Pedicel Tissues Research Articles

Morphological and genetic characterization of the muscadine fruit abscission zone.

Muscadines face limitations to fresh market production due to high manual labor costs. Mechanical harvesting holds promise for reducing the costs associated with muscadine production but requires cultivars with easily detached fruit at maturity. This study aimed to determine muscadine fruit and pedicel characteristics influencing fruit detachment force (FDF) and to unravel the genes, hormones, and regulatory networks governing muscadine abscission. We characterized the FDF of muscadine fruit across 18 genotypes and at four developmental stages. Following this, we performed a transcriptome analysis using the mature pedicel tissue of two genotypes, a genotype with high FDF at maturity and a genotype with low FDF at maturity, to identify differentially expressed and uniquely expressed genes contributing to fruit detachment. We found that pedicel length, pedicel-fruit junction area, and fruit diameter positively correlated with FDF. This study also identified novel candidate genes, transcription factor families, and pathways associated with muscadine fruit abscission. These findings provide valuable knowledge on the progression of fruit abscission and insights for reducing FDF, particularly in developing machine-harvestable muscadine cultivars and fostering sustainability and efficiency in muscadine production.

TDZ-induced two-step regeneration and histological analysis of morphogenesis from pedicel tissue of Rhododendron dauricum L., a semi-evergreen species

TDZ-induced two-step regeneration and histological analysis of morphogenesis from pedicel tissue of Rhododendron dauricum L., a semi-evergreen species

Pedicel anatomy and histology in tomato vary according to genotype and water-deficit environment, affecting fruit mass

The growth and composition of fleshy fruits depend on resource acquisition and distribution in the plant. In tomato, the pedicel serves as the final connection between plant and fruit. However, very few quantitative data are available for the conducting tissues of the pedicel, nor is their genetic variability known. In the present study, a histological approach was combined with process-based modeling to evaluate the potential contribution made by the anatomy and histology of the pedicel to variations in fruit mass. Eleven genotypes were characterized and the impact of water deficit was studied for a single genotype using stress intensity and stage of application as variables. The results highlighted extensive variations in the relative proportions of the different pedicel tissues and in the absolute areas of xylem and phloem between genotypes. The model suggests that the variations in the area of the pedicel’s vascular tissues induced by differences in genotype and water-deficit environments partly contributed to fruit mass variability. They therefore warrant phenotyping for use in the development of plant strains adapted to future environmental constraints. The results also demonstrated the need to develop non-invasive in vivo measurement methods to establish the number and size of active vessels and the flow rates in these vessels to improve prediction of water fluxes in plant architecture.

Hydrogen sulfide inhibits the abscission of tomato pedicel through reconstruction of a basipetal auxin gradient

Abscission is an important developmental process and an essential agricultural trait. Auxin and ethylene are two phytohormones with important roles in the complex, but still elusive signaling network of abscission. Here, we found that hydrogen sulfide (H2S), a newly identified gasotransmitter, inhibits the initiation of tomato pedicel abscission. The underlying mechanism was explored through transcriptome profile analysis in various pedicel tissues with or without H2S treatment in the early abscission stage. The data suggested that H2S strongly influences the global transcription of pedicel tissues, exerts differential expression regulation along the pedicel, and markedly influences both the auxin and ethylene signaling pathways. Computational analysis revealed that H2S reconstructs a basipetal auxin gradient along the pedicel at 4 h after treatment; this finding was further substantiated by the GUS-staining results of DR5::GUS pedicels. The inhibitory effect of H2S to the ethylene signaling pathway might be an indirect action. Moreover, the subtilisin-like proteinase family members involved in the release of peptide signal molecules are critical components of the abscission signaling network downstream of auxin and ethylene.

The role of the secondary phloem during the development of the grapevine Berry Shrivel ripening disorder

Berry Shrivel (BS) is a post-veraison physiological ripening disorder of grapevine berries. Its symptoms encompass low pH, reduced content of sugars and anthocyanins, and loss of turgor leading to berries shriveling. Evidence for the primary causes of BS is still speculative and anatomical studies are scarce. So far, anatomical studies have determined necrotic cells, degraded primary phloem cells and hardening of secondary phloem cells in the rachis of BS affected grapes. The picture is far from being complete. Herein we report in-depth analyses of the ultrastructure, anatomy and spatial elementary analysis of rachis and pedicel tissues of BS symptomatic grape clusters with different symptom severity. We hypothesize that structural changes in the vascular system of BS affected grape clusters could alter transport functions of the phloem tissue and contribute to the appearance of BS symptoms. By applying different microscopic techniques (LM, SEM, TEM and EDS) we found a number of anatomical differences in both, rachis and pedicels, between H and BS symptomatic grapes, which include: (i) extended areas of collapsed cells and cell wall thickenings in the secondary phloem in BS samples; (ii) reduced number of cell layers in the cambium in BS samples; (iii) higher rate of callose deposition on sieve plates that are additionally covered with a carbohydrate-like material in BS samples; and (iv) reduced (up to 60%) estimated sieve tube conductivity in BS samples.

Plant Thin Cell Layers: A 40-Year Celebration

The concept of a thin cell layer (TCL) was initially presented by Tran Thanh Van in two key papers exactly 40 years ago. At that time, Nicotiana tabacum was the model plant used to establish three main pathways for de novo organogenesis by developing a flower, vegetative bud, and root “programme” from pedicel tissue. Over the last 40 years, a wealth of research in plant tissue culture based on TCLs has emerged, fortifying the importance of this very simple technique, and highlighting its fundamental importance as a key tool in plant cell and tissue differentiation as well as organ development. This review not only highlights the achievements made using TCLs in the plant kingdom over these 40 years, it also reports on the success of this technique in ornamentals, fruit and forestry species, vegetables, and medicinal plants. There is overwhelming evidence of the importance of this technique for plant biotechnology, and it provides one solution for the mass clonal propagation of plants, use in bioreactors, genetic transformation, or micropropagation.

Transcriptome Analysis of Tomato Flower Pedicel Tissues Reveals Abscission Zone-Specific Modulation of Key Meristem Activity Genes

Tomato flower abscises at the anatomically distinct abscission zone that separates the pedicel into basal and apical portions. During abscission, cell separation occurs only at the abscission zone indicating distinctive molecular regulation in its cells. We conducted a transcriptome analysis of tomato pedicel tissues during ethylene promoted abscission. We found that the abscission zone was the most active site with the largest set of differentially expressed genes when compared with basal and apical portions. Gene Ontology analyses revealed enriched transcription regulation and hydrolase activities in the abscission zone. We also demonstrate coordinated responses of hormone and cell wall related genes. Besides, a number of ESTs representing homologs of key Arabidopsis shoot apical meristem activity genes were found to be preferentially expressed in the abscission zone, including WUSCHEL (WUS), KNAT6, LATERAL ORGAN BOUNDARIES DOMAIN PROTEIN 1(LBD1), and BELL-like homeodomain protein 1 (BLH1), as well as tomato axillary meristem genes BLIND (Bl) and LATERAL SUPPRESSOR (Ls). More interestingly, the homologs of WUS and the potential functional partner OVATE FAMILIY PROTEIN (OFP) were subsequently down regulated during abscission while Bl and AGL12 were continuously and specifically induced in the abscission zone. The expression patterns of meristem activity genes corroborate the idea that cells of the abscission zone confer meristem-like nature and coincide with the course of abscission and post-abscission cell differentiation. Our data therefore propose a possible regulatory scheme in tomato involving meristem genes that may be required not only for the abscission zone development, but also for abscission.

MACROCALYX and JOINTLESS Interact in the Transcriptional Regulation of Tomato Fruit Abscission Zone Development

Abscission in plants is a crucial process used to shed organs such as leaves, flowers, and fruits when they are senescent, damaged, or mature. Abscission occurs at predetermined positions called abscission zones (AZs). Although the regulation of fruit abscission is essential for agriculture, the developmental mechanisms remain unclear. Here, we describe a novel transcription factor regulating the development of tomato (Solanum lycopersicum) pedicel AZs. We found that the development of tomato pedicel AZs requires the gene MACROCALYX (MC), which was previously identified as a sepal size regulator and encodes a MADS-box transcription factor. MC has significant sequence similarity to Arabidopsis (Arabidopsis thaliana) FRUITFULL, which is involved in the regulation of fruit dehiscent zone development. The MC protein interacted physically with another MADS-box protein, JOINTLESS, which is known as a regulator of fruit abscission; the resulting heterodimer acquired a specific DNA-binding activity. Transcriptome analyses of pedicels at the preabscission stage revealed that the expression of the genes involved in phytohormone-related functions, cell wall modifications, fatty acid metabolism, and transcription factors is regulated by MC and JOINTLESS. The regulated genes include homologs of Arabidopsis WUSCHEL, REGULATOR OF AXILLARY MERISTEMS, CUP-SHAPED COTYLEDON, and LATERAL SUPPRESSOR. These Arabidopsis genes encode well-characterized transcription factors regulating meristem maintenance, axillary meristem development, and boundary formation in plant tissues. The tomato homologs were specifically expressed in AZs but not in other pedicel tissues, suggesting that these transcription factors may play key roles in pedicel AZ development.

Molecular Cloning and Expression of Phytoene Synthase, Lycopene Beta-cyclase, and Beta-carotene Hydroxylase Genes in Persimmon (Diospyros kaki L.) Fruits

Persimmon is not only an important fruit, which is eaten as a fresh fruit, but also traditionally used for many medicinal purposes, among which carotenoids contribute significantly to the color and nutritional value of persimmon fruit. Phytoene synthase (PSY), lycopene beta-cyclase (LCYB), and beta-carotene hydroxylase (BCH) are three important enzymes of carotenoid biosynthesis. In this study, cDNA and genomic sequences of DkPSY, DkLCYB, and DkBCH were isolated by rapid amplification of cDNA ends and polymerase chain reaction (PCR) using RNA and DNA isolated from the flesh tissues of persimmon used as template. Sequence analysis demonstrated that the individual cDNA and deduced proteins showed high identities to those of three carotenogenic cDNAs and proteins from other plants. Real-time quantitative PCR analysis revealed the tissue-specific expression patterns of DkPSY, DkLCYB, and DkBCH genes in fruit of persimmon, in which expression level of DkBCH was strongest among three genes analyzed. And, in different tissues, the expression level of peel tissue was higher than that of flesh and pedicel tissues.

Fuzzy Pedicel: A New Postharvest Disease of Banana.

Banana fruit of the Cavendish subgroup, Musa acuminata, are significant international commodities. Recently, a transnational company attempted to develop single fruit (fingers) as a product in the United States. In the summer of 2007, an unknown problem developed (hereafter, "fuzzy pedicel"), wherein mats of fluffy gray to white mycelial mats covered large portions of the pedicel surface of fruit when they were packed in gas-permeable containers. Fungi from two genera sporulated on examined pedicels: Sporothrix, which occurred on 72% of the affected pedicels, and Fusarium (6%); other fungi were sterile. From pedicel tissue, four genera of fungi were isolated on potato dextrose agar: Sporothrix and Fusarium and, less frequently, Pestalotiopsis and Nigrospora. Based on alignment with internal transcribed spacer and β-tubulin sequence data, the Sporothrix isolates were closely related to those in an environmental Ophiostoma/Sporothrix clade that contains Sporothrix stylites, S. humicola, and S. pallida but not the human pathogen S. schenkii. Based on EF1α gene sequences, four species in the Gibberella fujikuroi species complex (Fusarium proliferatum, F. pseudocircinatum, F. sacchari, and F. verticillioides) and two unnamed taxa in the F. incarnatum-equiseti species complex were identified. After artificial inoculation, representative Sporothrix and Fusarium isolates caused fuzzy pedicel symptoms on fruit of 'Grand Nain,' a commercial Cavendish cultivar. Fuzzy pedicel development was inhibited at 14°C (temperature at which fruit are shipped) but developed at 25°C (temperature at which fruit are marketed). Sporothrix isolates were insensitive to thiophanate-methyl fungicide in vitro and when used to treat pedicel surfaces prior to inoculation. Thus, it appears that benzimidazole fungicides would be ineffective as postharvest treatments for this problem. In summary, a new postharvest disease of banana, fuzzy pedicel, affects single fingers. It is caused by Sporothrix sp. and several species of Fusarium. Sporothrix spp. and F. pseudocircinatum have not been reported previously on banana.

A mutational approach to the study of seed development in maize

The maize seed comprises two major compartments, the embryo and the endosperm, both originating from the double fertilization event. The embryogenetic process allows the formation of a well-differentiated embryonic axis, surrounded by a single massive cotyledon, the scutellum. The mature endosperm constitutes the bulk of the seed and comprises specific regions containing reserve proteins, complex carbohydrates, and oils. To gain more insight into molecular events that underlie seed development, three monogenic mutants were characterized, referred to as emp (empty pericarp) on the basis of their extreme endosperm reduction, first recognizable at about 12 d after pollination. Their histological analysis reveals a partial development of the endosperm domains as well as loss of adhesion between pedicel tissues and the basal transfer layer. In the endosperm, programmed cell death (PCD) is delayed. The embryo appears retarded in its growth, but not impaired in its morphogenesis. The mutants can be rescued by culturing immature embryos, even though the seedlings appear retarded in their growth. The analysis of seeds with discordant embryo-endosperm phenotype (mutant embryo, normal endosperm and vice-versa), obtained using B-A translocations, suggests that emp expression in the embryo is necessary, but not sufficient, for proper seed development. In all three mutants the picture emerging is one of a general delay in processes related to growth, as a result of a mutation affecting endosperm development as a primary event.

The presence of oxalate in the pericarp and fruit pedicel is not linked to a shortage of fruit calcium and increase in cracking incidence in litchi

SummaryConcentrations of oxalate and calcium in soluble or structural forms, as calcium oxalate in the pericarp, or as oxalate in the fruit pedicel, and the distribution of calcium in the pericarp and fruit pedicel were studied in litchi (Litchi chinensis Sonn.) using cracking-resistant cv. ‘Huaizhi’ and cracking-susceptible cv. ‘Nuomici’. Oxalate in the pericarp existed mainly in a soluble form and was significantly (P < 0.05) higher in ‘Huaizhi’ than in ‘Nuomici’. The concentration of oxalate was higher than the amount of calcium oxalate. Calcium was first mobilised for the construction of cell walls in the pericarp, despite the high concentration of oxalate in the tissue. ‘Huaizhi’ fruit accumulated more structural calcium and calcium oxalate in the pericarp than ‘Nuomici’ fruit. There was no difference in soluble calcium between the two cultivars. Calcium oxalate was located chiefly in the epidermis of the pericarp, and increased in concentration within 50 d after anthesis (DAA) in ‘Nuomici’ and 64 DAA in ‘Huaizhi’, then decreased as structural calcium increased, indicating that calcium sequestered by oxalate could be remobilised.The fruit pedicel had higher concentrations of oxalate than the pericarp. X-ray microanalysis showed abundant calcium in pedicel tissue adjoining the fruit base, and less calcium in tissues at the fruit base and in pedicel tissue 1 cm from the fruit, suggesting that the pedicel serves as a bottleneck to calcium movement. This bottleneck is not likely to be caused by oxalate in the pedicel. Oxalate in the pericarp and in the fruit pedicel is not linked to a shortage of fruit calcium or to an increase in cracking incidence in litchi.

Seasonal Development of Ontogenic Resistance to Downy Mildew in Grape Berries and Rachises

ABSTRACT Clusters of Vitis vinifera and V. labrusca are reported to become resistant to Plasmopara viticola at stages of development ranging from 1 to 6 weeks postbloom. It has been suggested that resistance is associated with loss of the infection court as stomata are converted to lenticels, but the time of onset, cultivar variation, and seasonal variation in ontogenic resistance has remained uncertain, as has the comparative susceptibility of stem tissue within the fruit cluster. In New York, we inoculated clusters of V. vinifera cvs. Chardonnay and Riesling and V. labrusca cvs. Concord and Niagara at stages from prebloom until 5 to 6 weeks postbloom. Berries were infected and supported profuse sporulation until 2 weeks postbloom, and pedicel tissue remained susceptible until 4 weeks postbloom. Although berries on later-inoculated clusters failed to support sporulation, discoloration and necrosis of berry tissues was often noted, and necrosis of the pedicel within such clusters often led to further discoloration, shriveling, reduced size, or loss of berries. When the epidermis of discolored berries that initially failed to support sporulation was cut, the pathogen emerged and sporulated through incisions, indicating that lack of sporulation on older symptomatic berries was due to infection at an early stage of berry development followed by conversion of functional stomata to lenticels during latency. We repeated the study on Chardonnay and Riesling vines in South Australia and found that the period of berry and rachis susceptibility was greatly increased. The protracted susceptibility of the host was related to the increased duration and phenological heterogeneity of bloom and berry development in the warmer climate of South Australia. The time of onset and subsequent expression of ontogenic resistance to P. viticola may thus be modified by climate and should be weighed in transposing results from one climatic area to another. Our results can be used to refine forecast models for grapevine downy mildew to account for changes in berry and rachis susceptibility, and to focus fungicide application schedules upon the most critical periods for protection of fruit.

Pedicel development in Arabidopsis thaliana: Contribution of vascular positioning and the role of the BREVIPEDICELLUS and ERECTA genes

Although the regulation of Arabidopsis floral meristem patterning and determinacy has been studied in detail, very little is known about the genetic mechanisms directing development of the pedicel, the short stem linking the flower to the inflorescence axis. Here, we provide evidence that the pedicel consists of a proximal portion derived from the young flower primordium, and a bulged distal region that emerges from tissue at the bases of sepals in the floral bud. Distal pedicel growth is controlled by the KNOTTED1-like homeobox gene BREVIPEDICELLUS ( BP), as 35S::BP plants show excessive proliferation of pedicel tissue, while loss of BP conditions a radial constriction around the distal pedicel circumference. Mutant radial constrictions project proximally along abaxial and lateral sides of pedicels, leading to occasional downward bending at the distal pedicel. This effect is severely enhanced in a loss-of-function erecta ( er) background, resulting in radially constricted tissue along the entire abaxial side of pedicels and downward-oriented flowers and fruit. Analysis of pedicel vascular patterns revealed biasing of vasculature towards the abaxial side, consistent with a role for BP and ER in regulating a vascular-borne growth inhibitory signal. BP expression in a reporter line marked boundaries between the inflorescence stem and lateral organs and the receptacle and floral organs. This boundary expression appears to be important to prevent homeotic displacement of node and lateral organ fates into underlying stem tissue. To investigate interactions between pedicel and flower development, we crossed bp er into various floral mutant backgrounds. Formation of laterally-oriented bends in bp lfy er pedicels paralleled phyllotaxy changes, consistent with a model where the architecture of mutant stems is controlled by both organ positioning and vasculature patterns. Collectively, our results indicate that the BP gene acts in Arabidopsis stems to confer a growth-competent state that counteracts lateral-organ associated asymmetries and effectively radializes internode and pedicel growth and differentiation patterns.

Evidence of Programmed Cell Death in Post-Phloem Transport Cells of the Maternal Pedicel Tissue in Developing Caryopsis of Maize

We present cellular- and ultracellular-level studies here to show developmental programmed cell death (PCD) of placento-chalazal (P-C) cell layers in maternal pedicel tissue in developing caryopses of normal seed (Mn1) and in the invertase-deficient miniature (mn1) seed mutant in maize (Zea mays). PCD was evidenced by loss of nuclei and all subcellular membranous organizations in many P-C layers. The terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling (TUNEL) stain that is diagnostic of apoptotic-like PCD identified spatially and temporally two distinctive subdomains, which coincided with nucellar and integumental P-C layers based on their developmental origins. The early phase of PCD in the nucellar P-C was TUNEL negative and was specific to only the fertilized caryopses, indicating that the signaling for PCD in these maternal cells originated in the zygotic tissues. In fact, the initiation of PCD coincided with endosperm cellularization and was rapidly and coordinately completed prior to the beginning of the major storage phase in endosperm. Cell shape in these cell layers was also influenced by the genotype of filial endosperm. The later phase of PCD was restricted to the integumental P-C layers underneath the nucellar cells and was TUNEL positive in both genotypes. The two subdomains of the P-C layers were also distinguishable by unique cell wall-associated phenolic compounds. Based on collective evidence, we infer that the nucellar PCD may have osmolytic etiology and may lead to activation of the post-phloem transport function of the P-C layer, whereas the integumental PCD was senescent related, in particular, protecting the maturing seed against microbes that may be transported from the maternal tissue.

Orchid Biotechnology in Production and Improvement

Orchid Biotechnology in Production and Improvement

Identification and Characterization of Three Orchid MADS-Box Genes of the AP1/AGL9 Subfamily during Floral Transition

Gene expressions associated with in vitro floral transition in an orchid hybrid (Dendrobium grex Madame Thong-In) were investigated by differential display. One clone, orchid transitional growth related gene 7 (otg7), encoding a new MADS-box gene, was identified to be specifically expressed in the transitional shoot apical meristem (TSAM). Using this clone as a probe, three orchid MADS-box genes, DOMADS1, DOMADS2, and DOMADS3, were subsequently isolated from the TSAM cDNA library. Phylogenetic analyses show that DOMADS1 and DOMADS2 are new members of the AGL2 subfamily and SQUA subfamily, respectively. DOMADS3 contains the signature amino acids as with the members in the independent OSMADS1 subfamily separated from the AGL2 subfamily. All three of the DOMADS genes were expressed in the TSAM during floral transition and later in mature flowers. DOMADS1 RNA was uniformly expressed in both of the inflorescence meristem and the floral primordium and later localized in all of the floral organs. DOMADS2 showed a novel expression pattern that has not been previously characterized for any other MADS-box genes. DOMADS2 transcript was expressed early in the 6-week-old vegetative shoot apical meristem in which the obvious morphological change to floral development had yet to occur. It was expressed throughout the process of floral transition and later in the columns of mature flowers. The onset of DOMADS3 transcription was in the early TSAM at the stage before the differentiation of the first flower primordium. Later, DOMADS3 transcript was only detectable in the pedicel tissues. Our results suggest that the DOMADS genes play important roles in the process of floral transition.

Characterization of pedicel β‐glucuronidase activity in developing maize (Zea mays) kernels

A conspicuous endogenous maize (Zea mays L.) β‐glucuronidase (GUS) activity was observed in histochemical assays of non‐transformed maize kernels, confounding the use of Escherichia coli gusA as a reporter gene. Appearance of the endogenous activity was developmentally dependent and highly tissue‐specific, being localized to the upper pedicel (basal maternal kernel) tissues where the black layer forms in the latter stages of kernel development. Pedicel homogenates exhibited GUS activity using either p‐nitrophenyl‐β‐D‐glucuronide or 4‐methylumbelliferyl‐β‐D‐glucuronide (MUG) as substrates. Pedicel GUS was apparently not the result of endophyte contamination of enzyme isolates since no endophytes could be cultured. The MUG‐based activity had a pH optimum of 4 to 5 and was separable into two isoforms by anion exchange chromatography with Km values for MUG of 2.2 and 2.7 µM for the early‐ and late‐eluting forms, respectively. The pedicel GUS isoforms had very similar characteristics: native Mr of approximately 32000, stimulation by assay at 60°C, inhibition at high ionic strength or in the presence of EDTA and relative insensitivity to the E. coli GUS inhibitor saccharic acid‐1,4‐lactone. Only the early‐eluting form, however, was capable of hydrolyzing the histocbemical GUS substrate 5‐bromo‐4‐chloro‐3‐indoyl‐β‐D‐glucuronide. Neither isoform exhibited antifungal activity against Fusarium moniliforme. In contrast to the in vitro activity, pedicel endogenous GUS measured histochemically was completely inhibited by saccharic acid‐1,4‐lactone, unaffected by EDTA and greatly decreased by incubation at elevated assay temperature. A modification of the standard histochemical GUS assay allowed complete suppression of endogenous GUS activity while enhancing E. coli‐derived GUS activity in kernels transiently expressing the gusA gene. Possible roles of these endogenous GUS activities within the black layer region of the kernel pedicel are proposed.

Breaking Strength of Pedicel and Grain Shattering Habit in Two Species of Buckwheat (Fagopyrum spp.)

The grain shattering habit was examined in nine common buckwheat cultivars/strains (Fagopyrum esculentum Moench.) and four tartary buckwheat strains (F. tataricum Gaertner). As indices of grain shattering habit, the breaking bending strength and breaking tensile strength of the pedicel and the pedicel diameter were measured. Thin longitudinal pedicel sections were also observed. The breaking strength showed significant differences among cultivars, but the stage of seed maturity influenced the grain shattering habit. The two breaking strengths were larger in common buckwheat than in tartary buckwheat, and these differences may be explained by the pedicel diameter. The abscission layer was not observed in the pedicel tissue of the buckwheat cultivars.

Immunolocalization of a Unique Form of Maize Kernel Glutamine Synthetase Using a Monoclonal Antibody.

The pedicel (basal maternal tissue) of maize (Zea mays L.) kernels contains a physically and kinetically unique form of glutamine synthetase (GSp1) that is involved in the conversion of transport forms of nitrogen into glutamine for uptake by the developing endosperm (M.J. Muhitch [1989] Plant Physiol 91: 868-875). A monoclonal antibody has been raised against this kernel-specific GS that does not cross-react either with a second GS isozyme found in the pedicel or with the GS isozymes from the embryo, roots, or leaves. When used as a probe for tissue printing, the antibody labeled the pedicel tissue uniformly and also labeled some of the pericarp surrounding the lower endosperm. Silver-enhanced immunogold staining of whole-kernel paraffin sections revealed the presence of GSp1 in both the vascular tissue that terminates in the pedicel and the pedicel parenchyma cells, which are located between the vascular tissue and the basal endosperm transfer cells. Light staining of the subaleurone was also noted. The tissue-specific localization of GSp1 within the pedicel is consistent with its role in the metabolism of nitrogenous transport compounds as they are unloaded from the phloem.