Pumpkin (Cucurbita sp.) seed globulin III. Comparison of subunit structures among seed globulins of various Cucurbita species and characterization of peptide components

Various Cucurbita seed globulins showed patterns similar toone another on SDS-gel electrophoresis, and ß bandsfor unreduced globulins and , ', and ' bands for reduced ones.On gel electrophoresis in 6 M urea, reduced globulin gave twoacidic and two basic bands. These corresponded to and ' chainsand ₁ and ₂ chains, respectively, identified by two-dimensionalurea-SDS gel electrophoresis. The compositions of the and ßsubunits were proposed. (Received September 8, 1977; )     

Pumpkin (Cucurbita sp.) seed globulin V. Proteolytic activities involved in globulin degradation in ungerminated seeds

Two proteolytic activities I and II involved in the globulindegradation were detected in pumpkin seeds. Activity I, hydrolyzing and ß subunits of the globulin to form F_ß,was found in both dry seeds and cycloheximide-treated cotyledons,and decreased during germination. Activity II, hydrolyzing F_ßto produce small peptides and amino acids, was not observedin dry seeds but found in cycloheximide-treated cotyledons,increased up to 4 days, and gradually decreased during germination. Activity I gave limited hydrolytic products from the globulinand the chain, but not from F_ß, the chain and some animal proteins. It was inhibitedby EDTA. On the other hand, activity II hydrolyzed F_ßand the chain faster than the globulin, the chain and some animal proteins. It was inhibitedby EDTA and p-chloromer-curibenzoate, and activated by ß-mercaptoethanol,dithiothreitol and CoCl₂. Optimum pH's were at about 6.8 andat 6.0 to 6.8 for activities I and II, respectively. The degradation process of the globulin can be divided intotwo steps: the first step is the conversion of globulin to F_ßand the second step, F_ß to small peptides and aminoacids. (Received November 9, 1979; )     

Fractionation of Nitrogen Isotopes during the Uptake and Assimilation of Ammonia by Plants

Two varieties (Nihonbare and Koshihikari) of rice plants (Oryzasativa L.) were grown hydro-ponically with two levels (20 and100 mg N liter ^–1) of ammonia. Variations in levels ofnatural abundance of ¹⁵N (¹⁵N) were analyzed in the ammoniaand organic nitrogen of shoots and roots, as well as in theammonia in the culture solution. There was substantial fractionationof nitrogen isotopes during the uptake of ammonia. When plantsabsorbed a large proportion of ammonia from a solution witha low concentration, less negative ¹⁵N values in plants andhigh positive ¹⁵N values in the ammonia remaining in solutionwere observed. The reverse was found when a smaller fractionof ammonia was absorbed from a solution with a higher concentrationof ammonia. The ^l5N values of ammonia in shoots and roots werehigher than in the respective constituent organic nitrogen,suggesting the fractionation of nitrogen isotopes during theassimilation of ammonia. Wild-type and mutant cells of the cyanobacterium(blue-green alga) Synechococcus PCC 7942 were grown in nitrate-or ammonia-containing medium as the source of nitrogen. Fractionationof nitrogen isotopes during the uptake of nitrate was limited,whereas that during the uptake of ammonia was considerable. ¹ In this report, the term ammonia refers indiscriminately toboth NH₃ or NH₄⁺. (Received June 13, 1991; Accepted September 12, 1991)     

Discrimination and characterization of photosystem I-and photosystem II-induced 515-nm absorbance changes in chloroplasts II. Separate local fields in thylakoids indicated by differential responses of the 515-nm absorbance change

Flash-induced 515-nm and 475-nm absorbance changes in spinachchloroplasts were investigated in the presence of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU). DCMU reduced the magnitude of the 515-nmabsorbance change by half and almost completely diminished theabsorbance change at 475-nm. The reduction of the 475-nm absorbancechange paralleled the inhibition of the photosystem II (PS II)light reaction. When chloroplasts were illuminated with red or far-red light,the ratio of A₅₁₅/A₄₇₅ changed depending on the photosystemactivated. Wide variations in the A₅₁₅/A₄₇₅ ratio observed insubchloroplast particle preparations were probably due to theenrichment and activation of one of the photosystems. We suggest that the photosynthetic pigments in the thylakoidmembrane are heterogeneously distributed, and chlorophyll bmolecules that may be responsible for the 475- nm absorbancechange are affected by the local field formed by the PS II lightreaction. On the other hand, an electric field due to the PSI reaction probably induced the absorbance change at 515-nm (Received February 24, 1978; )     

Uptake of Thallium, a Toxic Heavy-Metal, in the Cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. Leopoliensis) PCC 7942

Uptake of the toxic heavy-metal, thallium, was studied in thecyanobacterium Synechococcus R-2 (PCC 7942) using clinicallyavailable ²⁰¹Tl ⁺. Thallium was found to distribute across theplasmalemma passively, and so the accumulation ratio of theion ([Tl⁺]_i/[Tl⁺]_o) could be used to calculate the apparentmembrane potential (­_i,o) of the cells (^ETI⁺_i,o = ­_i,o).The permeability of the plasmalemma to TI⁺ (^PTI⁺ 1 to 5 nms^–1)is higher than that of K⁺. Valinomycin does not increase thepermeability of TI⁺. Transient changes in the ­_i,o of cells,because of electrogenic transport of ions, could be detectedfrom its effects upon the uptake rate of TI⁺. HCO^–₃ hyperpolarizedSynechococcus cells, whereas NH⁺₄, CH₃NH⁺, and K⁺ led to depolarization.The use of TI⁺ as a reporter of ­_i,o has some inherent limitations.Tl⁺ is toxic at very low concentrations (inhibitory effectsare apparent after about 6 h at concentrations as low as 1 mmolm^–3). The rate of equilibration is slow (t_1/25 to 20 min).Equilibration of TI⁺ takes about 2 h, which limits its valueas a membrane potential probe. Large amounts of TI⁺ bind tothe surface of the cells making the method impracticable formeasuring accumulation ratios of less than about 10 (­_i,o)values smaller than about –60 mV). Cultures continuouslyexposed to Tl⁺ (10 mmol m^–3) eventually become TI⁺ resistantby actively extruding TI⁺ (µTI⁺_i,o= –3±0.2kJ mol^–1) and so thallium cannot be used as a ­_i,oprobe in such cells. (Received October 28, 1997; Accepted August 31, 1998)     

Variation in Natural Abundance of 15N among Plant Parts and in 15N/14N Fractionation during N2 Fixation in the Legume-Rhizobia Symbiotic System

Sixteen legumes were grown in N-free media so that N was suppliedentirely by symbiotic N₂ fixation. The plant tissues were analyzedfor natural ¹⁵N abundance (expressed as ¹⁵N per mil relativeto air N₂) with a ratio mass spectrometer. The nodules of desmodium,centro, siratro, soybean and winged bean showed high enrichmentin ¹⁵N (+9), while red clover showed slight enrichment (+2).The nodules of 9 other forage legumes (Townsville stylo, whiteclover, alsike clover, common vetch, Chinese milk vetch, senna,alfalfa, ladino clover, and hairy vetch) showed little enrichmentin ¹⁵N. In all the legumes investigated, particularly in the ureide-transportingplants such as desmodium, centro, siratro, soybean, winged beanand field bean, the ¹⁵N value of the shoots was negative (–3.2).The ¹⁵N value of the shoots in winged bean and field bean variedby about 1 depending on the Rhizobium strains used. The isotopicmass balance of 13 legumes indicated that isotopic fractionationoccurs during N₂ fixation by the legume-rhizobia symbiosis witha preference for ¹⁴N over ¹⁵N, resulting in a ¹⁵N value of –0.2to –2 in the whole plant. The results indicate that ¹⁵N/¹⁴N isotopic discrimination witha preference for the lighter atom may occur in both N₂ fixationand export of fixed N from nodules. ¹Present address: Department of Soils and Fertilizers, NationalAgriculture Research Center, Kannondai, Tsukuba, Ibaraki 305,Japan. (Received October 8, 1985; Accepted April 7, 1986)     

Ammonia Regulation of Intermediary Metabolism in Photosynthesizing and Respiring Chlorella pyrenoidosa: Comparative Effects of Methylamine

The natural ¹³C abundance (¹³C value) of the field-grown leguminousplants (soybean, kidney bean, pea, azuki bean, mung bean, peanutand cowpea) was investigated by mass spectrometry with a precisionbetter than %0.2 for ¹³C. Among organs of premature plants,the leaves had the most negative values, and the nodules generallyhad the least negative values, and other organs, fruits, stemsand roots, showed intermediate values. In the soybeans so farinvestigated, the grains of nodulating plants exhibited higher¹³C values than nonnodulating lines. The ¹³C values of the grainsvaried depending on the species: peanuts showed the most negativevalues. Possible causes underlying these variations are discussed. (Received March 2, 1983; Accepted May 27, 1983)     

Isolation of Subunits of Coupling Factor 1 from Maize and Spinach Chloroplasts and Properties of Combinations of Subunits with ATPase Activity

Subunits (, ß, ) and mixtures of subunits ( ß, , ß , ß ) were isolated without denaturationfrom a chloroform extract of chloroplast coupling factor 1 (CF₁)from maize (Zea mays var. Ushiku 5-4) and from spinach by fastprotein liquid chromatography (FPLC), on an anion-exchange columnof Mono-Q in the presence of n-octylglucoside (OG) and on achromatofocusing column of Mono-P. The ß -subunitcomplex (CF¹ ß ) was the minimum unit required forATPase activity, as was confirmed by the reconstituted complexof ß and subunits. An subunit isolated from maizeinhibited the ATPase activity of CF₁ ß from bothmaize and spinach. CF₁ ß was found to contain anOG-dependent Mg²⁺-ATPase. The ATPase activity of CF₁ ß required divalent cations, such as Mg²⁺ or Mn²⁺, for its expressionin the presence of OG; its optimum pH was 8.0 and it was markedlyinhibited by NaN₃. The enzyme hydrolyzed ATP in prefernece toGTP but not CTP, UTP, ADP, AMP or pNPP. Lineweaver-Burk plotsof its activity were curvilinear in the range of 0.6–0.7mM ATP.Mg²⁺. ¹Present address: Department of Biology, School of Education,Waseda University, Shinjuku-ku, Tokyo, 160 Japan. (Received February 15, 1989; Accepted April 20, 1989)     

Carbon Isotope Ratios of Epidermal and Mesophyll Tissues from Leaves of C3 and CAM Plants

The ¹³C values for epidermal and mesophyll tissues of two C₃plants, Commelina communis and Tulipa gesneriana, and a CAMplant, Kalancho daigremontiana, were measured. The values forthe tissues of both C3 plants were similar. In young leavesof Kalancho, the epidermis and the mesophyll showed S13C valueswhich were nearly identical, and similar to those found in C3plants. However, markedly more negative values for epidermalcompared to mesophyll tissue, were obtained in the mature Kalancholeaf. This is consistent with the facts that the epidermis ina CAM leaf is formed when leaves engage in C₃ photosynthesisand that subsequent dark CO₂ fixation in guard cells or mesophyllcells makes only a small contribution to total epidermal carbon. (Received January 27, 1981; Accepted May 14, 1981)     

Effects of Gibberellins and Prohexadione on the Activities of Oryzain and {alpha}-Amylase in Rice Seeds

Oryzains, cysteine proteinases of rice seeds, are induced byGA₃ in germinating rice seeds [Abe et al. (1987) Agric. Biol.Chem. 51: 1509]. The effects of GA₁, GA₃, GA₄, GA₉, and GA₂₀on the production of oryzain and -amylase were investigatedin embryoless half- and whole-seeds of rice (cv. Nipponbare).When gibberellins (GAs) were incubated with embryoless half-seeds,GA₁, GA₃ and GA₄ induced oryzain and -amylase, but GA₉, andGA₂₀ did not. GA₉ and GAM induced oryzain and -amylase productionin whole seeds, but this production was inhibited by the simultaneousapplication of prohexadione, an inhibitor of 2ß- and3ß-hydroxylation of GAs. Prohexadione did not inhibitthe activities of oryzain and -amylase induced by GA₁. Theseresults suggest that GAs possessing the 3ß-hydroxylgroup induce activities of oryzain and -amylase in rice seedsand that GA₉ and GA₂₀ have activity only after they are convertedmetabolically to active GAs, probably GA₄ and GA₁, respectively.GA₁, was more active than GA₄ in both half seeds and wholeseeds incubation. Oryzain and -amylase activities induced byGA₄ were significantly inhibited in the presence of 10^–4M prohexadione. This suggests that the conversion of GA₁, toGA₄ (13-hydroxylation) might be inhibited at a high dose ofprohexadione in whole seeds. ⁴Present address: Institute of Food Development, Kyung Hee University,Suwon 449-701, Korea     

Variations of Natural 13C Abundances in Leguminous Plants

The natural ¹³C abundance (¹³C value) of the field-grown leguminousplants (soybean, kidney bean, pea, azuki bean, mung bean, peanutand cowpea) was investigated by mass spectrometry with a precisionbetter than %0.2 for ¹³C. Among organs of premature plants,the leaves had the most negative values, and the nodules generallyhad the least negative values, and other organs, fruits, stemsand roots, showed intermediate values. In the soybeans so farinvestigated, the grains of nodulating plants exhibited higher¹³C values than nonnodulating lines. The ¹³C values of the grainsvaried depending on the species: peanuts showed the most negativevalues. Possible causes underlying these variations are discussed. ³Institute of Biological Sciences, University of Tsukuba, Sakura-mura,Ibaraki 305, Japan. (Received December 3, 1982; Accepted May 25, 1983)     

Photophosphorylation in intact algae: Effects of inhibitors, intensity of light, electron acceptor and donors

The luciferin-luciferase method was used to determine ATP extractedfrom darkmaintained and light-exposed samples of the green algaChlorella pyrenoidosa and of the blue-green alga Anacystis nidulans.A few measurements on Synechococcus lividus (a bluegreen thermophile,clone 65?C) are also reported.

1. The light-minus-dark ATP levels (ATP) from aerobic cells ofChlorella and Anacystis were negative; however, ATP from Synechococcuswas positive. Large positive ATP was obtained in regularly grown(RG: moderate light) Chlorella treated with oligomycin; darklevels were reduced, light levels remained essentially unaffected.In high-light exposed (HLE) Chlorella, oligomycin reduced bothlight and dark ATP levels, but positive ATP was still obtained.However, in Anacystis, which has a different organization ofthylakoid membrane, oligomycin severely reduced both the lightand the dark ATP levels and the ATP remained negative.
2. Theoligomycin (12 µM) treated Chlorella and the untreatedAnacystis and Synechococcus show the presence of cyclic photophosphorylationunder conditions in which the non-cyclic electron flow fromphotosystem II to photosystem I is blocked by 10 µM 3-(3,4-dichlorophenyl)-l,l-dimethylurea(DCMU), or not allowed to operate by the absence of CO₂. Cyclicphotophosphorylation ranged from 10–30% of the maximumATP in RG, to 40–50% in HLE Chlorella. In RG Chlorella,cyclic and non-cyclic (in the absence of DCMU) photophosphorylation(ATP) saturate at about 10³ ergs cm^–2 sec^–1 and10⁴ ergs cm^–2 sec^–1 and 10⁴ ergs cm^–2 sec^–1red (>640 nm) light, respectively; a lag was observed inthe light curve.
3. In Chlorella, the addition of the photosystemI electron acceptormethyl viologen (MV; 1 mM) increased ATPby twofold. Furtheraddition of DCMU (25 µm) reduced thisto the level observedwith DCMU alone. If 1 mM reduced dichlorophenolindophenol orphenazine methosulphate (DCPIPH₂ or PMSH₂, respectively)wasadded along with DCMU, the ATP level was 30–40% ofthecontrol. Further addition of MV increased the JATP to be70–80%of that of the control. These and other resultsconfirm thepresence of both non-cyclic and cyclic photophosphorylationin vivo, the former predominating in Chlorella, and the latterin Anacystis and Synechococcus.

(Received May 1, 1973; )     

Pumpkin (Cucurbita sp.) seed globulin VI. Proteolytic activities appearing in germinating cotyledons

N--benzoyl D,L-arginine p-nitroanilide (BAPA), leucine p-nitroanilide(LPA) and casein hydrolytic activities were assayed in germinatingcotyledons. BAPA hydrolytic activity was not detected in dryseeds, but increased rapidly from 1 to 4 days of germinationand then decreased. LPA and casein hydrolytic activities weredetected in dry seeds and increased from 2 to 4 days. Caseinhydrolytic activity decreased faster than the other two activities. BAPA hydrolytic enzyme was partially purified. It was inhibitedby p-chloromercuribenzoate and activated by ß-mercaptoethanoland dithiothreitol, but was not affected by EDTA, phenylmethylsulfonylfluoride, pumpkin trypsin inhibitor and several divalent cations.It had no ability to hydrolyze globulin or the chain to produce F_ß or smaller polypeptides,respectively, which was referred to as proteolytic activityI in the preceding paper (14), but released small peptides andamino acids from the chain and F_ß. However, it wasdifferent from proteolytic enzyme II which was present in dryseeds and inhibited by EDTA (14). Pumpkin trypsin inhibitor was purified. Its molecular weightwas estimated to be 10,500 by gel filtration. It did not inhibitthe BAPA hydrolytic enzyme. Both proteolytic activities I andII were also not reduced by the inhibitor (14). The inhibitoryactivity decreased gradually during germination. (Received November 9, 1979; )     

Nucleoside Triphosphate(NTP)-Binding Proteins and Endogenous ADP-ribosyl Transferase in Neurospora crassa

Nucleoside triphosphate(NTP)-binding proteins were detectedin the crude extract of mycelia of Neurospora crassa, whichwas treated with 1% Lubrol PX and fractionated by gel filtration.Protein fractions showing the capacity to bind [³⁵S]ATPS or[³⁵S]GTPS were designated as AGN1 to 6. The binding of [³⁵S]ATPSor [³⁵S]GTPS was prevented in the presence of 0.1 mM ATP orGTP except that in fractions AGN1 and 2, the presence of GTPstimulated the binding of [³⁵S] ATPS to ATP(NTP)-binding proteins.ATP or GTP was 1 to 2 orders of magnitude more effective thanCTP or UTP in preventing the binding of [³⁵S]GTPS in AGN1, 2and 5. Among these fractions AGN1, 2, 5 and 6 showed activityto hydrolyze 1 nM [–³²P]ATP or [–³²P]GTP. NTP-bindingproteins bound with [³⁵S]ATPS or [³⁵S]GTPS had lower apparentmolecular weights than the same proteins without bound nucleotide.Proteins bound with [³⁵S]ATPS or [³⁵S]GTPS and those [³²P]ADP-ribosylatedby endogenous ADP-ribosyl transferase in each fraction wereanalyzed by SDS-PAGE. About 20 species of ATP or ATP-GTP-bindingproteins were detected, several of which were ADP-ribosylated.The binding of [³⁵S]ATPS or [³⁵S]GTPS to NTP-binding proteinswas confirmed by the comparison of non-boiled and boiled samplesimmediately before loading to SDS-PAGE. ATP, GTP, CTP or UTPat the concentration of 0.1 mM effectively removed [³³S]ATPSor [³⁵S]GTPS bound to NTP-binding proteins. (Received December 10, 1990; Accepted April 18, 1991)     

Pumpkin (Cucurbita sp.) seed globulin IV. Terminal sequences of the acidic and basic peptide chains and identification of a pyroglutamyl peptide chain

Pumpkin seed globulin is composed of heterogeneous polypeptidechains, acidic and chains and basic ₁ and ₂ chains (12). This study showed that the basicchains had similar N-terminal sequences, Gly-Leu-Asp-Glu-Thr-Ile-for the ₁ chain and Gly-Leu-Glu-Glu-Thr-Ile- for ₂. On the contrary,the N-terminal sequences of the acidic and chains were dissimilar, Ile-Gln-Gly-Tyr- for the chain and no N-terminal residue for the chain, according to routine terminal analysis. Pyrrolidonylpeptidase digestion of the chain and its thermolysin digestion followed by Edman degradationsrevealed that the N-terminal sequence of the chain was < Glu-Ile-Glu-Gln-Gln-Glu-Pro(Trp,Ser)-. The N-terminal sequences and the C-terminal residuesindicated that the acidic and chains were more heterogeneous than the basic ₁ and ₂ chains.A preliminary study on the degradation of storage globulin isalso presented. (Received November 9, 1979; )     

Effects of blue light deficiency on acclimation of light energy partitioning in PSII and CO2 assimilation capacity to high irradiance in spinach leaves

Blue light effects on the acclimation of energy partitioningcharacteristics in PSII and CO₂ assimilation capacity in spinachto high growth irradiance were investigated. Plants were grownhydroponically in different light treatments that were a combinationof two light qualities and two irradiances, i.e. white lightand blue-deficient light at photosynthetic photon flux densities(PPFDs) of 100 and 500 µmol m^–2 s^–1. The CO₂assimilation rate, the quantum efficiency of PSII (PSII) andthermal dissipation activity / in young, fully expanded leaves were measured under 1,600 µmol m^–2 s^–1white light. The CO₂ assimilation rate and PSII were higher,while / was lower in plants grown under high irradiancethan in plants grown under low irradiance. These responses wereobserved irrespective of the presence or absence of blue lightduring growth. The extent of the increase in the CO₂ assimilationrate and PSII and the decrease in / by high growth irradiance was smaller under blue light-deficient conditions. These resultsindicate that blue light helps to boost the acclimation responsesof energy partitioning in PSII and CO₂ assimilation to highirradiance. Similarly, leaf N, Cyt f and Chl contents per unitleaf area increased by high growth irradiance, and the extentof the increment in leaf N, Cyt f and Chl was smaller underblue light-deficient conditions. Regression analysis showedthat the differences in energy partitioning in PSII and CO₂assimilation between plants grown under high white light andhigh blue-deficient light were closely related to the differencein leaf N.     

Effect of Low Relative Humidity on {delta}13C Value in Two C3 Grasses and in Panicum milioides, a C3-C4 Intermediate Species

When grown under conditions of low relative humidity, the C₃–C₄intermediate Panicum milioides, as well as the C₃ grasses Triticumaestivum and Poa pratense, exhibited ¹³C values which were upto 2–7%o less negative than the ¹³C values of the correspondingplants grown at high relative humidity. At both humidity levels,there was no evidence of a substantial contribution of phosphoenolpyruvatecarboxylase to carbon gain in Panicum milioides     

Water Potential and Mechanical Properties of the Cell Wall of Hypocotyls of Dark-Grown Squash (Cucurbita maxima Duch.) under Water-Stress Conditions

Hypocotyl growth of seedlings of dark-grown squash (Cucurbitamaxima Duch.) was greatly reduced by the addition of 60mM polyethyleneglycol (PEG) to hydroponic solution (water stress). Apoplastic solution (A) and cell sap (C) were separately collectedfrom the hypocotyl segments by a centrifugation method. Theosmotic potentials of A (_A) and C (_c), and (=_c–_A) ofstressed hypocotyls were always lower than those of unstressedhypocotyls. Suction force was measured by immersing the segments into solutionsof different concentrations of mannitol. Suction force was significantlycorrelated with _C (r= –0.99). The mechanical properties of the cell wall of hypocotyl segmentswere measured by stressrelaxation technique. Minimum stressrelaxation time (T_o), relaxation rate (R) and residual stressof unstressed hypocotyls were low during the growth period andincreased when the growth ceased. T_o and R of stressed hypocotylsdecreased one day after the stress treatment, but the residualstress was not decreased by the water stress throughout theexperiment. These results suggest that the suppressed growth of dark-grownsquash hypocotyls under water stress was due neither to thereduction of the osmotic potential difference between innerand outer space of the cell, nor to the decrease in suctionforce, but was partly due to the unchanged mechanical propertiesof the cell wall, as represented by one stress-relaxation parameter,residual stress. (Received February 5, 1988; Accepted September 8, 1988)     

BACTERIAL BREAKDOWN OF {varepsilon}-CAPROLACTAM AND ITS CYCLIC OLIGOMERS

Eleven different types of bacteria were isolated which werecapable of growing on -caprolactam, the monomeric material fornylon 6 polyamide, as the sole source of both carbon and nitrogen. The optimal concentration of -caprolactam for the bacterialgrowth was about 0.6% in a synthetic liquid medium enrichedwith a small amount of yeast extract. The bacterial strains grew also on -butyrolactam, -valerolactamand the -amino acids corresponding to these lactams and -caprolactam.Ammonium adipate was a good substrate for the growth of allthe strains. One strain of Corynebacterium aurantiacum was found to be capableof utilizing cyclic and linear oligomers of 6-aminocaproic acidwith an exception of cyclic dimer. The strains of corynebacteria required vitamin B₁ for growth. Metabolism of -caprolactam and related compounds is discussedbriefly. (Received September 9, 1965; )     

Effect of O2 on the Kinetics of the Flash-Induced 518 nm Absorbance Change in Vivo

The kinetics of the flash induced 518 nm absorbance change (A₅₁₈)in lettuce leaves were found to be dependent on O₂ concentration.(1) Either a lower O₂ partial pressure or the addition of weakred background illumination accelerated the decay of (A₅₁₈)while far-red background light induced a transient acceleration.(2) In the presence of background red light the accelerateddecay could be restored to the original dark level by the additionof O₂. A linear relationship was found between the intensityof red background light and the O₂ pressure required for thisrestoration. (3) The O₂ dependence of (A₅₁₈) decay halftimewas biphasic, the sensitive phase saturating at 0.3 atmospheresO₂ independent of input light energy while the O₂ concentrationneeded to saturate the second phase increased with increasinginput light energy (increasing flash frequency). (4) Treatmentwith N, N'-dicyclohexylcarbodiimide (DCCD) or KCN eliminatedall O₂ and background light effects and DCMU treatment inhibitedall but the sensitive phase of the O₂ dependence on (A₅₁₈) decayhalftime. (5) The extent of the lag phase in the dark recoveryof (A₅₁₈) normally present after preillumination induced accelerationof decay was decreased with added O₂ or KCN. (6) It was concludedthat O₂ competes directly with background red light inducedelectron transport to PS I acceptors to influence the (A₅₁₈)decay. A possible mechanism involving the O₂ sensitive ferredoxin-thioredoxin-reductaseactivation of chloroplast coupling factor 1 ATP-hydrolase activitywas discussed. (Received December 17, 1982; Accepted April 28, 1983)