Showing papers on "Shoot published in 1994"

Heavy metal accumulation and tolerance in British populations of the metallophyte Thlaspi caerulescens J. & C. Presl (Brassicaceae)

Abstract: SUMMARY Heavy metai uptake, accumulation and tolerance were investigated in five British populations of the metallophyte Thlaspi caerulescens from metalliferous sites from the north and south Pennines orefields. Analysis of field samples showed mean shoot Zn, Pb and Cd concentrations of up to 21000, 660 and 164/zMug g-1 respectively. A solution culture experiment designed to investigate both tolerance and metal accumulation is reported. Indices of tolerance of five populations to 12 metals (Ag, Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Zn) showed few population differences but unexpectedly high tolerance to metals not present at elevated concentrations in the parent soils. This was paralleled by exceptionally high uptakes of all metals studied. Zn, Cd, Co, Mn and Ni were readily transported to the shoot whereas Al, Cr Cu, Fe and Pb were predominantly immobilized in the roots. The data suggest common mechanisms of absorption and transport of several metals in this species.

Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

Abstract: The influence of varied supply of phosphorus (10 and 250 mmol P m -3 ), potassium (50 and 2010 mmol K m -3 ) and magnesium (20 and 1000 mmol Mg m -3 ) on the partitioning of dry matter and carbohydrates (reducing sugars, sucrose and starch) between shoots and roots was studied in bean (Phaseolus vulgaris) plants grown in nutrient solution over a 12 d period. Shoot and root growth were quite differently affected by low supply of P, K, and Mg. The shoot/root dry weight ratios were 4.9 in the control (sufficient plants), 1.8 in P-deficient, 6.9 in K-deficient and 10.2 in Mg-deficient plants. In primary (source) leaves, but not in trifoliate leaves, concentrations of reducing sugars, sucrose and starch were also differently affected by low nutrient supply

Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scots pine stands

Abstract: The LAI-2000 plant canopy analyzer (Li-Cor, Inc., Lincoln, NE) was tested at six experimental plots of Scots pine (Pinus sylvestris L.) in central Sweden at peak leaf area in August and after litterfall in October 1990. An independent estimate of leaf area index for August 1990 was obtained based on an empirically derived regression of needle area on stem sapwood area, and the decrease in leaf area between the two measurements was estimated from measurements of litterfall. A strong linear relationship was found between estimates by the LAI-2000 (L(Li-Cor)) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that L(Li-Cor) was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, L(Li-Cor) corresponds to L multiplied by a factor (beta) characterizing the mutual shading of needles on the shoot. The shading factor, beta, was equal to the ratio of spherically projected shoot area to spherically projected needle area, where the spherically projected area is defined as the average projection (silhouette) area taken over all directions in space. The quantity betaL was defined as the shoot silhouette area index (SSAI), and an equation for the relationship between SSAI and the mean silhouette to total area ratio (mean STAR) of shoots was derived. Measured values of mean STAR for Scots pine indicated that L(Li-Cor) corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was only partly detected by the LAI-2000, possibly because SSAI did not change to the same degree as L, i.e., there was an increase in the factor beta. This hypothesis is supported by data showing a large increase in mean STAR with shoot age.

Cytokinins and plant development : an overview

Abstract: This chapter presents a summary of the involvement of cytokinins in seed germination, de novo bud formation, release of buds from apical dominance, leaf expansion, reproductive development, and senescence. The effects of cytokinins on seed germination are not as pronounced; however, numerous studies have shown that cytokinins can influence germination, particularly when conditions are suboptimal for germination. Endogenous cytokinins have been measured in germinating seeds of various species. The level of cytokinin is generally low in dry seeds and initially decreases even further, but then increases during germination. The classic studies by F. Skoog and C. O. Miller demonstrated the dramatic effects of cytokinins on shoot differentiation in tobacco callus. The endogenous cytokinins as well as the metabolism of exogenous cytokinins were determined in relation to adventitious bud regeneration. Cytokinins can inhibit oxidation and prevent the sharp rise in respiration usually occurring during senescence.

Salt tolerance is not associated with the sodium accumulation of two maize hybrids

Abstract: In this report, we test the hypothesis that Na+ accumulation in the shoot in maize is negatively correlated with salt tolerance. Salt tolerance is defined as a percentage of the control on a dry weight basis. Two hybrids (Pioneer hybrid 3578 and Pioneer hybrid 3772) differing widely in Na+ accumulation were compared. Plants were treated with two types of salinity for 15 days (80 mol m-3 NaCl or 80 mol m-3 NaCl plus 8.75 mol m-3 CaCl2). Ion concentrations (Na+, K+, Ca2+ and Cl-) were measured in the roots, stalks, sheaths and leaves of plants harvested every third day. Ion concentrations were significantly affected by the treatments. Na+ and Cl- concentrations increased with salinity treatments; K+ and Ca2+ concentrations decreased. Supplemental Ca2+ increased Ca2+ and decreased Na+ concentrations. Hybrid 3772 maintained very low Na+ concentrations in the shoots, whereas 3578 did not. The largest distinction between the hybrids was in the ability to transport Na+ to the shoot; hybrid 3578 transported Na+ at twice the rate of hybrid 3772. In general, ion transport to the shoot appeared to be a function of root ion concentration. This model could account for the effects of NaCl salinity and supplemental Ca2+ on ion transport, although Na+ transport was complicated by an apparent reabsorption mechanism in the root and mesocotyl. The lack of correlation of Na+ accumulation in the shoot and other ion parameters with growth indicated that the mineral nutrition of the plants was not correlated with salt tolerance. It was concluded that the growth response of maize to salinity was primarily affected by osmotic factors.

Growth, physiological and anatomical responses of two wheat genotypes to waterlogging and nutrient supply

Abstract: In order to investigate the responses of plant genotypes to waterlogging and nutrient supply, physiological, morphological, and anatomical features were determined for two genotypes of winter wheat (Triticum aestivum), «Bayles» and «Savannah». Plants were grown in a growth chamber and fertilized with half-strength or full-strength Hoagland's solution during 17 d of waterlogging. Waterlogging reduced leaf water potential, stomatal conductance, photosynthesis, chlorophyll content, shoot nitrogen content, shoot and root growth for both Bayles and Savannah; however, there were more adverse effects on Bayles than on Savannah

Effects of NaCl on Flows of N and Mineral Ions and on NO3- Reduction Rate within Whole Plants of Salt-Sensitive Bean and Salt-Tolerant Cotton

Abstract: The effects of NaCl on the transport rates of cations, NO3-, and reduced N compounds between roots and shoot and on NO3- assimilation rate were examined on plants of two species differing in their sensitivity to salinity, bean (Phaseolus vulgare L. cv Gabriella) and cotton (Gossypium hirsutum L. cv Akala). Biomass production after 20 d in response to 50 and 100 mM NaCl decreased by 48 and 59% in bean, but only 6 and 14% in cotton. The comparison of the flow patterns obtained for control and NaCl-fed plants showed that salinity induced a general decrease in all the fluxes involved in partitioning of N and the various ions. This decrease was markedly higher in bean than in cotton. Within either species, the different flows (uptake, xylem flux, phloem flux) of a given element were affected by NaCl to the same extent with minor exceptions. No specific effect of salinity on any of the components of N partitioning were discerned. The greater sensitivity of nitrate reductase activity to NaCl in bean leaves compared to cotton leaves seems to be due to a decreased compartmentalization of ions rather than to a difference in salt tolerance of the enzyme itself. Overall, our data show that alteration of mineral nutrition is not solely the reflection of a decreased growth rate, but also is a general process that impairs uptake of all the minerals even at mild NaCl salinity.

A humic acid improves growth of tomato seedling in solution culture

Abstract: The effects of humic acid (HA) on nutrient accumulation and growth of tomato seedlings were evaluated in a solution of limited nutrient availability in a greenhouse. HA additions were made to the nutrient solution at rates of 0, 640, 1280, or 2560 mg/L. The addition of 1280 mg/L HA produced significant increases in shoot accumulation of P, K, Ca, Mg, Fe, Mn, and Zn as well as increased accumulation of N, Ca, Fe, Zn, and Cu in roots. Fresh and dry weights of roots were also increased, However, on comparing nutrient accumulation in plants treated with 1280 mg/L HA and those given an additional supply of nutrients equivalent to those supplied by HA at the 1280 mg/L rate, shoots accumulated more N, P, K, Fe, and Cu, while roots accumulated more K and Ca. Therefore these increases do not appear to be associated with nutrients contained in HA. Eectrolyte leakage, as an indication of membrane permeability, did not differ as a consequence of HA additions. However, electrolyte leakage correlated positivel...

Nitrogen Source Regulation of Growth and Photosynthesis in Beta vulgaris L.

Abstract: Sugar beets (Beta vulgaris L cv F58-554H1) were grown hydroponically in a 16-h light, 8-h dark period at a photosynthetic photon flux density of 05 mmol m-2 s-1 for 4 weeks in half-Hoagland culture solution containing only nitrate-nitrogen Half of the plants were then transferred to half-Hoagland solution with ammonium-nitrogen (735mM), while the other half continued on 75 mM nitrate Growth analysis was carried out by sampling the plants at 3-d intervals over a period of 21 d Compared to plants supplied with nitrate, ammonium initially slowed the growth of shoots more than roots Ammonium reduced both the area expansion of individual leaves and the relative water content of these leaves, but increased the amount of dry matter/area The increase in specific leaf weight in ammonium-grown leaves was associated with a doubling of chloroplast volume, as much as a 62% rise in chlorophyll content, and a 43-fold higher accumulation of soluble protein Ammonium nutrition substantially decreased the rate of expansion of photosynthetic (leaf) surface but did not decrease the rate of photosynthesis per area; in fact, net photosynthetic CO2 exchange rates were slightly higher than in nitrate plants, due to the build-up in stromal enzymes of the Calvin cycle, several of which increased in total extractable activity on a leaf area basis, eg ribulose-1,5-biphosphate carboxylase oxygenase, sedoheptulose-1,7-biphosphatase Nitrogen source had no effect on stomatal conductance Rates of photosynthesis per chlorophyll were decreased slightly in ammonium-grown leaves, possibly due to an increased CO2-diffusion resistance associated with the enlarged chloroplasts

Cadmium and nickel accumulation in rice plants. Effects on mineral nutrition and possible interactions of abscisic and gibberellic acids

Abstract: Rice plants accumulate high quantities of Cd and Ni when grown for 10 days in a medium containing these heavy metals. Accompanying Cd and Ni uptake, a decrease in shoot and root length was observed, though dry matter accumulation was not affected accordingly. Metal treatments also induced a decrease in K, Ca and Mg contents in the plants, particularly in the shoots, indicating that Cd and Ni interfered not only with nutrient uptake but also with nutrient distribution into the different plant parts. Addition of abscisic acid (ABA) or gibberellic acid (GA3) to the external solution could not overcome the depressing effects of the metals on nutrient acquisition, and even induced a further decrease of Ca content in Ni-treated plants. Both hormones also reduced, significantly, heavy metal incorporation into the plants. Additionally, hormonal applications affected the transport of Cd and Ni to the shoots, resulting in a higher percentage of the metals taken up remaining in the roots.

Salinity Tolerance Mechanisms of Six C4 Turfgrasses

Abstract: Physiological responses to salinity and relative salt tolerance of six C 4 turfgrasses were investigated. Grasses were grown in solution culture containing 1, 100, 200, 300, and 400 m M NaCl. Salinity tolerance was assessed according to reduction in relative shoot growth and turf quality with increased salinity. Manilagrass cv. Matrella (FC13521) ( Zoysia matrella (L.) Merr.), seashore paspalum (Hawaii selection) ( Paspalum vaginatum Swartz), and St. Augustinegrass (Hawaii selection) (Stenotaphrum secundatum Walt.) were tolerant, shoot growth being reduced 50% at ≈400 mM salinity. Bermudagrass cv. Tifway (Cynodon dactylon × C. transvaalensis Burtt-Davey) was intermediate in tolerance, shoot growth being reduced 50% at ≈270 mM salinity. Japanese lawngrass cv. Korean common (Zoysia japonica Steud) was salt- sensitive, while centipedegrass (common) (Eremochloa ophiuroides (Munro) Hack.) was very salt-sensitive, with total shoot mortality occurring at ≈230 and 170 mM salinity, respectively. Salinity tolerance was associated with exclusion of Na + and Cl - from shoots, a process aided by leaf salt glands in manilagrass and bermudagrass. Shoot Na + and Cl - levels were high at low (100 to 200 mM) salinity in centipedegrass and Japanese lawngrass resulting in leaf burn and shoot die- back. Levels of glycinebetaine and proline, proposed cytoplasmic compatible solutes, increased with increased salinity in the shoots of all grasses except centipedegrass, with tissue water levels reaching 107 and 96 m M at 400 mM salinity in bermudagrass and manilagrass, respectively. Glycinebetaine and proline may make a significant contribution to cytoplasmic osmotic adjustment under salinity in all grasses except centipedegrass.

Compartmentation and transport of zinc in barley primary leaves as basic mechanisms involved in zinc tolerance

Abstract: The heavy metal zinc was administered to barley seedlings by increasing its concentration in the hydroponic medium. The most dramatic effect was a severe inhibition of root elongation with little effect on root biomass production. The growth of primary leaves was little affected although the zinc content of the primary leaves increased several-fold. A detailed compartment analysis was performed for 10-d-old barley primary leaves. Under low zinc nutrition (2mmol m −3), highest zinc contents were observed in the cytoplasm of mesophyll protoplasts. At inhibitory zinc concentrations in the hydroponic medium (400 μmol m −3), zinc levels dramatically and preferentially increased in the apoplastic space. Elevated zinc levels were also observed in the epidermal cells, and to a lesser extent, in mesophyll vacuoles. The cytoplasmic content of mesophyll protoplasts was unchanged, indicating perfect zinc homeostasis within the leaf. In order to understand the transport mechanisms underlying the steady-state distribution profile, we used 65Zn to conduct uptake experiments with leaves whose lower epidermis had been stripped. The leaves were placed on zinc solutions of varying concentrations containing 65Zn for 5 min to 6 h. After the incubation, the leaves were fractionated into mesophyll and epidermis protoplasts and residue, the latter mainly representing cell wall. Adsorption of Zn to the extracellular matrix was 100 times faster than Zn uptake into the cells. By far the largest portion taken up into the mesophyll protoplasts rapidly appeared in the vacuolar compartment. These results demonstrate the importance of compartmentation and transport as homeostatic mechanisms within the leaves to handle high, possibly toxic, zinc levels in the shoot.

Influence of Light

Abstract: Both light and NO3- are necessary for the appearance of nitrate reductase (NR) activity (NRA) in photosynthetic tissues. To define the light effect more precisely, we examined the response to light/ dark transitions on NRA, NR protein (NRP), and NR mRNA in 6-dold maize (Zea mays cv W64A x W182E) seedlings that had been grown in a lightldark regime for 5 d and then induced with 5 mM KNOB for 24 h. The decay of NRA and NR mRNA in the shoot was immediate, but there were only minor changes in NRP during the initial 4 h in the dark. In root tissues, in contrast, there was a 4-h delay in the loss of NRA, NRP, and NR mRNA after transfer to the dark. When the seedlings were returned to light after a 2-h interval in the dark, shoot NRA reached 92% of the initial levels within 30 min of illumination. These results indicate that in the shoots (a) NR message production requires light and (b) the NRP that appears with light treatment and that is active is inactivated in the dark. The NRP can be reactivated when the light is turned on after short periods of darkness (2 h). Root tissues, on the other hand, probably respond to the supply of photosynthetically produced metabolites rather than to immediate products of the light reactions of photosynthesis. Early work by Hageman and Flesher (1960) demonstrated that both light and NOs- were important environmental signals for the appearance of NRA. Since then it has been observed in many studies that Nos- reduction is accelerated in green tissues in the presence of light (reviewed by Srivas

Demography of shallow eelgrass (Zostera marina) populations-shoot dynamics and biomass development

Abstract: Although Zostera marina (eelgrass) is a widespread and well examined seagrass we provide here a first study of shoot demography and growth, conducted by following cohorts of eelgrass shoots during an annual cycle in six perennial populations in Limfjorden, Denmark. The formation of leaf shoots on side-branches occurred throughout the year but peaked in May-June and declined at reduced light availability. Maximum mortality of over-wintering leaf shoots coincided with the flowering season, whereas new leaf shoots had the highest mortality in late summer and most were lost at an early age (mean half-life of 50 days) presumably due to shading within the dense stands (...)

Seasonal diet of capuchin monkeys (Cebus apella) in a semideciduous forest in south-east Brazil

Abstract: The diet of capuchin monkeys, Cebus apella, in a 250 ha semideciduous forest in south-east Brazil was studied for 44 consecutive months. Based on 367 feeding bouts the diet of capuchins was 53.9% fruit pulp, 16.0% seeds, 11.1% flowers, 6.3% leaves and new shoots, 1.5% roots and 13.9% corn from plantations surrounding the forest. Seventy-one plant species were consumed by capuchins. Food availability was markedly seasonal. During the dry season the fleshy fruit availability decreased, and at that time the capuchins became seed predators and flower- eaters. Several fruits eaten by capuchins in the dry season were not consumed by other frugivorous vertebrates, such as howler monkeys, parrots or squirrels, allowing capuchins to avoid competition with other arboreal frugivores. In semideciduous forests where fleshy fruits are less abundant than in the wet forests capuchins are important seed predators.

Retranslocation of carbon reserves from the woody storage tissues into the fruit as a response to defoliation stress during the ripening period in Vitis vinifera L.

Abstract: A technique for reliable labeling of the carbon reserves of the trunk and roots without labeling the current year's growth of grapevines was developed in order to study retranslocation of carbon from the perennial storage tissues into the fruit in response to defoliation stress during the ripening period. A special training system with two shoots was used: the lower one (feeding shoot) was cut back and defoliated to one single leaf (14CO2-feeding leaf) while the other (main shoot) was topped to 12 leaves. The potted plants were placed in a water bath at 30 °C to increase root temperature and therefore their sink activity. Additionally, a cold barrier (2–4 °C) was installed at the base of the main shoot to inhibit acropetal 14C translocation. Using this method, we were able to direct labeled assimilates to trunk and roots in preference to the current year's growth. On vines with root and shoot at ambient temperature, 44% of the 14C activity was found in the main shoot 16 h after feeding whereas only 2% was found in the temperature-treated vines. At the onset of fruit ripening, and at three-week intervals thereafter until harvest, potted grapevines were fed with 14CO2 using the temperature treatment described above. Sixteen hours after feeding, half of the vines of each group were defoliated by removing all except the two uppermost main leaves. Three weeks after each treatment, vines were destructively harvested and the dry weight and 14C incorporation determined for all plant parts. Under non-stressing conditions, there was no retranslocation of carbon reserves to support fruit maturation. Vines responded to defoliation stress by altering the natural translocation pattern and directing carbon stored in the lower parts to the fruit. In the three weeks following veraison (the inception of ripening in the grape berry), 12% of the labeled carbon reserves was translocated to the fruit of defoliated plants compared to 1.6% found in the clusters of control vines. Retranslocation from trunk and roots was highest during the middle of the ripening period, when 32% of the labeled carbon was found in the fruit compared to 0.7% in control plants. Defoliation during this period also caused major changes in dry-matter partitioning: the fruit represented 31% of total plant biomass compared to 21% measured in the control vines. Root growth was reduced by defoliation at veraison and during the ripening period. Defoliation three weeks before harvest did not affect dry matter or 14C partitioning.

Branching Mutant rms-2 in Pisum sativum (Grafting Studies and Endogenous Indole-3-Acetic Acid Levels).

Abstract: Isogenic lines of pea (Pisum sativum L.) were used to determine the physiological site of action of the Rms-2 gene, which maintains apical dominance, and its effect on endogenous free indole-3-acetic acid (IAA) levels. In mutant rms-2 scions, which normally produce lateral branches below node 3 and above node 7, apical dominance was almost fully restored by grafting to Rms-2 (wild-type) stocks. In the reciprocal grafts, rms-2 stocks did not promote branching in wild-type shoots. Together, these results suggest that the Rms-2 gene inhibits branching in the shoot of pea by controlling the synthesis of a translocatable (hormone-like) substance that is produced in the roots and/or cotyledons and in the shoot. At all stages, including the stage at which aerial lateral buds commence outgrowth, the level of IAA in rms-2 shoots was elevated (up to 5-fold) in comparison with that in wild-type shoots. The internode length of rms-2 plants was 40% less than in wild-type plants, and the mutant plants allocated significantly more dry weight to the shoot than to the root in comparison with wild-type plants. Grafting to wild-type stocks did not normalize IAA levels or internode length in rms-2 scions, even though it inhibited branching, suggesting that the involvement of Rms-2 in the control of IAA level and internode length may be confined to processes in the shoot.

Potential of Trichoderma spp. as consistent plant growth stimulators

Abstract: In a series of repeated trials, six Trichoderma spp strains, applied as a dried powder from a liquid fermentation in molasses/yeast medium, proved to be consistent at promoting the growth of lettuce (Latuca sativa L) seedlings grown in a peat-sand potting compost in the glasshouse Strains WT, 92, 20, and 75 at 075% or 1% w:w concentrations increased shoot dry weight by up to 26%, although WT did inhibit germination For example, after 4 days only 13% of seeds sown in WT 1% w:w treated compost had germinated, whereas in other treatments germination was consistently greater than 32% WT increased shoot fresh and dry weights by 143 g and 06 g per pot, respectively, without affecting the root dry weights, to give concomitant increases in shoot: root ratios of fresh and dry weight The potential use of these Trichoderma spp strains for plant growth promotion is discussed

Water relations, gas exchange, and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L.

Abstract: Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deeprooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological performance of leaves were found, but mobilization of carbohydrates from burls strongly stimulated growth of fall resprouts compared to spring resprouts, despite low exposed leaf area of the fall shoots. During summer drought, resprouts exhibited improved water status and carbon fixation compared to mature plant shoots. Shoot growth of Q. ilex was apparently extended due to deep rooting so that initial slower growth during spring and early summer as compared to A. unedo was compensated. Tissue nutrient contents varied only slightly and are postulated to be of minor importance in controlling rate of shoot growth, perhaps due to the relatively fertile soil of the site. Fall flowering appeared to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results demonstrate that comparative examinations utilizing vegetation elements with differing morphological and physiological adaptations can be used to analyze relatively complex phenomena related to resprouting behavior. The studies provide an important multi-dimensional background framework for further studies of resprouting in the European Mediterranean region.

Seasonal changes in bud dormancy in relation to bud morphology, water and starch content, and abscisic acid concentration in adult trees of Betula pubescens

Abstract: Annual cycles of change in bud morphology, bud burst ability, abscisic acid (ABA) concentration, and starch and water content were studied in mid-crown terminal buds of short shoots and underground basal buds of Betula pubescens Ehrh. In particular, we investigated the roles of ABA and bud water content in the regulation of bud growth. Basal buds differed morphologically from terminal buds of short shoots in that their leaf initials did not develop into embryonic foliage leaves and their total size did not increase significantly during summer. Bud burst ability, measured by forcing detached short shoots and stumps under controlled conditions, was maintained in the basal buds throughout the year, whereas the terminal buds of short shoots remained dormant until October, thereafter their bud burst ability increased gradually and reached a maximum in March-April. The ABA concentration of the basal buds was relatively constant throughout the sampling period (1-3 micro g g(DW) (-1)), whereas that of the terminal buds of short shoots, which was much higher (5-10 micro g g(DW) (-1)), showed a distinct seasonal cycle with a maximum from August to November. Bud ABA concentration decreased during the first 10 days of forcing, especially in basal buds. In both bud types, the amount of starch increased toward the autumn, declined in November, and was negligible in the terminal buds of short shoots between January and March, but in April, the amount was high again in both bud types. Water content varied characteristically in both bud types, although more distinctly in the terminal buds of short shoots, with an increase in spring before bud burst and a decrease during the summer until September. The significant morphological and physiological differences between the mid-crown terminal buds of short shoots and the underground basal buds may partly explain the characteristic growth habit of the basal buds and their development into coppice shoots after cutting the tree. The results also indicate a role for ABA in maintaining dormancy of the terminal buds of short shoots and emphasize the relationship between tissue water status and ABA concentration.

Implications of calcium nutrition on the response of Phaseolus vulgaris L. to salinity

Abstract: The effect of Ca2+ level in the growth medium on the response of germination and early seedling growth of Phaseolus vulgaris to NaCl salinity was investigated. When NaCl concentration was increased germination and early seedling growth was decreased. The addition of Ca2+ to the media increased both germination percentage and seedling growth. Chloride concentrations were not affected by the level of Ca2+. Potassium and Ca2+ concentrations and transport from roots to shoots were decreased by NaCl, but were restored by increasing Ca2+ in the medium. The opposite was true for Na+. Leakage of NO3- and H2PO4- was increased by salinity and reduced by high Ca2+ in the medium. The results are discussed in terms of the beneficial effects of calcium for plant growth under saline conditions.

Effects of benzoic and cinnamic acids on growth, mineral composition, and chlorophyll content of soybean.

Abstract: Organic acids are major water-soluble allelochemicals found in soil infested with quackgrass and are involved in several processes that are important in plant growth and development. This study was carried out to gain more information on the effects of benzoic acid (BEN) andtrans-cinnamic acid (CIN) on growth, mineral composition, and chlorophyll content of soybean [Glycine max (L.) Merr. cv. Maple Bell] grown in nutrient solution. The two allelochemicals reduced root and shoot dry biomass of soybean. Treated plants had fewer lateral roots and tended to grow more horizontally compared to the untreated plants. Lateral roots were stunted and less flexible. The amounts of P, K, Mg, Mn, Cl−, and SO42− were lower, and Zn and Fe contents were higher in roots of plants grown with BEN or CIN as compared to untreated plants. Shoots of plants grown with the allelochemical showed greater accumulation of Ca, Mg, and Zn, whereas P and Fe contents were reduced. The BEN and CIN also caused reductions in leaf chlorophyll content. The BEN and CIN may be responsible for negative allelopathic effects of quackgrass on soybean by inhibiting root growth, by altering ion uptake and transport, and by reducing chlorophyll content.

Compensatory responses of CO2 exchange and biomass allocation and their effects on the relative growth rate of ponderosa pine in different CO2 and temperature regimes.

Abstract: Increases in the concentration of atmospheric carbon dioxide may have a fertilizing effect on plant growth by increasing photosynthetic rates and therefore may offset potential growth decreases caused by the stress associated with higher temperatures and lower precipitation. However, plant growth is determined both by rates of net photosynthesis and by proportional allocation of fixed carbon to autotrophic tissue and heterotrophic tissue. Although CO2 fertilization may enhance growth by increasing leaf-level assimilation rates, reallocation of biomass from leaves to stems and roots in response to higher concentrations of CO2 and higher temperatures may reduce whole-plant assimilation and offset photosynthetic gains. We measured growth parameters, photosynthesis, respiration, and biomass allocation of Pinus ponderosa seedlings grown for 2 months in 2×2 factorial treatments of 350 or 650μ bar CO2 and 10/25° C or 15/30° C night/day temperatures. After 1 month in treatment conditions, total seedling biomass was higher in elevated CO2, and temperature significantly enhanced the positive CO2 effect. However, after 2 months the effect of CO2 on total biomass decreased and relative growth rates did not differ among CO2 and temperature treatments over the 2-month growth period even though photosynthetic rates increased ≈7% in high CO2 treatments and decreased ≈10% in high temperature treatments. Additionally, CO2 enhancement decreased root respiration and high temperatures increased shoot respiration. Based on CO2 exchange rates, CO2 fertilization should have increased relative growth rates (RGR) and high temperatures should have decreased RGR. Higher photosynthetic rates caused by CO2 fertilization appear to have been mitigated during the second month of exposure to treatment conditions by a ≈3% decrease in allocation of biomass to leaves and a ≈9% increase in root:shoot ratio. It was not clear why diminished photosynthetic rates and increased respiration rates at high temperatures did not result in lower RGR. Significant diametrical and potentially compensatory responses of CO2 exchange and biomass allocation and the lack of differences in RGR of ponderosa pine after 2 months of exposure of high CO2 indicate that the effects of CO2 fertilization and temperature on whole-plant growth are determined by complex shifts in biomass allocation and gas exchange that may, for some species, maintain constant growth rates as climate and atmospheric CO2 concentrations change. These complex responses must be considered together to predict plant growth reactions to global atmospheric change, and the potential of forest ecosystems to sequester larger amounts of carbon in the future.

Is the release of phytosiderophores in zinc-deficient wheat plants a response to impaired iron utilization?

Abstract: The effect of zinc nutritional status on the time course of phytosiderophore release, and uptake of iron and translocation of iron to the shoot, was studied in nutrient solution cultures for two cultivars of wheat (Triticum aestivum. cv. Aroona: T. durum, cv. Duratit) differing in their susceptibility to zinc deficiency. In the zinc-efficient cultivar Aroona, under zinc deficiency translocation of iron from roots to shoot was significantly decreased in 13- and 15-day-old plants, whereas release of phytosiderophores was enhanced when the plants were 16 days old. As zinc deficiency became more severe in older plains, translocation of iron to the shoot was further decreased and release of phytosiderophores was further enhanced. Resupplying zinc in nutrient solution to zinc-deficient plants significantly increased the translocation of iron to the shoot after 48 and 72 h. Concomitantly the release of phytosiderophores was repressed. The other cultivar Durati classified as zinc-inefficient in field observations differed from cv. Aroona by showing a lower rate of phytosiderophore release under Zinc deficiency, and a less impaired translocation of iron to the shoot. Foliar application of iron citrate to zinc-deficient Aroona plants repressed the release of phytosiderophores and increased iron concentrations in shoot and roots. Application of 55Fe to the leaves demonstrated that retranslocation of iron from the shoot to the roots was not affected by the zinc nutritional status. It is concluded that enhanced release of phytosiderophores in zinc-deficient wheat plants was induced primarily by impaired trans-location of iron lo the shoot.

Nitrogen Reserve Mobilization during Regrowth of Medicago sativa L. (Relationships between Availability and Regrowth Yield).

Abstract: An experiment was designed to study the role of N and C reserves on regrowth of the shoots following defoliation of forage species. Starch and N accumulation in root and crown tissue of nonnodulated Medicago sativa L. were modified during regrowth by applying different levels of N and different cutting heights. Plants were obtained with similar crown and root dry weights, but having either low starch and high tissue N or high starch and low tissue N. The plants were then submitted to a second defoliation and supplied with optimal N nutrition, and N flow from reserve was quantified using pulse-chase 15N labeling. Maximum yields following the second regrowth were obtained from those plants having a high tissue N, despite their low level of nonstructural carbohydrate. When N in the roots and crown exceeded 5 mg N plant-1 at the beginning of regrowth, about 68% was translocated to regrowing shoots. Highly significant correlations were also found between the amounts of N available in roots and crown at the beginning of regrowth and (a) the amount of N that was mobilized to new tissues, (b) the amount of N taken up during the regrowth period, and (c) the final shoot yield after 24 d of regrowth. No similar correlations were found for plants that varied in their initial starch content of roots and crown. It is suggested that N reserves were used mainly during the first 10 d after defoliation, and that the resulting aerial growth during this period should be sufficient to restore N2 fixation and/or N uptake to levels equal to those prior to defoliation. These data emphasize (a) the importance of root N reserves in initiating and sustaining new shoot growth, and (b) the need for a re-evaluation of the contribution of C reserves to shoot regrowth.

Effect of NaCl salinity on growth, pigment and mineral element contents, and gas exchange of broad bean and pea plants

Abstract: Increasing salinity of growth medium induced a reduction in growth and transpiration rate. The concentrations of chlorophylls and carotenoids were increased in most cases in broad bean leaves while in pea plants they remained more or less unchanged with the rise of salinization up to 80mM NaCl. Thereabove a significant decrease in these contents was observed. A stimulation of the net photosynthetic rate of pea was observed at the lowest levels of NaCl but at the highest levels inhibitory effect was recorded. In broad bean all salinization levels inhibited photosynthetic activity, but dark respiration of both plant species was stimulated. The content of Na+ in the roots and shoots of both species increased at increasing salinity. In broad bean, Ca2+ concentration in shoots and K+ and Ca2+ contents of roots increased at increasing salinization, while in pea plants, the content of K+ and Ca2+ was almost unaffected by salinity. Salinity induced an increase in the content of these ions in pea roots. Mg2+ content in shoots and roots of both broad bean and pea decreased at increasing salinity except in roots of pea, where it was generally increased.