Castor Bean Seedlings Research Articles

An Active Sucrose Carrier (Scr1) that is Predominantly Expressed in the Seedling of Ricinus communis L.

During the germination of Ricinus communis seedlings sucrose is released from the endosperm and taken up by the cotyledons for their growth and for export to the rapidly growing hypocotyl and roots. Both the mesophyll cells and the phloem of castor bean possess active sucrose carriers. We isolated one of these carriers by heterologous screening with the spinach sucrose carrier cDNA for further investigation of sucrose transport at the cellular level. The deduced peptide sequence of this sucrose carrier (Scr1) has 12 putative membrane spanning domains and shares homology with other transporters of the major facilitator superfamily (MFS). When expressed in Saccharomyces cerevistae , Scr1 shows active sucrose transport that can be inhibited by PCMBS or CCCP. According to the pH-dependence the carrier seems related to SUC2 of Arabidopsis and Plantago , which are phloem-specific in these plants. It also shows a relatively high specificity for sucrose, compared with maltose or raffinose. Scr1 is expressed in equal amounts in all organs of a 6-day-old castor bean seedling and to a lesser extent in green sink and source leaves.

Plant histochemistry by correlation peak imaging.

Using a new NMR correlation-peak imaging technique, we were able to investigate noninvasively the spatial distribution of carbohydrates and amino acids in the hypocotyl of castor bean seedlings. In addition to the expected high sucrose concentration in the phloem area of the vascular bundles, we could also observe high levels of sucrose in the cortex parenchyma, but low levels in the pith parenchyma. In contrast, the glucose concentration was found to be lower in the cortex parenchyma than in the pith parenchyma. Glutamine and/or glutamate was detected in the cortex parenchyma and in the vascular bundles. Lysine and arginine were mainly visible in the vascular bundles, whereas valine was observed in the cortex parenchyma, but not in the vascular bundles. Although the physiological significance of these metabolite distribution patterns is not known, they demonstrate the potential of spectroscopic NMR imaging to study noninvasively the physiology and spatial metabolic heterogeneity of living plants.

Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings

Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings

Changes in the composition of globoids in castor bean cotyledons and endosperm during early seedling growth with and without complete mineral nutrients

AbstractThe endosperm and cotyledon tissues of Ricinus communis seeds and young seedlings were examined for changes in the mineral nutrient composition of globoids during early seedling growth. The effect on globoid composition of providing mineral nutrients to the developing seedling was also investigated. Globoids in endosperm and cotyledon tissues of castor bean seeds contained P, Mg and K, as well as trace amounts of Ca, Fe and Zn. Irrespective of the addition of mineral nutrients, K content in globoids of endosperm and cotyledon tissues declined significantly during initial seedling growth. During early seedling growth, amounts of Fe, Zn and Ca increased in cotyledon globoids. Ca contents of globoids of endosperm tissues also increased. The changes in Fe, Zn and Ca globoid contents were not influenced by providing mineral nutrients to growing castor bean seedlings.

Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings

The metal micronutrients (MN) copper, iron, manganese, and zinc are transported via the phloem in the course of remobilization and circulation. The extent of these processes and transport species are still largely unknown. The Ricinus seedling was used to study the transport of these metal micronutrients as well as their interactions with the plant‐endogenous chelator nicotianamine (NA) by daily measurements of the concentrations in the seedling parts and in the sieve tube sap obtained from a cut at the hypocotyl hook.The concentrations of these micronutrients in the phloem exudate decreased slightly from day 4 to day 8 of seedling development. Maximum values at day 4 were 65 μM for Zn, 63 μM for Fe, 27 μM for Cu, and 12 μM for Mn. The phloem transport rates reached maxima of 0.12 nmol cm−2h−1 for Zn and Fe at days 6 and 7, corresponding to the maximum exudation rates. The magnitude of these transport rates were in agreement with the net translocation rates estimated by analyses of the concentrations in the individual seedling parts.The NA content of the seedlings increased from day 0 (seed before sowing) until day 8, from 16 nmol to 474 nmol, which corresponds to an average net synthesis rate of about 100 nmol day−1 between the days 4 and 8. The NA:MN ratio was constant at 0.5 in the seedlings within this period. The NA concentrations and the sum of the concentrations of all four micronutrients in the sieve tube sap showed a constant ratio of 1.25 over the entire experimental period. Thus, both complex partners were subject to a cotransport in the phloem.Removal of the supplying endosperm led to a decrease in MN and NA concentrations in the sieve tube sap to about 80% while an average excess of NA of 1.1 was maintained. Since the concentrations of other amino acids, also possible chelators of metal micronutrients, fall to about 10% after removal of the endosperm, their role seems to be negligible as vehicles of MN transport in the phloem. Thus it is suggested that the divalent micronutrients considered in this study are loaded and maybe transported as NA complexes.

Growth, carbohydrates and associated invertase and amylase activities in castor bean and maize as affected by metribuzin and NaCl

Growth parameters (leaf area, length of shoot and root, water content and dry matter accumulation), contents of reducing sugars and saccharose as well as activities of α- and β-amylases of castor bean and maize seedlings and adult plants supplemented with 0.5 μg g-1 and 2.5 μg g-1 of metribuzin either alone or in combination with 50 μg g-1 NaCl, were increased significantly whereas at high concentrations (5 and 10 μg g-1) of herbicide, an opposite response was apparent. On the other hand, polysaccharide content and invertase activity of castor bean and maize seedlings and adult plants were significantly decreased in response to low concentrations (0.5 and 2.5 μg g-1) of metribuzin and increased significantly at high concentrations (5 and 10 μg g-1) of the herbicide either alone or in combination with 50 μg g-1 NaCl. Total carbohydrate contents of castor bean and maize seedlings and whole plants treated with herbicide either alone or in combination with NaCl did not change significantly. Growth parameters, carbohydrate fractions contents and activities of enzymes in both castor bean and maize seedlings and whole plants treated with herbicide alone were consistently higher than those values detected in plants treated with herbicide in combination with NaCl.

Effects of metribuzin herbicide on nitrogen, pigments, protease and nitrate reductase activity of normal and NaCl-stressed castor bean and maize plants

Addition of 0.5 and 2.5 gm-3 of metribuzin into Hoagland nutrient media, either alone or in combination with NaCl, induced significant decreases in nitrate-, amino-, ammonia-, and total soluble-N contents, whereas significant increases in these nitrogen fractions were apparent in maize and castor bean seedlings and plants treated with high concentrations (5 and 10 g m-3) of the herbicide, again either alone or in combination with NaCl. Protein- and total-N contents increased and decreased at low and high concentrations of the herbicide, respectively. The contents of chlorophyllsa andb, as well as carotenoids of both castor bean and maize seedlings and plants treated with low concentration of herbicide, either alone or supplemented with NaCl, were unaffected, whereas at high concentrations of the herbicide a significant decrease in chloroplast pigments was found. Nitrate reductase activity (NRA) was increased significantly at low concentrations of the herbicide alone and decreased significantly at high levels. Inclusion of NaCl into the herbicide media induced significant decreases in NRA of both castor bean and maize seedlings and plants. Unlike NRA changes, protease activity was increased significantly with high concentrations (5 and 10 g m-3) of metribuzin and decreased significantly with its low (0.5 and 2.5 g m-3) concentrations.

Gradients of Turgor, Osmotic Pressure, and Water Potential in the Cortex of the Hypocotyl of Growing Ricinus Seedlings

To evaluate the possible role of solute transport during extension growth, water and solute relations of cortex cells of the growing hypocotyl of 5-day-old castor bean seedlings (Ricinus communis L.) were determined using the cell pressure probe. Because the osmotic pressure of individual cells (pi(i)) was also determined, the water potential (psi) could be evaluated as well at the cell level. In the rapidly growing part of the hypocotyl of well-watered plants, turgor increased from 0.37 megapascal in the outer to 1.04 megapascal in the inner cortex. Thus, there were steep gradients of turgor of up to 0.7 megapascal (7 bar) over a distance of only 470 micrometer. In the more basal and rather mature region, gradients were less pronounced. Because cell turgor approximately pi(i) and psi approximately 0 across the cortex, there were also no gradients of psi across the tissue. Gradients of cell turgor and pi(i) increased when the endosperm was removed from the cotyledons, allowing for a better water supply. They were reduced by increasing the osmotic pressure of the root medium or by cutting off the cotyledons or the entire hook. If the root was excised to interrupt the main source for water, effects became more pronounced. Gradients completely disappeared and turgor fell to 0.3 megapascal in all layers within 1.5 hours. When excised hypocotyls were infiltrated with 0.5 millimolar CaCl(2) solution under pressure via the cut surface, gradients in turgor could be restored or even increased. When turgor was measured in individual cortical cells while pressurizing the xylem, rapid responses were recorded and changes of turgor exceeded that of applied pressure. Gradients could also be reestablished in excised hypocotyls by abrading the cuticle, allowing for a water supply from the wet environment. The steep gradients of turgor and osmotic pressure suggest a considerable supply of osmotic solutes from the phloem to the growing tissue. On the basis of a new theoretical approach, the data are discussed in terms of a coupling between water and solute flows and of a compartmentation of water and solutes, both of which affect water status and extension growth.

Organ-Specific Occurrence and Expression of the Isoforms of Nonspecific Lipid Transfer Protein in Castor Bean Seedlings, and Molecular Cloning of a Full-Length cDNA for a Cotyledon-Specific Isoform1

Four kinds of nonspecific lipid transfer proteins (nsLTP) were purified from different organs of castor bean (Ricinus communis L.) seedlings. Amino acid compositions and amino-terminal sequences of the four nsLTPs were determined and compared with those of castor bean isoforms, nsLTP-A, -B, and -C, previously reported [Takishima et al. (1986) Biochim. Biophys. Acta 870, 248-255; Takishima et al. (1988) Eur. J. Biochem. 177, 241-249]. Two isoforms from the cotyledons were identified as nsLTP-A and -C, one isoform from the endosperms as nsLTP-B, and the other was a new isoform from the axes. This new isoform was named nsLTP-D and its amino acid sequence was determined. These results demonstrated organ-specific occurrence of the nsLTP isoforms in castor bean seedlings. The isoforms nsLTP-A, -B, -C, and -D showed similar transfer activity not only for phosphatidylcholine and phosphatidylethanolamine but also for monogalactosyldiacylglycerol, although the homology among their amino acid sequences ranged from 70 to 30%. Two cDNA clones (pnsLTP-C and pnsLTP-D) for nsLTPs of castor bean seedlings were isolated and sequenced. pnsLTP-C was the cDNA clone for nsLTP-C expressed in the cotyledons, and pnsLTP-D was that for nsLTP-D in the axis. A coupled in vitro transcription-translation analysis of both cDNA clones revealed that pnsLTP-C encodes the full-length of nsLTP-C precursor (pro-nsLTP-C), while pnsLTP-D encodes a part of nsLTP-D precursor. PronsLTP-C contained a 24-amino acid pre-sequence preceding the mature nsLTP-C (92 amino acids).(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of plant peroxisomes in iso‐osmotic metrizamide

Methods were developed for isolating highly‐purified peroxisomes under iso‐osmotic conditions from 3 plant parts, namely cotyledons of cotton (Gossypium hirsutum L.) seedlings, endosperm of castor bean (Ricinus communis L.) seedlings and leaves of mature spinach (Spinaca oleracea L.) plants. Purification was achieved by sedimentation of the organelles into metrizamide gradients centrifuged in a vertical rotor (VTi 50). Gradients consisted of an upper transition layer (1:1 mixture of homogenizing medium and 0.25 M metrizamide), a linear 0.25–0.76 M metrizamide gradient and a 0.76 M metrizamide pad. Peroxisomes from all 3 plant parts were recovered in a major band at a density ranging from 1.24 to 1.27 g cm−3, which is a density range similar to that for peroxisomes isolated in sucrose gradients. The percent of the total gradient cytochrome c oxidase (mitochondria marker) activity recovered in peroxisome fractions ranged from 1.5% in endosperm to 2.8% in leaves, while a plastid marker (chlorophyll or galactosyl transferase activity) ranged from undetectable in leaf peroxisome fractions to 3.6% in endosperm peroxisome fractions. Intactness of the peroxisomes was judged to be 69%, 89% and 78% for the cotyledon, endosperm and leaf peroxisomes, respectively. Isolated peroxisomes were stable for at least 5 h in metrizamide medium. Microscopic (bright‐field and transmission electron microscopy) assessments verified that the peroxisomes were morphologically intact and fractions were essentially free of contaminating organelles. Metrizamide is an excellent iso‐osmotic medium for purifying peroxisomes from these plant organs and tissue.

Regulation of expression of the casbene synthetase gene during elicitation of castor bean seedlings with pectic fragments

A castor bean cDNA library has been constructed in the expression vector λgt11. Screening of 30,000 plaques with antibodies against casbene synthetase yielded six positive clones, from which three purified clones were obtained after sequential screening. The cDNA inserts in these clones ranged in size from 200 to 500 base pairs and were shown to share homologous sequences. One of the clones (pCS4) was examined in hybrid-selected and hybrid-arrested translation experiments and shown to contain a partial sequence of the casbene synthetase coding region. Northern analysis using the pCS4 clone as a probe revealed that the total hybridizable casbene synthetase mRNA amount increased to a maximum at 6 h after treatment of seedlings with pectic fragment elicitor and then decreased steadily with almost the same kinetics as observed previously for the changes in the translatable casbene synthetase mRNA activity under these same conditions. Run-on transcription experiments were performed with nuclei isolated from castor bean seedlings at various time periods after treatment with pectic fragment elicitors. Transcription of the casbene synthetase gene was first detected at 2 h after elicitation, rose to a maximum at 5 h, and fell rapidly thereafter. These results suggest that the accumulation of casbene synthetase, and hence casbene, is governed primarily by the rate of transcription of the casbene synthetase gene during elicitation by pectic fragments.

Biosynthesis of Nonspecific Lipid Transfer Proteins in Germinating Castor Bean Seeds

The biosynthesis of nonspecific lipid transfer proteins (ns-LTPs) in germinating castor bean (Ricinus communis L.) seeds were investigated. Lipid transfer activities of ns-LTPs in the cotyledons, axis, and endosperm increased with growth after germination. The activity increases were accompanied by increased amounts of ns-LTPs in each tissue, as measured by immunoblot using anti-ns-LTP serum. These results suggest that the ns-LTPs are synthesized de novo in each tissue after germination and not activated from inactive proteins synthesized before germination. Comparison of the immunoblot products in each tissue from 4-day-old seedlings indicate the occurrence of tissue-specific isoforms of ns-LTPs; 9 kilodaltons (major) and 7 kilodaltons (minor) in the cotyledons, and 7 kilodaltons (major) and 9 kilodaltons (minor) in the axis, whereas only the 8-kilodalton ns-LTP is present in the endosperm. In vitro translation from poly(A)(+) RNAs from three tissues of castor bean seedlings and the detection of immunoprecipitated products indicate that translatable mRNAs for ns-LTPs exist in the three tissues a day before the synthesis of ns-LTPs; the translation products, which are 3.5 to 4.0 kilodaltons larger than ns-LTPs, were processed to the mature ns-LTPs. The production of mature ns-LTPs from translatable mRNAs without any delay suggests that gene expression of ns-LTPs in castor bean seedlings is controlled at a step before the formation of translatable mRNAs.

Starch synthase and starch branching enzyme from germinating castor bean endosperm

Sucrose, but not starch, accumulates to high levels during fat utilization in young castor bean seedlings. High activities of starch synthase, starch branching enzyme and starch phosphorylase were present in the tissue but the very low ADPG pyrophosphorylase activity probably accounts for the low level of starch accumulation. DEAE-cellulose chromatography resolved a single ADPG starch synthase with both primed and citrate-stimulated (unprimed) activities. Three isozymes of branching enzyme were resolved, one co-eluting with starch synthase. ADPG and UDPG starch synthase activities were present in plastid-rich pellets (marker, RuBisCO). Treatment with {3-[(3-cholamido-propyl) dimethylammonio] 1-propane-sulphonate} (CHAPS) solubilized 75% of these activities. The remainder is attributed to starch granule-bound starch synthase. The effect of various glucan primers on the activities of soluble ADPG starch synthase and starch phosphorylase were determined.

Uptake of amino acids by plants from the soil: A comparative study with castor bean seedlings grown under natural and axenic soil conditions

Castor bean seedlings grown in different media (soil, quartz sand, or liquid culture) under natural or axenic conditions take up14C labelled proline when offered to the rooting medium at concentrations similar to those occuring in the soil. Most of the absorbed proline was transferred through the root into the xylem without metabolic conversion, though some conversion to glutamine and alamine occurred.

An Antibody to the Castor Bean Glyoxysomal Lipase (62 kD) also Binds to a 62 kD Protein in Extracts from Many Young Oilseed Plants

An antibody raised against purified glyoxysomal lipase (triacylglycerol hydrolase EC 3.1.1.3.) from castor bean (relative molecular weight of 62,000) also binds to a protein with a relative molecular weight of 62,000 in extracts of food reserve tissues from many young oilseed plants. These plants include Brassica napus L., Zea mays L., Arachis hypogaea L., Glycine max L., Gossipium hirsutum L., Cucurbita pepo L., Helianthus annuus L., Pisum sativum L., and Cicer arietinum L. The antibody caused inhibition of triacylglycerol hydrolysis by the lipases in extracts from seedlings of corn, oilseed rape, castor bean, soybean, and peanut. The pattern of antilipase binding to the 62 kilodalton protein in subcellular fractions from these other seedlings was consistent with the patterns of lipase activity reported in the literature and it is suggested that lipases from these oil seeds all have a subunit with a molecular weight of 62,000. The protein was only found in the food reserve tissues and was not present in extracts of roots and leaves of mature plants. In addition, the immunoreactive 62 kilodalton polypeptide was not detectable in lima beans and only at very low levels in kidney beans. Both these seeds are known to contain very little storage lipid and would not be expected to contain lipase. With the exception of the acid lipase of castor bean, ungerminated seeds do not generally contain active lipases. The immunoreactive 62 kilodalton protein could not be detected in the ungerminated seeds of most plants and only at very low low levels in others.

The effect of the embryo axis and exogenous sucrose on lipolysis and glyoxysomal enzyme development in Ricinus communis (castor bean) endosperm and cotyledons

Post‐germinative growth in castor bean (Ricinus communis L. cv. Hale) seedlings was investigated to determine whether lipolytic enzyme synthesis and lipid breakdown was a function of the embryo axis or simply based on a source‐sink mechanism connected with sucrose produced during mobilization of storage lipid. Endosperm and cotyledons were excised from the embryo axis at 24 h intervals and were then incubated in Petri dishes containing water or 0.1 M sucrose for 24 h. Excised endosperm showed similar or higher malate synthase (MS, EC 4.1.3.2) and isocitrate lyase (ICL, EC 4.1.3.1) activities and increased lipolysis when compared with endosperm obtained from similarly intact seedlings of the same age. In contrast, cotyledonary ICL and MS activity was up to 50% lower and lipolysis was only slightly affected in excised material when compared with cotyledons obtained from intact seedlings. Incubating endosperm in sucrose had no effect on the development of the above enzyme activities or lipid content, when compared with material incubated in water only. In contrast, cotyledonary MS and ICL activities were up to 70% lower in sucrose and lipolysis substantially inhibited. Lipid breakdown and the development of lipolytic enzyme activity in cotyledons seem to be dependent on the presence of the endosperm. It is concluded that enzyme regulation in castor bean seedlings cannot entirely be explained by axis control or source‐sink relationships.

Biosynthesis of the Macrocyclic Diterpene Casbene in Castor Bean (Ricinus communis L.) Seedlings

Casbene is a macrocyclic diterpene hydrocarbon that is produced in young castor bean (Ricinus communis L.) seedlings after they are exposed to Rhizopus stolonifer or other fungi. The activities of enzymes that participate in casbene biosynthesis were measured in cell-free extracts of 67-hour castor bean seedlings (a) that had been exposed to R. stolonifer spores 18 hours prior to the preparation of extracts, and (b) that were maintained under aseptic conditions throughout. Activity for the conversion of mevalonate to isopentenyl pyrophosphate does not change significantly after infection. On the other hand, the activities of farnesyl pyrophosphate synthetase (geranyl transferase), geranylgeranyl pyrophosphate synthetase (farnesyl transferase), and casbene synthetase are all substantially greater in infected tissues in comparison with control seedlings maintained under sterile conditions. The subcellular localization of these enzymes of casbene biosynthesis was investigated in preparations of microsomes, mitochondria, glyoxysomes, and proplastids that were resolved by centrifugation in linear and step sucrose density gradients of homogenates of castor bean endosperm tissue from both infected and sterile castor bean seedlings. Isopentenyl pyrophosphate isomerase and geranyl transferase activities are associated with proplastids from both infected and sterile seedlings. Significant levels of farnesyl transferase and casbene synthetase are found only in association with the proplastids of infected tissues and not in the proplastids of sterile tissues. From these results, it appears that at least the last two steps of casbene biosynthesis, geranylgeranyl pyrophosphate synthetase and casbene synthetase, are induced during the process of infection, and that the enzymes responsible for the conversion of isopentenyl pyrophosphate to casbene are localized in proplastids.

Biosynthesis of the Macrocyclic Diterpene Casbene in Castor Bean (Ricinus communis L.) Seedlings

FARNESYL TRANSFERASE (FARNESYL PYROPHOSPHATE: isopentenyl pyrophosphate farnesyl transferase; geranylgeranyl pyrophosphate synthetase) was purified at least 400-fold from extracts of castor bean (Ricinus communis L.) seedlings that were elicited by exposure for 10 h to Rhizopus stolonifer spores. The purified enzyme was free of isopentenyl pyrophosphate isomerase and phosphatase activities which interfere with prenyl transferase assays. The purified enzyme showed a broad optimum for farnesyl transfer between pH 8 and 9. The molecular weight of the enzyme was estimated to be 72,000 +/- 3,000 from its behavior on a calibrated G-100 Sephadex molecular sieving column. Mg(2+) ion at 4 millimolar gave the greatest stimulation of activity; Mn(2+) ion gave a small stimulation at 0.5 millimolar, but was inhibitory at higher concentrations. Farnesyl pyrophosphate (K(m) = 0.5 micromolar) in combination with isopentenyl pyrophosphate (K(m) = 3.5 micromolar) was the most effective substrate for the production of geranylgeranyl pyrophosphate. Geranyl pyrophosphate (K(m) = 24 micromolar) could replace farnesyl pyrophosphate as the allylic pyrophosphate substrate, but dimethylallyl pyrophosphate was not utilized by the enzyme. One peak of farnesyl transferase activity (geranylgeranyl pyrophosphate synthetase) and two peaks of geranyl transferase activity (farnesyl pyrophosphate synthetases) from extracts of whole elicited seedlings were resolved by DEAE A-25 Sephadex sievorptive ion exchange chromatography. These results suggest that the pathway for geranylgeranyl pyrophosphate synthesis in elicited castor bean seedlings involves the successive actions of two enzymes-a geranyl transferase which utilizes dimethylallypyrophosphate and isopentenyl pyrophosphate as substrates and a farnesyl transferase which utilizes the farnesyl pyrophosphate produced in the first step and isopentenyl pyrophosphate as substrates.

Glycoproteins in the Matrix of Glyoxysomes in Endosperm of Castor Bean Seedlings

The matrix of glyoxysomes from endosperm of castor bean (Ricinus communis cv Hale) seedlings has been analyzed for the presence of glycosylated proteins. Glyoxysome preparations were monitored for organelle homogeneity by electron microscopy and enzyme marker activities. Glyoxysomes were essentially free of endoplasmic reticulum, mitochondria, and protein bodies. At least eight glyoxysomal matrix glycopeptides ranging in size from 39 to 160 kilodaltons were identified by their affinity for concanavalin A. The glyoxysomal glycoproteins were shown to be radioactively labeled when endosperm was allowed to incorporate glucosamine. Incorporation of glucosamine was inhibited by tunicamycin under conditions which did not inhibit protein synthesis. Hydrolysis of glyoxysomal extracts and subsequent analysis by paper chromatography showed that the labeled precursor was incorporated into the glycoprotein without prior dispersion of the label into amino acids. The present data demonstrate the occurrence of N-linked, high mannose oligosaccharides on polypeptides of the glyoxysomal matrix. This finding is discussed in relation to pathways of protein maturation and transport during glyoxysomal biogenesis.

Lectins in Castor Bean Seedlings

The amounts of the two lectins (ricin and Ricinus communis agglutinin) in tissues of castor bean seedlings were followed during germination and early growth. For measurement, lectins in extracts were separately eluted from Sepharose columns; an antibody to the agglutinin was also used to detect the lectins by immunodiffusion. The endosperm of the dry seed contains 3.5 mg total lectin (5.6% of the total seed protein), which declines by 50% by day 4 and more rapidly thereafter as the tissue is completely consumed. The cotyledons of the dry seed also contain lectins but the amounts are less than 1% of those in the endosperm, and, as in the endosperm, they are constituents of the albumin fraction of the isolated protein bodies. No lectins were detected in the green cotyledons of 10-day seedlings that had been exposed to light from day 5. The embryonic axes of 2-day seedlings contained very small amounts of lectins but they were not detectable in the aerial parts of seedlings grown for 3 weeks or in cells from endosperm grown in tissue culture.The ability of proteinases and glycosidases (isolated from endosperm of 4-day seedlings) to hydrolyze the lectins was examined. No hydrolysis of the two lectins was observed, but the subunits, separated by reduction with 2-mercaptoethanol, were hydrolyzed slowly by a proteinase and some release of mannose was observed in the presence of the glycosidases. Ricin was converted to its subunits by cysteine and an enzyme in an endosperm extract accelerated chain separation by glutathione.