Myo-Inositol Esters of Indole-3-acetic Acid as Seed Auxin Precursors of Zea mays L

Indole-3-acetyl-myo-inositol esters constitute 30% of the low molecular weight derivatives of indole-3-acetic acid (IAA) in seeds of Zea mays. [¹⁴C]Indole-3-acetyl-myo-inositol was applied to a cut in the endosperm of the seed and found to be transported from endosperm to shoot at 400 times the rate of transport of free IAA. The rate of transport of indole-3-acetyl-myo-inositol from endosperm to shoot was 6.3 picomoles per shoot per hour and thus adequate to serve as the seed auxin precursor for the free IAA diffusing downward from the shoot tip. Indole-3-acetyl-myo-inositol is the first seed auxin precursor to be identified.     

Purification and properties of Acid phosphatase from plump and shriveled seeds of triticale

A major triticale (X Triticosecale Wittmack) endosperm acid phosphatase (EC 3.1.2.2) (APase) from sib-lines producing plump and shriveled seed was purified 140- and 230-fold to a specific activity of 94 and 153 micromoles per minute per milligram protein respectively, by ammonium sulfate fractionation, ion-exchange chromatography, chromatofocusing, affinity column chromatography, and gel filtration. The purified enzyme from both materials is a monomeric glycoprotein with an apparent molecular weight of 45,700 ± 500 containing 12% carbohydrate and an apparent isoelectric point of pH 5.9. It hydrolyzes tri- and di-phosphate of nucleosides as well as phosphate esters and exhibits characteristics of ATP-hydrolase and phosphatase. About 2-fold more of the APase was isolated from shriveled seeds, and the purified enzyme exhibited 3- and 5-fold higher V_max for p-nitrophenyl phosphate and ATP, respectively, than that of plump seed. The I₅₀ for Pi concentration was 5.5-fold higher in APase of shriveled seed than the plump one. These varied quantitative and kinetic properties substantiate the role of APase in lines with shriveled seeds being reduction of starch accumulation by depleting substrates and energy supply in the cytosol.     

Phosphoenolpyruvate carboxylase activity and concentration in the endosperm of developing and germinating castor oil seeds

Monospecific polyclonal antibodies against maize leaf phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were utilized to examine the subunit composition and developmental profile of endosperm PEPC in developing and germinating castor oil seeds (Ricinus communis L. cv Baker 296). PEPC from developing endosperm consists of a single type of 100-kilodalton subunit, whereas the enzyme from 2- to 5-day germinated endosperm appears to contain equal proportions of immunologically related 103- and 108-kilodalton subunits. The maximal activity of PEPC in developing endosperms (2.67 micromoles oxaloacetate produced per minute per gram fresh weight) is approximately 20-fold and threefold greater than that of fully mature (dry seed) and germinating endosperms, respectively. The most significant increase in the activity and concentration of endosperm PEPC occurs during the middle cotyledon to full cotyledon stage of seed development; this period coincides with the most active phase of storage oil accumulation by ripening castor oil seeds. The data are compatible with the recent proposal (RG Smith, DA Gauthier, DT Dennis, DH Turpin [1992] Plant Physiol 1233-1238) that PEPC plays a fundamental role in vivo in the cytosolic production of an important substrate (malate) for fatty acid biosynthesis by developing castor oil seed leucoplasts. Immediately following seed imbibition, PEPC activity and concentration increase in parallel, with the greatest levels attained by the third day of germination. It is suggested that during this early phase of seed germination PEPC has a critical function to build up cellular dicarboxylic acid pools required to initiate significant activities of both the tricarboxylic acid and glyoxylate cycles.     

Degree of pectin methyl esterification in endosperm cell walls is involved in embryo bending in Arabidopsis thaliana

The endosperm is a transitory structure involved in proper embryo elongation. The cell walls of mature seed endosperm are generally composed of a uniform distribution of cellulose, unesterified homogalacturonans, and arabinans. Recent studies suggest that changes in cell wall properties during endosperm development could be related to embryo growth. The degree of methyl esterification of homogalacturonans may be involved in this endosperm tissue remodelling. The relevance of the degree of homogalacturonan methyl esterification during seed development was determined by immunohistochemical analyses using a panel of probes with specificity for homogalaturonans with different degrees of methyl esterification. Low-esterified and un-esterified homogalacturonans were abundant in endosperm cells during embryo bending and were also detected in mature embryos. BIDXII (BDX) could be involved in seed development, because bdx-1 mutants had misshapen embryos. The methyl esterification pattern described for WT seeds was different during bdx-1 seed development; un-esterified homogalacturonans were scarcely present in the cell walls of endosperm in bending embryos and mature seeds. Our results suggested that the degree of methyl esterification of homogalacturonans in the endosperm cell wall may be involved in proper embryo development.     

MG2+, K+-DEPENDENT PHOSPHATASE ACTIVITY DURING SEED DEVELOPMENT IN NICOTIANA TABACUM

Cation-dependent phosphatase activity was followed in developing Nicotiana tabacum (tobacco) seeds from pre-pollination to seed maturity. Enzyme activity increased rapidly up to 6 days post-pollination, then dropped off until 13 days after pollination. At 15 days post-pollination, enzyme activity had increased again, and at 17 days post-pollination, it reached its highest level. At 19 days post-pollination (seed maturity) enzyme activity was still 28% higher than that of the pre-pollination stage. Since the two peaks in enzyme activity correlate very highly with endosperm growth (first peak) and embryo growth (second peak), it is suggested that the Mg²⁺, K⁺-dependent phosphatase activity detected in this study is associated with the active transport of nutrients to the endosperm and embryo during seed development. The relatively high amount of enzyme activity remaining in the mature seed may represent a store of transport phosphatase that will be available for immediate use at the time of germination and early seedling growth.     

Characterization of the activity of fatty-acid epoxide hydrolase in seeds of castor bean (Ricinus communis L.)

Epoxide hydrolase (EC 3.3.2.3) activity was measured with [1-¹⁴C]cis-9,10-epoxystearic acid as the substrate. Homogenates were prepared from the endosperm tissue of germinating seeds of castor bean (Ricinus communis L. zanzibariensis). The activity of fatty-acid epoxide hydrolase was characterized with respect to dependence on time, amount of protein, pH and temperature. Analyses of enzyme distribution in endosperm, cotyledons, root and hypocotyl showed the highest total activity in the endosperm, less in the cotyledons and low activity in the root and hypocotyl. The specific activity was similar for cotyledons and endosperm. Analysis of the temporal expression of the enzyme in the endosperm during germination revealed high activity already in the imbibed seed. Activity was maximal between days four to six and then decreased at the end of one week. Subcellular fractionation of endosperm revealed a dual distribution of activity between the glyoxysomal and the cytosolic fractions.     

The role of phytic Acid in the wheat grain

The concentrations of adenosine triphosphate and phytic acid in testa, embryo plus scutellum, aleurone, and endosperm fractions from grain of Triticum vulgare cv. Insignia have been determined during development under both normal conditions and those of water stress. Phytic acid was not detected in the endosperm. In the embryo plus scutellum and aleurone fractions there was a rapid build-up of phytic acid, but the adenosine triphosphate level did not change markedly at this time. These results are not consistent with physiological roles previously suggested for phytic acid other than the role of phytin as a phosphorus and cation store for the germinating seed.     

Level of Abscisic Acid in Integuments, Nucellus, Endosperm, and Embryo of Peach Seeds (Prunus persica L. cv Springcrest) during Development

Free abscisic acid (ABA) in integuments, nucellus, endosperm, and embryo was determined throughout seed development of peach (Prunus persica L. cv Springcrest). Quantification of ABA was performed using combined high performance liquid chromatography-radioimmunoassay based on a monoclonal antibody raised against free (S)-ABA. In the integuments and endosperm, ABA concentration remained constant during the first 100 days after anthesis and rose in the following days when fresh weight was rapidly decreasing. In the nucellus, the ABA concentration variation pattern paralleled that of tissue growth. ABA concentration in the embryo increased constantly with the growth of the tissues to reach a maximum at the last growth stage. The role of ABA in peach seeds is discussed in relation to the development of the different seed tissues.     

Morphogenic studies in tissue cultures of the parasiteSantalum album L.

Whole seeds, excised embryos, and excised endosperm ofSantalum album were aseptically cultured with a view to studying seed germination in isolation from the host species, and to establishing callus cultures from both embryo and endosperm for comparative studies et their morphogenesis. Seed germination and seedling formation occurred normally only on modified White's medium supplemented with casein hydrolysate or coconut milk, or with both substances. Neither the excised embryo nor the endosperm grew on any of the culture media tested. However in about 17 per cent seed cultures on White's medium supplemented with 2,4-D, kinetin, and yeast extract, the endosperm degenerated, whereas the embryo callused and subsequently differentiated into innumerable embryoids; eventually the embryoids developed into normal plantlets. Callusing of the endosperm occurred also in seed cultures on four media supplemented variously with 2,4-D, kinetin, and yeast extract. Although the endosperm tissue grew through several passages no organ fornation was observed.     

Concentration and Metabolic Turnover of Indoles in Germinating Kernels of Zea mays L

The amounts and rates of metabolic turnover of the indolylic compounds in germinating kernels of sweet corn were determined. Knowledge of pool size and rate of pool turnover has permitted: (a) identification of indole-3-acetyl-myo-inositol as the major chemical form for transport of indole-3-acetic acid (IAA) from endosperm to shoot; (b) demonstration that the free IAA of the endosperm is turning over rapidly with a half-life of 3.2 hours; (c) identification of esters of IAA as the immediate precursors of IAA in the endosperm and shoot; (d) demonstration that neither tryptophan nor tryptamine is a major precursor of IAA for the seed or shoot; (e) identification of IAA-myo-inositol glycosides as precursors of IAA-myo-inositol.     

Seed development in Malpighiaceae species with an emphasis on the relationships between nutritive tissues

Malpighiaceae ovules have a well-developed nucellus; previous observations indicate that during seed development, the endosperm does not proliferate, thus, remaining scarce. This study aimed at identifying the nutritive tissues during seed development in Malpighiaceae, focusing especially on the endosperm. We analysed the seed development of Janusia mediterranea, J. occhionii, Mascagnia cordifolia, and Tetrapterys chamaecerasifolia, which were collected and processed by traditional methods for light microscopy. Ovules are subcampylotropous, crassinucellate and unitegmic in Janusia and bitegmic in M. cordifolia and T. chamaecerasifolia. The nucellus is well developed and protrudes through the micropyle, touching the funicular obturator. During development, a pachychalaza is formed, and the integuments coalesce in bitegmic species. Through a series of nucellar cell divisions, the perisperm is formed. In Janusia species, the endosperm is not produced. In M. cordifolia and T. chamaecerasifolia, the endosperm is nuclear, but it is scarce and ephemeral. The mature seed is exalbuminous, and the perisperm is consumed, and thus, the mature embryo is total. The absence of endosperm in Janusia is newly observed for the family and indicates functional transfer for the abundant perisperm.     

Ricinosomes provide an early indicator of suspensor and endosperm cells destined to die during late seed development in quinoa (Chenopodium quinoa)

Background and Aims

In mature quinoa (Chenopodium quinoa) seeds, the lasting endosperm forms a micropylar cone covering the radicle. The suspensor cells lie within the centre of the cone. During the final stage of seed development, the cells of the lasting endosperm accumulate protein and lipids while the rest are crushed and disintegrated. Both the suspensor and endosperm die progressively from the innermost layers surrounding the embryo and extending towards the nucellar tissue. Ricinosomes are endoplasmic reticulum-derived organelles that accumulate both the pro-form and the mature form of cysteine endopeptidase (Cys-EP), first identified in castor bean (Ricinus communis) endosperm during germination. This study sought to identify associations between the presence of ricinosomes and programmed cell death (PCD) hallmarks in suspensor and endosperm cells predestined to die during quinoa seed development.

Methods

A structural study using light microscopy and transmission electron microscopy was performed. To detect the presence of Cys-EP, both western blot and in situ immunolocalization assays were carried out using anti-R. communis Cys-EP antibody. A TUNEL assay was used to determine DNA fragmentation.

Results and Conclusions

Except for the one or two cell layers that constitute the lasting endosperm in the mature seed, ricinosomes were found in suspensor and endosperm cells. These cells were also the site of morphological abnormalities, including misshapen and fragmented nuclei, vesiculation of the cytosol, vacuole collapse and cell wall disorganization. It is proposed that, in suspensor and endosperm cells, the early detection of Cys-EP in ricinosomes predicts the occurrence of PCD during late seed development.     

Changes in the Strength of Lettuce Endosperm during Germination

The forces required to puncture intact lettuce (Lactuca sativa) seed and pericarp, endosperm and embryo were measured by the Instron Universal Testing Machine. It required about 0.6 newton to puncture the endosperm in seeds imbibed in the dark at 6, 12 and 24 hours. Endosperm of seeds imbibed in the light or in dark with gibberellic acid required about 4.2 newtons at 6 and at 12 hours and only about 0.15 newton at 24 hours. Forces required to puncture embryo at all treatments and times remained constant at about 0.3 newton. Changes in the strength of the endosperm do not appear to be related directly to protrusion of the radicle.     

Endogenous abscisic acid signaling towards storage reserve filling in developing seed tissues of castor bean (Ricinus communis L.)

Abscisic acid (ABA; free form) is a naturally occurring physiological growth hormone of higher plants. A detailed study involving the time course growth of developing seed tissues associated with endogenous levels of free ABA were investigated using a novel enzyme-linked immunosorbent assay. Seed filling in castor (Ricinuc communis L.) endosperm, embryo, and pod is marked with a rapid increase in fresh weight during the mid-developmental stages [21–42 days after pollination (DAP)], followed by a steady decline at the maturation stages (42–63 DAP) accompanied with a rapid lipid synthesis (in endosperm and embryo) during the same period, except for in pod. Endogenous ABA levels in endosperm (0.001–0.32 μg/g) and embryo (0.003–0.13 μg/g) followed a concurrent pattern with seed reserve filling, showing a rapid increase during the mid-developmental stages 21–42 DAP, whereas ABA levels in seed pod (0.2–22.9 μg/g) showed a different accumulation pattern with rapid increase and decline during the early-mid developmental stages, preceded by the maximal increase during the maturation stage (63 DAP). Together, our results provide evidence for the association of endogenous ABA in seed filling as well as in reserve deposition and provides clue for the effective usage of exogenous ABA concentrations in developing seeds with a focus, on improving seed reserve complex in castor.     

Effect of Deseeding on the Indole-3-acetic Acid Content of Shoots and Roots of Zea mays Seedlings

We wished to determine the effect of endosperm removal on the amounts of free and esterified indole-3-acetic acid (IAA) in young Zea mays seedlings. The increases of IAA derived from endosperm and from biosynthesis, but without correction for catabolic losses, were 0.9 picomole of free IAA per shoot per hour, and 1.1 picomoles per shoot per hour of ester IAA. After deseeding, free IAA in the shoot declines by 40% following kernel removal and total (free + ester) IAA declines at a rate of about 1 picomole per shoot per hour. A slight, but insignificant increase of ester IAA occurs following endosperm removal. In the primary roots, the decreases of free IAA and total (free + ester) IAA are accelerated by seed removal. Thus, the endosperm appears to be a major source of IAA for the shoot and root.