Diurnal Fluctuations in Growth and CO2 Exchange in Dactylis glomerata

Diurnal fluctuations in dry matter accumulation and leaf extensionof seedlings of Dactylis glomerata were followed through a 16-hlight period and a subsequent 8-h dark period at 20 °C.Themeasured increase in dry weight during the light period andthe decrease during the dark period showed a very good agreementwith calculated dry weight changes derived from the rates ofcarbon dioxide exchange of whole seedlings. Although dry weightof the leaf blades decreased during the dark period, leaf expansioncontinued throughout the 24-h period with associated changesin the ratio of fresh weight to dry weight of the leaf blades.     

Turnover of Fatty Acids during Natural Senescence of Arabidopsis, Brachypodium, and Switchgrass and in Arabidopsis β-Oxidation Mutants

During leaf senescence, macromolecule breakdown occurs and nutrients are translocated to support growth of new vegetative tissues, seeds, or other storage organs. In this study, we determined the fatty acid levels and profiles in Arabidopsis (Arabidopsis thaliana), Brachypodium distachyon, and switchgrass (Panicum virgatum) leaves during natural senescence. In young leaves, fatty acids represent 4% to 5% of dry weight and approximately 10% of the chemical energy content of the leaf tissues. In all three species, fatty acid levels in leaves began to decline at the onset of leaf senescence and progressively decreased as senescence advanced, resulting in a greater than 80% decline in fatty acids on a dry weight basis. During senescence, Arabidopsis leaves lost 1.6% of fatty acids per day at a rate of 2.1 μg per leaf (0.6 μg mg⁻¹ dry weight). Triacylglycerol levels remained less than 1% of total lipids at all stages. In contrast to glycerolipids, aliphatic surface waxes of Arabidopsis leaves were much more stable, showing only minor reduction during senescence. We also examined three Arabidopsis mutants, acx1acx2, lacs6lacs7, and kat2, which are blocked in enzyme activities of β-oxidation and are defective in lipid mobilization during seed germination. In each case, no major differences in the fatty acid contents of leaves were observed between these mutants and the wild type, indicating that several mutations in β-oxidation that cause reduced breakdown of reserve oil in seeds do not substantially reduce the degradation of fatty acids during leaf senescence.     

Lower and Upper Critical Zinc Levels in Relation to Cotton Growth and Development

Solution culture experiments in the greenhouse were conducted to determine the lower and upper critical Zn levels relative to early cotton (Gossypium hirsutum L.) growth and development. Upland cotton ‘Coker 310’ was grown in nutrient solution with fourteen Zn levels ranging from 0 to 10,000 μg/liter. The plants were grown for 31 days, harvested and analyzed for Zn. At Zn levels of less than 20 μg/I, top dry weight, root dry weight, plant height, node number and squares produced were reduced as compared to plants supplied with adequate Zn. Toxicities were induced at 2000 μg/I and higher. Root dry weight was not influenced by Zn levels to 10,000 μg/I. The lower critical Zn levels where Zn is required at a minimum concentration for maximum growth were from 8 to 11 μg/I in blades 1 through 5, respectively. The upper critical Zn levels where maximum Zn concentration in blade tissue can be tolerated for maximum growth were from 130 to 300 μg/g for blades 1 to 5, respectively. Blade 3, the recently matured leaf, was selected as the representative tissue for analysis. The lower and upper critical Zn levels in blade 3 were 11 and 200 μg/g, respectively.     

Dry weight and chemical changes during decomposition of tropical macrophytes in lobo reservoir — São Paulo,Brazil

During decomposition, petioles and leaf blades of Nymphoides indica (L.) O. Kuntze and stems and leaves of Polygonum ferrugineum Wedd. from the Lobo Reservoir, Sao Paulo, Brazil, showed an initial phase (first seven days) of loss of dry weight, soluble carbohydrates, lipids, polyphenols, phosphorus, potassium and ash content. In both species, the decomposition of leaves and leaf blades was faster than that of stems and petioles. At the end of the experiment (after 149 days) leaf blades of N. indica had lost 98% of the initial dry weight. Except for nitrogen and ash, which increased, all the other components showed two distinct phases during the process with intensive loss during the initial phase and a gradual and reduced loss during the longer second phase.The nutritional value of the detritus and the consequence of nutrient re-cycling in the metabolism of Lobo Reservoir are discussed.     

Response of Cynodon dactylon to prolonged water deficits under saline conditions

Competition for available water resources in both arid and semi-arid locations has led to greater scrutiny of turfgrass irrigation. Irrigation management strategies, including deficit irrigation, need further investigation. The objective of this research was to determine the physiological response of bermudagrass (Cynodon dactylon (L.) Pers.) to prolonged water deficits under saline conditions. Bermudagrass was grown in large columns packed with three different soil types (sandy loam, silt loam and clay). Synthesized saline irrigation water was applied at three different salinity levels (1.5, 3.0 and 6.0 dS/m). Two previous experiments that were conducted with these columns over a 3.5 year period led to differential profile salinization in all 27 columns. At the end of this 3.5 year period, all irrigations were terminated and plant growth and water status were monitored over a 95 day dry-down period. Midday stomatal conductance, leaf water potential, canopy temperature, soil water in storage and stolon elongation were measured over the experimental period. On day 95, above ground tissue was harvested for dry weight and elemental tissue analysis. Midday stomatal conductance decreased around day 30 in all columns regardless of soil salinity. This decrease was not associated with a threshold leaf water potential, as midday leaf water potentials remained constant over a 60 day period. Stolon elongation also ceased before any deviation in the midday leaf water potential occurred. A concomitant reduction in evapo ranspiration was not associated with the measured decrease in stomatal conductance. This would suggest that bermudagrass may have regulated stomatal activity to compensate for lower conductances during periods of greater stress and/or that measured midday stomatal conductances cannot always be directly coupled to extended time evapotranspiration measurements.     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II

Abstract. Vegetative plants of soybean [ Glycine max (L.) Merr. cv. Wells II] grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse-grown (GG) plants after 16 d of treatment. Outdoor-grown (OG) plants, which were subjected to additional environmental stresses including ultraviolet radiation, wind loading, and uncontrolled temperature and humidity fluctuations, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24–45% FL). Reduction in dry weight gain due to mechanical stress corresponded to a decrease in relative growth rate (RGR). Decreases in net assimilation rate and leaf area ratio contributed equally to the lower RGR of shaken plants, indicating that seismic stress inhibits dry weight accumulation by decreasing both the photosynthetic efficiency and the assimilatory surface of soybean.     

Maximum Vegetative Growth Potential and Seasonal Patterns of Resource Dynamics during Peach Growth

The maximum vegetative growth potential of two peach [Prunuspersica (L.) Batsch] cultivars that differ in the timing ofresource demand for reproductive growth was determined in termsof stem extension, stem and leaf dry weight accumulation, andtrunk radial increment on defruited trees. The maximum vegetativegrowth potentials were similar on the two cultivars indicatingthat the greater partitioning of dry weight to vegetative growthfrequently observed on early maturing cultivars compared tolate maturing cultivars is the result of a shorter period ofcompetition between reproductive and vegetative growth, ratherthan a genetic difference in vegetative growth potential. Onboth cultivars, stem extension and leaf dry weight accumulationceased in mid-summer, however stem dry weight accumulation andtrunk radial increment increase continued through the autumn. The presence of fruit did not have a detectable effect on thefinal stem length, stem dry weight or leaf dry weight on theearly maturing cultivar, but it reduced final stem length anddry weight by 43 and 56%, respectively on the late maturingcultivar. The presence of fruit did decrease stem length, stemdry weight and leaf dry weight on the early maturing cultivarfor 1 month prior to and 1 month after fruit harvest. Fruitdecreased final trunk radial increment by 42 and 77% on theearly and late maturing cultivars, respectively. These reductionsin vegetative growth indicate that resource partitioning tovegetative growth was reduced by competition with fruit growth. Comparison of stem relative extension rates and stem and leafrelative growth rates on fruited and defruited trees indicatedthat vegetative growth was resource-limited shortly after vegetativebud break on fruited trees of both cultivars. This period ofresource-limited vegetative growth corresponded to a periodof resource-limited fruit growth identified in an earlier study.During the period of resource-limited vegetative growth, assimilatesupply was low due to low leaf area index, and carbohydratedemand was relatively high due to high vegetative and reproductivegrowth potentials, creating resource-limited growth conditions.Copyright1995, 1999 Academic Press Maximum vegetative growth potential, carbon economy, partitioning, resource availability, resource limitation, source-limited growth, growth analysis, relative growth rate, peach, Prunus persica (L.) Batsch     

Inverse gradients in leaf wax δD and δ13C values along grass blades of Miscanthus sinensis: Implications for leaf wax reproduction and plant physiology

Compound specific hydrogen and carbon isotopic ratios of higher plant leaf waxes have been extensively used in paleoclimate and paleoenvironmental reconstructions. However, studies so far have focused on the comparison of leaf wax isotopic differences in bulk leaf samples between different plant species. We sampled three different varieties of tall grasses (Miscanthus sinensis) in six segments from base to tip and determined hydrogen and carbon isotopic ratios of leaf waxes, as well as hydrogen and oxygen isotopic ratios of leaf water samples. We found an increasing, base-to-tip hydrogen isotopic gradient along the grass blades that can probably be attributed to active leaf wax regeneration over the growth season. Carbon isotopic ratios, on the other hand, show opposite trends to hydrogen isotopic ratios along the grass blades, which may reflect different photosynthetic efficiencies at different blade locales.     

Physio-morphological and structural changes in common bermudagrass and Kentucky bluegrass during salt stress

Environmental pollution has increased human attention toward developing green spaces every day. One of the most important goals in developing green spaces is to create beautiful and pleasant scenes and consequently creating mental relaxation; turfs are the most important plants for this purpose. One factor which affects the growth of plants in arid and semi-arid regions is the salinity of the water and soil; therefore, using some types of turfgrasses which are tolerant to salinity is a key factor for culturing them more in the city landscapes in such regions. The aim of this study was to investigate the physio-morphological and structural changes in common bermudagrass (Cynodon dactylon [L.] Pers., as more tolerant species) and Kentucky bluegrass (Poa pratensis L., as less tolerant species) under salt stress condition. The salt stress treatments were applied by seven concentrations of NaCl + CaCl₂ (1:1 proportion based on the final EC) including: 0.0, 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 dS m^?1. This study was conducted in a completely randomized design with factorial arrangements, each treatment with four replications. Data were analyzed and means were compared using LSD test at 5 % level. Results showed that with increasing salinity levels Kentucky bluegrass started to decrease in visual quality at 2.5 dS m^?1, but bermudagrass’ visual quality was still acceptable at 5.0 dS m^?1. Furthermore, increasing the salinity level caused a reduction in the following indices in both species: shoot height, shoot fresh and dry weight, root fresh and dry weight, leaf area, photosynthetic rate, total chlorophyll, and starch level. However, the reducing sugar levels and indices of proline, and catalase and superoxide dismutase enzymes had shown an increasing trend while salinity increased. However, reducing sugar levels, and catalase and superoxide dismutase activities decreased at salinity levels higher than 10 dS m^?1. Structural studies showed that bermudagrass, with help of bulliform cells, could prevent water loss and tolerate the higher salinity levels. Based on these results, it can be concluded that under the no salinity condition Kentucky bluegrass has more folded leaves than common bermudagrass, however, bermudagrass is more tolerant because of thicker epidermis. Under high salinity conditions, bermudagrass kept their leaves folded, whereas the leaf structure was drastically damaged in bluegrass and no folded leaf was seen at 15 dS m^?1. Further ultrastructural studies are needed to clarify more the changes occurring in leaves under salinity stress condition.     

Silicon distribution and accumulation in shoot tissue of the tropical forage grass Brachiaria brizantha

Silicon (Si) accumulation in organs and cells is one of the most prominent characteristics of plants of the family Poaceae. Many species from this family are used as forage plants for animal feeding. The present study investigates in Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. Marandu: (1) the dry matter production and Si content in shoot due to soil Si fertilizations; (2) the Si distribution among shoot parts; and (3) the silica deposition and localization in leaves. Plants of B. brizantha cv. Marandu were grown under contrasting Si supplies in soil and nutrient solution. Silica deposition and distribution in grass leaf blades were observed using light microscope and scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDXS). Silicon concentration in the B. brizantha shoot increased according to the Si supply. Silicon in grass leaves decreased following the order: mature leaf blades > recently expanded leaf blades > non-expanded leaf blades. Silicon accumulates mainly on the upper (adaxial) epidermis of the grass leaf blades and, especially, on the bulliform cells. The Si distribution on adaxial leaf blade surface is non uniform and reflects a silica deposition exclusively on the cell wall of bulliform cells.     

Growth of bean and tomato plants as affected by root absorbed growth substances and atmospheric carbon dioxide

Summary Bean and tomato plants were grown in solution culture root media containing pre-determined concentrations of gibberellin A₃ (GA), 1-naphthaleneacetic acid (NAA), N⁶-benzyladenine (BA), (2-chloroethyl)trimethylammonium chloride (CCC), and at atmospheric levels of 300 and 1000 ppm of CO₂. Net assimilation rates (NAR), relative growth rates (RGR), leaf area ratios (LAR), root to top dry weight ratios (R/T) and changes in dry weight, size, and form of each organ were recorded.Gibberellin had no effect on RGR of either plant species but increased the NAR of tomatoes at 1000 ppm CO₂. Total dry weight was only slightly affected by GA but root growth and R/T were markedly depressed. CCC had no effect on NAR, but decreased RCR and LAR. Root growth of beans and R/T in both plants were promoted by CCC. NAR and RGR were strongly inhibited by BA and NAA. Inhibition of stem and leaf growth by CCC and NAA was greater than that for roots; thus, R/T ratios were increased. Root branching was promoted by NAA.High (1000 ppm), compared to the low (300 ppm), atmospheric levels of CO₂ generally promoted root growth and produced an increase in the R/T, both in the absence and presence of chemical treatment. The multiplicity of effects of the rootabsorbed chemical growth substances and CO₂ on growth and photosynthesis is discussed.Journal article No 3883 of the Michigan Agricultural Experiment Station.NATO Fellow, University of Pisa, Italy.     

Contribution to the study of heterogeneity in the leaves of a spring wheat plant

The effect of the individual leaf blades of spring wheat on the dry matter of stalks, chaff and grain (caryopses), of spikes and total overground part, was studied. In the experimental plants the individual leaf blades were detached according to the scheme given, at the beginning of shooting, (A), at the beginning of earing (B), and at the beginning of flowering (C). The dry matter (fresh weight) of the stalk was least decreased if either the lowest or the uppermost leaf blade was severed during the developmental phase of shooting. The dry as well as the fresh weights of chaff were least affected in those plants where the leaf blade was removed during the developmental phase of flowering. Both the dry and fresh weights of caryopses were least decreased if either the lowest or the uppermost leaf blade was removed during the developmental phase of flowering. The dry weight as well as the relative water content of chaff and ear grains were most decreased following removal of leaf blades during the developmental phase of shooting. The relative water content of chaff, grains and ears was most decreased following removal of developed leaf blades during the developmental phase of earing. It was confirmed that in addition to the photosynthetic activity of leaves the photosynthesis of other parts of the stem system (stalk internodes, ear awns etc.) participated in the production of total dry matter of experimental plants. The photosynthetic activity of leaf blades was particularly high up to the earing phase, while subsequently the photosynthesis of extrafoliar area (stalk internodes and ears) predominated. In spite of this, participation of the total leaf area is very high in the formation of grain dry matter (over 50%), as well as of the total dry matter of plant (over 80%).     

Leaf and Tiller Production of Prairie Grass (Bromus willdenowii Kunth) and Two Ryegrass (Lolium) Species

A detailed morphological study of three prairie grass cultivars(Bromus willdenowii Kunth) was conducted under ‘vegetative’and ‘reproductive’ growth conditions (short andlong photoperiods) and at different temperatures. Perennialryegrass (Lolium perenne L.) and Westerwolds ryegrass (Loliummuhiflorum Lam.) were compared during vegetative growth. Prairie grass had higher leaf appearance rates (leaves per tillerper day) and lower site filling (tillers per tiller per leafappearance interval) than the ryegrass species. Tillering rates(tillers per tiller per day) were also lower, except under vegetativeconditions at 4C. Low tiller number in prairie grass was notdue to lack of tiller sites but a result of poor filling ofthese sites. Lower site filling occurred because of increaseddelays in appearance of the youngest axillary tiller and lackof axillary tillers emerging from basal tiller buds. In prairiegrass, no tillers came from coleoptile buds while only occasionallydid prophyll buds develop tillers. Low tiller number in prairiegrass was compensated for by greater tiller weight. Prairiegrass had more live leaves per tiller, greater area per leafand a high leaf area per plant. Considerable variation between cultivars was found in prairiegrass. The cultivar ‘Bellegarde’ had high leaf appearance,large leaves and rapid reproductive development, but had lowlevels of site filling, tillering rate, final tiller numberand herbage quality during reproductive growth. ‘Primabel’tended to have the opposite levels for these parameters, while‘Grasslands Matua’ was intermediate and possiblyprovided the best balance of all plant parameters. prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., temperature, photoperiod, leaf appearance, leaf area, tillering, site filling, tillering sites, yield     

Fatty acid synthesis by slices from developing leaves

Fatty acid synthesis was studied in successive leaf sections from the base to the tip of developing barley (Hordeum vulgare L.), maize (Zea mays L.), rye grass (Lolium perenne L.) and wheat (Triticum aestivium L.) leaves. The basal regions of the leaves had the lowest rates of fatty acid synthesis and accumulated small amounts of very long chain fatty acids. Fatty acid synthesis was highest in the middle leaf sections in all four plants. Linolenic acid synthesis from [1-¹⁴C]acetate was highest in the distal leaf sections of rye grass. The labelling of the fatty acids of individual lipids of rye grass was examined and it was found that [¹⁴C]linolenic acid was highest in the galactolipids. Synthesis of this acid in the galactolipids was most active in leaf segment C. Only traces of [¹⁴C]linolenic acid were ever found in phosphatidylcholine and it is concluded that this phospholipid cannot serve as a substrate for linoleic acid desaturation in rye grass. The synthesis of fatty acids was sensitive to arsenite, fluoride and the herbicide EPTC. The latter was only inhibitory towards those leaf segments which made very long chain fatty acids. Formation of fatty acids from [1-¹⁴C]acetate was also studied in chloroplasts prepared from successive leaf sections of rye grass. Chloroplasts isolated from the middle leaf sections had the highest activity. Palmitic and oleic acids were the main fatty acid products in all chloroplast preparations. Linolenic acid synthesis was highest in chlorplasts isolated from the distal leaf sections of rye grass.     

Differences in the responses of stem diameter and pod thickness to drought stress during the grain filling stage in soybean plants

This study investigated the factor of the physiological characteristics causing the reduction of yield of soybean plants (Glycine max (L.) Merr.) by drought stress, by monitoring changes in stem diameter and pod thickness, and photosynthetic activity, partitioning of ¹³C-labeled photosynthate. Drought stress reduced the whole plant dry weight due to the decrease in leaf and pod dry matter accumulation; however, this stress did not have a significant effect on stem growth. Leaf photosynthesis was also severely decreased by drought stress in the early stage of stress treatment as leaf water potential decreased. Imposition of stress decreased pod thickness, but stem diameter increased. The adverse effect of drought stress on pod thickness was more evident at night than during the day. The stem diameter also shrank during the day and expanded at night, but the nocturnal increase in stem diameter during drought stress treatment was greater for stressed plants compared with well-watered controls. Drought stress significantly promoted ¹³C partitioning from the fed leaf to other parts of the plant; the stem was the largest beneficiary. Soluble carbohydrates accumulated in various plant parts under the influence of the stress, but starch concentration declined in all organs except the stem. These results indicated that stem growth was promoted by drought stress compared to pod growth at the early grain-filling stage.     

Effect of dikegulac on growth and alkaloid production inCatharanthus roseus (L.) G. Don. (pink flowered)

Application of sodium-dikegulac reduced plant height with associated increase in branch and leaf number and root biomass inC. roseus (L.) G. DON. Chlorophyll content reduced significantly after first month of 100 and 250 μg/ml DK application. However, such reduction was replaced by significant rise after forth month in 250 μg/ml DK application and fifth month in 100 μg/ml DK application followed by appreciable decline only in 250 μg/ml DK treatment but 100 μg/ml DK maintained higher level till harvest. Total sugar content was significantly high during forth and fifth month stage of growth after DK application. Amino acid content was higher during third to fifth month in 100 μg/ml DK treatment and during third to forth month in 250 μg/ml DK treatment. Tryptophan, on the other hand showed higher content at the fifth month stage of growth after application of DK in both the concentrations. Leaf and root dry weight as well as total alkaloid content were highest in 100 μg/ml DK application. DK, therefore, appears to be a potential chemical for increasing biomass and alkaloid content inC. roseus.     

EFFECTS OF GIBBERELLIN AND AMO-1618 ON GROWTH,DRY-MATTER ACCUMULATION,CHLOROPHYLL CONTENT AND PEROXIDASE ACTIVITY OF CITRUS SEEDLINGS

Monselise , S. P., and A. H. Halevy . (Hebrew U., Rehovot, Israel.) Effects of gibberellin and AMO–1618 on growth, dry-matter accumulation, chlorophyll content and peroxidase activity of citrus seedlings. Amer. Jour. Bot. 49(4): 405–412. Illus. 1962.—Sweet-lime seedlings, 6 months old, were sprayed with gibberellic acid (GA) and a growth retardant, AMO–1618, alone and in combination, at concentrations ranging between SO and 1600 ppm. Increasing concentrations of GA progressively increased shoot and internode length, did not influence number of leaves, and decreased leaf area. Dry weight of shoots was progressively increased up to 400 ppm, while dry weights of leaves and roots were decreased over all GA concentrations. Total dry weight of plants was increased by GA when related to leaf area or weight and to total chlorophyll content, which indicates a higher synthetic efficiency of leaves. This could not be detected by manometric determinations using leaf discs. It is suggested that a short determination period and/or work with detached leaves are responsible for failures to detect increased photosynthetic activity of GA-treated leaves. Chlorophyll content of leaves was decreased by increasing GA concentrations; it is shown that this is not due to “dilution” over a larger area of leaves. Peroxidase activity of leaves was only slightly reduced by GA, while it was increased by AMC–1618, acting as antagonist to GA. This is remarkable, since AMO–1618 did not clearly affect other procperties of citrus seedlings which are only slightly responsive to this chemical.     

Nucleic Acid Metabolism of Vicia faba during Germination and Growth

During the growth of Vicia faba seedlings in the absence of an external nitrogen supply, the cotyledons decreased rapidly in dry weight and nucleic acid content. In the developing shoot the dry weight increased rapidly for four weeks and then very slowly over the next two weeks growth; the nucleic acid content of the shoot increased to a maximum after 4 weeks growth and decreased in amount during the next 2 weeks. On the other hand the roots increased in both dry weight and nucleic acid content throughout the growth period, although they only accounted for a small proportion of the total dry weight and nucleic acid content of the plant. These changes during germination and growth are discussed in relation to those occurring during these developmental stages in other plants.     

Short and Long Term Fluctuations of the Leaf Mass Per Area of Tomato Plants--Implications for Growth Models

The leaf mass per unit leaf area (LMA) is a key variable inmany growth models, since it is often used to predict leaf areaexpansion from leaf dry weight increase, orvice versa. Influencesof source-sink balance on leaf area, leaf dry weight, LMA, andleaf content in non-structural carbohydrates were investigatedin glasshouse tomato crops. The source-sink balance was manipulatedby artificial shading, CO₂enrichment or fruit removal usingdifferent tomato cultivars. Leaf area was hardly affected bycompetition for assimilates except under extreme conditions.In contrast, leaf dry weight, and consequently LMA, underwentlarge and rapid fluctuations in response to any factor thatchanged source and sink activities. A 60% reduction of photosyntheticallyactive radiation involved a 24% decrease in LMA after 10 d.Carbon dioxide enrichment and fruit removal induced about a45% and 15% increase in LMA, respectively, on plants with twofruiting trusses, but hardly affected LMA of producing plants.No significant cultivar effect could be identified. Changesin starch and soluble sugar content in leaves accounted foronly 29% of diurnal variations in LMA, suggesting regular fluctuationsof other components. We propose that structural LMA varies betweena maximum and a minimum value according to the ratio of assimilatesupply and demand during leaf development. Leaf area is independentof the supply of assimilates when the minimum structural LMAis realised. When the maximum structural LMA is attained, astorage pool of assimilates may accumulate in leaves duringperiods of high supply and low demand. We present a model includingthese hypotheses, which predicts structural and non-structuralLMA variations of plants with different source-sink ratios.Copyright1998 Annals of Botany Company Tomato,Lycopersicon esculentumMill., SLA, SLW, leaf growth, vegetative sink strength, assimilate competition, source-sink ratio, non-structural carbohydrate, models.