Light or ethylene treatments induce transverse cell enlargement in etiolated maize mesocotyls

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.

Regulated redox processes at the plasmalemma of plant root cells and their function in iron uptake

Plants take up iron as ferric chelates or, after reduction, as ferrous ions. Ferric reduction takes place at the plasma membrane of the root epidermis cells by a transmembrane redox system, which can be activated when iron is getting short. It is proposed that this inducible system, with NADPH as electron donor, is separate from a system, presumably present in all plant cells, which transports electrons from NADH or NADPH to ferricyanide, or, in vivo, oxygen.

Insolubilization of hydroxyproline-rich cell wall glycoprotein in aerated carrot root slices

The hydroxyproline-rich glycoprotein of plant cell walls is secreted from the cytoplasm as a soluble monomer which slowly becomes insolubilized. A tyrosine derivative, isodityrosine, is formed in the cell wall during this insolubilization and could serve as a protein-protein crosslink. Glycoprotein insolubilization is inhibited by peroxidase inhibitors and free radical scavengers, the most effective of which is L-ascorbate. These data support a hypothesis that the hydroxyproline-rich cell wall glycoprotein forms a covalently crosslinked wall network under the control of an extracellular peroxidase/ascorbate oxidase system.

An investigation into the roles of photosynthesis and respiration in h efflux from aerated suspensions of asparagus mesophyll cells

Aerated and stirred suspensions of mechanically isolated Asparagus sprengeri Regel mesophyll cells were used to investigate the roles of respiration and photosynthesis in net H(+) efflux. Rates varied between 0.12 and 1.99 nanomoles H(+) per 10(6) cells per minute or 3 and 40 nanomoles H(+) per milligram chlorophyll per minute. The mean rate of H(+) efflux was 10% greater in the dark. 3-(3,4-Dichlorophenyl)-l,l-dimethylurea, an inhibitor of noncyclic photophosphorylation, did not inhibit H(+) efflux from illuminated cells. Bubbling with N(2) or addition of oligomycin, an inhibitor of mitochondrial ATP production, resulted in rapid and virtually complete inhibition of H(+) efflux in light or dark. In the absence of aeration, H(+) efflux came to a halt but resumed with aeration or illumination. When aeration was switched to CO(2)-free air, rates of H(+) efflux were reduced 43% in the dark and 57% in the light. Oligomycin eliminated dark CO(2) fixation but not photosynthetic CO(2) fixation. It is suggested that H(+) efflux is dependent on respiration and dark CO(2) fixation, but independent of photosynthesis.

Does ethylene play a role in the release of lateral buds (tillers) from apical dominance in oats?

The growth of lateral buds (tillers), which are undergoing release from apical dominance, was measured in upright and gravistimulated intact Avena sativa L. cv. ;Victory' (oat) shoots as well as in isolated Avena stem segments treated with kinetin and sucrose. During release, the tiller bud initially shows a slow rate of elongation accompanied by swelling. It is followed by a more rapid rate of elongation. Ethylene (C(2)H(4)) production in shoot segments containing a tiller bud was found to occur at the onset of tiller swelling during gravistimulation as well as during inflorescence emergence. Exogenous application of indoleacetic acid or C(2)H(4) inhibits kinetin-induced tiller bud swelling and elongation. However, stem segments pulsed for 24 hours in C(2)H(4) or the C(2)H(4) biosynthesis precursor, 1-amino-cyclopropane-1-carboxylic acid (ACC) and then transferred to kinetin and sucrose, showed a significant increase in swelling elongation as compared with segments maintained under the same conditions but without C(2)H(4) or ACC in the pulse. Segments pulsed for 24 hours with kinetin and sucrose plus the ACC biosynthesis inhibitor, aminoethoxyvinylglycine, or the C(2)H(4) action inhibitor, CO(2), then transferred to kinetin and sucrose medium, showed inhibition of tiller swelling during the pulse and of subsequent elongation. These results indicate that C(2)H(4) plays a role in promoting tiller swelling during the onset of tiller release from apical dominance and may act as a modulator hormone in promoting tiller elongation in the presence of cytokinin.

Isodityrosine, a new cross-linking amino acid from plant cell-wall glycoprotein

1. Cell-wall hydrolysates from calli of all higher plants tested contained a new phenolic amino acid for which the trivial name isodityrosine is proposed. Isodityrosine was shown to be an oxidatively coupled dimer of tyrosine with the two tyrosine units linked by a diphenyl ether bridge. 2. The amount of isodityrosine in sodium dodecyl sulphate-insoluble cell-wall preparations was proportional to the amount of hydroxyproline. 3. Acidified chlorite split the diphenyl ether bridge of isodityrosine, and concomitantly solubilized the cell-wall glycoprotein. 4. Dithiothreitol inhibited isodityrosine synthesis in vivo, and suppressed in parallel the covalent binding of newly synthesized protein in the cell wall. 5. It is suggested that isodityrosine is an inter-polypeptide cross-link responsible for the insolubility of plant cell-wall glycoprotein.