Phytochrome induces changes in the immunodetectable level of a wall peroxidase that precede growth changes in maize seedlings

Red light-induced inhibition of maize (Zea mays) mesocotyl elongation: evaluation of apoplastic metabolites

Light is a crucial factor affecting plant growth and development. Besides providing the energy for photosynthesis, light serves as a sensory cue to control the adaptation of plants to environmental changes. We used the etiolated maize (Zea mays ) seedlings as a model system to study the red light-regulated growth. Exposure of the maize seedlings to red light resulted in growth inhibition of mesocotyls. We demonstrate for the first time (to the best our knowledge) that red light affected the patterns of apoplastic fluid (AF) metabolites extracted from the mesocotyl segments. By means of the untargeted gas chromatography-mass spectrometry (GC-MS)-based metabolomics approach, we identified 44 metabolites in the AF of maize mesocotyls and characterised the dynamics of their relative tissue abundances. The characteristic metabolite patterns of mesocotyls dominated with mono- and disaccharides, organic acids, amino acids, and other nitrogen-containing compounds. Upon red light irradiation, the contents of β -alanine, putrescine and trans -aconitate significantly increased (P -value<0.05). In contrast, there was a significant decrease in the total ascorbate content in the AF of maize mesocotyls. The regulatory role of apoplastic metabolites in the red light-induced inhibition of maize mesocotyl elongation is discussed.

APYRASE1/2 mediate red light-induced de-etiolation growth in Arabidopsis seedlings

In etiolated seedlings, red light (R) activates phytochrome and initiates signals that generate major changes at molecular and physiological levels. These changes include inhibition of hypocotyl growth and promotion of the growth of primary roots, apical hooks, and cotyledons. An earlier report showed that the sharp decrease in hypocotyl growth rapidly induced by R was accompanied by an equally rapid decrease in the transcript and protein levels of two closely related apyrases (APYs; nucleoside triphosphate-diphosphohydrolases) in Arabidopsis (Arabidopsis thaliana), APY1 and APY2, enzymes whose expression alters auxin transport and growth in seedlings. Here, we report that single knockouts of either APY inhibit R-induced promotion of the growth of primary roots, apical hooks, and cotyledons, and RNAi-induced suppression of APY1 expression in the background of apy2 inhibits R-induced apical hook opening. When R-irradiated primary roots and apical hook-cotyledons began to show a gradual increase in their growth relative to dark controls, they concurrently showed increased levels of APY protein, but in hook-cotyledon tissue, this occurred without parallel increases in their transcripts. In wild-type seedlings whose root growth is suppressed by the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the R-induced increased APY expression in roots was also inhibited. In unirradiated plants, the constitutive expression of APY2 promoted both hook opening and changes in the transcript abundance of Small Auxin Upregulated RNA (SAUR), SAUR17 and SAUR50 that help mediate de-etiolation. These results provide evidence that the expression of APY1/APY2 is regulated by R and that APY1/APY2 participate in the signaling pathway by which phytochrome induces differential growth changes in different tissues of etiolated seedlings.

2-DE-based proteomic analysis of protein changes associated with etiolated mesocotyl growth in Zea mays

Background

The mesocotyl connects the coleoptilar node and the basal part of the seminal root of maize (Zea mays) seedling. The mesocotyl pushes the shoot of the seedling out of the soil during seed germination; thus, its growth is highly related to deep-sowing tolerance. Although many studies on the maize mesocotyl have been carried out at physiological and molecular levels, the proteomic changes associated with cellular and physiological activities during mesocotyl growth are still unknown.

Results

In the present study, the maize hybrid Zhengdan 958 was used to study mesocotyl growth and accompanying protein changes. The dark-grown etiolated mesocotyls exhibited a slow-fast-slow feature, with significant changes in the levels of indole-3-acetic acid (IAA) and cellulose and the activity of peroxidase (POD). In particular, POD activity increased with mesocotyl growth, showing higher activity at the mature (lower) end of the mesocotyl. For the proteomic analysis, soluble proteins were extracted from etiolated mesocotyls dark-grown for 48 h, 84 h, and 132 h, corresponding to the initial, rapid, and slow growth periods, respectively, and subjected to separation by two-dimensional gel electrophoresis (2-DE). As a result, 88 differentially abundant proteins (DAPs) were identified using MALDI-TOF-TOF analysis. At 48 h, most DAPs were stress proteins, heat shock proteins and storage proteins; at 84 h, oxidation/reduction proteins, carbohydrate biogenesis-related proteins and cytoskeleton-related proteins were highly accumulated; at 132 h, the most striking DAPs were those involved in the synthesis and modification of the cell wall and the biogenesis of carbohydrates. Gene ontology (GO) analysis showed that changes in the abundance and proportion of DAPs were consistent with cellular and physiological activities and biological processes during mesocotyl growth. The accumulation of nine DAPs of interest was verified by immunoblotting and RT-qPCR.

Conclusions

The present study revealed that the protein patterns in 2-D gels differed greatly with mesocotyl growth. At different growth periods, a specific set of DAPs participate in various biological processes and underlie the cellular and physiological activities of the mesocotyl. These results contributed to the understanding of mesocotyl growth and the cultivation of maize lines with deep-sowing tolerance.

Involvement of calcium-mediated effects on ROS metabolism in the regulation of growth improvement under salinity

Salinity reduces Ca(2+) availability, transport, and mobility to growing regions of the plant and supplemental Ca(2+) is known to reduce salinity damages. This study was undertaken to unravel some of the ameliorative mechanisms of Ca(2+) on salt stress at the cellular and tissue levels. Zea mays L. plants were grown in nutrient solution containing 1 or 80 mM NaCl with various Ca(2+) levels. Measurements of growth and physiological parameters, such as ion imbalance, indicated that the Ca(2+)-induced alleviation mechanisms differed between plant organs. Under salinity, H(2)O(2) levels increased in the leaf-growing tissue with increasing levels of supplemental Ca(2+) and reached the levels of control plants, whereas superoxide levels remained low at all Ca(2+) levels, indicating that Ca(2+) affected growth by increasing H(2)O(2) but not superoxide levels. Salinity completely abolished apoplastic peroxidase activity. Supplemental Ca(2+) increased its activity only slightly. However, under salinity, polyamine oxidase (PAO) activity was shifted toward the leaf base probably as an adaptive mechanism aimed at restoring normal levels of reactive oxygen species (ROS) at the expansion zone where NADPH oxidase could no longer provide the required ROS for growth. Interestingly, addition of Ca(2+) shifted the PAO-activity peak back to its original location in addition to its enhancement. The increase in PAO activity in conjunction with low levels of apoplastic peroxidase is supportive of cellular growth via nonenzymatic wall loosening derived by the increase in H(2)O(2) and less supportive of the peroxidase-mediated cross-linking of wall material. Thus extracellular Ca(2+) can modulate ROS levels at specific tissue localization and developmental stages thereby affecting cellular extension.

Identification and Characterization of Cell Wall Proteins of a Toxic Dinoflagellate Alexandrium catenella Using 2-D DIGE and MALDI TOF-TOF Mass Spectrometry

The cell wall is an important subcellular component of dinoflagellate cells with regard to various aspects of cell surface-associated ecophysiology, but the full range of cell wall proteins (CWPs) and their functions remain to be elucidated. This study identified and characterized CWPs of a toxic dinoflagellate, Alexandrium catenella, using a combination of 2D fluorescence difference gel electrophoresis (DIGE) and MALDI TOF-TOF mass spectrometry approaches. Using sequential extraction and temperature shock methods, sequentially extracted CWPs and protoplast proteins, respectively, were separated from A. catenella. From the comparison between sequentially extracted CWPs labeled with Cy3 and protoplast proteins labeled with Cy5, 120 CWPs were confidently identified in the 2D DIGE gel. These proteins gave positive identification of protein orthologues in the protein database using de novo sequence analysis and homology-based search. The majority of the prominent CWPs identified were hypothetical or putative proteins with unknown function or no annotation, while cell wall modification enzymes, cell wall structural proteins, transporter/binding proteins, and signaling and defense proteins were tentatively identified in agreement with the expected role of the extracellular matrix in cell physiology. This work represents the first attempt to investigate dinoflagellate CWPs and provides a potential tool for future comprehensive characterization of dinoflagellate CWPs and elucidation of their physiological functions.

Phosphorus nutrition and mycorrhiza effects on grass leaf growth. P status- and size-mediated effects on growth zone kinematics

This study tested whether leaf elongation rate (LER, mm h(-1)) and its components--average relative elemental growth rate (REGRavg, mm mm(-1) h(-1)) and leaf growth zone length (L(LGZ), mm)--are related to phosphorus (P) concentration in the growth zone (P(LGZ) mg P g(-1) tissue water) of Lolium perenne L. cv. Condesa and whether such relationships are modified by the arbuscular mycorrhizal fungus (AMF) Glomus hoi. Mycorrhizal and non-mycorrhizal plants were grown at a range of P supply rates and analysed at either the same plant age or the same tiller size (defined by the length of the sheath of the youngest fully expanded leaf). Both improved P supply (up to 95%) and AMF (up to 21%) strongly increased LER. In tillers of even-aged plants, this was due to increased REGRavg and L(LGZ). In even-sized tillers, it was exclusively due to increased REGRavg. REGRavg was strictly related to P(LGZ) (r2 = 0.95) and independent of tiller size. Conversely, L(LGZ) strictly depended on tiller size (r2 = 0.88) and not on P(LGZ). Hence, P status affected leaf growth directly only through effects on relative tissue expansion rates. Symbiosis with AMF did not modify these relationships. Thus, no evidence for P status-independent effects of AMF on LER was found.

Two cell wall associated peroxidases from Arabidopsis influence root elongation

Two class III peroxidases from Arabidopsis, AtPrx33 and Atprx34, have been studied in this paper. Their encoding genes are mainly expressed in roots; AtPrx33 transcripts were also found in leaves and stems. Light activates the expression of both genes in seedlings. Transformed seedlings producing AtPrx33-GFP or AtPrx34-GFP fusion proteins under the control of the CaMV 35S promoter exhibit fluorescence in the cell walls of roots, showing that the two peroxidases are localized in the apoplast, which is in line with their affinity for the Ca(2+)-pectate structure. The role they can play in cell wall was investigated using (1) insertion mutants that have suppressed or reduced expression of AtPrx33 or AtPrx34 genes, respectively, (2) a double mutant with no AtPrx33 and a reduced level of Atprx34 transcripts, (3) a mutant overexpressing AtPrx34 under the control of the CaMV 35S promoter. The major phenotypic consequences of these genetic manipulations were observed on the variation of the length of seedling roots. Seedlings lacking AtPrx33 transcripts have shorter roots than the wild-type controls and roots are still shorter in the double mutant. Seedlings overexpressing AtPrx34 exhibit significantly longer roots. These modifications of root length are accompanied by corresponding changes of cell length. The results suggest that AtPrx33 and Atprx34, two highly homologous Arabidopsis peroxidases, are involved in the reactions that promote cell elongation and that this occurs most likely within cell walls.

Isolation and proteomic alalysis of cell wall-deficientHaematococcus pluvialis mutants

The green alga Haematococcus pluvialis has a plant-like cell wall consisting of glycoproteins and cellulose that is modified during the cell cycle and under various conditions. These features allow Haematococcus to be used as a model organism for studying cell wall biology. Development of the Haematococcus model is hampered by the absence of mutants that could provide insight into the biosynthesis and assembly of wall components. Haematococcus mutants (WM#537 and WM#2978) (WM--wall mutant) with defective cell walls were obtained by chemical mutagenesis. WM#537 features a secondary wall of considerably reduced thickness, whereas WM#2978 possesses a somewhat reduced secondary wall with little intervening space between the wall and plasmalemma. 2-DE revealed that a majority of the cell wall proteins were present in the wild-type and mutant cell walls throughout the cell cycle. PMF identified 55 wall protein orthologs from these strains, including a subset of induced proteins known to be involved in wall construction, remodeling, and defense. Down-regulation of certain wall proteins in the two mutants was associated with the wall defects, whereas overexpression of other proteins may have compensated for the defective walls in the two mutants.

Preparation of single cells from aggregatedTaxus suspension cultures for population analysis

A method for the isolation of single plant cells from Taxus suspension cultures has been developed for the analysis of single cells via rapid throughput techniques such as flow cytometry. Several cell wall specific enzymes, such as pectinase, pectolyase Y-23, macerozyme, Driselase(R), and cellulase were tested for efficacy in producing single cell suspensions. The method was optimized for single cell yield, viability, time, and representivity of aggregated cell cultures. The best combination for single cell isolation was found to be 0.5% (w/v) pectolyase Y-23 and 0.04% (w/v) cellulase. High viability (>95%) and high yields of single cell aggregates (>90%) were obtained following 4 hours of digestion for four separate Taxus cell lines. In addition, methyl jasmonate elicitation (200 microM) was found to have no effect on three of the four tested Taxus lines. Isolated single cells were statistically similar to untreated cell cultures for peroxidase activity (model cell wall protein) and paclitaxel content (secondary metabolite produced in Taxus cell cultures). In comparison, protoplasts showed marked changes in both peroxidase activity and paclitaxel content as compared to untreated cultures. The use of flow cytometry was demonstrated with isolated cells that were found to have > 99% viability upon staining with fluorescein diacetate. The development of a method for the isolation of single plant cells will allow the study of population dynamics and culture variability on a single cell level for the development of population models of plant cell cultures and secondary metabolism.

A novel beta-glucosidase from the cell wall of maize (Zea mays L.): rapid purification and partial characterization

Plants have a variety of glycosidic conjugates of hormones, defense compounds, and other molecules that are hydrolyzed by beta-glucosidases (beta-D-glucoside glucohydrolases, E.C. 3.2.1.21). Workers have reported several beta-glucosidases from maize (Zea mays L.; Poaceae), but have localized them mostly by indirect means. We have purified and partly characterized a 58-Ku beta-glucosidase from maize, which we conclude from a partial sequence analysis, from kinetic data, and from its localization is not identical to any of those already reported. A monoclonal antibody, mWP 19, binds this enzyme, and localizes it in the cell walls of maize coleoptiles. An earlier report showed that mWP19 inhibits peroxidase activity in crude cell wall extracts and can immunoprecipitate peroxidase activity from these extracts, yet purified preparations of the 58 Ku protein had little or no peroxidase activity. The level of sequence similarity between beta-glucosidases and peroxidases makes it unlikely that these enzymes share epitopes in common. Contrary to a previous conclusion, these results suggest that the enzyme recognized by mWP19 is not a peroxidase, but there is a wall peroxidase closely associated with the 58 Ku beta-glucosidase in crude preparations. Other workers also have co-purified distinct proteins with beta-glucosidases. We found no significant charge in the level of immunodetectable beta-glucosidase in mesocotyls or coleoptiles that precedes the red light-induced changes in the growth rate of these tissues.

Nucellain, a barley homolog of the dicot vacuolar-processing protease, is localized in nucellar cell walls

The nucellus is a complex maternal grain tissue that embeds and feeds the developing cereal endosperm and embryo. Differential screening of a barley (Hordeum vulgare) cDNA library from 5-d-old ovaries resulted in the isolation of two cDNA clones encoding nucellus-specific homologs of the vacuolar-processing enzyme of castor bean (Ricinus communis). Based on the sequence of these barley clones, which are called nucellains, a homolog from developing corn (Zea mays) grains was also identified. In dicots the vacuolar-processing enzyme is believed to be involved in the processing of vacuolar storage proteins. RNA-blot and in situ-hybridization analyses detected nucellain transcripts in autolysing nucellus parenchyma cells, in the nucellar projection, and in the nucellar epidermis. No nucellain transcripts were detected in the highly vacuolate endosperm or in the other maternal tissues of developing grains such as the testa or the pericarp. Using an antibody raised against castor bean vacuolar-processing protease, a single polypeptide was recognized in protein extracts from barley grains. Immunogold-labeling experiments with this antibody localized the nucellain epitope not in the vacuoles, but in the cell walls of all nucellar cell types. We propose that nucellain plays a role in processing and/or turnover of cell wall proteins in developing cereal grains.

Light regulation of the abundance of mRNA encoding a nucleolin-like protein localized in the nucleoli of pea nuclei

A cDNA encoding a nucleolar protein was selected from a pea (Pisum sativum) plumule library, cloned, and sequenced. The translated sequence of the cDNA has significant percent identity to Xenopus laevis nucleolin (31%), the alfalfa (Medicago sativa) nucleolin homolog (66%), and the yeast (Saccharomyces cerevisiae) nucleolin homolog (NSR1) (28%). It also has sequence patterns in its primary structure that are characteristic of all nucleolins, including an N-terminal acidic motif, RNA recognition motifs, and a C-terminal Gly- and Arg-rich domain. By immunoblot analysis, the polyclonal antibodies used to select the cDNA bind selectively to a 90-kD protein in purified pea nuclei and nucleoli and to an 88-kD protein in extracts of Escherichia coli expressing the cDNA. In immunolocalization assays of pea plumule cells, the antibodies stained primarily a region surrounding the fibrillar center of nucleoli, where animal nucleolins are typically found. Southern analysis indicated that the pea nucleolin-like protein is encoded by a single gene, and northern analysis showed that the labeled cDNA binds to a single band of RNA, approximately the same size and the cDNA. After irradiation of etiolated pea seedlings by red light, the mRNA level in plumules decreased during the 1st hour and then increased to a peak of six times the 0-h level at 12 h. Far-red light reversed this effect of red light, and the mRNA accumulation from red/far-red light irradiation was equal to that found in the dark control. This indicates that phytochrome may regulate the expression of this gene.

The use of antibodies to study the architecture and developmental regulation of plant cell walls

This review covers the generation and use of antibodies to defined components of plant and algal cell walls and how these have contributed to our understanding of the spatial and developmental regulation of cell walls. Particular emphasis is placed upon the generation and characterization of monoclonal antibodies to matrix polysaccharides, extensins, and arabinogalactan-proteins of higher plants, and algal polysaccharides and glycoproteins. Immunolocalization studies are discussed in relation to the identification of molecular domains within cell walls, cell adhesion, cell differentiation, and the establishment of plant interactions with other organisms.

STRUCTURE AND BIOGENESIS OF THE CELL WALLS OF GRASSES

The chemical structures of the primary cell walls of the grasses and their progenitors differ from those of all other flowering plant species. They vary in the complex glycans that interlace and cross-link the cellulose microfibrils to form a strong framework, in the nature of the gel matrix surrounding this framework, and in the types of aromatic substances and structural proteins that covalently cross-link the primary and secondary walls and lock cells into shape. This review focuses on the chemistry of the unique polysaccharides, aromatic substances, and proteins of the grasses and how these structural elements are synthesized and assembled into dynamic and functional cell walls. Despite wide differences in wall composition, the developmental physiology of grasses is similar to that of all flowering plants. Grass cells respond similarly to environmental cues and growth regulators, exhibit the same alterations in physical properties of the wall to allow cell growth, and possess similar patterns of wall biogenesis during the development of specific cell and tissue types. Possible unifying mechanisms of growth are suggested to explain how grasses perform the same wall functions as other plants but with different constituents and architecture.

Light-modulated abundance of an mRNA encoding a calmodulin-regulated, chromatin-associated NTPase in pea

A CDNA encoding a 47 kDa nucleoside triphosphatase (NTPase) that is associated with the chromatin of pea nuclei has been cloned and sequenced. The translated sequence of the cDNA includes several domains predicted by known biochemical properties of the enzyme, including five motifs characteristic of the ATP-binding domain of many proteins, several potential casein kinase II phosphorylation sites, a helix-turn-helix region characteristic of DNA-binding proteins, and a potential calmodulin-binding domain. The deduced primary structure also includes an N-terminal sequence that is a predicted signal peptide and an internal sequence that could serve as a bipartite-type nuclear localization signal. Both in situ immunocytochemistry of pea plumules and immunoblots of purified cell fractions indicate that most of the immunodetectable NTPase is within the nucleus, a compartment proteins typically reach through nuclear pores rather than through the endoplasmic reticulum pathway. The translated sequence has some similarity to that of human lamin C, but not high enough to account for the earlier observation that IgG against human lamin C binds to the NTPase in immunoblots. Northern blot analysis shows that the NTPase MRNA is strongly expressed in etiolated plumules, but only poorly or not at all in the leaf and stem tissues of light-grown plants. Accumulation of NTPase mRNA in etiolated seedlings is stimulated by brief treatments with both red and far-red light, as is characteristic of very low-fluence phytochrome responses. Southern blotting with pea genomic DNA indicates the NTPase is likely to be encoded by a single gene.

Molecular cloning and expression analysis of peroxidase genes from wheat

A PCR-based screening approach was used to isolate genomic clones from wheat encoding peroxidase isozymes. Three complete genes (pox1, pox2 and pox4) and one truncated gene (pox3) were characterized. The nucleotide sequences predicted mature proteins of 31 kDa, in which all the highly conserved motifs of secreted plant peroxidases were preserved. The coding regions showed 73-83% DNA sequence identity, with the highest level of similarity noted for the tandemly oriented pox2 and pox3. Expression of respective pox genes in various tissues of wheat was assessed by the RT-PCR technique, which showed that all four genes are active. The primary pox1 mRNA was spliced to remove three introns, whereas processing of the other pox transcripts involved only two intervening sequences. Splicing occurred at consensus GU/AG splice sites except for the first introns of pox1, pox2 and pox4 transcripts, where processing took place at unusual GC donor sites. The RNA analysis suggested that the pox1, pox2 and pox4 genes are predominantly expressed in roots. Lower levels of expression were found for pox4 and pox3 in leaves. Infection of wheat by the powdery mildew fungus selectively induced expression of pox2 in leaves.

Developmental regulation and phytochrome-mediated induction of mRNAs encoding a proline-rich protein, glycine-rich proteins, and hydroxyproline-rich glycoproteins in Phaseolus vulgaris L

We have studied developmental and light regulation of mRNAs encoding a putative cell wall proline-rich protein (PvPRP1), cell wall glycine-rich proteins (GRPs), and cell wall hydroxyproline-rich glycoproteins (HRGPs) in bean (Phaseolus vulgaris). Light increases the levels of these mRNAs 2- to 150-fold in highly spatially regulated patterns during seedling development. These mRNA changes include differential regulation of transcripts derived from the GRP and HRGP multigene families. In 6-day-old light-grown seedlings, the PvPRP1 and GRP1.0 mRNAs were most abundant in the apical region of hypocotyls, epicotyls, and roots. In contrast, several HRGP transcripts were most abundant in the mature region of hypocotyls and roots in light-grown seedlings. When etiolated 6-day-old seedlings were illuminated with white light for 8 hr, maximal accumulation of PvPRP1 and GRP1.0 mRNAs occurred in the apical hook, whereas HRGP and GRP1.8 mRNAs accumulated in the mature region of hypocotyls. Etiolated seedlings subjected to a pulse of red light accumulated PvPRP1, GRP, and HRGP mRNAs in the hypocotyls. Far-red light inhibited red light induction of these mRNAs, indicating a phytochrome-mediated process. The possible roles of PRPs, GRPs, and HRGPs in cell differentiation and photomorphogenesis are discussed.

Adaptation to dim-red light leads to a nongradient pattern of stem elongation in cucumis seedlings

Relative growth rate determinations on 5-millimeter regions of cucumber (Cucumis sativus L.) hypocotyls show that dim-red light-grown seedlings have an even distribution of growth along the stem axis. This contrasts with the apical to basal graded decline in growth rate seen in dark-grown seedlings, including dark-grown cucumber seedlings used as controls in this study. Dark-grown seedlings convert to the nongradient pattern when transferred to dim-red light. The small amount of light required suggests that the change in developmental pattern may happen in the natural light environment.

Cell Wall Free Space of Cucumis Hypocotyls Contains NAD and a Blue Light-Regulated Peroxidase Activity

Solutions were obtained from the cell wall free space of red light-grown cucumber (Cucumis sativus L.) hypocotyl sections by a low-speed centrifugation technique. The centrifugate contained NAD and peroxidase but no detectable cytoplasmic contamination, as indicated by the absence of the activity of glucose-6-phosphate dehydrogenase from the cell wall solution. Peroxidase activity centrifuged from the cell wall of red light-grown cucumber hypocotyl section could be resolved into at least three cathodic isoforms and two anodic isoforms by isoelectric focusing. Treatment of red light-grown cucumber seedlings with a 10-minute pulse of high-intensity blue light increased the level of cell wall peroxidase by about 60% and caused a qualitative change in the anodic isoforms of this enzyme. The increase in peroxidase activity was detectable within 25 minutes after the start of the blue light pulse, was maximal at 35 minutes, and declined to control levels by 45 minutes of irradiation. The inhibitory effect of blue light on hypocotyl elongation was more rapid than the effect of blue light on total wall peroxidase activity, leading to the conclusion that growth and peroxidase activity are not causally related.

Transient Gene Expression in Intact and Organized Rice Tissues

Regulated gene expression of chimeric genes has been studied extensively in electroporated protoplasts. The applicability of these assays is limited, however, because protoplasts are not always physiologically identical to the cells from which they are derived. We have developed a procedure to electroporate DNA into intact and organized leaf structures of rice. Optimization of the new gene delivery system mainly involved eliminating explant-released nucleases, prolonging the DNA/explant incubation time, and expanding the pulse time. Using a [beta]-glucuronidase gene under the control of constitutive promoters, we demonstrated that all cell types within a leaf base were susceptible to electroporation-mediated DNA uptake. Although the technique was initially developed for leaf bases of young etiolated rice seedlings, we proved that it was equally applicable both to other monocotyledons, including wheat, maize, and barley, and to other explants, such as etiolated and green sheath and lamina tissues from rice. Transient gene expression assays with electroporated leaf bases showed that the promoter from a pea light-harvesting chlorophyll a/b-binding protein gene displayed both light- and chloroplast-dependent expression in rice, and that the promoter from the Arabidopsis S-adenosylmethionine synthetase gene was, as in transgenic Arabidopsis and tobacco, preferentially expressed in cells surrounding the vascular bundles.

Transient Gene Expression in Intact and Organized Rice Tissues

Regulated gene expression of chimeric genes has been studied extensively in electroporated protoplasts. The applicability of these assays is limited, however, because protoplasts are not always physiologically identical to the cells from which they are derived. We have developed a procedure to electroporate DNA into intact and organized leaf structures of rice. Optimization of the new gene delivery system mainly involved eliminating explant-released nucleases, prolonging the DNA/explant incubation time, and expanding the pulse time. Using a [beta]-glucuronidase gene under the control of constitutive promoters, we demonstrated that all cell types within a leaf base were susceptible to electroporation-mediated DNA uptake. Although the technique was initially developed for leaf bases of young etiolated rice seedlings, we proved that it was equally applicable both to other monocotyledons, including wheat, maize, and barley, and to other explants, such as etiolated and green sheath and lamina tissues from rice. Transient gene expression assays with electroporated leaf bases showed that the promoter from a pea light-harvesting chlorophyll a/b-binding protein gene displayed both light- and chloroplast-dependent expression in rice, and that the promoter from the Arabidopsis S-adenosylmethionine synthetase gene was, as in transgenic Arabidopsis and tobacco, preferentially expressed in cells surrounding the vascular bundles.