Responses of nitrate assimilation and N translocation in tomato (Lycopersicon esculentum Mill) to reduced ambient air humidity

The impact of low humidity in ambient air on water relations,nitrate uptake, and translocation of recently absorbed nitrogen,was investigated in 5-week-old tomato (Lycopersicon esculentumMill cv. Ailsa Craig) plants grown hydroponically in a completenutrient solution. Plants were subjected to dry air (relativehumidity 2–4% for 6 h. The transpiration rate increasedseveral-fold and the shoot water content decreased by almost20%, whereas root water content was unaffected. No effect onin vitro nitrate reductase (NR) activity was detected when usingan EDTA-contraining assay buffer. Replacement of EDTA with Mg²⁺revealed a significant decline in shoot NR activity, which suggestsphosphorylation of the enzyme during the stress treatment. Plantswere grown in a split-root system, in which one root half wasfed ¹⁵N-nitrate during the treatment, in order to determinenitrate uptake and translocation of recently absorbed nitrogenin the plants. Uptake of nitrate was substantially inhibited,but the proportion of absorbed ¹⁵N that was translocated tothe shoots was only slightly affected. In untreated plants,71% of the ¹⁵N recovered in roots had been retranslocated fromthe shoots, whereas in plants subjected to stress the deliveryof ¹⁵N from shoots to roots appeared to be completely inhibited.The data show that lowered humidity in air has significant effectson both uptake of nitrate as well as translocation of nitrogenwithin the plants. Some of these effects appear to be commonwith those observed in plants subjected to reduced water potentialsin the root environment and point to the possibility of theshoot water relations being highly influential on nitrogen uptakeand translocation. Key words: Air humidity, nitrate assimilation, nitrate reductase activity, nitrogen translocation, tomato, water stress     

The Effect of Calcium Starvation on Assimilate Partitioning and Mineral Distribution of the Phloem

Populus plants were grown in a medium lacking calcium and exposedto ¹⁴CO₂. In contrast to plants in the complete nutrient medium,the percentage amount of ¹⁴C-assimilates increased in the leavesof calcium-deficient plants and decreased in the stem and theroots. When plants were grown without potassium or magnesiumno differences in the amount of ¹⁴C-label occurred in comparisonwith plants in the complete nutrient medium. Translocation wasrecorded by microautoradiography. It was observed that considerableamounts of labelled photoassimilates were unloaded from thephloem in the middle part of the stem in plants of the completenutrient medium. In contrast, during calcium starvation ¹⁴C-labelwas restricted to the phloem of the stem. In addition, the concentrationsof magnesium and phosphorus showed a remarkable increase instem sieve tubes of calcium-deficient plants. When sieve tubesof source leaves from Populus, barley and maize were comparedwith those of sink leaves, the latter showed higher calciumconcentrations. The results suggest that calcium is a necessaryfactor in the regulation of phloem translocation. Key words: Calcium deficiency, phloem translocation, sieve element loading and unloading, X-ray microanalysis     

Water Potential, Translocation and Assimilate Partitioning

Lang, A. and Thorpe, M. R. 1986. Water potential, translocationand assimilate partitioning.—J. exp. Bot. 37: 495–503. The effect of water status upon translocation and assimilatepartitioning is examined both from theory and in an experimentwith young Phaseolus plants. Theory predicts that translocationis unlikely to be directly affected by water status. However,water potential differences within plants should influence translocationflow, with regions at lower potentials attracting disproportionatelylarge shares of assimilate. This prediction is supported in the experiment with Phaseolusin which the pattern of partitioning in the root changed rapidlyin response to bathing portions of it in solutions of differentosmolarity. The relevance of these findings to the growth of plants undernatural conditions is considered and evidence is presented thatwater potential gradients may be an Important factor in thecontrol of partitioning Key words: Phloem translocation, xylem transport, partitioning, water potential, control, osmotic potential     

Effects of Plant Growth Regulators on Grain-filling and Yield of Rice

Effects of three phytohormones (IAA₁, GA₃ and kinetin) on grain-fillingand the pattern of ³²P translocation from individual leavesto grains were studied at intervals of 7 days during the progressof reproductive development of rice (Oryza saliva L. cv. Jaya).The plants were sprayed with 100 µg ml^–1 aqueoussolutions of the hormones at 100 days, when the plants wereentering the reproductive stage. Kinetin produced a pronouncedeffect on grain-filling as well as on ³²P mobilization fromindividual leaf to grains and increased yield, possibly by increasingleaf longevity. GA₃ and IAA also increased the grain-fillingand ³²P mobilization significantly over control but the effectswere less marked than those of kinetin. Oryza sativa L., rice, grain yield, translocation, growth regulators, gibberellic acid, indol-3-yl acetic acid, kinetin     

Effects of Low Oxygen on Photosynthesis, Translocation and Growth in Green Pepper (Capsicum annuum)

Green pepper (Capsicum annuum cv. Bell Boy) plants were exposedin chambers to low (2%) oxygen and controlled carbon dioxideconcentrations. Vegetative and fruiting plants showed short-termincreases in net photosynthesis in low oxygen or elevated carbondioxide (up to 900 µl CO₂ l^–1). Photosynthesis ofyoung vegetative plants increased in low oxygen in the short-termbut there was no long-term benefit. Low oxygen enhancement ofphotosynthesis declined with time and after 10 d, leaf areaand root dry weight were less than in plants grown in normalair. Labelled assimilates were translocated from leaves to otherregions at similar rates in low oxygen and normal air. Low oxygenreduced respiratory losses from leaves and reduced the proportionof soluble carbohydrate converted to polysaccharide in all plantparts. Thus, low-oxygen environments decrease the utilisationof assimilates which then may lead to inhibition of photosynthesis. Capsicum annuum, photosynthesis, photorespiration, translocation, utilization of assimilates     

Sulphate Transport into Plants and Excised Roots of Soybean (Glycine max L.)

The rates of sulphate transport into intact and excised rootsof soybean (Glycine max L.) were not significantly differentin the first hour and were maximal at pH 7. However, intactroots accumulated four times as much sulphate as excised rootsin 24 h, because of a marked reduction in the rate of transportby excised roots. The continued high rates of transport intointact roots were observed in plants kept in the light, andobserved in darkened plants growing in 1 per cent sucrose. Similarly,sulphate accumulation by excised roots was stimulated 2-foldby 1 per cent sucrose. The characteristics of sulphate accumulation by roots were notuseful in predicting sulphate translocation to the leaves. Transportto the leaves was maximal at pH 2–3, was almost totallylight-dependent and was not enhanced by growing plants in sucrose. Sulphate transport, Glycine max L., soybean, excised roots     

Mechanism of Anucleate Cell Production in the oriC-Deleted Mutants of Bacillus subtilis

We constructed oriC-deleted mutants of Bacillus subtilis byintegrating the minimal replication region of plasmid pLS32into the proA (115°), spoIIIJ (360°) and thrS (256°)loci of the chromosome, respectively. All three mutants producedanucleate cells and the DNA/protein ratio was lower than thatof the wild-type strain when grown in nutrient broth. However,when grown in minimal-glucose medium, the frequency of anucleatecells was reduced in all of them and the DNA/protein ratio wasrestored to normal. Especially, the oriC-deleted mutant in whichthe plasmid was integrated near oriC produced almost no anucleatecell. These results indicate that initiation frequency of chromosomereplication from the integrated plasmid origin were reduceddisproportionately to cell mass increase in rich medium, whichin turn disrupted coordination between DNA replication cycleand cell division cycle. The locations of the plasmid originrelative to the natural oriC locus affected the production ofanucleate cell remarkably, suggesting that partition mechanismof chromosome was also impaired by the translocation of itsreplication origin.     

Translocation of Photoassimilates Between Sister Ramets in Two Rhizomatous Forest Herbs

Autoradiography and liquid scintillation techniques were usedto trace the pattern of photoassimilate translocation in twoperennial forest herbs, Aster acuminatus Michx. and Clintoniaborealis (Ait.) Raf. Vegetative shoots of C. borealis emergeearly each spring from the growing apices of a long-lived rhizomesystem. Vegetative shoots of A. acuminatus emerge in late springfrom rhizomes that decay within 2 years. In both species rametssurvive for only one growing season. Any connected plants aresisters. Mature leaves of these two species were exposed for1 h periods to ¹⁴CO₂ during spring and summer. Radioactivitycould subsequently be detected in exposed leaves (16–84per cent, depending on the season), adjacent above ground plantparts (0.7–23 per cent), roots and rhizomes (4.9–84per cent) and, when present, flowers (4–8.5 per cent).Old rhizomes of C. borealis are prominent storage sites forphotosynthate. In A. acuminatus, no significant translocationbetween sister ramets (i.e. above ground shoots connected bya common rhizome) was observed. In C. borealis, there was small,but consistent translocation between sister ramets (0.2–4per cent). Disturbance of unexposed sister ramets by defoliation,shading or herbivory increased the flow of photoassimilatesto disturbed parts in C. borealis, but not in A. acuminatus.Based on the absence of translocation flow, ramets of A. acuminatusmay be regarded as physiologically independent. Connected rametsof C. borealis show physiological integration. These resultsare correlated with ecological differences between the two species. Aster acuminatus, Clintonia borealis, translocation, ramet, vegetative reproduction, forest herb     

Variation in Photorespiration in Lolium

The rate of photorespiration in several grass species was shownto be highly variable and dependent on the species, genotype,and conditions under which the plants were grown. Photorespiration,measured as oxygen uptake, was negligible in Cenchrus ciliarisand Paspalum dilatatum but significant in Lolium spp. and Festucaarundinacea. There were significant differences in the rateof photorespiration among plants within a Lolium populationof diverse origin and these differences were independent ofthe conditions under which the plants were grown. Among thetemperate grasses there was a significant correlation betweenphotorespiration and the CO₂-compensation concentration andboth parameters were very low in P. dilatatum. Plants grownin day/night temperatures of 15/10 °C compared with 25/20°C had faster rates of dark respiration but slower ratesof light respiration when measured at the same temperature.Photorespiration was faster than dark respiration although differencesin respiration among plants in the light were not shown in thedark.     

The Growth and Physiology of Pinus strobus L. Seedlings as Affected by Various Nutritional Levels of Nitrogen and Phosphorus

Potted white pine (Pinus strobus L.) seedlings were grown ingravel either in outdoor cold frames or in growth chambers.They were watered every second day with a salt solution containingdifferent amounts of nitrogen and phosphorus. After 13 weeksof growth individual seedlings were illuminated separately for8 h in the presence of ¹⁴CO₂ and the rates of their apparentphotosynthesis, respiration, and translocation of recent ¹⁴C-photosynthateto their roots were observed. Roots were extracted with 80 percent ethanol and the nature of various ¹⁴C compounds in theextract was determined by paper chromatography. The best over-all growth of plants, mycorrhizal development,apparent photosynthesis, and translocation of recent photosynthateto the roots were observed in plants grown at the intermediatelevels of N and P nutrition. Sucrose was always the dominant form in which recently translocated¹⁴C occurred in the roots, although with increased nitrogensupply there was increased hydrolysis of sucrose to hexosesand appearance of ¹⁴C in the amino- and organic acids.     

The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

The effects of NO^-₃ and NH⁺₄ nutrition on hydroponically grownwheat (Triticum aestivum L.) and maize (Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH⁺₄ than with NO^-₃ nutrition.The shoot:root ratios of wheat plants were increased with NH⁺₄compared to NO^-₃ nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO^-₃ and NH⁺₄-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH⁺₄-fedwheat plants were reduced to 85% of those 12 mM NO^-₃-fed wheatplants. In maize supplied with 4 and 12 mM NH⁺₄ the photosyntheticrates were 87 and 82% respectively of those of NO^-₃-fed plants.Reduced photosynthetic rates of NH⁺₄ compared to NO^-₃-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH⁺₄ compared to NO^-₃ nutrition.Differences in the partitioning of biomass between the shootsand roots of NO^-₃-and NH⁺₄-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH⁺₄- thanin NO^-₃-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH⁺₄-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem     

Uptake and Assimilation of Nitrate by Corn Roots During and After Induction of the Nitrate Uptake System

Dark-grown, decapitated corn (Zea mays L.) seedlings that hadbeen grown without nitrogen were used to characterize relationshipsamong uptake, translocation and in vivo reduction of [¹⁵N] nitrateduring induction of the nitrate uptake process and throughoutthe subsequent steady-state period. During induction, cumulativenitrate reduction increased from less than 20%of cumulativenitrate uptake to about 30%Concurrently, translocation of nitrateincreased from less than 30%to over 50%of that absorbed. Duringthe following steady-state period, partitioning of incomingnitrate between reduction and translocation remained relativelyconstant. Initially, removal of the endosperm had little effecton nitrate uptake, but by 6 h cumulative uptake had been depressed30%relative to control plants. In contrast, endosperm removallimited nitrate reduction within 1 h, and as a consequence nitratereduction during the 6 h exposure period was 60% less in endosperm-freetissues. Collectively these observations indicate that nitrateuptake and reduction are independent processes, since they developat dissimilar rates upon initial exposure to nitrate, and sincethey differ markedly in response to endosperm removal. However,the constancy of nitrate reduction during steady-state uptake(30% of incoming nitrate), does reflect an association betweenthe two processes. Key words: uptake, reduction, -N translocation, Induction, Post-induction     

14C-Translocation in Kalanchoe pinnata at two Different Stages of Development

Mayoral, M. L. and Medina, E. 1985. ¹⁴C-translocation in Kalanchoepinnata at two different stages of development.—J. exp.Bot. 36: 1405–1413 Translocation of ¹⁴C-compounds from mature leaves was measuredin plants of Kalanchoe pinnata to determine the interactionbetween plant age and CAM phase when CO² is taken up. Matureleaves of 4 and 12 month old plants were fed with ¹⁴CO² eitherduring CAM phase 1 (midnight) or at the beginning of CAM phase4 (early afternoon). Export of ¹⁴C activity from source leaves,and distribution of ¹⁴C activity in soluble and insoluble compoundswas measured both in source leaves and sink organs. In 4 monthold plants 4 d were needed to export 76% of total ¹⁴C activityincorporated during CAM phase 1, while leaves labelled at thebeginning of CAM phase 4 exported 44% of total ¹⁴C activityafter 4 h, and 80% after 24 h. In both cases the major fractionof total radioactivity translocated was found in the roots inthe form of neutral sugars. Differences in translocation patternsare due to distribution of ¹⁴C in the source leaves, 96 % of¹⁴C taken up during CAM phase 1 is found in the insoluble fractionat the end of the subsequent phase 3, while 93 % of total radioactivitytaken up at the beginning of phase 4 is found in the solublefraction at the end of this phase. In 12 month old plants labelledduring phase 1 very little translocation could be detected atthe end of phase 3, while only 20% of total radioactivity wastranslocated from leaves labelled during phase 4 and measured4 h later. ¹⁴C activity in the older leaves had a similar distributionin soluble and insoluble fractions as the one determined inthe younger plants. Ability to translocate carbon compoundsfrom source leaves during phase 3 was shown by loading matureleaves at dawn with ¹⁴C-sucrose. Here again, mature leaves ofyounger plants showed faster translocation of radioactivitythan those of older plants Key words: Kalanchoe, crassulacean acid metabolism, translocation, sink, source relationships     

Effects of Root Pruning on Translocation of Photosynthates in Phaseolus vulgaris L

Root pruning increased the level of ethanol soluble sugars inred kidney bean plants (Phaseolus vulgaris L. ) grown in aeratednutrient solution. However, the concentration gradient of thesesugars down the stem and its translocation velocity remainedunchanged. Removal of 50% of the roots had no effect on thetotal photosynthates exported from source leaves but the finaldistribution pattern of photosynthates was altered; less movingtoward the upper plant parts, and accumulation occurring inthe lower stems. Translocation velocity of photosynthates towardthe upper plant parts was drastically reduced by root pruning. Key words: Phaseolus vulgaris, Photosynthate translocation, Root pruning     

The Translocation of Lead and Copper in Two Submerged Aquatic Angiosperm Species

The translocation of lead and copper was studied in two speciesof submerged aquatic angiosperm, Potamogeton crispus L. andPotamogeton pectinatus L. A perspex container incorporatinga potters' clay seal around the stems of intact plants was designedfor the chemical separation of the shoot and root environmentsduring 11–21 d treatment periods. Metal solutions wereadded to the root or shoot environments and concentrations weremonitored in waters and sediments. A technique was developedfor the direct quantitative analysis of metals in small (0.02–0.2mg) segments of water plant tissue, using the graphite rod attachmentto an atomic absorption spectrophotometer. Experimental resultsindicated minimal translocation of lead, but extensive acropetaltranslocation of copper to particular sites of accumulation.     

Influence of Shade on the Growth and Sink Activity of Young Flower Heads and Peduncles of White Clover (Trifolium repens L.)

The influence of shade on the growth and sink activity of youngflower heads and peduncles of white clover (Trifolium repensL.) plants was measured in controlled environments. Measurementof the peduncle elongation rate using a linear voltage displacementtransducer showed that when the inflorescence alone was shaded,peduncle elongation was higher than in the light. Translocationstudies using ¹¹C-labelling techniques showed that shading theinflorescence alone had little effect on translocation of assimilatesinto the inflorescence but induced a major change in partitioningof assimilates within it. Peduncle elongation induced by shadeaccompanied an increase in partitioning of photoassimilatesto the peduncle, at the expense of the flower head. Key words: White clover, partitioning, translocation     

Pinitol occurrence in soybean plants as affected by temperature and plant growth regulators

Unsuitable temperatures are frequently encountered by soybean(Glycine max L. Merr.) plants grown in the field. Certain polyolshave been reported to protect plants from high temperature orfrost damage. Controlled environment studies were conductedto investigate the effect of stressful temperature regimes onthe content of pinitol (3-O-methyl-D-chiro-inositol) in soybeanplants. Hydroponically-grown soybean plants were subjected tohigh (35/30 C) or low (15/10 C) day/night temperature stresses,and pinitol content in different plant parts was determinedusing high performance liquid chromatography (HPLC). A syntheticplant growth regulator, PGR-IV, was foliarly applied to theplants to evaluate its effect on pinitol content in differentplant components. Uniformly-labelled ¹⁴C-glucose was fed intothe leaves via the transpiration stream, and the effects ofhigh temperature and EXP-S1089, another synthetic plant growthregulator, on the incorporation of ¹⁴C-glucose into pinitolwas evaluated using HPLC separation and scintillation spectrometry.High-temperature stress significantly increased plant pinitolcontent and the incorporation of ¹⁴C-glucose into pinitol, butdecreased the content of sucrose, glucose and fructose. Underlow-temperature stress, there was hardly any change in pinitolcontent, but a drastic increase in soluble sugars. PGR-IV enhancedpinitol translocation from leaves to stems and roots, whileEXP-S1089 increased pinitol/sucrose ratio. Accumulation of pinitolmay be an adjustment mechanism of the plant to reduce high-temperaturedamage, but not low-temperature injuries. Key words: Pinitol, soybean, temperature, plant growth regulator     

Abscisic Acid Translocation and Influence of Water Stress on Grain Abscisic Acid Content

The movement of foliar applied [1-¹⁴C]abscisic acid (ABA) inwheat plants (Triticum aestivum L., cv. Kolibri) was investigatedat two stages of grain development (1000 grains, weight 19 and24 g dry matter). [1–¹⁴C]ABA seemed to be readily translocated within 12h into the developing grains as well as in other plant parts.A subsequent rapid metabolism took place leading to a decreasedactivity of the ABA-containing chromatogram fraction in theyounger plants 48 h after application. The metabolism seemodto be less intensive in the older grains, where the activityrunning with the ABA increased over 64 h. Treating the leaves of barley plants (Hordeum vulgare, L., cv.Union) 2 weeks after anthesis with a gentle stream of warm air(36° C) resulted in a significant increase in the ABA contentof all parts of the ear. The results mentioned above indicatethat this may be partially due to translocation from other partsof the plant such as the leaves.     

Respiration and Phloem Translocation in the Roots of Chickpea (Cicer arietinum)

Root growth in chickpea (Cicer arietinum) has been studied fromthe early vegetative phase to the reproductive stage in orderto elucidate its growth and maintenance respiration and to quantifythe translocation of assimilates from shoot to root. A carbonbalance has been drawn for this purpose using the growth andrespiration data. The increase in the sieve tube cross-sectionalarea was also followed simultaneously. Plants growing in a nutrient culture medium were studied todetermine the relative growth rate (RGR) 5–60 d aftergermination. RGR declined from 113 to 41 mg d^–1 g^–1during the measurement period. Simultaneous with the RGR analysis,respiration rate was also measured using an oxygen electrode.The respiration rate declined as the plants aged and a drasticreduction was recorded following anthesis. The relationshipbetween RGR and respiration rate was used to extrapolate themaintenance respiration (m) and growth respiration (1/Y_EG).The respiration quotient (r.q.) of the roots was 1.2 and theQ₁₀ in the range 20–25 °C was 2·2. A carbon balance for the roots was constructed by subtractingthe carbon lost during respiration from that gained during growth.The roots were found to respire no less than 80% of the carbontranslocated. The increase in the cross-sectional area composed of sieve tubeswas measured near the root-shoot junction as the plants grew.Chickpea has storied sieve plates which simplifies these measurements.Their cross-sectional area increased during growth mainly becauseof an increase in sieve tube number. The diameter of individualsieve tubes remained constant. Specific mass transfer (SMT) values for seive tubes into theroots have been computed during various stages of growth. SMTvalues were relatively constant before anthesis (approx. 6·5g h^–1 cm^–2), but decreased following anthesis. Wedid not evaluate possible retranslocation from roots: any suchretranslocation would have the effect of increasing our SMTvalues. Chickpea, Cicer arietinum, legume, root, respiration, phloem, translocation, carbon balance, specific mass transfer, sieve-tube dimensions     

In Vitro Induction of Haploid, Diploid, and Triploid Androgenic Embryoids and Plantlets in Datura metal L.

Pollen plantlets of Datura metel L. have been successfully rearedin vitro through anther culture on a nutrient medium supplementedwith coconut milk (15 per cent v/v) The early segmentation patternof the proembryos and their subsequent differentiation intoheart, torpedo, and cotyledonary stages were traced. More than100 plantlets were grown to maturity on soil. They grew normallyand produced flowers. Root-tip and leaf-squash preparationsshowed variable numbers of chromosomes in their cells, and thisindicated the occurrence of ploidy plants among the population.Frequency determinations showed the predominant types to bediploid (70 per cent), triploid (24 per cent), and haploid (6per cent). Differences in the morphology of mature plants inregard to floral size, meiotic irregularities in PMCs, formationof giant pollen grains, differential fruitset, somatic mosaicismin respect of chromosome number, and aneuploidy of cells, wererecorded. The origin of diploid and triploid plants is discussed.