The Role of C2H4 in anaerobic induction of cocklebur seed germination

Non-dormant small cocklebur seeds (Xanthium pennsylvanicum Wallr.)are potentiated to germinate, if they are subjected to anaerobiccondition for certain time periods after being sufficientlypre-soaked under aerobic conditions. This is termed "anaerobicinduction" of seed germination. Such induction was slightlyinhibited by CO₂ applied during anaerobiosis, but markedly promotedby C²H⁴ Thus, C²H⁴ can exert its action even in anaerobiosis,but does not enhance the fermentative CO₂ evolution. No actualanaerobic induction occurred when over 1? O₂ was present, evenif C²H⁴ had been applied. Therefore, anaerobic induction seemsto be due to a concerted action of some anaerobically proceedingevents and the anaerobically produced C²H⁴. (Received May 31, 1976; )     

Contrasted Effects of CO2 on the Regulation of Dormancy and Germination in Xanthium pennsylvanicum and Setaria faberi Seeds

The effects of CO₂ on dormancy and germination were examinedusing seeds of cocklebur (Xanthium pennsylvanicum Wallr.) andgiant foxtail (Setaria faberi Herrm.). The rate of germinationof the giant foxtail seeds as well as cocklebur was promotedby exogenously applied CO₂ at a concentration of 30 mmol mol^-1regardless of the sowing conditions. However, seeds which failedto germinate in the presence of CO₂, entered a secondary phaseof dormancy under unfavourable germination conditions. If CO₂was applied to seeds under conditions such as water stress imposedwith a 200 mol m^-3 mannitol solution, a hypoxic atmosphere of100 mmol mol^-1 O₂ or a treatment of 0·1 mol m^-3 ABA,development of secondary dormancy was accelerated. These contrastedeffects of CO₂ were observed in ecological studies. Under naturalfield conditions germination of buried giant foxtail seeds respondedpositively to CO₂ during a period of release from primary dormancyfrom Feb. to May, but CO₂ accelerated secondary dormancy commencingin early Jun. In other words, in the presence of CO₂, both theenvironmental conditions and the germination states of the seedsclearly showed secondary dormancy-inducing effects. Thus, itseems that CO₂ has contrasted effects on regulation of dormancyand germination of seeds depending on the germination conditions.Copyright1995, 1999 Academic Press Xanthium pennsylvanicum, cocklebur, Setaria faberi, giant foxtail, CO₂, water stress, hypoxia, ABA, germination, secondary dormancy     

Differential Responsiveness in Zonal Growth of Cocklebur Seed Axes to CO2, C2H4, O2 and Respiration Inhibitors

The axial growth of de-coated cocklebur (Xanthium pennsylvanicumWallr.) seeds, whose axes were divided into 4 zones, was examinedin relation to the temperature-dependent shift of the effectof C₂H₄ on germination. At 23?C, where both C₂H₄ and CO₂ stimulatedgermination, CO₂ promoted the axial growth at the radicle tipzone, whereas C₂H₄ promoted growth in the proximal portion ofthe axis. At 33?C, C₂H₄ inhibited germination, and stronglysuppressed the growth at the radicle tip, whereas the effectof CO₂ did not change. The inhibition of growth at the radicletip zone was alleviated by O₂ enrichment, which also reversedthe inhibition of germination. It is thus apparent that thetemperature-dependent shift of the action of C₂H₄ is associatedwith a temperature-dependent responsiveness of the radicle tipzone to C₂H₄. Growth of the radicle tip zone was sensitive toNaN₃, whereas the proximal portion was sensitive to benzohydroxamicacid, an inhibitor of alternative respiration, suggesting thatthere may be an increase in the operation of the alternativerespiration path along a gradient of axial tissue from the tiptowards the cotyledonary side. The effects of CO₂ and C₂H₄ arediscussed in relation to the different respiratory activitiesin each axial zone of cocklebur seeds. (Received May 9, 1986; Accepted November 6, 1986)     

Interrelation between Ethylene and Carbon Dioxide in Relation to Respiration and Adenylate Content in the Pre-Germination Period of Cocklebur Seeds

Effects of C₂H₄ and CO₂ on respiration of pre-soaked upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds during a pre-germinationperiod were examined in relation to effects of the two gaseson germination. At 33?C, cocklebur seed germination was greatlystimulated. This high temperature-stimulated germination wasseverely inhibited by C₂H₄, but not by CO₂, although both gasesstimulated germination at 23?C. C₂H₄ promoted seed respirationat 23?C, but its promotive effect decreases with increasingtemperature and disappeared at about 35?C, while CO₂ stimulatedrespiration regardless of temperature. CO₂ augmented the operationof the CN-sensitive, cytochrome path (CP) regardless of temperature,resulting in an increase in the ratio of the CP flux to a CN-resistant,alternative path (AP) flux. On the other hand, C₂H₄ augmentedthe operation of both paths, particularly of the AP, at 23?C,where it promoted germination. However, at 33?C where germinationis suppressed by C₂H₄, C₂H₄ preferentially stimulated respirationvia the AP, thus leading to an extremely high ratio of AP toCP. The inhibitory effect of C₂H₄ on germination at 33?C disappearedcompletely in enriched O₂, under which conditions CP is knownto be augmented. At 23?C, CO₂ and C₂H₄ acted independently incontrolling seed respiration, but they were antagonistic at33?C. The independent action appeared when the AP flux was verylow relative to the CP flux, while the antagonism appeared whenthe AP flux had risen. This differential action of the two gasesat different temperatures was also observed in the ATP level,adenylate pool size and energy charge of the axial tissues.These results suggest that the germination-controlling actionsof both CO₂ and C₂H₄ are fundamentally manifested through themodification of respiratory systems. However, the germination-inhibitingeffect of C₂H₄ at 33 ?C was not removed by inhibitors of AP,and there was little difference in the adenylate compounds betweenthe C₂H₄-treated and non-treated seeds at 33?C. Therefore, thephysiological action of C₂H₄ can not be explained only in termsof regulation of the respiratory system. (Received January 24, 1986; Accepted November 17, 1986)     

Possible involvement of ethylene-activated {beta}-cyanoalanine synthase in the regulation of cocklebur seed germination

A possible involvement of ß-cyanoalanine synthase(CAS: EC 4.4.1.9 [EC] ) in germination processes of seeds was demonstratedusing pre-soaked upper seeds of cocklebur (Xanthium pennsylvanicumWallr.). Pretreatment in anoxia not only with KCN but also cysteine,as the substrates for CAS, stimulated the subsequent germinationof cocklebur seeds in air. However, the effect of cysteine wasmanifested even in air when applied together with C₂H₄, andits effect was further enhanced in combination with KCN. Thegermination-stimulating effect of KCN was intensified by C₂H₄only when 0₂ was present. In contrast, serine, another substrateof CAS, was effective in air only when combined with C₂H₄ and/orKCN. The addition of cysteine greatly reduced the cyanogenicglycoside content of seeds, but increased HCN evolution. Onthe other hand, glutathione did not have any effect on cockleburseed germination, HCN evolution or bound cyanogen content, suggestingthat cysteine is not acting as a reducing reagent. It is suggestedthat CAS regulates the process of cocklebur seed germinationby the dual action of enlarging the pool of amino acids andsupplying sulphydryl bases, the latter being more determinatelyimportant. Serine is effective only via the former action, whilecysteine would act via both. Key words: Cyanide, cyanogenic glycoside, ß-cyanoalanine synthase, seed germination, Xanthium pennsylvanicum     

Further Study on the Involvement of Cyanide-Resistant Respiration in the Germination of Cocklebur Seeds

The effect of propyl-gallate (PG) and benzohydroxamic acid (BHAM),inhibitors of cyanide-resistant, alternative respiration path(AP), on germination were examined using after-ripened upperand lower cocklebur (Xanthium pennsylvanicum Wallr.) seeds pre-soakedat 23?C for various periods. Germination was strongly suppressedby PG or BHAM at concentration above 2 mM. However, germinationwas enhanced by low concentrations of PG or BHAM (0.25 or 0.5mM) which reduced some portions of AP operation. Similarly,the high temperature-induced germination of pre-soaked upperseeds was promoted by the same low concentration range of PGor BHAM, in which PG and BHAM were effective only when appliedat the start of high temperature incubation. The inhibitionof germination by C₂H₄ at high temperature occurred only whenseeds were exposed to C₂H₄ during the earlier period of hightemperature incubation, and delayed application tended to promotetheir germination, although most of germinated seeds did notexhibit the normal germination behaviour of predominant radicleprotrusion. If the upper seeds had been subjected to a short-timepre-soaking, the inhibition of high temperature-induced germinationby C₂H₄ was prevented by the low concentrations of PG or BHAM,although the germination restored was mostly an abnormal, predominantlycotyldonary growth, suggesting that the germination inhibitionby C₂H₄ may be involved in some step of axial growth or in thegrowth of some specific axial zone. The lower concentrationsof PG or BHAM were promotive to the axial growth even at 33?C.Based on these results, the involvement of AP in cocklebur seedgerminaton is discussed in relation to the differential growthof axial and cotyledonary tissues. (Received May 2, 1986; Accepted October 27, 1986)     

Dormancy and impotency of cocklebur seeds I. CO2, C2H4 O2 and high temperature

High O₂ tensions, CO₄, C₂H₄ and high temperatures were effectivenot only in breaking the dormancy of cocklebur (Xanthium pennsylvanicumWallr.) seeds but also in increasing the germination potentialof the nondormant but small seeds. There were few qualitativedifferences in response to these factors between the dormantand impotent seeds. Unlike CO₂, however, enriched O₂ and C₂H₄were stimulative even at the low temperature of 13°C. Germination induced by CO₂, C₂H₄ and high temperature treatmentswas lowered when endogenously evolved C₂H₄ or CO₂ was removed,whereas the effect of O₂ enrichment was not affected by theirremoval. CO₂ and high temperatures remarkably stimulated C₂H₄production, whereas O₂ enrichment had no such effect. C₂H₄ productivity was lower in the dormant than non-dormantseeds, suggesting that the after-ripening is characterized byincreasing C₂H₄ production. (Received August 20, 1974; )     

Dormancy and impotency of cocklebur seeds III. CO2- and C2H4-dependent growth of the embryonic axis and cotyledon segments

Growth of segments of embryonic axes and cotyledons excisedfrom dormant or nondormant cocklebur (Xanthium pennsylvanicumWallr.) seeds and CO₂ and C₂H₄ production in these segmentswere examined in relation to the effects of temperature, CO₂and C₂H₄. Both the nondormant axes and cotyledons grew evenat low temperatures below 23°C, but the dormant ones failedto grow. There was only little difference in the CO₂ evolutionbetween the nondormant and dormant ones, but both the axis andcotyledon segments from the dormant seeds exhibited little orno C₂H₄ productivity, unlike the nondormant ones, at low temperatures.However, a high temperature of 33°C caused rapid extensiongrowth and C₂2H₄ production even in dormant axes and cotyledons. The inability of dormant axes and cotyledons to grow disappearedcompletely in the presence of C₂H₄ at fairly low concentrations.Removal of endogenous CO₂ and C₂H₄ reduced the growth in bothaxes and cotyledons, while exogenous CO₂ mainly enhaced axialgrowth although exogenous C₂H₄ strongly stimulated the growthof both organs. Regardless of the dormant status, however, maximumgrowth of these organs occurred when C₂H₄ was given togetherwith CO₂. We suggest that dormancy in cocklebur seeds is dueto the lack of growing ability in both organs, caused by thelack of C₂H₄ productivity in both dormant axes and cotyledons,particularly in the former. (Received December 2, 1974; )     

Ethylene Production in Pea and Cocklebur Seeds of Differing Vigour

Relationships between seed vigour and ethylene (C₂H₄) productionwere studied using C₂H₄-responsive fatty cocklebur seeds (Xanthiumpennsyhanicum Wallr.) and C₂H₄-insensitive starchy pea seeds(Pisum sativum L. cv. Alaska), which had been harvested in differentyears and subjected to different storage conditions. In bothspecies, the seeds with the highest vigour evolved the largestamounts of C₂H₄ during a period of water imbibition. The reductionof C₂H₄ production in cocklebur seeds occurred concomitantlywith the reduction in the growth potentials of both axial andcotyledonary tissues. Similarly, the activity of ACC-C₂H₄ conversionincreased with soaking, and was greater in seeds of high vigourcompared with those of low vigour. However, the change in ACCcontent in pea seeds differed from that in cocklebur seeds.That is, pea seeds with high vigour accumulated less ACC duringan imbibition period than those with low vigour. From theseresults it was suggested that the inferior C₂H₄ production bylow vigour pea seeds is mainly attributable to low ACC-C₂H₄conversion, whereas that by low vigour cocklebur seeds is dueto the shortage of ACC supply in addition to the reduced ACC-C₂H₄conversion. However, germination of deteriorated cocklebur seedswas not restored by exposure to ACC or C₂H₄, suggesting thatthe loss of seed vigour reduces the responsiveness of seedsto C₂H₄ as well as C₂H₄ production. Key words: Pea, cocklebur, seed vigour, ethylene production, 1-aminocyclopropane-1-carboxylic acid     

Possible Involvement of the Alternative Respiration System in the Ethylene-stimulated Germination of Cocklebur Seeds

Respiration of nondormant upper cocklebur (Xanthium pensylvanicum Wallr.) seeds was enhanced by exogenous C₂H₄, proportionally to the concentration of C₂H₄ and the duration of presoaking of the seeds. Benzohydroxamic acid (BHM) and salicylhydroxamic acid (SHM), inhibitors of alternative respiration, inhibited both the germination of nondormant lower cocklebur seeds and the respiration of the upper seeds presoaked for periods of 12 to 30 hours. Both the growth and respiration of axial and cotyledonary tissues were also inhibited by BHM. Moreover, BHM inhibited both the C₂H₄-induced germination of the upper seeds and their C₂H₄-stimulated respiration; the inhibition occurred only with concomitant addition of C₂H₄ and BHM. The respiration of seeds with a secondary dormancy induced by presoaking for prolonged periods was markedly stimulated by C₂H₄ but not suppressed by BHM. It was suggested that the alternative respiration system may be involved in the normal germination process of cocklebur seeds, secondary dormancy may result from its inactivation, and C₂H₄ may exert its germination-promoting action by stimulating the alternative respiration. The effects of BHM and SHM can suggest but not prove the involvement of the alternative respiration in seed germination.     

Promotion of Cocklebur Seed Germination by Allyl, Sulfur and Cyanogenic Compounds

The effects of allyl, sulfur and cyanogenic compounds on thegermination of upper cocklebur (Xanthium pennsylvanicum Wallr.)seeds were examined. Mercaptoethanol and methylmercaptan aswell as KCN, substrates for rßcyanoalanine synthase(CAS), and H₂S and thiocyanate, the products of the CAS catalyzingreaction, were effective in promoting germination, suggestingthe involvement of CAS in germination. Most of allyl compounds, especially allylthiourea, as well asethylene which activated CAS [Hasegawa et al. (1994) Physiol.Plant. 91: 141], promoted the germination in an abnormal typewhich occurred by the predominant growth of cotyledons as didC₂H₄ [Katoh and Esashi (1975) Plant Cell Physiol. 16: 687].However, they failed to activate CAS unlike ethylene, and toliberate free ethylene during an incubation period. It was thuspossible that an C₂H₄-like double bond within allyl compoundscan act to promote seed germination. (Received June 10, 1996; Accepted August 21, 1996)     

Dormancy and impotency of cocklebur seeds II. Phase sequence in germination process

Interactions of C₂H₄, CO₂, O₂ and high temperature in stimulatinggermination of cocklebur (Xanthium pennsylvanicum Wallr.) seedswere studied and the phase sensitive to each factor during germinationwas determined. The combination of CO₂ and enriched O₂, andparticularly that of C₂H₄ and enriched O₂, much more effectivelystimulated germination than CO₂ and C₂H₄. At low temperature,however, the cooperation of CO₂ and enriched O₂ was lost andonly the effect of C₂H₄ in combination with CO₂ or enrichedO₂ remained. Carbon dioxide stimulated C₂H₄ production and induced germinationwhen it was applied in the first period of water imbibition,corresponding to the passive thrust forming phase. C₂H₄ becameeffective after the CO₂-responsive phase. In contrast, bothO₂ enrichment and high temperature became increasingly effectivewith the imbibition times. Anaerobiosis applied during the firstperiod of the germination process showed no inhibitory effect,whereas CO₂ and C₂H₄ were stimulative even under such a condition. (Received August 26, 1974; )     

Control of the germination of secondary dormant cocklebur seeds by various germination stimulants

The responsiveness of non-dormant, upper cocklebur (Xanthiumpennsylvanicum Wallr.) seeds to various germination stimulants,such as CO₂ C₂H₄ CS(NH₂)₂, BA and enriched O₂, decreased withincreasing periods of water imbibition and was completely lostin the state of secondary dormancy. Unlike CO₂ BA and CS(NH₂)₂however, C₂H₂ and enriched O₂ effectively prevented the developmentof secondary dormancy, and their combination was the most effectivefor stimulating the germination of seeds which had undergoneimbibition for a long time. CS(NH₂)₂ and BA were effective,not by themselves but either under anaerobiosis or elevatedO₂ tension. Growth of the axial and cotyledonary segments excisedfrom aged seeds remained responsive to these germination stimulantsand could be further stimulated by exogenous C₂H₂. With imbibitionat a lower temperature, the seeds maintained high germinationin response to various stimulants and a high rate of C₂H₂ andCO₂ production during a long period of water imbibition. Theseresults are discussed in terms of the two possible causes forthe loss of responsiveness or induction of the secondary dormancy. (Received June 27, 1978; )     

Light Actions in the Germination of Cocklebur Seeds: IV. DISAPPEARANCE OF RED LIGHT-REQUIREMENT FOR THE GERMINATION OF UPPER SEEDS SUBJECT TO ANOXIA, CHILLING, CYANIDE OR AZIDEPRETREATMENT

Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actionsin the germination of cocklebur seeds. IV. Disappearance ofred light-requirement for the germination of upper seeds subjectto anoxia, chilling, cyanide or azide pretreatmenL—J.exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic uppercocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreatingwith anoxia, chilling, cyanide or azide, which stimulates theirdark germination, were examined in relation to light actions.Prior to experiments, seeds were pre-soaked at 23 °C inthe dark for 1 or 2 weeks to remove the pre-existing Pfr. Whenthe prctreatment conditions were suboptimal for germinationinduction, the stimulating effects of the pretreatments on germinationduring a subsequent dark period at 23 °C were manifest onlywhen seeds were irradiated with red light before or after thepretreatment Red light promotion was reversed by blue or far-redlight treatment. However, both prc-chilling for 6 d at 8 °Cand prctreatment with 1· 5 mol m ^{– 3} NaN³ for 2d could induce full germination without red light exposure.On the other hand, both pre-exposure to anoxia for 8 d and pretreatmentwith 30 mol m^–3 KCN could induce the dark germinationonly when germination occurred at 33 °C which is known toaugment the ratio of an alternative respiration flux to a cytochromeone. Moreover, the dark germination in response to these inductionswere strongly inhibited by the inhibitors of alternative respiration,propyl gallate and benzohydroxamic acid, applied during a subsequentdark period. It was thus suggested that Pfr has some relationto the operation of two respiration systems of cocklebur seeds,but it is not indispensable to germination of this positivelyphotoblastic seed. Key words: Anoxia, azide, blue light, chilling cyanide, dark germination, far-red light, red light, seed germination, X anthium pennsylvanicum     

Reversal of ethylene action on cocklebur seed germination in relation to duration of pre-treatment soaking and temperature

Abstract At 23°C, both C₂H₄ and CO₂ stimulated the germination of freshly imbibed upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds, but C₂H₄, unlike CO₂, changed to an inhibitor of germination under some soaking conditions. However, when seeds were pre-soaked for more than several hours at 23 °C prior to treatment, C₂H₄ strongly inhibited their germination at 33 °C, the degree of inhibition increasing with the duration of pre-soaking. Maximum inhibition occurred at 1–3 cm³ m^?3 C₂H₄ when seeds were pre-soaked for 1 week; further increases of C₂H₄ concentration and pre-soaking period decreased the inhibitory effect. C₂H₄ was synergistic with CO₂ when C₂H₄ promoted germination, whereas it was antagonistic when inhibitory. Such a transition of the C₂H₄ action occurred at ca. 27 °C. Also 1-andnocyclopropane-1-carboxylic acid, a C₂H₄ precursor, inhibited the germination of pre-soaked seeds at 33 °C, although it promoted the germination at 23 °C. When pre-soaked seeds were prepared for germination by chilling at 8 °C for 3 d, the inhibitory effect of C₂H₄ on the subsequent germination was manifested even at 23 °C. The reversal of the C₂H₄ action from promotion to inhibition in cocklebur seed germination is discussed in relation to the engagement of two respiratory pathways in the imbibed seeds.     

Antagonism Between Malate and Ethylene in the Regulation of Avena sativa Coleoptile Elongation

Etiolated Avena sativa L. coleoptile sections were used to determinethe influence of C₂H₄ on in vivo and in vitro rates of CO₂ fixation,and to measure the influence of various permutations of C₂H₄,CO₂, and malate on growth. Whereas 1 mM malate or 320 µI^-1 CO₂ stimulated growth by approximately 100 per cent, inhibitionof growth by 10-8 µ I_-1 C₂H₄ was substantial only in thepresence of malate or CO₂ The increase in growth rate in responseto these two agents was eliminated by the simultaneous applicationof C₂H₄. The in vivo rate of dark [¹⁴C]bicarbonate fixationand in vitro enzymic assays of fixation were not measurablyinhibited by C₂H₄. These results are discussed in the lightof evidence which indicates that CO₂-stimulated growth is mediatedby dark fixation. The data do not support the view that C₂H₄inhibition of growth results from an inhibition of fixation,but suggests that C₂H₄ may inhibit some step in the processby which malate stimulates growth.     

Effects of 2,5-norbornadiene on cocklebur seed germination and rice coleoptile elongation in response to CO2 and C2H4

To examine in more detail the mechanisms of cocklebur (Xanthium pennsylvanicum Wallr.) seed germination and rice (Oryza sativa L. cv. Sasanishiki) coleoptile elongation that were responsive to both C₂H₄ and CO₂, the effects of NBD (2,5-norbornadiene), a cyclic olefin known as a competitive inhibitor of C₂H₄, on those phenomena were tested under various conditions. NBD strongly inhibited germination of cocklebur seeds and their axial and cotyledonary growth. The NBD effects were significantly negated by endogenously evolved and exogenously applied CO₂ regardless of incubation temperature. Similarly, the inhibitory NBD effect was negated by C₂H₄ at 23°C, but at 33°C a low concentration (3 1/L) of C₂H₄ rather enhanced the inhibitory NBD effect. This phenomenon reflected the growth responses of the tip zone of axial tissues in cocklebur seeds to NBD and C₂H₄, in which both gases were antagonistic in regulating the axial growth at 23°C but additive in inhibiting it at 33°C. Maximal negation of these inhibitory NBD effects was brought about by simultaneous application of CO₂ and C₂H₄. Similarly, elongation of rice coleoptiles was suppressed by NBD, and when they were immature, its inhibitory action was counteracted by both C₂H₄ and CO₂, especially during simultaneous application. However, the inhibitory NBD effect was completely negated by C₂H₄ applied alone at concentrations above 500 1/L regardless of the physiological age of coleoptiles. These inhibitory NBD effects are additional evidence suggesting that C₂H₄ acts as a growth regulator in both cocklebur seed germination and rice coleoptile elongation. That NBD was capable of counteracting CO₂ action in some cases but was incapable of negating inhibitory C₂H₄ action, such as that observed in cocklebur seeds, suggests that NBD acts with some side effects besides being a competitive inhibitor of C₂H₄ actions.     

Activity of the Pentose Phosphate Pathway and Changes in Nicotinamide Nucleotide Content during Germination of Seeds of Cicer arietinum L.

Changes in the level of nicotinamide nucleotides, rate of ¹⁴CO₂output from [1^–14C] or [6¹⁴ C₆/C₁ ratios, glucose-6-phosphatedehydrogenase, 6-phosphogluconate dehydrogenase, and NAD kinaseactivities were determined during the first 72 h of germinationof seeds of Cicer arietinum L. The level of oxidized and reducedforms of nicotinamide nucleotides, together with the activityof glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase,NAD kinase, and C₆/C₁ ratios, suggest that the pentose phosphatepathway is activated during early germination in cotyledonsof chick pea seeds. The results obtained in embryonic axes seemsto indicate a lower participation of the PP pathway, probablydue to the development of the activity of the glycolytic-TCApathway.     

Effect of Temperature and External pH on the Cytoplasmic pH of Chara corallina

Cytoplasmic pH (pH_c) in Chara corallina was measured (from [¹⁴C]stribution)as a function of external pH (pH₀)and temperature. With pH₀near 7, pH_c at 25?C is 7.80; pH_cincreases by 0.005 pH units?C^–1 temperature decrease, i.e. pH_c at 5 ?C is 7.90. WithpH? near 5.5, the increase in pH_c with decreasing temperatureis 0.015 units ?C^–1 between 25 and 15?C, but 0.005 units?C^–1 between 15 and 5?C. This implies a more precise regulationof pH_c with variations in pH_o at 5 or 15 ?C compared with 25?C. The observed dp H_c/dT is generally smaller than the –0.017units ?C^–1 needed to maintain a constant H⁺/OH^–1,or a constant fractional ionization of histidine in protein,with variation in temperature. It is closer to that needed tomaintain the fractional ionization of phosphorylated compoundsor of CO₂–HCO₃^– The value of dpH_c/dT has importantimplications for several regulatory aspects of cell metabolism.These include (all as a function of temperature) the rates ofenzyme reactions, the _H+ at the plasmalemma(and hence the energy available for cotransport processes),and the mechanism for pH_c regulation by the control of bidirectionalH⁺ fluxes at the plasmalemma.     

Light Actions in the Germination of Cocklebur Seeds: I. DIFFERENCES IN THE LIGHT RESPONSES OF THE UPPER AND LOWER SEEDS

Germination responses to light were studied in the upper andlower seeds of cocklebur (Xanthium pennsylvanicum Wallr.). Thelower seed was dark-germinating and negatively photoblastic;the upper one had a red-light (R) requirement and was positivelyphotoblastic. Germination of the lower seeds was inhibited bya prolonged single irradiation with R, blue (B) or far-red (FR)light applied during imbibition. The maximal inhibitory effectof a single irradiation occurred 9 h and 13 h after the startof soaking at 33 °C and 23 °C, respectively. However,the inhibitory effect of R differed from that of B and FR, byonly delaying germination. A single exposure to B or FR lightcould be replaced by intermittent B or FR irradiation, and theireffects were repeatedly reversible by the following R irradiation.If the upper seeds were not exposed to R during imbibition,they failed to germinate even at 33 °C which was optimalfor germination, and the promotive effect of R increased withdelay of its application time. The photoperceptive locus incocklebur seeds was the axial tissue for all B, R and FR. Lightreceived by the cotyledonary tissue had little effect. Germinationdimorphism in response to light is discussed with respect tothe phytochrome content and the ageing of axial tissues. Key words: Blue light, Dimorphism, Far red light, Germination, Red light, Xanthium seed