Leaf Extension in Zea mays: III. FIELD MEASUREMENTS OF LEAF EXTENSION IN RESPONSE TO TEMPERATURE AND LEAF WATER POTENTIAL

Leaf extension rates of young maize plants were measured inthe field. Large diurnal fluctuations of air temperature fromabout 5—35°C caused extension rates to vary from 0·4mm h^–1– 3·6 mm h^–1. When the temperatureof the shoot apical meristem was kept at 30–34°C,extension rates remained constant, despite diurnal fluctuationsof air temperature. Leaf water potentials () above –8 or –9 bars hadlittle apparent effect on extension rate. It was concluded that gradients within leaves could account for this.     

Analysis of the Nitrogen Response of Leaf Extension in Lolium temulentum Seedlings

Lolium temulentum seedlings were grown on a nutrient mediumcontaining NH₄NO₂ at 0, 0·1, 0·5, 1·0 and4·3 mmoll^–1 as the sole N source. Relative andabsolute extension rates, maximal leaf size, duration of extensiongrowth, rate of leaf appearance and plastochron index were determinedfrom the parameters of Richards functions fitted to lengthsof laminae measured at intervals after sowing. The final lengthof leaf I was relatively insensitive to N whereas mean relativeextension rate was increased and duration of growth decreasedwith increasing NH₄NO₂ concentration. Leaves 2 and 3 enlargedprogressively with N at concentrations up to 1·0 mmoll^–1but were unresponsive thereafter. There was no significant correlationbetween final length and mean relative extension rate for leaves1 to 3. Leaves 4 to 6 continued to show increasing length beyond1·0 mmoll^–1 N and final length was significantlycorrelated with mean relative extension rate. Increasing N increasedthe rate of leaf appearance by decreasing the duration of leafextension and plastochron. These results are discussed in relationto the control of leaf and N turnover. Lolium temulentum, rye grass, leaf extension, nitrogen, Richards function, growth analysis     

Turgor, Growth and Rheological Gradients of Wheat Roots Following Osmotic Stress

The growth rate of hydroponically grown wheat roots was reducedby mannitol solutions of various osmotic pressures. For example,following 24 h exposure to 0·96 MPa mannitol root elongationwas reduced from 1· mm h^–1 to 0·1 mm h^–1 Mature cell length was reduced from 290 µm in unstressedroots to 100 µm in 0·96 MPa mannitol. This indicatesa reduction in cell production rate from about 4 per h in theunstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressedroots but became shorter as growth ceased in the proximal regionsat higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressedroots was between 0·5 and 0·6 MPa but declinedto 0·41 MPa over the next 50 mm. Following 24 h in 0·48(200 mol m^–3) or 0·72 MPa (300 mol m^–) mannitol,turgor along the apical 50 mm was indistinguishable from thatof unstressed roots but turgor declined more steeply in theregion 5·10 mm from the tip. At the highest level ofstress (0·96 MPa or 400 mol m^–3 mannitol) turgordeclined steeply within the apical 20 mm. Key words: Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment     

A Sensitive Auxanometer for Field Use

The essential characteristics of an auxanometer designed tomeasure the extension rates of grass leaves in the field areoutlined. The construction, using a linear-variable differentialtransformer (LVDT) to measure displacement, is described. Laboratorytests showed a linear relation between output and armature displacement,which was independent of changes in temperature between 1 and24 °C. Field tests on winter wheat leaves showed good agreementbetween auxanometer and rule measurements of leaf extensionmade over time periods of 24, 12, and 2 h. The tests and ananalysis of the errors, including the thermal expansion of theauxanometer stand, show that this auxanometer can reliably andaccurately measure leaf extension rates of between 0·1and 10 mm h^–1 in wind speeds up to 4·5 m s^–1.     

The Structure and Function of Pine Forest in Central Himalaya. I. Dry Matter Dynamics

The present study deals with structure and function of fourareas of Himalayan chir pine forest. Tree layer was monospecificon all sites with varied density and basal cover in the rangeof 540–1630 individuals per ha and 25·0–47·2m²ha^–1, respectively. Shrubs having low density were sparselydistributed. All allometric equations relating to biomass ofdifferent components, to circumference at breast height (cbh)were significant, with the exception of that for cone biomass.Total vegetation biomass (115–236 t ha^–1) was distributedas 113–283 t ha^–1 in trees. 0·56–0·82t ha^–1 in shrubs and 1·63–2·57 t ha^–1in herbs. Total forest floor biomass including herbaceous litterranged between 9·6 and 13·6 t ha^–1. Of thetotal annual litter fall (4·26–7·38 t ha^–1),60·3–75·1 per cent was distributed in leaflitter and 24·9–39·7 per cent in wood litter.Turnover rate of tree litter varied from 0·45 to 0·53,whereas rates for shrubs and herbs were assumed to 1. Net primaryproduction of total vegetation ranged between 9·91 and21·2 t ha^–1 year^–1, of which the contributionof trees, shrubs and herbs was 76·5– 88·1per cent 0·6–1·8 per cent and 11·3–21·5per cent, respectively. A compartment model of dry matter onthe basis of mean data across sites was developed to show drymatter storage and flow of dry matter within the ecosystem. Pinus roxburghii forest, biomass, litter fall, net primary production, compartmental transfer     

Plant Growth in Relation to the Supply and Uptake of NO3-: A Comparison Between Relative Addition Rate and External Concentration as Driving Variables

Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO₃^– by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO₃^– at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d^–1, or constant external concentrations ([NO₃^–)of 3, 10, 20, and 100 mmol m^–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d^-1, although growth was notlimited by N supply at RAR =0.18 d^-1. Growth rates showed littlechange with [NO₃–] between 10–100 mmol m^–3(RGR=0·15 –0·16 d^-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO₃^–, accumulation of NO₃^– in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO₃^– from 1 mol m^–3 solutions were assessed relativeto the growth-related requirement for NO₃^–, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d^–1 , but decreased thereafter to a theoretical minimumvalue at RGR     

Control of Wheat Root Elongation Growth: I. EFFECTS OF IONS ON GROWTH RATE, WALL RHEOLOGY AND CELL WATER RELATIONS

Pritchard, J., Tomos, A. D. and Wyn Jones, R. G. 1987. Controlof wheat root elongation growth. I. Effects of ions on growthrate, wall rheology and cell water relations.—J. exp.Bot. 38: 948–959. The nature of the ions in the bathing medium of hydroponicallygrown wheat seedlings strongly influenced root growth rate.In 0·5 mol m^–3 CaSO₄ the growth rate was 32 mm24 h^–1 (used as 100% control rate). K⁺ and SO^– ions(10 mol m^–3) each inhibited extension growth (to about40% and 70% of the control value respectively). In the absenceof K⁺, Cl^– greatly reduced the inhibition due to SO₄^2–.Measurement of tissue plasticity and elasticity in the expandingzone with an Instron-type tensiometer indicated that both werea function of growth rate although relationship of plasticityto growth rate was the steeper and the more pronounced. Turgor pressure at the proximal end of the expanding zone wasnot correlated to growth, being approximately 0·65 MPain all treatments. In mature tissue turgor pressure varied withtreatment, but was also not related to growth rate. Cell membranehydraulic conductivity (5 x 10^–7 ± 1·3 (10)m s^–1 MPa^–2) was not influenced by the presenceof K⁺. We propose that K⁺ and SO₄^{2 –} influence root growthrates by modulating the rheological properties of the wallsof the expanding cell. The physiological significance of these properties is discussed. Key words: Growth, wall extensibility, turgor pressure, wheat roots     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Distribution of Growth in the Apical Region of the Shoot of Lupinus albus

The purpose of the investigation is the determination of thevolumes and numbers of cells of the meristematic dome and ofeach of the first 7 primordia and internodes at the apex ofthe shoot of Lupinui albus. This system occupies a zone whichis about 0·4 mm. in length. Techniques are describedfor dissecting the region in which the observations are made,for determining the numbers of cells and the volumes of theseveral fragments. From the number of cells and the volume ofeach fragment an average cell volume it calculated. It is shown that in the midphase of the plastochron the domecontains 3,500 cells and has a volume of 1·6 x10^–3mm.³,the first primordium contains 1,630 cells and has a volume of0·38 x10^–3 mm.³, and the first intemode containsabout 700 cells and has a volume of about 1·4 x10^–3mm³The number of cells and the volume of the primordium increaseexponentially with increasing plastochron age, and the seventhprimordium contains 26,000 cells and has a volume of 20·9x 10^–3mm³ The seventh intemode contains about 5,000 cellsand has a volume of 8·6x10^–3mm³ The average cell volume in the dome is 4·7 x 10^–7mm.³in the first primorndium it is 2·3 x 10^–7mm.³ andin the first internode it is 20·9x 10^–7mm.³ Inthe seventh primordium the average cell volume increases to7·9 x 10^–7mm.³ In the internodes there is little,if. any, change in cell volume from the first to the seventhof the series. The significance of these changes is discussed.     

Responses by Coleoptiles of Intact Rice Seedlings to Anoxia: K+ Net Uptake from the External Solution and Translocation from the Caryopses

This study evaluated the effects of anoxia on K⁺ uptake andtranslocation in 3–4-d-old, intact, rice seedlings (Oryzasativa L. cv. Calrose). Rates of net K⁺ uptake from the mediumover 24 h by coleoptiles of anoxic seedlings were inhibitedby 83–91 %, when compared with rates in aerated seedlings.Similar uptake rates, and degree of inhibition due to anoxia,were found for Rb⁺ when supplied over 1·5–2 h,starting 22 h after imposing anoxia. The Rb⁺ uptake indicatedthat intact coleoptiles take up ions directly from the externalsolution. Monovalent cation (K⁺ and Rb⁺) net uptake from thesolution was inhibited by anoxia to the same degree for thecoleoptiles of intact seedlings and for coleoptiles excised,‘aged’, and supplied with exogenous glucose. Transportof endogenous K⁺ from caryopses to coleoptiles was inhibitedless by anoxia than net K⁺ uptake from the solution, the inhibitionbeing 55 % rather than 87 %. Despite these inhibitions,osmotic pressures of sap (_sap) expressed from coleoptiles ofseedlings exposed to 48 h of anoxia, with or without exogenousK⁺, were 0·66 ± 0·03 MPa; however,the contributions of K⁺ to _sap were 23 and 16 %, respectively.After 24 h of anoxia, the K⁺ concentrations in the basal10 mm of the coleoptiles of seedlings with or without exogenousK⁺, were similar to those in aerated seedlings with exogenousK⁺. In contrast, K⁺ concentrations had decreased in aeratedseedlings without exogenous K⁺, presumably due to ‘dilution’by growth; fresh weight gains of the coleoptile being 3·6-to 4·7-fold greater in aerated than in anoxic seedlings.Deposition rates of K⁺ along the axes of the coleoptiles werecalculated for the anoxic seedlings only, for which we assessedthe elongation zone to be only the basal 4 mm. K⁺ depositionin the basal 6 mm was similar for seedlings with or withoutexogenous K⁺, at 0·6–0·87 µmolg^–1 f. wt h^–1. Deposition rates in zones above6 mm from the base were greater for seedlings with, thanwithout, exogenous K⁺; the latter were sometimes negative. Weconclude that for the coleoptiles of rice seedlings, anoxiainhibits net K⁺ uptake from the external solution to a muchlarger extent than K⁺ translocation from the caryopses. Furthermore,K⁺ concentrations in the elongation zone of the coleoptilesof anoxic seedlings were maintained to a remarkable degree,contributing to maintenance of _sap in cells of these elongatingtissues.     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

Ascorbate enhancement of H1 histamine receptor sensitivity coincides with ascorbate oxidation inhibition by histamine receptors

Ascorbate has previously been shown to enhance both ₁- and ₂-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to _1- and ₂-adrenergic receptors. Physiological concentrations of ascorbate (50 µM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 µM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 µM histamine (5–500 µM ascorbate) and 0.3 µM histamine (15–500 µM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37°C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 µg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 µM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min·µg protein^–1·ml^–1, compared with rates for transfected ANG II membrane (0.055 min·µg protein^–1·ml^–1), untransfected membrane (0.052 min·µg protein^–1·ml^–1), creatine kinase (0.0082 min·µg protein^–1·ml^–1), keyhole limpet hemocyanin (0.00092 min·µg protein^–1·ml^–1), and osmotically lysed aortic rings (0.00057 min·µg wet weight^–1·ml^–1). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state. molecular complementarity; vitamin C; seven-transmembrane-spanning membrane receptors     

Proton Fluxes and the Activity of a Stelar Proton Pump in Onion Roots

The xylem vessels of excised adventitious roots of onion, Alliumcepa, were perfused with unbuffered nutrient solution adjustedinitially to either pH 9·3 or 3·9; the pH of thesolution after passage through the xylem, at rates not lessthan 2 xylem volume changes min^–1, was close to pH 6·5in both instances. The flux of H⁺ across the xylem/symplastboundary into mildly alkaline, phosphate-buffered solutionsperfusing the vessels could be increased greatly with increasingbuffer strength, up to a maximum value between 0·5–1·0pmol H⁺ mm^–2 s^–1. The apparent neutralization ofacidic malic acid buffers had a slightly lower maximum capacity,equivalent to –0·3 to –0·5 pmol H⁺mm^–2 s^–1. The addition of 5·0 pmol m^–3fusicoccin (FC) to the xylem perfusion solution stimulated theentry of H⁺ into the xylem; in unbuffered perfusion solutionsthe pH fell to pH 3·6 after a lag of 25–35 min.FC additions to phosphate-buffered solutions also stimulatedthe H⁺ flux to an extent similar to that in unbuffered solution,viz. 0·2–0·4 pmol mm^–2 s^–1. The release of K⁺ (³⁶Rb-labelled) into xylem sap transientlyincreased as the [K⁺] in weakly buffered perfusion solutionswas raised stepwise; a very marked increase being seen whenthe concentration was raised to 100 mol m^–3 from 40 molm^–3. The addition of 5·0 mmol m^–3 FC to theperfusing solution containing 100 mol m^–3 K⁺ rapidly decreasedthe K⁺ flux to the xylem as the H⁺ flux increased. Fusicoccinalso inhibited the flux of K⁺ into unbuffered perfusion solutionsbut the effect appeared reversible. Addition of 10 mmol m^–3abscisic acid (ABA) to the perfusion solution quickly producedtransient increases in both K⁺ and H⁺ fluxes into the xylem.In this and other experiments using weakly phosphate-bufferedperfusing solutions, H⁺ fluxes were comparable in size to thoseof K⁺ The results are consistent with the idea that the stele of onionroots contains a proton trarislocating ATPase whose activityresponds to the pH of the xylem sap. It is evident that theactivity of the proton secreting and proton neutralizing mechanismsin the xylem parenchyma control the movement of other ions acrossthe xylem/symplast boundary. Key words: Xylem perfusion, fusicoccin, abscisic acid, pH gradient     

Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.)

The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg^–1 s^–1for cable roots and 3·27±0·12 µmolkg^–1 s^–1 for fine roots. The Q₁₀ for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m^–3 and 3·4mol m^–3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Structure and Function of Oak Forests in Central Himalaya. I. Dry Matter Dynamics

The present study deals with structure and functioning of threeareas of Himalayan oak forest. Low- and mid-altitude oaks, namelyQuercus leucotrichophora, and Quercus floribunda, form predominantevergreen forests in Central and Western Himalaya. The totaltree basal cover ranged between 33·89 m² ha^–1 (Q.floribunda site) to 36·83 m² ha^–1 (Q. leucotrichophorasite). The density ranged between 570 and 760 individuals ha^–1.Allometric equations relating biomass of different tree componentsto GBH (girth at breast height) were significant with the exceptionof leaf biomass in Q. leucotrichophora and Rhododendron arboreum.Total vegetation biomass (29·40–467·0 tha^–1) was distributed as 377·1 t ha^–1 intrees, 5·40 t ha^–1 in shrubs and 1·23 tha^–1 in herbs. Total forest floor biomass ranged between4·6 and 6·2 t ha^–1. Of the total annuallitter fall (4·7–4·8 t ha^–1), 77·5% was contributed by leaf litter, 17·8 % by wood litterand 4·7 % by miscellaneous litter. Turnover rate of treelitter varied from 0·66 to 0·70. Net primary productionof total vegetation ranged between 15·9 and 20·6t ha^–1 yr^–1, of which the contribution of trees,shrubs and herbs was 81·2 %, 8·6 % and 10·2%, respectively. A compartment model of dry matter on the basisof mean data across sites was developed to show dry matter storageand flow of dry matter within the system. Quercus leucotrichophora forest, Q. floribunda forest, Q. lanuginosa forest, biomass, litter fall, net primary production, compartmental transfer     

Transnodal Transport of 14C in Nitella flexilis: I. TANDEM CELLS WITHOUT APPLIED PRESSURE GRADIENTS

Using NaH¹⁴CO₃ (0·01-0·03 mol m^–3) fed to5·0 mm of Nitella flexilis in artificial pond water at22–25°C, we have found that uptake in 5 min or in1 h varies with the streaming rate of the fed cell and is reducedby anoxia over the uptake position. We have also found thatthe %¹⁴C transported across the node between two internodalcells in tandem is highly sensitive to the streaming rate ineach cell, to the physiological state of the cells (summer versuswinter), to the method of feeding (5 min versus 1 h) and tocovering the node, particularly with winter cells or summercells preconditioned for 3 h in the dark and run in the dark.Transnodal transport by plasmodesmata is sensitive to anoxiaand seems to be at least partly active. Key words: Node, plasmodesmata, anoxia, active transport, influx     

Dexamethasone treatment causes resistance to insulin-stimulated cellular potassium uptake in the rat

Patients treated with glucocorticoids have elevated skeletal muscle ouabain binding sites. The major Na⁺-K⁺-ATPase (NKA) isoform proteins found in muscle, ₂ and ₁, are increased by 50% in rats treated for 14 days with the synthetic glucocorticoid dexamethasone (DEX). This study addressed whether the DEX-induced increase in the muscle NKA pool leads to increased insulin-stimulated cellular K⁺ uptake that could precipitate hypokalemia. Rats were treated with DEX or vehicle via osmotic minipumps at one of two doses: 0.02 mg·kg^–1·day^–1 for 14 days (low DEX; n = 5 pairs) or 0.1 mg·kg^–1·day^–1 for 7 days (high DEX; n = 6 pairs). Insulin was infused at a rate of 5 mU·kg^–1·min^–1 over 2.5 h in conscious rats. Insulin-stimulated cellular K⁺ and glucose uptake rates were assessed in vivo by measuring the exogenous K⁺ infusion () and glucose infusion (G_inf) rates needed to maintain constant plasma K⁺ and glucose concentrations during insulin infusion. DEX at both doses decreased insulin-stimulated glucose uptake as previously reported. G_inf (in mmol·kg^–1·h^–1) was 10.2 ± 0.6 in vehicle-treated rats, 5.8 ± 0.8 in low-DEX-treated rats, and 5.2 ± 0.6 in high-DEX-treated rats. High DEX treatment also reduced insulin-stimulated K⁺ uptake. (in mmol·kg^–1·h^–1) was 0.53 ± 0.08 in vehicle-treated rats, 0.49 ± 0.14 in low-DEX-treated rats, and 0.27 ± 0.08 in high-DEX-treated rats. DEX treatment did not alter urinary K⁺ excretion. NKA ₂-isoform levels in the low-DEX-treated group, measured by immunoblotting, were unchanged, but they increased by 38 ± 15% (soleus) and by 67 ± 3% (gastrocnemius) in the high-DEX treatment group. The NKA ₁-isoform level was unchanged. These results provide novel evidence for the insulin resistance of K⁺ clearance during chronic DEX treatment. Insulin-stimulated cellular K⁺ uptake was significantly depressed despite increased muscle sodium pump pool size. skeletal muscle; sodium pump; Na⁺-K⁺-ATPase     

Structure and Function of Oak Forests in Central Himalaya. II. Nutrient Dynamics

This paper elucidates nutrient dynamics in oak forests previouslyinvestigated for dry matter dynamics. The nutrient concentrationsin different life forms were of the order: herb > shrub >tree, whereas the standing state of nutrients were of the order:tree > shrub > herb. Soil, litter and vegetation, respectively,accounted for 32·4–98·0 %; 0·3–3·5%, and 10·2–66·6 % of the total nutrientsin the system. Considerable reductions (8·5–41·7%)in concentrations of nutrients in leaves occurred during senescence.The uptake of nutrients by vegetation, and also by differentcomponents with and without adjustment for internal recycling,has been calculated separately. Annual transfer of litter (above+ below ground) to the soil by vegetation was 115·9–187N, 7·5–15·6 P, 122·7–195·1Ca, 36·1–48·8 K and 2·88–5·16Na kg ha^–1 yr^–1. Turnover rate and turnover timefor different nutrients ranged between 0·66–0·84yr^–1 and 1·19–1·56 yr^–1, respectively.Compartment models for nutrient dynamics have been developedto represent the distribution of nutrient contents and net annualfluxes within the system. Quercus leucotrichophora forest, Q.floribunda forest, Q. lanuginosa forest, Nutrient concentration, standing state, uptake, internal cycling, turnover