Manipulation of xylem transport affects Zn and Mn transport into developing wheat grains of cultured ears

Zinc and manganese loading into developing wheat grain is little understood at present. The objective of this work was to investigate factors that may affect the rate of transport of Zn and Mn into developing wheat grain of cultured ears. Ears 18-22 days post-anthesis were cultured in solutions containing labelled Zn and Mn. The effect of additions of Cu, Fe, citrate, malate and EDTA to the culture solution was observed. The effect of humidity and awn removal as well as the sucrose status of the ears on Zn and Mn transport was also investigated. The effect of high concentration of Zn and Mn on [¹⁴C]-sucrose transport was determined. High humidity almost completely blocked transport of Zn and Mn into the grain. Awn removal reduced the transport of Zn and Mn to the lemma but not the grain. When the ears were depleted of sucrose (by maintaining them in the dark prior to labelling) transport of Zn and Mn to the grain was reduced compared to ears cultured with sucrose. The presence of Cu reduced the loading of Zn into the grain. There was little effect of Cu on Mn transport or Fe on either Zn or Mn transport. High concentrations of Zn and Mn in the culture solution did not affect [¹⁴C]-sucrose loading into the grain but loading of Zn and Mn was limited at high concentrations suggesting membrane saturation. This study demonstrates that sucrose status and humidity clearly influence the transport of Zn and Mn into the grain, and that other ions may influence Zn and Mn transport.     

Uptake and distribution of 65Zn and 54Mn in wheat grown at sufficient and deficient levels of Zn and Mn II. During grain development

We investigated the uptake and distribution of Zn and Mn inwheat during grain development. Plants were grown in a chelate-bufferednutrient solution with one of the following treatments: control,low Zn or low Mn. Plants were dual-labelled with ⁶⁵Zn and ⁵⁴Mnat 2 and 8 wk post-anthesis for 5 and 24 h, respectively. Afterlabelling, the plants were separated into individual componentsfor analysis. In the plants harvested at 8 wk after anthesis,spikelets were separated into individual structures and analysedfor radioactivity. Little or no root-supplied ⁵⁴Mn was distributed to the leavesof both the controls and low-Mn plants during the grain developmentstages studied here. More ⁵⁴Mn was distributed to the head at8 wk than at 2 wk post-anthesis. In contrast, root-supplied⁶⁵Zn was transported to the leaves at 2 and 8 wk post-anthesis.More⁶⁵Zn was distributed to the leaves of the low-Zn plants thanthe controls during grain development.More esZn was detectedin the head towards grain maturity. Relatively larger amountsof ⁵⁴Mn than ⁶⁵Zn were found in different parts of the florets.Labelled Mn was found in relatively large quantities in thepalea, lemma and in the glumes, even though most ⁵⁴Mn was foundin the grain. A large percentage of the grain MMn was in theouter pericarp. During grain development leaves may still require Zn but notMn, which may be due to the requirement of Zn in maintainingmembrane structure and function. Distribution of Zn and Mn withinthe spikelets suggests that Zn may enter the grain via the phloemwhile Mnmay enter the grain via the xylem. Key words: Zinc, manganese, nutrient transport, grain development, wheat, Triticum aestivum     

Import of sucrose and its transformation to starch in the developing sorghum caryopsis

Levels of soluble and bound invertases and amylases were studied in relation to the changes in the free sugars and the accumulation of starch in the developing sorghum [Sorghum bicolor (L.) Moench, cv. spv. 351] caryopsis and its associated bractspedicel. Besides sucrose, glucose and fructose as the principal sugars, small amounts of sugars of the raffinose series were detected in the developing caryopsis. Through out the period of caryopsis development, the amount of reducing sugars was higher than that of sucrose. With the advancement in the development of the caryopsis, the contents and levels of sucrose rose with a concomitant fall in the activity of soluble acid (pH 4.8) invertase (EC 3.2.1.26) in the endosperm. In the pericarp-aleurone layer, the activity of soluble acid invertase predominated over soluble neutral (pH 7.5) invertase (EC 3.2.1.27). The activity of bound acid invertase declined with the ageing of the caryopsis. In bracts-pedicel, the activity of bound invertase and the levels of reducing sugars peaked around 18 days post anthesis. In these organs, the level of starch gradually decreased concomitantly with an increase in its level in the developing caryopsis. Amylases (EC 3.2.1.1 and 3.2.1.2) are distributed in the endosperm as well as in the pericarp-aleurone layer. On culturing detached ears in [U-¹⁴C]-sucrose solution for 6 h in the dark at 25°C, 80–90% of the ¹⁴C of extracted major sugars (i.e. sucrose + glucose + fructose) of the caryopsis appeared in sucrose alone. In comparison with the effects of glucose or fructose, transport into the caryopsis of ¹⁴C from [U-¹⁴C]-sucrose supplied to detached ears was promoted by the addition to the radiolabelled sucrose solution of 1% unlabelled sucrose. Addition to the [U-¹⁴C]-sucrose solution fed to the detached ears of 20 mM NaN₃ or HgCl₂ or galactose, lowered the amount of ¹⁴C in the free sugars and starch of the earyopsis.     

The cellular pathway of photosynthate transfer in the developing wheat grain. III. A structural analysis and physiological studies of the pathway from the endosperm cavity to the starchy endosperm

The cellular pathway of sucrose transfer from the endosperm cavity to the starchy endosperm of developing grains of wheat (Triticum turgidum) has been elucidated. The modified aleurone and sub-aleurone cells exhibit a dense cytoplasm enriched in mitochondria and endoplasmic relicilium. Significantly, the sub-aleurone cells are characterized by secondary wall ingrowths. Numerous plasmodesmata interconnect all cells between the modified aleurone and starchy endosperm. The pro-tonophore carbonylcyanide-m-chlorophenyl hydrazone (CCCP) slowed [¹⁴C]sucrose uptake by grain tissue slices enriched in modified aleurone and sub-aleurone cells but had no effect on uptake by the starchy endosperm. The fluorescent weak acid sulphorhodamine G (SRG) was preferentially accumulated by the modified aleurone and sub-aleurone cells, and this uptake was sensitive to CCCP. The combined plasma membrane surface areas of the modified aleurone and sub-aleurone cells appeared to be sufficient to support the in vivo rates of sucrose transfer to the starchy endosperm. Plasmolysis of intact excised grain inhibited [¹⁴C]sucrose transfer from the endosperm cavity to the starchy endosperm. The sulphydryl group modifier p-chloromercuribenzenesulphonie acid (PCMBS) decreased [¹⁴C]sucrose uptake by the modified aleurone and sub-aleurone cells but had little effect on uptake by the starchy endosperm. In contrast, when PCMBS and [¹⁴C]sucrose were supplied to the endosperm cavity of intact excised grain, PCMBS slowed accumulation by all tissues equally. Estimates of potential sucrose fluxes through the interconnecting plasmodesmata were found to be within the published range. It is concluded that the bulk of sucrose is accumulated from the endosperm cavity by the modified aleurone and sub-aleurone cells and subsequently transferred through the symplast to the starchy endosperm.     

Transport and Metabolism of a Sucrose Analog (1'-Fluorosucrose) into Zea mays L. Endosperm without Invertase Hydrolysis

1′-Fluorosucrose (FS), a sucrose analog resistant to hydrolysis by invertase, was transported from husk leaves into maize (Zea mays L., Pioneer Hybrid 3320) kernels with the same magnitude and kinetics as sucrose. ¹⁴C-Label from [¹⁴C]FS and [¹⁴C]sucrose in separate experiments was distributed similarly between the pedicel, endosperm, and embryo with time. FS passed through maternal tissue and was absorbed intact into the endosperm where it was metabolized and used in synthesis of sucrose and methanol-chloroform-water insolubles. Accumulation of [¹⁴C] sucrose from supplied [¹⁴C]glucosyl-FS indicated that the glucose moiety from the breakdown of sucrose (here FS), which normally occurs in the process of starch synthesis in maize endosperm, was available to the pool of substrates for resynthesis of sucrose. Uptake of FS into maize endosperm without hydrolysis suggests that despite the presence of invertase in maternal tissues and the hydrolysis of a large percentage of sucrose unloaded from the phloem, hexoses are not specifically needed for uptake into maize endosperm.     

Light or high (30°C) temperature effects on l-[U-C]leucine incorporation and protein patterns in embryos and endosperm during the early phase of germination of the negatively photoblastic and thermosensitive seeds of Phacelia tanacetifolia

The activities of l-[U-¹⁴C]leucine uptake and incorporation into proteins of embryos and endosperm of seeds of Phacelia tanacetifolia Benth. cv Bleu-Clair were analysed during the first 24 h of incubation under conditions optimal for germination (16°C in darkness) and in two inhibitory conditions: 16°C in the light and 30°C in darkness. Blocking germination induced by light or 30°C was accompanied by the inhibition of l-[U-¹⁴C]leucine uptake and incorporation in embryos. In the endosperm, the activation of l-[U-¹⁴C]leucine uptake was of the same magnitude for the non-inhibited and the light-inhibited seeds and much higher for the 30°C-inhibited seeds; the activation of l-[U-¹⁴C]leucine incorporation was quantitatively similar in all three conditions, with the patterns of newly synthesised proteins qualitatively different in the endosperm from light- or 30°C-inhibited seeds. The results showed that germination of P. tanacetifolia seeds is controlled by light or super-optimal temperature through the inhibition of the activation of transport and protein synthetic activities in embryo without effect on the endosperm. We suggest, on the basis of the translational activity, the possibility that in the inhibitory conditions the blockade of the embryo to operate as a sink affects the transition of the endosperm to operation as a source.     

C]GA(12)-Aldehyde, [C]GA(12), and [H]- and [C]GA(53) Metabolism by Elongating Pea Pericarp

Gibberellins (GAs) are either required for, or at least promote, the growth of the pea (Pisum sativum L.) fruit. Whether the pericarp of the pea fruit produces GAs in situ and/or whether GAs are transported into the pericarp from the developing seeds or maternal plant is currently unknown. The objective of this research was to investigate whether the pericarp tissue contains enzymes capable of metabolizing GAs from [¹⁴C]GA₁₂-7-aldehyde ([¹⁴C]GA₁₂ald) to biologically active GAs. The metabolism of GAs early in the biosynthetic pathway, [¹⁴C]GA₁₂ and [¹⁴C]GA₁₂ald, was investigated in pericarp tissue isolated from 4-day-old pea fruits. [¹⁴C]GA₁₂ald was metabolized primarily to [¹⁴C]GA₁₂ald-conjugate, [¹⁴C]GA₁₂, [¹⁴C]GA₅₃, and polar conjugate-like products by isolated pericarp. In contrast, [¹⁴C]GA₁₂ was converted primarily to [¹⁴C]GA₅₃ and polar conjugate-like products. Upon further investigations with intact 4-day-old fruits on the plant, [¹⁴C]GA₁₂ was found to be converted to a product which copurified with endogenous GA₂₀. Lastly, [²H]GA₂₀ and [²H]GA₁ were recovered 48 hours after application of [²H]- and [¹⁴C]GA₅₃ to pericarp tissue of intact 3-day-old pea fruits. These results demonstrate that pericarp tissue metabolizes GAs and suggests a function for pericarp GA metabolism during fruit growth.     

Sink Metabolism in Tomato Fruit : II. Phloem Unloading and Sugar Uptake

Analysis of [³H]-(fructosyl)-sucrose translocation in tomato (Lycopersicon esculentum Mill.) indicates that phloem unloading in the fruit occurs, at least in part, to the apoplast followed by extracellular hydrolysis. Apoplastic sucrose, glucose, and fructose concentrations were estimated as 1 to 7, 12 to 49, and 8 to 63 millimolar, respectively in the tomato fruit pericarp tissue. Hexose concentrations were at least four-fold greater than sucrose at all developmental stages. Short-term uptake of [¹⁴C]sucrose, -glucose, and -fructose in tomato pericarp disks showed first order kinetics over the physiologically relevant concentration range. The uptake rate of [¹⁴C]-(glucosyl)-1′-fluorosucrose was identical to the rate of [¹⁴C]sucrose uptake, suggesting sucrose may be taken up directly without prior extracellular hydrolysis. Short-term uptake of all three sugars was insensitive to 10 micromolar carbonyl cyanide m-chlorophenylhydrazone and to 10 micromolar p-chloromercuribenzene sulfonic acid. However, long-term accumulation of glucose was sensitive to carbonyl cyanide m-chlorophenylhydrazone. Together these results suggest that although sucrose is at least partially hydrolyzed in the apoplast, sucrose may enter the metabolic carbohydrate pool directly. In addition, sugar uptake across the plasma membrane does not appear to be energy dependent, suggesting that sugar accumulation in the tomato fruit is driven by subsequent intracellular metabolism and/or active uptake at the tonoplast.     

Translocation and Metabolism of Endosperm-Applied [2-C] Indoleacetic Acid in Etiolated Avena sativa L. Seedlings

The role of free indole-3-acetic acid (IAA) in the endosperm of Avena sativa L. seedlings was investigated to determine its contribution to free IAA in the shoot. [2-¹⁴C]IAA was injected into the endosperm of darkgrown seedlings and the transport and metabolism of the [¹⁴C]-labeled compounds determined. It was concluded that translocation of free IAA directly from the endosperm is probably not a significant source of free IAA in the shoot, mainly because even small amounts of [¹⁴C]IAA introduced into the endosperm were rapidly metabolized. This suggested that, in Avena, free IAA does not normally exist in the liquid endosperm.     

Uptake and distribution of 65Zn and 54Mn in wheat grownat sufficient and deficient levels of Zn and Mn: I. During vegetative growth

The uptake and distribution of ⁶⁵Zn and ⁵⁴Mn by wheat (Triticumaestivum cv. Aroona) was investigated. Plantswere grown in achelate-buffered nutrient solution with either sufficient Znand Mn, low Zn or low Mn. A single representative seminal rootfrom 14-d-old and 42-d-old plants was dual-labelled with ⁶⁵Znand ⁵⁴Mn. The 14-d-old plants were harvested every 10 min from10–140 min of labelling, whilst the 42-d-old plants wereharvested after 2 h of labelling. At harvest, each plant wasseparated into leaves, main stem, unexposedroots, and tillers.In addition, the crown was separatedfrom the stem in the 14-d-oldplants In the control plants labelled at 14 d, ⁶⁵Zn was firstdetectedand accumulated in the crown of the roots after 40–60min. Labelled Zn was then detected in the stem, followed bythe leaves. The oldest and youngest leaves received less ⁶⁵Znthan the second and third oldest leaves. The plants grown underlow Zn conditions accumulated more ⁶⁵Zn in their older leavesand transferred ⁶³Zn to the unexposed roots. Distribution of⁵⁴Mn was similar in the controls to that of ⁶⁵Zn, except theolder leaves received no HMn, At the second harvest, a similardistribution pattern of ⁶⁵Zn and ⁵⁴Mn was observed with regardto leaf age. Large amounts of ⁶⁵Zn and ⁵⁴Mn were detected withinthe unexposed roots of all treatments. It is suggested thatthe distribution of root-supplied Zn and Mn may be determinedby micronutrient status and its relationship with leaf transpirationrates. Key words: Distribution, manganese, vegetative growth, wheat, zinc     

The cellular pathway of postphloem sugar transport in developing tomato fruit

The cellular pathway of postphloem sugar transport was elucidated in the outer pericarp of tomato (Lycopersicon esculentum Mill cv. Floradade) fruit at 13–14 and 23–25 days after anthesis (DAA). These developmental stages are characterized by phloem-imported sugars being accumulated as starch and hexose, respectively. The symplasmic tracer, 5(6)-carboxyfluorescein, loaded into the storage parenchyma cells of pericarp discs, moved readily in the younger fruit but was immobile in fruit at 23–25 DAA. Symplasmic mobility of [¹⁴C]glucose was found to be identical to 5(6)-carboxyfluorescein. For the older fruit, the pericarp apoplasm was shown to be freely permeable to the apoplasmic tracer, trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate. Indeed, the transport capacity of the pericarp apoplasm was such that the steady-state rate of in-vitro glucose uptake by pericarp discs accounted fully for the estimated rate of in-vivo glucose accumulation. For fruit at 23–25 DAA, the inhibitory effects of the sulfhydryl group modifier, p-chloromer-curibenzenesulfonic acid (PCMBS), on [¹⁴C]glucose and [¹⁴C]fructose uptake by the pericarp discs depended on the osmolality of the external solution. The inhibition was most pronounced for pericarp discs enriched in storage parenchyma. Consistent with the PCMBS study, strong fluorescent signals were exhibited by the storage parenchyma cells of pericarp discs exposed to the membrane-impermeable thiol-binding fluorochrome, mono-bromotrimethylammoniobimane. The fluorescent weak acid, sulphorhodamine G, was accumulated preferentially by the storage parenchyma cells. Accumulation of sulphorhodamine G was halted by the ATPase inhibitor erythrosin B, suggesting the presence of a plasma-membrane-bound H⁺-ATPase. A linkage between the putative H⁺-ATPase activity and hexose transport was demonstrated by an erythrosin-B inhibition of [¹⁴C]glucose and [¹⁴C]fructose uptake. In contrast, comparable evidence for an energy-coupled hexose porter could not be found in the pericarp of younger fruit at 13–14 DAA. Overall, the data are interpreted to indicate that: (i) The postphloem cellular pathway in the outer fruit pericarp shifts from the symplasm during starch accumulation (13–14 DAA) to the apoplasm for rapid hexose accumulation (23–25 DAA). (ii) An energy-coupled plasma-membrane hexose carrier is expressed specifically in storage parenchyma cells at the latter stage of fruit development.     

Influence of Etherel and Gibberellic Acid on Carbon Metabolism, Growth, and Essential Oil Accumulation in Spearmint (Mentha Spicata)

Changes in growth parameters and ¹⁴CO₂ and [U-¹⁴C]-sucrose incorporation into the primary metabolic pools and essential oil were investigated in leaves and stems of M. spicata treated with etherel and gibberellic acid (GA). Compared to the control, GA and etherel treatments induced significant phenotypic changes and a decrease in chlorophyll content, CO₂ exchange rate, and stomatal conductance. Treatment with etherel led to increased total incorporation of ¹⁴CO₂ into the leaves wheras total incorporation from ¹⁴C sucrose was decreased. When ¹⁴CO₂ was fed, the incorporation into the ethanol soluble fraction, sugars, organic acids, and essential oil was significantly higher in etherel treated leaves than in the control. However, [U-¹⁴C]-sucrose feeding led to decreased label incorporation in the ethanol-soluble fraction, sugars, organic acids, and essential oils compared to the control. When ¹⁴CO₂ was fed to GA treated leaves, label incorporation in ethanol-insoluble fraction, sugars, and oils was significantly higher than in the control. In contrast, when [U-¹⁴C]-sucrose was fed the incorporation in the ethanol soluble fraction, sugars, organic acids, and oil was significantly lower than in the control. Hence the hormone treatment induces a differential utilization of precursors for oil biosynthesis and accumulation and differences in partitioning of label between leaf and stem. Etherel and GA influence the partitioning of primary photosynthetic metabolites and thus modify plant growth and essential oil accumulation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Contrasting accumulation biokinetics and distribution of Am, Co, Cs, Mn and Zn during the whole development time of the eggs of the common cuttlefish, Sepia officinalis

Cuttlefish eggs were exposed to ²⁴¹Am, Co, Cs, Mn and Zn for different periods of time during the 50-d of the embryonic development at 17 °C. Exposures were carried out using background dissolved concentrations of the metals, using the corresponding γ-emitting radiotracers (²⁴¹Am, ⁵⁷Co, ¹³⁴Cs, ⁵⁴Mn and ⁶⁵Zn). Eggs were then placed in non-contaminating conditions. Experiments allowed assessing 1) the uptake and depuration kinetics of the selected elements and 2) their distribution among the different egg compartments (i.e. eggshell, vitellus, peri-vitelline fluid and embryo). ²⁴¹Am, Co and Zn were accumulated continuously by the eggs all along the development time, whereas Mn reached saturation after one month of exposure. Interestingly, the uptake kinetics of Cs tightly followed the weight variation of the eggs, mainly because of water influx/outflux. During the first month of the embryonic life, ²⁴¹Am, Co, Cs, Mn and Zn remained associated with the eggshell, indicating that the latter acted as an efficient shield against their penetration. Nevertheless, from this time onwards, Co, Cs, Mn and Zn accumulated more or less efficiently in the embryo according to the following order: Cs > Zn > Mn > Co. ²⁴¹Am was the only element tested that did not cross the eggshell all along the exposure time. The depuration kinetics revealed that the retention capacity of the eggs varied during the embryonic life. The contrasting accumulation biokinetics are discussed in terms of chemical and biological processes occurring during the cuttlefish egg development.     

Starch synthesis in developing wheat grain

The effect of light on the in-vivo rate of starch synthesis in the endosperm of developing wheat (Triticum aestivum cv. Mardler) grain was studied. Individual grains from spikelets grown on the same spike either in darkness or bright light showed no difference in their ability to accumulate radioactivity or to convert this to starch over a 14-h period. Similarly, there was no difference in final grain dry weight between spikes which had been kept in either darkness or normal light from 10 d post anthesis. In contrast, when half-grains (grain which had been bisected longitudinally along the crease region) were incubated by being submerged in culture solution (in vitro) the incorporation of [¹⁴C]sucrose into starch was stimulated by increased irradiance. Further experiments showed that the in-vitro dependence on light could be linked to the availability of oxygen. We suggest that in vitro the diffusion of oxygen into the endosperm cells combined with an increased rate of respiration of the tissue during the incubation causes this limitation. Thus the dependence of starch synthesis on light is an artefact of the in-vitro incubation system. The photosynthetic ability of the green pericarp tissue can be used to prevent the development of anoxia in the endosperm tissue of half-grains incubated in vitro. In conclusion, we propose that starch synthesis in vivo is not dependent on oxygen production by photosynthesis in the green layer of the pericarp.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - dpa days post anthesis - PCA perchloric acid     

The effect of cell turgor on sugar uptake in strawberry fruit cortex tissue

A reduction in cell turgor has been shown to stimulate sugar uptake in several plant sink tissues and it may regulate the import of assimilate into the sink apoplast, as well as maintain cell turgor. To determine whether cell turgor influences sugar uptake by strawberry (Fragaria x ananassa Duch. cv. Brighton) fruit cortex tissue, disks were cut from greenhouse-grown primary fruit at the green-white stage of development and placed in buffered incubation solutions containing either mannitol or ethylene glycol as an osmoticum. Cell turgor of fruit disks was calculated from the difference between the water potential of bathing solution and tissue solute potential after incubation at various osmolarities. Cell turgor increased when tissue disks were placed into mannitol incubation solutions more dilute than the water potential of fresh tissue (about 415 mOsmol kg^?1). The rate of uptake of [¹⁴C]-sucrose or [¹⁴C]-glucose decreased as osmolarity of the incubation solution increased, i.e. as cell turgor declined. Cell turgor and the rate of [¹⁴C]-sucrose uptake were unaffected when rapidly permeating ethylene glycol was used as an osmoticum. A decrease in cell turgor reduced both the V_max of the saturable (carrier mediated) kinetic component of sucrose uptake, and the slope of the linear (diffusional) component. The sulfhydryl binding reagent p-chloromercuibenzenesulfonic acid, an inhibitor of the plasma membrane sucrose carrier, strongly inhibited only the saturable component of sucrose uptake. Increased uptake of the nonmetabolizable sugar, O-methyl-glucose, at high turgor was similar to that of glucose, indicating that carrier activity was influenced by cell turgor, not cell metabolism. Turgor did not influence efflux of [¹⁴C]-sucrose from disks and had no effect on cell viability. Strawberry fruit cells do not possess a sugar uptake system that is stimulated by a reduction in turgor.     

Biosynthesis of lysine and other amino acids in the developing maize endosperm

Tracer studies with aspartic acid-[4-¹⁴C], alanine-[1-¹⁴C] acetate-[2-¹⁴C] and diaminopimelic acid-[1,(7)-¹⁴C] injected into the developing endosperm of maize revealed that the biosynthesis of lysine and other amino acids occurs in this organ. The data suggest that lysine is synthesized via the diaminopimelic acid pathway.     

Seed effects on gibberellin metabolism in pea pericarp

Pea fruit (Pisum sativum L.) is a model system for studying the effect of seeds on fruit growth in order to understand coordination of organ development. The metabolism of ¹⁴C-labeled gibberellin A₁₂ (GA₁₂) by pea pericarp was followed using a method that allows access to the seeds while maintaining pericarp growth in situ. Identification and quantitation of GAs in pea pericarp was accomplished by combined gas chromatography-mass spectrometry following extensive purification of the putative GAs. Here we report for the first time that the metabolism of [¹⁴C]GA₁₂ to [¹⁴C]GA₁₉ and [¹⁴C]GA₂₀ occurs in pericarp of seeded pea fruit. Removal of seeds from the pericarp inhibited the conversion of radiolabeled GA₁₉ to GA₂₀ and caused the accumulation of radiolabeled and endogenous GA₁₉. Deseeded pericarp contained no detectable GA₂₀, GA₁, or GA₈, whereas pericarp with seeds contained endogenous and radiolabeled GA₂₀ and endogenous GA₁. These data strongly suggest that seeds are required for normal GA biosynthesis in the pericarp, specifically the conversion of GA₁₉ to GA₂₀.     

The transport of substances out of developing fruits in relation to the induction of apical senescence in Pisum sativum line G2

Apical sencscence in G2 peas occurs only in long days in the presence of fruit. The effect of fruits could be caused by the export of a senescence hormone from the fruits to the shoot tip. Export of radiolabeled material from developing fruits of G2 peas grown in long days was therefore examined following injection of the pods with [¹⁴C]-sucrose, [¹⁴C]-acetate, or [¹⁴C]-mevalonate or after allowing the pods to photosynthesize in ¹⁴CO₂ for 48 h. In all cases a small amount (<1%) of radioactivity was exported, primarily to the younger fruits on the same side of the plant and the to the shoot apex. After feeding ¹⁴CO₂ to the fruit, the radiolabeled material partitioned into acidic ethyl acctate and possessed a carboxyl group. While this radioactivity had chromatographic properties similar to abscisic acid (ABA) in a number of solvent systems, it was not identical to either ABA, phascic acid or dihydrophaseic acid. The nature of the labeled material found in the apex was different in short days, in which senescence does not occur, or when the leaves were the source of the radioactive compounds. The labeled material in the apex was similar after feeding ¹⁴CO₂, [¹⁴C]-acctatc, or [¹⁴C]-sucrose, but different if the fruits were injected with[¹⁴C]-mevalonate.Identification of the chemical nature of the labeled material in the apex was not possible due to the small amount present. Parallel purification of an extract from treated fruits led to the identification of N-benzoylaspartate and N-phenylacetyl-aspartate. The radiolabeled substance from the apex was run with these two chemically synthesized compounds on several gas chromatogtaphic columns, and was also recrystallized together several times. The label and the pure material did not have identical retention times; neither did they co-purify so that, while similar, the material exported to the apex is not the above compounds.