Chlorophyll formation and glycine metabolism in laevulinic acid treated barley leaves

Laevulinic acid (LA) inhibited chlorophyll formation and δ-aminolaevulinic acid (ALA) accumulation in dark-grown barley leaves. Mole ratios (ALA: chlorophyll × 8) indicate that LA decreased ALA production by about 30%. The turnover of glycine-[¹⁴C] in 7-day-old leaves treated with LA was 70% slower than in control tissue and this resulted in an increase in endogenous glycine. Total amino acid also increased in LA treated leaves. The data indicate that any contribution made by glycine to ALA synthesis in LA-treated barley leaves would be significantly restricted.     

Glycine metabolism and chlorophyll synthesis in barley leaves

α-Hydroxypyridine methane sulphonic acid (HPMS), isonicotinyl hydrazide (INH) and nialamide inhibit chlorophyll synthesis in etiolated barley leaves exposed to light. HPMS lowered the rate of protochlorophyllide regeneration but had little effect on the synthesis of protochlorophyll (P630) from exogenous $\text{δ}$-aminolaevulinic acid (ALA). The addition of glycine to HPMS treated leaves partially overcame the inhibition of chlorophyll synthesis. Glycine-[¹⁴C] was readily incorporated into ALA in dark-grown leaves. HPMS treatment increased the sp. act. of ALA in leaves fed glycine-[¹⁴C]. Glycollate oxidation was lower in extracts from HPMS treated leaves. Plants may therefore have two pathways for ALA production with the glutamate pathway becoming more important in conditions where photorespiration is high.     

Effect of 2,2′-bipyridyl on porphyrin synthesis in etiolated and light-treated barley leaves

The effects of 2,2′-bipyridyl on porphyrin formation differed in illuminated and dark-treated barley leaves. In the dark, bipyridyl treatment increased photoconvertible protochlorophyllide (Pchlide, P650) and decreased the protohaem content. The increase in Pchlide could not be wholly accounted for by a diversion of ‘substrate’ from protohaem synthesis. The rate of Pchlide regeneration was slightly higher in chelator treated leaves which suggests increased δ-aminolaevulinic acid (ALA) synthesis. Only small quantities of Mg-protoporphyrinmonomethylester (Mg-protoME) were detected in etiolated leaves treated with bipyridyl in the dark. Protochlorophyll (P630) synthesis from exogenously supplied ALA was lower in the chelator treatments. The results suggest that only when substantial quantities of ALA are being utilized in dark-grown leaves does a ‘metal’ become limiting in the bipyridyl treated leaves. In the light, bipyridyl inhibited chlorophyll synthesis, again suggesting that when substantial amounts of ALA were being utilized a ‘metal’ becomes rate limiting. Bipyridyl treatment also inhibited ALA production in light-treated leaves. The incorporation of glycine-[¹⁴C] into ALA in the presence of bipyridyl was severely restricted compared to the incorporation of glutamate-[¹⁴C]. The data suggest two pathways for ALA synthesis; the classical ALA-synthetase which utilizes glycine and is operative in dark-grown leaves and a second enzyme system, which uses glutamate, and is of quantitative importance in the light.     

The effect of red and far red light on the desaturation of Fatty acids in barley leaves

Barley (Hordeum vulgare) leaf tissue was either (a) exposed to continuous red light or (b) exposed to red, far red, or red followed by far red light. The fatty acid composition and incorporation of acetate-2-¹⁴C into linolenate were determined. Changes occurred in the fatty acid composition of dark-grown barley leaves regardless of whether the plants were subsequently exposed to red light or whether the tissue remained in the dark. Measurements were also made of the fatty acids of the coleoptile. Red light treatment did not reduce the lag period for the synthesis of linolenate when chlorophyll synthesis was inhibited. It appears that the desaturation process per se in the synthesis of linolenate is not phytochrome-mediated but may appear to be phytochrome mediated if, possibly, galactolipid and chlorophyll syntheses occur concomitantly.     

The effect of haem on chlorophyll synthesis in barley leaves

Exogenously supplied bovine haemin, fed to etiolated barley leaves, inhibited chlorophyll synthesis in leaves exposed to light. Haemin inhibited the regeneration of protochlorophyllide (P650) and the conversion of exogenously supplied δ-aminolaevulinate (ALA) to protochlorophyll (P630). The effect of haemin on chlorophyll production was overcome by incubating the leaves in water in the dark before light treatment, suggesting the operation of a rapid haem destruction mechanism in leaves. Protohaem turnover in dark-grown leaves was between 8 and 9 hr, based on the rate of degradation of erogenous haemin and the rate of protohaem breakdown in laevulinic acid (LA) treated leaves. The rate constant for haem destruction was 85 pmol/nmol/hr in the dark and 45 pmol/nmol/hr after 4 hr light. There was no evidence that light affects the synthesis of protohaem. It appears that the regulation of endogenous levels of protohaem is by breakdown and it is this mechanism which is under light control. Haem considerably decreased the incorporation of radioactivity from glycollate-[¹⁴C], glycine-[¹⁴C] and glutamate-[¹⁴C] into accumulated ALA in the presence of LA.     

Studies on Protein Synthesis by Senescing and Kinetin-treated Barley Leaves

Using sterile conditions, changes in total protein synthesis were followed. over an 8 day incubation period, in detached first seedling leaves of barley from 8 day old plants during senescence and after kinetin treatment. In senescing leaves, total ¹⁴C-alanine incorporation was enhanced by nearly 20% within 6 h of leaf detachment and by about 30 % after 24 h. Kinetin treatment stimulated protein synthesis even more, for total incorporation was promoted ca. 50 % after 6 h and by ca. 60 % after 24 h incubation. The leaf supernatant (30,000 ×g for 30 min) proteins were separated on DEAE-Sephadex (A-50) columns into approximately 14 fractions and changes in ¹⁴C labelling of these fractions were studied following leaf detachment and on incubation on water or kinetin for 6 days. In senescing leaves, ¹⁴C-incorporation into supernatant proteins was sustained, even as protein levels declined rapidly The varied stabilities of the different leaf proteins was suggested by the characteristically changing specific activities of the different protein fractions. Although kinetin greatly promoted incorporation into all protein fractions, no evidence was surmised of specific effects on individual leaf proteins. Studies of changes in total protein synthesis in attached senescing first seedling leaves taken from plants aged 7 to 27 days revealed a relatively small increase in ¹⁴C-incorporation. However, incorporation could be greatly increased in leaves up to 15 days old by detaching and preincubating such leaves for up to 2 days on water, prior to measurement. The promotion of ¹⁴C-incorporation into protcins follwing leaf excision could result from early changes in permeability and precursor pool size.     

Far-red induced changes of the protochlorophyllide components in wheat leaves

Biosynthesis of chlorophyll is partly controlled by the phytochrome system. In order to study the effects of an activated phytochrome system on the protochlorophyllide (PChlide) biosynthesis without accompanying phototransformation to chlorophyll, wheat seedlings (Triticum aestivum L. cv. Starke II Weibull) were irradiated with long wavelength far-red light of low intensity. Absorption spectra were measured in vivo after different times in the far-red light or in darkness. The relationship between the different PChlide forms, the absorbance ratio _{650nm636 nm} changed with age in darkness, and the change was more pronounced when the leaves were grown in far-red light. Absorption spectra of dark-grown leaves always showed a maximum in the red region at 650 nm. For leaves grown in far-red light the absorption at 636 nm was high, with a maximum at the 5 day stage where it exceeded the absorption at 650 nm. At the same time there was a maximum in the total amount of PChlide accumulated in the leaves, about 30% more than in leaves grown in darkness. But the amount of the directly phototransformable PChlide, mainly PChlide_650–657, was not increased. The amount of PChlide_628–632, or more probably the amount of (PChlide_628–632, + PChlide _636–657) was thus higher in young wheat leaves grown in far-red light than in those grown in darkness. After the 5 day stage the absorption at 636 nm relative to 650 nm decreased with age, and at the 8 day stage the spectra were almost the same in both types of leaves. Low temperature fluorescence spectra of the leaves also showed a change in the ratio between the different PChlide forms. The height of the fluorescence peak at 632 nm relative to the peak at 657 nm was higher in leaves grown in far-red light than in dark-grown leaves. – After exposure of the leaves to a light flash, the half time for the Shibata shift was measured. It increased with age both for leaves grown in darkness and in far-red light; but in older leaves grown in far-red light (7–8 days) the half time was slightly longer than in dark-grown leaves. – The chlorophyll accumulation in white light as well as the leaf unrolling were faster for leaves pre-irradiated with far-red light. The total length of the seedlings was equal or somewhat shorter in far-red light, but the length of the coleoptile was markedly reduced from 8.1 ± 0.1 cm for dark-grown seedlings to 5.2 ± 0.1 cm for seedlings grown in far-red light.     

Chlorophyll accumulation and breakdown in light-grown barley transferred to darkness: effect of seedling age

Diurnally grown barley (Hordeum vulgare L. cv. Clipper) seedlings of various ages (3–4, 5–6 and 10–11-days-old) were transferred to darkness for 17 h and changes in leaf fresh weight, chlorophyll a, chlorophyll b and protochlorophyllide measured. The results were consistent with previous evidence of a light-independent chlorophyll biosynthetic pathway in light-grown barley. There was a net gain in chlorophyll (μg leaf^-1) in 5–6- and 10–11-day-old plants after 17 h dark treatment. The amounts of chlorophyll that accumulated were similar (5.9 and 4.3 μg Chl leaf^-1), despite a twofold difference in leaf size at T₀. The rate of leaf expansion in 5–6-day-old plants greatly exceeded the rate of chlorophyll accumulation and leaves were noticeably paler after dark treatment i.e. there was a reduction in chlorophyll concentration (μg g fresh weight^-1) in spite of an increase in chlorophyll content (μg leaf^-1). The ability of light-grown barley to accumulate chlorophyll in darkness was a function of seedling age. Very young seedlings (3–4-day-old) generally lost chlorophyll in darkness. The decrease in chlorophyll per leaf resulted mainly from loss of chlorophyll b. Preferential loss of chlorophyll b resulted in dramatic increases in the chlorophyll a:b ratio. Since 3–4-day-old seedlings (1) accumulated 5-aminolevulinic acid in the presence of levulinic acid at a rate comparable to older seedlings, and (2) converted exogenous 5-aminolevulinic acid to chlorophyll in the absence of light, it is unlikely that failure of the youngest plants to accumulate chlorophyll in darkness was due to blocks at these steps in the pathway. Net loss of chlorophyll (μg leaf^-1) in 3–4-day-old seedlings in darkness was eliminated by the addition of chloramphenicol, which occasionally produced a small, but significant, gain in total chlorophyll. These results imply that chlorophyll degradation in young barley leaves is strongly influenced by the chloroplast genome, and is a major factor influencing changes in chlorophyll levels in darkness. The present findings are consistent with the suggestion that the failure of 3–4-day-old barley seedlings to accumulate chlorophyll in darkness may be due to chlorophyll turnover in which the rate of degradation exceeds the rate of synthesis.     

Effect of second-leaf removal or kinetin treatment on the nucleic acid metabolism of senescing first seedling leaf of barley

1. Changes in nucleic acid metabolism in first seedling leaves of barley plants during aging (from 7 to 27 days) were followed, and the effect of continual removal of the second leaf and basal meristem or of treating the first leaf with 20p.p.m. kinetin on these changes was examined. During aging of the first seedling leaves the ribosomal RNA, DNA and soluble RNA declined, with ribosomal RNA showing the most rapid fall. This was, however, accompanied by increased incorporation of ³²P into RNA, which reached its peak on the fifteenth day. 2. Second-leaf removal partially suppressed first-leaf senescence as judged by retarded chlorophyll and nucleic acid decline and by a decreased extent of RNA labelling. Treatment with kinetin, however, did not prove effective. 3. No significant differences in the sucrose-gradient pattern of ³²P-labelled nucleic acids or in the ³²P-labelled nucleotide composition of RNA fractions during aging or during the two treatments were noted, except for a decrease in CMP content of soluble RNA during aging. 4. The results demonstrate that important changes in RNA metabolism are associated with leaf senescence.     

Factors of between- and within-plant distribution of Metopolophium dirhodum (Hom., Aphididae) on small grain cereals

Abstract: The relationship between abundance of rose‐grain aphid Metopolophium dirhodum (Walker) and leaf chlorophyll content of spring wheat, spring oats and winter barley was investigated. Within production stands of each crop 18–25 plots were established, located at places with different plant quality where aphids were counted on particular leaves of 50–100 tillers, and the leaf chlorophyll content and area were determined. In all stands aphid numbers × tiller^?1 increased exponentially with chlorophyll content (r² = 0.783–0.933). This parallel variation may be explained by increased nitrogen content and assimilate production of vigorous chlorophyll‐rich plants. The aphid numbers on leaves of particular order (within‐plant distribution) were also correlated with leaf chlorophyll content (r² = 0.373–0.827). However, in oats and barley the analysis of variance of residuals of log aphids × leaf^?1 versus leaf chlorophyll regression revealed a significant effect of leaf position (the order of the leaf from the top of the plant). The magnitude of residuals was positively related to leaf size and may be related to the intensity of phloem transport from the source leaves to sink organs.     

Chlorophyll turnover in etiolated greening barley transferred to darkness: Isotopic (1-14C glutamic acid) evidence of dark chlorophyll synthesis in the absence of chlorophyll accumulation

Synthesis of chlorophyll was initiated in 5- to 6-day-old dark-grown barley (Hordeum vulgare L. cv. Clipper)seedlings by exposing them to light in the presence of 1-¹⁴ C glutamic acid supplied via the roots.The plants were then returned to darkness. At the end of light treatment (_T) and after 7 or 18 h dark treatment chlorophylls a and b were extracted, quantified (μgleaf¹). purified by HPLC to their magnesium-free derivatives (pheophytin a and b) and their molar radioactivities determined. After 2 h exposure to light followed by 6 h illumination in the presence of 1-¹⁴ C glutamic acid, seedlings had accumulated 4-7 nmol chlorophyll leaf¹ and had incorporated between 900-1 350 Bq (g fresh weight)¹ of radioactive label into the chlorophyll pool. When seedlings were transferred to darkness, label continued to be incorporated and after 18 h the radioactivity of the chlorophyll pool had increased by 300-700 Bq (g fresh weight)¹. Net chlorophyll content, however, remained constant during dark treatment. The increase in radioactivity of the chlorophyll pool in darkness represented the difference between a net increase of label incorporated into chlorophyll a and a small loss of label from chlorophyll b. The absence of measurable radioactivity in the phytol moiety of labelled chlorophyll a, extracted at the endof dark treatment, demonstrated thatincorporation of label was into the tetrapyrrole moiely of chlorophyll and not into the phytol chain. Light-independent incorporation of 1-¹⁴ C glutamic acid into chlorophyll of greening barley seedlings transferred to darkness indicates that chlorophyll synthesis continues when light is withheld. We interpret the net gain in radioactivity of chlorophyll in darkness, in the absence of a net gain in chlorophyll content, to chlorophyll turnover i.e. to simultaneous synthesis and breakdown of chlorophyll when etiolated greening barley seedlings are transferred to darkness.     

Influence of age and illumination on distribution of several calvin cycle enzymes in greening barley leaves

Activities of phosphoriboisomerase, phosphoribulokinase, and ribulose 1,5-diphosphate carboxylase, protein content, and chlorophyll accumulation in dark-grown barley seedlings were measured before and after illumination. Enzymatic activities, levels of soluble protein, and accumulation (upon illumination) of chlorophyll in leaves declined from tips toward the base. In response to increasing time of illumination, chlorophyll accumulation and activities of phosphoribulokinase and ribulose 1,5-diphosphate carboxylase (enzymes located in chloroplasts) increased most in tip portions whereas activity of phosphoriboisomerase and levels of soluble protein (constituents not confined to chloroplasts) increased similarly in all sections of the leaf. Maximum activity of phosphoribulokinase and maximum accumulation of chlorophyll shifted toward median portions of the leaf blade with increased age of seedling before illumination. Maximum activity of ribulose 1,5-diphosphate carboxylase and maximum level of soluble protein occurred in all leaf sections when the seedlings were 7 days of age before illumination.     

Influence of Age and Light on the Distribution and Development of Nitrate Reductase in Greening Barley Leaves

The relation between leaf age and the induction of nitrate reductase activity by continuous and intermittent light was studied with barley seedlings (Hordeum vulgare L. cv. Club Mariout). In general, nitrate reductase activity declined as the period of growth in darkness was extended beyond 5 days. Maximum activity was found near the leaf tip while activity was lowest in the morphologically youngest tissue near the base of the lamina. Increased activity was observed after continuous illumination of dark-grown seedlings for 24 hours. The increase in activity in response to light was greatly reduced when the dark pretreatment period was extended beyond 8 days. The amount of nitrate reductase activity present in the different sections of the leaf was closely related to the amount of polyribosomes present. The pattern of chlorophyll accumulation closely parallelled that of increases in nitrate reductase activity. The initial lag in the induction of nitrate reductase activity was removed by a 10-minute light treatment 6 hours before placing dark-grown barley seedlings in light. The enzyme was also induced under flashing light with various dark intervals. These induction curves closely resembled those of chlorophyll accumulation under the same conditions. The development of photosynthetic CO₂ fixation follows the same induction pattern in this system. Our results suggest that photosynthetic products may be required for the induction of significant levels of nitrate reductase activity in leaves of dark-grown seedlings, although other light effects may not be discounted.     

CHLOROPLAST STRUCTURE AND FUNCTION IN CULTURED TOBACCO TISSUE

A comparative study was made of the ability of cultured pith tissue, leaves of buds induced from callus, and mature leaf tissue of Nicotiana tabacum L. ‘Maryland Mammoth’ to fix carbon, as determined by light-induced C¹⁴O₂ incorporation. Photosynthetic ability was then correlated with the fine structure of chloroplasts from these tissues. The light to dark incorporation ratio for C¹⁴O₂ was at least 3 times as great in the leaf tissue as in growing cultured tissue. The chlorophyll content of the leaf tissue was 10 times as great. The carbon fixation pattern of all the tissues, as determined by radioautographs of chromatogramed extracts, was qualitatively the same. The rate of sucrose synthesis differed greatly, since 20% of the total radioactivity of the extracts from mature leaf tissue appeared in sucrose, while only 1.0% was found in sucrose from callus extracts. The incorporation of C¹⁴O₂ into sugars was inhibited in all the tissue by DCMU (3,4-dichlorophenyl,1, 1-dimethylurea). Cultured tissue past the log phase of growth was intermediate between the younger cultured tissue and the leaf tissue in its chlorophyll content and ability to incorporate C¹⁴O₂ in the light. Proplastids from dark-grown callus possessed stroma lamellae, but prolamellar bodies were not observed. The chloroplasts from growing callus were partially differentiated in comparison with chloroplasts from mature leaf tissue, since each granum had only 4-7 lamellae. Chloroplasts from callus past the log phase of growth were indistinguishable from those in mature leaves. This study establishes that the differentiation of chloroplasts in cultured tissue is a function of the growth rate of the tissue. The growth rate and degree of differentiation of the tissue can be regulated, so a well-defined system is available for the experimental study of chloroplast differentiation.     

Translocation and metabolism of glycine betaine by barley plants in relation to water stress

The glycine betaine which accumulated in shoots of young barley plants (Hordeum vulgare L.) during an episode of water stress did not undergo net destruction upon relief of stress, but its distribution among plant organs changed. During stress, betaine accumulated primarily in mature leaves, whereas it was found mainly in young leaves after rewatering. Well-watered, stressed, and stressed-rewatered plants were supplied with [methyl-¹⁴C]betaine (8.5 nmol) via an abraded spot on the second leaf blade, and incubated for 3 d. In all three treatments the added ¹⁴C migrated more or less extensively from the second leaf blade, but was recovered quantitatively from various plant organs in the form of betaine; no labeled degradation products were found in any organ. When 0.5 mol of [methyl-¹⁴C]betaine was applied via an abraded spot to the second leaf blades of well-watered, mildly-stressed, and stressed-rewatered plants, ¹⁴C was translocated out of the blades at velocities of about 0.2–0.3 cm/min which were similar to velocities found for applied [¹⁴C]sucrose. Heat-girdling of the sheath prevented export of [¹⁴C]betaine from the blade. When 0.5 mol [³H]sucrose and 0.5 mol [¹⁴C]betaine were suppled simultaneously to second leaf blades, the ³H/¹⁴C ratio in the sheath tissue was the same as that of the supplied mixture. After supplying tracer [¹⁴C]betaine aldehyde (the immediate precursor of betaine) to the second leaf blade, the ¹⁴C which was translocated into the sheath was in the form of betaine. Thus, betaine synthesized by mature leaves during stress behaves as an inert end product and upon rewatering is translocated to the expanding leaves, most probably via the phloem. Accordingly, it is suggested that the level of betaine in a barley plant might serve as a useful cumulative index of the water stress experienced during growth.     

Stress-dependent redistribution of abscisic acid (ABA) in Hordeum vulgare L leaves: the role of epidermal ABA metabolism, tonoplastic transport and the cuticle

When ¹⁴C-labelled abscisic acid ([¹⁴C]ABA) was supplied to isolated protoplasts of the barley leaf at pH 6, initial rates of metabolism were about five times higher in epidermal cell protoplasts than in mesophyll cell protoplasts if equal cytosolic volumes were considered. In spite of the fact that epidermal cells make up only about 35% of the total water space in barley leaves, and despite the small cytosolic volume of these cells, in intact leaves all epidermal cells would thus metabolize half as much ABA per unit time as the mesophyll cells (0–27 and 0–51 mmol h^?1 m^?3 leaf water). Therefore, under these conditions epidermal cells seem to be a stronger sink than mesophyll cells for ABA that arrives via the transpiration stream. However, at an apoplastic pH of 7–25, which occurs in stressed leaves, the proportion of total metabolized ABA would be much smaller in epidermal than in mesophyll cells (0–029 and 0–204 mmolh^?l m^?3 leaf water). Our results indicate that under conditions of slightly alkaline apoplastic pH the epidermis may serve as the main source for fast stress-dependent ABA redistribution into the guard cell apoplast. This is partly the result of ABA transport across the epidermal tonoplast, which is dependent on the apoplastic pH and possibly on the cytosolic calcium concentration. The cuticle seems to be of no particular importance in stress-induced apoplastic ABA shifts and cannot be regarded as a significant sink for high ABA concentrations under stress.     

Photochlorophyllide (P650) turnover in dark-grown barley leaves

Laevulinate (LA) induced an increase in protochlorophyllide (P650) in dark-grown ageing barley leaves. The increase was due to a suppression of a P650 breakdown mechanism. The LA inhibition of P650 destruction allowed an estimate to be made of turnover of P650 in ageing etiolated leaves. The rate constant for P650 destruction in 8-day-old dark-grown leaves was 139 pmol/nmol/hr with a half life of 5 hr.     

Phytol Changes in Dark Grown Leaves of Barley after Varying Light Treatments

Gas chromatographic determinations revealed a certain amount of free phytol in dark-grown barley leaves. When a short light impulse or continuous light is given to the leaves, the phytol pool is partly emptied due to esterification of chlorophyllide a. The regeneration is slow during the first 2–3 hours. A pretreatment with light flashes followed by a dark period accelerates the regeneration, which stops however after approximately 30 min. Some evidence points to the existence of an acceptor for excess phytol entering at this stage. Connections between phytol changes during irradiation and the lag phase of chlorophyll formation are discussed.     

MACROMOLECULAR PHYSIOLOGY OF PLASTIDS : VIII. Pigment and Membrane Formation in Plastids of Barley Greening under Low Light Intensity

Sequential changes occurring in the etioplasts of the primary leaf of 7-day-old dark-grown barley seedlings upon continuous illumination with 20 lux have been investigated by electron microscopy, in vivo spectrophotometry, and thin-layer chromatography. Following photoconversion of the protochlorophyllide pigment to chlorophyllide and the structural transformation of the crystalline prolamellar bodies, the tubules of the prolamellar bodies are dispersed into the primary lamellar layers. As both chlorophyll a and b accumulate, extensive formation of grana takes place. After 4 hr of greening, protochlorophyllide starts to reaccumulate, and concomitantly both large and small crystalline prolamellar bodies are formed. This protochlorophyllide is rapidly photoconverted upon exposure of the leaves to high light intensity, which also effects a rapid reorganization of the recrystallized prolamellar bodies into primary lamellar layers.     

Effects of glyphosate on the movement of assimilates of two Lolium perenne L. populations with differential herbicide sensitivity

Glyphosate applications trigger the depletion of aromatic amino acid pools and the decrease of photosynthesis that results in changes in carbon metabolism. The aim of this work was to determine the effect of glyphosate on the export of ¹⁴C from ¹⁴C-glucose to the main sinks, by comparing a glyphosate-resistant Lolium perenne population with a susceptible one. Untreated plants of the two populations grown in hydroponics were labeled with ¹⁴C-glucose applied at the youngest expanded leaf at the tillering stage. Similar ¹⁴C-glucose absorption and ¹⁴C distribution patterns were recorded in both populations. In another experiment, half of the plants of each population were treated with glyphosate, whereas the other half was sprayed with water (controls). Glucose absorption did not vary under glyphosate treatment, regardless of the sensitivity of each population to the herbicide. However, the translocation of ¹⁴C and its distribution patterns were significantly affected by glyphosate within 1 day in the susceptible population. The treated susceptible plants showed 57% higher ¹⁴C retention at the labeled area than their controls. The lower ¹⁴C movement significantly affected the unexpanded leaves and the apical meristem on the labeled tiller. Moreover, the ¹⁴C released from roots was significantly decreased by glyphosate only in the susceptible plants. Glyphosate did not influence leaf absorption, translocation, or release of ¹⁴C-labeled glucose plus radiolabeled metabolites in the resistant population.