The interrelationship between the accumulation of lipids, protein and the level of acyl carrier protein during the development of Brassica napus L. pollen

RNA-Seq Highlights Molecular Events Associated With Impaired Pollen-Pistil Interactions Following Short-Term Heat Stress in Brassica napus

The global climate change is leading to increased frequency of heatwaves with crops getting exposed to extreme temperature events. Such temperature spikes during the reproductive stage of plant development can harm crop fertility and productivity. Here we report the response of short-term heat stress events on the pollen and pistil tissues in a commercially grown cultivar of Brassica napus. Our data reveals that short-term temperature spikes not only affect pollen fitness but also impair the ability of the pistil to support pollen germination and pollen tube growth and that the heat stress sensitivity of pistil can have severe consequences for seed set and yield. Comparative transcriptome profiling of non-stressed and heat-stressed (40°C for 30 min) pollen and pistil (stigma + style) highlighted the underlying cellular mechanisms involved in heat stress response in these reproductive tissues. In pollen, cell wall organization and cellular transport-related genes possibly regulate pollen fitness under heat stress while the heat stress-induced repression of transcription factor encoding transcripts is a feature of the pistil response. Overall, high temperature altered the expression of genes involved in protein processing, regulation of transcription, pollen-pistil interactions, and misregulation of cellular organization, transport, and metabolism. Our results show that short episodes of high-temperature exposure in B. napus modulate key regulatory pathways disrupted reproductive processes, ultimately translating to yield loss. Further investigations on the genes and networks identified in the present study pave a way toward genetic improvement of the thermotolerance and reproductive performance of B. napus varieties.

Deciphering the roles of acyl-CoA-binding proteins in plant cells

Lipid trafficking is vital for metabolite exchange and signal communications between organelles and endomembranes. Acyl-CoA-binding proteins (ACBPs) are involved in the intracellular transport, protection, and pool formation of acyl-CoA esters, which are important intermediates and regulators in lipid metabolism and cellular signaling. In this review, we highlight recent advances in our understanding of plant ACBP families from a cellular and developmental perspective. Plant ACBPs have been extensively studied in Arabidopsis thaliana (a dicot) and to a lesser extent in Oryza sativa (a monocot). Thus far, they have been detected in the plasma membrane, vesicles, endoplasmic reticulum, Golgi apparatus, apoplast, cytosol, nuclear periphery, and peroxisomes. In combination with biochemical and molecular genetic tools, the widespread subcellular distribution of respective ACBP members has been explicitly linked to their functions in lipid metabolism during development and in response to stresses. At the cellular level, strong expression of specific ACBP homologs in specialized cells, such as embryos, stem epidermis, guard cells, male gametophytes, and phloem sap, is of relevance to their corresponding distinct roles in organ development and stress responses. Other interesting patterns in their subcellular localization and spatial expression that prompt new directions in future investigations are discussed.

Epigenetic events in plant male germ cell heat stress responses

A review on pollen epigenetics. Plants grow in an ever-changing environment and are used to environmental fluctuations such as high and low temperatures during their life cycles. To cope with adverse conditions, plants have evolved intricate short-term and long-term mechanisms to respond and adapt to external stresses. The plant's ability to respond to stresses largely depends on its capacity to modulate the transcriptome rapidly and specifically. Epigenetic mechanisms, including DNA methylation, chromatin dynamics and small RNAs, play an essential role in the regulation of stress-responsive gene expression. Stress-related covalent modifications of DNA and histones can be passed on during mitosis and meiosis to the next generation and provide a memory that enables the plant and even its offspring to adopt better to a subsequent stress. Plant reproduction, in particular pollen development, is the most stress-sensitive process in the life cycle of the organism. In particular, developmental stages around the meiotic and mitotic divisions are the most vulnerable. In this review, we highlight the current understanding of epigenetic mechanisms involved in pollen development and speculate on their roles in pollen heat stress response.

Acyl-CoA-Binding Proteins (ACBPs) in Plant Development

Acyl-CoA-binding proteins (ACBPs) play a pivotal role in fatty acid metabolism because they can transport medium- and long-chain acyl-CoA esters. In eukaryotic cells, ACBPs are involved in intracellular trafficking of acyl-CoA esters and formation of a cytosolic acyl-CoA pool. In addition to these ubiquitous functions, more specific non-redundant roles of plant ACBP subclasses are implicated by the existence of multigene families with variable molecular masses, ligand specificities, functional domains (e.g. protein-protein interaction domains), subcellular locations and gene expression patterns. In this chapter, recent progress in the characterization of ACBPs from the model dicot plant, Arabidopsis thaliana, and the model monocot, Oryza sativa, and their emerging roles in plant growth and development are discussed. The functional significance of respective members of the plant ACBP families in various developmental and physiological processes such as seed development and germination, stem cuticle formation, pollen development, leaf senescence, peroxisomal fatty acid β-oxidation and phloem-mediated lipid transport is highlighted.

The binding versatility of plant acyl-CoA-binding proteins and their significance in lipid metabolism

Acyl-CoA esters are the activated form of fatty acids and play important roles in lipid metabolism and the regulation of cell functions. They are bound and transported by nonenzymic proteins such as the acyl-CoA-binding proteins (ACBPs). Although plant ACBPs were so named by virtue of amino acid homology to existing yeast and mammalian counterparts, recent studies revealed that ligand specificities of plant ACBPs are not restricted to acyl-CoA esters. Arabidopsis and rice ACBPs also interact with phospholipids, and their affinities to different acyl-CoA species and phospholipid classes vary amongst isoforms. Their ligands also include heavy metals. Interactors of plant ACBPs are further diversified due to the evolution of protein-protein interacting domains. This review summarizes our current understanding of plant ACBPs with a focus on their binding versatility. Their broad ligand range is of paramount significance in serving a multitude of functions during development and stress responses as discussed herein. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Plant Cytosolic Acyl-CoA-Binding Proteins

A gene family encoding six members of acyl-CoA-binding proteins (ACBP) exists in Arabidopsis and they are designated as AtACBP1-AtACBP6. They have been observed to play pivotal roles in plant lipid metabolism, consistent to the abilities of recombinant AtACBP in binding different medium- and long-chain acyl-CoA esters in vitro. While AtACBP1 and AtACBP2 are membrane-associated proteins with ankyrin repeats and AtACBP3 contains a signaling peptide for targeting to the apoplast, AtACBP4, AtACBP5 and AtACBP6 represent the cytosolic forms in the AtACBP family. They were verified to be subcellularly localized in the cytosol using diverse experimental methods, including cell fractionation followed by western blot analysis, immunoelectron microscopy and confocal laser-scanning microscopy using autofluorescence-tagged fusions. AtACBP4 (73.2 kDa) and AtACBP5 (70.1 kDa) are the largest, while AtACBP6 (10.4 kDa) is the smallest. Their binding affinities to oleoyl-CoA esters suggested that they can potentially transfer oleoyl-CoA esters from the plastids to the endoplasmic reticulum, facilitating the subsequent biosynthesis of non-plastidial membrane lipids in Arabidopsis. Recent studies on ACBP, extended from a dicot (Arabidopsis) to a monocot, revealed that six ACBP are also encoded in rice (Oryza sativa). Interestingly, three small rice ACBP (OsACBP1, OsACBP2 and OsACBP3) are present in the cytosol in comparison to one (AtACBP6) in Arabidopsis. In this review, the combinatory and distinct roles of the cytosolic AtACBP are discussed, including their functions in pollen and seed development, light-dependent regulation and substrate affinities to acyl-CoA esters.

Genome-wide survey and expression analysis of the putative non-specific lipid transfer proteins in Brassica rapa L

BACKGROUND

Plant non-specific lipid transfer proteins (nsLtps) are small, basic proteins encoded by multigene families and have reported functions in many physiological processes such as mediating phospholipid transfer, defense reactions against phytopathogens, the adaptation of plants to various environmental conditions, and sexual reproduction. To date, no genome-wide overview of the Brassica rapa nsLtp (BrnsLtp) gene family has been performed. Therefore, as the first step and as a helpful strategy to elucidate the functions of BrnsLtps, a genome-wide study for this gene family is necessary.

METHODOLOGY/PRINCIPAL FINDING

In this study, a total of 63 putative BrnsLtp genes were identified through a comprehensive in silico analysis of the whole genome of B. rapa. Based on the sequence similarities, these BrnsLtps was grouped into nine types (I, II, III, IV, V, VI, VIII, IX, and XI). There is no type VII nsLtps in B. rapa, and a new type, XI nsLtps, was identified in B. rapa. Furthermore, nine type II AtLtps have no homologous genes in B. rapa. Gene duplication analysis demonstrated that the conserved collinear block of each BrnsLtp is highly identical to those in Arabidopsis and that both segmental duplications and tandem duplications seem to play equal roles in the diversification of this gene family. Expression analysis indicated that 29 out of the 63 BrnsLtps showed specific expression patterns. After careful comparison and analysis, we hypothesize that some of the type I BrnsLtps may function like Arabidopsis pathogenesis-related-14 (PR-14) proteins to protect the plant from phytopathogen attack. Eleven BrnsLtps with inflorescence-specific expression may play important roles in sexual reproduction. Additionally, BrnsLtpI.3 may have functions similar to Arabidopsis LTP1.

CONCLUSIONS/SIGNIFICANCE

The genome-wide identification, bioinformatic analysis and expression analysis of BrnsLtp genes should facilitate research of this gene family and polyploidy evolution and provide new insight towards elucidating their biological functions in plants.

Genome-wide association study dissects the genetic architecture of oil biosynthesis in maize kernels

Maize kernel oil is a valuable source of nutrition. Here we extensively examine the genetic architecture of maize oil biosynthesis in a genome-wide association study using 1.03 million SNPs characterized in 368 maize inbred lines, including 'high-oil' lines. We identified 74 loci significantly associated with kernel oil concentration and fatty acid composition (P < 1.8 × 10(-6)), which we subsequently examined using expression quantitative trait loci (QTL) mapping, linkage mapping and coexpression analysis. More than half of the identified loci localized in mapped QTL intervals, and one-third of the candidate genes were annotated as enzymes in the oil metabolic pathway. The 26 loci associated with oil concentration could explain up to 83% of the phenotypic variation using a simple additive model. Our results provide insights into the genetic basis of oil biosynthesis in maize kernels and may facilitate marker-based breeding for oil quantity and quality.

Pollen vacuoles and their significance

Vacuoles of several types can be observed in pollen throughout its development. Their physiological significance reflects the complexity of the biological process leading to functional pollen grains. Vacuolisation always occurs during pollen development but when ripe pollen is shed the extensive translucent vacuoles present in the vegetative parts in previous stages are absent. Vacuole functions vary according to developmental stage but in ripe pollen they are mainly storage sites for reserves. Vacuoles cause pollen to increase in size by water accumulation and therefore confer some degree of resistance to water stress. Modalities of vacuolisation occur in pollen in the same manner as in other tissues. In most cases, autophagic vacuoles degrade organelles, as in the microspore after meiosis, and can be regarded as cytoplasm clean-up following the transition from the diploid sporophytic to the haploid gametophytic state. This also occurs in the generative cell but not in sperm cells. Finally, vacuoles have a function when microspores are used for pollen embryogenesis in biotechnology being targets for stress induction and afterwards contributing to cytoplasmic rearrangement in competent microspores.

Interaction of lipid bodies with other cell organelles in the maturing pollen of Magnolia x soulangeana (Magnoliaceae)

The pollen grain maturation in Magnolia x soulangeana was studied ultrastructurally and cytochemically using both the light and transmission electron microscope. Emphasis was given on the storage lipid bodies of the vegetative cell (VC) and their interaction with other cell organelles. Stereological analysis of electron micrographs was performed to evaluate the variation in volume density (V(V)), surface density, and surface-to-volume ratio (S/V) of various cell organelles during pollen maturation. The size and numerical density of the lipid bodies, and their frequency of association with other cell organelles, were also determined. It was noted that during pollen ontogeny and maturation, the lipid bodies changed their pattern of distribution in the VC cytoplasm, which may be a good marker for the succeeding stages of pollen development. Also, the size, osmiophily, and V(V) of the lipid bodies were progressively reduced during pollen maturation whereas the S/V was significantly increased. This seems to indicate that the lipid bodies are mobilized in part during this period of pollen maturation. In particular, the intermediate and mature pollen showed a high percentage of lipid bodies establishing a physical contact with either glyoxysomes, either protein storage vacuoles, or small vesicles presumably originated from dictyosomes. This physical contact was found in both the chemically fixed and rapid freeze-fixed pollen indicating that it is neither artifactual nor casual. On the basis of this intimate association with other cell organelles and the morphometric analysis performed, we suggest that the mobilization of lipid bodies is likely mediated not only by glyoxysomes but also by other catabolic pathways involving the interaction of lipid bodies with either protein storage vacuoles or small Golgi vesicles.

Characterization of a pollen-preferential gene, BAN102, from Chinese cabbage

We isolated and characterized a pollen-preferential gene, BAN102, from Chinese cabbage and analyzed the activity of its promoter. There were three or four copies of the BAN102 gene in the Chinese cabbage genome that specifically expressed in pollen and pollen tube. There were 2137 bp of BAN102 genomic clone comprising 186 bp of protein coding region, and 1178 bp of 5' and 773 bp of 3' non-coding regions. TATA box were located at 1071 nt of the promoter region while the polyadenylation signal and polyadenylation site were at 1470 and 1486 nt of the 3' non-coding region. BLAST search of BAN102 sequence showed that coding region of BAN102 gene was the greatest percent similarity with arabinogalactan protein (AGP23) gene from Arabidopsis thaliana. Promoter analysis using GUS gene as a reporter showed that the pollen-specificity of BAN102 resided within the -112 to -44 bp of proximal promoter from the transient expression in tobacco and Chinese cabbage plants.

Low temperature treatment at the young microspore stage induces protein changes in rice anthers

Male reproductive development in rice is very sensitive to various forms of environmental stresses including low temperature. A few days of cold treatment (<20 degrees C) at the young microspore stage induce severe pollen sterility and thus large grain yield reductions. To investigate this phenomenon, anther proteins at the early stages of microspore development, with or without cold treatment at 12 degrees C, were extracted, separated by two-dimensional gel electrophoresis, and compared. The cold-sensitive cultivar Doongara and the relatively cold-tolerant cultivar HSC55 were used. The abundance of 37 anther proteins was changed more than 2-fold after 1, 2, and 4 days of cold treatment in cv. Doongara. Among them, one protein was newly induced, 32 protein spots were up-regulated, and four protein spots were down-regulated. Of these 37 protein spots, we identified two anther-specific proteins (putative lipid transfer protein and Osg6B) and a calreticulin that were down-regulated and a cystine synthase, a beta-6 subunit of the 20 S proteasome, an H protein of the glycine cleavage system, cytochrome c oxidase subunit VB, an osmotin protein homologue, a putative 6-phosphogluconolactonase, a putative adenylate kinase, a putative cysteine proteinase inhibitor, ribosomal protein S12E, a caffeoyl-CoA O-methyltransferase, and a monodehydroascorbate reductase that were up-regulated. Identification of these proteins is available upon request. Accumulation of these proteins did not vary greatly after cold treatment in panicles of cv. Doongara or in the anthers of the cv. HSC55. The newly induced protein named Oryza sativa cold-induced anther protein (OsCIA) was identified as an unknown protein. The OsCIA protein was detected in panicles, leaves, and seedling tissues under normal growth conditions. Quantitative real time RT-PCR analysis of OsCIA mRNA expression showed no significant change between low temperature-treated and untreated plants. A possible regulatory role for the newly induced protein is proposed.

Agrobacterium-mediated transformation and generation of male sterile lines of Australian canola

An efficient protocol for Agrobacterium-mediated transformation of Australian commercial canola cultivars using seedling explants is described. Seedling explants provide flexibility and reduction in labour and maintenance costs of explant sources. Five commercial genotypes of canola were successfully transformed using the developed protocol. A transformation efficiency of 67% was obtained for genotypes Oscar and RK7 from cotyledon explants, which was higher than the rate for the most commonly used cultivar Westar (33%). Comparison of different seedling explants showed that although transgenic plants could be regenerated from all explant types (cotyledons, hypocotyls, and roots) used, the number of plants regenerated per explant type varied among the cultivars. Cotyledons produced the maximum number of transgenic shoots (RK7, RI25, Oscar, and Westar cultivars), whereas root explants produced the lowest numbers of shoots. Therefore, cotyledons and hypocotyls can be considered as ideal explants for the Agrobacterium-mediated transformation of these Australian canola cultivars. Integration and expression of the introduced transgene were analysed by DNA gel blot, leaf disc test, and GUS expression assays. Analysis of progeny showed that the transgene was stably inherited. The possibility of producing male sterile lines using an antisense approach was also explored. For this, Bcp1, a gene shown to be vital for viable pollen development, was targetted. Pollen ablation and lack of seed set were observed in the transgenic plants. Histochemical tests showed an intact tapetum layer and well developed pollen in control plants, whereas degraded tapetum and ablated pollen were noted in the transgenic plants. These results indicate that it is possible to generate stable transgenic male-sterile lines of canola using this strategy.

Novel patterns of ectopic cell plate growth and lipid body distribution in the Arabidopsis gemini pollen1 mutant

The nature of aberrant gametophytic cell divisions and altered pollen cell fate in the gemini pollen1 (gem1) mutant was investigated through ultrastructural analysis. The earliest noticeable defect in gem1 was the appearance of extended membrane profiles at the early bicellular stage. These were replaced by ectopic internal walls, which divided the cytoplasm into twin or multiple cell compartments. Complete or partial internal walls were callosic with highly complex profiles, indicating failed guidance or deregulated cell plate growth. Extended membrane profiles and delayed callose synthesis at division sites further suggested a novel pattern of cell plate assembly in gem1. Multiple cell compartments in gem1 adopted vegetative cell fate with regard to lipid body distribution. In the wild type, lipid bodies appear specifically in the vegetative cell, whereas in gem1, lipid bodies accumulated in all cytoplasmic compartments. Our results support the hypothesis that altered pollen cell fate in gem1 results from abnormal inheritance of cell fate determinants as a result of disturbed cytokinesis.

Brassicaceae express multiple isoforms of biotin carboxyl carrier protein in a tissue-specific manner

Plastidial acetyl-coenzyme A carboxylase from most plants is a multi-enzyme complex comprised of four different subunits. One of these subunits, the biotin carboxyl carrier protein (BCCP), was previously proposed to be encoded by a single gene in Arabidopsis. We report and characterize here a second Arabidopsis BCCP (AtBCCP2) cDNA with 42% amino acid identity to AtBCCP1 and 75% identity to a class of oilseed rape (Brassica napus) BCCPs. Both Arabidopsis BCCP isoforms were expressed in Escherichia coli and found to be biotinylated and supported carboxylation activity when reconstituted with purified, recombinant Arabidopsis biotin carboxylase. In vitro translated AtBCCP2 was competent for import into pea (Pisum sativum) chloroplasts and processed to a 25-kD polypeptide. Extracts of Arabidopsis seeds contained biotinylated polypeptides of 35 and 25 kD, in agreement with the masses of recombinant AtBCCP1 and 2, respectively. AtBCCP1 protein was present in developing tissues from roots, leaves, flowers, siliques, and seeds, whereas AtBCCP2 protein was primarily expressed in 7 to 10 d-after-flowering seeds at levels approximately 2-fold less abundant than AtBCCP1. AtBCCP1 transcript reflected these protein expression profiles present in all developing organs and highest in 14-d leaves and siliques, whereas AtBCCP2 transcript was present in flowers and siliques. In protein blots, four different BCCP isoforms were detected in developing seeds from oilseed rape. Of these, a 35-kD BCCP was detected in immature leaves and developing seeds, whereas developing seeds also contained 22-, 25-, and 37-kD isoforms highly expressed 21 d after flowering. These data indicate that oilseed plants in the family Brassicaceae contain at least one to three seed-up-regulated BCCP isoforms, depending upon genome complexity.

Ultrastructural characterization of male sterile33 (ms33) mutant in Arabidopsis affected in pollen desiccation and maturation

The MS33 gene in Arabidopsis is required for stamen filament growth and for pollen maturation. The objective of this study was to characterize the effects of ms33 mutation on pollen development at the ultrastructural level. There were no differences between the wild type and ms33 mutant pollen development before the first mitotic division of microspores. At the bicellular pollen stage, the first signs of abnormalities were observed in the ms33 tapetum, which started to degenerate early and released osmiophilic material in the anther locule. In ms33 pollen, the endintine was thicker, and exintine thinner, than in the wild type, and the mutant pollen had large vacuoles. Later in development, the mutant pollen underwent second mitosis and produced two normal-looking sperm cells; however, the intine was precociously formed, and there were abnormalities in tryphine deposition on the pollen wall, in the size of vacuoles, and in the formation of lipid bodies in the vegetative cell cytoplasm. Based on these observations it is suggested that mutation in the MS33 gene interferes with intine formation and tryphine deposition, both of which negatively affect pollen desiccation resulting in large, highly vacuolate pollen that are nonviable.Key words: Arabidopsis, male sterility, mutant, pollen, tapetum, ultrastructure.

Characterization of MZm3-3, a Zea mays tapetum-specific transcript

A cDNA, MZm3-3, was isolated by differential screening of a cDNA library from Zea mays meiotic stage anthers against cDNA of 3-week-old seedlings. Characterization of this cDNA indicated that the MZm3-3 gene is expressed specifically during male gametogenesis. Its expression is highly and preferentially detected in the tapetum, from the pollen mother cell to uninucleated microspore stages. It encodes a short alkaline protein of 10.6 kDa, with a conserved pattern of eight cysteine residues. Sequence analysis showed that these features are shared with lipid transfer proteins and some male-flower-specific proteins. The presence of a putative signal peptide indicates that MZm3-3 enters into the secretory pathway to then be released into the anther loculus. Based on these features, the secretory activity of the tapetum and the temporal expression pattern of MZm3-3, a contribution to pollen coat formation is suggested. Southern blot analyses demonstrated the presence of closely related genes, indicating that MZm3-3 belongs to a multigene family.

Molecular cloning of a cDNA encoding a pollen extracellular protein as a potential source of a pollen allergen in Brassica rapa

A polyclonal antiserum was raised against the extracellular pollen proteins of Brassica rapa and used for screening the expression cDNA libraries made from immature anthers. We obtained five groups of cDNA clones, including cDNAs similar to PCP1, thioredoxin, and lipid transfer protein (LTP). Recombinant protein of the cDNA clone showing sequence similarity to LTP was demonstrated to bind IgE of a patient allergic to Brassica pollen. The cDNA clone reported here, therefore, represents a novel pollen allergen of Brassica rapa.

A cDNA clone encoding an IgE-binding protein from Brassica anther has significant sequence similarity to Ca(2+)-binding proteins

Thirteen cDNA clones encoding IgE-binding proteins were isolated from expression libraries of anthers of Brassica rapa L. and B. napus L. using serum IgE from a patient who was specifically allergic to Brassica pollen. These clones were divided into two groups, I and II, based on the sequence similarity. All the group I cDNAs predicted the same protein of 79 amino acids, while the group II predicted a protein of 83 amino acids with microheterogeneity. Both of the deduced amino acid sequences contained two regions with sequence similarity to Ca(2+)-binding sites of Ca(2+)-binding proteins such as calmodulin. However flanking sequences were distinct from that of calmodulin or other Ca(2+)-binding proteins. RNA-gel blot analysis showed the genes of group I and II were preferentially expressed in anthers at the later developmental stage and in mature pollen. The recombinant proteins produced in Escherichia coli was recognized in immunoblot analysis by the IgE of a Brassica pollen allergic patient, but not by the Ige of a non-allergic patient. The cDNA clones reported here, therefore, represent pollen allergens of Brassica species.

Differential, temporal and spatial expression of genes involved in storage oil and oleosin accumulation in developing rapeseed embryos: implications for the role of oleosins and the mechanisms of oil-body formation

The temporal and spatial expression of oleosin and delta 9-stearoyl-ACP desaturase genes and their products has been examined in developing embryos of rapeseed, Brassica napus L. var. Topas. Expression of oleosin and stearate desaturase genes was measured by in situ hybridisation at five different stages of development ranging from the torpedo stage to a mature-desiccating embryo. The temporal pattern of gene expression varied dramatically between the two classes of gene. Stearate desaturase gene expression was relatively high, even at the torpedo stage, whereas oleosin gene expression was barely detectable at this stage. By the stage of maximum embryo fresh weight, stearate desaturase gene expression had declined considerably while oleosin gene expression was at its height. In contrast to their differential temporal expression, the in situ labelling of both classes of embryo-specific gene showed similar, relatively uniform patterns of spatial expression throughout the embryo sections. Immunogold labelling of ultra-thin sections from radicle tissue with anti-oleosin antibodies showed similar patterns to sections from cotyledon tissue. However, whereas at least three oleosin isoforms were detectable on western blots of homogenates from cotyledons, only one isoform was found in radicles. This suggests that some of the oleosin isoforms may be expressed differentially in the various types of embryo tissue. The differential timing of stearate desaturase and oleosin gene expression was mirrored by similar differences in the timing of the accumulation of their ultimate products, i.e. storage oil and oleosin proteins.(ABSTRACT TRUNCATED AT 250 WORDS)