Molecular Cloning of Plant Spermidine Synthases

Four cDNAs for spermidine synthase (SPDS), which converts thediamine putrescine to the higher polyamine spermidine usingdecarboxylated S-adenosylmethionine as the co-factor, were isolatedfrom Nicotiana sylvestris, Hyoscyamus niger, and Arabidopsisthaliana. When the N. sylvestris SPDS cDNA was expressed ina SPDS-deficient E. coli mutant, the recombinant protein showedhigh SPDS activity, but did not have any spermine synthase activity.The plant SPDSs have molecular masses of about 34 kDa, possessthe co-factor binding motifs which have been proposed for S-adenosylmethionine,and are more homologous in amino acid sequence to tobacco putrescineN-methyltransferase (PMT) than to SPDSs from mammals and E.coli. The SPDS gene is expressed in root, stem, and leaf inN. sylvestris, whereas the PMT gene is expressed only in root.The potential evolution of plant SPDS and PMT, and their evolutionaryrelationships with animal SPDS are discussed. (Received September 3, 1997; Accepted November 5, 1997)     

Yield-Respiration Relationships at Different Bean (Phaseolus vulgaris) Plant Densities

Bean (Phaseolus vulgaris L.) plants were grown, one to fiveplants per pot, with a non-limiting supply of mineral nutrients.As plant density increased, seed and N yield per plant decreased,but those per pot remained fairly constant. The shoot: rootratio and the contribution of roots to total plant respirationwere also almost constant with changing density; the Q₁₀ forshoot respiration was higher at maximal densities. However,growth respiratory C losses per plant over the growth periodon a seed dry matter of N yield basis were not dependent onplant densities tested. Phaseolus vulgaris L., yield, respiration, plant density     

A New Model Relating Crop Yield and Plant Arrangement

A new model is proposed which relates the weight of plants totheir spatial arrangement. The weight of each plant is calculatedas the integral of the function f(r) = L(cr² + 1)^–2 overan area allocated to it, r being distance from the plant, withL and c parameters to be specified. The model is thus concise,general, in that it can be used to describe the effects of anyspatial arrangement on plant weight, and the parameters L andc have a biological interpretation. It is also consistent withthe commonly-used relationship between plant weight (w) anddensity (p), w^–1 = a+bp. We show for carrots (Daucus carota L.) and red beet (Beta vulgarisL.), that the mean weights fitted by the model agree as wellwith the experimentally observed mean plot weight as those fittedby more complex models with more parameters, some of which arenot as general. We show also that the parameter c can be predictedfrom the time from sowing to harvest, with good results whentested on sets of data independent of those to which the modelhad been fitted. The assumptions on which the model is based,its application, and extensions to it are discussed. Crop yield, plant density, plant arrangement, carrot, Daucus carota L., red beet, Beta vulgaris L., soya bean, Glycine max L., mathematical model     

A modified framework for the regional assessment of climate and human impacts on net primary productivity

Improving models that depict the components of net primary production (NPP) in ecosystems will help us to better understand how climate change and human activities affect the biosphere. In this study, NPP_gap was introduced into the present human appropriation of net primary production (HANPP) framework. We introduced NPP_gap in this study as potential NPP (NPP_pot) minus the sum of ecosystem NPP (NPP_eco) and HANPP, which relates to the ability of models to depict NPP components. Using the Lhasa River region of the Tibetan Plateau, we examined temporal and spatial variations in the components of NPP over a 10-year period. Results showed that NPP_pot, HANPP and NPP_eco increased from 2000 to 2010, but at different rates and with different spatial patterns. NPP_gap each year ranged from −9.2% to 13.1% for each site and on average composed 1.2% of the total NPP_pot. NPP_gap was significantly correlated with precipitation, plant biodiversity, plant height and soil properties. NPP_gap increased if either of the previous 2 years had been wet years with relative high precipitation. An increase in the richness of palatable species would lead to a larger NPP_gap through more compensatory growth. The large fluctuation level of NPP_gap reflected the higher stability of vegetation productivity, which is caused by higher plant heights and soil maximum water capacity. This study showed the potential of the HANPP framework in regional assessment of climate and human impacts on net primary productivity. The use of the NPP_gap measure reflects the gap in our knowledge and our ability to accurately estimate the components of NPP.     

The Effect of Lenient Defoliation on the Nitrogen Economy of White Clover: The Contribution of Mineral Nitrogen to Plant Nitrogen Accumulation During Regrowth

Single plants of white clover (Trifolium repens L.) were grownfrom stolon cuttings rooted in sand. All plants were inoculatedwith Rhizobium trifolii, and for 14 weeks received nutrientsolution containing 0.5 mg N each week, as either ammonium ornitrate. Plants were then leniently defoliated or were leftintact and a ¹⁵N-labelled N source was applied at intervalsof 4 d to replace the unlabelled N. Lement defoliation removedfully expanded leaves only; the remaining immature leaves accountedfor 39–44% of the total. At harvests over the following21 d, leaf numbers were counted and dry matter (DM), N contentsand ¹⁵N enrichments of individual plant organs were determined. Rates of leaf emergence and expansion were accelerated in defoliatedplants; numbers of young leaves were similar in defoliated andintact plants. Total DM and N content were less in defoliatedthan intact plants and were not affected by form of N supplied.DM of young leaves, growing points and stolons and N contentof young leaves were, however, greater when ammonium ratherthan nitrate N was supplied. Rates of increase in the contentof plant total N were 8.2 ± 1.36 mg N d^-1 and 10.2±1.82 mg N d^-1 in defoliated and intact plants respectively.The increases were predominantly due to N₂ fixation, since recoveryof ¹⁵N showed that less than 1% of the increment in plant totalN was assimilated mineral N. Nevertheless, the contributionof mineral N to plant total N was 50% more in defoliated thanin intact plants; higher amounts of mineral N were found particularlyin young leaves and growing points. Partitioning of mineralN to nodulated roots increased over time and was greater whenammonium rather than nitrate N was present. White clover, Trifolium repens L. cv. S184, lenient defoliation, N accumulation, N₂ fixation     

Identification of Cytokinins in Root Exudate of the Rice Plant

Cytokinins, cis-zeatin and cis- and (trans-ribosylzeatin, wereidentified in the root exudate of the rice plant (Oryza sativa,indica cultivar IR-24) after several chromatographic separationsand combined gas-liquid chromatography-selected ion monitoring(GC-SIM) analysis. The presence of trans-zeatin ribotide wassuggested by enzyme hydrolysis, subsequent chromatographic separationand GC-SIM. The comparatively high content of the ribotide inthe root exudate suggests the form of cytokinins to be transportedfrom roots to other parts in the rice plant. (Received July 22, 1982; Accepted November 25, 1982)     

The Effect of Defoliation on the Nitrogen Economy of White Clover: Regrowth and the Remobilization of Plant Organic Nitrogen

Single plants of white clover (Trifolium repens) were establishedfrom stolon cuttings rooted in acid-washed silver sand. Allplants were inoculated with Rhizobium trifolii, and receivednutrient solution containing 0·5 mg ¹⁵N as either ammoniumor nitrate weekly for 12 weeks (i.e. 6 mg ¹⁵N in total). Plantswere then leniently defoliated or left intact, and the labelledN supply was replaced with unlabelled N. Lenient defoliationremoved fully expanded leaves only, leaving immature leaveswhich accounted for 50–55% of the total; growing pointnumbers were not reduced. Nodules, leaves and growing pointswere counted over the following 21 d period, and d. wts, N contents,and ¹⁵N enrichments of individual plant organs were determined. Defoliated plants had fewer nodules, but numbers of growingpoints were unaffected by defoliation. The rates of both leafemergence and expansion were accelerated in defoliated plants;in consequence the number of young leaves remained less thanin intact plants until day 21. Total dry matter (DM) and N accumulationwere less in defoliated plants, and a greater proportion oftotal plant DM was invested in roots. About 97 % of plant totalN was derived from fixed atmospheric N, but there was incompletemixing of fixed and mineral N within the plant. Relatively moremineral N was incorporated into roots, whereas there was relativelymore fixed N in nodules. There was isotopic evidence that Nwas remobilized from root and stolon tissue for leaf regrowthafter defoliation; approximately 2 % of plant N turned overdaily in the 7-d period after defoliation, and this contributedabout 50% of the N increment in leaf tissue. White clover, Trifolium repens L. cv. SI84, lenient defoliation, N economy, regrowth, N remobilization     

The Physiology of Plant Nutation: I. NUTATION AND GEOTROPIC RESPONSE

The nutation of plant organs has been considered to be eitherthe result of a geotropic feedback loop or produced by an endogenousoscillator. Observations have been made of the angular displacementof Phaseolus seedlings during response to a gravitational stimulus.Nutational oscillations have been observed during the correctivemovement of the stimulated plants in many cases. Geotropic movementcan, however, occur in plants not exhibiting nutation. Theseobservations are considered to support the hypothesis that themovements of nutation in Phaseolus have an endogenous originunconnected with geotropic reactions. A theoretical model isproposed to account for the observed nutational behaviour ofbean seedlings.     

Growth of Individuals in Plant Populations

Relationships between individual plant weight and net photosynthesisper day (G(t, x) function of plant weight) in plant populationsof various stand structures were simulated based on a canopyphotosynthesis model. The G(t, x) functions of plant weightare determined mainly by LAI (leaf area index), the relationshipbetween individual plant weight and leaf area, canopy structureand extinction coefficient. The concave relationship betweenindividual plant weight and leaf area at small LAI (<2),at small extinction coefficient (< 0.5), or at the canopystructure having the maximum leaf area density at the bottomproduces a concave G(t, x) function, which generates negativeskewness of plant weight. The linear relationship between individualplant weight and leaf area at large LAI (> 2) produces aconvex G(t, x) function, which generates positive skewness ofplant weight. These simulation results coincide with G(t, x)functions obtained experimentally and with the well-known phenomenonof stand dynamics in which skewness of plant weight becomesnegative in the early growth stage and then increases to a positivevalue as a stand grows and becomes crowded. Helianthus annuus L., individual plant size, mean growth rate, canopy photosynthesis model, skewness, stand structure     

Plant allometry, leaf nitrogen and phosphorus stoichiometry, and interspecific trends in annual growth rates

• Background Life forms as diverse as unicellular algae,zooplankton, vascular plants, and mammals appear to obey quarter-powerscaling rules. Among the most famous of these rules is Kleiber's(i.e. basal metabolic rates scale as the three-quarters powerof body mass), which has a botanical analogue (i.e. annual plantgrowth rates scale as the three-quarters power of total bodymass). Numerous theories have tried to explain why these rulesexist, but each has been heavily criticized either on conceptualor empirical grounds. • N,P-Stoichiometry Recent models predicting growth rateson the basis of how total cell, tissue, or organism nitrogenand phosphorus are allocated, respectively, to protein and rRNAcontents may provide the answer, particularly in light of theobservation that annual plant growth rates scale linearly withrespect to standing leaf mass and that total leaf mass scalesisometrically with respect to nitrogen but as the three-quarterspower of leaf phosphorus. For example, when these relationshipsare juxtaposed with other allometric trends, a simple N,P-stoichiometricmodel successfully predicts the relative growth rates of 131diverse C₃ and C₄ species. • Conclusions The melding of allometric and N,P-stoichiometrictheoretical insights provides a robust modelling approach thatconceptually links the subcellular ‘machinery’ ofprotein/ribosomal metabolism to observed growth rates of uni-and multicellular organisms. Because the operation of this ‘machinery’is basic to the biology of all life forms, its allometry mayprovide a mechanistic explanation for the apparent ubiquityof quarter-power scaling rules.     

Handbook of Plant Science

At a bookshelf-bending 4·5 kg, a bank-balance-denting£250, edited by a highly distinguished plant scientist,and released in the publisher's bicentenary year, you are entitledto expect something really special from this Handbook of PlantScience (HoPS). However, on reading in the front matter thatHoPS ‘re-publishes a selection of recent and topical articlesfrom Wiley's landmark [internet-based] Encyclopedia of LifeSciences (ELS)’ I wondered if there really could be anythingspecial about this hard-copy collection. However, I was initiallyreassured by the Preface, which explains that the EditorialAdvisory Board (all from the John Innes Centre, UK) commissionednew peer-reviewed articles for HoPS to fill in gaps in the existingplant-related ELS articles. So, something new and thereforespecial was in prospect after all. In view of the enormity of present-day plant science, an editorialdecision was taken     

Environment Dependent Chlorosis in a Mutant Plant of Festuca pratensis, Huds

The chlorophyll content of the leaf tissue from a chlorotichomozygous recessive mutant plant of Festuca pratensis was affectedby variation in the light and temperature regimes to which theplants were exposed. Chlorophyll content was depressed whenthe plant grew rapidly, but was similar to that of normal greenplants when grown slowly under low-light and low-temperatureregimes. Chlorotic plants showed a reduction in dry weight,percentage dry matter, and plastid number but an increase inthe ratio of chlorophyll a : chlorophyll b compared to normalplants.The chloroplasts of the rapidly grown chlorotic plantsshowed a reduced lamellar structure.     

Nitrogen States in Plant Ecosystems: A Viewpoint

Terrestrial ecosystems are considered to be in only two possiblestates: N unsaturated or N saturated. This view lacks rigourand has led to three differing concepts of N saturation: (1)a continuum of changes in N states and processes; (2) a thresholdpoint, when N output increases; and (3) any equilibrium state,when N output equals N input. A simple model of ecosystem Ncontent, input and output is used to point out that, strictly,there are four possible N states of ecosystems: (1) at equilibrium,but N unsaturated and N-limited, so that they will respond toadditional N input with increased N accumulation; (2) not atequilibrium and accumulating N, either in response to additionalN input, or more commonly in nature, when recovering from fire,other disturbance or unfavourable conditions; (3) at equilibriumbut truly N saturated and not N-limited, so that any additionalN input is matched by equal N output; and (4) not at equilibriumand losing N because of disturbance or soil changes inducedby N addition itself or other factors. Most natural ecosystemsare, for most of the time, in one of the two non-equilibriumstates, especially in short-term N-addition experiments. Itis not meaningful to regard them as being either N saturatedor N-limited. Copyright 2000 Annals of Botany Company Nitrogen saturation, deposition, leaching, nitrification, plant ecosystems, forest     

Uptake and Redistribution of 15N Within an Established Asparagus Crop after Application of 15N-labelled Nitrogen Fertilizer

The uptake and redistribution of ¹⁵N within a 6-year-old asparagus(Asparagus officinalis L.) crop were examined for applicationsof ¹⁵N-enriched ammonium sulphate (5 g N m^-2) either prior togrowth of foliage (commonly called 'fern'), prior to harvest,or early-harvest prior to the main period of spear (newly-emerged,edible, unexpanded shoot) production. During the harvest inspring, 38 kg N ha^-1 was removed in harvested spears, but thiswas small compared to the 710 kg N ha^-1 present in crowns androots. Limited uptake of ¹⁵ N occurred during harvest from thepre-harvest and early-harvest applications (11 and 4% of the¹⁵N applied, respectively) and the lack of plant uptake of Nfrom soil was also evident from an accumulation of inorganicN in unfertilized soil during spring. These results indicatethat N in spears was derived largely from remobilisation ofN stored in the crowns and roots. Most plant uptake of added ¹⁵N occurred during the first 8 weeksof foliage growth in summer, when 282 kg N ha^-1 had accumulatedin the above-ground foliage. After this 8 week period, foliagefrom the early-harvest treatment contained 24% of the ¹⁵N applied.Fifteen weeks later (late autumn), foliage was senescing andthe ¹⁵N content of senesced foliage in all treatments had declinedby 90% due to remobilisation and translocation into the crownand root tissue. Similarly, foliage N had declined from 282to 24 kg N ha^-1 and this remobilised N was equivalent to approximately40% of the total plant N present prior to foliage growth. During the subsequent spring period, the ¹⁵N enrichment of spearswas about twice that of the crowns and roots. Thus, there waspreferential remobilisation of recently-absorbed, stored N fornew spear growth.Copyright 1994, 1999 Academic Press Asparagus, Asparagus officinalis, nitrogen, ¹⁵N, redistribution, remobilisation, uptake     

The Application of 31P Nuclear Magnetic Resonance to Higher Plant Tissue: I. DETECTION OF SPECTRA

³¹P nuclear magnetic resonance (NMR) spectra are described fora variety of plant tissues, including sections of mature potatotuber (Solanum tuberosum) and sections of maize seedling (Zeamays). The experimental procedures for obtaining such spectra,using a conventional high field spectrometer, are discussedin detail. Assignments are given for the observed resonancesand the results are discussed in relation to the storage formsof plant phosphate. Attention is drawn to the power of the techniqueto distinguish the cytoplasm and vacuole in vivo, through thewell-known pH dependence of the ³¹P chemical shifts.     

Interaction between Nitrogen Deficit of a Plant and Nitrogen Content in the Old Leaves

We examined changes in nitrogen content of the first leavesin relation to growth and nitrogen status of sunflower (Helianthusannuus L.) plants that were raised hydroponically at two irradiancelevels (high and low light, HL and LL) and at two nitrogen concentrations(high and low nitrogen, HN and LN). Initial increases in totaldry mass and total nitrogen of the whole plant were faster inHL-plants than in LL-plants irrespective of nitrogen supply,but in LN-plants the increase in total nitrogen was soon blunted.When plants grown under the same irradiance were compared, nitrogencontent of the first leaves (leaf N) decreased faster in LN-plantsthan in HN-plants, while for the plants grown at the same nitrogenconcentrations, it decreased faster in HL-plants than in LL-plants.Since these changes in leaf N were not explained solely by thechanges in plant dry mass or plant nitrogen, we introduced anindex, ‘nitrogen deficit (ND^*)’, to quantify nitrogendeficit of the whole plant. ND^* was expressed as ND^*(t)=[N_max–N(t)]xDM(t),where N_max and N(t) were nitrogen contents in the young, expandingleaves that had just unfolded to expand, at the initial stagewith sufficient nitrogen and at time t, respectively, and DM(t),plant dry mass at t. The decrease in leaf N was expressed asa liner function of ND^* irrespective of the growth conditions,which indicates validity of this index. Limitation of the useof ND^*, and mechanisms by which leaves sense nitrogen demandare also discussed. (Received June 17, 1996; Accepted August 30, 1996)     

Further Investigations of Liposoluble Fluorescent Compounds in Senescing Plant Cells

The accumulation of liposoluble fluorescent compounds with excitationand emission fluorescent maxima in the bands of 350–370nm and 410–440 nm respectively has been observed in thedegrading (the late stationary phase) blue-green algae Anabaenavariabilis K?tz and Anabaena cylindrica Lemm. cells, in thedark-senescing cotyledons from Phaseolus vulgaris L., and inmore than 1-year-old leaves of evergreen plants (Ligustrum japonicumThunb. and Osmanthus fortunei Carr.)- Spectral and chromatographicproperties of the compounds are rather similar to those previouslydescribed in the cells of other senescing plant species. Therole of lipid peroxidation in the formation of fluorescent pigmentsand in the ageing of plant cells is discussed. Key words: Fluorescent pigment, Anabaena sp, Senescence     

The Pattern of Respiration Rate in the Vegetative Barley Plant

In two experiments with young barley plants, respiration rate,carbohydrate content and growth rate of the whole plant weremeasured. When 18-day-old plants were darkened the rate of respirationand the levels of soluble carbohydrate fell in parallel overthe following 30 h. When the dark respiration rate of plantswas followed from 7 to 24 days respiration rate and solublecarbohydrate levels did not change together, nor did the respirationrate (R) follow the empirical relationship with photosynthesis(P) and d. wt (W) R = aW + bP, suggested by McCree. Hordeum distichum L. (Lam), barley, respiration, carbohydrate content     

A Model for the Growth of Individuals in Plant Populations Cultivated at Different Concentrations of Fertilizer Solution

The growth of mean individual weight is the joint outcome ofthe growth of the individuals comprising a population. Fromthe growth data of individual weight in radish (Raphanus sativusL. var. radiculus Pers.) populations cultivated at differentconcentrations of ammonium sulphate solution, a deterministicmodel was proposed for integrating individual plant weight intomean weight per plant in a population. The model constructiondepended on the relation between mean individual weight andthe amount of fertilizer supplied to a population, and uponPearson's type VII distribution. The model related the weightof any individual to the amount of fertilizer. The fitness ofthe model to observed data was satisfactory, although the modelwas simple. Using the model, properties of the growth of componentindividuals of a population were examined in relation to thegrowth of mean individual weight. fertilizer, growth, individual, mean, Pearson's type VII distribution, plant weight, population, radish, Raphanus sativus L. var. radicula Pers     

A Model of the Leaf Extension Rate of Tall Fescue in Response to Nitrogen and Temperature

The leaf extension rate (LER) of tall fescue (Festuca arundinaceaSchreb.) was studied in the field under various nitrogen andtemperature regimes. The LER was closely related to temperaturewhen N was not limiting plant growth. Two distinct relationshipsbetween the LER and the temperature were obtained, one for vegetativegrowth and one for the reproductive period. These relationships,described by a Gompertz function, were exponential at temperaturesbelow 8 °C and linear at temperatures above 8 °C. Theymade possible the calculation of an optimal LER correspondingto non-limiting N conditions for plant growth. The strong influence of the temperature on the LER was stillobserved under N limiting conditions. The N status of the swardswas described by the ratio between the actual N content (N_actual)and the optimal N content (N_optimal). The N_optimal was definedas the N content experienced at a non-limiting level of N nutritionbut without N luxury consumption. The N_optimal, expressed asa function of dry matter yield, declined during growth. Theeffect of the N status of the swards on the LER was analysedby calculating the ratio between the actual LER and the optimalLER, and relating it to the ratio between N_actual and N_optimal.It was shown that these two ratios were highly correlated. Leaf extension, Festuca arundinacea, nitrogen, temperature