Changes in the shapes of leaves and flowers upon overexpression of cytochrome P450 in Arabidopsis.
(9/1585)
In Arabidopsis, the two-dimensional expansion of leaves is regulated via the polarized elongation of cells. The ROTUNDIFOLIA3 (ROT3) protein, a member of the family of cytochromes P450, is involved in this process and regulates leaf length. Transgenic plants that overexpressed a wild-type ROT3 gene had longer leaves than parent plants, without any changes in leaf width. The shapes of floral organs were also altered, but elongation of the stem, roots, and hypocotyls was unaffected. To our knowledge, no similar specific regulation of leaf length has been reported previously. Transgenic plants overexpressing the rot3-2 gene had enlarged leaf blades but leaf petioles of normal length. Morphological alterations in such transgenic plants were associated with changes in shape of leaf cells. The ROT3 gene seems to play an important role in the polar elongation of leafy organs and should be a useful tool for the biodesign of plant organs. (+info)
Bromelain, from pineapple stems, proteolytically blocks activation of extracellular regulated kinase-2 in T cells.
(10/1585)
Recently, it has emerged that extracellular proteases have specific regulatory roles in modulating immune responses. Proteases may act as signaling molecules to activate the Raf-1/extracellular regulated kinase (ERK)-2 pathway to participate in mitogenesis, apoptosis, and cytokine production. Most reports on the role of protease-mediated cell signaling, however, focus on their stimulatory effects. In this study, we show for the first time that extracellular proteases may also block signal transduction. We show that bromelain, a mixture of cysteine proteases from pineapple stems, blocks activation of ERK-2 in Th0 cells stimulated via the TCR with anti-CD3epsilon mAb, or stimulated with combined PMA and calcium ionophore. The inhibitory activity of bromelain was dependent on its proteolytic activity, as ERK-2 inhibition was abrogated by E-64, a selective cysteine protease inhibitor. However, inhibitory effects were not caused by nonspecific proteolysis, as the protease trypsin had no effect on ERK activation. Bromelain also inhibited PMA-induced IL-2, IFN-gamma, and IL-4 mRNA accumulation, but had no effect on TCR-induced cytokine mRNA production. This data suggests a critical requirement for ERK-2 in PMA-induced cytokine production, but not TCR-induced cytokine production. Bromelain did not act on ERK-2 directly, as it also inhibited p21ras activation, an effector molecule upstream from ERK-2 in the Raf-1/MEK/ERK-2 kinase signaling cascade. The results indicate that bromelain is a novel inhibitor of T cell signal transduction and suggests a novel role for extracellular proteases as inhibitors of intracellular signal transduction pathways. (+info)
Starch and the control of kernel number in maize at low water potentials.
(11/1585)
After reproduction is initiated in plants, subsequent reproductive development is sometimes interrupted, which decreases the final number of seeds and fruits. We subjected maize (Zea mays L.) to low water potentials (psi(w)) that frequently cause this kind of failure. We observed metabolite pools and enzyme activities in the developing ovaries while we manipulated the sugar stream by feeding sucrose (Suc) to the stems. Low psi(w) imposed for 5 d around pollination allowed embryos to form, but abortion occurred and kernel number decreased markedly. The ovary contained starch that nearly disappeared during this abortion. Analyses showed that all of the intermediates in starch synthesis were depleted. However, when labeled Suc was fed to the stems, label arrived at the ovaries. Solute accumulated and caused osmotic adjustment. Suc accumulated, but other intermediates did not, showing that a partial block in starch synthesis occurred at the first step in Suc utilization. This step was mediated by invertase, which had low activity. Because of the block, Suc feeding only partially prevented starch disappearance and abortion. These results indicate that young embryos abort when the sugar stream is interrupted sufficiently to deplete starch during early ovary development, and this abortion results in a loss of mature seeds and fruits. At low psi(w), maintaining the sugar stream partially prevented the abortion, but invertase regulated the synthesis of ovary starch and partially prevented full recovery. (+info)
Root formation in ethylene-insensitive plants.
(12/1585)
Experiments with ethylene-insensitive tomato (Lycopersicon esculentum) and petunia (Petunia x hybrida) plants were conducted to determine if normal or adventitious root formation is affected by ethylene insensitivity. Ethylene-insensitive Never ripe (NR) tomato plants produced more below-ground root mass but fewer above-ground adventitious roots than wild-type Pearson plants. Applied auxin (indole-3-butyric acid) increased adventitious root formation on vegetative stem cuttings of wild-type plants but had little or no effect on rooting of NR plants. Reduced adventitious root formation was also observed in ethylene-insensitive transgenic petunia plants. Applied 1-aminocyclopropane-1-carboxylic acid increased adventitious root formation on vegetative stem cuttings from NR and wild-type plants, but NR cuttings produced fewer adventitious roots than wild-type cuttings. These data suggest that the promotive effect of auxin on adventitious rooting is influenced by ethylene responsiveness. Seedling root growth of tomato in response to mechanical impedance was also influenced by ethylene sensitivity. Ninety-six percent of wild-type seedlings germinated and grown on sand for 7 d grew normal roots into the medium, whereas 47% of NR seedlings displayed elongated tap-roots, shortened hypocotyls, and did not penetrate the medium. These data indicate that ethylene has a critical role in various responses of roots to environmental stimuli. (+info)
Tobacco O-methyltransferases involved in phenylpropanoid metabolism. The different caffeoyl-coenzyme A/5-hydroxyferuloyl-coenzyme A 3/5-O-methyltransferase and caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase classes have distinct substrate specificities and expression patterns.
(13/1585)
The biosynthesis of lignin monomers involves two methylation steps catalyzed by orthodiphenol-O-methyltransferases: caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferases (COMTs) and caffeoyl-coenzyme A (CoA)/5-hydroxyferuloyl-CoA 3/5-O-methyltransferases (CCoAOMTs). Two COMT classes (I and II) were already known to occur in tobacco (Nicotiana tabacum) and three distinct CCoAOMT classes have now been characterized. These three CCoAOMT classes displayed a maximum level of expression at different stages of stem development, in accordance with their involvement in the synthesis of lignin guaiacyl units. Expression profiles upon tobacco mosaic virus infection of tobacco leaves revealed a biphasic pattern of induction for COMT I, COMT II, and CCoAOMTs. The different isoforms were expressed in Escherichia coli and our results showed that CCoAOMTs and, more surprisingly, COMTs efficiently methylated hydroxycinnamoyl-CoA esters. COMT I was also active toward 5-hydroxyconiferyl alcohol, indicating that COMT I that catalyzes syringyl unit synthesis in planta may operate at the free acid, CoA ester, or alcohol levels. COMT II that is highly inducible by infection also accepted caffeoyl-CoA as a substrate, thus suggesting a role in ferulate derivative deposition in the walls of infected cells. Tobacco appears to possess an array of O-methyltransferase isoforms with variable efficiency toward the diverse plant o-diphenolic substrates. (+info)
Crystal structure of cardosin A, a glycosylated and Arg-Gly-Asp-containing aspartic proteinase from the flowers of Cynara cardunculus L.
(14/1585)
Aspartic proteinases (AP) have been widely studied within the living world, but so far no plant AP have been structurally characterized. The refined cardosin A crystallographic structure includes two molecules, built up by two glycosylated peptide chains (31 and 15 kDa each). The fold of cardosin A is typical within the AP family. The glycosyl content is described by 19 sugar rings attached to Asn-67 and Asn-257. They are localized on the molecular surface away from the conserved active site and show a new glycan of the plant complex type. A hydrogen bond between Gln-126 and Manbeta4 renders the monosaccharide oxygen O-2 sterically inaccessible to accept a xylosyl residue, therefore explaining the new type of the identified plant glycan. The Arg-Gly-Asp sequence, which has been shown to be involved in recognition of a putative cardosin A receptor, was found in a loop between two beta-strands on the molecular surface opposite the active site cleft. Based on the crystal structure, a possible mechanism whereby cardosin A might be orientated at the cell surface of the style to interact with its putative receptor from pollen is proposed. The biological implications of these findings are also discussed. (+info)
Methods for calculating factors of safety for plant stems.
(15/1585)
The concept of a 'factor of safety' is used by biologists and engineers who generally agree that structures must be mechanically reliable, i.e. that structures must be capable of coping with unprecedented loads without failing. These factors can be calculated for individual structures or for a population of otherwise equivalent mechanical structures differing in their load capabilities. Objective methods for quantifying factors of safety for biological structures are nevertheless difficult to devise because (1) actual (working) loads are defined by environmental conditions that can vary widely, (2) breaking loads (capability) of otherwise mechanically equivalent structures can likewise vary as a result of developmental variation, and (3) specific criteria for failure must be determined a priori. In this paper, we illustrate and discuss two methods for computing factors of safety for plants. One method works well for individual stems or entire plants, the other is useful when dealing with a population of conspecifics exhibiting a norm of reaction. Both methods require estimates of the actual and breaking bending (or torsional) moments experienced by stems, and both are amenable to dealing with any biologically reasonable criterion for failure. However, the two methods differ in terms of the assumptions made and the types of data that need to be gathered. The advantage of the first method is that it estimates the potential for survival of an individual stem or plant. The disadvantage is that it neglects natural variation among otherwise mechanically homologous individuals. The advantage of the second (statistical) approach is that it estimates the probability of survival of a population in a particular habitat. The disadvantage of this approach is that it sheds little light on the probability of an individual's survival. (+info)
Sequential and coordinated action of phytochromes A and B during Arabidopsis stem growth revealed by kinetic analysis.
(16/1585)
Photoreceptor proteins of the phytochrome family mediate light-induced inhibition of stem (hypocotyl) elongation during the development of photoautotrophy in seedlings. Analyses of overt mutant phenotypes have established the importance of phytochromes A and B (phyA and phyB) in this developmental process, but kinetic information that would augment emerging molecular models of phytochrome signal transduction is absent. We have addressed this deficiency by genetically dissecting phytochrome-response kinetics, after having solved the technical issues that previously limited growth studies of small Arabidopsis seedlings. We show here, with resolution on the order of minutes, that phyA initiated hypocotyl growth inhibition upon the onset of continuous red light. This primary contribution of phyA began to decrease after 3 hr of irradiation, the same time at which immunochemically detectable phyA disappeared and an exclusively phyB-dependent phase of inhibition began. The sequential and coordinated actions of phyA and phyB in red light were not observed in far-red light, which inhibited growth persistently through an exclusively phyA-mediated pathway. (+info)