Effects of enzymatically digested microsome fractions on red-light-enhanced pelletability of pea phytochrome in vitro in the presence of calcium ion

The 130,000 ?g supernatant of Sephadex G-50 filtrate and a 78,000?g microsomal fraction were prepared separately from homogenatesof etiolated pea (Pisum sativum L. cv. Alaska) shoots. The pelletabilityof phytochrome increased ca. 10-fold by exposure of the filtrateto red light and mixing the filtrate with the microsomal fractionin the dark at ca. 0?C. The increase of pelletable phytochromewas inhibited by 84% when the microsomal fraction digested withtrypsin was used. Phospholipase C (Clostridium welchii) digestionof the microsome inhibited no more than 13% of the pelletability.Although phospholipase A₂ (Crotalus terrificus terrificus) digestioninhibited 43% of the pelletability, addition of defatted albuminduring the enzymatic digestion completely restored the levelof the pelletability. The decrease of RNA content of the microsomalfractions by ribonuclease A digestion did not result in a proportionalinhibition of the pelletability. These results indicate thatproteinaceous component in the microsomal fraction is essentialfor phytochrome pelletability in vitro, that RNA and polar headsof phospholipids are unlikely to be the partner for the binding,and that products of phospholipase A₂ digestion inhibit thepelletability partially. (Received September 12, 1979; )     

Effects of Aldehyde Fixation on Adenosine Triphosphatase and Peroxidase Activities in Maize Root Tips

The effects of aldehyde fixation of excised roots and subcellularfractions of Zea mays have been studied in relation to the preservationof ATP-ase and peroxidase activities. Total peroxidase was littleaffected by either formaldehyde or glutaraldehyde whereas ATP-aseshowed considerable loss of activity, particularly with glutaraldehyde.The activity remaining after fixation was dependent on boththe concentration of fixative and the pH of fixation. Subcellularfractions differed in their response to fixation with the cellwall fraction generally showing higher retention of activitythan the mitochondrial or microsomal fractions.     

Desiccation and Free Radical Mediated Changes in Plant Membranes

Senaratna, T., McKersie, B. D. and Borochov, A. 1987. Desiccationand free radical mediated changes in plant membranes.—J.exp. Bot. 38: 2005-2014. In vitro treatment of microsomal membranes from the axes ofsoybean (Glycine max (L.) Merr.) seeds with free radicals simulatesthe type of membrane injury observed following a lethal desiccationstress—the accumulation of free fatty acids in the membranebilayer, the loss of lipid-P, and the formation of gel phasedomains. The major phospholipids in the microsomal fractionwere phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol.Although these treatments induced an extensive loss of totalphospholipid from the microsomal fraction following desiccation,the ratio of the major phospholipids remained unchanged. Neitherlysophosphatides nor phosphatidic acid accumulated in the fraction,but free fatty acid levels increased. Therefore, cleavage ofboth acyl chains from the phospholipid molecule occurred followingdesiccation of the axes and in vitro free radical treatmentof the membrane. Both treatments also promoted formation of gel phase domainsas shown by wide angle x-ray diffraction and increased microviscosityas determined by the fluorescent probe, DPH (1,6-diphenyl-1,3,5-hexatriene).This could be simulated in liposomes prepared from the totalmicrosomal lipid fraction by the addition of saturated freefatty acids (16:0 and 18:0) at the levels observed followingstress. In contrast, the addition of unsaturated fatty acidsperturbed the bilayer and reduced microviscosity. The inclusionof both saturated and unsaturated free fatty acids as observedin vivo promoted a response similar to that observed with onlythe addition of the saturated free fatty acids. Desiccation of the axes also promoted a loss of microsomal protein,which was recovered in the 165 000 x g supernatant, and an apparentloss of thiol groups from the membrane as determined by a thiolspecific fluorescence probe, dansylaziridine. This loss of thiolgroups could also be simulated by exposure of the membranesto gamma irradiation, which was used as a non-enzymatic sourceof free radicals. Collectively, these data support the hypothesisthat membrane disassembly following desiccation stress is mediatedby a free radical mechanism, and that the consequent de-esterificationof membrane phospholipid and accumulation of saturated freefatty acids alter the physical properties of the membrane. Key words: Membrane microviscosity, membrane fluidity, free fatty acids     

The Structural Organization of Ribonucleic Acid Associated with Soybean Microsomes

The microsomal fraction of soybean (Glycine max) hypocotylswas characterized using analytical and electron microscope techniques.Two microsomal sub-fractions (smooth and rough vesicles) wereseparated by untracentrifugation. Analysis showed that the ribonucleicacid (RNA) of the microsomal fraction cannot be completely accountedfor by the ribosomes, and that some of the RNA is associatedwith the membranes in a non-ribosomal form. A similar conclusionwas reached by using ethylenediaminetetra-acetic acid (EDTA)to disperse the ribosomal material. Although no visible robosomesremained after the treatment with EDTA, the microsomal fractionretained a quarter of its RNA. Ribonuclease removed all themocrosomal RNA without visibly altering the membrane structureexamined in cross section. When hypocotyl tissue sections wereincubated with ¹⁴C amino-acids, the microsomes incorporatedthe radioactive label more rapidly than any other subcellularfraction. This was especially true in the rapidly growing zoneof the hypocotyl. Smooth microsomes were 75 per cent as activeas rough microsomes. These observations are discussed with referenceto the structural organization of the microsomal RNA and itsrole in protein synthesis.     

Localization and Kinetic Properties of {beta}-Glycerophosphatase in Barley Roots

The study of ß-glycerophosphatase activity in cell-wallpreparations and in excised root tips from barley seedlingssupports the view that the former, which constitutes about 20per cent of the activity of the whole homogenate, representsthe fraction located at the surface of the roots in vivo. Theactivities of the cell-wall suspension and intact roots arevirtually identical, and further show identical relations topH, substrate concentration (K_m), and competitive inhibitionby molybdate and inorganic phosphate (K_i). The enzyme must thereforebe freely exposed to the external solution without any permeabilitybarrier separating it from either substrate or inhibitors. Theabsence of any lag phase in the hydrolysis in excised root tipssuggests that the surface enzyme may be limited to the outermostlayers of the root. The solubilization of some of the activityof the cell-wall preparation by treatment with sodium chlorideand ammonium sulphate suggest that surface activity may havebeen lost from these preparations rather than adsorbed duringhomogenization and extraction. The K_m and pH-activity curveof the supernatant activity remaining after centrifugation ofthe cell-wall fraction indicate that only this enzyme and noother detectable glycerophosphatase exists in the roots.     

Evidence that Ethylene is not Involved in Red-light-induced Stimulation of Chlorophyll Formation in Etiolated Cucumber Cotyledons

The involvement of ethylene in red-light-induced stimulationof chlorophyll (Chl) formation was studied because one of thered-light effects on Chl formation (the lateappearing effect)interacts with the ethylene effect in 3-day-old excised etiolatedcotyledons of cucumber (Cucumis sativus L. cv. Aonagajibai).Ethylene production by etiolated cotyledons of intact seedlingsin the dark is enhanced by a red-light pulse, but the effectdoes not occur in excised cotyledons. Application of ethylenein the dark to 3-day-old intact seedlings has little effecton Chl formation in the cotyledon during subsequent continuousillumination, although ethylene pretreatment of 5-day-old seedlingssignificantly stimulates Chl formation. Removal of endogenousethylene by mercuric perchlorate [Hg(ClO₄)₂] does not specificallysuppress the red-light action on Chl formation in both attachedand excised cotyledons. Inhibition of ethylene synthesis byaminoethoxyvinylglycine does not affect the red-light effecton Chl formation in excised cotyledons. These facts indicatethat ethylene does not operate as a mediator of red light instimulating Chi formation in either attached or excised cotyledons. (Received December 13, 1981; Accepted March 30, 1981)     

Plasma membrane isolation from freshwater and salt-tolerant species of Chara: antibody cross-reactions and phosphohydrolase activities

Plasma membranes were isolated using the aqueous polymer two-phasepartition method from the algae Chara corallina and Chara longifolia,algae which differ in their ability to grow in saline environments.Enrichment of plasma membrane and depletion of tonoplast relativeto the microsomal fraction was monitored using phosphohydrolaseassays and crossreactions to antibodies raised against higherplant transporters. Antibodies to the vacuolar ATPase and pyrophosphatasecross-reacted with epitopes in the microsomal fraction, butshowed little affinity for the plasma membrane fraction. Pyrophosphataseactivity also declined in the plasma membrane fraction relativeto the microsomal fraction. The V-type H⁺ -ATPase activity,sensitive to nitrate or bafilomycin, was low in both fractions,though the cross-reaction to the antibody was reduced in theplasma membrane fraction. By contrast, the antibody recognitionof a P-type H⁺-ATPase amino acid sequence from Arabidopsis didnot occur strongly in the anticipated 90–100 kDa range.While there was enhanced recognition of a polypeptide at around140 kDa in the plasma membrane fraction, salt treatment of Charalongifolia resulted in plasma membrane fractions with reducedamounts of this epitope, but no change in vanadate-sensitiveATPase activity, suggesting that it does not represent the onlyP-type ATPase. Microsomal membranes from saltadapted C. longifoliahave higher reactivity with the antibody to the tonoplast ATPase. Key words: Chara, plasma membrane, salt tolerance, ATPase     

CHANGE OF B-TYPE HAEM CONTENT IN RELATION TO PEROXIDASE BIOSYNTHESIS IN INJURED SWEET POTATO ROOTS

The methods of quantitative analysis of b-type haem in plantswere investigated. With an improved method developed was determinedthe haem content in the supernatant, mitochondrial, and microsomalfractions of sweet potato tissue. The activities of peroxidase,catalase, and cytochrome oxidase, as well as the contents ofb-type haem and acid-insoluble nitrogen in the cellular fractionswere determined at different incubation times after cuttingof sweet potato tissue. Peroxidase and catalase increased withtime in each celluler fraction, following a short lag phase.In the mitochondrial fraction, b-type haem, cytochrome oxidase,and acid insoluble nitrogen increased linearly with time. Inthe microsomal and supernatant fraction, b-type haem increasedwith time following a short lag phase. The increase in haemcontent of the supernatant fraction appeared to be associatedwith peroxidase formation. Time course analysis showed that ⁵⁹Fe-incorporation into b-typehaem of the supernatant fraction increased with time and thatincorporation was markedly inhibited by blasticidin S. The incorporationof ⁵⁹Fe into mitochondrial haem did not increase with time andwas not inhibited by blasticidin S. Blasticidin S inhibited⁵⁹Fe-incorporation into microsomal haem. Time course analysisof b-type haem content, ⁵⁹Fe-incorporation into b-type haem,and peroxidase activity suggest that in the injured tissue haemis synthesized from low molecular weight compounds and is incorporatedinto peroxidase as the haem moiety. ¹ This paper constitutes Part 57 of the Phytopathological Chemistryof Sweet Potato with Black Rot. ² Present address: Institute for Plant Virus Research, Chiba.     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time     

Protonemal Morphogenesis of the Moss Tetraphis pellucida Hedw. in Culture and in the Wild

In axenic culture, the protonemal filaments of Tetraphis pellucidaderived from either spores and gemmae, or excised stems andleaves, share a mixture of attributes of chloronemata and caulonemata.Indirect immunofluorescence reveals that the tip cells containcortical and endoplasmic arrays of microtubules at interphase,and phragmoplasts associated with cell plate formation, butpre-prophase bands are absent. Protonemal plates originate fromthe same sites as filamentous protonemal side branches or directlyfrom young gemmae or excised stem fragments. These plates havea cylindrical base, the latter producing a single gametophorebud, and a unistratose lamina. The gametophores produce gemmacups in culture with the vegetative life cycle taking approximately28 d. Gibberellic acid (GA₃) has no visible effect on protonemal morphogenesiswhereas the auxin naphthalene acetic acid (NAA) suppresses plateand side branch formation. In the presence of kinetin the platesare callus-like and produce supernumerary buds. Abscisic acid(ABA) induces malformed plates and filaments with swollen cells,similar to those found in ageing cultures. Rhizoids are produced in abundance from gametophores and protonemalplates in nature but were never seen in culture. In the wild,rhizoids produce numerous protonemal plates and occasional gametophorebuds. The former are the main source of new shoots. The filamentousprotonemal phase in nature mainly comprises upright filamentscontaining one or more abscission cells. The protonemal plates in Tetraphis are homologous with thosein the allied genus Tetrodontium but are very different fromthose in Diphyscium and Sphagnum. Differences between cultureand nature are attributed to lower nutrient levels and irradiancesin the wild. Tetraphis pellucida, protonema, moss, morphogenesis, immunocytochemistry, gemmae, tip growth, vegetative reproduction     

Stimulation by Monovalent Cations of Adenosine Triphosphatase Activity in Extracts of Petiole Tissues3

Adenosine triphosphatase activity has been studied in fractionatedextracts of isolated phloem and xylem tissues of Heracleum mantegazzianumSomm. et Lev. and of petioles of Helianthus annuus L. Enzymeactivity in the microsomal fraction is maximal with ATP as substrate.Monovalent cations stimulate activity, but only below pH 7·0.Divalent cations are inhibitory. Stimulation of ATPase activityby monovalent cations is increased in preparations which haveeither been derived from acetone powders or pre-treated withdithiothreitol or cysteine.     

Phosphorylated intermediates of two hepatic microsomal ATPases.

The hepatic microsomal Ca2+- and Mg2+-dependent ATPase phosphoenzyme intermediates were distinguished by using the chelators EGTA and CDTA (trans-cyclohexane-1,2-diamine-NNN'N'-tetra-acetic acid). The Ca2+-ATPase intermediate is a hydroxylamine-labile base-labile 125 000-Mr phosphoprotein. The Mg2+-ATPase intermediate is a hydroxylamine-stable base-stable 30 000-Mr phosphoprotein. This enzyme intermediate probably reflects the large basal ATPase activity of hepatic microsomal fraction. It is dependent on Mg2+, since formation of the phosphoenzyme is abolished in the presence of CDTA. Under these conditions, the basal ATPase activity is dramatically decreased. These data demonstrate two separate and distinct enzymes which are responsible for the two ATPase activities of hepatic microsomal fraction. Furthermore, these data indicate that more meaningful data about the microsomal Ca2+-ATPase might be obtained if the free ion concentrations are controlled with CDTA.     

Incorporation of serine and ethanolamine into the phospholipids in rabbit retina.

The incorporation of serine and ethanolamine into phospholipids in rabbit retinal subcellular fractions and in excised retinas was studied in vitro, and some enzymic properties of the incorporation of phospholipid bases by base exchange were examined in the microsomal fraction. The retina was found to have a higher rate of base exchange for the incorporation of phospholipid bases than other tissues. The retinal microsomal fraction possessed the highest specific activity of base exchange, while the rod outer segment had very little activity. These results suggest that the phospholipids in the rod outer segment may be transferred from the inner segment of the photorecepter cell. The apparent Km values for serine and ethanolamine in the microsomal fraction decreased with decreasing Ca2+ concentration. Although no further increase of incorporation of serine and ethanolamine occurred after 40 min in the microsomal fraction, continuous incorporation of both bases into phospholipids was seen for 3 hr in excised retina. Illumination did not significantly affect the incorporation of serine and ethanolamine in excised retina or in the rod outer segment fraction. Base exchange reaction thus may not play a direct role in the visual process.     

Membranes carrying acid hydrolases in pea seedling roots

Subcellular localization of acid hydrolases in pea seedlingroots was studied by differential and sucrose density gradientcentrifugations. Significant parts of hydrolase activities inthe tissue were recovered in mitochondrial and microsomal fractions.Sedimentable phosphatase was separated into two subtractions:denser and lighter membrane fractions. The distribution of phosphataseactivity after sucrose density gradient centrifugation of thedenser fraction coincided with that of antimycin AinsensitiveNADH-cytochrome c reductase activity. Electron microscopic observationssuggested that the fraction contained only microsomes. RNasein the denser fraction seemed to associate with ribosomes. Phosphataseand RNase were solubilized by sonic treatment in the presenceof high concentrations of salt. On the other hand, a-amylasewas tightly bound to a membrane. The results are discussed withspecial regard to the relationship between the membranes andlysosomes. (Received May 4, 1973; )     

Effect of 13-hydroperoxyoctadecadienoic acid on the supply of arachidonic acid for prostaglandin synthesis from arachidonoyl-CoA mediated by the cytosolic or microsomal acyl-CoA hydrolase in rabbit kidney medulla

The effects of 13-hydroperoxyoctadecadienoic acid (13-HPODE) on the cytosolic or microsomal acyl-CoA hydrolase (ACH) activity in rabbit kidney medulla and on the ACH-mediated prostaglandin (PG) formation from arachidonoyl-CoA (AA-CoA) were examined. 13-HPODE (10, 20, and 50 microM) had no effect on the cytosolic ACH activity but significantly inhibited the activity of the microsomal enzyme (43-57% inhibition). PG formation was measured as follows: AA-CoA (20 nmol) was preincubated with the cytosolic or microsomal fraction (as the source of ACH) in the presence or absence of 13-HPODE for 5 min at 37 degrees C, followed by incubation with the microsomal fraction (as the source of PG-synthesizing enzymes), hydroquinone and reduced glutathione for 5 min at 37 degrees C, and the PGs formed were measured by HPLC, with use of 9-anthryldiazomethane for derivatization. 13-HPODE reduced the PG formation when the microsomal fraction, but not the cytosolic fraction, was used as the source of ACH (10, 20, and 50 microM; 28-55% inhibition). These results suggest that 13-HPODE may modulate PG levels in rabbit kidney medulla by inhibiting the microsomal ACH activity.     

Studies in Plant Growth Hormones: V. CHROMATOGRAPHY OF HORMONES IN EXCISED AND INTACT ROOTS OF TOMATO SEEDLINGS

1. An examination has been made of the hormones present in extractsof excised roots and intact seedling roots of tomato. Acid andneutral ether-soluble fractions and the ether-insoluble aqueousfraction were chromatographed, and the chromatograms assayedusing oat coleoptile sections. 2. The pattern of hormone activity in excised roots differedlittle from that in seedling roots. 3. On chromatograms of the aqueous fraction developed in isopropanol/ammonia, growth promotion occurred at the position of 3-indolylaceticacid (IAA, Rf 0·5) and sometimes at the position of 3-indolylacetonitrile(IAN, Rf 0·8). When the IAA zone was eluted off the paperand rechromatographed, it formed the IAN zone and another zoneof promotion at Rf 0·1–0·2. 4. When the aqueous fraction was developed in n-butanol/ammonia,promotion occurred at the position of IAA (Rf 0·15),at Rf 0·5, and at the position of IAN (Rf 0-85). Thesezones have been called X, Y, and Z respectively. They were alsoformed when the IAA zone in wopropanol/ammonia was rechromatographedin ammoniacal n-butanol. It is shown that X and Y are interconvertible,and that each can form Z on rechromatography; also, there issome evidence that Z can form X and Y. When Z was separatedinto ether-soluble (acid and neutral) and ether-insoluble fractionswith sodium bicarbonate solution and chromatographed in iiopropanol/ammonia,growth resulted at the position of Z in the neutral and aqueousfractions, but in the acid fraction it occurred at Rf 0·24–O·35.Comparison with other chromatograms indicates that this lastzone does not occur in the aqueous fraction but has been formedas a result of extraction with sodium bicarbonate solution. 5. The zones found in the aqueous fraction also occurred insmall quantities in acid and neutral ethereal fractions in anumber of experiments. 6. The ethereal fractions gave no chromogenic reactions withferric chloride/ perchloric acid, nitrous/nitric acid, or p-dimethylaminobenzaldehyde(MeAB). In the aqueous fraction only MeAB gave a reaction (yellow)which showed any consistent correlation with biological activity.A yellow colour with this reagent is not a characteristic chromogenicreaction of indole compounds. It is suggested that a non-indolehormone system may be operating in tomato roots.     

The Auxin Activity Extractable from Excised Tomato Roots by Cold 80 per cent. Methanol

Extracts of excised tomato roots prepared with cold aqueousmethanol have been partitioned between ethyl acetate and waterand chromatograms of the two fractions bioassayed by an Avenacoleoptile straight growth test and sprayed with various reagentsincluding those giving colour reactions with indole compounds.The greater part of the auxin activity is in the aqueous fractionand chromatograms of this fraction give positive indole reactions. The aqueous fraction chromatographed with isopropanol/ammonia/watershows two zones of growth-promoting activity. The zone of lowerRf contains tryptophane and unidentified ninhydrin-positivematerial. Tryptophane accounts for the activity of the Ehrlich-positiveregion of this zone. The activity of the zone of higher Rf isassociated with ninhydrin-positive material; this activity can,by use of other solvents, be distinguished in Rf from that ofthe common amino-acids which would occur in this zone on theprimary chromatograms. Chromatograms of the aqueous fractionalso show the presence of urea and of a phenol, neither of whichare associated with the zones of growth-promoting activity. The ethyl acetate fraction, and particularly the acid fractionof this, contains growth-promoting activity which, in a rangeof solvents, always corresponds in Rf to IAA. The acid fractioncontains a growth inhibitor corresponding in Rf to the ß-inhibitorof other workers. A zone of growth-promoting activity near thesolvent front on isopropanol/ammonia/water chromatograms containsmore than one active component, but IAN appears to be absent.     

甜菜夜蛾抗氯氟氰菊酯品系相对适合度、抗性生化机理及抗性遗传方式

比较了甜菜夜蛾Spodoptera exigua 抗氯氟氰菊酯品系和敏感品系的繁殖和生长发育特征。结果表明：抗性品系幼虫发育历期延长、蛹重减轻、化蛹率和产卵量降低,抗性品系的适合度为0.61,抗性品系在繁殖和生长发育上存在明显的生存劣势。用两品系3龄幼虫分别测定胡椒基丁醚（PBO）、增效磷SV₁）、脱叶磷（DEF）和顺丁烯二酸二乙酯（DEM）对氯氟氰菊酯的增效作用,抗性品系增效倍数与敏感品系增效倍数之比分别为14.1、14.8、2.3和2.3倍,胡椒基丁醚和增效磷对氯氟氰菊酯增效作用最明显,表明多功能氧化酶参与了甜菜夜蛾对氯氟氰菊酯的抗性。抗性品系3龄幼虫酯酶和谷胱甘肽S-转移酶的活性分别为敏感品系的1.05倍和0.91倍, 抗性品系5龄幼虫多功能氧化酶O-脱甲基活性为敏感品系的1.05倍,两品系间3种酶的活性差异不显著,表明甜菜夜蛾对氯氟氰菊酯的抗性与酯酶、谷胱甘肽S-转移酶及多功能氧化酶O-脱甲基酶活性无关。用剂量对数死亡机率值回归线分析法研究甜菜夜蛾对氯氟氰菊酯的抗性遗传规律,表明甜菜夜蛾对氯氟氰菊酯的抗性为常染色体遗传、多基因控制;正、反交后代的显性度分别为0.61和0.43,抗性遗传为不完全显性。     

Setogenesis and molting in planktonic crustaceans

The formation of new setae, termed setogenesis, is describedfor two taxa of planktonic crustaceans: euphausiids, Euphausiapacifica and Thysanoessa spinifera, and a calanoid copepod,Calanus marshallae. Characteristics of setal formation and eversionat ecdysis are described from two time-series of animals preservedat known intervals in their molt cycle. Results from these laboratoryreference series indicate that previous interpretations of setogenesisin the literature can by synthesized to describe a dynamic processof setal formation which is common to all crustacean taxa. The morphological characteristics of developing setae are usedto designate three specific phases in the molt cycle of planktoniccrustaceans (premolt, postmolt, and intermolt). This stagingtechnique may be used to study field-oriented problems relatedto molting in small planktonic crustaceans.     

The Uptake of Growth Substances: V. VARIATION IN THE UPTAKE OF A SERIES OF CHLORINATED PHENOXYACETIC ACIDS BY STEM TISSUES4GOSSYPIUM HIRSUTUM AND ITS RELATIONSHIP TO DIFFERENCES IN AUXIN ACTIVITY

When segments excised from the etiolated hypocotyls of Gossypiumhirsutum are pretreated in buffer, the subsequent uptake ofradioactive 2,4-dichlorophenoxyacetic acid (2,4-D-1-¹⁴C) isdepressed and the net loss of radioactivity which normally followsa phase of positive uptake by freshly excised segments doesnot take place. Uptake by fresh segments, in contrast with uptakeafter pretreatment, has a high Q₁₀ and is markedly depressedby both 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 3-indolylaceticacid. On these grounds it is proposed that net loss resultsfrom the release of material accumulated by a specific mechanismwhich, with time, becomes inoperative. Additional experimentssuggest that part of the 2,4-D taken up by stem segments ofTriticum vulgare and Avena sativa is accumulated by a similarmechanism. For 1-cm segments, entry is most rapid through the cut ends,and the effects of pretreatment exert their maximal effectsin the tissue near the ends. Therefore very short segments havebeen used to compare the courses of uptake of phenoxyaceticacid (POA) and its 2-, 4-, 2,6-, 2,4- and 2,4,5- chloro- derivatives.The patterns observed are similar to those previously reportedfor 1 -cm segments, although the differences between compoundsare greater. The courses of uptake of 2,4-D and 2,4,5-T, bothterminate in a phase when there is a net loss. POA and the 2-chloro-substitutedacid (2-CPA) are both continuously accumulated. No net lossis found with either the 2,6- (2,6-D) or the 4- chloro (4-CPA)compounds but the rates of uptake progressively decrease toa low level. It is proposed that the processes which determine the patternof uptake of chlorinated phenoxyacetic acids include two typesof accumulation. With Type I accumulation the mechanisms involvedrapidly become disorganized after tissues are excised from theplant. Type 2 accumulation, on the other hand, is stable. Theavailable data indicate that Type I accumulation is peculiarto compounds with marked auxin-like properties.