Showing papers on "Shoot published in 1986"

The partitioning of nitrate assimilation between root and shoot of higher plants

Abstract: The partitioning of nitrate assimilation between root and shoot of higher plant species is indicated by the relative proportions of total plant nitrate reductase activity (NRA) in the two plant parts and the relative concentrations of nitrate and reduced N in the xylem sap. These have been collated here from the literature and temperate and tropical species compared. Both the distribution of NRA and xylem sap nitrate: reduced N indicate that the following four generalizations can be made. 1Temperate, perennial species growing in low external nitrate concentrations (about 1 mol m−3) carry out most of their nitrate assimilation in the root. As external nitrate concentration increases (in the range found in agricultural soils, 1–20 mol m−3), shoot nitrate assimilation becomes increasingly important. 2Temperate, annual legume species growing in low external nitrate concentrations carry out most of their nitrate assimilation in the root. Shoot nitrate assimilation increases in importance as external nitrate concentration is increased. 3Temperate, annual non-legume species vary greatly in their partitioning of nitrate assimilation between root and shoot when growing in low external nitrate concentrations. Regardless of the proportion carried out in the root at low external nitrate concentrations, nitrate assimilation in the shoot becomes increasingly important as external nitrate concentration is increased. 4Tropical and subtropical species, annual and perennial, carry out a substantial proportion of their nitrate assimilation in the shoot when growing in low external nitrate concentrations. The partitioning of nitrate assimilation between root and shoot remains constant as external nitrate concentration increases. It is proposed that a greater proportion of nitrate assimilation occurs in the shoot when an increase in the rate of nitrate uptake does not induce an increase in NR level in the root. Thus, a greater proportion of the nitrate taken up remains unassimilated and is passed into the xylem. A constant partitioning of nitrate assimilation between root and shoot is achieved by balancing NR levels in the root with rates of nitrate uptake. The advantages and disadvantages of assimilating nitrate in either the root or shoot are discussed in relation to temperate and tropical habitats.

Regulation of the Soybean-Rhizobium Nodule Symbiosis by Shoot and Root Factors

Abstract: The availability of soybean mutants with altered symbiotic properties allowed an investigation of the shoot or root control of the relevant phenotype. By means of grafts between these mutants and wild-type plants (cultivar Bragg and Williams), we demonstrated that supernodulation as well as hypernodulation (nitrate tolerance in nodulation and lack of autoregulation) is shoot controlled in two mutants (nts382 and nts1116) belonging most likely to two separate complementation groups. The supernodulation phenotype was expressed on roots of the parent cultivar Bragg as well as the roots of cultivar Williams. Likewise it was shown that non-nodulation (resistance to Bradyrhizobium) is root controlled in mutant nod49. The shoot control of nodule initiation is epistatically suppressed by the non-nodulation, root-expressed mutation. These findings suggest that different plant organs can influence the expression of the nodulation phenotype.

Input of carbon to soil from wheat plants

Abstract: The growth of wheat plants and the distribution of labelled photosynthate from pulse-labelling with 14CO2 were measured periodically during the growing season in the field. During early growth there was approximately the same proportion of photosynthate translocated below ground and retained in the shoots. Of the 14C below ground about a half was respired and a quarter each was in the soil and roots. This distribution changed exponentially during growth with an increasing proportion of 14C remaining in the shoots and a corresponding decreasing proportion being translated below ground, which was only a few percent by flowering. From this information the total input of carbon to the soil from the crop was calculated to be 1305 kg Cha−1. Comparison of these estimates with those from previous experiments suggest that differences do occur due to the stage of growth of the plant, the environmental conditions, soil type and microbial activity.

Plant regeneration from protoplast-derived callus of rice (Oryza sativa L.).

Abstract: Protoplasts isolated from cultured rice cells of an A-58 cytoplasmic male sterile line (A-58 MS)(Oryza sativa L.) were used to investigate the regeneration of rice plants. A cultured cell line (T3) of A-58 MS with a high growth rate and dense cytoplasm was selected. About 10% of the protoplasts prepared from this established cell line plated in RY-2 (a new medium) formed colonies. The calli formed shoots and roots in the regeneration medium and developed into whole plants.

Salt-Induced Damage to Rice Plants and Alleviation Effect of Silicate

Abstract: Rice plants were grown hydroponicaIly in the presence of either NaCI, sea water, or polyethylene glycol (PEG: average molecular weights of 7,800–9,000) at an osmotic potential of up to 186 mOsmol/kg, equivalent to 100 mM NaCI or 20% sea water, and the growth and mineral composition of the plants were compared. NaCI was the most detrimental agent, followed by sea water and PEG. Mineral contents, including nitrogen, phosphorus, potassium, and calcium were not significantly affected by the treatments. Removal of silicate from the culture solution brought about a more severe growth reduction in rice plants subjected to 100 mM NaCI stress. In the plants which received silicate, the contents of sodium in the shoots were nearly half of those in the shoots of plants which did not receive silicate.

Genotypic variability for callus formation and plant regeneration in rice (Oryza sativa L.).

Abstract: Sixty rice varieties (Oryza sativa L.), belonging to three subspecies, japonica, indica and javanica (some japonicaXindica hybrids were included), were compared for their capacity for callus growth and plant regeneration. Tissue cultures initiated from mature seeds on Murashige and Skoog's (1962) medium with 2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) were transferred to a medium containing 0.02 mg/l 2,4-D and 10 mg/l kinetin, from which plantlets were regenerated. Large variabilities in callus growth and plant regeneration potentials were revealed among the varieties tested. Most japonica varieties formed a callus that weighed more than 100 mg per seed 30 days after inoculation, and showed a relatively high regenerative potential, whereas indica varieties, japonica-indica hybrids and javanica varieties showed poor callus growth and plant regeneration, although considerable varietal variation was observed in each subspecies. The callus growth potential was not correlated with the plant regeneration potential. Histological observations revealed that the epithelium cells of the scutellum mainly proliferated to form a callus, from which shoot and root primordia were differentiated independently from each other. The shoot primordia developed into plantlets when roots were formed adventitiously. In a few cases, shoots and roots were bilaterally initiated from a single primordium.

The effect of root temperature on the uptake of nitrogen and the relative size of the root system in Lolium perenne. I. Solutions containing both NH+4 and NO3−

Abstract: Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH4+, NO3− and K+ were frequently monitored and adjusted to set values. In a pre-experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C. When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature-dependent, steady value (phase 2). The fresh: freeze-dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1). In both growth phases and at all temperatures, plants absorbed more NH4+ than NO4+, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH4+. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH4+. Specific absorption rates for NH4+, NOx−, K+ and H2PO4− showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2. The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes.

Carbon-nitrogen interactions in CO2-enriched white oak: physiological and long-term perspectives

Abstract: Summary The responses of forest trees to atmospheric CO, enrichment will depend in part on carbon-nutrient linkages. Insights into the possible long-term ecological consequences of CO? enrichment can be gained from studying physiological responses in short-term experiments. One-year-old white oak (Quercus alba L.) seedlings were grown in unfertilized forest soil for 40 weeks in controlledenvironment chambers with ambient (362 ~1 1-l) or elevated (690 ~1 l- ‘) CO*. As previously reported, seedling dry weight was 85% greater in the elevated CO* environment, despite severe nitrogen deficiency in all seedlings. The increase in growth occurred without a concomitant increase in nitrogen uptake, indicating an increase in nitrogen-use efficiency in elevated CO,. The weight of new buds was greater in elevated CO*, suggesting that shoot growth in the next year would have been enhanced relative to that of seedlings in ambient CO 2. However, there was less translocatable nitrogen in perennial woody tissue in elevated C02; thus, further increases in nitrogen-use efficiency may not be possible. The leaves that abscised from seedlings in elevated CO, contained higher amounts of soluble sugars and tannin and a lower amount of lignin compared with amounts in abscised leaves in ambient CO*. Based on 1ignin:N and 1ignin:P ratios, the rates of litter decomposition might not be greatly affected by CO* enrichment, but the total amount of nitrogen returned to soil would be lower in elevated CO,.

Plant regeneration by organogenesis in Glycine max.

Abstract: A procedure for the regeneration of fertile plants by organogenesis from tissue cultures of soybeans, Glycine max is described. Seeds were germinated on reduced inorganic salt MS medium containing 5μM BA. Cotyledonary nodes were excised and cultured on the same medium. Presence of BA in the medium during seed germination and culture of nodal explants was required for multiple shoot and shoot-bud formation. Histological analyses established the de novo nature of shoot regeneration. Separate reduction of the concentration of inorganic salts or substitution of sucrose for fructose during culture had minimal effects on the regeneration response. Conversely, if the BA was reduced, the inhibition response could not be overcome by increased salt concentration or altered carbon source.

Use of concentrated macronutrient solutions to separate osmotic from nacl-specific effects on plant-growth

Abstract: The aim was to distinguish between osmotic and ion-specific effects of NaCl on plant growth and ion uptake by comparing plants grown in isosmotic solutions with and without NaCI. Preliminary experiments showed that polyethylene glycol 4000 and mannitol were unsuitable for even very-short-term studies because they caused immediate reductions in leaf elongation rate when plants were transferred from NaCl to isosmotic solutions of these compounds. However, concentrated solutions of macronutrients (modified Hoagland's nutrients) did not change the elongation rate. Barley, wheat, Egyptian clover and white clover were grown in NaCl and concentrated macronutrient solutions of matching osmotic pressures. After 14 days, plants grown in concentrated macronutrients were smaller than controls (plants in normal strength nutrient solution) but had similar root : shoot ratios. NaCl-grown plants were less than half the size of plants in concentrated macronutrients, and had higher root : shoot ratios. NaCl-induced phosphate uptake did not cause this additional reduction in shoot growth. For barley, net transport of K+, Mg2+, Ca2+ and total nitrogen from the roots (per g root dry wt) was lower in NaCl-grown plants than in controls, but uptake by the shoot (per g shoot dry wt) of these minerals was similar. By contrast, both transport and uptake of these minerals in concentrated macronutrient-grown plants resembled control plants. NaCl-grown barley and wheat plants had higher osmotic pressures in both growing and mature tissue than did controls and macronutrient-grown plants, but a lower rate of uptake of solutes generating this osmotic pressure. We raise the possibility that growth in NaCl may be limited by a reduced rate of transport of an essential nutrient to the shoot.

Plant-induced changes in the rhizosphere of maize and wheat

Abstract: The release of organic materials by roots of maize and wheat was studied using a growth chamber with a14CO2 atmosphere at constant total CO2 concentration and constant specific activity. The distribution of14C within shoots, roots and soil was determined for both plants after 4 and 6 weeks. After 6 weeks, 1.5% of the total amount of14C fixed by maize was found as a residue in the soil, while for wheat this figure was 2.0%.

Effects of photon irradiance on the growth of shoots and roots, on the rate of initiation of mycorrhizal infection and on the growth of infection units in Trifolium subterraneum L.

Abstract: SUMMARY The effects of photon irradiance on the growth of young plants (up to three weeks old) of Trifolium subterraneum L. and on the development of mycorrhizal root systems were studied with plants grown in a soil/sand mixture inoculated with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe. Total plant growth was lower when photon irradiance was 100 μmol m−2 s−1, compared with 450 μmol m−2 s−1. Fresh weight of shoots was unaffected, but the fresh weight/dry weight ratio was increased at the lower irradiance in shoots, but not in roots. The main effect of decreased irradiance on the growth of the root system was a reduction in the numbers of first- and second-order lateral roots initiated. The average rate of extension of axial and lateral roots was only slightly reduced. The fraction of the root length infected was lower at the lower irradiance, particularly in the first two weeks. Development of infection was analyzed in terms of the role of formation of mycorrhizal entry-points (A) and the average rate of growth of infection units (B). Reduction in the fraction of the root length infected was found to be due to a reduction in A. B was remarkably constant at the two irradiances and in the different root subsystems. Thus both roots and infection units respond by making fewer units of unaltered rate of growth.

Mechanism of phosphorus-induced zinc deficiency in cotton. II. Evidence for impaired shoot control of phosphorus uptake and translocation under zinc deficiency

Abstract: Cotton (Gossypium hirsutum L. cv. Deltapine 15/21) plants were precultured for 19 to 25 days under controlled climatic conditions in nutrient solutions with different levels of Zn. With the onset of visual Zn-deficiency symptoms the pH of the nutrient solution decreased from 6.0 to about 5.0. In contrast, Zn-sufficient plants raised the pH of the nutrient solution to about 7.0. In short-term studies it could be demonstrated that the Zn nutritional status of the plants remarkably influenced the uptake and translocation rates of mineral nutrients. Compared to Zn-sufficient plants, P uptake rate in severely Zn-deficient plants was increased by a factor of 2 to 3, whereas the uptake rates of K, Ca and particularly NO3 decreased. The accumulation of P in the roots of Zn-deficient plants was either not affected or even lower than in Zn-sufficient plants. Thus, Zn deficiency had a specific enhancement effect on root to shoot transport of P. This enhancement effect of Zn deficiency on uptake and transport of P was similar at nutrient solution pH values of 7.0 and 5.8; i.e. it was not the result of acidification of the nutrient solution. After application of 36CI, 86Rb and 32P to plant stems, basipetal transport of 36CI and 86Rb was not affected by the Zn nutritional status of the plants. However, in Zn-deficient plants, only 7.8% of the 32P was translocated basipetally compared to 34% in the Zn-sufficient plants. A resupply of Zn for 19 h to Zn-deficient plants enhanced basipetal 32P transport. The results indicate that a feedback mechanism in the shoots is impaired in Zn-deficient plants which controls the P uptake by roots and especially the P transport from roots to shoots. As a result of this impairment toxic concentrations of P accumulate in the leaves. The mechanism responsible is likely the retranslocation of P in the phloem from shoots to roots.

Growth comparisons of a supernodulating soybean (Glycine max) mutant and its wild‐type parent

Abstract: The growth of a supernodulating, nitrate-tolerant soybean [Glycine max (L.) Merr.] mutant nts382 (nitrate-tolerant symbiosis) was compared to that of its wild-type parent, cv. Bragg, over the first 50 days after sowing. Plants were grown either inoculated in the absence of an external nitrogen source or uninoculated in the presence of 5 mM KNO3. For both treatments, nts382 growth up to 13 days after planting was faster than that of cv. Bragg. Thereafter, supernodulation of inoculated nts382 occurred and growth of cv. Bragg was faster; shoot and root dry weight increments and leaf area were greater in cv. Bragg, but the N content of nts382 was higher. Relative growth and net assimilation rates were lower in nts382, which had faster shoot and root respiration rates. Shoot growth of uninoculated plants was similar for both mutant and wild-type but roots of nts382 were slightly smaller than those of cv. Bragg. Total plant N content was similar in uninoculated cv. Bragg and nts382 but the latter had a higher leaf N content. Early lateral root formation (prior to nodule emergence) was greater in nts382 regardless of whether rhizobia or KJNO3 were present. We conclude that nts382 has some inherent differences from its parent but that supernodulation significantly retards plant growth.

The allocation of minerals to seeds in Senecio vulgaris plants subjected to nutrient shortage.

Abstract: (1) This experiment was to determine how parental nutrient shortage affects the allocation of specific nutrients to seeds in Senecio vulgaris, a short-lived monocarpic plant. (2) Plants were grown from seed, and supplied with Hoagland's nutrient solution at five concentrations: 100% (control), 80%, 60%, 40% and 20%. Biomass allocation to reproductive and vegetative parts was determined, and analysis for N, P, K, Ca, Mg, Fe and S carried out on seeds and shoots. Seeds from field-grown plants from three contrasting soils were also analysed chemically. (3) Relative biomass allocation to reproduction remained constant in spite of large differences in total plant weight. (4) The seeds were largely buffered from the differences in parental nutrient status. Seeds from the field-grown plants gave broadly similar results to those from greenhouse plants. (5) K, Ca and Fe were consistently less concentrated in the seeds than in the shoots. N, P and S were consistently more concentrated in the seeds. Mg was more concentrated in the seeds only in the three treatments with the lowest nutrient supply. (6) The fraction of the plant's total content of any one element which was allocated to its seeds varied widely. In plants on 100% Hoagland solution, it ranged from 4% of total K to 38% of total P. In the most nutrient-deprived plants it ranged from 2.5% of total Fe to 52% of total P. (7) In contrast to the constant proportional allocation of biomass to the seeds, the allocation of minerals to them increased with nutrient shortage (except in the case of iron). (8) The results are discussed in relation to the question of the most appropriate currency in which to measure reproductive allocation in plants.

Comparative physiology of burned and unburned Rhus laurina after chaparral wildfire.

Abstract: Laurel Sumac (Rhus laurina) is a dominant member of the coastal chaparral community of southern California that survives periodic burning by wildfires by resprouting from a lignotuber (root crown). We investigated the physiological basis for resprouting by comparing shoot elongation, leaf nitrogen content, tissue water status, leaf conductance to water vapor diffusion, and photosynthetic rates of post-fire R. laurina to those of adjacent unburned shrubs. Resprouts had higher rates of shoot elongation, leaf conductance, and photosynthesis than mature, unburned shrubs. Leaf nitrogen contents were elevated in burned shrubs even though their leaves developed interveinal chlorosis. A comparison of soil water potential to predawn water potential indicated that roots of R. laurina remain active below 2 m during the first summer drought after wildfire. Our results support the hypothesis that lignotubers not only contain dormant buds that develop into aerial shoots after wildfire but they also supply nutrient resources that enhance shoot elongation. Because R. laurina is relatively sensitive to drought, yet very successful in its rapid recovery after fire, maintaining an active root system after shoot removal may be the primary function of the massive lignotuber formed by this species.

Ammonium Nutrition in Ricinus communis: Its Effect on Plant Growth and the Chemical Composition of the Whole Plant, Xylem and Phloem Saps

Abstract: Allen, S. and Smith, J. A. C. 1986. Ammonium nutrition in Ricinus communis: its effect on plant growth and the chemical composition of the whole plant, xylem and phloem saps.—J. exp. Bot. 37: 1599-1610. The growth and chemical composition of Ricinus communis cultivated hydroponically on 12 mol m 3 NO3-N were compared with plants raised on a range of NH4-N concentrations. At NH^-N concentrations between 0-5 and 4 0 mol m " 3, freshand dry-weight yields of 62-d-old plants were not significantly different from those of the NOJ-N controls. Growth was reduced at 0-2 mol m*3 NH4 -N and was associated with increased root : shoot and C : organic N ratios, suggesting that the plants were N-limited. At 8 0 mol m "3 NH? -N, growth was greatly restricted and the plants exhibited symptoms of severe 'NH4 toxicity'. Plants growing on NH4 -N showed marked acidification of the rooting medium, this effect being greatest on media supporting the highest growth rates. Shoot carboxylate content per unit dry weight was lower at most NH4 -N concentrations than in the NOJ-N controls, although it increased at the lowest NH4-N levels. Root carboxylate content was comparable on the two N sources, but also increased substantially at the lowest NH4 -N levels. N source had little effect on inorganic-cation content at the whole-plant level, while NO 3 and carboxylate were replaced by Cl~ as the dominant anion in the NH4 -N plants. This was reflected in the ionic composition of the xylem and leaf-cell saps, the latter containing about 100 mol m"3 Cl" in plants on 8 0 mol m"3 NH4. Xylem-sap organic-N concentration increased more than threefold with NH4 -N (with glutamine being the dominant compound irrespective of N source) while in leaf-cell sap it increased more than 12-fold on NH4-N media (with arginine becoming the dominant species). In the phloem, N source had little or no effect on inorganic-cation, sucrose or organic-N concentrations or sap pH, but sap from NH4-N plants contained high levels of CI" and serine. Collectively, the results suggested that the toxic effects of high NH4 concentrations were not the result of medium acidification, reduced inorganic-cation or carboxylate levels, or restricted carbohydrate availability, as is commonly supposed. Rather, NH4 toxicity in R. communis is probably the result of changes in protein N turnover and impairment of the photorespiratory N cycle. Key words—Ricinus, ammonium nutrition, nitrate, whole-plant composition, xylem, phloem, amino acids, carboxylate. Correspondence to: Department of Biological Sciences, University of Dundee, Dundee DDI 4HN, U.K.

The measurement of C transfers within the rhizosphere of wheat grown in field plots

Abstract: The translocation of C to the roots of wheat grown in field plots was measured by supplying a pulse of 14 CO 2 to the shoots of individual plants. The root system of each labelled plant was enclosed in a cylinder with a lid providing a gas-light seal around the emerging shoot. Plants were pulse-labelled at 7 or 10 weeks from emergence and the 14 C content of the shoots, soil + roots and rhizosphere CO 2 measured at flowering. The time of labelling had a strong effect on translocation of C to the roots with 19.2 and 6.2% of the 14 C activity, supplied to the shoots at 7 and 10 weeks respectively, present in the soil + roots and rhizosphere CO 2 fractions. The high proportion of the 14 C activity translocated to the roots released as rhizosphere CO 2 (65.4 and 45.3% from the 7 and 10 week labellings respectively) confirmed results from earlier growth cabinet experiments. Soil fumigation with chloropicrin almost halved the 14 C activity recovered in the rhizosphere CO 2 for plants labelled at 7 weeks and reduced the 14 C activity recovered in a soil fraction equated with root-derived material. It is uncertain if the apparent reduction in root production was due to inhibition by chloropicrin residues or to a stimulation of root growth in untreated plots by organisms eliminated from fumigated plots.

Distribution of nitrate assimilation between the root and shoot of legumes and a comparison with wheat

Abstract: Legumes of the Phaseoleae (Glycine max L. Merr., Phaseolus coccineus L., P. vulgaris L., Vigna radiata L. Wilczek and V. unguiculata L. Walp.), when grown on 10 mM nitrate, had a low in vitro nitrate reductase (NR) activity in the root compared to the shoot (<15%). In legumes of the Vicieae (Cicer aerietinum L., Pisum sativum L. and Vicia faba L.), Genisteae (Lupinus albus L.) and Trifolieae (Medicago sativa L. and M. truncatula Gaertn.), 30–60% of their total NR activity was in the root. The Phaseoleae had a higher nitrate content in the shoot. Decreasing the nitrate supply increased the relative proportion of NR activity in the root of garden pea (Pisum sativum) and wheat but did not alter the predominantly leaf-based assimilation of nitrate in Phaseolus vulgaris. When in vitro NR activity of the pea shoot was compared with the in vivo NR activity and the rate of accumulation of reduced N by this tissue, similar values were obtained. In vitro NR activity of the wheat shoot was 5 times its in vivo NR activity and 12 times its rate of accumulation of reduced N.

Tissue culture and plant regeneration from immature embryo explants of Barley, Hordeum vulgare.

Abstract: Immature embryo explants taken 8 days after anthesis were used to establish callus cultures of spring barley. Two types of calli were observed. A soft, watery callus produced a limited number of shoots and a harder, more compact, yellowish callus gave rise to numerous green primordia and shoots. Gamborg's B5 basal medium supplemented with either 2,4-D (2,4-dichlorophenoxyacetic acid) or Cl3 POP (2,4,5-trichlorophenoxypropionic acid) was found to give good callus growth and shoot initiation. Media containing 2,4-D at 1.0 mg L−1 or Cl3 POP at 5.0 mg L−1 produced numerous cultures resulting in regeneration of plants. Plantlets developed roots on basal medium with Cl3 POP at 1.0 mg L−1 or on auxin-free medium. Twenty genetically diverse genotypes were screened to determine if these techniques were suitable for a wide range of spring barley cultivars. Regeneration of plantlets was obtained for 19 of the 20 genotypes approximately 4 months after culture initiation. Lines differed in the ability to develop vigorously growing calli and in the ability of calli to develop large numbers of shoots and regenerated plantlets.

Effects of temperature on shoot growth in northern provenances of Pinus sylvestris L.

Abstract: Effects of temperature on shoot growth in northern provenances of Pinus sylvestris L. were studied under natural long-day conditions (Lat. 69 degrees 39' N) at controlled temperatures. The optimum constant temperature for formation of stem unit primordia in the terminal resting bud was 18 to 21 degrees C. Stem unit number decreased linearly with temperature between 15 and 9 degrees C. Temperature during bud formation had a significant effect on final stem unit length achieved in the following year. Final shoot length was significantly affected by temperature during shoot elongation. The optimum constant temperature for elongation growth was 18 to 21 degrees C. The rate of shoot elongation was positively correlated with the number of stem units.

Timing of defoliation and its effect on bud development, starch reserves, and sap sugar concentration in sugar maple

Abstract: Sapling sugar maple (Acersaccharum Marsh.) trees were defoliated artificially at 10-day intervals beginning May 27 and ending August 5, 1981. Refoliation, terminal bud and shoot development, and xylem starch and sap sugar concentration were observed in defoliated and control trees. All defoliated trees refoliated, but decreasingly with later defoliation. Defoliation caused an acceleration in the rate of primordia initiation in terminal shoot apices. After early season defoliations, the developing buds in the axils of the removed leaves abscissed, but axillary and terminal buds on the refoliated terminal shoots survived through winter. In late season defoliation, most buds of refoliated shoots did not survive and the next year's growth depended on axillary buds formed prior to defoliation. Thus, when progressing from early to late defoliations, the next year's shoot growth depended decreasingly on the last-formed and increasingly on the first-formed portions of the previous year's shoot. Early October star...

ACCUMULATION OF PHOSPHORUS, DRY MATTER AND BETAINE DURING NaCl STRESS OF SPLIT-ROOT CITRUS SEEDLINGS COLONIZED WITH VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI ON ZERO, ONE OR TWO HALVES.

Abstract: SUMMARY Sodium chloride tolerance and phosphorus content were examined in split-root Carrizo citrange seedlings [Poncirus trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] colonized with a vesiculararbuscular mycorrhizal fungus (Glomus intraradices Schenck & Smith) on zero, one or two root halves. Plants were treated with NaCl at 0, 25, 50 or 100 mm, and the degree of stress was measured as reduction of dry matter accumulation and rise in level of leaf proline-betaine (stachydrine). Shoot and root dry weight production during this period decreased with increasing levels of salt. Absolute reductions were similar for plants inoculated on one vs two half-root systems, but percentage decreases were less in the latter due to greater overall growth in all treatments. Betaine levels in leaf tissues were positively related to soil salt levels for each mycorrhizal treatment. Significant differences in betaine levels were also detected in plants with and without mycorrhizal fungi, and mean levels tended to be higher for those colonized on one vs two halves of their root system. In contrast, a half-root system and its fungal symbiont supplied enough phosphorus to allow concentrations of leaf P to equal those of fully infected root systems, yet the two groups did not show equal growth under control conditions or percentage reductions with NaCl stress.

The impact of a pathogen (puccinia lagenophorae) on populations of groundsel (senecio vulgaris) overwintering in the field ii. reproduction

Abstract: SUMMARY (1) Reproduction during the spring was studied in monocultures of groundsel (Senecio vulgaris L.) overwintered in the field. In the autumn, populations had been either inoculated with a fungal pathogen (Puccinia lagenophorae), which caused rust disease, or left as controls. The effects of rust infection were examined in relation to status within a hierarchical population (assessed by sub-classes based on shoot dry weights). (2) In control populations, the first capitulum buds were produced in late February. The onset of flowering became progressively delayed as status within the hierarchy declined. In all sub-classes of the population, rust infection during the previous autumn delayed flowering in the spring by 1-2 weeks. (3) The percentage of plants within a sub-class that were reproductive (bore buds or capitula) in March and April declined as status in the hierarchy decreased. In classes of comparable status, fewer plants flowered in inoculated than in control populations. (4) In April, sub-classes with low mean dry weights in both populations produced fewer buds and mature capitula. The number of florets per capitulum were also decreased in lower status classes. Rust inhibited all measured components of reproduction in all classes. (5) During May, many large control plants senesced and their reproductive output declined. Thus, most sub-classes of control populations produced a similar number of florets. In contrast, vegetative growth in inoculated populations continued and all measures of reproduction were far greater in the class of highest status than in any other. There was a seven-fold increase in the contribution of this class to floret production (70%) relative to its frequency in the original population. In control populations, there was no more than a two-fold difference between floret production and frequency in the parent population. (6) Infection resulted in no significant change in the percentage of florets that developed into seed or in the viability of seed. (7) Over the duration of this experiment, the potential seed production of control populations (calculated from capitulum production, florets per capitulum and percentage seed set) was >460 000 seeds m-2. Populations that had been rust-infected in the autumn potentially produced 183 000 seeds m-2, a reduction of >60% compared