Photoactivation of Oxygen-Evolving Enzyme in Dark-Grown Pine Cotyledons: Relationship between Assembly of Photosystem II Proteins and Integration of Manganese and Calcium

Dark-grown cotyledons of pine (Pinus thunbergit) did not exhibitO₂ evolution, but this capability was rapidly activated by illuminationfor a short period (photoactivation). To examine the biochemicalchanges which accompany the process of photoactivation in gymnosperms,a method enabling the preparation of highly active O₂-evolvingphotosystem II (PS II) membranes was applied to light-grown,dark-grown, and photoactivated cotyledons. PS II membranes preparedfrom light-grown cotyledons exhibited high O₂-evolving activity,and contained all the intrinsic proteins as well as the threeextrinsic proteins (32, 23 and 17 kDa) associated with PS II.These membranes were also found to contain 4.4 Mn and 0.83 Ca/PSII reaction center. PS II membranes from dark-grown cotyledonscontained all the intrinsic proteins, but preserved only 32kDa extrinsic protein, and zero Mn and 0.85 Ca/PS II reactioncenter. The two extrinsic proteins (23 and 17 kDa) absent inthe PS II membranes from dark-grown cotyledons were, however,present as mature forms in whole thylakoid membranes from thecorresponding sample. The PS II membranes isolated from photoactivatedcotyledons showed a high activity of O₂ evolution and retainedthe three extrinsic proteins, 5.3 Mn and 1.1 Ca/PS II reactioncenter, respectively. The results indicated that Mn and thetwo extrinsic proteins were tightly integrated in the O₂-evolvingapparatusduring the process of photoactivation but integration of Capreceded the integration of Mn by photoactivation. (Received December 9, 1991; Accepted February 1, 1992)     

Evidence for Predominant Participation of Photosystem II{beta}-Units in Nitrogen Formation by Hydroxylamine-Treated Tobacco Chloroplasts

Relative optical cross sections for flash-induced O₂- and N₂-productionwith water and 1 mM NH₂OH as electron donors to PSII, respectively,as well as that for PSI-mediated O²-uptake have been measuredin tobacco chloroplasts by mass spectrometry. In the wild typetobacco these three reactions are driven by three populationsof photosynthetic units different with respect to the antennasize. The antenna size of O₂-evolving units is twice as largecompared to the N₂-evolving one, but both of these have thesame spectral characteristics in the far red region. In contrastto the wild type, the antenna sizes of O₂- and N₂-evolving unitsin the chlorophyll b-deficient tobacco mutant Su/su var. Aureaare the same as the sizes of the N₂-evolying units in the wildtype chloroplasts. Taking into account the data of Thielen andVan Gorkom [Biochim. Biophys. Acta (1981) 635:111] on a strongdifference in the relative amounts of PSII_ß and PSII_ßin the mutant compared with the wild type (the ratio about 1: 3 and 3 : 1 , respectively) it is concluded that mainly thestroma-exposed PSII_ß units are competent to N₂-evolution. (Received November 11, 1993; Accepted April 25, 1994)     

Inhibition of Zeatin-Induced Growth of Cucumber Cotyledons by Sulfite Ions

The inhibitory effects of sulfite ions on zeatin-induced cellexpansion in cotyledons excised from dark-grown seedlings ofcucumber (Cucumis sativus L.) were examined. With 50 µMzeatin the growth rate in white light was about twice that ofthe control. Addition of Na₂SO₃ in the growth medium inhibitedthe zeatin-induced growth of cotyledons. Zeatin-treatment increasedthe osmotic potential in cell sap of cotyledons, while sulfitedecreased it. These treatments had no significant effect onpotassium concentration. Sulfite inhibited the zeatin-inducedincrease in contents of fructose and glucose, but did not affectsucrose content. The relative contents of non-cellulosic constituentsof cell walls fell with the advance of culture. This decreasewas repressed by sulfite, indicating that inhibition of expansiongrowth in cucumber cotyledons by sulfite ions was the resultof alterations in the cell wall structure due to changes inthe cell wall metabolism. (Received June 12, 1984; Accepted October 24, 1984)     

Dimethipin (2,3-Dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide) Effects on Soybean Seedling Growth and Metabolism

Three-day-old dark-grown soybean [Glycine max (L.) Merr.] seedlingswere transferred to 2 mM CaSO₄ or 10^–5 M dimethipin in2 nM CaSO₄ and root-fed via liquid culture. Plants were placedin continuous darkness or in continuous white light (200 µE.m^–2?s^–11,PAR) at 25?C. Dimethipin inhibited root and shoot elongationin dark-grown plants after 24 h and 48 h, respectively. In thelight, root elongation was inhibited also after 24 h, but hypocotylelongation was not significantly affected. Extractable phenylalanineammonia-lyase (PAL) activity per axis in dimethipin-treateddark-grown axes was not generally affected but, in the lightdimethipin caused a significant decrease in PAL activity (24to 96 h). Total soluble hydroxyphenolics in axes were not affectedby dimethipin in light- or dark-grown plants. Anthocyanin andchlorophyll levels were lowered in hypocotyls of dimethipin-treatedplants after 48 to 96 h. Soluble protein in hypocotyls of light-or dark-grown seedlings was not substantially affected by dimethipin.Nitrate reductase (NR) activity (per organ) was generally notaffected by dimethipin in light-grown cotyledons, but in theroots of these seedlings, NR activity was significantly decreased.Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide,LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide,BAPA) indicated little effect on enzyme activities per organin roots and hypocotyls. These data suggest that dimethipinat low concentrations can cause significant growth inhibitionin soybean seedlings grown in either light or darkness and thatfurthermore, extractable activities of some enzymes associatedwith nitrogen metabolism and secondary metabolism are alteredby this chemical. Light also plays a role in the activity ofthis chemical. (Received November 29, 1983; Accepted January 25, 1984)     

Alteration of Soybean Seedling Development in Darkness and Light by the Stay-green Mutation cytG and Gd1d2

The stay-green mutations cytG and Gd₁d₂ prevent the normal yellowingduring senescence of soybean (Glycine max) leaves and cotyledons.Because light plays such an important role in regulating morphogenesisand it promotes the formation of chlorophyll (Chl), we determinedthe effect of cytG and Gd₁d₂ (in a cv. Clark background) onthe development and some light responses of seedlings. AlthoughcytG and Gd₁d₂ seeds, particularly the cotyledons, are greenwhen mature, 44 and 71 % respectively of this Chl broke downwhen the seeds were germinated in darkness. Chlorophyllidesand phaeophytins were not present in the seeds in significantamounts. cytG and Gd₁d₂ as well as wild type (cv. Clark) seedlingsdeveloped a full etiolation syndrome (morphology and lack ofChl) in darkness. Light induced rapid Chl accumulation in thedark-grown seedlings with no apparent difference among the threeisolines. A short (8 h) exposure to light induced some Chl inthe cotyledons of dark-grown plants, and 22 h of light producedfour times more. Following return to darkness, the 8-h groupshowed very little breakdown over the next 12 d. After the 22-hgroup was returned to darkness, the wild-type lost Chl steadily,but Gd₁d₂ and eventually also cytG inhibited this breakdown.In the 22-h group, the Chl a/b ratio decreased in wild typeand cytG indicating preferential breakdown of Chl a relativeto Chl b; however, Gd₁d₂ prevented this change. cytG and Gd₁d₂seem to act preferentially on Chl breakdown rather than synthesis.Copyright1995, 1999 Academic Press Glycine max, soybean, chlorophyll, chlorophyll a/b ratio, cotyledons, etiolation, cytG, Gd₁d₂, mutations, senescence     

Weak Light-Induced Oxygen Consumption Observed during Photoreactivation Is Coupled to the Recovery of Oxygen Evolving Activity

During photoreactivation of the O₂-evolving center in Tris-inactivated/Mn-depletedthylakoids, a slow O₂-consumption occurred. This O₂-consumptionbecame detectable when the O₂-evolving activity of thylakoidswas inactivated by Tris-treatment and decreased as photoreactivationproceeded. The O₂-consumption and photoreactivation similarlyrequired Mn²⁺ at µM levels in addition to PSII electrondonors and shared severa common characteristics. Stimulationof O₂-consumption and photoreactivation by these cofactors werealways accompanied by enhancement in chlorophyll fluorescenceinduction, suggesting the involvement of a Mehler-type reactionin photoreactivation. Although the electron transport due tothis O₂-consumption was rapid enough to oxidize 4 Mn²⁺ ionsto reconstitute the tetranuclear Mn-cluster in each O₂-evolvingcenter in a few seconds, actual recovery of O₂-evolving activityoccurred more slowly in a few minutes. It was inferred thatphotoreactivation in Tris-inactivated thylakoids is not a simplephotooxidation of Mn2²⁺ but involves more complicated processeswhich are coupled to the Mehlertype electron transport fromPSII to oxygen via PSI. (Received July 11, 1994; Accepted August 23, 1996)     

Change in Nitrate-Reducing Activity in Squash Seedlings with NO2 Fumigation

Nitrogen dioxide (NO₂) fumigation inhibited nitrate reductase(NR, EC 1.6.6.1 [EC] ) activity assayed by an in vivo system in thecotyledons, but not in the first leaves, of squash (Cucurbitamaxima Duch.) seedlings. The inhibition was recovered when theseedlings were transferred to NO₂-free conditions, indicatingthat the effect of NO₂ was reversible. The NADH content in thecotyledons, photosynthetic O₂ evolution and respiratory O₂ uptakedid not change notably under NO₂ fumigation. Nitrate contentsin the cotyledons and first leaves did not change with NO₂ fumigation,but nitrite, ammonium and rapidly-metabolized amino acids contentsincreased. The inhibitory effect of NO₂ was also observed inthe in vitro assay, though the inhibition rate was smaller thanthat in the in vivo assay. These results indicate that the inhibitoryeffect of NO₂ on NR activity in squash cotyledons was derivedin part from the decrease in the amount of active NR due toammonium and/or amino acids accumulated in the tissue underNO₂ fumigation. (Received February 12, 1985; Accepted May 27, 1985)     

CO2-Fixation, Glycolate Formation, and Enzyme Activities of Photorespiration and Photosynthesis during Greening and Senescence of Sunflower Cotyledons

Time-courses of ¹⁴CO₂-fixation and of enzyme activities involvedin photorespiration and photosynthesis were determined duringthe life span of cotyledons from sunflower seedlings (Helianthusannuus L.). Glycolate formation in vivo was estimated from theresults of combined labelling and inhibitor experiments. NADPH-glyceraldehyde-3-phosphatedehydrogenase, NADPH-glyoxylate reductase and chlorophyll werewell correlated with the time-course of ¹⁴CO₂-fixation (photosynthesis).There was, however, a considerable discrepancy between the developmentalsequence of photosynthesis and that of both ribulose-l,5-bisphosphatecarboxylase and glycolate oxidase. Furthermore, time-coursesof glycolate oxidase activity in vitro and of glycolate formationin vivo differed significantly. Therefore, the use of glycolateoxidase as a marker for the activity of photorespiration ingreening sunflower cotyledons may be questionable. Results from¹⁴CO₂-labelling experiments with cotyledons treated with theglycolate oxidase inhibitor 2-hydroxy butynoic acid suggestthat glycolate formation relative to CO₂-fixation is reducedin senescent cotyledons. Key words: Development, glycolate oxidase, photorespiration, ribulose-l,5-bisphosphate carboxylase, oxygenase     

Organic Acid Metabolism in Cellular Organelles of Vigna cylindrica (Mitorisasage) Cotyledons

In starchy cotyledons of Vigna cylindrica (L.) Skeels (Mitorisasage)during seed germination, the enzymes of the glyoxylate cyclewere located in the matrix of mitochondria. Glyoxysomes wereabsent. The glyoxylate cycle in the mitochondria supplies organicacids to the tricarboxylic acid cycle. In mitochondria, isocitratelyase activity was much higher than malate synthase activity.Part of the glyoxylate thus produced in mitochondria may benonenzymatically converted to formate by H₂O₂ and the formatethen converted to CO₂ by peroxidase or by formic dehydrogenase.The activity of superoxide dismutase, which supplies H₂O₂, washigher in mitochondria than in peroxisomes. The remaining glyoxylatein mitochondria is possibly converted to glycine by alanine-glyoxylateaminotransferase or transported to peroxisomes which lackedisocitrate lyase activity but had high malate synthase activity.In peroxisomes, glyoxylate may be also produced from urate,as is suggested by the fairly high activities of uricase, allantoinaseand allantoicase. Judging from the enzyme distribution, Vignaperoxisomes should be capable of producing malate, oxalacetate,citrate, isocitrate and a-ketoglutarate. ¹Present address: Department of Horticulture, College of Agricultureand Animal Science, Yeugnam University, Gyeongsan 632, Korea. (Received May 27, 1987; Accepted October 7, 1987)     

Enhancement of Denitrifying Activity in Cells of Roseobacter denitrificans Grown Aerobically in the Light

The effects of light on denitrifying activity during growthwere studied in an aerobic photosynthetic bacterium, Roseobacterdenitrificans (formerly Erythrobacter sp. OCh 114). When aerobicallygrown cells were transferred to anaerobic conditions in thepresence of nitrate, this bacterium exhibited denitrifying activity,with either succinate or malate serving as an electron donorin addition to endogenous substrates. The final product of denitrificationwas identified as nitrous oxide (N₂O), a result that confirmsthe presence of nitrate and nitrite reductases, but not N₂Oreductase, in these cells. Illumination during aerobic growthcaused a marked enhancement of the denitrifying activity. Theactivity increased with increasing intensity of light up to40 mW cm^–2 and was over 20 times that in dark-grown cells.Enhancement of denitrifying activity in illuminated cells wasclosely related to increases in levels of components that areinvolved in the denitrifying pathway, namely, nitrate and nitritereductases. Development of a denitrifying system under aerobicconditions and the enhancement of denitrifying ability by lightin Roseobacter denitrificans are unique characteristics, unlikethose of other known denitrifying bacteria. (Received October 29, 1990; Accepted January 17, 1991)     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Influence of Axis Removal on Amino-, Carboxy- and Endopeptidase Activities in Cotyledons of Germinating Vigna mungo Seeds

Endopeptidase (azocaseolytic enzyme) and carboxypeptidase activitiesin cotyledons of germinating Vigna mungo seeds increased until3 days after the onset of imbibition and decreased thereafter.In detached and incubated cotyledons, the endopeptidase activityincreased only a little while the carboxypeptidase activitycontinued increasing even after 3 days of incubation. The activitiesof leucine-aminopeptidase and alanine-aminopeptidase, exceptfor that of one leucine-aminopeptidase isoenzyme relativelyabundantly present in unimbibed dry cotyledons, increased slightlyon the first day and declined during germination. In detachedcotyledons, the activities maintained their initial levels throughoutthe incubation period. When cotyledons were detached from germinatingseedlings on days 2 and 4 then incubated, the endopeptidaseactivity started to decrease just after removal of the axisbut the carboxypeptidase activity increased more markedly thanwhen the axis remained attached. Exogenously supplied GA₃, kinetin,IAA, or their combinations, showed no significant effect onthe developmental patterns of the endopeptidase and carboxypeptidaseactivities in cotyledons. These results are discussed in relationto the role of the axis in controlling peptidase formation incotyledons of germinating V. mungo seeds. (Received November 18, 1983; Accepted February 28, 1984)     

Changes in Nitrogenase Activity and Nodule Diffusion Resistance of Subterranean Clover in Response to pO2

Diffusion resistance to oxygen within nodules was calculatedusing the respiratory quotient (RQ) of nodules from intact plantsof subterranean clover (Trifolium subterraneum L.) cv. SeatonPark nodulated by Rhizobiun trifolii WU95. From 21 to 52% O₂,the RQ remained between 0.94 and 1.04, whereas at 10% O₂, theRQ was 1.65. When nodulated roots of intact plants were exposedto sub-ambient pO₂ in a continuous flow-through system, respirationdeclined immediately, followed by a partial recovery within30 min. The magnitude of the final respiration rate was dependentupon the pO₂ in the gas stream. Initial rates of respirationwere re-established after 24 h at sub-ambient pO₂ as a resultof changes in the resistance of the variable barrier to oxygendiffusion within the nodules. Nitrogenase activity also decreasedlinearly with decreasing pO₂ in the gas stream, but partialrecovery occurred after 24 h incubation at sub-ambient pO₂.Maximum rates of nitrogenase activity occurred at rhizosphereoxygen concentrations between 21% and 36% O₂. Resistance tothe diffusion of oxygen within the nodules increased at supra-ambientpO₂ and at oxygen concentrations above 36% O₂, resulted in adecrease in both nitrogenase activity and nodulated root respiration.The diffusion resistance of nodules to oxygen increased rapidlyin the presence of either supra-ambient pO₂ or saturating pC₂H₂.Reductions in nodule diffusion resistance either during recoveryfrom exposure to 10% acetylene or to sub-ambient pO₂ occurredmore slowly. It is concluded that subterranean clover is welladapted for maximum nitrogen fixation at ambient pO₂. Key words: Nitrogenase activity, oxygen, subterranean clover, diffusion resistance     

Inhibition of nitrogenase activity and nodule oxygen permeability by water deficit

Short-term effects of water deficit on nitrogenase activitywere investigated with hydroponically grown soybean plants (Glycinemax L. Merr. cv. Biloxi) by adding polyethylene glycol (PEG)to the hydroponic solution and measuring nitrogenase activity,nodule respiration, and permeability to oxygen diffusion (P_o).These experiments showed a rapid decrease in acetylene reductionactivity (ARA) and nodule respiration. A consequence of thedecreased respiration rate was that P_o calculated by Fick'sLaw also decreased. However, these results following PEG treatmentwere in direct conflict with a previous report of stabilityin P_o determined by using an alternative technique. To resolvethis conflict, an hypothesis describing a sequence of responsesto the initial PEG treatment is presented. An important findingof this study was that the response to water deficit inducedby PEG occurred in two stages. The first stage of decreasednodule activity was O₂-limited and could be reversed by exposingthe nodules to elevated pO₂. The second stage which developedafter 24 h of exposure to PEG resulted in substantial loss innodule activity and this activity could not be recovered withincreased pO₂. Severe water deficit treatments disrupt noduleactivity to such a degree that O₂ is no longer the major limitation. Key words: Glycine max, N₂ fixation, soybean, oxygen permeability, water deficit     

Hydrogen Effect on Nitrogenase (C2H2 Reduction) Response to Oxygen in Bradyrhizobium japonicum-Phaseoleae Symbioses

The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup⁺ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO₂, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO₂, nitrogenaseactivity of Hup⁺ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO₂ for ARA (COP), from 35.3 to 40.3 kPa O₂, and the ARA atsupraoptimal pO₂; at suboptimal PO₂ there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H₂ effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O₂ limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata     

Regeneration of Ribulose 1,5-bisphosphate and Ribulose 1,5-bisphosphate carboxylase/oxygenase Activity Associated with Lack of Oxygen Inhibition of Photosynthesis at Low Temperature

The nature of the lack of oxygen inhibition of C₃-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO²), 21 kPa p(O₂), balance N₂) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O₂). At 20°C, lowering p(O₂) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O₂) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O₂). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O₂) suggestingthat RuBP regeneration was reduced at low p(O₂) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O₂) was 24% higherthan at 21 kPa p(O₂). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O₂). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase     

Nitric oxide attenuates IGF-I-induced aortic smooth muscle cell motility by decreasing Rac1 activity: essential role of PTP-PEST and p130cas

Recent data support the hypothesis that reactive oxygen species (ROS) play a central role in the initiation and progression of vascular diseases. An important vasoprotective function related to the regulation of ROS levels appears to be the antioxidant capacity of nitric oxide (NO). We previously reported that treatment with NO decreases phosphotyrosine levels of adapter protein p130^cas by increasing protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein (PTP-PEST) activity, which leads to the suppression of agonist-induced H₂O₂ elevation and motility in cultured rat aortic smooth muscle cells (SMCs). The present study was performed to investigate the hypotheses that 1) IGF-I increases the activity of the small GTPase Rac1 as well as H₂O₂ levels and 2) NO suppresses IGF-I-induced H₂O₂ elevation by decreasing Rac1 activity via increased PTP-PEST activity and dephosphorylation of p130^cas. We report that IGF-I induces phosphorylation of p130^cas and activation of Rac1 and that NO attenuates these effects. The effects of NO are mimicked by the overexpression of PTP-PEST or dominant-negative (dn)-p130^cas and antagonized by the expression of dn-PTP-PEST or p130^cas. We conclude that IGF-I induces rat aortic SMC motility by increasing phosphotyrosine levels of p130^cas and activating Rac1 and that NO decreases motility by activating PTP-PEST, inducing dephosphorylating p130^cas, and decreasing Rac1 activity. Decreased Rac1 activity lowers intracellular H₂O₂ levels, thus attenuating cell motility. hydrogen peroxide; protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein; p130^cas     

Alanine aminotransferase from Cucurbita moschata cotyledons

Alanine aminotransferase increased in pumpkin cotyledons duringgermination with the greatest increase occurring in green cotyledons.The enzyme was found in the soluble fraction and was inhibitedby NH₂OH and p-chloromercuribenzoate. Pyridoxal phosphate andglutathione or dithiothreitol overcame die respective inhibition.Dialysis of the enzyme reduced enzyme activity but the activitywas restored by the addition of pyridoxal phosphate. Alanineaminotransferase was proposed to play a major role in the synthesisof the alanine which occurs in pumpkin cotyledons during germination. (Received September 17, 1975; )     

Studies on the change of the respiratory system in roots in relation to the growth of plants II. Activity of iron-containing oxidases in roots of cereal crops with the aging of plants

Distribution of iron-containing oxidases in aging nodal rootsof rice and wheat was studied. Activities of cytochrome c oxidase(1.9.3.1 [EC] , cytochrome c : O₂ oxidoreductase), catalase (1.11.1.6 [EC] ,H₂O₂: H₂O₂ oxidoreductase) and peroxidase (1.11.1.7 [EC] , donor:H₂O₂ oxidoreductase) in wheat roots were comparatively higherthan were those in rice roots at corresponding stages. Cytochromec oxidase in roots remained active throughout the lives of therice and wheat crops. In rice roots, catalase seemed to playa distinct role around the panicle formation stage. Decay ofcatalase activity took place earlier than did that of peroxidaseand cytochrome c oxidase activities. In wheat roots similarenzyme activity changes were not observed. Data may suggestthat the high activity of iron containing oxidases at the panicleformation stage (I) may be chiefly due to catalase activityin rice roots. ¹Paper presented at the 14th Annual Meeting of the Society ofthe Science of Soil and Manure, Japan (1968). (Received November 21, 1968; )     

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)