Turnover of Carbohydrates in Relation to Growth in Apple Trees. I. Seasonal Variation of Growth and Carbohydrate Reserves

Growth in young apple trees of the rootstocks MM. 106 and M.7 was estimated by changes in d. wt., and growth in the differentregions of the two rootstocks was compared. Changes in d. wtwere compared with changes in extractable carbohydrates in MM.106 trees. The seasonal variations in d. wt, extractable carbohydratesand residues, are discussed in relation to utilization of reserveand current assimilates in the different regions of plant duringwinter, autumn, spring and summer. Malus sylvestris L, apple, carbohydrate, growth     

The Distribution of 14C-labelled Assimilates in Young Apple Trees as Influenced by Doses of Supplementary Nitrogen: II. Soluble Carbohydrates and Amino Acids

Methanol extracts of young MM.104 apple trees fed ¹⁴CO₂ viaa single leaf were fractionated to compare ¹⁴C activity in totalsoluble sugar and amino acid components. ¹⁴C activity in aminoacids increased after the supply of ammonium nitrate to thesoil in plants where ¹⁴C labelled carbohydrates were presentin the roots. Estimates of specific carbon activity gave lowervalues for the amino acid carbon than the general value fortotal soluble carbohydrates. The fractionation of subsequentmethanol extracts of MM.104 roots has shown that sucrose hadlower specific activity than other components. Although thelevels of activity would accord with sucrose being a substratefor amino acid synthesis, an alternative explanation for theobserved results involving a cyclical system for transferringnitrogen is postulated.     

Partitioning of 14C Labelled Assimilates in Arctium tomentosum

Plants of the biennial Arctium tomentosum were grown from seedto seed-set in an open field under three different treatments:control plants receiving full light intensity, plants with aleaf area reduced by 45 per cent, and shaded plants receivingonly 20 per cent of natural illumination. At various stagesof development the youngest fully expanded leaf of one plantin each treatment was exposed to ¹⁴CO₂ for half an hour. Subsequentdistribution of labelled assimilates in various plant partswas determined after eight hours. In the first year, the mostdominant sink was the tap root irrespective of variation inassimilate supply. During the production of new vegetative growthin the second season, a larger amount of radioactive photosynthatewas recovered from above ground parts, especially during formationof lateral branches. Seed filling consumed 80–90 per centof labelled carbon exported from the exposed leaf. In the secondyear, the most pronounced difference between treatments wasin the degree of apical dominance, being highest in shaded plantsand lowest in the plants with cut leaves. Results from ¹⁴C experimentsagreed fairly well with a ‘partitioning coefficient’derived from a growth analysis of plants grown independentlyunder the same experimental conditions. Reasons for discrepanciesbetween the ¹⁴C results and the partitioning coefficient arediscussed. Arctium tomentosum, burdock, variation in assimilate supply, assimilate distribution, ¹⁴CO₂, labelling, growth analysis     

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.     

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.     

春季根外追10B后苹果对硼的吸收和分酯（简报）

“红星”苹果新梢迅速生长期间,用10B标记基中部成熟中,10d后,非标记部位Bdff值（ug)之和约为标记位的1．5倍,向新梢顶部嫩叶的运输量高于基部老叶,“辽伏”苹果花期整株根外施10B 350ug.ml^-1,5d后,硼肥利用率为5．2％,地上部新生器官10B分配率最高,根部10B甚微,根外追施的10B在成熟组织中有较强的移动性,可运送到新生器官。     

The Effect of the Autumn Senescence of Leaves on the Internal Cycling of Nitrogen for the Spring Growth of Apple Trees

The internal cycling of nitrogen (N) has been studied in applerootstocks grown in sand culture and subjected to a constantN supply, or defoliation, or withholding the N supply in theautumn in order to manipulate the amount of N stored over thewinter. The trees subsequently received either no N or 8–0mol N m^–3 (labelled with ¹⁵N to 498 atom%) with the irrigationthe following spring in order to determine the effect of thecurrent N supply on the remobilization of N for leaf growth. Provision of an autumnal N supply delayed leaf senescence andreduced the amount of N withdrawn from leaves from 156 mg Nplant^–1 to 91 mg N plant^–1. Loss of protein ribulose1,5-bisphosphate carboxylase/oxygenase (RUBISCO) accounted for83–87% of the soluble protein N lost during leaf senescence,there being a preferential loss of RUBISCO compared with othersoluble leaf proteins. Remobilization of N from perennial woody tissues (stems androots) in the spring was used predominantly for leaf growth.The amount of N remobilized depended upon the size of the Nstore, but was unaffected by the current N supply, demonstratingthat fertilization of trees does not alter the efficiency withwhich they cycle N. Degradation of RUBISCO in the autumn accountedfor between 32% and 48% of the N subsequently remobilized forleaf growth the following spring, suggesting that RUBISCO hasa role as a summer store for N. Key words: Malus domestica, Borkh, nitrogen, senescence, ribulose 1, 5-bisphosphate carboxylase, oxygenase, storage, remobilization     

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     

Effect of Top Pruning on Stem Carbohydrates Reserves and Foliar 14CO2 Assimilation in Mulberry Trees during Autumn

Removal of shoot tops from mulberry plants in autumn hastenedthe accumulation of starch in the stems even though photosynthesisin the remaining uppermost leaves was supressed. The proportionof the amount of ¹⁴CO₂ assimilate taken into the veins and thecontents of foliar carbohydrates and protein were not affectedby pruning. (Received December 22, 1983; Accepted March 21, 1984)     

Metabolism of Carbon-14 Labelled Arginine, Citrulline and Ornithine in Intact Apple Stems

A study was made of the absorption and metabolism of arginine-guanido-¹⁴C, citrulline-carbamyl-¹⁴C and ornithine 1-¹⁴C which had been applied to apple stem internodes by a perfusion technique at intervals throughout the year. The results showed that these amino acids were interconverted according to the Krebs-Henseleit cycle always in the direction arginine-ornithine-citrulline-arginine. In addition ornithine was degraded by another pathway with loss of CO₂. This loss was particularly extensive during the period June to August when labelled proline and glutamic acid were also found. The evidence is consistent with the initial breakdown of ornithine taking place via glutamic semi-aldehyde.     

Kernel Abortion in Maize : II. Distribution of C among Kernel Carbohydrates

This study was designed to compare the uptake and distribution of ¹⁴C among fructose, glucose, sucrose, and starch in the cob, pedicel, and endosperm tissues of maize (Zea mays L.) kernels induced to abort by high temperature with those that develop normally. Kernels cultured in vitro at 30 and 35°C were transferred to [¹⁴C]sucrose media 10 days after pollination. Kernels cultured at 35°C aborted prior to the onset of linear dry matter accumulation. Significant uptake into the cob, pedicel, and endosperm of radioactivity associated with the soluble and starch fractions of the tissues was detected after 24 hours in culture on labeled media. After 8 days in culture on [¹⁴C]sucrose media, 48 and 40% of the radioactivity associated with the cob carbohydrates was found in the reducing sugars at 30 and 35°C, respectively. This indicates that some of the sucrose taken up by the cob tissue was cleaved to fructose and glucose in the cob. Of the total carbohydrates, a higher percentage of label was associated with sucrose and a lower percentage with fructose and glucose in pedicel tissue of kernels cultured at 35°C compared to kernels cultured at 30°C. These results indicate that sucrose was not cleaved to fructose and glucose as rapidly during the unloading process in the pedicel of kernels induced to abort by high temperature. Kernels cultured at 35°C had a much lower proportion of label associated with endosperm starch (29%) than did kernels cultured at 30°C (89%). Kernels cultured at 35°C had a correspondingly higher proportion of ¹⁴C in endosperm fructose, glucose, and sucrose. These results indicate that starch synthesis in the endosperm is strongly inhibited in kernels induced to abort by high temperature even though there is an adequate supply of sugar.     

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.     

14C-Studies on Apple Trees III. The Influence of Season on Storage and Mobilization of Labelled Compounds

The present paper reports an attempt to elucidate the storage and mobilization processes in 1-year-old apple rootstocks by studying the ¹⁴C content of different parts of the tree following application of ¹⁴CO₂. The translocation of the ¹⁴C taken up from the leaves to other parts proceeds at the highest rate during the first few days after the application of ¹⁴C. The distribution in shoots, trunk and roots after application of ¹⁴C during May, July, August, and in part of September depends in particular upon the intensity of growth in the various parts. From the lime of the application of ¹⁴C until leaf-fall, 40–50 per cent of the ¹⁴C initially absorbed disappears from the tree. After exposure to ¹⁴C during October, and in part of September, a relatively large part of the ¹⁴C applied goes to the root. In this case there is a considerable reduction in the ¹⁴C-conlent from leaf-fall to the following spring after leafing, especially in the root, although relatively speaking reduction is also considerable in the bark of the parts above ground, and it is most pronounced in the methanol (80 %) soluble fraction. The reduction takes place primarily during spring, and comprises, after application during October, for the whole tree 20–25 per cent of the ¹⁴C initially absorbed. Only 13–17 per cent of this amount was recovered in the newly developed shoots and leaves in the following June.     

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.     

Carbohydrates of the freshwater alga Tribonema aequale. II. Preliminary photosynthetic studies with 14C

Tribonema aequale Pascher was cultured for 30 min and 2 h in Na₂ ¹⁴CO₃. An aliquot of the 2 h material was grown for a further 45 h in culture medium devoid of ¹⁴C. The alga was sequentially extracted and the respective radioactivities of the extracts were measured. Evidence is presented that not only mannitol and glucose, but also the water-soluble glucose-containing polysaccharides, are active metabolites. The polysaccharides soluble in 4% aqueous alkali appear to be continuously synthesised and that soluble in 18% alkali is apparently incorporated into the insoluble non-extractable polysaccharide during growth.     

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.     

Transport of 14C-labelled Assimilates and 32P-labelled Phosphate in Salix viminalis in Relation to Phyllotaxis and Leaf Age

Autoradiographic techniques have been used to investigate thetransport of ¹⁴C-assimilates and ³²P-phosphate in relation tophyllotaxis and age of leaves in Salix viminalis. The leavesborne on the young shoots of S. viminalis are arranged in fiveorthostichies. Three of these orthostichies share one main transportchannel, a second channel being shared by the leaves on theremaining two orthostichies. Where two orthostichies are separatedby an angular distance of 72°, transport may occur betweenleaves on these orthostichies. In addition to the phyllotaxis of the leafy shoot, it has beendemonstrated that the age of the leaf is a factor which determinesthe distribution of materials between leaves.     

The Responses of Young Apple Trees to Supplementary Nitrogen and their Relation to Carbohydrate Resources

Supplementary nitrogen was supplied as ammonium nitrate to pottedtrees of MM.106 apple rootstock during the summer period ofextension growth or during autumn after the end of shoot extension.Effects of autumn nitrogen in the current year were small butsummer nitrogen stimulated shoot growth markedly and increasedleaf-area duration. Neither total root growth nor relative carbohydratecontent were reduced by the treatments. Indeed no direct effectof treatment on relative carbohydrate content was observed.Although a smaller fraction of the total photosynthate was utilizedfor root growth when shoot growth was stimulated by extra nitrogen,total dry-matter production on the basis of available lightenergy intercepted was greater or more efficient when growthwas increased. Additional nitrogen, however, did not preventa seasonal decline in the apparent efficiency of utilizationof incident light energy.     

Seasonal Variations in Absorption and Metabolism of Carbon-14 Labelled Arginine in Intact Apple Stem Tissue

At intervals through the year a study was made of the absorption and metabolism of arginine-C 14(U) which had been perfused into the wood of apple stem internodes. Absorption was greater during the period May to September than at any other time of the year. The metabolic breakdown of arginine took place only after absorption but the products found varied widely with season. From the analyses it is concluded that arginine is metabolized by the Krebs-Henseleit cycle at all times of the year, in addition to which during the period from May to August there are other pathways in operation that result in a more extensive breakdown so that all the N in arginine becomes available for new growth.     

Absorption, Distribution, Metabolism and Leaching of [14C] ABA during Culture of Apple Embryos

Barthe, Ph. and Bulard, C. 1987. Absorption, distribution, metabolismand leaching of [¹⁴C] ABA during culture of apple embryos.—J.exp. Bot. 38: 1002–1011. It has been known for some time that dormant embryos, laid flaton damp filter-paper one cotyledon only being in direct contactwith it (C/2M mode of culture), exhibit unequal growth and greeningof their cotyledons. The aim of this work was to investigatewhether this particular mode of culture led to detectable differencesbetween the two cotyledons in the distribution and metabolismof [¹⁴C] abscisic acid (ABA). Two different approaches wereused, the material in both cases being dormant embryos of Pyrusmalus L. cv. Golden Delicious cultured at 23°C in darkness.In a first experiment, the embryos were cultured directly inthe C/2M mode and in the presence of 10^–2 mol m^–3[¹⁴C] ABA. In these conditions marked differences in the distributionof radioactivity between the lower (LC) and upper (UC) cotyledonappear after 24 h of culture. After 5 d, amounts of total radioactivitywere four times higher in LC than in UC, and the level of ABAwas three times higher. Metabolism was extremely active in LC,since certain metabolites were found in relative percentages(percentages with respect to the total radioactivity of thecotyledon) equivalent to (esters, glucosides), or even higher(dihydrophaseic acid, DPA) than those found in UC. It is suggestedthat this high level of metabolism in LC limits the availabilityof the transportable molecule, that is to say ABA. In a secondexperiment double culturing was carried out. The embryos werefirst cultured in the presence of 10^–2 mol m^–3 [¹⁴C]ABA in conditions which ensured equal distribution of ABA andits metabolites between the two cotyledons. After 5 d they weretransferred to an ABA-free medium and cultured in the C/2M mode.After 2 d and 5 d of culture, dissymmetry between the two cotyledonswas again noted; UC this time containing greater amounts ofradioactivity than LC. The differences, however, were less markedthan in the first experiment. This dissymmetry is due to leachingof a certain amount of radioactivity from LC, which is onlypartially compensated for by migration from UC. Key words: ¹⁴C-ABA distribution, leaching and metabolism, embryo culture, embryo dormancy