14C-Studies on Apple Trees. I. The Effect of the Fruit on the Translocation and Distribution of Photosynthates

The presence of fruits affects the translocation and distribution of photosynthates from apple leaves to other organs of the tree. An attempt has been made to study the relationship in greater detail by following the distribution of ¹⁴C introduced in the form of ¹⁴CO₂ on shoots with and without fruits, respectively. Determinations of the ¹⁴C-content were made on different parts of the shoot sampled at varying intervals after the introduction of the tracer. The ^l4C-labelling and the content of sorbitol and sugar in the leaves were determined by means of paper chromatography. A total of nearly 90 per cent of the ¹⁴C taken up by the leaves can be transferred to a fruit close by, the majority during the first 4 to 5 days following the addition of the ¹⁴C. The content of ¹⁴C in the leaves is reduced more rapidly in shoots with fruits than in those without. Young leaves retain more of the added ¹⁴C than do fully developed ones. The greatest changes with time are found in the methanol-soluble ¹⁴C-compounds. Immediately following application, the leaves contain 58 to 80 per cent of the ¹⁴C added in sorbitol, 7 to 9 per cent in sucrose, and 1 to 4 per cent in the form of glucose. Within 5 days after the introduction of ¹⁴C the amount of ¹⁴C-sorbitol is reduced very considerably, while in certain cases the amount of ¹⁴C-glucose increases. The ¹⁴C-sorbitol content was higher in leaves from shoots without fruits than in those from fruit-bearing shoots, and this applied also to the total contents of sorbitol and of glucose.     

14C-Studies on Apple Trees. II. Distribution of Photosynthates from Top and Base Leaves from Extension Shoots

The photosynthates from leaves from extension shoots may be used either for new growth of the shoot itself, or for growth in other parts of the tree. An attempt has been made to elucidate this problem by determining the content of ¹⁴C in long shoots to which ¹⁴CO₂ was applied either through fully developed leaves at the base, or through very young leaves at the apex. In the case of ¹⁴C application at the base, 80 per cent or more of the ¹⁴C initially taken up disappears from the shoot, and only a very minor part is translocated upwards in the shoot. When the leaves at the apex are exposed, on the other hand, 80 per cent of the ¹⁴C absorbed is retained in the leaves and shoot components treated as long as there is still considerable terminal growth taking place, although a small percentage is deposited in the lower parts of the shoot. At the same time, a much higher proportion is incorporated into methanol-insoluble components. As terminal growth decreases, a larger proportion of the ¹⁴C activity of the apex leaves also disappears from the shoot. The distribution of activity between the sorbitol, sucrose, glucose and fructose fractions was not significantly different in young and in fully developed leaves. The ¹⁴C labelling in the sugar fraction was highest for sorbitol, then sucrose, but decreases with time compared to glucose and fructose.     

14C-Studies on Apple Trees. VIII. The Seasonal Variation and Nature of Reserves

The nature, seasonal variation and mobilization of reserves in Malus × domestica have been studied by means of ¹⁴C, carbohydrate analyses and extractions of xylem sap. Following exposure to ¹⁴CO₂ in the autumn, the majority of the ¹⁴C absorbed is found in the root. During the winter and in particular the spring the amounts of ¹⁴C in the top and root are reduced to approximately 40 per cent of the autumn values; in the root the amount of dry matter was also considerably reduced. In the tops, most of the ¹⁴C absorbed was found as methanol (80 %)-soluble ¹⁴C which also showed the greatest seasonal reduction; sorbitol, sucrose or glucose in particular are responsible for the decrease in concentration within this fraction. Maximum values for methanol-insoluble ¹⁴C were found in March. In the root, the highest values for absolute changes were found for methanolinsoluble ¹⁴C. Hydrolysis of this fraction showed considerable activity in glucose. In the root there was also considerable activity in a precipitated fraction of the methanol extract. Eluates of xylem sap from apple branches contained primarily sorbitol, the highest concentration of which was found at the beginning of March. For a tree with a dry matter weight of about 300 g, the utilization of reserves from the tree in the spring was calculated to be at least 13 g of dry matter. However, only a minor part (less than 25 per cent) of the latter appears to serve as building material for new growth.     

14C-Studies on Apple Trees. VII. The Early Seasonal Growth in Leaves, Flowers and Shoots as Dependent upon Current Photosynthates and Existing Reserves

The young leaves' consumption proper of photosynthates and their contribution to the growth of flowers, fruits and shoots by exposing spurs and shoots to ¹⁴CO₂ at the earliest stages of the growth period in apple trees (Malus X domestica) were studied. By a parallel determination of the growth intensity in various organs an attempt is made to evaluate their relative dependence on current photosynthates and on reserves from inside the tree. The proper fixation of ¹⁴C by growth in the exposed leaves is high in the earliest phases of growth. The fixation of ¹⁴C is considerable in the flowers, including the petals, immediately prior to flowering, in intensely growing fruits, and in the woody parts of the current year's shoots, when the main part of the terminal growth has been completed. Under conditions of high intensity of growth in an organ, the total fixation by growth in the parts studied may amount to as much as 80–90% of the ¹⁴C absorbed. Only in the very earliest phases of development does the growth of flowers and shoots appear to be based to a greater extent on materials supplied from reserves than from current photosynthesis. Quantitatively the greater part by far of the total new growth in fruits and shoots appears to be based on materials from current photosynthesis.     

Effects of Nitrogen Fertilizer on the Distribution of Photosynthate during Grain Growth of Spring Wheat

The distribution of photosynthate labelled with ¹⁴C was studiedin spring wheat grown with different amounts of nitrogen fertilizerin the three years 1972–4, after exposing the flag leafor the leaf below the flag leaf to ¹⁴CO₂ at 6–10 or 19–26days after anthesis. The movement of ¹⁴C to ears was unaffectedby nitrogen fertilizer except after early exposure in 1973,when nitrogen increased the retention of ¹⁴C in stems at maturity The concentration of sugar in the top part of the shoot at theend of the day was unaffected by nitrogen in 1973, but at 22days after anthesis in 1974 the concentration of sucrose inthe glumes and rachis, and in the flag leaf lamina was increasedby nitrogen. Loss of sugar by translocation and respirationduring the night may explain why this increase in concentrationwas not reflected in the ¹⁴C distribution 24 h after supplying¹⁴C. The proportion of the total ¹⁴C content of the shoot that wasin the ear at maturity ranged from 68 to 95 per cent dependingon when and to which leaf the ¹⁴CO₂ was supplied. Less than5 per cent remained in the leaf exposed to ¹⁴CO₂. The proportionof the final ear weight contributed by the leaf below the flagleaf was about half that contributed by the flag leaf. In 1974 about 24 per cent of the ¹⁴C absorbed by the flag leaf,and 56 per cent of that absorbed by the second leaf, was lostby maturity, presumably by respiration. Most loss occurred inthe first 24 h.     

UPTAKE AND RELEASE OF [14C]ADENINE DERIVATIVES AT BEDS OF MAMMALIAN CORTICAL SYNAPTOSOMES IN A SUPERFUSION SYSTEM

(1) Synaptosomal fractions from guinea pig neocortical dispersions prepared in sucrose solutions were deposited from saline media as ‘beds’ on nylon bolting cloth. When incubated with 0.5–10 μm -[¹⁴C]adenine or adenosine in glucose bicarbonate salines, uptake of ¹⁴C from adenosine proceeded at about four times the rate of uptake of [¹⁴C]adenine. This contrasted with the relative uptake of the two compounds to neocortical tissue slices or to beds made from mitochondrial fractions, where uptake was similar with the two precursors. Uptake of both precursors to synaptosome beds was much greater than uptake of inosine. (2) Synaptosome beds, [¹⁴C]adenosine-loaded, contained 88 per cent of the ¹⁴C as 5′-adenine nucleotides, the remainder being present as cyclic AMP, inosine, hypoxanthine and adenosine. When superfused, the ¹⁴C output consisted mainly of adenosine, inosine and hypoxanthine, with some 7 per cent of 5′-nucleotides and 4 per cent of cyclic AMP. (3) Electrical pulses and the addition of 50 mm -KCl each increased the efflux of ¹⁴C from superfused [¹⁴C]adenosine-loaded beds. The superfusates issuing after excitation contained the same ¹⁴C-labelled compounds as issued before, with a small increase in the proportional yield of adenosine. The additional output of ¹⁴C following electrical pulses was diminished by about 50 per cent by 0.5 μm -tetrodotoxin while that following KCl was not affected; it was however prevented when the superfusing fluids were free of Ca²⁺.     

Involvement of Exported Photosynthetic Products in the CO2Exchange of the Skeletal Shoots of Pine

CO₂exchange in the leafy and skeletal parts of attached shoots of Pinus sylvestrisL. was measured with an infrared gas-analyzer in an open differential system during daylight hours. The ¹⁴CO₂assimilation rates in the leafy parts of shoots and ¹⁴CO₂evolution from current photosynthetic products in the lower skeletal part of shoots were measured in afternoons. Chlorophyll content was measured in the needles of the same shoot. The carbon of exported assimilates contributed only about 4% to CO₂exchange in the heterotrophic tree tissues. Only this component of CO₂evolution from the surface of the skeletal part of the tree was related to the losses of the net primary photosynthetic production (NPP) in the aboveground part of the pine stand during the current growth period.     

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     

14C-Studies on Apple Trees. V. Translocation of Labelled Compounds from Leaves to Fruit and their Conversion within the Fruit

Following application of ¹⁴CO₂ to fruit spur leaves, the majority of the ¹⁴C absorbed is transfered to the fruit on the same spur, and the total content of ¹⁴C within the leaf-fruit system as a whole remains virtually constant with time. The considerable reduction in activity in the leaves is accounted for mainly by a decrease in the amount of ¹⁴C-sorbitol, although relatively speaking the decrease in ¹⁴C-sucrose is also considerable. The major part of the activity of the sugar fraction in the conducting tissues between blade and fruit (petiol, spur) is found in sorbitol. Immediately following uptake of ¹⁴C yia the leaves a large part of the activity of the sugar fraction in the fruit is found in sorbitol; but this activity is rapidly reduced, accompanied by an increase in sucrose activity, and over longer periods of time increases in particular in glucose and fruclose activity, and in that of methanol insoluble compounds. The changes in activity distribution in the fruit vary with the variety of fruit and the dates within the growing season. By injecting labelled sorbitol directly into the fruit sorbitol is converted into sucrose, glucose and fructose, while injection of labelled sucrose, glucose and fructose has yielded proof of interconversions between these compounds but no measurable amounts of surbitol. After application of ¹⁴CO₂ directly to the outer skin of the fruit considerably less of the activity is found in sorbitol than is the case in leaves following exposure to ¹⁴CO₂. A minor, but significant, translocation of ¹⁴C away from the fruit was found to take place following the application of labelled ¹⁴C compounds to the fruit. The smallness of the respiratory loss of ¹⁴C in the leaf-fruit system is discussed. It is concluded that in apple trees considerable translocation occurs in the form of sorbitol which in the fruits rapidly converted into other compounds.     

Auxin Transport within Intact Dormant and Active White Ash Shoots

Transport of indoleacetic acid-1¹⁴C following application to the buds of intact white ash (Fraxinus americana L.) shoots proceeds at a velocity of about 1.3 centimeters per hour in actively growing seedlings, but only 0.3 centimeter per hour in dormant seedlings. The rapid movement is metabolically controlled, and at 1 C or in a nitrogen environment it is reduced to 0.2 centimeter per hour, suggesting that the slower movement is due to diffusion. The transport profile for growing shoots shows a logarithmic decrease in activity in stems treated for 3 hours. However, over longer treatment intervals, especially after 12 hours, a steady state of recoverable activity occurs in the more basal stem segments. Cold-treated shoots acquire the capacity for rapid transport 7 days after they are placed into favorable growing conditions, at which time dormancy callose disappears from the phloem, respiratory activity of the stem tissue increases, and mitotic reactivation occurs in the bud. Following shoot reactivation, the velocity and amount of exogenously supplied indoleacetic acid transported remained relatively uniform until the onset of the succeeding dormant period. Five per cent, or less, of the applied tracer moves into the shoot, with substantial portions remaining as indoleacetic acid.     

14C-Studies on Apple Trees. IV. Photosynthate Consumption in Fruits in Relation to the Leaf-Fruit Ratio and to the Leaf-Fruit Position

The photosynthate consumption in apple fruits in relation to the leaf/fruit ratio was studied in sections of branches of the Graasten and Golden Delicious varieties by exposure to ¹⁴CO₂during July and August. A significant, negative correlation was found between the fixation of ¹⁴C in the fruits in terms of percent of the total amount of ¹⁴C absorbed and the leaf/fruit ratio of the branch sections. The leaf area required for the saturation of one fruit was found to be ca. 190 and 230 cm² (14 and 17 leaves) in the case of Golden Delicious, and ca. 400 and 670 cm² (25 and 42 leaves) for Graasten in July and August, respectively, calculated under conditions of large leaf areas per fruit. In such cases a fairly good, reverse proportionality exists between the ¹⁴C fixation in the fruit in terms of percent and the leaf area expressed in multiples of saturation area. At low leaf/fruit ratios, however, the actual saturation area is found to be lower than the theoretically computed one. The translocation of the ¹⁴C assimilated in the leaves of the extension shoots or of spurs without fruits to fruits on other spurs was on the whole promoted by a decreasing leaf/fruit ratio in the parts in question; similarly the greatest transport took place on the side where the leaf/fruit ratio was lowest. The fixation was often greatest in the fruit closest to the treated leaves, hut in a number of cases the value was higher for the second closest or even further removed fruits. In this connection the importance of the size of the fruit and the vascular connections is discussed.     

Seasonal Changes in the Distribution of Photo-assimilated C in Young Pine Plants

Pinus strobus L. plants in their third year of growth were permitted to photoassimilate ¹⁴CO₂ for about 1 hour at monthly intervals between April and October, and the subsequent distribution of ¹⁴C in these plants was determined 8 hours, 1 month, 2 months or 4 months after photo-assimilation. In this way, the fate of ¹⁴CO₂ photo-assimilated during different months of the growing season was observed.

In the spring, old needles played a significant role in photo-assimilating ¹⁴CO₂ and exporting current photosynthate to the developing new shoots and roots. By July, the new shoot had replaced the old shoot both as the primary photo-assimilating part of the plant and as an exporter, particularly to the root.

The root received current photosynthate from the shoot throughout the entire growing season, although plant analysis only 8 hours after photo-assimilation did not always reveal this. Translocation of recent photosynthate from shoot to root was particularly high in August, September, and October.

The amounts of photo-assimilated ¹⁴C lost from the plants over a 4 month interval, principally through respiration and photorespiration, were about one-half of that absorbed during photo-assimilation, with the greatest loss occurring within the first month.

     

Labelling of lupine nodule metabolites with 14CO2 assimilated from the leaves

On feeding ¹⁴CO₂ to the shoots of lupine (25 mCi per plant) 30 min was the minimal time needed to determine the incorporation of label into bacteroid compounds. The predominant incorporation, exhibited in all root, nodule and bacteroid samples after 30 min exposure, was into sucrose (45–90% of the corresponding fraction radioactivity) of the neutral fraction; into malate (30–40%) of the acid fraction; into aspartic acid and asparagine (60–80% in sum) of the basic fraction. The composition of carbon compounds containing the greatest amount of ¹⁴C in the cytosol of nodules and in bacteroids was similar. Their radioactivity after 30 min exposure was for bacteroids (nCi per g of bacteroid fr. wt): sucrose 5.73, glucose 1.00, malate 0.15, succinate 0.11; for the nodule cytosol (nCi per g of nodule fr. wt): sucrose 200.00, glucose 8.40, malate 9.34, succinate 8.50. Thus it was demonstrated that in lupine, sucrose is the main photoassimilate entering not only into nodules but also into bacteroids. The biosynthesis of aspartic acid and asparagine occurs during nitrogen fixation in bacteroids.     

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.     

Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer

Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO₂ respiredduring the whole period of grain growth varied from 163 to 443g m^–2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO₂ lost was respired by the ear. The additionof 180 kg N ha^–1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO₂ lost by the ears.The semi-dwarf varieties lost less CO₂ from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the¹⁴C contents of shoots sampled immediately after a 30 s exposureto ¹⁴CO₂ and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 16–28 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment     

Ethanol inhibits phosphatidylcholine and phosphatidylethanolamine biosynthesis in human leukemic monocyte-like U937 cells

The effect of ethanol (ETOH) on the incorporation of [¹⁴C]oleic acid (18:1) into lipid in human monocyte-like U937 cells was investigated. With increasing time of exposure to ETOH, the percentage of the label distributed into neutral lipid (NL) declined from 35 per cent (3 h) to 10 per cent (24 h) accompanied by increased incorporation into phospholipid (PL). [¹⁴C] 18 : 1 was preferentially incorporated into triglyceride (TG) and phosphatidylcholine (PC), comprising over 65 per cent and 50 per cent of the label associated with NL and PL, respectively. Low concentrations of ETOH (⩽ 1·0 per cent; v/v) had no effect. At concentrations greater than 1·5 per cent, there was enhanced incorporation into TG and diacylglycerol (DAG) in a 24-h incubation period, while at 16 h the label in phosphatidylethanolamine (PE) was decreased. The effect of ETOH on the CDP-choline or ethanolamine pathway was examined by monitoring the incorporation of [³H]choline or [¹⁴C]ethanolamine into PC or PE, respectively. At low concentrations ETOH had no effect on either choline uptake or the incorporation into PC. Higher concentrations (≥ 1·5 per cent) for 3 and 6 h resulted in a slightly decreased choline uptake, and the reduction (40–50 per cent) of incorporation into PC suggests that the CDP-choline pathway was inhibited. There was a similar inhibition of the incorporation of [¹⁴C]ethanolamine into PE. When the cells were incubated for 3 h in the presence of 2 per cent ETOH and with labelled 18 : 1 and PL-base, the ratios of incorporation (base/18 : 1) into PC and PE fractions decreased, indicating that the major inhibition lay in blockage of the availability of the base moiety for PL formation. Analysis of the distribution of the label into metabolites revealed that ETOH inhibited the conversion of [¹⁴C] ethanolamine into [¹⁴C]phosphorylethanolamine. The reduction in incorporation was not due to the enhanced breakdown of base-labelled PL. Our results indicate that ETOH has an inhibitory effect on the CDP-choline or ethanolamine pathway.     

HCO−3 uptake through the roots and its effect on the productivity of willow cuttings

Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and ¹⁴C–labelled sodium bicarbonate was fed to the roots. Uptake of ¹⁴C-label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, ¹⁴C-label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid-labile products, whereas after the 48 h feeding period most of the label was in acid-stable products. A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m^?3 NaHCO₃. After a 4-week growing period we determined the biomass of leaves, shoots, roots and cuttings. Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m^?3 NaHCO₃, but a higher concentration of NaHCO₃ (1.470 mol m^?3) caused a slight decrease in the dry matter production. At 0.737 mol m^?3 NaHCO₃ the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.     

The translocation of 14C photosynthate from leaves and pods in Phaseolus vulgaris

Field experiments were undertaken to study the pattern of distribution of photosynthate produced by the leaves and the pods of Phaseolus vulgaris (cv. Purley King) by means of the ¹⁴C technique. It was found that the ^UC photosynthate produced by a trifoliate leaf (38 days after anthesis) was shared almost equally between the leaf and the pod at its axil with 33–50% of the fixed ¹⁴C finding its way to the seeds in that pod. However, during the early stages of pod development (10 days after anthesis) some 13–14% of the fixed ¹⁴C was detected in the stem, indicating the inadequacy of the pod as a sink at that stage. When the pod was treated, virtually no ¹⁴C was detected in other parts of the plant. Of the ¹⁴C fixed by pod photosynthesis in the later stages (38 days after anthesis), 55–60% was translocated to the seeds within the same pod. These results indicate the importance of current photosynthesis during the pod fill stage in P. vulgaris as has been suggested in other grain legume crops.     

Terpene Biosynthesis in Cell-free Extracts and Excised Shoots from Wedgwood Iris

Excised shoots and cell-free extracts prepared from Wedgwood iris (Iris hollandica Hoog. “Wedgwood”) shoots metabolized ¹⁴C-labeled mevalonic acid (MVA). By using cell-free extracts, the ¹⁴C from MVA-1-¹⁴C was recovered as ¹⁴CO₂, while that from MVA-2-¹⁴C was recovered as neutral terpenes, acid-hydrolyzable terpenes, or ¹⁴CO₂. Also, under optimal incubation conditions, 12.8 nanomoles R-MVA-2-¹⁴C was incorporated into neutral terpenes per milligram fresh weight per hour. In contrast, excised shoots incorporated only 0.58 nanomoles R-MVA-2-¹⁴C per mg fresh weight per hour. Labeled products identified from the cell-free system were squalene, farnesol, geranylgeraniol, and compounds that are converted to farnesol and geranylgeraniol after alkaline hydrolysis. Squalene and a 4,4-dimethylsterol were identified as products from excised shoots but not the terpene alcohols or the alkaline-hydrolyzable compounds.     

Studies on Cassava, Manihot utilissima. II. Biosynthesis of Asparagine-14C from 14C-labelled Hydrogen Cyanide and its Relations with Cyanogenesis

Seeds and seedlings of Manihot utilissima were analysed for cyanogenic glycosides und free amino acids, with special reference to valine and isoleucine which serve as precursors of the aglycone moieties of linamarin and lotaustralin. Seeds contained traces of valine and isoleucine but no glycosides, whereas seedlings contained high concentrations of these amino acids and glycosides. Illumination of seedlings led to a steep increase in the concentration of glycosides followed by a decrease without excretion of detectable HCN. Seeds accumulated asparagine, while seedlings accumulated both asparagine and glutamine in the storage and transport of nitrogen. Seedlings incorporated 13.2 per cent of label from valine-¹⁴C(U) and 2.4 per cent of label from isoleucine-¹⁴C(U)into linamarin and lotaustralin, respectively. In both cases, appreciable amounts of label were also incorporated into asparagine. 49 per cent of label from H¹⁴CN was incorporated inio asparagine in which ca. 98 per cent of total radioactivity was located in the amide-carbon atom. The different patterns of labelling which occurred during the assimilation of H¹⁴CN and ¹⁴CO₂ showed that cyanide metabolism did not proceed via CO₂, and that M. utilissima contains an efficient enzyme-system which catalyses the conversion on high concentrations of HCN into asparagine, which subsequently enters different metabolic pools involved with respiration, protein and carbohydrate syntheses. Cyanogenesis in M. utilissima appears lo be directly influenced by available pools of valine and isoleucine, and the metabolism of HCN released from linamarin and lotaustralin by the action of linamarase may be directly related to respiratory and synthetic processes by way of the incorporation of HCN as a unit into asparagine.