Showing papers on "Shoot published in 1999"

Biomass allocation in plants: ontogeny or optimality? a test along three resource gradients

Abstract: We examined biomass allocation patterns throughout the entire vegetative growth phase for three species of annual plants along three separate gradients of resource availability to determine whether observed patterns of allocational plasticity are consistent with optimal partitioning theory. Individuals of the annual plant species Abutilon theophrasti, Chenopodium album, and Polygonum pensylvanicum were grown from locally field-gathered seed in controlled greenhouse conditions across gradients of light, nutrients, and water. Frequent harvests were used to determine the growth and allocation (root vs. shoot, and leaf area vs. biomass) responses of these plants over a 57-d period. Growth analysis revealed that each species displayed significant plasticity in growth rates and substantial amounts of ontogenetic drift in root:shoot biomass ratios and ratios of leaf area to biomass across each of the three resource gradients. Ontogenetically controlled comparisons of root:shoot and leaf area ratios across light ...

Elevated CO2 and plant structure: a review

Abstract: Summary Consequences of increasing atmospheric CO2 concentration on plant structure, an important determinant of physiological and competitive success, have not received sufficient attention in the literature. Understanding how increasing carbon input will influence plant developmental processes, and resultant form, will help bridge the gap between physiological response and ecosystem level phenomena. Growth in elevated CO2 alters plant structure through its effects on both primary and secondary meristems of shoots and roots. Although not well established, a review of the literature suggests that cell division, cell expansion, and cell patterning may be affected, driven mainly by increased substrate (sucrose) availability and perhaps also by differential expression of genes involved in cell cycling (e.g. cyclins) or cell expansion (e.g. xyloglucan endotransglycosylase). Few studies, however, have attempted to elucidate the mechanistic basis for increased growth at the cellular level. Regardless of specific mechanisms involved, plant leaf size and anatomy are often altered by growth in elevated CO2, but the magnitude of these changes, which often decreases as leaves mature, hinges upon plant genetic plasticity, nutrient availability, temperature, and phenology. Increased leaf growth results more often from increased cell expansion rather than increased division. Leaves of crop species exhibit greater increases in leaf thickness than do leaves of wild species. Increased mesophyll and vascular tissue cross-sectional areas, important determinates of photosynthetic rates and assimilate transport capacity, are often reported. Few studies, however, have quantified characteristics more reflective of leaf function such as spatial relationships among chlorenchyma cells (size, orientation, and surface area), intercellular spaces, and conductive tissue. Greater leaf size and/or more leaves per plant are often noted; plants grown in elevated CO2 exhibited increased leaf area per plant in 66% of studies, compared to 28% of observations reporting no change, and 6% reported a decrease in whole plant leaf area. This resulted in an average net increase in leaf area per plant of 24%. Crop species showed the greatest average increase in whole plant leaf area (+ 37%) compared to tree species (+ 14%) and wild, nonwoody species (+ 15%). Conversely, tree species and wild, nontrees showed the greatest reduction in specific leaf area (– 14% and – 20%) compared to crop plants (– 6%). Alterations in developmental processes at the shoot apex and within the vascular cambium contributed to increased plant height, altered branching characteristics, and increased stem diameters. The ratio of internode length to node number often increased, but the length and sometimes the number of branches per node was greater, suggesting reduced apical dominance. Data concerning effects of elevated CO2 on stem/branch anatomy, vital for understanding potential shifts in functional relationships of leaves with stems, roots with stems, and leaves with roots, are too few to make generalizations. Growth in elevated CO2 typically leads to increased root length, diameter, and altered branching patterns. Altered branching characteristics in both shoots and roots may impact competitive relationships above and below the ground. Understanding how increased carbon assimilation affects growth processes (cell division, cell expansion, and cell patterning) will facilitate a better understanding of how plant form will change as atmospheric CO2 increases. Knowing how basic growth processes respond to increased carbon inputs may also provide a mechanistic basis for the differential phenotypic plasticity exhibited by different plant species/functional types to elevated CO2.

Effects of silicon on enzyme activity and sodium, potassium and calcium concentration in barley under salt stress

Abstract: Two contrasting barley (Hordeum vulgare L) cultivars: Kepin No7 (salt sensitive), and Jian 4 (salt tolerant) were grown in a hydroponics system containing 120 mol m-3 NaCl only and 120 mol m-3 NaCl with 10 mol m-3 Si (as potassium silicate) Compared with the plants treated with salt alone, superoxide dismutase (SOD) activity in plant leaves and H+-ATPase activity in plant roots increased, and malondialdehyde (MDA) concentration in plant leaves decreased significantly for both cultivars when treated with salt and Si The addition of Si was also found to reduce sodium but increase potassium concentrations in shoots and roots of salt-stressed barley Sodium uptake and transport into shoots from roots was greatly inhibited by added Si under salt stress conditions However, Si addition exhibited little effect on calcium concentrations in shoots of salt-stressed barley Thus, Si-enhanced salt tolerance is attributed to selective uptake and transport of potassium and sodium by plants The results of the present study suggest that Si is involved in the metabolic or physiological changes in plants

Antisense Repression of Vacuolar and Cell Wall Invertase in Transgenic Carrot Alters Early Plant Development and Sucrose Partitioning

Abstract: To unravel the functions of cell wall and vacuolar invertases in carrot, we used an antisense technique to generate transgenic carrot plants with reduced enzyme activity. Phenotypic alterations appeared at very early stages of development; indeed, the morphology of cotyledon-stage embryos was markedly changed. At the stage at which control plantlets had two to three leaves and one primary root, shoots of transgenic plantlets did not separate into individual leaves but consisted of stunted, interconnected green structures. When transgenic plantlets were grown on media containing a mixture of sucrose, glucose, and fructose rather than sucrose alone, the malformation was alleviated, and plantlets looked normal. Plantlets from hexose-containing media produced mature plants when transferred to soil. Plants expressing antisense mRNA for cell wall invertase had a bushy appearance due to the development of extra leaves, which accumulated elevated levels of sucrose and starch. Simultaneously, tap root development was markedly reduced, and the resulting smaller organs contained lower levels of carbohydrates. Compared with control plants, the dry weight leaf-to-root ratio of cell wall invertase antisense plants was shifted from 1:3 to 17:1. Plants expressing antisense mRNA for vacuolar invertase also had more leaves than did control plants, but tap roots developed normally, although they were smaller, and the leaf-to-root ratio was 1.5:1. Again, the carbohydrate content of leaves was elevated, and that of roots was reduced. Our data suggest that acid invertases play an important role in early plant development, most likely via control of sugar composition and metabolic fluxes. Later in plant development, both isoenzymes seem to have important functions in sucrose partitioning.

Arabidopsis Roots and Shoots Have Different Mechanisms for Hypoxic Stress Tolerance

Abstract: Arabidopsis has inducible responses for tolerance of O 2 deficiency. Plants previously exposed to 5% O 2 were more tolerant than the controls to hypoxic stress (0.1% O 2 for 48 h) in both roots and shoots, but hypoxic acclimation did not improve tolerance to anoxia (0% O 2 ). The acclimation of shoots was not dependent on the roots: increased shoot tolerance was observed when the roots of the plants were removed. An adh (alcohol dehydrogenase) null mutant did not show acclimation of the roots but retained the shoot survival response. Abscisic acid treatment also differentiated the root and shoot responses; pretreatment induced root survival in hypoxic stress conditions (0.1% O 2 ) but did not induce any increase in the survival of shoots. Cycloheximide blocked both root and shoot acclimation, indicating that both acclimation mechanisms are dependent on protein synthesis.

Drought-induced Changes in Shoot and Root Growth of Young Cotton Plants

Abstract: An understanding of the response of plants to water deficits is important in efforts to model cotton (Gossypium hirsutum L.) growth, estimate irrigation needs, and breed drought-resistant cultivars. This study examined shoot and root growth of a longand a short-season cotton cultivar after a brief drought and subsequent recovery period. Seeds were planted in fritted clay-filled pots in a growth room under fluorescent lights at about 27 (C. Plants were divided at 36 d after planting into drought-treatment and watered-control groups. Plants were sampled after a 13-d drought and again after a 10-d recovery period. There were no treatment-by-genotype interactions. At the end of the drought and recovery, height, leaf P.F. Pace, DEKALB Genetics Corporation, 3100 Sycamore Road, DeKalb, IL 60115; Harry T. Cralle, Department of Soil and Crop Sciences, Texas AM Sherif H. M. El-Halawany (deceased), Cotton Research Institute, Agricultural Research Center, Ministry of Agriculture, Giza, Egypt; J. Tom Cothren , Department of Soil and Crop Sciences, Texas AM Scott A. Senseman, Department of Soil and Crop Sciences, Texas AM Masle and Passioura, 1987). Several studies have shown that drought inhibits cotton canopy development. Krieg and Sung (1986) determined that drought decreases the number of leaves on sympodial branches of cotton. Leaf area of glasshouse-grown cotton also was inhibited when the percentage of soil-available water was less than 51 ± 15% (Rosenthal et al., 1987). Cutler and Rains (1977) concluded that predawn leaf water potentials below $0.5 MPa were accompanied by decreased leaf elongation rate. Leaf expansion of 55-d-old cotton plants slowed after 2 d of withholding water, which meant that leaf growth was more sensitive than root elongation to drought (Ball et al., 1994). Similarly, McMichael and Quisenberry (1991) found that terminal drought decreased the shoot:root ratio. Drought also reduced the growth, development, and distribution of cotton roots (Malik et al., 1979; Taylor, 1983). Root growth of 55-d-old cotton was reduced after 6 d of withholding water (Ball et al., 1994). The number of roots elongating decreased by 35% during the drought. Planting early-maturing cultivars can decrease the amount of water used by cotton, and other traits in future cotton cultivars may further decrease the amount of water used. Quisenberry et al. (1981) found considerable variability for heat tolerance, root growth, dry matter accumulation, and water use efficiency among exotic cotton strains under dryland conditions. Gerik and co-authors (1996) compared two short-season cotton cultivars and found that one, Tamcot HQ95, yielded more than other, GP74, regardless of the level of water stress. They concluded that the photosynthetic capacity of Tamcot HQ95 might be greater than that of GP74. Root elongation during drought may help plants get deeper water, thus avoiding water deficits near the soil surface. Elongation also could reduce the water lost by drainage when precipitation allows recovery after the drought (Ludlow and Muchow, 1990). If, however, water is unavailable deeper in the soil profile, longer roots may reduce shoot dry weight and harvest index by allowing the preferential partitioning of photosynthate to roots at the expense of shoots. This study examined various measures of shoot and root growth of one longand one short-season cotton cultivar after a drought of limited duration and a subsequent recovery period. MATERIALS AND METHODS A long-season cotton, ‘Stoneville 506,’, and a short-season cotton, ‘Tamcot HQ95,’ were planted in pots (9-L volume, 20 cm deep) filled with fritted clay (Absorb-N-Dry, Balcones Co., Flatonia, TX). Filter paper at the bottom of the pots retained the fritted clay while allowing for drainage. Two plants were seeded per pot and were supplied with distilled water every other day for 10 d. The pots were then watered with a nutrient solution of 0.90 g L of 2020-20 NPK fertilizer (Peters Professional All Purpose Plant Food, Spectrum Group, Division of United Industries Corp., St. Louis, MO) until 36 d after planting. This fertilizer was selected because soil tests showed that the fritted clay had very low levels of N, P, and K and that nutrients would be quickly leached from this well-drained soil. Water or nutrient solution, when applied, was added until an excess drained from the bottom of the pot. The experiment 185 JOURNAL OF COTTON SCIENCE, Volume 3, Issue 4, 1999 was conducted in a growth room under fluorescent lights providing a photosynthetic photon flux density of 700 )mol m s for 16 h d. Temperature was maintained at 127 (C. At 36 d after planting, plants were randomly divided into drought-treatment and watered-control groups. The drought-treated plants were not watered for 13 d. At the end of this drought treatment (49 d after planting), control and drought-treated plants were sampled and height, number of nodes, leaf area, and taproot length were measured. Secondary root length of fresh roots was measured by a Comair Root Length Scanner (Commonwealth Aircraft Corp. Ltd, Melbourne, Australia). Leaves, stems, and tap and secondary roots were dried for 48 h at 90 (C before dry weights were determined. The shoot:root weight ratio was calculated from the dry weights. At 49 d after planting, the remaining droughttreated plants were watered during a 10-d recovery period. At 59 d after planting, both treatments were sampled as described above. The experiment was a randomized complete block design with two blocks. Each block had four pots of each cultivar. Each pot had two plants. The experiment was repeated twice. There was no interaction between treatment and experimental run, so data from the two runs were pooled for statistical analysis. The cultivar primary effect was insignificant, so data also were pooled across cultivar. This analysis used the SAS System (SAS Institute, Cary, NC). RESULTS AND DISCUSSION At the end of the drought treatment, droughttreated plants had significantly (P < 0.05) lower height, less leaf area, fewer nodes, and lower dry weights of stems and leaves than did the controls (Table 1). Additionally, the drought-treated plants had a lower shoot:root ratio (Table 2) than did the controls at this sampling, 49 d after planting. There were no differences between the two treatments in the lengths of the secondary roots or in the dry weight of the secondary or taproots at the end of the drought period (Table 3). However, the droughttreated plants had a significantly (P < 0.01) greater tap root length than did the controls at this time (49 d after planting). The taproot dry weight in the drought-treated plants was identical to that of controls, so the drought-related elongation occurred at the expense of taproot thickening. While the drought-treated plants had a taproot dry weight per length of only 0.011 g cm, the corresponding measurement for the well-watered controls were Table 1. Heights and dry weights of stem, leaf area and dry weight, and node number in drought-treated and control plants of Stoneville 506 and Tamcot HQ95 at the end of the drought, 49 d after planting.† Means are followed by standard errors of the mean in parentheses.

Acquisition of N by external hyphae of an arbuscular mycorrhizal fungus and its impact on physiological responses in maize under drought-stressed and well-watered conditions

Abstract: This study examined the uptake of nitrogen by external hyphae of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) and its impact on physiological responses in maize plants subjected to well-watered or drought-stressed conditions. Plants were grown in compartmented boxes divided by a nylon mesh (40 μm) into a root compartment and a hyphal compartment. Maize plants (Zea mays cv. 'Tuxpeno sequia' selection cycle C0) were exposed to 2 weeks of drought 56 days after sowing. A ^[15]N tracer was applied as K^[15]NO_[3] to the hyphal compartment at a distance of 5 cm from the root compartment. Root and shoot samples were then analyzed for ^[15]N atom % excess (APE), glutamine synthetase (GS) activity, protein concentration and nutritional status. Evapotranspiration rate and stomatal resistance were monitored daily to determine the degree of drought stress. The APE values for AM shoots and roots were 32% and 33% higher than non-AM shoots and roots, respectively, under drought conditions. This provides clear evidence that the external mycelium of AM fungus transports considerable amounts of ^[15]NO_[3]^[– ]to the host plant under drought conditions. Drought-stressed AM roots had 28% higher GS activity, possibly as a consequence of higher hyphal acquisition of NO_[3]^[–] ions. Mycorrhizal colonization significantly increased the host plant P status regardless of soil moisture regime. In addition, the N status of drought-stressed AM shoots and roots was slightly higher than stressed non-AM shoots and roots. The improved nutritional status may assist AM plants to exploit available soil moisture more efficiently and to maintain higher leaf relative water content under moderate drought conditions.

Self-shading, carbon gain and leaf dynamics: a test of alternative optimality models

Abstract: A simple model of shoot-level carbon gain is presented addressing the optimal number and life span of leaves in relation to alternative optimality criteria: (1) maximizing carbon export from the shoot, or (2) maximizing the rate of leaf production at the shoot tip. Additionally, the processes that cause declining assimilation with leaf age are considered in relation to (1) leaf position on the shoot (e.g., self-shading) versus (2) leaf age per se. Using these alternative scenarios, only a model based on position-dependent assimilation and maximization of leaf production rates resulted in quantitative predictions for all aspects of leaf dynamics on the shoot (i.e., leaf number, life span, and birth rate), while other approaches predicted that one or more parameters would be infinite. This formulation of the model also predicted that leaves should be maintained on the shoot until the diurnal carbon balance declines to zero, in contrast with other scenarios which predict that leaves should be shed while maintaining a positive carbon balance. Predictions of the model were supported by the results of a field study of carbon gain and leaf dynamics in saplings of three species of tropical pioneer trees (Carica papaya, Cecropia obtusifolia, and Hampea nutricia) which differ in the number of leaves per shoot. The results illustrate that in these fast-growing plants, leaf production and height growth may be more appropriate measures of performance than net carbon export from the shoot, and suggest that leaf senescence is primarily a function of the position of a leaf within the canopy, rather than its chronological age.

Interspecific differences in above-ground growth patterns result in spatial and temporal partitioning of light among species in a tall-grass meadow

Abstract: 1 We compared allometric growth patterns, canopy structure and light interception for individual shoots of different species in a tall-grass meadow. 2 The vertical distributions of above-ground biomass, leaf area, height and leaf angles were measured, both early and late in the season, for individual shoots of Miscanthus sinensis (the dominant species), Lespedeza bicolor, Lysimachia clethroides, Astilbe thunbergii and Potentilla freyniana. A canopy model was developed to calculate light absorption by individual shoots. Light absorption per unit mass (Φmass) was used to quantify the efficiency with which plants utilized biomass to capture light. 3 The leaf mass ratio (LMR), average specific leaf area (SLA) and therefore the leaf area ratio (LAR) decreased with shoot height and light availability. Light absorption per unit leaf area (Φarea) increased with shoot height, and this increase was observed to be much stronger at greater than at smaller shoot heights. 4 In the taller species (Miscanthus and Lespedeza) Φmass (the product of LAR and Φarea) increased, while in the shortest species (Potentilla) it decreased with shoot height. Clones of Miscanthus and Lespedeza may thus increase total light capture by allocating shoot biomass among fewer taller shoots, and a clone of Potentilla by producing a larger number of shorter shoots. 5 Shoots of the shorter species were equally efficient in capturing light (i.e. they had similar Φmass) early in the season, but less efficient later in the season than shoots of the taller species. Shorter species appear to be able to use the earlier part of the season for efficient light capture, while shoots of taller species gain an advantage from their height later in the season. 6 This study shows how different above-ground growth patterns of the species in a tall-grass meadow allow them to use different positions in vertical space and different periods of the season to absorb light efficiently. This is a clear example of niche separation and helps to explain the coexistence of these species.

AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis.

Abstract: The AXR1 gene of Arabidopsis is required for many auxin responses. The highly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-12 plants. In the wild type, the pattern of lateral shoot development depends on the developmental stage of the plant. During prolonged vegetative growth, axillary shoots arise and develop in a basal-apical sequence. After floral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. For both patterns, the axr1 mutation does not affect the timing of axillary meristem formation; however, subsequent lateral shoot development proceeds more rapidly in axr1 plants. The outgrowth of lateral inflorescences from excised cauline nodes of wild-type plants is inhibited by apical auxin. axr1-12 nodes are resistant to this inhibition. These results provide evidence for common control of axillary growth in both patterns, and suggest a role for auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia.

Root water flow and growth of aspen (Populus tremuloides) at low root temperatures

Abstract: Effects of root zone temperature on growth, shoot water relations, and root water flow were studied in 1-year-old aspen (Populus tremuloides Michx.) seedlings. Seedlings were grown in solution culture and exposed to day/night air temperatures of 22/16 degrees C and solution culture temperatures of 5, 10, or 20 degrees C for 28 days after bud flush. Compared with root growth at 20 degrees C, root growth was completely inhibited at 5 degrees C and inhibited by 97% at 10 degrees C. The 5 and 10 degrees C treatments severely reduced shoot growth, leaf size, and total leaf area. Root water flow was inhibited by the 5 and 10 degrees C treatments. However, when seedlings were grown for 28 days at 5 degrees C and root water flow was measured at 20 degrees C, there was an increase in flow rate. This increase in root water flow was similar in magnitude to the decrease in root water flow observed when seedlings were grown for 28 days at 20 degrees C and root water flow was measured at 5 degrees C. Reduced root water flow of seedlings grown at 5 and 10 degrees C resulted in decreased stomatal conductance, net assimilation, and shoot water potentials. Root water flow was positively correlated with leaf size, total leaf area, shoot length, and new root growth. Transferring seedlings from 5 to 20 degrees C for 24 h significantly increased root water flow, shoot water potential, and net photosynthesis, whereas transferring seedlings from 10 to 20 degrees C resulted in only a slightly increased shoot water potential. Transferring seedlings from 20 to 5 degrees C greatly reduced root water flow, stomatal conductance, and net photosynthesis, whereas shoot water potential decreased only slightly.

Relationship between Relative Water Content, Nitrogen Pools, and Growth of Phaseolus vulgaris L. and P. acutifolius A. Gray during Water Deficit

Abstract: Phaseolus acutifolius A. Gray is a potential source of stress-tolerant traits for Phaseolus vulgaris L. through interspecific hybrids. The objective of this study was to quantify the effects of water-deficit stress on vegetative growth, shoot relative water content (RWC), and leaf concentrations of proline, polyamines, and related metabolites in P. vulgaris compared with P. acutifolius. Stress-induced changes in N metabolism putatively related to stress tolerance have not been investigated previously in P. acutifolius. Replicate pots, each containing three 5-d-old plants in 18.9 L of soil with 4 L of available water, were subjected to water deficit by withholding water (terminal drought) or were maintained under well-watered (control) conditions. Compared with controls, stressed plants of both species accumulated approximately 55% less shoot dry matter. Root dry matter accumulation was inhibited to a greater degree in P. acutifolius (70% for two genotypes) than in P. vulgaris (14 and 27% for two genotypes). P. acutifolius maintained greater shoot RWC than P. vulgaris. In droughted plants of P. acutifolius, leaf arginine and proline concentrations did not change, total polyamine (Σ agmatine + putrescine + spermidine + spermine) concentrations decreased, and ammonia increased compared with controls. In P. vulgaris, water deficit increased concentrations of arginine (>30%) and proline (>300%), whereas total polyamine and ammonia concentrations did not change compared with controls. In all four genotypes examined, proline concentration was inversely related to RWC (R 2 ≥ 0.90). Leaf proline concentration is an indicator of plant water status in Phaseolus but not of tolerance or sensitivity of vegetative growth to water deficit.

Morphological factors determining salt tolerance in citrus seedlings: the shoot to root ratio modulates passive root uptake of chloride ions and their accumulation in leaves

Abstract: The results presented in this work were obtained with two citrus genotypes, the chloride-tolerant Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and the chloride-sensitive Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.]. The data show that chloride uptake under salinization is driven by passive forces. In both species, net rates of chloride root uptake increased linearly, without saturation, with the increase of external NaCI concentrations (30-240 mol m -3 ). Uptake rates, on a μg g root dry weight -1 h -1 basis, in Cleopatra and Carrizo decreased (from 38 to 21) and increased (from 21 to 35), respectively, with the increase (about three-fold) of the shoot to root ratio. With the appropriate shoot to root ratio in each genotype, it was demonstrated that at identical external doses of NaCI, Cl - uptake rates and Cl - xylem concentrations in the two species were very similar. Root pruning and defoliation showed that the amount of chloride taken by the plant was a function of the size of the root system, whereas leaf chloride concentration, the parameter responsible for salt damage, was dependent upon leaf biomass. Measurements of water transpiration suggested that chloride root uptake and leaf accumulation might be linked to water absorption and transpiration rates, respectively. The data indicate that plant morphology is a crucial factor determining salt-tolerance in citrus.

Relationships between shoot to root ratio, growth and leaf soluble protein concentration of Pisum sativum, Phaseolus vulgaris and Triticum aestivum under different nutrient deficiencies

Abstract: Relations between shoot to root dry weight ratio (S : R), total plant dry weight (DW), shoot and plant N concentration and leaf soluble protein concentration were examined for pea (Pisum sativum L.), common bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) under different nutrient deficiencies. A regression model incorporating leaf soluble protein concentration and plant DW could explain greater than 80% of the variation in S : R within and between treatments for pea supplied different concentrations of NO 3 - or NH 4 + in solid substrate; pea and bean supplied different concentrations of N, P, K and Mg in liquid culture; and wheat supplied different concentrations of N, P, K, Mg, Ca and S in liquid culture. Addition of shoot or plant N concentration to the model explained little more of the variation in S : R. It is concluded that results are consistent with the proposal that macronutrient effects on S : R are primarily mediated through their effects on protein synthesis and growth.

Autoinhibition of indoleacetic acid transport in the shoots of two‐branched pea (Pisum sativum) plants and its relationship to correlative dominance

Abstract: Two-branched pea plants (Pisum sativum L. cv. Lisa ZS) with different dominance degrees, obtained by removing the epicotyl shortly after germination, were used to study the interaction between the polar transport of indoleacetic acid (IAA) in both branches of the plants and its relationship to correlative dominance. The dominant shoot had higher transport capacity for 3 H-IAA, exported more IAA out of its apex and possessed more endogenous IAA in apex and the first internode than the dominated one. Decapitation of the dominant shoot resulted in a rapid resumption of growth in the dominated shoot, accompanied by a considerable increase in its capacity to export endogenous IAA and to transport 3 H-IAA. Parallel experiments with intact two-branched plants and Y-formed explants showed that the 3 H-IAA transport on one side was inhibited by the other branch apex or by pre-application of 12 C-IAA to the cut stump of the decapitated side. The higher the concentration of 12 C-IAA applied to the cut stump of one side of the Y-form explant was used, the stronger the 3 H-IAA transport was inhibited and the more the transported IAA was conjugated above the junction on the other side. The results of these experiments support the autoinhibition hypothesis at junctions. The relationship between elongation growth and IAA export/ transport in the two-branch pea plants is considered.

Effects of salinity on growth, ion content, and osmotic relations in Halopyrum mucronatum (L.) Stapf.

Abstract: Halopyrum mucronatum (L.) Stapf. is a perennial grass found on the coastal dunes of Karachi, Pakistan. Halopyrum mucronatum plants were grown in 0, 90,180, and 360 mol m‐3 NaCl in a sand culture using a sub‐irrigation method. Fresh and dry weight of roots and shoots peaked at 90 mol m‐3 NaCl. A further increase in salinity inhibited plant growth, ultimately resulting in plant death at 360 mol m‐3 NaCl. The relative growth rate of plants was highest between 60 and 90 days after final salinity concentrations were reached. Maximum succulence was noted in 90 mol m‐3 NaCl. Water potential and osmotic potential of plants became more negative with an increase in salinity, while plants lost turgor with increasing salinity. Time of harvest did not have any significant effect on the water relations of plants. Sodium (Na) and chloride (Cl) content of plants increased with an increase in salinity, while calcium (Ca), magnesium (Mg), and potassium (K) content decreased. Glycinebetaine content of shoots increa...

Impact of phosphorus supply on root exudation, aerenchyma formation and methane emission of rice plants

Abstract: This study evaluated the impact of P supply on rice plant development and the methane budget of rice fields by 2 different approaches: (1) root growth, exudation and aerenchyma formation were recorded in an experiment with hydroponic solution; (2) dissolved CH4 concentration and CH4 emission were investigated in a pot experiment. In both approaches, we used three different cultivars and three levels of P supply. In the experiment with solution culture (0.5 ppm, 5 ppm, and 10 ppm P), root exudation ranged between 0.5 to 36.7μmol C plant−1 h−1 and increased steadily with plant growth at given P level. Low P supply resulted in • depressed shoot growth but increased root growth in culture solution. • increments in the root/shoot ratio by factors of 1.4 to 1.9 at flowering stage. • enhanced the development of root aerenchyma, and • stimulation of root exudation per plant by factors of 1.3–1.8 as compared to medium P supply and by factors of 2.1–2.4 as compared to high P supply.

Seed mass versus seedling performance in Scots pine: a maternally dependent trait

Abstract: It is generally accepted that larger seeds give rise to seedlings with better performance. On the other hand, the size that a seed reaches is genetically determined by at least two different traits ; the genetic variability of the developing embryo and the genetic variability of the maternal plant. Thus, the relative contributions of these two traits affect seedling performance by influencing seed size. In this paper, I investigate the effect of seed size on seedling performance in the Scots pine (Pinus sylvestris). From eight maternal plants, 50 seeds were planted in each of two soil types (800 seeds in total), and seedling performance was monitored for 1 yr. Seed mass proved to be highly constant within maternal plants. Soil type influenced emergence and survival; however, the effect of soil type differed depending on maternal origin. Seed mass was positively correlated with seedling emergence, although this relationship was not found for seedling survival or date of emergence. The initial growth of the shoot was also positively correlated with seed mass. However, after one growing season, seed mass had no effect on seedling performance, which depended exclusively on maternal origin. Nevertheless, the mean mass of seeds produced by plants was positively correlated with mean values of growth parameters. Thus, first-year seedling performance seems to be a maternal trait indirectly associated with seed size.

Phialophora graminicola, a dark septate fungus, is a beneficial associate of the grass Vulpia ciliata ssp. ambigua.

Abstract: Seedlings of the annual grass Vulpia ciliata ssp. ambigua were grown in sterilized sand with a dark septate root fungus, Phialophora graminicola, which had been isolated from a natural population of the grass. Tiller number and shoot, root and total biomass of seedlings grown with P. graminicola were enhanced relative to uninoculated control plants in a growth room and a glasshouse experiment. Root length of seedlings grown with P. graminicola was significantly increased, but no effects of the fungus on root diameter, number of root hairs or specific root length were recorded. Root nitrogen content and shoot, root and total phosphorus contents of seedlings grown with the fungus were enhanced, but shoot nitrogen concentration of these plants was reduced. Shoot biomass and specific root length of inoculated plants were positively associated with the number of P. graminicola colonies re-isolated from roots. These data indicate that P. graminicola acts as a beneficial associate of V. ciliata ssp. ambigua seedlings under controlled conditions.

Changes in growth and nitrogen assimilation in barley seedlings under cadmium stress

Abstract: Barley (Hordeum vulgare L. cv. Martin) plants grown in solution culture, were exposed to increasing cadmium (Cd) concentration (0, 5, 10, 25, 50, and 100 μM) for a duration of 12 days. The sequence of important biochemical steps of nitrate (NO3) assimilation were studied in roots and shoots as a function of external Cd concentration. Cadmium uptake in roots and shoots increased gradually with Cd concentration in the medium. This Cd accumulation lowered substantially root and shoot biomass. The nitrate reductase (NR, EC 1.6.6.1) and nitrite reductase (NiR, EC 1.6.6.4) activities declined under Cd stress. Concurrently, tissue NO3 contents and xylem sap NO3 concentration were also decreased in Cd‐treated plants. These results suggest that Cd could exert an inhibitory effect on the assimilatory NO3 reducing system (NR and NiR) through a restriction of NO3 availability in the tissues. We therefore examined, in short‐term experiments (12 h), the impact of Cd on NO3 uptake and the two reductases in nitr...

Effects of mycorrhizal fungus isolates on mineral acquisition by Panicum virgatum in acidic soil

Abstract: Plant ability to withstand acidic soil mineral deficiencies and toxicities can be enhanced by root-arbuscular mycorrhizal fungus (AMF) symbioses. The AMF benefits to plants may be attributed to enhanced plant acquisition of mineral nutrients essential to plant growth and restricted acquisition of toxic elements. Switchgrass (Panicum virgatum L.) was grown in pHCa (soil:10 mM CaCl2, 1 : 1) 4 and 5 soil (Typic Hapludult) inoculated with Glomus clarum, G. diaphanum, G. etunicatum, G. intraradices, Gigasporaalbida, Gi. margarita, Gi. rosea, and Acaulosporamorrowiae to determine differences among AMF isolates for mineral acquisition. Shoots of mycorrhizal (AM) plants had 6.2-fold P concentration differences when grown in pHCa 4 soil and 2.9-fold in pHCa 5 soil. Acquisition trends for the other mineral nutrients essential for plant growth were similar for AM plants grown in pHCa 4 and 5 soil, and differences among AMF isolates were generally higher for plants grown in pHCa 4 than in pHCa 5 soil. Both declines and increases in shoot concentrations of N, S, K, Ca, Mg, Zn, Cu, and Mn relative to nonmycorrhizal (nonAM) plants were noted for many AM plants. Differences among AM plants for N and Mg concentrations were relatively small (<2-fold) and were large (2- to 9-fold) for the other minerals. Shoot concentrations of mineral nutrients did not relate well to dry matter produced or to percentage root colonization. Except for Mn and one AMF isolate, shoot concentrations of Mn, Fe, B, and Al in AM plants were lower than in nonAM plants, and differences among AM plants for these minerals ranged from a low of 1.8-fold for Fe to as high as 6.9-fold for Mn. Some AMF isolates were effective in overcoming acidic soil mineral deficiency and toxicity problems that commonly occur with plants grown in acidic soil.

Growth, flowering, and population dynamics of temperate Western Australian seagrasses

Abstract: Quantification of module size, teat, rhizome and clonal growth flowering intensity and shoot population dynamics of 7 temperate Western Australian seagrasses (Amphibolis antarctica, A. griffithii, Posidonia australis, P. sinuosa, P. angustifolia, Heterozostera tasmanica, Thalassodendron pachyrhizum) developing 8 monospecific stands reveals that these plants have different plant morphologies, display a wide repertoire of growth patterns, and exhibit substantial variability in their capacity to flower. Leaf production rate ranged between 2.6 (P. sinuosa) and 26 leaves yr -1 (A. antarctica), and leaf life-span varied between 85 (A. antarctica) and 245 d (P. sinuosa). Most of the species extended their horizontal rhizomes at rates slower than 10 cm yr 1 . The highest rate of new short shoot formation by vertical rhizomes was observed in A. antarctica (on average each vertical rhizome annually produced 1.5 new short shoots), and the lowest in T pachyrhizum (only 1 new short shoot would be recruited from 65 vertical rhizomes). Horizontal rhizomes produced I new short shoot every 17 (H. tasmanica) or 582 d (P. sinuosa). Flowering intensity varied from 0 (P. sinuosa) to 7% flowering short shoots yr -1 (P. australis). The median age of the short shoots in these populations ranged from 367 (H. tasmanica) to 1000 d (P. sinuosa). Clonal growth was the main mechanism providing short shoots in these temperate Western Australian meadows. Short shoot recruitment balanced short shoot mortality rate in most populations, indicating that they were in steady-state with the colonisation process. These species maintain their meadows through different plant strategies as a result of their different growth programmes and the variability in sexual reproduction success. The large differences in flowering intensity found across temperate Western Australian seagrasses suggest that sexual reproduction may play an important role for meadow maintenance anti recovery.

Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources.

Abstract: 1. It is claimed that the quality of foliage following defoliation depends on carbon/nutrient balance of the tree. To study the importance of sink/source regulation for the quality of foliage, as well as for its quantity, Pinus sylvestris trees were defoliated and fertilized both in southern Finland and at the tree line in northern Finland. 2. The pattern of defoliation in a shoot was more decisive for quantitative changes in new foliage than its extent: removal of similar amounts of foliage from different branch parts led to different outcomes. 3. Defoliation of 50% spread evenly within a shoot, or applied to the basal part of a shoot only, did not alter production of new foliage, whereas defoliation applied to the apical part of a shoot decreased the mass and length of needles in the new shoot. Defoliation of apically located 1-year-old needles of the branch leader shoot, but not of 2-year-old ones, significantly reduced the mass and length of needles in new shoots. 4. These results are consistent with the explanation that damage alters the ability of shoots and branches to form strong meristematic sinks and that sink strength determines the ability of these meristems to draw resources from the common pool of the tree. 5. Defoliation of the main photosynthate source lowered concentrations of the fructose and glucose, indicating shortage of carbon. However, whole-tree defoliation did not affect the concentrations of individual foliar sugars. 6. Traits describing pine shoot growth correlated negatively with foliar phenolic concentrations but not with concentrations of other secondary compounds. Concentrations of foliage phenolics consistently increased after defoliation, while terpenoids, putatively the main class of defensive compounds in Scots Pine, did not respond to defoliation. Defoliation of a branch or a whole tree had only slight effects on the concentrations of fibre, mono- and sesquiterpenes, resin acids or nitrogen. 7. Likewise, fertilization significantly increased the concentration of some sesquiterpenes only in pine foliage. Whole-branch defoliation and fertilization together had no effect on the concentration of fibre or nitrogen in pine foliage. 8. Altogether, the amount of foliar biomass removed, nutrients or carbon did not explain in any consistent way the qualitative changes in the pine foliage. Instead, results were consistent with simple physiological dependence of foliar traits on sink strength. Production of terpenoids reflected increased sink strength, but the production of phenolics was negatively correlated with sink strength. 9. The difference between shoot growth characteristics and foliage concentrations of phenolics and, on the other hand, terpenoids, may have a biosynthetic, instead of an ecological or evolutionary explanation. Protein synthesis, and thereby possibilities for growth, competes with phenolic synthesis (via phenylalanine) but not with terpenoid synthesis. 10. These results indicate that in Scots Pine the predicted trade-off between growth and production of pooled carbon-rich secondary compounds was found in phenolics but presumably for reasons external to the carbon/nutrient balance and growth/differentiation balance hypotheses. Instead, terpenoids did not behave as predicted by these theories.

Enhanced UV-B radiation under field conditions increases anthocyanin and reduces the risk of photoinhibition but does not affect growth in the carnivorous plant Pinguicula vulgaris

Abstract: The effects of enhanced UV-B radiation were investigated in the carnivorous plant Pinguicula vulgaris in a field experiment performed in Abisko, North Sweden (68° 21′ N, 18° 49′ E, 380 m above sea level). Potted plants were exposed to either ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion. No effect was observed on either the epicuticular (external) or cellular (internal) UV absorbing capacity of the leaves. However, the anthocyanin content was more than doubled by supplemental UV-B radiation. In laboratory experiments, the anthocyanin rich, UV-B treated leaves were less susceptible to a low temperature/high light photoinhibitory treatment, as judged by in vivo chlorophyll fluorescence measurements. Yet, this potential benefit did not considerably affect the growth of the plant in the field (leaf area and dry mass, reproductive dry mass, flowering frequency, senescence rates, dry mass of winter buds). However, there was a marginally significant increase in root dry mass and in the root to shoot ratio, which may underlie the significant increase in the nitrogen content of the leaves. We suggest that P. vulgaris is resistant against UV-B radiation damage and that the possible negative effects of additional UV-B radiation on the growth of these plants may have been effectively counterbalanced by the lower risk of photoinhibition, due to the concomitant increase in anthocyanins.