SEARCH · PubMed Health

Results for “Seedlings”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2003

Photosynthate distribution patterns in cherrybark oak seedling sprouts.

We used 14C tracers to determine photosynthate distribution in cherrybark oak (Quercus pagoda Raf.) seedling sprouts following release from competing mid-story vegetation. Fall acquisition of labeled photosynthates by seedlings followed expected source-sink patterns, with root and basal stem tissues serving as the primary sinks. Four months after the seedlings had been labeled with 14C, they were clipped to induce sprouting. First-flush stem and leaf tissues of the resulting seedling sprouts were the primary sinks for labeled photosynthates stored in root tissues. Second-flush stem and leaf tissues, and first-flush stem and leaf tissues the following growing season, were not primary sinks for labeled photosynthates stored in root tissues despite the high radioactivity in root tissues. Root tissues appeared to deposit photosynthates in a layering process whereby the last photosynthates stored in new xylem were the first to be depleted during the initiation of a growth flush the following spring. There were more labeled photosynthates in roots of released seedling sprouts compared with non-released seedling sprouts, indicating increased vigor of released seedling sprouts in response to greater light availability. In contrast, stem and source leaf tissues of non-released seedling sprouts contained greater percentages of labeled photosynthates compared with released seedling sprouts, indicating either greater sink strength or poorly developed xylem and phloem pathways that created inefficiencies in distribution to root tissues. The 14C distribution coefficients confirmed the distribution patterns and provided additional information on the important sinks in released and non-released cherrybark oak seedling sprouts.

Photosynthesis↗

PubMed2005

Does proximity to mature trees influence ectomycorrhizal fungus communities of Douglas-fir seedlings?

The influence of mature trees on colonization of Douglas-fir (Pseudotsuga menziesii) seedlings by ectomycorrhizal fungi (EMF) is not well understood. Here, the EMF communities of seedlings planted near and far from trees are compared with each other, with EMF of seedlings potted in field soils and with EMF of mature trees. Seedlings were planted within 6 m, or beyond 16 m, from residual Douglas-fir trees in recently harvested green-tree retention units in Washington State, USA, or potted in soils gathered from near each residual tree. Mature tree roots were sampled by partly excavating the root system. The EMF communities were assessed by polymerase chain reaction-restriction fragment length polymorphism and sequence analysis of ribosomal RNA genes. Seedlings near trees had higher species richness and diversity of EMF communities compared with seedlings far from trees. The EMF communities of seedlings near trees were more similar to those of mature trees, while seedlings far from trees were more similar to glasshouse seedlings. By enhancing the EMF diversity of seedlings, residual trees may maintain or accelerate the re-establishment of mycorrhizal communities associated with mature forests.

Ecosystem↗

PubMed2000

Influence of insect larvae and seedling roots on the host-finding ability of Steinernema feltiae (Nematoda: Steinernematidae).

The ability of nematode foragers to locate appropriate insect hosts is essential to their performance as successful biological control agents. We investigated the host-finding ability and chemotaxis of Steinernema feltiae in the presence of cues from Galleria mellonella larvae and tomato and radish seedling roots, given individually and in combination, over 120 min. In agar arena tests, infective juveniles of S. feltiae responded positively to unsterilized and sterilized larvae and tomato seedling roots and negatively to unsterilized radish seedling roots. This negative response changed following surface sterilization of these seeds. The response of the infective juveniles to a combination of larva and seedling roots depended on the nature of the individual cues and their proximity to each other. For example, the response of the nematodes to a combination of cues from a sterilized larva and an unsterilized tomato seedling root placed adjacent to each other was intermediate to the separate responses to cues from a sterilized larva and an unsterilized tomato seedling root given individually. However, the response of the nematodes to a combination of adjacent cues from a sterilized larva and an unsterilized radish seedling root was not significantly different from that to cues from an unsterilized radish seedling root given individually. When the cues from the larva and seedling roots were separated by a distance, the response of the nematodes favored the larva. However, this positive effect was lessened when the larva was surface sterilized as compared with the response to the unsterilized larva. The altered responses of the infective juveniles to target cues following surface sterilization suggest that cues from the larval cuticle and seedling roots, such as those associated with their surface microflora, may significantly influence their host-finding ability. The use of entomopathogenic nematodes as biological control agents under field applications can be improved by careful consideration of the application protocols and by the recognition that chemical alterations of the soil rhizosphere may influence their host-finding ability.

Animals↗

PubMed2002

Molecular dissection of seedling-vigor and associated physiological traits in rice.

seedling-vigor is important for crop establishment. There have been reported quantitative trait locus (QTL) analyses on seedling-vigor related morphological traits. However, physiological understanding of these detected QTLs is rather limited. In this study, we employed a recombinant inbred population to detect QTLs for seedling-vigor traits and physiological traits related to seedling-vigor. Germination rate and seedling growth were measured to quantify seedling-vigor. Total amylase activity, alpha-amylase activity, reducing sugar content, root activity and seed weight were determined. Correlations were observed between the seedling-vigor and physiological traits. QTL analysis reveals that the intervals of RG393-C1087-RZ403 on chromosome 3, C246-RM26-C1447 and R830-R3166-RG360-C734b on chromosome 5, and the interval of Waxy on chromosome 6 are the four main chromosomal regions controlling seedling-vigor. Several QTLs for amylase activities, reducing sugar content and root activity were localized in the similar regions as the QTLs for seedling-vigor. The results suggest that these traits were under the control of pleiotropic and/or closely linked QTLs. The implications of the results in the understanding of the physiological basis of seedling-vigor were discussed.

Journal Article↗

PubMed2003

Overproduced ethylene causes programmed cell death leading to temperature-sensitive lethality in hybrid seedlings from the cross Nicotiana suaveolens x N. tabacum.

Reproductive isolation mechanisms (RIMs) often become obstacles in crossbreeding. Hybrid lethality is a subtype of RIM but its physiological mechanism remains poorly elucidated. Interspecific hybrids of Nicotiana suaveolens Lehm. x N. tabacum L. cv. Hicks-2 expressed temperature-sensitive lethality. This lethality was induced by programmed cell death (PCD) that was accompanied by the characteristic changes of animal apoptosis in hybrid seedlings at 28 degrees C but not at 36 degrees C. When hybrid seedlings were cultured at 28 degrees C, DNA fragmentation started in the cotyledon, and nuclear fragmentation subsequently progressed with lethal symptoms spreading throughout the seedlings. At 28 degrees C, ethylene production in hybrid seedlings was detectable at a high level compared with the level in parental seedlings. In contrast, the ethylene production rate in hybrid seedlings cultured at 36 degrees C was equal to that in parental seedlings. Treatment with ethylene biosynthetic inhibitors, amino-oxyacetic acid and amino-ethoxyvinyl glycine, suppressed lethal symptoms and apoptotic changes, and also prolonged survival of hybrid seedlings. Thus, the increase in the ethylene production rate correlated closely with expression of lethal symptoms and apoptotic changes in hybrid seedlings. From these observations, we conclude that overproduced ethylene acts as an essential factor mediating PCD and subsequent lethality in hybrid seedlings. Furthermore, the present study has provided the first evidence that ethylene is involved in the phenomenon of hybrid lethality.

Aminooxyacetic Acid↗

PubMed1994

Interaction of ozone exposure and Fusarium subglutinans inoculation on growth and disease development of loblolly pine seedlings.

Seedlings from ten half-sib families of loblolly pine (Pinus taeda) were exposed in open-top chambers to carbon-filtered air (CF), non-filtered air (NF), or air amended with ozone to 1.7 or 2.5 times ambient. After 105 days of exposure, half the seedlings within each family were wounded but not inoculated and half were wounded and inoculated with the pitch canker fungus, Fusarium subglutinans, to which five families were relatively resistant. After an additional 50 days of ozone treatment, seedling growth and canker development were recorded. Cankers were significantly (sigma < or = 0.05) smaller among resistant compared to susceptible families, and were significantly larger among seedlings receiving the highest (2.5) compared to the ambient (NF) ozone treatment. The wound scars of non-inoculated seedlings were also significantly larger among seedlings receiving the 2.5 compared to the NF treatment, but these dimensions did not differ significantly with seedling family or resistance. The weights of needles and large roots were significantly smaller at the 2.5 compared to the 1.7 ozone treatment for inoculated but not for non-inoculated seedlings; this resulted in a significant interaction for ozone and inoculation effects. Among resistant families, root weights were significantly smaller for inoculated seedlings. Diameter growth and dry weights of needles were significantly smaller among inoculated compared to non-inoculated seedlings, but did not differ between NF and 2.5 ozone treatments.

Journal Article↗

PubMed1994

90Sr uptake by Pinus ponderosa and Pinus radiata seedlings inoculated with ectomycorrhizal fungi.

Strontium-90 ((90)Sr) is a radionuclide characteristic of fallout from nuclear reactor accidents and nuclear weapons testing. Prior studies have shown that Pinus ponderosa and P. radiata seedlings can remove appreciable quantities of (90)Sr from soil and store it in plant tissue. In this study, we inoculated P. ponderosa and P. radiata seedlings with one of five isolates of ectomycorrhizal fungi. Inoculated and noninoculated (control) seedlings were compared for their ability to remove (90)Sr from an organic growth medium. Seedlings were grown in a growth chamber in glass tubes containing 165 cm(3) of sphagnum peat moss and perlite (1 : 1 (v/v)) and, except in the controls, the fungal inoculum. After 3 months, 5978 Bq of (90)Sr in 1 ml of sterile, distilled, deionized water was added. Seedlings were grown for an additional month and then harvested. P. ponderosa seedlings with ectomycorrhizae accumulated 3.0-6.0% of the (90)Sr; bioconcentration ratios (Bq (90)Sr cm(-3) plant tissue/Bq (90)Sr cm(-3) growth medium) ranged from 98-162. Ectomycorrhizal P. radiata seedlings accumulated 6.0-6.9% of the (90)Sr; bioconcentration ratios ranged from 88-133. Nonmycorrhizal P. ponderosa and P. radiata seedlings accumulated only 0.6 and 0.7% of the (90)Sr and had bioconcentration ratios of 28 and 27, respectively. Ectomycorrhizal P. ponderosa and P. radiata seedlings are able to remove 3-5 times more (90)Sr from contaminated soil than seedlings without ectomycorrhizae.

Journal Article↗

PubMed2000

Stress indications in copper- and nickel-exposed Scots pine seedlings.

Scots pine nursery seedlings were planted in pots, five seedlings per treatment, and placed in an experimental field at the University of Oulu in northern Finland at the beginning of June 1997. Copper and nickel sulphates were mixed with forest mineral soil before seedling planting. The metal levels ranged from 0 to 25 mg Ni kg(-1) dry soil and 0 to 50 mg Cu kg(-1) in dry soil and in combinations of both metals. Current year's needles for element analyses, EDS microanalyses, microscopy and glutathione and peroxidase activity analyses were collected from 1-5 seedlings per treatment in September. Seedling biomass in controls, Cu25 and Cu50 differed significantly from the Ni25Cu50 treatment. The root/shoot ratio was highest in the Ni5 treatment, indicating good root growth, though the roots were visibly healthier in the Cu25 treatment than in the Ni5 treatment. At higher Ni levels, the condition of roots deteriorated. The proportion of plasmolysed mesophyll cells was highest in the Ni25 treatment. Copper-treated seedlings did not suffer from Cu stress, because no severe injuries were seen in either the roots or the needles in Cu-exposed seedlings. The needle concentrations of Cu increased only slightly due to treatments. Ni accumulation in needles increased with increasing concentrations in soil. Needles of Cu-treated seedlings had less oxidized glutathione than those of Ni-treated seedlings, but the roots had higher, not significantly, peroxidase activity levels. Light-colored, swollen thylakoids were occasionally observed in the Ni25Cu50 treatment, indicating some interaction between Ni and Cu. Ni seemed to cause more oxidative stress to the seedlings than copper, which was manifested as a decreased GSH level and an increased proportion of GSSG in the Ni treatments. Copper together with nickel strongly decreased root growth, the root/shoot ratio being lowest in the Ni25Cu50 treatment.

Journal Article↗

PubMed2002

Influence of litter and weather on seedling recruitment in a mixed oak-pine woodland.

The effects of regular litter removal and annual variation in temperature and precipitation on seedling recruitment of species differing in their seed size and mode of dispersal were studied in a 16-year (1984-1999) experiment in a mixed oak-pine wood in southern Poland. Litter was the most important factor in determining spatial variability in seedling recruitment, whereas differences in climatic conditions among years, especially temperature fluctuations in late winter and early spring, determined the temporal variability in seedling recruitment. Compared with control plots, significantly more new individuals of bryophytes and seedlings as well as a number of new species of vascular plants were noted in the litter-removal plots over the 16-year study. Litter strongly impeded seedling emergence of small-seeded species. The negative effect of litter on seedling recruitment of large-seeded species and the recruitment of new shoots in species growing clonally was much weaker. There was a significant positive correlation between the numbers of seedlings in the litter-removal and control plots and temperatures in January to March. In the litter-removal plots this mainly affected small-seeded species. Seedling recruitment was less consistently related to variation in precipitation. Positive relationships were found only between the number of seedlings of large-seeded species in the litter-removal plots and precipitation in July of the current year and in September of the previous year, and between the number of seedlings in the control plots and precipitation in September and November of the previous year.

Bryopsida↗

PubMed2000

Abscisic acid and hypoxic induction of anoxia tolerance in roots of lettuce seedlings.

Lettuce (Lactuca sativa L.) seedlings were subjected to anoxic stress after ABA-pretreatment (ABA-PT) or hypoxic-pretreatment (H-PT). The H-PT increased the survivability of the anoxia in roots of the seedlings by 5.2-fold compared to that of non-pretreated (N-PT) seedlings. ABA-PT also increased the survivability at concentrations greater than 1 microM, and the survivability increased with increasing ABA doses. At 100 microM ABA, the survivability was 4.5-fold greater than that of N-PT seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots became 3.1- and 3.4-fold greater than that of N-PT seedlings following 100 microM ABA-PT and H-PT seedlings, respectively. After the onset of anoxic stress, ADH activities in all roots increased, but the activities in H-PT and ABA-PT roots remained much greater than that in N-PT roots, and the average ethanol production rate for the initial 6 h was 5.3, 4.0 and 1.4 micromol g(-1) FW h(-1) for H-PT, ABA-PT and N-PT roots, respectively. Roots of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the ABA-PT and H-PT seedlings than in the N-PT seedlings. These results suggest that the ABA-PT and H-PT may maintain ATP levels due to activation of ethanolic fermentation, which may be one of the causes of the increasing anoxia tolerance in the seedling roots. Measurement of endogenous ABA levels, however, showed that ABA levels did not increase during the H-PT, suggesting that the H-PT does not increase tolerance through an increase in ABA levels.

Abscisic Acid↗

PubMed1992

Water relations and gas exchange of Acer saccharum seedlings in contrasting natural light and water regimes.

Field measurements were made of leaf photosynthesis (A), stomatal conductance (g) and leaf water relations for sugar maple (Acer saccharum Marsh.) seedlings growing in a forest understory, small gap or large clearing habitat in southwestern Wisconsin, USA. Predawn water status, leaf gas exchange and plasticity in field and laboratory water relations characteristics were compared among contrasting light environments in a wet year (1987) and a dry year (1988) to evaluate possible interactions between light and water availability in these habitats. Leaf water potentials (Psi(leaf)) at predawn and midday were lower for clearing than gap or understory seedlings. Acclimation of tissue osmotic potentials to light environment was observed among habitats but did not occur within any of the habitats in response to prolonged drought. During a summer drought in 1988, decreases in daily maximum g (g(max)) and maximum A (A(max)) in clearing seedlings were correlated with predawn Psi(leaf), which reached a seasonal minimum of -2.0 MPa. Under well-watered conditions, diurnal fluctuations in Psi(leaf) of up to 2.0 MPa in clearing seedlings occurred along with large midday depressions of A and g. In a wet year, strong stomatal responses to leaf-to-air vapor pressure difference (VPD) in sunny habitats were observed over nine diurnal courses of gas exchange measurements on seedlings in a gap and a clearing. Increasing stomatal limitations to photosynthesis appeared to be responsible for the reduction in A at high VPD for clearing seedlings. In understory seedlings, however, low water-use efficiency and development of leaf water deficits in sunflecks was related to reduced stomatal limitations to photosynthesis relative to seedlings in sunny habitats. Predawn Psi(leaf) and VPD appear to be important factors limiting carbon assimilation in sugar maple seedlings in light-saturating irradiances, primarily through stomatal closure. The overall results are consistent with the idea that sugar maple seedlings exhibit "conservative" water use patterns and have low drought tolerance. Leaf water relations and patterns of water use should be considered in studies of acclimation and species photosynthetic performance in contrasting light environments.

Journal Article↗

PubMed1993

Growth and nutrition of nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings under phosphorus limitation.

The association of ectomycorrhizal fungi with tree roots enhances the acquisition of phosphorus (P) from the soil. In addition to increasing the uptake of H(2)PO(4) (-) (P(i)), mycorrhizal fungi may increase the spectrum of P sources utilized by tree roots by mediating the dissolution of insoluble metallophosphate salts or the hydrolysis of organic P compounds. To investigate the role of ectomycorrhizal fungi in enhancing P acquisition by tree roots, pitch pine (Pinus rigida Mill.) seedlings were grown in sand culture with or without the ectomycorrhizal symbiont Pisolithus tinctorius Coker and Couch under various conditions of P limitation. Compared with nonmycorrhizal seedlings, seedlings inoculated with P. tinctorius exhibited a greater capacity to function under P limitation as evidenced by superior growth and the maintenance of normal foliar ion composition at low P(i) concentrations. Nonmycorrhizal seedlings subjected to P-limiting conditions exhibited depressed K and P and elevated Na concentrations in foliage. The association of P. tinctorius with pitch pine seedling roots maintained foliar K concentrations and prevented the accumulation of Na under P limitation. Nonmycorrhizal seedlings were unable to obtain P from either solid AlPO(4) or inositol hexaphosphate (IHP), whereas seedlings inoculated with P. tinctorius utilized AlPO(4), but not IHP as a P source. Root surface acid phosphatase (APase) activity was depressed in roots infected with the mycorrhizal symbiont and was negatively correlated with seedling growth on all P sources. Root APase activity was negatively correlated with foliar P concentrations in seedlings grown on P(i), but was not correlated with foliar P concentrations in seedlings cultured with AlPO(4) or IHP.

Journal Article↗

PubMed1996

Growth, water relations and solute accumulation in osmotically stressed seedlings of the tropical tree Colophospermum mopane.

Root and hypocotyl elongation, water status and solute accumulation were studied in osmotically stressed seedlings of the tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard, which grows in hot arid areas of southern and central Africa. Seeds were imbibed for 24 h and then subjected to a polyethylene-glycol-generated osmotic stress of -0.03 (control), -0.2, -0.8, -1.6 or -2.0 MPa for 60 h. Seedlings subjected to moderate water stress (-0.2 MPa) had higher root growth rates (2.41 +/- 0.24 mm h(-1)), greater final root lengths (111 +/- 3.8 mm) and longer cells immediately behind the root elongation zone than control seedlings (1.70 +/- 0.15 mm h(-1) and 93 +/- 3.9 mm, respectively). Root lengths of seedlings in the -0.8 and -1.6 MPa treatments were similar to those of control seedlings, whereas the -2.0 MPa seedlings had significantly shorter roots. Both root and hypocotyl tissues exhibited considerable osmotic adjustment to the external water potential treatments. Seedlings in the -0.03, -0.2, and -0.8 MPa treatments had similar cell turgor pressures (0.69 +/- 0.10, 0.68 +/- 0.07 and 0.57 +/- 0.04 MPa, respectively), whereas the -2.0 MPa treatment lowered cell turgor pressure to 0.17 +/- 0.04 MPa. Root vacuolar osmotic pressures were generally similar to sap osmotic pressures, indicating that the increased root elongation observed in moderately water-stressed seedlings was not caused by increased turgor pressure difference. Neutral-fraction solute concentrations, including the osmoticum pinitol, increased approximately two-fold in root sap in response to a low external water potential. In hypocotyl sap of seedlings in the -2.0 MPa treatment, pinitol more than doubled, sucrose increased from about 2 to 75 mol m(-3) but glucose and fructose remained unchanged and, as a result, total sugars increased only slightly. The benefits of rapid early root elongation and osmoticum accumulation under conditions of water stress are discussed in relation to seedling establishment.

Journal Article↗

PubMed1997

Seasonal photosynthetic responses to light and temperature in white spruce (Picea glauca) seedlings planted under an aspen (Populus tremuloides) canopy and in the open.

Photosynthetic light and temperature response curves were measured seasonally in seedlings of white spruce (Picea glauca (Moench.) Voss) grown for two years in the understory of aspen (Populus tremuloides Michx.) or in the open in central Alberta. Light-saturated rate of net photosynthesis, the optimum temperature for net photosynthesis, transpiration rate, photochemical efficiency, and stomatal and mesophyll conductances increased from spring to summer and declined thereafter, whereas dark respiration rate and compensation and saturation points were highest in spring. Depression of photosynthetic parameters was greater in open-grown seedlings than in understory seedlings during the periods in spring and autumn when night frosts were common. Net photosynthetic rates were similar in understory and open-grown seedlings in summer, but they were significantly lower in open-grown seedlings in spring and autumn. Significantly lower transpiration rates and stomatal conductances in open-grown seedlings than in understory seedlings were also observed at 15 and 25 degrees C in the autumn. Shoot and needle growth were less in open-grown seedlings than in understory seedlings. In summer, when irradiances were low in the aspen understory, understory white spruce seedlings maintained a positive carbon balance by decreasing their compensation and saturation points and increasing their photochemical efficiency compared to spring and autumn.

Journal Article↗

PubMed2000

Effects of nitrogen source and defoliation on growth and biological dinitrogen fixation of Gliricidia sepium seedlings.

Effects of four N sources and two defoliation treatments on growth and nitrogenase activity of Gliricidia sepium (Jacq.) Walp seedlings were studied in a greenhouse. All nutrients were supplied in irrigation water to the sterile growing medium. The N sources were: (1) 100 mg l(-1) of N supplied as NO(3) (-) (high-NO(3) (-)), (2) 50 mg l(-1) of N supplied as NO(3) (-) and inoculation with Rhizobium spp. medium-NO(3) (-)), (3)100 mg l(-1) of N supplied as NH(4)NO(3), and (4) inoculation with Rhizobium spp without mineral N (N(2)). At 35 weeks after sowing, mean total biomass was 130.5, 50.5, 22.9 and 17.4 g seedling(-1) in the NH(4)NO(3), N(2), medium-NO(3) (-) and high-NO(3) (-) treatments, respectively. The root/shoot ratio was high in all of the N treatments (1.73-2.77) because the seedlings had big taproots. The medium-NO(3) (-) treatment completely inhibited nodulation, whereas seedlings in the N(2) treatment were profusely nodulated. At 32 weeks after sowing, groups of seedlings in the N(2) and high-NO(3) (-) treatments were subjected to 50 or 100% defoliation. Closed-chamber acetylene reduction assays of intact root systems were conducted to compare nitrogenase activity at 7, 14 and 28 days after defoliation (DAD). At 7 and 14 DAD, nitrogenase activity of completely and partially defoliated seedlings was about 10 and 60%, respectively, of that of undefoliated controls. At 28 DAD, nitrogenase activity of completely defoliated seedlings was twice the predefoliation value, whereas nitrogenase activity of partially defoliated seedlings was only 87% of the predefoliation value. Recovery of nitrogenase activity was strongly correlated with foliage regrowth in the completely defoliated seedlings, but not in the partially defoliated seedlings. Abundant belowground C and N reserves in the large taproot probably contributed to the rapid recovery from defoliation. Accumulation of belowground biomass may also improve defoliation tolerance of mature trees.

Journal Article↗

PubMed2001

Role of boron in drought resistance in Norway spruce (Picea abies) seedlings.

Norway spruce (Picea abies (L.) Karst.) seedlings fertilized with boron (B) at three rates were grown in a 3:7 mix of forest humus and quartz sand for 18 weeks. Half of the seedlings were not watered during the last 9 days of the experiment (drought treatment). The role of B in drought resistance was assessed by comparing the effects of seedling internal B concentration on the water relations, photosynthesis, growth and nutrition of well-watered and drought-treated seedlings. At the end of the drought treatment, needle B concentrations were 7.0 mg x kg(-1) at the lowest B supply rate and 17.5 and 23.5 mg x kg(-1), respectively, at the higher supply rates. Seedlings at the lowest B supply rate had fewer root tips and mycorrhizas than seedlings at the higher B supply rates. Drought treatment had a more pronounced effect on the water relations and net photosynthetic rate of seedlings than B treatment. Although seedlings at the higher B supply rates lost water more rapidly than seedlings at the low B supply rate-leading to faster stomatal closure and decreased photosynthesis-drought did not affect their final height, whereas drought reduced height growth of seedlings at the low B supply rate.

Boron↗

PubMed1987

Activities of isolated mitochondria and mitochondrial enzymes from aerobically and anaerobically germinated barnyard grass (echinochloa) seedlings.

Activity of mitochondria isolated from whole seedlings of Echinochloa crus-galli (L.) Beauv. var oryzicola germinated under aerobic and anaerobic conditions for 5 to 7 days was investigated. Mitochondria from both treatments exhibited good respiratory control and ADP/O ratios. Although O(2) uptake was low in anaerobic mitochondria, activity rapidly increased when the seedlings were transferred to air. Mitochondria from both aerobically and anaerobically grown seedlings of E. crus-galli var oryzicola maintained up to 66% of their initial respiration rate in the presence of both cyanide and salicylhydroxamic acid, and the inhibitory effects of cyanide and azide were additive. In addition, antimycin A was not an effective inhibitor of respiration. Reduced-minus-oxidized absorption spectra revealed that cytochromes a, a(3), and b were reduced to a greater extent and cytochrome c was reduced to a lesser extent in anaerobically germinated seedlings relative to that in aerobically germinated seedlings. An absorption maximum in the cytochrome d region of the spectrum was reduced to the same extent under both germination conditions and an absorption maximum at 577 nm was present only in anaerobically germinated seedlings. Anaerobically germinated seedlings contained 70% of the cytochrome c oxidase activity found in air grown seedlings. Upon exposure to air, the developmental pattern of this enzyme in anaerobically germinated seedlings was similar to air controls. Succinate dehydrogenase activity in anaerobic seedlings was only 45% of the activity found in aerobically germinated seeds, but within 1 hour of exposure to air, the activity had increased to control levels. The results suggest that mitochondria isolated from E. crus-galli var oryzicola differ from other plants studied and that the potential for mitochondrial function during anaerobiosis exists.

Journal Article↗

PubMed2005

Soil modification by different tree species influences the extent of seedling ectomycorrhizal infection.

Established vegetation can facilitate the ectomycorrhizal infection of seedlings, but it is not known whether this interaction is limited by the phylogenetic relatedness of trees and seedlings. We use a series of bioassay experiments to test whether soil modification by different ectomycorrhizal tree species causes different levels of seedling infection, whether the extent of seedling infection is a function of the relatedness of tree and seedling, and whether the effect of trees on seedlings is mediated by biotic or abiotic soil factors. We found that soils from under different tree species do vary in their mycorrhizal infectiveness. However, this variation is not related to the genetic relatedness of trees and seedlings but instead, appears to be an attribute of the overstory species, irrespective of seedling species, mediated through a suite of humus- and base-cation-related abiotic effects on soils. Modification of abiotic soil properties by overstory trees should be considered as an important factor in the effect of different overstory trees on the extent of seedling mycorrhizal infection.

Ecosystem↗