Biosynthesis of folic acid compounds in plants VI. The occurrence and properties of the dihydrofolate-synthesizing enzyme in pea seedlings

An enzyme, which catalyzes the formation of dihydrofolate fromdihydropteroic acid and L-glutamic acid, was found in pea seedlings.The enzyme was purified approximately 25-fold from the crudeextracts of pea seedlings, and its some properties were investigated.Optimum pH for the enzyme activity was found to be 8.8. Pteroicand tetrahydropteroic acids were not active as substrate. Theenzymatic reaction required as cofactors ATP, divalent (Mg²⁺or Mn²⁺) and univalent (K⁺, NH₄⁺ or Rb⁺) cations. The productwas characterized as dihydrofolic acid by bioautography. MICHAELIS constants for L-glutamic acid, ATP, dihydropteroicacid and Mg²⁺ were 7.0x10^–4, 9.0x10^–5, 3.5x10^–6and 1.2x10^–3 M, respectively. The MICHAELIS constant forMn²⁺ was 3.0x10^–4. The enzyme was inhibited by PCMB orsilver nitrate and, to some extent, by L-aspartic acid. Inhibitionby PCMB was completely reversed by addition of 2-mercaptoethanol.Enzyme activity was distributed widely among plants. The importanceof magnesium and potassium ions for enzyme catalysis is discussed. ¹For the previous paper, Part V, see Reference (30). (Received March 28, 1970; )     

The occurrence and properties of dihydrofolate reductase in pea seedlings

Dihydrofolate reductase (E.C. 1.5.1.3 [EC] ) was found in pea seedlingsand was partially purified by treatments with ammonium sulfate,protamine sulfate and by DEAE-cellulose column chromatography.Some properties of the enzyme were investigated. Optimum pHfor the reaction was 6.5. In the enzyme reaction, FAH₂ and NADPH₂were specifically required. MICHAELIS constants for FAH₂ andNADPH₂ were 4.3x10^–6 M and 4.0x10^–5 M, respectively.Folate antagonists such as aminopterin, methotrexate and pyrimethaminewere potent inhibitors of this enzyme. Enzyme activity was almostcompletely inhibited at a concentration of 10^–7 M of aminopterinand methotrexate and 10^–6 M of pyrimethamine. Growth of germinating pea seeds was inhibited by aminopterin,methotrexate and pyrimethamine, and it recovered significantlywith a tetrahydro-derivative of folate, CF, but not with dihydrofolicor folic acid. These results suggest that growth inhibitionof pea seedlings by these antagonists is due to inhibition ofdihydrofolate reductase in seedlings. ¹Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants IV. (For the previous paper, Part III, seeReference (21)) . Part of this paper was presented at the AnnualMeeting of the Agricultural Chemical Society of Japan held atTokyo on April 4, 1967 (Received October 8, 1969; )     

THE DISTRIBUTION OF FORMYLTETRAHYDROFOLATE SYNTHETASE IN PLANTS, AND THE PURIFICATION AND PROPERTIES OF THE ENZYME FROM PEA SEEDLINGS

1. Formyltetrahydrofolate synthetase (E. C. 6. 3. 4. 3) was foundto be widely distributed in higher plants and the high enzymeactivity was observed in green leaves of Brassica and Alliumspecies, spinach, and in pea seedlings. In pea seedlings, theenzyme activity changed during the course of germination, andmost of the enzyme activity was located in a soluble fractionof the cytoplasm.
2. The enzyme was labile and lost the activityrapidly, even whenstored at 5 in the presence of 0.1 M mercaptoethanol.It was,however, found that ammonium sulfate was very effectivein stabilizingthe enzyme activity.
3. The enzyme has been purifiedapproximately 500-fold from extractsof pea seedlings by treatmentswith ammonium sulfate, protaminesulfate, hydroxylapatite, calciumphosphate gel, and DEAE-cellulosecolumn chromatography.
4. Thepurified enzyme was specific for formate, ATP and FAH₄,andthe Michaelis constants for these reactants were 2.1 10^–2M, 5.1 10^–4 M, and 5.6 10^–3 M, respectively.
5. The optimum pH was found to be 8.0, and the optimal temperaturewas observed at 37. Both NH₄^$ and a divalent cation (Mg^SS orMn^SS) were required for the optimal activity.

¹ Studies on the Enzymatic Synthesis and Metabolism of FolateCoenzymes in Plants. II. (For the previous paper see reference(8)) A part of this paper was presented at the Meeting of theKansai Division of the Agricultural Chemical Society of Japan,Kyoto, January 29, 1966.     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

The Relationship Between Growth and Oxygen Uptake in Hypoxic Rice Seedlings

Atwell, B. J. and Green way, H. 1987. The relationship betweengrowth and oxygen uptake in hypoxic rice seedlings.—J.exp. Bot. 38: 454–465. Rice seedlings (Oryza saliva L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO₂. Compared with seedlings grown at 0·250 mol O₂ m^–3,the dry weight of the growing seedling was 14% lower at 0·110mol O₂ m^–3 and 60% lower at 0 mol O₂ m^–3. Decreasesin fresh weight were similar but not identical to decreasesin dry weight, possibly because leaf growth was suppressed evenabove 0·110 mol O₂ m^–3. Oxygen deficiency inhibitedroot growth more severely than coleoptile growth. Coleoptiles from seedlings grown in aerated solution were exposedto an atmosphere of pure N₂ for 30 min. Anoxia caused a declinein ATP content and energy charge, suggestive of decreased oxidativephosphorylation. It is not clear whether the decline in oxidativephosphorylation was solely responsible for impaired growth inhypoxia. In seedlings growing at O₂ concentrations less than 0·110mol O₂ m^–3, significant amounts of ethanol were synthesized.The rate of O₂ uptake decreased markedly below 0·06 molO₂ m^–3; this was presumably near the external O₂ concentrationat which oxidative phosphorylation became limited by the supplyof O₂. The stage of development of the seedlings appeared toinfluence O₂ uptake, possibly through changes in conductanceof the tissue to O₂. Uncouplers were used to confirm that thecritical O₂ concentration was dependent on O₂ diffusion ratherthan enzyme kinetics. Impaired growth above 0·110 molO₂ m^–3 may have been due to a decreased activity of oxygenasesof relatively low affinity for O₂, which in turn altered cellmetabolism. Key words: Growth, oxygen uptake, rice seedlings, hypoxia     

Asparagusic acid, a new plant growth inhibitor in etiolated young asparagus shoots

Yellow prisms of asparagusic acid, with a molecular formulaof C₄H₆O₂S₂ were isolated from etiolated asparagus tissues (Asparagusofficinalis L.). This acid inhibits growth in lettuce and otherseedlings when applied in concentrations of 6.67x10^–7Mto 6.67xl0^–7M. The extent of activity was very similarto that of abscisic acid. ¹ A well known shift reagent in the NMR spectrum (1). (Received April 12, 1972; )     

The NADP$-specific isocitrate dehydrogenase of Rhodospirillum rubrum

The NADP^$-specific isocitrate dehydrogenase was partially purifiedfrom photosynthetically-grown Rhodospirillum rubrum. The pHoptimum is between 7.5 and 9.0 in phosphate buffer. The apparentKm is 3.1x10^–5 M for isocitrate, 5.1x10^–5 M forNADP^$, 1.7x10^–5 M for manganese, 1.5x10^–4 M formagnesium, and 3.5x10^–3 M for inorganic orthophosphate.Arsenate exerts a slight inhibition. The Q₁₀ between 17.5°Cand 40°C is 1.62, and the energy of activation at 25°Cis 9.74 Kcal/mole. Glyoxylate and oxalacetate cause concertedinhibition of the enzyme activity. Various nucleotides inhibitthe activity. The kinetics of inhibition by ATP was found tobe mixed type with respect to NADP^$ and isocitrate, the K_i valuesbeing 1.17x10^–3 M and 1.10x10^–3 M respectively.The inhibition between ATP and orthophosphate is competitivewith a K_i of 10^–4M. Thiol binding reagents are inhibitory;this inhibition is reversed by cysteine or reduced glutathione. (Received October 1, 1971; )     

The occurrence and properties of methenyltetrahydrofolate cyclohydrolase in plants

Methenyltetrahydrofolate cyclohydrolase (E.C. 3.5.4.9 [EC] ), whichis responsible for the enzymatic conversion of 5,10-methenyl-H₄FAto 10-formyl-H₄FA, has been found in various plant tissues.The enzyme was partially purified from pea seedlings and someof its properties were investigated. It was unstable, but wasstabilized by the addition of 25% glycerol. The enzyme was purifiedabout 60-fold by fractionation with ammonium sulfate and columnchromatography on DEAE-cellulose in the presence of 25% glycerol.Optimum pH for the reaction was 7.7. Michaelis constants for5,10-methenyl-H₄FA in the forward reaction, and for 10-formyl-H₄FAin the reverse reaction were 4x10^–5M and 2x10^–4M,respectively. The apparent equilibrium constant for the reactionwas calculated as 50. Enzyme activity was greatly inhibitedby the reduced forms of folate derivatives. The probable participationof this enzyme in the regulation of folate coenzyme levels inplant tissues has been suggested. ¹ Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants, VI. (For Part V, see Reference (5) ). Partof this paper was presented at the 22nd annual meeting of theJapan Vitamin Society held at Hiroshima on October 14, 1970. ² Present address: Sizuoka Eiwa Junior College, Ikeda, Shizuoka. (Received September 9, 1972; )     

Enzymes involved in the last steps of the biosynthesis of mannitol in brown algae

Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17 [EC] ) and mannitol-1-phosphatase(EC number yet unassigned) were detected in the brown algae,Spatoglossum pacificum and Dictyota dichotoma. The enzymes wereextracted from algal fronds and their properties were investigatedusing partially purified preparations. Mannitol-1-phosphatase shows maximum activity at pH 7. The enzymehad a narrow substrate specificity. The Km value for mannitol-1-phosphateis 8.3x10^–4 M (30°C, pH 7.0). The enzyme is activatedby Mg⁺⁺ and Mn⁺⁺and is strongly inhibited by PCMB, Hg⁺⁺and NaF. Mannitol-1-phosphate dehydrogenase showed maximum activitiesat pH values 6.5 and 10.2 in reductive and oxidative reactions,respectively. The dehydrogenase also showed narrow substratespecificity; mannitol-1-phosphate and NAD or fructose-6-phosphateand NADH₂ are utilized, respectively, in oxidative and reductivereactions by the enzyme. Km values for these substrates andthe coenzymes are 2.5x10^–4 M and 7.1x10^–5 M forthe first pair and 2.8x10^–4 M and 1.3x10^–5 M forthe latter pair. This enzyme was strongly inhibited by PCMBand Hg⁺⁺, but was only slightly affected by adenosine phosphates. Possible roles of these enzymes in the biosynthesis of mannitolin brown algae are discussed. ¹ Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 233. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and in part by a grant to one of us (T.Ikawa) from the Matsunaga Science Foundation. ² Present address: Chemical and Physical Laboratory, HoechstJapan Research Laboratory, Minamidai, Kawagoe, Japan. (Received February 22, 1972; )     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

A sulfite-dependent adenosine triphosphatase of Thiobacillus thiooxidans. Its partial purification and some properties

A sulfite-dependent ATPase [EC 3.6.1.3 [EC] ] of Thiobacillus thiooxidanswas activated and solubilized by treatment with trypsin [EC3.4.4.4 [EC] ], and purified 84-fold with a 32% recovery. It requiredboth Mg²⁺ and SO₃^2– for full activity, and its optimumpH was found at 7.5–8.0. Mn²⁺, Co²⁺, and Ca²⁺ could partiallysubstitute for Mg²⁺, while SeO₃^2– and CrO₄^2– couldpartially substitute for SO₃^2–. The enzyme hydrolyzed ATP and deoxy-ATP most rapidly and otherphosphate esters were poorer substrates. The apparent Km valuefor ATP was 0.33 mM. The enzyme activity was strongly inhibitedby 0.2 mM NaN₃ and 10 mM NaF. (Received July 27, 1977; )     

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     

Some Experimental and Theoretical Observations Concerning Mass Flow in the Vascular Bundles of Heracleum

The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, L_EE = 5 ? 10–⁴ mho cm^–1,L_pE = 9 ? 10^–6 cm³ s^–1 cm^–2 volt^–1 cm,and L_PP = 0.16 cm³ s^–1 cm^–2 (J cm^–3)^–1cm. In uncut phloem strands L_EE is about 1 ? 10^–3 mhocm^–1. In xylem in 2 x 10^–3 N KCI, L_pp = 50 to 225,L_PE = 2 ? 10^–4, and L^EE = 4 ? 10^–3. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga ‘long distance’ current pathway can be the majormotive ‘force’ for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm^–1endogenous in the phloem.     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

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     

Phosphate Uptake in the Cyanobacterium Synechococcus R-2 PCC 7942

Phosphate uptake rates in Synechococcus R-2 in BG-11 media (anitrate-based medium, not phosphate limited) were measured usingcells grown semi-continuously and in continuous culture. Netuptake of phosphate is proportional to external concentration.Growing cells at pH_o 10 have a net uptake rate of about 600pmol m^–2 s^–1 phosphate, but the isotopic flux for³²P phosphate was about 4 nmol m^–2 s^–1. There appearsto be a constitutive over-capacity for phosphate uptake. TheK_m and V_max, of the saturable component were not significantlydifferent at pH_o 7.5 and 10, hence the transport system probablyrecognizes both H₂PO^–₄and HPO^2–₄. The intracellularinorganic phosphate concentration is about 3 to 10 mol m^–3,but there is an intracellular polyphosphate store of about 400mol m^–3. Intracellular inorganic phosphate is 25 to 50kJ mol^–1 from electrochemical equilibrium in both thelight and dark and at pH_o 7.5 and 10. Phosphate uptake is veryslow in the dark ( 100 pmol m^–2 s^–1) and is light-activated(pH_o 7.51.3 nmol m^–2 s^–1, pH_o 10600 pmol m^–2s^–1). Uptake has an irreversible requirement for Mg²⁺in the medium. Uptake in the light is strongly Na⁺-dependent.Phosphate uptake was negatively electrogenic (net negative chargetaken up when transporting phosphate) at pH_o 7.5, but positivelyelectrogenic at pH_o 10. This seems to exclude a sodium motiveforce driven mechanism. An ATP-driven phosphate uptake mechanismneeds to have a stoichiometry of one phosphate taken up perATP (1 PO_{4 in}/ATP) to be thermodynamically possible under allthe conditions tested in the present study. (Received June 16, 1997; Accepted September 4, 1997)     

Allocation of Organ Biomass in Perfect and Imperfect Flowers

Perianth M_P, gynoecium M_G, and androecium M_A dry-weight biomass(in g) of 39 species of perfect flowers was measured. Thesedata were pooled with published data from an additional 51 speciesand used to determine size-dependent variations in (M_G and M_A)in terms of the hypothesis that the quotient of M_G and M_A exceeds1·0 for out-breeding (xenogamous) species and less than1·0 for in-breeding (autogamous) species. Ordinary leastsquare regression of the pooled data (n = 90) showed M_G = 0·118M^0·916_P (r² = 0·884) and M_A = 0·186 M^0·975_P(r² = 0·865), indicating that the biomass of the gynoeciumproportionally decrease as floral size increases. The exponentsof these regressions indicate that the ratio of gynoecial toandroecial biomass decreased with increasing floral size suchthat comparatively small flowers (M_P < 0·0021 g) hadM_G/M_A > 1·0 (predicted for 'out-breeders') while comparativelylarger flowers (M_P > 0·0021 g) had M_G /M_A < 1·0(predicted for 'in-breeders'). Thus, on average, the type ofbreeding system was a size-dependent phenomenon. To test whether the biomass of a floral organ-type is a legitimateindicator of gender reproductive effort, the biomass (in g)of stamen filaments M_m and anther sacs M_AS of 39 species wasdetermined. Least square regression of these data showed M_AS= 0·188 M^0·854_fil (r² = 0·967), indicatingthat species with larger stamen filaments, on the average, boreproportionally smaller anther sacs and thereby cautioning againstthe uncritical use of the allocation of biomass to floral organ-typeas a strict gauge of gender-function investment. To determine whether the loss of one gender-function resultsin proportional reallocation of biomass to the remaining gender-function,the size-dependency of androecial and gynoecial biomass wasdetermined for a total of 33 perfect and imperfect flowers ofCucumis melo. Regression of the data obtained from perfect flowersyielded M_A = 0·402 M^1·47_P (r² = 0·898)and M_G = 4·63 M^1·36_P (r² = 0·842). SinceM_G/M_A M^0·11_P , the biomass allocation to the gynoeciumrelative to the androecium decreased with increasing floralsize. This result was consistent with the broad interpecificcomparison based on 90 species with perfect flowers . Regressionof the data for imperfect flowers yielded M_A = 0·151M^1·02_P (r² = 0·675) and M_G = 4·68 M^1·47_P(r² = 0·996), indicating a near allometric relation forthe androecium and a strong positive anisometry for the gynoecium.Thus, for flowers of comparable size, a loss of female genderobtains a modest to significant again in androecial biomasswhereas the loss of male gender yields only a slight increasein gynoecial biomass. Collectively, the results of these studies indicate that biomassallocation patterns are size-dependent phenomena whose complexitieshave been largely ignored in the literature.Copyright 1993,1999 Academic Press Allometry, floral biomass, reproduction     

Regulation of IBA synthetase from maize (Zea mays L.) by drought stress and ABA

The rate of indole-3-butyric acid (IBA) synthesis in maize seedlingsis dependent on the culture conditions of the plants. When theseedlings were grown on filter paper soaked with different amountsof water, the activity of IBA synthetase differed strongly.High amounts of water (150 and 200 ml per bowl) inhibited IBAsynthesis completely in vitro, whereas 30 and 50 ml water perbowl increased the activity dramatically. Under conditions whereIBA synthetase was inhibited (150 ml H₂O), an increase of enzymeactivity was observed when abscisic acid (ABA) was exogenouslyadded in concentrations between 510^–4 to 510^–7M. Under ‘drought’ conditions (50 ml H₂O per bowl)the same ABA concentrations were inhibitory. Jasmonic acid andsalicylic acid also enhanced IBA synthetase activity to someextent, whereas indole-3-acetic acid (IAA) and kinetin had noeffect. Activity could also be enhanced by osmotic stress (NaCIand sorbitol), but not under temperature stress. In accompanyinginvestigations the endogenous contents of IAA, IBA, and ABAunder the different culture conditions have been determinedas well as the energy charge of the seedlings. Similar observationshave been made with Amaranthus, wheat and pea seedlings Key words: Abscisic acid, Amaranthus paniculatus, drought stress, inole-3-butyric acid biosynthesis, Pisum sativum, Triticum aestivum, Zea mays     

Nitrogen utilization by plant species from acid heathland soils: II. Growth and shoot/root partitioning of NO3- assimilation at constant low pH and varying NO3-/NH4+ ratio

The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m^–3N, varying the N0₃^–/NH₄⁺ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N0₃^–/NH₄⁺ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH₄⁺ by NO₃^– tended to enhance the plant's growth ratewhen compared to NH₄⁺ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO₃^–increasing from 0 to 100%. In the presence of NH₄⁺, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH₄⁺. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO₃^–in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO₃^– [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO₃^– <0.20), D. flexuosashowed a strong preference for NO₃^– at low external nitrate(the relative uptake ratio for N0₃^– reaching a value of2.0 at 10% NO₃^–). The ecological significance of thisprominent high preference for NO₃^– at low NO₃^–/NH₄⁺ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N0₃^–/NH₄⁺ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate     

14C2H4: Distribution of 14C-labeled tissue metabolites in pea seedlings

The ¹⁴C-metabolite distribution pattern following ¹⁴C₂H₄ metabolismin intact pea seedlings (Pisum sativum L.) was determined undervarious conditions. After a 24 hr exposure to ¹⁴C₂H₄, the majorityof ¹⁴C-metabolites were water-soluble (60–70%) with lesseramounts in the protein (10–15%), lipid (1%), and insoluble(1–2%) fractions. Ion exchange chromatography of the water-solublecomponents into basic, neutral, and acidic fractions revealeda 50 : 40 : 10 distribution, respectively. Chromatography ofthe neutral fraction revealed two regions of radioactivity (Rf=0.38)and 0.63 which did not cochromatograph with twenty-two knownsugars or neutral metabolites. Chromatograms of the basic fractioncontained 3 regions of radioactivity. Similar distribution patternswere noted when ¹⁴C₂H₄ exposure was followed by a 6 hr air chaseor when 5% CO₂, an antagonist of ethylene action, was presentduring the exposure. Marked differences in the ¹⁴C-metabolite distribution patternswere obtained when ¹⁴CO₂ was substituted for ¹⁴C₂H₄. These resultsindicate that the metabolic pathway involved in ethylene metabolismis different from that involved in intermediary carbon metabolism. ¹ Contribution No. 2338 from Central Research and DevelopmentDepartment, Experimental Station, E. I. du Pont de Nemours andCompany, Wilmington, Delaware. (Received June 28, 1976; )