Asymmetric Distribution of Glucose and Indole-3-Acetyl-myo-Inositol in Geostimulated Zea mays Seedlings

Indole-3-acetyl-myo-inositol occurs in both the kernel and vegetative shoot of germinating Zea mays seedlings. The effect of a gravitational stimulus on the transport of [³H]-5-indole-3-acetyl-myo-inositol and [U-¹⁴C]-d-glucose from the kernel to the seedling shoot was studied. Both labeled glucose and labeled indole-3-acetyl-myo-inositol become asymmetrically distributed in the mesocotyl cortex of the shoot with more radioactivity occurring in the bottom half of a horizontally placed seedling. Asymmetric distribution of [³H]indole-3-acetic acid, derived from the applied [³H]indole-3-acetyl-myo-inositol, occurred more rapidly than distribution of total ³H-radioactivity. These findings demonstrate that the gravitational stimulus can induce an asymmetric distribution of substances being transported from kernel to shoot. They also indicate that, in addition to the transport asymmetry, gravity affects the steady state amount of indole-3-acetic acid derived from indole-3-acetyl-myo-inositol.     

Biosynthesis of γ-aminobutyric acid from spermine in maize seedlings

The administration of labelled spermine [tetramethylene-1,4-¹⁴C] to Zea mays shoots resulted in the formation of radioactive γ-aminobutyric acid (GABA). A chemical degradation of radioactive GABA suggested that its radioactivity was located on C-1 and C-4, indicating that GABA is a product of spermine metabolism in maize seedlings.     

Ontogenetic Changes in the Transport of Indol-3yl-acetic Acid into Maize Roots from the Shoot and Caryopsis

The quantities of endogenous indol-3yl-acetic acid (IAA) in endosperms and scutella of 6-day-old maize seedlings (Zea mays L. cv Giant White Horsetooth) were determined by a fluorimetric method. Endosperms were found to contain 33.4 nanograms IAA per plant, and scutella 7.5 nanograms IAA per plant. [5-³H]IAA applied to endosperms of 6-day-old seedlings moved into the roots and radioactivity accumulated at the apex of the primary root within 8 hours. Two to 7-day-old seedlings were treated simultaneously with [5-³H]IAA in the endosperm and [2-¹⁴C] IAA on the shoot apex. The patterns of transport into the root were found to change during ontogeny: in successively older plants, transport from the shoot into the roots increased relative to transport from the endosperm into the roots. The auxin required for the growth of maize roots could, therefore, partially be contributed by the shoot and endosperm. Ontogenetic changes in the relative importance of these two supplies could be of significance for the integration of growth and development between shoot and root.     

Translocation of Radiolabeled Indole-3-Acetic Acid and Indole-3-Acetyl-myo-Inositol from Kernel to Shoot of Zea mays L.

Either 5-[³H]indole-3-acetic acid (IAA) or 5-[³H]indole-3-acetyl-myo-inositol was applied to the endosperm of kernels of dark-grown Zea mays seedlings. The distribution of total radioactivity, radiolabeled indole-3-acetic acid, and radiolabeled ester conjugated indole-3-acetic acid, in the shoots was then determined. Differences were found in the distribution and chemical form of the radiolabeled indole-3-acetic acid in the shoot depending upon whether 5-[³H]indole-3-acetic acid or 5-[³H]indole-3-acetyl-myo-inositol was applied to the endosperm. We demonstrated that indole-3-acetyl-myo-inositol applied to the endosperm provides both free and ester conjugated indole-3-acetic acid to the mesocotyl and coleoptile. Free indole-3-acetic acid applied to the endosperm supplies some of the indole-3-acetic acid in the mesocotyl but essentially no indole-3-acetic acid to the coleoptile or primary leaves. It is concluded that free IAA from the endosperm is not a source of IAA for the coleoptile. Neither radioactive indole-3-acetyl-myo-inositol nor IAA accumulates in the tip of the coleoptile or the mesocotyl node and thus these studies do not explain how the coleoptile tip controls the amount of IAA in the shoot.     

An NMR method for the study of proton transport across phospholipid vesicles

We have identified [1-¹⁴C]-oxindole-3-acetic acid as a catabolic product of [1-¹⁴C]-indole-3-acetic acid metabolism in Zea mays seedlings. The isolation, and chemical and mass spectral characterization of oxindole-3-acetic acid from corn kernel tissue is described together with data suggesting oxindole-3-acetic acid to be a major catabolic product of indole-3-acetic acid.     

PROVENANCE OF THE ACETYL GROUP OF ACETYLCHOLINE AND COMPARTMENTATION OF ACETYL-CoA AND KREBS CYCLE INTERMEDIATES IN THE BRAIN IN VIVO

—The origin of the acetyl group in acetyl-CoA which is used for the synthesis of ACh in the brain and the relationship of the cholinergic nerve endings to the biochemically defined cerebral compartments of the Krebs cycle intermediates and amino acids were studied by comparing the transfer of radioactivity from intracisternally injected labelled precursors into the acetyl moiety of ACh, glutamate, glutamine, ‘citrate’(= citrate +cis-aconitate + isocitrate), and lipids in the brain of rats. The substrates used for injections were [1-¹⁴C]acetate, [2-¹⁴C]acetate, [4-¹⁴C]acetoacetate, [1-¹⁴C]butyrate, [1, 5-¹⁴C]citrate, [2-¹⁴C]glucose, [5-¹⁴C]glutamate, 3-hydroxy[3-¹⁴C]butyrate, [2-¹⁴C]lactate, [U-¹⁴C]leucine, [2-¹⁴C]pyruvate and [³H]acetylaspartate. The highest specific radioactivity of the acetyl group of ACh was observed 4 min after the injection of [2-¹⁴C]pyruvate. The contribution of pyruvate, lactate and glucose to the biosynthesis of ACh is considerably higher than the contribution of acetoacetate, 3-hydroxybutyrate and acetate; that of citrate and leucine is very low. No incorporation of label from [5-¹⁴C]glutamate into ACh was observed. Pyruvate appears to be the most important precursor of the acetyl group of ACh. The incorporation of label from [1, 5-¹⁴C]citrate into ACh was very low although citrate did enter the cells, was metabolized rapidly, did not interfere with the metabolism of ACh and the distribution of radioactivity from it in subcellular fractions of the brain was exactly the same as from [2-¹⁴C]pyruvate. It appears unlikely that citrate, glutamate or acetate act as transporters of intramitochondrially generated acetyl groups for the biosynthesis of ACh. Carnitine increased the incorporation of label from [1-¹⁴C]acetate into brain lipids and lowered its incorporation into ACh. Differences in the degree of labelling which various radioactive precursors produce in brain glutamine as compared to glutamate, previously described after intravenous, intra-arterial, or intraperitoneal administration, were confirmed using direct administration into the cerebrospinal fluid. Specific radioactivities of brain glutamine were higher than those of glutamate after injections of [1-¹⁴C]acetate, [2-¹⁴C]acetate, [1-¹⁴C]butyrate, [1,5-¹⁴C]citrate, [³H]acetylaspartate, [U-¹⁴C]leucine, and also after [2-¹⁴C]pyruvate and [4-¹⁴C]acetoacetate. The intracisternal route possibly favours the entry of substrates into the glutamine-synthesizing (‘small’) compartment. Increasing the amount of injected [2-¹⁴C]pyruvate lowered the glutamine/glutamate specific radioactivity ratio. The incorporation of ¹⁴C from [1-¹⁴C]acetate into brain lipids was several times higher than that from other compounds. By the extent of incorporation into brain lipids the substrates formed four groups: acetate > butyrate, acetoacetate, 3-hydroxybutyrate, citrate > pyruvate, lactate, acetylaspartate > glucose, glutamate. The ratios of specific radioactivity of ‘citrate’ over that of ACh and of glutamine over that of ACh were significantly higher after the administration of [1-¹⁴C]acetate than after [2-¹⁴C]pyruvate. The results indicate that the [1-¹⁴C]acetyl-CoA arising from [1-¹⁴C]acetate does not enter the same pool as the [1-¹⁴C]acetyl-CoA arising from [2-¹⁴C]pyruvate, and that the cholinergic nerve endings do not form a part of the acetate-utilizing and glutamine-synthesizing (‘small’) metabolic compartment in the brain. The distribution of radioactivity in subcellular fractions of the brain after the injection of [1-¹⁴C]acetate was different from that after [1, 5-¹⁴C]citrate. This suggests that [1-¹⁴C]acetate and [1, 5-¹⁴C]citrate are utilized in different subdivisions of the ‘;small’ compartment.     

Uptake and distribution of sodium and potassium by corn seedlings : I. Role of the mesocotyl in ;sodium exclusion'

The distribution of sodium and potassium throughout corn (Zea mays L. [A632 × Crows 3640] × Oh 43) plants is not simply a matter of uptake by cortical cells and irreversible delivery to the xylem for upward transport. We show that sodium, but not potassium, accumulates in the mesocotyl of corn seedlings grown on NaCl medium. Upon transfer to NaCl-free medium, total sodium is reduced by export through the roots but remains at high levels within the mesocotyl. We report experiments which consider uptake from the xylem.

Shoots excised at the seed were allowed to transpire solutions containing ²²Na and ⁴²K. Potassium uptake within the mesocotyl was very sensitive to concentration, increasing 27-fold between 1 and 10 millimolar. Sodium uptake was dependent upon the square root of the concentration suggesting active accumulation. At sodium concentrations below 1 millimolar, more than 80% of the sodium in the plant was retained in the mesocotyl. Both the uptake by and retention within the mesocotyl were dependent upon transpiration rate as well as concentration. We discuss the limitations of measuring uptake from a finite, depletable medium. The mesocotyl is a modified root with a cuticularized epidermis. We discuss the feasibility of using this `plastic-coated root' as a model for root transport studies.

     

Physiological Studies of a Synthetic Gibberellin-Like Bioregulator: II. Effect of Site of Application on Biological Activity

The biological activity of the synthetic gibberellin agonist AC-94,377 (1-[3-chlorophthalimido]-cyclohexanecarboxamide) in certain plants is strictly dependent on the site of application. Root application of AC-94,377 at concentrations greater than or equal to 1 micromolar to seedlings of dwarf corn (Zea mays L. var d₅), dwarf rice (Oryza sativa L. cv Tan-ginbozu), and sunflower (Helianthus annuus L. cv NK265) seedlings resulted in readily measurable gibberellin-like biological activity. Application of up to 10 micrograms of AC-94,377 to the shoots of these same species had no effect. AC-94,377 was metabolized to more polar products in both dwarf corn and sunflower seedlings. After 4 days of continuous root treatment with [¹⁴C]AC-94,377, greater than 70% of the recovered ¹⁴C was found in the form of unmetabolized AC-94,377. In contrast, only 30 to 40% of the recovered ¹⁴C was unmetabolized 4 days after shoot treatment. Translocation studies demonstrated that the movement of [¹⁴C]AC-94,377 was limited and occurred almost exclusively in an apoplastic fashion. Four days after leaf treatment, less than 1.5% (corn) or 4% (sunflower) of the recovered radioactivity had moved away from the treated area. It was concluded that the lack of biological activity of AC-94,377 following shoot treatment resulted principally from limited phloem mobility and to a lesser extent from accelerated metabolic breakdown.     

Biosynthesis of triterpenoid sapogenols in soybean and alfalfa seedlings

By incubation of germinating soybeans with mevalonate-[2-¹⁴C] (MVA), radioactivity was incorporated into four sapogenols which were identified by TLC. Unequivocal evidence for the identity of three of the four sapogenols was provided by co-crystallization to constant specific radioactivity. The partition of incorporated radioactivity into lipid- and water-soluble fractions and the pattern of radioactivity of individual sapogenols varied with the mode of administering labeled substrates to soybean seedlings, such as incubation of germinating soybeans with MVA-[2-¹⁴C], immersion of roots into MVA-[2-¹⁴C] or foliar application of squalene-[¹⁴C]. When alfalfa seedlings were incubated with MVA-[2-¹⁴C], about two-thirds of the radioactivity incorporated into the sapogenols was associated with medicagenic acid.     

Biosynthesis and metabolism of gramine in Lupinus hartwegii

The administration of l-tryptophan-[3-¹⁴C] to Lupinus hartwegii (3-day-old seedlings and 8-week-old plants) resulted in the formation of gramine-[methylene-¹⁴C], indicating that gramine is produced by the same biosynthetic route in this species as in barley. Radioactive indole-3-aldehyde, labelled specifically on its aldehyde carbon, was isolated from the 8-week-old plants. However no significant amount of this compound was detected in 7-day-old seedlings, and it is suggested that indole-3-aldehyde is formed by the metabolism of gramine in the maturing plant.     

Effect of a Longitudinally Applied Voltage Upon the Growth of Zea mays Seedlings

The electrical parameters that affect young seedling growth were investigated. Voltages ranging from 5 to 40 volts were applied longitudinally along the mesocotyl region of 4-day old Zea mays L. (cv Silver Queen) seedlings for periods of 3 or 4 hours. It was determined that: (a) making the tips of the seedlings electrically positive relative to the base strongly inhibited shoot growth at 5 volts, whereas the reverse polarity had no effect; (b) at higher voltages, making the tip of the seedlings negative caused less growth inhibition than the reverse polarity at each voltage level; (c) the higher the applied voltage the greater the degree of inhibition; and, (d) the more growth inhibition experienced by the plants the poorer, and slower, their recovery. Previous observations of a relationship between the amount of free indole-3-acetic acid in the mesocotyl cortex and the growth rate of the mesocotyl and of gravitropism-induced movement of labeled indole-3-acetic acid from the seed to the shoot lead to the prediction of a voltage-dependent gating of the movement of indole-3-acetic acid from the stele to the cortex. This provided the basis for attempting to alter the growth rate of seedlings by means of an applied voltage.     

Transport and Metabolism of 1-Aminocyclopropane-1-carboxylic Acid in Sunflower (Helianthus annuus L.) Seedlings

Transport and metabolism of [2,3-¹⁴C] 1-aminocyclopropane-1-carboxylic acid (ACC) from roots to shoots in 4-day-old sunflower (Helianthus annuus L.) seedlings were studied. [¹⁴C]ACC was detected in, and ¹⁴C₂H₄ was evolved from, shoots 0.5 hours after [¹⁴C]ACC was supplied to roots. Ethylene emanation from the shoots returned to normal levels after 6 hours. The roots showed a similar pattern, although at 24 hours ethylene emanation was still slightly higher than in those plants that did not receive ACC. [¹⁴C]N-malonyl-ACC (MACC) was detected in both tissues at all times sampled. [¹⁴C]MACC levels surpassed [¹⁴C]ACC levels in the shoot at 2 hours, whereas [¹⁴C]MACC levels in the root remained below [¹⁴C]ACC levels until 6 hours, after which they were higher. Thin-layer chromatography analysis identified [¹⁴C] ACC in 1-hour shoot extracts, and [¹⁴C]MACC was identified in root tissues at 1 and 12 hours after treatment. [¹⁴C]ACC and [¹⁴C] MACC in the xylem sap of treated seedlings were identified by thin-layer chromatography. Xylem transport of [¹⁴C]ACC in treated seedlings, and transport of ACC in untreated seedlings, was confirmed by gas chromatography-mass spectrometry. Some evidence for the presence of [¹⁴C]MACC in xylem sap in [¹⁴C]ACC-treated seedlings is presented. A substantial amount of radioactivity in both ACC and MACC fractions was detected leaking from the roots over 24 hours. A second radiolabeled volatile compound was trapped in a CO₂-trapping solution but not in mercuric perchlorate. Levels of this compound were highest after the peak of ACC levels and before peak MACC levels in both tissues, suggesting that an alternate pathway of ACC metabolism was operating in this system.     

In situ translocation of volicitin by beet armyworm larvae to maize and systemic immobility of the herbivore elicitor <Emphasis Type="Italic">in planta</Emphasis>

Volicitin (N-[17-hydroxylinolenoyl]-l glutamine) present in the regurgitant of beet armyworm (Spodoptera exigua) activates the emissions of volatile organic compounds (VOCs) when in contact with damaged corn (Zea mays L.) leaves. VOC emission in turn serves as a signaling defense for the plant by attracting female parasitic wasps that prey on herbivore larvae. Chemical tracking of volicitin within plants has yet to be reported. Here we present biochemical data that beet armyworm regurgitant serves as a vector for the introduction of volicitin to the site of leaf damage under natural feeding conditions. Corn seedlings were ¹⁴CO₂-labeled in situ, and beet armyworm larvae were allowed to feed on the labeled leaves. Herbivore oral secretions collected from late-third-instar larvae contained approximately 120 pmol volicitin (0.05 nCi pmol^–1) per larva. When radiochemically labeled larvae were placed on unlabeled leaves, the amount of volicitin introduced to the damaged site was approximately 5.0 nCi (calc. 100 pmol/larvae). The mobility of volicitin in leaves was examined by allowing radiolabeled beet armyworms to feed on unlabeled plants. In such tracking experiments, radioactivity was not detected in the upper leaves; however, the exogenous application of 5 nCi of [U-¹⁴C]sucrose to the lower leaf did result in subsequent radioactivity being detected in the upper portion of the plant. The detection of labeled sucrose with the same radioactivity as that of administered volicitin indicated that volicitin was not readily transported to undamaged leaves and that volicitin may not directly serve as a mobile messenger in triggering the emissions of VOCs systemically.Abbreviations BAW Beet armyworm (Spodoptera exigua) - dpm Disintegrations per minute - FAA Fatty acid amide - JA Jasmonic acid - VOC Volatile organic compound     

Biosynthesis of sitosterol in barley seedlings

A method is described for the chemical synthesis of stigmasta-5,24-dien-3β-ol-[26-¹⁴C] and (24S)-24-ethylcholesta-5,25-dien-3β-ol-[26-¹⁴C] (clerosterol). 28-Isofucosterol-[7-³H₂] fed to developing barley seedlings (Hordeum vulgare) was incorporated into sitosterol and stigmasterol confirming the utilisation of a 24-ethylidene sterol intermediate in 24α-ethyl sterol production in this plant. Also, the use of mevalonic acid-[2-¹⁴C(4R)-4-³H₁] verified the loss of the C-25 hydrogen of 28-isofucosterol during its conversion into sitosterol and stigmasterol in agreement with the previously postulated isomerisation of the 24-ethylidene sterol to a Δ²⁴⁽²⁵⁾-sterol prior to reduction. However, feeding stigmasta-5,24-dien-3β-ol [26-¹⁴C] to barley seedlings gave very low incorporation into sitosterol. Attempts to trap radioactivity from mevalonic-[2-¹⁴C(4R)-4-³H₁] in stigmasta-5,24-dien-3β-ol when this unlabelled sterol was administered to barley seedlings gave only a very small incorporation although both 28-isofucosterol and sitosterol were labelled.     

Metabolism of tritiated gibberellin a(20) in maize

After the application of 2.36 Curies per millimole [2,3-³H]gibberellin A₂₀ (GA₂₀) to 21-day-old maize (Zea mays L., hybrid CM7 × CM49) plants, etiolated maize seedlings, or maturing maize cobs, a number of ³H-metabolites were observed. The principal acidic (pH 3.0), ethyl acetate-soluble metabolite was identified as [³H]GA₁ on the basis of co-chromatography with standard [³H]GA₁ on SiO₂ partition, high resolution isocratic elution reverse phase C₁₈ high performance liquid chromatography and gas-liquid chromatography radiocounting. Two other acidic metabolites were identified similarly as [³H]GA₈ and C/D ring-rearranged [³H]GA₂₀, although gas-liquid chromatography radiocounting was not performed on these metabolites. Numerous acidic, butanol-soluble (e.g. ethyl acetate-insoluble) metabolites were observed with retention times on C₁₈ high performance liquid chromatography radiocounting similar to those of authentic glucosyl conjugates of GA₁ and GA₈, or with retention times where conjugates of GA₂₀ would be expected to elute. Conversion to [³H]GA₁ was greatest (23% of methanol extractable radioactivity) in 21-day-old maize plants. In etiolated maize seedlings, the C/D ring-rearranged [³H]GA₂₀-like metabolite was the major acidic product, while conversion to [³H]GA₁ was low.     

Metabolism of [14C]indole-3-acetic acid by the cortical and stelar tissues of Zea mays L. roots

Reverse-phase high-performance liquid chromatography was used to analyse ¹⁴C-labelled metabolites of indole-3-acetic acid (IAA) formed in the cortical and stelar tissues of Zea mays roots. After a 2-h incubation in [¹⁴C]IAA, stelar segments had metabolised between 1–6% of the methanol-extractable radioactivity compared with 91–92% by the cortical segments. The pattern of metabolites produced by cortical segments was similar to that produced by intact segments bathed in aqueous solutions of [¹⁴C]IAA. In contrast, when IAA was supplied in agar blocks to stelar tissue protruding from the basal ends of segments, negligible metabolism was evident. On the basis of its retention characteristics both before and after methylation, the major metabolite of [¹⁴C]IAA in Zea mays root segments was tentatively identified by high-performance liquid chromatography as oxindole-3-acetic acid.Abbreviations HPLC High-performance liquid chromatography - IAA Indole-3-acetic acid     

Red Light-Regulated Growth : I. Changes in the Abundance of Indoleacetic Acid and a 22-Kilodalton Auxin-Binding Protein in the Maize Mesocotyl

We examined the changes in the levels of indoleacetic acid (IAA), IAA esters, and a 22-kilodalton subunit auxin-binding protein (ABP1) in apical mesocotyl tissue of maize (Zea mays L.) during continuous red light (R) irradiation. These changes were compared with the kinetics of R-induced growth inhibition in the same tissue. Upon the onset of continuous irradiation, growth decreased in a continuous manner following a brief lag period. The decrease in growth continued for 5 hours, then remained constant at 25% of the dark rate. The abundance of ABP1 and the level of free IAA both decreased in the mesocotyl. Only the kinetics of the decrease in IAA within the apical mesocotyl correlated with the initial change in growth, although growth continued to decrease even after IAA content reached its final level, 50% of the dark control. This decrease in IAA within the mesocotyl probably occurs primarily by a change in its transport within the shoot since auxin applied as a pulse moved basipetally in R-irradiated tissue at the same rate but with half the area as dark control tissue. In situ localization of auxin in etiolated maize shoots revealed that R-irradiated shoots contained less auxin in the epidermis than the dark controls. Irradiated mesocotyl grew 50% less than the dark controls even when incubated in an optimal level of auxin. However, irradiated and dark tissue contained essentially the same amount of radioactivity after incubation in [¹⁴C]IAA indicating that the light treatment does not affect the uptake into the tissue through the cut end, although it is possible that a small subset of cells within the mesocotyl is affected. These observations support the hypothesis that R causes a decrease in the level of auxin in epidermal cells of the mesocotyl, consequently constraining the growth of the entire mesocotyl.     

Tracing cell wall biogenesis in intact cells and plants : selective turnover and alteration of soluble and cell wall polysaccharides in grasses

Cells of proso millet (Panicum miliaceum L. cv Abarr) in liquid culture and leaves of maize seedlings (Zea mays L. cv LH51 × LH1131) readily incorporated d-[U-¹⁴C]glucose and l-[U-¹⁴C]arabinose into soluble and cell wall polymers. Radioactivity from arabinose accumulated selectively in polymers containing arabinose or xylose because a salvage pathway and C-4 epimerase yield both nucleotide-pentoses. On the other hand, radioactivity from glucose was found in all sugars and polymers. Pulse-chase experiments with proso millet cells in liquid culture demonstrated turnover of buffer soluble polymers within minutes and accumulation of radioactive polymers in the cell wall. In leaves of maize seedlings, radioactive polymers accumulated quickly and peaked 30 hours after the pulse then decreased slowly for the remaining time course. During further growth of the seedlings, radioactive polymers became more tenaciously bound in the cell wall. Sugars were constantly recycled from turnover of polysaccharides of the cell wall. Arabinose, hydrolyzed from glucuronoarabinoxylans, and glucose, hydrolyzed from mixed-linkage (1→3, 1→4)β-d-glucans, constituted most of the sugar participating in turnover. Arabinogalactans were a large portion of the buffer soluble (cytoplasmic) polymers of both proso millet cells and maize seedlings, and these polymers also exhibited turnover. Our results indicate that the primary cell wall is not simply a sink for various polysaccharide components, but rather a dynamic compartment exhibiting long-term reorganization by turnover and alteration of specific polymers during development.     

Translocation of Indole-3-acetic Acid-1'-C and Tryptophan-1-C in Seedlings of Phaseolus coccineus L. and Zea mays L

Indole-3-acetic acid-1′-¹⁴C (IAA-¹⁴C) and tryptophan-1-¹⁴C injected in small amounts into cotyledons of Phaseolus coccineus L. seedlings were found to be translocated acropetally into the epicotyls and young shoots. Similarly IAA-¹⁴C was translocated acropetally into coleoptiles of Zea mays following injection into the endosperms. Labeled metabolites of the injected compounds were also extractable from shoot tissue. However, evidence that IAA-¹⁴C itself was translocated acropetally was obtained by collection in agar blocks applied to cut surfaces of coleoptiles of injected seedlings. The acropetal translocation in Phaseolus was shown not to occur in the transpiration stream but in living tissue. Cotyledons of Phaseolus coccineus and Phaseolus vulgaris contain extensive vascular tissue.     

Measurement of Protein Degradation in Leaves of Zea mays Using [H]Acetic Anhydride and Tritiated Water

The rate of protein degradation in Zea mays leaves has been estimated by using tritiated water and [³H]acetic anhydride as the labeling agents. Both methods circumvent many of the problems usually associated with measuring protein degradation in plants. The half-life of ribulose-1,5-bisphosphate carboxylase protein in second leaves of 13-day-old seedlings under continuous light was found to be 7.8 ± 0.9 days by the tritiated water technique and 6.5 ± 0.8 days by the [³H]acetic anhydride method. The half-lives determined under a 14-hour-light, 10-hour-dark photoperiod are 6.2 ± 0.8 days with tritiated water and 5.4 ± 0.4 days with [³H]acetic anhydride. Whereas the values obtained by the two methods do not differ significantly, the use of either method for the determination of protein half-life can be recommended.