Carbon and nitrogen partitioning in the biennial monocarp Arctium tomentosum Mill

Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data.Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.     

Turnover of Carbohydrates in Relation to Growth in Apple Trees. II. Distribution of 14C Assimilates Labelled in Autumn, Spring and Summer

One-year-old plants of the apple rootstocks MM. 106 and M.7were allowed to assimilate ¹⁴CO₂ in autumn, spring and summerand the distribution of the tracer within the plant over a growingseason was followed. In MM.106 distribution of the tracer intwo fractions of extractable carbohydrate and the residues representingstructural material, was determined. The results of the radioactivityassay are discussed in relation to seasonal patterns of assimilatesupply and demand in the different regions of the plant. Malus sylvestris L, apple, ¹⁴C assimilates, distribution of carbohydrates     

The Uptake of 14CO2 by Developing First Leaves of Barley and Partition of the Labelled Assimilates

The uptake of ¹⁴CO₂ by developing barley leaves of three ageswas followed using short presentation periods at the beginningor the end of the photoperiod. Partition of labelled carboninto ethanol-soluble and insoluble compounds, and movement oflabel within the plant were also examined. Young expanding leaves (day 6) retained most of the assimilatedcarbon and within 24 h 75–80 per cent of this was in ethanol-insolublecompounds. Leaves that were fully expanded took up rather more¹⁴CO₂ but exported a substantial amount of this to roots, leafbases including the stem apex, and to the developing secondleaf. Export occurred over periods up to 24 h, and by that time8- and 10-day-old leaves retained only 35 per cent and 15 percent respectively of the total label taken up. The label retainedin these leaves was predominantly in ethanol-soluble forms,whereas 75 per cent or more of the labelled carbon which wasexported from the leaves was found in ethanol-insoluble compounds.     

14C Photoassimilate Partitioning in Developing Sunflower Seeds

Changes with age of protein and oil content in field-grown Helianthusannuus seeds were followed during the grain filling period.Seeds were sampled from different zones on the flower head:peripheral, intermediate, and central. Regardless of seed position,at maturity protein and oil content accounted for approximately18% and 50% of the dry weight respectively. In an attempt todetermine the importance of the role of photosynthesis in grain-filling,¹⁴CO₂ was incorporated into sunflower leaves and translocatedradioactive photoassimilates in the seed were studied. ¹⁴C-labelledproducts including carbohydrates, nitrogenous compounds andlipids were determined as a function of seed position, lengthof chase period, and seed age. Within 8 h, ¹⁴C-labelled photosynthateis detected in the seed, up to 80% of seed-incorporated radioactivitybeing in the form of free sugars and organic acids. The conversionrate from free sugars to storage compounds (lipids, proteinsand starch) varies according to seed position and age. Lipidsconstitute the major photosynthetic sink, reaching levels ofgreater than 80% of the total seed-incorporated radioactivity.The effects of abscisic acid on uptake and partitioning of ¹⁴Csucrose into immature excised cotyledons were also studied. Key words: Sunflower, photosynthate, abscisic acid     

Respiration of 14C-labelled Assimilates in Stems of Willow

Willow cuttings were allowed to assimilate ¹⁴CO₂, and the changein the specific activity of phloem sap, collected as aphid honeydew,was compared with the change in the specific activity of the¹⁴CO₂ given off from the respiration of the labelled translocates.With young shoots (3–5 weeks old), the acceleration inthe specific activities of honeydew and respiratory CO₂ werevery similar. With 2–4-year-old mature stems, however,there was a considerable difference between the accelerationof the two specific activities, that of the honeydew alwaysbeing greater than respiratory CO₂. Studies have also been made on the rate of breakdown of ¹⁴C-labelledtranslocates in isolated and intact young shoots and maturestems. No differences between the isolated and intact stemswere apparent. The results are discussed in relation to possible translocationmechanisms, and the results of other workers in this field ofexperimentation.     

伊犁地区野生毛牛蒡与牛蒡的成分分析比较研究

对伊犁地区野生牛蒡属两种植物,即牛蒡和毛牛蒡根的主要营养及保健成分和主要矿质元素进行了分析,发现毛牛蒡和牛蒡的主要成分没有显著差异（P〈0．05）,说明毛牛蒡也是一种药食两用的野生资源。     

Tangential Movement of 14C-labelled Assimilates in Stems of Willow

It was shown that, when ¹⁴CO₂, was fed to a single leafy shootof a rooted willow cutting, activity appeared within 12 hrs.in honeydew collected from a colony of the aphid Tuberolachnussalignus (Gmelin), feeding on the opposite side of the stem20 cm. below the base of the leafy shoot. This was shown tobe due to a tangential movement of labelled materials throughthe bark. This tangential movement was found only in cuttings with limitedroot growth. Where an active root sink was present, extensivetangential movement was absent. Using two aphid colonies on either side of the stem, determinationsof the speed of tangential movement have been made. The highestvalue obtained was 10.6 mm./hr.     

The Partitioning of Photosynthetically Assimilated 14C into Amino Acids in Wheat 1. Partitioning During Transport to the Grain

When ¹⁴CO₂ was fed to flag leaf laminae at 20 d post-anthesis,the transport organs between the leaf and the grains containedappreciable ¹⁴C in glutamine, glutamate, serine, alanine, threonineand glycine. Smaller amounts of ¹⁴C were present in gamma-aminobutyricacid (GABA), aspartate and cysteine. Other amino acids whichwere labelled in the source leaf were not labelled in the transportorgans. The export of labelled glutamine, serine, glycine andthreonine from the source leaf was favoured in comparison tothe other amino acids mentioned. Threonine accumulated, andwas subsequently metabolised, in the rachis. [¹⁴C]GABA alsoaccumulated in the rachis. In the grains, the relative amountof soluble [¹⁴C]alanine increased with chase time. This wasprobably due to de novo synthesis and reflected the specialrole of alanine in grain nitrogen metabolism. Wheat, Triticum aestivum, ¹⁴CO₂, amino acids, transport, carbon metabolism     

The Rate of Growth and Partitioning of Assimilates in Young Grass Plants: A Mathematical Model

A model describing the increase in weight with time of younggrass plants is formulated. The parameters are the relativegrowth rates of the root and shoot systems; k, the ratio ofthe relative growth rate of the root system relative to thatof the shoot system; b, the weight of the root system when thatof the shoot system is unity, and u the rate of increase inweight of the whole plant per unit of shoot system per unitof time, k and b are the constants in the allometric formula,r = bs^k where r and are the weights of the root and shoot systems.The model enables the effect of changes in the distributionof assimilates between the root and shoot systems upon the rateof growth of the plant to be assessed. Data from a number ofexperiments are analysed in this manner and the significanceof the results discussed.     

Distribution Patterns of 14C in the Labelled Vitamin B6 Prepared with the Cell-suspension of Achromobacter cycloclastes

The biosynthetic pathway of vitamin B₆ (abbreviated as Be) has been studied with the cell-suspension of B₆-producing bacteria, Achromobacter cycloclastes A.M.S. 6201. The distribution of ¹⁴C in the Be molecule prepared with the cell-suspensions containing glycerol-1,3-¹⁴C, glycerol-2-¹⁴C or γ-aminobutyric acid-U-¹⁴C was investigated by using three novel degradation methods. The results showed that carbon skeletons of glycerol and γ-aminobutyric acid were used for the formation of the major part of B₆ carbon skeleton respectively. The implication of these compounds as precursors of B₆ was discussed.     

Small-RNA Deep Sequencing Reveals Arctium tomentosum as a Natural Host of Alstroemeria virus X and a New Putative Emaravirus

Background

Arctium species (Asteraceae) are distributed worldwide and are used as food and rich sources of secondary metabolites for the pharmaceutical industry, e.g., against avian influenza virus. RNA silencing is an antiviral defense mechanism that detects and destroys virus-derived double-stranded RNA, resulting in accumulation of virus-derived small RNAs (21–24 nucleotides) that can be used for generic detection of viruses by small-RNA deep sequencing (SRDS).

Methodology/Principal Findings

SRDS was used to detect viruses in the biennial wild plant species Arctium tomentosum (woolly burdock; family Asteraceae) displaying virus-like symptoms of vein yellowing and leaf mosaic in southern Finland. Assembly of the small-RNA reads resulted in contigs homologous to Alstroemeria virus X (AlsVX), a positive/single-stranded RNA virus of genus Potexvirus (family Alphaflexiviridae), or related to negative/single-stranded RNA viruses of the genus Emaravirus. The coat protein gene of AlsVX was 81% and 89% identical to the two AlsVX isolates from Japan and Norway, respectively. The deduced, partial nucleocapsid protein amino acid sequence of the emara-like virus was only 78% or less identical to reported emaraviruses and showed no variability among the virus isolates characterized. This virus—tentatively named as Woolly burdock yellow vein virus—was exclusively associated with yellow vein and leaf mosaic symptoms in woolly burdock, whereas AlsVX was detected in only one of the 52 plants tested.

Conclusions/Significance

These results provide novel information about natural virus infections in Acrtium species and reveal woolly burdock as the first natural host of AlsVX besides Alstroemeria (family Alstroemeriaceae). Results also revealed a new virus related to the recently emerged Emaravirus genus and demonstrated applicability of SRDS to detect negative-strand RNA viruses. SRDS potentiates virus surveys of wild plants, a research area underrepresented in plant virology, and helps reveal natural reservoirs of viruses that cause yield losses in cultivated plants.     

The Distribution of 14C-Labelled Assimilates in Young Apple Trees as Influenced by Doses of Supplementary Nitrogen: I. Total 14C Radioactivity in Extracts

Rooted shoots of apple rootstock MM.104 were grown in soil andsupplied with doses of ammonium nitrate at different stagesof shoot extension growth. ¹⁴CO₂ was supplied in associationwith the supplementary nitrogen via the largest healthy leafnear the base of the current season's shoot. Samples from thevarious regions of the plants were extracted, giving methanolicsolutions (containing principally sugars and soluble resources)and T.C.A. extracts (containing principally hydrolysis productsof available polysaccharides). These were counted for total¹⁴C activity using liquid scintillation spectrometry. Around90 per cent of the activity was present in the methanolic extracts.Virtually no ¹⁴C activity was transferred to the root regionbefore shoot extension was under way whereas up to 45 per centof the translocated activity occurred in the roots during andafter the main period of shoot extension. Nitrogen uptake hadbeen confined to these later stages but no influence of nitrogensupply on the gross distribution of ¹⁴C outside the source leafwas detected.     

The Sugars Concerned in the Tangential Movement of 14C-labelled Assimilates in Willow

Analysis of bark sectors through which tangential movement hadoccurred showed that sucrose was present in greater quantitiesthan glucose or fructose. No evidence could be gained from suchanalyses, however, as to which of these three sugars was themobile species. The use of ¹⁴CO₂ supplied to the leaves, revealed that after24 hours of tangential movement, the greatest proportion ofthe activity in the bark sectors was present in sucrose. Byprogressively reducing the time during which tangential movementwas allowed to occur in these tracer experiments, a patternof results was obtained which completely supports the assumptionthat ¹⁴C-labelled assimilates are transported in a tangentialmanner round the stem as sucrose. The presence of activity inglucose and fructose is merely due to their production fromlabelled sucrose.     

Distribution of 14C Assimilates in the Cowpea (Vigna unguiculata L.) in Relation to Fruit Abscission and Treatment with Benzyladenine

The distribution of ¹⁴C assimilates from ¹⁴C-sucrose was studiedin relation to premature fruit abscission in two cowpea cultivars,Adzuki and Mala. In both cultivars most of the radioactivitywas recovered in the fruits, constituting 63–85 per centof the total ¹⁴C imported from the fed leaflet. This was followedby the root, leaves and stem in descending order, except thatin Mala, import by the stem was greater than that by the leaves.Adzuki imported 56 per cent more ¹⁴C than Mala, from the fedleaflet. In Adzuki, which exhibits a relatively low degree ofabscission of young fruits, the ratio of ¹⁴C accumulated bypeduncle 1 (oldest) fruits to that of peduncle 3 (youngest)fruits was 0·31; while in Mala it was 0·61. Ratiosof the combined accumulation by peduncles 1 and 2 fruits topeduncle 3 fruits were 0·81 for Adzuki, and 1·88for Mala. The more mature fruits of Mala thus constituted amore potent sink for ¹⁴C assimilates than those of Adzuki. In Adzuki, benzyladenine treatment of young fruits at each pedunclewas not significantly effective in reversing or modifying thenormal gradient of assimilates in fruits of different ontogeny.However, in Mala, BA treatment of the youngest fruits caused43 per cent increase in ¹⁴C import, when compared with correspondingfruits of control plants. In Adzuki, BA had no significant effecton total fruit weight, whereas in Mala the weight was increasedby about 36 per cent.     

Changes in the Distribution of 14C-Labelled Assimilates in Sugar-beet with Variation of Temperature

Plants were allowed to assimilate ¹⁴CO₂ for 30 min at 5, 15,25, and 35 °C. The changes in ¹⁴C content of a mature expandedleaf (Leaf 4), young apical leaves, and storage root, were sequentiallyfollowed over a subsequent period of 24 h in continuous light.In a second experiment plants were transferred after ¹⁴CO₂ assimilationto temperatures of 10, 18, 26, and 34 °C, and the partitionof ¹⁴C between the ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was followed over a period of 72 h. The specific activities of the apical leaves and of the storageroot increased to a maximum 2 h after labelling at 25 °C,4 h at 15 and 35 °C, and 6 h at 5 °C suggesting thatthe optimum temperature for translocation of photosynthate wasabout 25 °C. The ¹⁴C partition to ethanol-soluble and ethanol-insoluble fractionsof the roots and leaves was largely attained in. 9 h. Littlerepartition of ¹⁴C assimilate fractions occurred as a resultof temperature change or growth. Root ethanol-insoluble activity,however, did increase significantly over the 72-h period : possiblecauses of this slow incorporation and their relevance to themechanism of sugar storage are discussed.     

Variation in 14C Partitioning in the Tips of Growing Stolons of Potato (Solanum tuberosum L.)

¹⁴C partitioning was examined in growing stolons of field-grownpotato (Solanum tuberosum L.) cv. Maris Piper. Considerablevariation was evident on single plants and on a fresh weightbasis many stolon tips, which showed no signs of sub-apicalswelling, had higher specific activities (cpm g^–1 f. wt)of ¹⁴C in both ethanol soluble and insoluble forms than larger,visibly tuberized stolons. Furthermore, many tips of low freshweight had a higher insoluble to soluble ¹⁴C ratio than visiblytuberized stolons suggesting greater efficiency of conversionof soluble ¹⁴C to insoluble ¹⁴C in the smaller stolons. Theresults suggest that the onset of visible ‘tuberization’,namely the sub-apical swelling of the stolon, is preceded byincreased soluble carbon accumulation at the stolon tip togetherwith an increase in the conversion of soluble to insoluble formsof carbon. Tuberization, ¹⁴C, stolon tip     

Hormonal Regulation of the Distribution of 14C-labelled Assimilates in the Flowering Shoot of Carnation

Evidence is presented that growth substances have a role indirecting the movement of assimilates towards the developingflowers of carnation. Removal of the terminal flower resultedin decreased upward movement of ¹⁴C-labelled assimilates froma source leaf on the flowering shoot. Applications of indole-3yl-aceticacid or gibberellic acid to the stump of the flower stem partiallyrestored the pattern of movement to that found in the intactshoot. Two gibberellin-like substances and one auxin-like substancewere detected in extracts of the floral tissues. Levels of growthsubstances appeared to be higher in the flower than elsewherein the flowering shoot.     

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     

Host-Parasite Relations in Loose Smut of Wheat: II. The Distribution of 14C-Labelled Assimilates

The effect of infection by Ustilago nuda on the distributionof ¹⁴C-assimilates in spring wheat plants at several stagesof growth was examined Only small differences were detectedbetween healthy and infected plants at the early stages, butthere were marked differences between the older plants The amountof assimilate exported by the fed leaf appeared to be dependenton the demand for assimilates in all plants, and was greatestduring a period of rapid growth of host or parasite, such asthe sporulation of the fungus in the infected ear The distributionof exported assimilates from the fed leaf of healthy plantsvaried with the position of the fed leaf, its stage of development,and the age of the plant, the pattern was very similar to thatfound in other plant diseases This pattern was altered by thepresence of the pathogen, which acted as an alternative siteof accumulation Totally different sites received ¹⁴C-labelledassimilates in infected plants, in some cases assimilates weretranslocated over unusually long distances, for example fromthe main shoot flag leaf to infected tiller ears. The differencein distribution correlated well with the differences in growthcaused by the pathogen. In addition, the ratio between the radioactivityin alcohol-insoluble and that in alcohol-soluble compounds wasaffected by the infection, in young infected plants more radioactivitywas present in the insoluble fraction and in older infectedplants in the soluble fraction     

Effects of Temperature on the Distribution of 14C-labelled Assimilates in the Flowering Shoot of Carnation

The pattern of distribution of ¹⁴C-labelled assimilates translocatedfrom a leaf on the flower stem of carnation was found to varywith both the ambient air temperature and the localized temperatureof the flower bud. A high bud temperature increased the proportionofassimilates moving into the floral tissues while a low budtemperature increased the proportion accumulating in the stemabove the source leaf. When the air temperature was raised independentlyof the bud temperature, the stem gained assimilates at the expenseof the flower, but if both air temperature and bud temperaturewere raised together, effects of bud temperature predominatedand movement of assimilates into the flower was promoted. Therole of the flower in mediating effects of temperature is discussedwith reference to the distribution of invertase activity inthe shoot.