI and CaCI2 (2:1 molar ratio) were added to achieve electrical conductivities (K1W) of 1.7, 12.2, and 15.1 dS m−1. Lysimeters were irrigated with tap water salinized to KlW levels of 0.8, 11.4, and 17.1 dS m−1. Timing of primordium initiation was expressed in accumulated thermal time measured in the soil (°C dsoil). A three‐piece linear‐spline model was developed to facilitate the statistical analysis and interpretation of primordium initiation. Parameters of the model corresponded to morphologically significant events. In both experimental locations, each genotype exhibited a similar response to increasing salinity. The rate of leaf primordium initiation decreased while the duration of this phase was unchanged. Salinity had no effect on the rate of spikelet primordium initiation of the genotypes, but the duration of this phase was shortened. As a result, the number of leaves on the main stem and the number of spikelets per spike were significantly reduced by salinity and the yield potential of both genotypes was severely limited.

Bud development in coastal Douglas-fir seedlings in response to different dormancy-induction treatments

Bud development in response to different dormancy-induction treatments in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) seedlings was investigated under commercial greenhouse conditions. There were three treatments: short day without moisture stress, short day with moisture stress, and long day with moisture stress. Within the first week in the short day treatments, neoformed-leaf initiation ended and bud-scale initiation began and ended. Rapid leaf initiation began in week 1 and was completed by week 5 for the short day with moisture stress treatment and week 6 for the short day without moisture stress treatment. Slow leaf initiation was completed by week 13. Crown cells became apparent within the pith during weeks 3–6; cell walls thickened between weeks 8 and 13. Within the first week of the long day with moisture stress treatment, neoformed-leaf initiation ended and bud-scale initiation began. Bud-scale initiation ended by week 3 or 4. Then slow leaf initiation began and continued until week 6. Rate of leaf initiation was rapid during weeks 8–10 and decreased slightly during weeks 10–13. By week 13, apical height had decreased markedly, indicating an imminent end to leaf initiation. Crown cells became apparent within the pith during weeks 5–13; cell walls thickened between weeks 10 and 13. Key words: bud development, dormancy induction, short days, moisture stress, Douglas-fir, seedlings.

Predicting leaf area development of sunflower

The effects of genotype and environment on canopy development of sunflower ( Helianthus annuus L.) have been the subject of much research. A framework was developed to analyse data from this research and predict leaf area of irrigated sunflower as affected by daily temperature, and the phenology of different cultivars and hybrids. Between emergence and anthesis, total leaf area per plant (TPLA) was determined as a logistic function of TPLA at anthesis and thermal time from emergence (TT). Total leaf area per plant at anthesis was linearly related to total leaf number for a range of cultivars and hybrids. Total leaf number was estimated as the product of the duration of the period emergence to head visible (in days) and the average leaf initiation rate in that period. Leaf initiation rate was related to the average temperature during this period. Senescent leaf area per plant (SPLA) was calculated as an exponential function of TT from head visible. Leaf area index (LAI) was determined as the difference at any time between TPLA and SPLA, multiplied by plant density and a density modifier, which allowed for the effect of density on leaf area per plant. Almost all variation in the TPLA and SPLA data was accounted for using inputs of TT and dates of phenological stages. When the model was tested on independent data it accounted for 93% of the observed variation in LAI.

Responses of two hybrid Populus clones to flooding, drought, and nitrogen availability. I. Morphology and growth

Repeated progressive drought and flooding stress were imposed on hybrid poplar clones Populus × euramericana 'Eugenei', and Populus tristis × Populus balsamifera ‘Tristis’ grown in pots in a greenhouse under two nitrogen levels. In both clones the rate of leaf initiation was promoted only in high-N plants subjected to minimum water stress. Water stress alone did not retard the rate of leaf initiation, but it significantly reduced leaf expansion of 'Eugenei', whereas only flooding led to smaller leaves in 'Tristis'. The addition of N stimulated leaf expansion, leaf chlorophyll and N concentrations, and leaf and stem biomass production across soil moisture levels, but the greatest effect of N was associated with minimum water stress. High N altered carbon allocation towards the aboveground portions, leading to lower root to shoot ratios. High N also appeared to stimulate initiation of fine roots. Soil moisture determined the amount of biomass that accumulated in roots, with highest root production in well-watered pots and lowest in flooded pots, with the droughted treatment in between. Leaves became thinner as soil moisture decreased from flooding. Stem biomass of 'Tristis' declined more under flooding than under drought, whereas 'Eugenei' displayed a greater reduction of stem biomass in droughty than in flooded soil. Key words: water stress, nitrogen, leaf and root morphology, root to shoot ratio, biomass, Populus, flooding.

CO_2 and Temperature Effects on Leaf Area Production in Two Annual Plant Species

We studied leaf area production in two annual plant species, Abutilon theophrasti and Amaranthus retroflexus, under three day/night temperature regimes (18°/14°, 28°/22°, and 38°/31°C) and two concentrations of carbon dioxide (400 and 700 @mL/L). The production of whole—plant leaf area during the first 30 d of growth was analyzed in terms of the leaf initiation rate, leaf expansion, individual leaf area, and, in Amaranthus, production of branch leaves. Temperature and CO2 influenced leaf area production through effects on the rate of development, determined by the production of nodes on the main stem (the plastochron index), and through shifts in the relationship between whole—plant leaf area and the number of main stem nodes. In Abutilon, leaf initiation rate was highest at 38°, but area of individual leaves was greatest 28°. Total leaf area was greatly reduced at 18° due to slow leaf initiation rates. Elevated CO2 concentration increased leaf initiation rate at 28°, resulting in an increase in whole—plant leaf area. In Amaranthus, leaf initiation rate increased with temperature, and was increased by elevated CO2 at 28°. Individual leaf area was greatest at 28°, and was increased by elevated CO2 at 28° but decreased at 38°. Branch leaf area displayed a similar response to CO2, but was greater at 38°. Overall, wholeplant leaf area was slightly increased at 38° relative to 28°, and elevated CO2 levels resulted in increased leaf area at 28° but decreased leaf area at 38°. The effects on leaf area closely parallel rates of biomass accumulation in the same experiment, suggesting that responses of developmental processes to elevated CO2 and interacting factors may play an important role in mediating effects on plant growth.

The influence of plant density on flower, fruit, and leaf demography in bush bean, Phaseolus vulgaris

The influence of plant population density on bush beans is analyzed in terms of its effect on flower, fruit, and leaf demography, biomass, and yield. Plants grown at the lowest density (solitary plants) did best in terms of leaf production, total leaf days, flowers, and production of marketable pods (i.e., having at least one seed). These plants also accumulated more biomass and had greater numbers of all components of yield. In addition, they showed greater proportionate allocation to reproduction. In all density treatments the second flower cohort (produced 33–35 days after seeds were sown) made the greatest contribution to yield (43–78%). When flower production began, the rate of leaf initiation declined; leaf mortality seemed coupled to the onset of fruit production and was most severe in plants that had many pods to mature. The probability that flowers produced under any density regime would become pods and that these pods in turn would become marketable pods was assessed. Pod production was broken down into two stages: the transition from flower to fruit and from fruit to marketable pod. The results suggest that the transition from flower to fruit is not resource-limited, but the transition from fruit to marketable pod is dependent on current resource supply. When the data are examined on a per pot basis, plants at the highest density were most productive in terms of nonproductive tissues. However, an intermediate density (equivalent to 200 plants/m2) produced the greatest total reproductive biomass and the greatest number of marketable pods per unit area. The value of leaf and flower demography as measures of uniformity of maturation, optimal planting density, and cultivar performance is discussed. Key words: density, flower demography, fruit demography, leaf demography, Phaseolus vulgaris, yield.

Factors affecting the number of leaves preceding the first inflorescence in the tomato

The effects of several environmental factors and plant growth regulators on the number of leaves preceding the first inflorescence (NLPI) of the tomato are reviewed. Differences in rate of leaf initiation and differences in the time to initiation of the first inflorescence both contribute to differences in the number of leaves preceding this inflorescence. Differences in the time to initiation of the first inflorescence can be explained by the hypothesis that the amount of assimilates available for the apex during the sensitive phase (approximately the first ten days from cotyledon expansion) has to reach a certain minimum before flower initiation can take place (the ‘nutrient diversion hypothesis’ of Sachs and Hackett, 1969). Therefore, factors that increase the total amount of assimilates in the plant (e.g. higher light intensity, lower temperature) as well as those that increase the competitive potential of the apex (e.g. lower temperature, certain plant growth regulators) decrease the number of leaves...

Shoot Meristem Activity during Floral Transition in Glycine max (L.) Merr.

The soybean (Glycine max [L.] Merr.) is a quantitative short-day (SD) plant requiring two inductive cycles for floral initiation, which occurs first in the most undifferentiated meristem in an axil of a main stem leaf. Floral initiation at the main stem apex, however, requires additional SD inductive cycles. Under continuous SD the transition to flowering in the main stem apex is completed after 8 SD cycles. Differentiation and organogenesis of the first flower in the terminal raceme is apparent after 10 SD cycles. The changes in apical size and geometry, nuclear DNA, and rate of leaf initiation were followed daily during this 10-d period and compared with apices from plants kept under noninductive long days (LD). At emergence all plants had initiated three trifoliolate leaf primordia and during the vegetative stage of development maintained a plastochron of 2.0 d/leaf. The plastochron was shortened to 1.0 d/leaf in SD plants on day 7, just prior to the end of the transition. Apical size and geometry remained unchanged until after 6 SD cycles when height of the dome decreased and there was less elongation of the rib meristem. Earlier events included significantly lower amounts of nuclear DNA in cells of SD apices after 1 and 3 SD cycles. Later, the amount of nuclear DNA increased in cells of SD apices beginning after 5 SD and peaking after 6 SD before decreasing back to control levels. Shifts in increasing proportions of the population of nuclei from the 4C to 2C condition occurred after 1 SD and 3 SD. As in other species, both of these shifts are apparently essential components for the floral transition at the shoot apex in soybean. The first shift, or "mitotic" stimulus, signals that the process of the floral transition has begun, while the second shift, or "floral" stimulus, is required for completion of the process.

Manipulation of bolting and flowering in celery (Apium graveolensL. var.dulce). II. Juvenility

SummaryAfter germination, a juvenile phase of development was apparent in cvs New Dwarf White and Celebrity. During this incompetent phase, plants were not induced flower even when subjected to chilling at 5°C for nine weeks. Juvenility ended and the plants became competent to perceive chilling as a vernalization stimulus when they had initiated 17 leaves including leaf primordia in cv. New Dwarf White and between 17 and 20 leaves in cv. Celebrity. After phase transition, the level of competence was not affected by plant age. The rate of leaf initiation in cv. New Dwarf White during juvenile and competent vegetative growth related linearly to temperature, increasing between 3 and 22.8°C and then declining over the range 22.8 to 37.4°C. The first 17 leaves of celery cv. New Dwarf White had longer plastochrons of 43° Cd (>3°C) each than subsequently initiated leaves with 29° Cd for each leaf. The thermal time requirement for completion of juvenile development after radicle emergence was 731° Cd> 3°C. In cv....

Primordium initiation at the stem apex as the primary event controlling plant development: preliminary evidence from wheat for the regulation of leaf development

Abstract. The results from field studies of 12 crops of winter wheat (two seasons, four sites in the U.K., four cultivars), in which leaf appearance and events at the mainstem apex were fully documented, were used to investigate the inter‐relationship between leaf initiation and appearance. It was shown that the progress of leaf appearance could be divided into two phases around collar initiation. During the first phase, which was common to all crops examined, leaf appearance was linearly related to leaf initiation, indicating that leaf appearance was not independently regulated by the environment but dependent on initiation. The slope of the second phase relationship varied between crops, indicating the intervention of an additional controlling factor. This shows that, for the first phase at least, the time course of leaf appearance was predetermined by the rate of leaf initiation at the stem apex.

Co-ordination of leaf emergence and leaf and spikelet primordium initiation in wheat

Abstract Leaf emergence and primordium initiation were measured in experiments done with different varieties in a wide range of environments. Leaf initiation, relative to leaf emergence, proceeded at a constant rate. After initiation of the first spikelet, the rate of primodium initiation (primordia per emerged leaf) changed to a faster, approximately constant, rate which was maintained until initiation of the terminal spikelet. Rate of leaf initiation (1.7 primordia per emerged leaf) was similar in all cases analysed. Rate of spikelet initiation varied from about 3.5 to 7 primordia per emerged leaf, and was negatively correlated with total number of leaves on the shoot, which varied from 7 to 14. A rectangular hyperbola describes the relation between rate of spikelet initiation and total number of leaves. The analysis shows that there is a metrical relationship between different elements of shoot development. A model is given which shows how ear initiation and stem elongation are modulated in shoots with differing total numbers of leaves. The relation between leaf emergence and primordium initiation suggests control of apex development by emerging leaves, or vice versa. An accumulation of growing leaves may regulate growth and development of the shoot apex.

Effects of temperature on leaf and curd initiation in relation to juvenility of cauliflower

Cauliflower plants ( Brassica oleracea L. var. botrytis subvar. cauliflora, cultivar ‘Delira’) were grown at 14 or 22°C to study the effect of temperature on leaf and curd initiation. The rate of leaf initiation depended on the leaf number: the first 11 leaves were initiated at a lower rate than the following leaves. A linear relationship was found between the number of leaves > 2 cm and the total number of initiated leaves of vegetative plants. The slope of the regression line was independent of temperature and different from unity. The time between initiation of a leaf and its attaining a length of 2 cm increased linearly with leaf number. The relationship between dry matter production or leaf area and the number of leaves > 2 cm was hardly influenced by temperature. By transferring plants from weak curd-inducing conditions (22°C) to strong curd-inducing conditions (14°C) at different times, the number of leaves at which the juvenile phase ended could be estimated by assessing the effect of the number of initiated leaves at the moment of transfer on the final number of leaves. For this cultivar, the juvenile phase ended when 16–18 leaves were initiated. During the juvenile phase, the linear relationship between the number of initiated leaves and the diameter of the apical dome was independent of temperature. After the juvenile phase, the apical dome diameter of vegetative plants at 22°C increased more slowly than at 14°C. The maximum dome diameter of vegetative plants was between 0.35 and 0.40 mm at both temperatures.