The compatible response in flowering plants is a complex process involving a series of cell communication events leading the pollen tube through the gynoecium to the ovule. We provide the first description of pollen tube growth in vivo in Arabidopsis thaliana. The structure and composition of the transmitting tissue of the septum are examined at the light microscope and transmission electron microscope levels. We demonstrate that once pollen tubes leave the extracellular matrix (ECM) of the central septum, they adhere to and travel along the ECM of the septum epidermis. This ECM, which surrounds the pollen tubes, is secreted through breaks in the cuticle of the septum surface. The transmitting tract ECM stains strongly for acidic polysaccharides. Monoclonal antibodies to esterified and low-esterified homogalacturonans (pectins) do not localize to this ECM. Yariv phenylglycoside and monoclonal antibodies to arabinogalactan proteins (AGPs) provide evidence that AGPs are a component of the septum epidermal ECM.& k w d : Key words Arabidopsis thaliana · Arabinogalactan proteins · High-pressure freezing/freeze substitution · Extracellular matrices · Pollination& b d y :
The pitchers of the tropical carnivorous plant Nepenthes alata are highly specialized organs for the attraction and capture of insects and absorption of nutrients from them. This study examined the structure and development of these pitchers, with particular focus on the nectaries and digestive glands. Immature pitchers developed at the tips of tendrils and were tightly sealed by a lid structure that opened during the end of pitcher elongation. Opened pitchers exposed a ridged peristome containing large nectaries. Like other members of the genus, a thick coating of epicuticular waxy scales covered the upper one-third of the pitcher. Scattered within this zone were cells resembling a stomatal complex with a protruding ridge. Cross sections showed that this ridge was formed by asymmetric divisions of the epidermal cells and lacked an underlying pore. The basal region of the trap had large multicellular glands that developed from single epidermal cells. These glands were closely associated with underlying vascular traces and provided a mechanism for supplying fluid to closed immature pitchers.
We previously isolated a partial soybean cDNA clone whose transcript abundance is increased upon infection by the sedentary, endoparasitic soybean cyst nematode Heterodera glycines. We now isolated the corresponding full-length cDNA and determined that the predicted gene product was similar to the group of cofactor-dependent phosphoglycerate mutase/bisphosphoglycerate mutase enzymes (PGM/bPGM; EC 5.4.2.1/5.4.2.4). We designated the corresponding soybean gene GmPGM. PGM and bPGM are key catalysts of glycolysis that have been well characterized in animals but not plants. Using the GmPGM cDNA sequence, we identified a homologous Arabidopsis thaliana gene, which we designated AtPGM. Histochemical GUS analyses of transgenic Arabidopsis plants containing the AtPGM promoter ::GUS construct revealed that the AtPGM promoter directs GUS expression in uninfected plants only to the shoot and root apical meristems. In infected plants, GUS staining also is evident in the nematode feeding structures induced by the cyst nematode Heterodera schachtii and by the root-knot nematode Meloidogyne incognita. Furthermore, we discovered that the AtPGM promoter was down-regulated by abscisic acid and hydroxyurea, whereas it was induced by sucrose, oryzalin, and auxin, thereby revealing expression characteristics typical of genes with roles in meristematic cells. Assessment of the auxin-inducible AUX1 gene promoter (a gene coding for a polar auxin transport protein) similarly revealed feeding cell and meristem expression, suggesting that auxin may be responsible for the observed tissue specificity of the AtPGM promoter. These results provide first insight into the possible roles of PGM/bPGM in plant physiology and in plant-pathogen interactions.
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