Influence of Glyphosate on Nitrate Reductase Activity in Soybean (Glycine max)

Experiments were conducted to determine the influence of glyphosate[N-(phosphonomethyl)glycine] on extractable nitrate reductaseactivity during light and dark growth of soybean (Glycine max)seedlings. Glyphosate (5?10^–4 M), applied via root-feedingto three-day-old etiolated seedling, significantly reduced enzymeactivity in roots (48 to 96 h) and leaves (96 h) of seedlingsplaced in the light, but had little effect on enzyme activityin cotyledons compared to enzyme levels in tissues of untreatedseedlings. During dark-growth, nitrate reductase activity increasedwith time in cotyledons of untreated seedlings (activity about85-fold less than in cotyledons of light-grown plants) but muchlower enzyme levels were found in cotyledons of glyphosate-treatedseedlings after 72 and 96 h. In leaves of dark-grown seedlings,glyphosate reduced nitrate reductase levels by 95%. Most inhibitionof extractable enzyme activity occurred in newly developingorgans (leaves and roots) which correlates well with reportsthat glyphosate is rapidly translocated to these sites. However,the fact that glyphosate inhibits growth prior to lowering enzymeactivity levels indicates a secondary effect on nitrate reductase. (Received May 18, 1984; Accepted February 12, 1985)     

Factors Influencing Adventitious Root Production in Cuttings of Griselinia littoralis and Griselinia lucida

Griselinia littoralis roots quickly and vigorously from cuttingsof seedlings and mature plants and also forms roots on detachedleaves. Cuttings root in the dark but leaves must be present.In contrast G. lucida roots vigorously only from cuttings takenfrom seedlings. Light is essential for root formation on oldermaterial. Detached leaves will not root. Although callus formationat the cut base commonly occurs in both species it is not directlyassociated with root formation. Griselinia littoralis Raoul Choix, Griselinia lucida Forst. f. Prodr., adventitious roots, stem cuttings, leaf cuttings, woody plants     

Carbon and Nutrient Allocation in Elymus farctus Seedlings after Burial with Sand

We report physiological aspects of the response of seedlingsof the strandline grass Elymus farctus to short-term burialwith sand. Seedlings were buried at the two-leaf stage for oneweek and compared with non-buried controls - before, duringand after burial. Photosynthetic CO₂ uptake was measured byinfrared gas analysis and carbon translocation from the youngestexpanded leaf was monitored after exposure to ¹⁴CO₂. The concentrationsof water-soluble carbohydrate, and total nitrogen, phosphorusand potassium in component organs were determined. Net photosynthetic capacity was almost completely inhibitedby 5 d of burial. However, plants uncovered after 7 d of burialrecovered full photosynthetic competence within 24 h. Therewas a sharp, sustained depression in the water-soluble carbohydrateconcentration of the roots and stems after burial, whereas leaves1–3 had much higher concentrations than non-buried plantsfor up to 20 d after uncovering. Burial virtually suppressedthe translocation of ¹⁴C to stem, roots and expanding leaves,and this effect persisted even after full recovery of net photosynthesis.The proportional allocation of total N, P and K to leaves wasincreased after burial, mainly at the expense of the roots.Changes both in nutrient concentration and in the relative massesof organs contributed to this effect. The apparent reversal of the normal source-sink relationshipsfor carbohydrate between photosynthetic and non-photosyntheticorgans, and the differential allocation of inorganic nutrients,may contribute to the maintenance of photosynthetic capacityduring burial. The rapid recovery of net photosynthesis afterre-exposure suggests that these responses may be advantageousfor survival of E. farctus seedlings in the early stages ofgrowth in a physically unstable and unpredictable environment. Sand burial, photosynthesis, translocation, nutrient allocation, Elymus farctus, sand couch grass     

涝渍胁迫对喜树幼苗形态和生理的影响

为了解喜树对涝渍土壤条件的适应性, 通过温室土培盆栽试验, 从形态和生理两方面探讨了涝渍胁迫对1年生喜树(Camptotheca acuminata)实生苗的影响, 试验分对照、轻度渍水、渍水和淹水等4个处理, 处理时间为 21 d。结果表明, 喜树根系生长以轻度渍水最好, 其次为对照, 而渍水和淹水的处理初生根系逐渐腐烂、死亡, 与之相对应, 轻度渍水处理的根系活力与对照无显著差异, 但渍水和淹水处理随着处理时间的延长逐渐下降, 同时观察到渍水和淹水的喜树茎在水面以下部位出现较多的皮孔。随着处理时间的延长, 轻度渍水处理喜树叶片内POD和SOD活性一直保持较高水平, 渍水和淹水处理则表现出先升高后下降的趋势, 各个处理叶片中O₂^-· 、H₂O₂和MDA含量有逐渐升高的趋势, 且各处理之间均表现为淹水>渍水>轻度淹水>对照。各处理根系LDH活性在处理前期较对照低, 而在处理的中后期, LDH活性均比对照高, 以渍水和淹水处理最高。因此, 喜树在轻度渍水条件下, 一方面由于皮孔和不定根的增多, 根系能够获得更多的氧气, 另一方面由于POD和SOD抗氧化酶活性的增强, 降低了O₂^-·和H₂O₂对细胞的伤害, 喜树能够在轻度渍水的立地上正常生长。     

The Distribution and Identity of Assimilates in Tomato with Special Reference to Stem Reserves

Much of the work on the distribution of ¹⁴C-labelled assimilatesin tomato has been done in winter under low light intensities,and consequently the reported distribution patterns of ¹⁴C maynot be representative of plants growing in high light. Further,there are several somewhat conflicting reports on patterns ofdistribution of ¹⁴C-assimilates in young tomato plants. We soughtto clarify the situation by studying the distribution of ¹⁴C-assimilatesin tomato plants of various ages grown in summer when the lightintensity was high. In addition, the role of the stem as a storageorgan for carbon was assessed by (a) identifying the chemicalfractions in the stem internode below a fed leaf and monitoring¹⁴ C activity in these fractions over a period of 49 d, and(b) measuring concentrations of unlabelled carbohydrates inthe stem over the life of the plant. The patterns of distribution of ¹⁴C-assimilates we found fortomato grown under high light intensity confirmed some of thosedescribed for plants grown under low light, but export of ¹⁴Cby fed leaves was generally higher than reported for much ofthe earlier work. Lower leaves of young plants exported over50% of the ¹⁴C they fixed, although export fell sharply as theplants aged. Initially, the roots and apical tuft were strongsinks for assimilates, but they had declined in importance bythe time plants reached the nine-leaf stage. On the other hand,the stem became progressively more important as a sink for ¹⁴C-assimilates.Older, lower leaves exported more of their ¹⁴C-assimilates tothe upper part of the plant than to the roots, whereas youngleaves near the top of the plant exported more of their assimilatesto the roots. The stem internode immediately below a fed leafhad about twice the ¹⁴C activity of the internode above theleaf. Mature leaves above and below a fed leaf rarely importedmuch ¹⁴C, even when in the correct phyllotactic relationshipto the fed leaf. In the first 3 d after feeding leaf 5 of nine-leaf plants, theorganic and amino acid pools and the neutral fraction of theinternode below the fed leaf had most of the ¹⁴C activity, butby 49 d after feeding, the ethanolic-insoluble, starch and lipidfractions had most of the ¹⁴C activity. Glucose, fructose andsucrose were the main sugars in the stem. Although concentrationsof these sugars and starch declined in the stem as the plantsmatured, there was little evidence to indicate their use infruit production. Stems of plants defoliated at the 44-leafstage had lower concentrations of sugars and starch at maturity,and produced less fruit than the controls. It was concludedthat tomato is sink rather than source limited with respectto carbon assimilates, and that the storage of carbon in thestem for a long period is possibly a residual perennial traitin tomato.Copyright 1994, 1999 Academic Press Lycopersicon esculentum, tomato, assimilate distribution, ¹⁴C, internode storage, sink-source relationships, starch, stem reserves, sugars     

Developmental and photobiological factors affecting photoperiodic induction in Arabidopsis thaliana Heynh. Landsberg erecta

We have tested whether the promotion of flowering by long days(LD) in Arabidopsis thaliana is a consequence of photoperiodicinduction. To achieve this, the flowering responses of Arabidopsisthaliana (L.) Heynh. Landsberg erecta (Ler) and the long-hypocotylmutants hy2, hy3 and hy4 were determined with respect to age,daylength and light quality. Ler was capable of distinguishingbetween short days (SD) and long days (LD) from about 4 d aftersowing at 20 C, the time at which cotyledons were expandingand greening. At this stage, the critical daylength was between8 h and 10 h. At 7 d, seedlings required five LD for inductionand, as the seedlings aged, they became more sensitive so thatby day 20, one LD was fully inductive. The response to SD innewly germinated seedlings was to delay flowering without alteringleaf number, but after about 10 d, delay of flowering by SDwas accompanied by extra leaves. In light quality experiments,blue light (B) was inductive for 5-d-old plants and in all subsequenttreatments, far-red (FR) caused induction in treatments at 12d and 18 d and low pressure sodium, equivalent to red, was notinductive at 5 d and 12 d, but partially inductive at day 18.Hence, both a specific blue-light photoreceptor and phytochromeA in High Irradiance Response mode promote floral induction.In daylength transfer experiments all three hy mutants respondedto LD by earlier flowering. Both hy2 and hy3 produced substantiallyfewer leaves than Ler in SD and hy3 flowered slightly earlierthan Ler. The hy4 mutants flowered later than Ler in SD andhad a higher leaf number. A scheme is proposed in which photoperiodicinduction depends on the ability of the plant to sense photoperiod,the stage of development and the photobiological input. We alsopropose that phytochrome A and the blue photoreceptor promoteflowering whereas phytochrome B promotes vegetative development. Key words: Arabidopsis thaliana, blue-absorbing photoreceptor, flowering, photoperiodic induction, phytochrome     

Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 40–60per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation     

The Occurrence of 1,3-{beta}-Glucanase in Healthy and Verticillium-infected, Resistant and Susceptible Tomato Plants

Leaf, stem, and root extracts of near-isogenic tomato plantscv. Craigella, resistant and susceptible to Verticillium albo-atrum,showed constitutive 1,3-ß-glucanase activity whichincreased following inoculation with the pathogen. Partiallypurified enzyme extracts were obtained by dialysing a 30–80%ammonium sulphate fraction of the tissue brei. The enzyme hadpH and temperature optima of 5?5 and 44 ?C respectively, withhigh activity between 50 and 60 ?C. The response to laminarinconcentration was linear between 1?2 and 7?5 mg ml^–1.Root inoculation of susceptible plants with 10⁶ propagules ml^–1V. albo-atrum led to a umform 300 per cent increase in all steminternodes except the terminal one, which was 500 per cent ofthe controls. No spatial relationship of enzyme activity tothe localization of fungus within the stem was apparent. Petioles,leaves, and roots of susceptible infected plants similarly showedan increase in activity but less than that in stems. Changedlevels of stern enzyme activity at different times after inoculationwere associated with reductions in the number of vessels containinghyphae. Extracts of plants of the resistant isoline showed increasedglucanase activity over controls, but this was substantiallylower than that in susceptible plants and was associated withthe greatly reduced mycelial colonization in resistant plants. It is concluded that single gene resistance in tomato to Verticilliumis not associated with innately higher levels of 1,3-ß-glucanasein healthy plants. The increased activity in infected plantsis proportional to the overall quantity of pathogen in the plantor of pathogenic metabolites.     

Effects of Root Temperature and Form of Nitrogen Nutrition on Nitrate Reductase Activity in Oilseed Rape (Brassica napus L.)

The effect of root temperature and form of inorganic nitrogensupply on in vitro nitrate reductase activity (NRA) was studiedin oilseed rape (Brassica napus L. cv. bien venu). Plants weregrown initially in flowing nutrient solution containing 10 µMNH₄NO₃ and then supplied with either nitrate or ammonium for15 d at root temperatures of 3, 7, 11 or 17 °C. Shoot temperatureregime was similar for all plants; 20/15 °C, day/night.Root NRA was highest when roots were grown at 3 and 7 °C.In laminae and petioles NRA was highest when roots were 11 or17 °C. The plants supplied with ammonium had much lowerlevels of NRA in roots after 5 d than the plants supplied onlywith nitrate. NRA in the laminae of plants supplied with ammoniumwas low relative to that in plants supplied with nitrate onlywhen root temperature was 11 or 17 °C. Values of the apparent activation energy (E_a) of NR, calculatedfrom the Arrhenius equation, in laminae and petioles were differentfrom roots suggesting difference in enzyme conformation. Evidencethat the temperature at which roots were growing affected E_awas equivocal. Oilseed rape, Brassica napus L., activation energy, ammonium, Arrhenius equation, nitrate, root temperature, nitrate reductase     

Changes in activity of antioxidative enzymes in wheat (Triticum aestivum) seedlings under cold acclimation

Activated oxygen species such as superoxide radicals, singlet oxygen, hydrogen peroxide and hydroxyl radicals can be produced in plants exposed to low, non-freezing, non-injurious temperatures. To prevent or alleviate oxidative injury, plants have evolved several mechanisms which include scavenging by natural antioxidants and enzymatic antioxidant systems such as superoxide dismutases, catalase and peroxidases. Although overproduction of hydrogen peroxide and increased tolerance to oxidative stress can be induced in wheat by low-temperature treatments, data concerning changes in the enzymatic antioxidant systems are almost absent. With the aim to provide this information, antioxidant enzyme (superoxide dismutases, catalase and peroxidases) activities were analysed in leaves and roots of Triticum aestivum cvs Brasilia (frost resistant in field) and Eridano (less frost resistant in field) seedlings grown at day/night temperatures of 24/22°C (control treatment) and 12/5°C (low-temperature treatment). Our data showed that superoxide dismutase activities were unaffected by low-temperature treatment both in leaves and roots. Catalase activity in leaves and roots was decreased in 12/5°C-grown seedlings, but Brasilia maintained higher catalase activity than Eridano. Differences were also observed in guaiacol peroxidase activities between control and acclimated seedlings: Higher guaiacol peroxidase activities were found in the leaves of 12/5°C-grown seedlings while in roots these activities were lower. Moreover, Brasilia guaiacol peroxidase activities were higher than Eridano. Superoxide dismutase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by low-temperature treatment. Changes in the activities of antioxidant enzymes induced by cold acclimation support the hypothesis that a frost-resistant wheat cultivar, in comparison with a less frost-resistant one, maintains a better defence against activated oxygen species during low-temperature treatment.     

Proline and Proline Metabolising Enzymes in in-vitro Selected NaCl-tolerant Brassica juncea L. under Salt Stress

The effect of salt stress was studied on proline accumulationand the activities of proline metabolic pathway enzymes in seedlingand leaf tissue of two genetically stable lines (SR2P1-2 andSR3P6-2) of in vitro selected NaCl-tolerant plants and parentcultivar Prakash of Brassica juncea L. Salt stress caused differentialenhancement in proline level in both seedlings and leaf tissueof plants at different developmental stages. The magnitude ofincrease in proline content was higher in SR3P6-2 line in seedlings(34 fold at 140 meq^-1 NaCl) as well as leaves (16 fold at 40d after sowing at 100 meq^-1 NaCl) compared to the parent cv.Prakash (29 fold in seedlings and five fold in leaves) and SR2P1-2(21 fold in seedlings and five fold in leaves) at similar stresslevels. Salt stress also resulted in changes in the activitiesof enzymes of proline metabolism. The activities of prolinebiosynthetic enzymes, pyrroline-5-carboxylate reductase andornithine aminotransferase, increased under salt stress bothin the seedlings and leaves. The range of increase in the activitiesof the two enzymes was relatively higher in SR3P6-2 (3·3-3·9fold) compared to the SR2P1-2 (1·8-2·8 fold) andparent cv. Prakash (1·5-2·8 fold). The activityof proline degrading enzyme, proline oxidase, decreased undersalt stress in both the tissues of all the lines; the reductionin activity was relatively greater in SR3P6-2 compared to SR2P1-2or cv. Prakash. The trend of changes in the enzyme activitieswas in tune with the increase in proline level, the magnitudeof change did not match the extent of increase in proline level.Copyright1995, 1999 Academic Press Brassica juncea L., NaCl-tolerant somaclones, proline content, ornithine aminotransferase, proline oxidase, pyrroline 5-carboxylate reductase     

The Influence of Plant Water Deficit on Distribution of 14C-labelled Assimilates in Cacao Seedlings

The relationship between plant water status and distributionof ¹⁴C-labelled assimilates in cacao (Theobroma cacao L.) wasevaluated after ¹⁴CO₂ pulse labelling leaves of seedlings subjectedto varying levels of water deficiency. The proportion of ¹⁴Cexported by source leaves was strongly affected by seedlingwater status. An increasing proportion of labelled assimilatesremained in source leaves at both 24-h and 72-h harvests aswater stress intensity increased. Water stress reduced the distributionof exported label to leaves and to the expanding flush in particularbut increased the proportion of label in stems and roots. Theresults suggest that current photoassimilates may be temporarilystored in source leaves and stems of cacao seedlings duringperiods of plant water deficit. The stress-induced changes inpartitioning of labelled carbon were in concordance with changesin shoot to root biomass ratios, which was likely due to greaterreduction in growth of above-ground organs to that of roots. Theobroma cacao L, assimilate partitioning, cacao, ¹⁴C-photoassimilate, water stress, water potential     

Influence of Soil and Air Temperature on I. Nucleotide Metabolism and Growth of Phaseolus vulgaris L. seedlings

Eight day old greenhouse grown Phaseolus vulgaris L. seedlingswere exposed to three different temperature regimes. The concentrationof the total free nucleotides, nucleoside triphosphates, RNAand protein was much more pronounced in seedlings exposed tothe interactive day/night temperature of 28 ?C (soil) and 15?C (air) of regime I. Seedlings treated to a low soil/air, day/nighttemperature of 15 ?C (regime II) had the lowest content of totalfree nucleotides, nucleoside triphosphates, RNA and protein.The nucleoside triphosphate content and energy charge valueof seedlings treated to a high soil/air, day/night temperatureof 28 ?C (regime III) declined much earlier than in the seedlingsexposed to temperature regimes I and II. The fresh and dry weightof seedlings exposed to temperature regime I was significantlyhigher than those seedlings exposed to the other two temperatureregimes. The slowest growth was observed in seedlings exposedto temperature regime II. The noticeably higher concentrationof ATP, pyridine nucleotides and root nodulation in seedlingsexposed to temperature regime I suggests that higher soil andlow air temperature enhances nitrogen metabolism in P. vulgarisseedlings.     

The Relationship of Abscisic Acid to Nitrate Reductase Activity in the Potato Plant

Abscisic acid (ABA) at 3.8 µM suppressed both in vivoand in vitro nitrate reductase activity in roots, stems andleaves of potato plants grown in solution culture. Suppressionwas maximal between 24 and 48 h, followed by recovery of activityat 72 h in roots and leaves and at 96 h in stems. Removal from ABA after 24 h resulted in complete recovery ofnitrate reductase activity in roots by 24 h and partial recoveryin leaves. ABA treatment enhanced nitrate accumulation in roots,decreased that of leaves, but had no effect on stem nitratecontent. ABA enhanced decay of the enzyme following nitrate removal;by 7 h activity in roots was 22.5% of the initial value comparedto 55% in the control. ABA showed a less drastic effect on lossof activity in leaves and stems. These results indicate thatABA suppression of nitrate reductase activity is not dependenton nitrate uptake, and although it reduced leaf nitrate contentthere was no clear relationship between tissue nitrate levelsand the ABA response. (Received September 13, 1984; Accepted July 1, 1985)     

Activities of Transaminases, Amylases and Proteases during Endosperm Degradation in Normal and Opaque-2 Zea mays L. cv. Maya

Transaminase, amylase and protease activities were comparedin seedlings of normal and Opaque-2 (o2) maize. Transaminaseactivity, greater in normal maize, was highest in the scutellumfrom which it decreased rapidly in activity from day 2 afterimbibition; only low activity was observed in endosperm andaxis tissue. Amylolytic activity, optimal around pH 5, was greater in normalmaize at all stages of endosperm degradation. Activity whichwas low on day 2, rose to a peak on day 6 and declined afterwards.The level of free sugars in the endosperm of normal was higherthan in o2 maize, and in both varieties was highly correlatedwith amylolysis. Protease activity, optimal at pH 3.6, was also greater in normalendosperms and increased up to day 6 and activity was maintainedat this level until around day 14. Although the activity ofall three enzyme systems examined was greater in normal maizethere were no apparent differences in the overall growth ofnormal and o2 seedlings during this period. Zea mays L, maize, corn, endosperm, enzyme activity, transaminase, amylase, protease     

Origin of Foliar Nitrogen and Changes in Free Amino-Acid Composition and Content of Leaves, Stubble, and Roots of Perennial Ryegrass During Re-growth after Defoliation

Nitrogen re-mobilization and changes in free amino acids werestudied as a function of time in leaves, stubble, and rootsduring ryegrass (Lolium perenne L.) re-growth. Experiments with¹⁵N labelling clearly showed that during the first days nearlyall the nitrogen in new leaves came from organic nitrogen re-mobilizedfrom roots and stubble. On the days of defoliation, stubblehad the highest content of free amino acids with 23 mg per gdry weight against 15 mg and 14 mg in leaves and roots, respectively.The major amino acids in leaves were asparagine (23% of totalcontent in free amino acids), aminobutyrate, serine, glutamine,and glutamate (between 7% and 15%) whereas in roots and stubblethe contribution of amides was high, especially asparagine (about50%). Re-growth after cutting was associated with a rapid increaseof the free amino acid content in leaves, with a progressivedecrease in roots while stubble content remained virtually unchanged.In leaves, asparagine increased from the first day of re-growth,while the aspartate level remained unchanged and glutamine increasedstrongly on the first day but decreased steadily during thenext few days of re-growth. Asparagine in stubble and rootschanged in opposite directions: in stubble it tended to increasewhereas in roots it clearly decreased. In contrast, stubbleand roots showed a similar decrease in glutamine. In these twoplant parts, as in leaves, aspartate remained at a low level.Results concerning free amino acids are discussed with referenceto nitrogen re-mobilization from source organs (stubble androots) to the sink organ (regrowing leaves). Key words: Lolium perenne L, re-growth, nitrogen, free amino acids, glutamine, asparagine     

Transpiration Stream of Desert Species: Resistances and Capacitances for a C3, a C4, and a CAM Plant

Transpiration rates and water potentials of three sympatricdesert perennials, a C3 subshrub (Encelia farinosa), a C₄ bunchgrass(Hilaria rigida), and a CAM succulent (Agave deserti), wereanalysed using an electrical circuit analogue that includedresistances and capacitances for the leaves, stems, and roots.The water storage capability of the organs differed considerably,capacitance ranging over 1000-fold from the thin leaves of H,rigida to the massive leaves of A. deserti, although the capacitanceper unit volume varied only 1.9-fold. The diurnal changes inwater storage could support maximum transpiration rates of H.rigida for 4 min, E. farinosa for 7 min, and A. deserti for16 h. The time constant for equilibration of water from storageto the xylem ranged from 29 s for roots of H. rigida to 52 minfor leaves of A. deserti. Resistances for such movement wererelatively low for the succulent leaves of A. deserti and wereup to about 50-fold higher for the three organs of E. farinosa.Xylem resistances calculated using the Hagen-Poiseuille lawand measured xylem dimensions were 2.1- to 2.1-fold lower thanresistances estimated from observed water potential drops, adiscrepancy which is in agreement with other published data.Contrary to data on other plants, the xylem resistances in theroots and leaves of E. farinosa and H. rigida averaged only15% of the stem xylem resistance. Key words: Capacitance, Xylem resistance, Transpiration stream, Desert     

Fatty acid composition of microsomal phospholipids and H+-ATPase activity in the roots of Scots pine seedlings grown at different root temperatures during flushing

The fatty acid composition of phospholipids in the microsomesand the vanadate-sensitive H⁺-ATPase activity of the roots ofone-year-old Scots pine (Pinus sylvestris L.) seedlings werestudied during flushing in spring. The seedlings in hydroponiccultures were subjected to different root temperatures (5, 12or 20°C). The shoot was maintained at 20/15° C (day/night)during the 35 d experiment. After 35 d at 5° C, root growthwas totally inhibited and shoot growth partly inhibited. In roots grown at 5° C the fatty acid composition of themicrosomal phospholipids and the degree of fatty acid unsaturation(bond index) were unchanged, while in roots grown at 12 and20° C the fatty acid composition changed and bond indexdecreased. At those root temperatures, the most obvious changewas a decline in the proportion of linolenic acid (C18:3). Inthe new white roots grown either at 12°C or 20°C theproportion of C18:2 was higher and the proportion of C18:3 lowerthan in 1-year-old roots. Independently of root temperature,H⁺-ATPase activity, determined on a fresh weight basis, declinedto half of the original activity during the experiment. Thedecline in H⁺ -ATPase activity was most rapid during the firstweek. In the old roots the decline in H⁺-ATPase activity followedclosely the decline in amount of membrane protein. In new rootsH⁺-ATPase activity was high and increased with increasing roottemperature. These results suggest that in the roots of Scotspine seedlings, vanadate-sensitive H⁺-ATPase activity is dependenton age, while changes in the microsomal fatty acid compositionof phospholipids are regulated mainly by root temperature. Key words: Fatty acids of phospholipids, microsomes, H⁺-ATPase, root temperature, Scots pine     

Nitrate Assimilation in Higher Plants with Special Reference to the Cocklebur (Xanthium pennsylvanicum Wallr.)

A soluble NADH-dependent nitrate reductase is described forthe shoot system of Xanthium. Young leaves and immature stemtissues contain high levels of the enzyme. They are relativelyrich in free amino acids and amides but store little free nitrate.The specific activity of the enzyme is lower in fully expandedleaves, although these leaves exhibit higher rates of fixationof carbon in photosynthesis than do younger leaves. Neithernitrate nor free amino acids accumulate in the mesophyll ofthe leaf. Older parts of the stem axis accumulate large amountsof soluble nitrogen, almost entirely as free nitrate. Reservesof nitrate in the shoot and root are rapidly depleted if nitrateis removed from the external medium. Nitrate reductase is apparently absent from roots of Xanthium.This finding is supported by analyses of bleeding sap from nitrate-fedplants which show that 95 per cent of the nitrogen exportedfrom roots is present as free nitrate. However, roots are capableof synthesizing and exporting large amounts of amino nitrogenif supplied with reduced nitrogen such as urea or ammonium. A scheme is presented summarizing the main features of the metabolismof nitrate in Xanthium and this is compared with the situationin nitrate-fed plants of the field pea (Pisum arvense L.), aspecies previously shown to be capable of reducing nitrate inits root system.