Assimilate partitioning in pigeonpea under two levels of drought and during recovery

The partitioning of¹⁴C-assimilates was studied in pigeonpea(Cajanus cajan L.) at vegetative and flowering stages (40 and 70 d after sowing, respectively) exposed to moderate and severe drought induced by withholding the irrigation. At vegetative stage, the ethanol soluble fraction in shoot decreased from 99 to 43.16 % between 0 and 120 h, whereas in underground part it increased from 1% to 56.84 % with maximum amount in nodules (35.51 %). Similar trend was observed in ethanol insoluble fraction. At moderate drought, a significant increase in soluble fraction (11.31 %) in nodules was observed. Stem showed significant reduction of assimilates (13.09 %). After flowering, the assimilates produced in leaves were exported to reproductive parts, especially under drought. In plants recovering from severe drought, 14C in soluble and insoluble fractions in reproductive parts was reduced to 85 % and 43 %, respectively, whereas leaf and nodules showed a significant increase. Thus the assimilate partitioning to different plant parts was dependent on growth stage and affected by drought.     

Remobilization patterns of C and N in soybeans with different sink-source ratios induced by various night temperatures

The effects of increased sink-source ratios, induced by elevating night temperatures, on remobilization of ¹⁴C-assimilates and N within field-grown soybeans (Glycine max [L.] Merr.) was investigated from preflowering to maturity. Raising the mean minimum night temperature for the entire growing season from 10 (check, uncontrolled) to 16°C increased seed growth without appreciable effect on final leaf area. Increasing this temperature to 24°C increased seed growth and reduced final leaf area. Leaves, stems, petioles, and pods acted as intermediate storage sites for ¹⁴C assimilates. Only plants with higher night temperatures remobilized some of the stored assimilates during the period of rapid seed growth. Even the seeds in the 24°C plants with the largest sink-source ratios did not utilize all the C-assimilates potentially available for remobilization. Nitrogen was readily remobilized from petioles, stems, and pods of all treatments as early as the beginning of seed development, but from the leaves only during late seed-filling. However, only plants with elevated night temperatures tended to remobilize all of the available N from vegetative tissues and pods. We concluded that a larger portion of stored assimilates may be remobilized to the seed if a strong seed sink can be sustained. It also appeared that with increasing sink-source ratios, N shortage might limit seed yield before a lack of C-assimilates would. A proposed model for soybean assimilate demand, distribution, partitioning, and remobilization is presented.     

Effect of Ophiobolus graminis infection on the assimilation and distribution of 14C in wheat

The uptake of ¹⁴C and movement of ¹⁴C-labelled assimilates in wheat plants inoculated with Ophiobolus graminis was examined following exposure of the second youngest leaf to ¹⁴CO₂. Autoradiographs of plants with infected seminal roots showed that assimilates were not translocated past the sites of root infection but accumulated in the undamaged portions of infected root systems, in particular the developing crown roots. There was no evidence that assimilates accumulated in the vicinity of O. graminis lesions. The net assimilation of ¹⁴CO₂ by wheat plants over a 5 h feeding period was not significantly affected by O. graminis infection. However, infection reduced the amount of ¹⁴C lost through respiration. Infection delayed the transfer of labelled assimilates from the fed leaf to the remainder of the plant but increased the proportion translocated to the roots. The latter effect was not apparent when infected plants were continuously irrigated during, and for 20 h following, the feeding period.     

Sugar metabolism and partitioning in cytosol and bacteroid fractions of chickpea nodules

The contents of free sugars in nodules of chickpea (Cicer arietinum) were maximum around flowering. In stem and root tissues, the relative incorporation of ¹⁴C from [¹⁴C]-labelled sucrose or glucose into extracted sucrose was over 70 %. In the former tissue, the relative incorporation of ¹⁴C from glutamate into sucrose was about 50 % at 50 d after sowing (DAS) but the same decreased to about 25 % at 80 DAS. However, from glutamate, 63–68 % of ¹⁴C from extracted sugars of root tissue appeared in invert sugars. Feeding via stem [¹⁴C]-glutamate to intact nodules led to intense labelling of sucrose and invert sugars in nodule cytosol. Upon injecting labelled sugars or glutamate into isolated nodules, maximum ¹⁴C appeared in glucose of this nodule fraction. In bacteroids, incorporation of ¹⁴C from glutamate was much higher in amino acids. In the cytosol of younger (50 DAS) nodules, sucrose was cleaved largely by soluble alkaline invertase (EC 3.2.1.26). However, sucrose cleavage in this fraction of older (80 DAS) nodules was catalysed by this enzyme as well as sucrose synthase (reversal, EC 2.4.1.13) and such nodules also contained higher activity of nitrogenase. The bacteroid fraction, which contained 10–17 % of nodule sugars, lacked the activities of sucrose-cleaving enzymes. The activities of ATP-dependent phosphofructokinase (EC 2.7.1.11), glyceraldehyde-3-phosphate dehydrogenase (EC 1.1.1.12), NADP⁺-dependent isocitrate dehydrogenase (EC 1.1.1.41) and malate dehydrogenase (EC 1.1.1.37) were higher in cytosol than bacteroids. However, the reverse was true for glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). The results suggest that in chickpea nodules sugar metabolism occurs largely via the glycolytic pathway in cytosol and the pentose phosphate pathway in bacteroids and there is some transport of glutamate from cytosol to bacteroids.     

Transport and Distribution of 14CO2 Assimilate in Lolium perenne in Response to Varying Nitrogen Supply to Halves of a Divided Root System

The movement of ¹⁴C assimilate from shoots to roots and its subsequent metabolism in the root of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Half of the N-deficient root system was supplied with either high NO₃-N or high NH₄-N for 16 hours or 6 days before ¹⁴CO₂ labeling of the shoots. The distribution of ¹⁴C in sugars, ethanol-soluble nitrogen and organic acids in roots appeared to be related to the N content of the tissue. Supply of high NO₃-N for 6 days resulted in significant internal translocation of N into the low N supplied root half. Both root halves also had similar patterns of ¹⁴C distribution among soluble and insoluble metabolites. However, NH₄-N supply for 6 days did not result in a significant increase of N in the low N supplied roots, thus only the high NH₄-N supplied roots displayed stimulated sugar metabolism, similar to that in both root halves in the high NO₃-N supply treatment. Percent transport of ₁₄C assimilates from shoot to root was influenced by form and level of N supplied to root halves. Root halves supplied with either high N source for 6 days accumulated greater amounts of ¹⁴C assimilate than the corresponding low N root half. However NH₄-N supply appeared to make roots stronger sinks since NH₄ supply resulted in significantly greater ¹⁴C accumulation in both the high NH₄ supplied and the low N root halves than did NO₃-N supply in corresponding root halves. The data suggest that factors other than root metabolism, such as N mediated metabolism in the shoot, may also influence the percent transport of assimilates to the root. Internal distribution of the incoming assimilate within the root system could be regulated by the metabolic activity or assimilate demand of the roots.     

14C-studies on Apple Trees. IX. Seasonal Changes in the Formation of Fruit Constituents and their Subsequent Conversions

The formation and subsequent conversions of ¹⁴C-labelled compounds were followed in fruits of Malus domestica cvs. Golden Delicious and Cox's Orange Pippin after labelling proximate leaves with ¹⁴CO₂ at different times during the growing season. A few hours after labelling of the leaves, the larger share of fruit ¹⁴C was detected in sorbitol. This share descreased rapidly except in the late autumn. When labelling about 1 July (c. 1 month after bloom), 40–60% of the fruit ¹⁴C was permanently fixed in the methanol and water insoluble fraction. 25% or more was primarily found in organic acids, but this declined during the season to a few per cent. When labelling at the end of July, the dominating feature was the establishment of a peak of temporarily insoluble ¹⁴C, returning back to the soluble form through October and November. This was particularly pronounced in‘Cox's Organe Pippin'. Labelling with ¹⁴C at the end of August and at the end of September yielded increasing amounts of ¹⁴C in sugars. The labelling of fructose predominated, but as the autumn progressed the amount of label in sucrose increased. This was due to a conversion from ¹⁴C-compounds of older origin as well as to a larger share of the imported assimilates turning into sucrose at this time of the year. During prolonged storage of harvested fruits at 3°C, ¹⁴C in fructose increased at the expense of ¹⁴C in sucrose.     

Fixation and distribution of 14C in Populus deltoides during dormancy induction

Photosynthetically fixed ¹⁴C was analyzed in various chemical fractions from leaves and stems of cottonwood (Populus deltoides Bartr. ex. Marsh.) during dormancy induction. Dormancy was induced by 8-h photoperiods and 20/14°C temperature regimes. Within 4 weeks under short days, terminal buds were set and leaf expansion and stem elongation had stopped. ¹⁴C₂ was fed to a leaf at Leaf Plastochron Index 7 for 30 min. Either after this 30 min feeding period or after a 48-h translocation period the plants were sampled, freeze-dried, extracted and analyzed for¹⁴C. ¹⁴C-fixation decreased during dormancy induction from 60% to 17% of the 3.7 MBq ¹⁴C applied at 0 week and 8 weeks, respectively. Percentage distribution of ¹⁴C in chemical fractions of source leaves reflected leaf age and translocation inhibition. In rapidly growing plants, considerable ¹⁴C was incorporated into leaf protein while most of the soluble¹⁴C-sugars were either metabolized or translocated out of the leaf. After terminal bud set, the percentage of ¹⁴C in the protein and residue fractions decreased rapidly and that in the sugar fraction increased. Percent distribution in stems closely reflected changing metabolic pathways of carbon flow as influenced by dormancy induction. For example, the ¹⁴C in structural carbohydrates decreased in 5 weeks under short days from 65 to less than 10% of the ¹⁴C recovered in the chemical fractions, thus indicating cambium inhibition. At the same time the percentage of ¹⁴C in starch and sugar increased indicating storage. Short term (after 30 min) incorporation of ¹⁴C into the protein and starch fractions of leaves changed relatively little throughout the 8-week induction period. In contrast the turnover rates of these fractions (¹⁴C present after 48 h) increased considerably after active growth of the whole plant stopped.     

Incorporation of 14CO2, 14C-phenylalanine and 14C-cinnamate into soluble and insoluble cinnamic derivatives in Mentha arvensis

With the successful development of methods for the isolation and purification of ethanol-insoluble cinnamic acid esters in mint it became possible to initiate kinetic, isotopic studies on purified, ‘insoluble’ derivatives of caffeic acid, ferulic acid and p-coumaric acid. Pulse-feeding experiments were conducted with ¹⁴CO₂, phenylalanine-U-¹⁴C and cinnamic acid-3-¹⁴C. The ferulic acid derivative exhibited a significant turnover as compared to the other insoluble derivatives which were relatively stable. Time-course tracer studies were performed to compare the turnover of soluble caffeic acid derivatives with ‘insoluble’ forms of caffeic acid. Caffeic acid associated with a macromolecular fraction consistently showed a higher specific activity than either soluble caffeic acid or the caffeic acid associated with a second insoluble derivative.     

Fixation of CO2 and Export of Photosynthate by the Carpel in Pisum sativum

Pods of Pisum sativum cv. Meteor were supplied with ¹⁴CO₂ and the fixation and distribution of the radiocarbon studied. A high fixation rate was found in all of the treated pods. In intact control plants about 60 per cent of the total radiocarbon fixed was exported from the carpet into the seeds of the treated pod in the 24 hour period following fixation. Almost all of the remainder was relained in the carpel itself. It was found that the seeds in the treated pod were the major sink for these fixation products and that the weight of the seed determined the level of import of radiocarbon from the carpel in both attached and detached pods. Removal of the seeds from the treated pod prior to ¹⁴CO₂ treatment reduced export from the fed carpel from 60 to 15 per cent, this being distributed mainly in the other pods and stem fractions. It appears that carpet photosynthate is likely to be of great importance in the growth and development of seeds enclosed by the carpel. control of fixation and export of radiocarbon seemed to be a function of the carpel and the seeds enclosed by the carpel and to be relatively independent of the rest of the plant. This could explain the absence of effect of GA on these processes.     

Partitioning and Utilization of Carbon and Nitrogen in Nodulated Roots and Nodules of Chickpea (Cicer arietinum) Grown at Two Moisture Levels

The partitioning and utilization of carbon (C) and nitrogen(N) in nodulated roots and nodules of chickpea (Cicer arietinumL.) was studied at two moisture levels at 10-d intervals 40–140d after sowing (DAS). More C was used in respiration and lessin growth of nodulated roots and nodules under water stresscompared to controls during all growth stages except at theearly vegetative stage. Similarly, less nitrogen was investedin dry matter of both nodules and nodulated roots under stress,except during the vegetative stage where more nitrogen was used.Calculated over the entire growth period, as much as 14 and20% of the total nitrogen and 3 and 4% of the total carbon fixedby the plant was lost to the rooting medium under controlledand stressed conditions, respectively. The efficiency of nitrogen fixation with respect to net C utilizationwas maximal during seed filling under both control and stressconditions However, the efficiency of nitrogen fixation wasalways greater under drier conditions. Carbon, chickpea (Cicer arietinum L.), nitrogen, nitrogen fixation, partitioning     

Effects of Benzyladenine on Bean Leaf Senescence and the Translocation of 14C-Assimilates

Treating primary leaves of bean plants with benzyladenine (BA) greatly increased the retention of photosynthetic assimilates in the treated leaves. Within 24 hours of treatment, the BA treated primary leaves retained 70 % of their assimilates and maintained this high level throughout the period studied. In contrast, the primary leaves of control plants retained 30 % at week 2, increased retention to 80 % between week 4 and 5 and dropped to 50 % during senescence at week 6. When the trifoliate leaves of 5 week old plants were fed ¹⁴CO₂, less than 1 % of the total activity was recovered from the BA treated leaves. It is concluded that the retardation of leaf senescence by BA on intact plants is not due to mobilization of metabolites from other plant parts, but is associated with a high retention of photosynthates.     

The fate of [14C]glutamate and [14C]malate in birch roots is strongly modified under inoculation with Paxillus involutus

The impact of inoculation with Paxillus involutus on the utilization of organic carbon compounds by birch roots was studied by feeding [¹⁴C]Glu or [¹⁴C]malate to the partners of the symbiosis, separately or in association, and by monitoring the subsequent distribution of ¹⁴C. Inoculation increased [¹⁴C]Glu and [¹⁴C]malate absorption capacities by up to eight and 17 times, respectively. Six- and 15-d-old mycorrhizal roots showed about four-fold higher [¹⁴C]Glu and [¹⁴C]malate absorption capacities compared with 60-d-old mycorrhizal roots, suggesting that the early stages of mycorrhiza formation induced higher requirements for C skeletons. Moreover, the results demonstrated that inoculation strongly modified the fate of [¹⁴C]Glu and [¹⁴C]malate. It was demonstrated that exogenously supplied Glu and malate might serve as C skeletons for amino acid synthesis in mycorrhizal birch roots and in the free-living fungus. Gln was the major ¹⁴C-sink in mycorrhizal roots and in the free-living P. involutus. In contrast, citrulline and insoluble compounds were the major ¹⁴C sinks in non-mycorrhizal roots, whatever the ¹⁴C source. It was concluded that mycorrhiza formation leads to a profound alteration of the metabolic fate of exogenously supplied C compounds. The ecological significance of amino acid and organic acid utilization by mycorrhizal plants is further discussed.     

Translocation of 14C-Assimilates in Roses

Movement of ¹⁴C-assimilates from young and mature leaves to young rose shoots (Rosa hybrida cv. Marimba) was examined in two developmental stages. In the first stage after bud breaking the young shoot, especially its tip, depends for its supply of assimilates mainly on the mature foliage. At this stage young leaves are powerful sinks and retain 97% of their own photosynthates. The translocated 3% move mainly to the roots. At a later stage, just after the appearance of the flower bud, most of the leaves on the shoot become a source. The upper leaves supply assimilates to the flower bud and to the upper part of the stem. The ¹⁴C-assimilates from the lower leaves move in two directions, the larger part being directed downward.     

Chickpea varietal response to integrated weed management under different irrigation regimes

Pakistan ranks third among the chickpea growing countries of the world. Chickpea need less water that is why it is preferred by the farmers of the arid and semi- arid zone. The chickpea crop is severely infested by many weeds which reduce its yield and also deteriorate the quality of the grains. The un-availability of high competitive cultivars also had impact on the annual yield production of chickpea crop. The focus of the study was to evaluate sound, feasible and economic weed management strategies to uplift the yield of chickpea crop. The Southern districts of Khyber Pakhtunkhwa are the major producer of chickpea crop. Therefore keeping in view the importance of the crop and as well as the problems associated with the crops, the experiments were conducted at Ahmad Wala Research Station Karak during years 2011^–12 and 2012–13 with Randomized Complete Block design with split split arrangement having four replications. Sowing was done on October 16th during both the studied years. To evaluate the potential of irrigation verses rainfed conditions five cultivars i.e. Karak-1, Karak-2, Sheenghar, Lawaghar and KC-98 and ten weed management techniques i.e. Stomp 330 EC (Pendimethalin), Stomp 330 EC + Hand Weeding (HW) at 60 DAS, Dual Gold 960 EC (S-Metolachlor), Dual Gold 960 EC + HW at 60 DAS, HW one time at (30 DAS), HW two times at (30 and 60 DAS), HW three times at (30, 60 and 90 DAS), White plastic mulch, Black plastic mulch and weedy check were tested. The data was recorded on the below mentioned parameters i.e. weed density m^?2 at 60 DAS, number of productive branches plant^?1, number of pods plant^?1, number of grain pods^?1, number of nodules plant^?1, grain yield (kg ha^?1) and Cost-benefit ratio (CBR). Results of the two years study revealed that with the exception of number of grains pods^?1, and cost benefit ratio, all the vegetative and yield parameters were significantly different during both the studied years. Comparing the effect of irrigation regimes versus rainfed conditions significantly (p < .05) difference was recorded in all parameters while the maximum values were in irrigated plots as compared to rainfed conditions. Significant (p < .05) difference was recorded in weeds density at 60 DAS (64.13 m^?2) found in irrigated plots as compared to rainfed conditions. The year wise comparison of the varieties was significant (p < .05) in number of pods plant^?1, grain yield (kg ha^?1). The varieties were also found with significant difference. After 60 days the minimum weed density (60.68 m^?2) was found in Karak-2 and the maximum weed density at 60 DAS (62.42 m^?2) was recorded in Sheenghar. Among the varieties the maximum values were found number of productive branches plant^?1 (15.89), number of pods plant^?1 (45.52), was found in Karak-1.The maximum number of grains pod^?1 (l.93) was found in Karak-2. The maximum number of nodules plant^?1 (28.54) in Sheenghar and grain yield (1484.1 kg ha^?1) and cost benefit ratio (3.32) was recorded in Lawaghar. The year wise comparison of weed management parameters was also significant in different parameters. However among the treatments after 60 DAS the minimum weed density (51.15 m^?2) was recorded in black and white plastic and the maximum weed density (99.54 m^?2) was recorded in the weedy check. Among the applied treatments for weed management the maximum number of productive branches plant^?1 (16.83), number of pods plant^?1 (52.46), number of grains pod^?1 (2.16) and grain yield (1659.75 kg ha^?1) was recorded in HW three times treatments while on the other hand maximum number of nodules plant^?1 (29.96) was recorded in both black and white plastic mulches. The maximum cost benefit ratio (3.39) was recorded in Stomp 330 EC. The minimum number of nodules plant^?1 (25.35) was found in Dual Gold EC 960 treated plots. The minimum number of productive branches plant^?1 (13.32), number of pods plant^?1 (31.47), number of grains pod^?1 (l.68) and grain yield (1148.4 kg ha^?1) was found in weedy check. The minimum cost benefit ratio (2.54) was found in black plastic mulches treated plots. From the above findings it is concluded that chickpea variety Lawaghar grown in the arid zone need subsequent irrigation. HW, black and white plastic mulches were found efficient for weed management but costly. However, the herbicide Stomp 330 EC was found efficient in weed control and gained maximum CBR in the experimental trial at Southern districts of Khyber Pakhtunkhwa province of Pakistan.     

Natural and dark-induced nodule senescence in chickpea: nodule functioning and H2O2 scavenging enzymes

An investigation was carried out on chickpea (Cicer arietinum L.) cv. C-235 inoculated withRhizobium sp.Cicer strain cv 4 Az^r. Nodule functioning was monitored at 15 d intervals starting from 45 days after sowing (DAS) and inoculation in order to study nodule development and senescence under natural and stress conditions (dark treatments of 18 and 66 h). Maximum rate of N₂-fixation was observed between 50 - 60 DAS. After this acetylene reducing activity (ARA) fell and it was negligible 75 DAS. This decline in ARA with ageing of plants and nodules was accompanied by a decline in leghemoglobin content and greening of the nodules. When 60 % of the nodule tissue had turned green 75 DAS, a sharp increase in nodule peroxidase activity (3.7 fold) was observed whereas the catalase activity was reduced by 50 % in comparison with the control. The glutathione-reductase and ascorbate-peroxidase activity followed a trend parallel to that in N₂-fixation, but the variation was much smaller. The changes in the total soluble carbohydrates, cytosolic proteins and nitrogen content per se were not expressive. Dark treatments induced premature senescence of the nodules as was evident from the marked decrease in ARA. However, the decline in leghemoglobin content was relatively small as compared to ARA. The changes in cytosolic proteins, total soluble carbohydrates, peroxidase activity, catalase activity, glutathione reductase activity and ascorbate peroxidase activity of nodules under dark-induced nodule senescence were almost parallel to those observed under natural senescence.     

Distribution of Soluble 14C-Labelled Assimilates as Related to Distribution of 14C-Benzyladenine in Shoot Tips of Hedera helix

The relationship between benzyladenine and assimilate distributions in shoot tips of English Ivy (Hedera helix L.) was studied. Exogenous applications of benzyladenine resulted in small amounts of the hormone moving to the apical meristem. The large part of the recovered benzyladenine was found in the young leaves of the shoot tip. Benzyladenine increased the amount of ¹⁴C-labelled assimilates in the shoot tip, but the distribution pattern of those assimilates within the tip was like that of the untreated control.     

Products of photosynthetic 14CO2 fixation and related enzyme activities in fruiting structures of chickpea

Fruiting structures of a number of legumes including chickpea are known to carry out photosynthetic CO₂ assimilation, but the pathway of CO₂ fixation and particularly the role of phosphoenolpyruvate carboxylase (EC 4.1.1.31) in these tissues is not clear. Activities of some key enzymes of the Calvin cycle and C₄ metabolism, rates of ¹⁴CO₂ fixation in light and dark, and initial products of photosynthetic ¹⁴CO₂ fixation were determined in podwall and seedcoat (fruiting structures) and their subtending leaf in chickpea (Cicer arietinum L.). Compared to activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and other Calvin cycle enzyme, viz. NADP⁺-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13), NAD⁺-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) and ribulose-5-phosphate kinase (EC 2.7.1.19), the levels of phosphoenolpyruvate carboxylase and other enzymes of C₄ metabolism viz. NADP⁺-malate dehydrogenase (EC 1.1.1.82), NAD⁺-malate dehydrogenase (EC 1.1.1.37), NADP⁺ malic enzyme (EC 1.1.1.40), NAD⁺-malic enzyme (EC 1.1.1.39), glutamate oxaloacetate transaminase (EC 2.6.1.1) and glutamate pyruvate transaminase (EC 2.6.1.2), were generally much higher in podwall and seedcoat than in the leaf. Podwall and seedcoat fixed ¹⁴CO₂ in light and dark at much higher rates than the leaf. Short-term assimilation of ¹⁴CO₂ by illuminated fruiting structures produced malate as the major labelled product with less labelling in 3-phosphoglycerate, whereas the leaf showed a major incorporation into 3-phosphoglycerate. It seems likely that the fruiting structures of chickpea utilize phosphoenolpyruvate carboxylase for recapturing the respired carbon dioxide.     

Mobilization and exudation of photo-assimilated14C by developing pods of groundnut (Arachis hypogaea L.)

Summary ‘Pod washings’ were collected from groundnut at three hour intervals for 24 hours after feeding the plants with¹⁴CO₂. Low radioactivity was found in the first four ‘Pod washings’ of 10 day old pods and the radioactivity increased with time. Highest radioactivity was found in washings of 20 and 30 day old pods and was twice the activity found in the washings of 50 day old pods. The radioactivity of both ethanol-soluble and insoluble fractions in pods was determined. The radioactivity mobilized into the pods increased with age and it was highest in 50 day old pods. The influence of the pod exudates on geocarposphere microflora during pod development is discussed.     

Translocation of 14C-labelled assimilates in cabbage during club root development

The effects of infection of root systems by Plasmodiophora brassicae on the translocation of ¹⁴C-labelled assimilates from the first and third leaves of cabbage seedlings were investigated. During the early phases of Plasmodium development, there were small differences in the distribution patterns of ¹⁴C-labelled assimilate between healthy and infected seedlings. At the end of growth of plasmodia and during resting spore formation, both first and third leaves exported more assimilates than corresponding leaves of healthy seedlings. When the infected roots were dissected into various regions after exposure of the fed leaves to ¹⁴CO₂, more assimilate accumulated in the club root region than in any other part.     

The simultaneous use of 14CO2 and 15N2 labelling techniques to study the carbon and nitrogen economy of legumes grown under natural conditions

A method based on simultaneous short-term exposure to ¹⁴CO₂ and ¹⁵N₂ is described for studying nitrogen fixation and distribution in legumes relative to carbon assimilation and use. Equipment designed to accomodate experiments under natural conditions with very little disturbance of the N₂ fixing association is used. It permits continuous measurement and regulation of variables such as air temperature, humidity and CO₂ concentration as well as soil aeration. Measurements of distribution and use of assimilates, respiration of nodulated roots, quantitative N₂ fixation and the distribution and fate of fixed N as a function of time lead to a precise estimation of C and N budgets for each labelling period. When experiments are done at several phenological stages they give a new insight into the complex C and N interrelations in legume symbiosis.
A series of trials throughout the growth period of Glycine max (L.) Merr. cv. Hodgson demonstrated the sensitivity of the method. The development of the plants from vegetative to reproductive stages was accompanied by a complete change in the distribution patterns of current assimilates and products of nitrogen fixation. Maximum sink strength moved from the leaves to the pods and seeds which ended up receiving 70% of the incoming C and 35% of the fixed N. The fact that up to 85% of fixed N in the plants was in the reproductive organs at maturity can be accounted for by remobilisation from vegetative parts.
The respiration of nodulated roots utilized 33% of carbon translocated to below-ground plant parts before nitrogen fixation started, but as much as 50% during the period of optimal fixation. The advantages and limitations of the isotopic method described are critically discussed as a prelude to future investigations.