Apoplastic barrier development and water transport in Zea mays seedling roots under salt and osmotic stresses.

The development of apoplastic barriers was studied in Zea mays seedling roots grown in hydroculture solution supplemented with 0-200 mM NaCl or 20% polyethylene glycol (PEG). Casparian bands in the endodermis of both NaCl- and PEG-treated roots were observed closer to the root tip in comparison with those of control roots, but the cell wall modifications in the endodermis and exodermis induced by salt and osmotic stresses differed. High salinity induced the formation of a multiseriate exodermis, which ranged from several cell layers to the entire cortex tissue but did not noticeably influence cell wall suberization in the endodermis. In contrast, osmotic stress accelerated suberization in both the endodermis and exodermis, but the exodermis induced by osmotic stress was limited to several cell layers in the outer cortex adjacent to the epidermis. The hydrostatic hydraulic conductivity (Lp) had decreased significantly after 1 day of PEG treatment, whereas in NaCl-treated roots, Lp decreased to a similar level after 5 days of treatment. Peroxidase activity in the roots increased significantly in response to NaCl and PEG treatments. These data indicate that salt stress and osmotic stress have different effects on the development of apoplastic barriers and water transport in Z. mays seedling roots.

Development of secretory cells and crystal cells in Eichhornia crassipes ramet shoot apex.

The distribution and development of secretory cells and crystal cells in young shoot apexes of water hyacinth were investigated through morphological and cytological analysis. The density of secretory cells and crystal cells were high in parenchyma tissues around the vascular bundles of shoot apexes. Three developmental stages of the secretory cells can be distinguished under transmission electron microscopy. Firstly, a large number of electron-dense vesicles formed in the cytoplasm, then fused with the tonoplast and released into the vacuole in the form of electron-dense droplets. As these droplets fused together, a large mass of dark material completely filled the vacuole. To this end, a secretion storage vacuole (SSV) formed. Secondly, an active secretion stage accompanied with degradation of the large electron-dense masses through an ill-defined autophagic process at periphery and in the limited internal regions of the SSV. Finally, after most storage substances were withdrawn, the materials remaining in the spent SSV consisted of an electron-dense network structure. The distribution and development of crystal cells in shoot apical tissue of water hyacinth were also studied by light and electron microscopy. Crystals initially formed at one site in the vacuole, where tube-like membrane structures formed crystal chambers. The chamber enlarged as the crystal grew in bidirectional manner and formed needle-shaped raphides. Most of these crystals finally occurred as raphide bundles, and the others appeared as block-like rhombohedral crystals in the vacuole. These results suggest that the formation of both secretory cells and crystal cells are involved in the metamorphosis of vacuoles and a role for vacuoles in water hyacinth rapid growth and tolerance.

[Analysis of tobacco regeneration plants from the protoplasts produced by electrofusion [corrected] in space].

Vacuolated mesophyll protoplasts of Nicotiana rustica L. were electrically fused with evacuolated protoplasts of the same genus (N. tabacum cv. 'Gexin No.1') during a 7-day space flight in the Chinese spacecraft "SZ-4". The initial cell division leading to micro-callus formation took place after landing (Fig.1). Higher plating efficiencies were observed in the flight samples than the control culture, but the frequency of plantlets regeneration reduced by about 20% of the control (Table 1). The hybrid characters were tested by chromosome counting, isozyme analysis and comparison of morphological characteristics (Figs.2-4). About 32% of the regenerates showed hybrid character. Leaf morphological modifications were found in 3 hybrids, i.e., H23, H25 and H27. After backcrossing with N. rustica, alterations in flower color and leaf shape occurred in the somatic hybrid H23 (Fig.5). These results demonstrate that the hybrids formed under microgravity condition could regenerate fertile plants.

Effects of Lantana camara leaf extract on the activity of superoxide dismutase and accumulation of H2O2 in water hyacinth leaf.

Water hyacinth (Eichhornia crassipes) is one of the most productive plants, but is also a troublesome weed in the world. In order to protect the public water system from chemical herbicides pollution, biological method has been suggested to control the growth and the reproduction of this weed. Lantana (Lantana camara L.) is an important weed of the family Verbenaceae and its leaf extract is highly toxic to water hyacinth. The results of this study showed that the extract of lantana leaves suppressed the emergence of leaf buds of water hyacinth plant, and caused the decay of its leaves by foliar spraying. In addition, the increase of SOD activity in water hyacinth leaves was in accordance with the accumulation of H(2)O(2) and the increase in degree of membrane peroxidation, while the activity of catalase, which might remove the excessive H(2)O(2) in water hyacinth leaves, was inhibited by treatment with lantana extract. At tissue level, high H(2)O(2) histochemical labeling was detected in guard cells after treatment with lantana extract. This overproduction of H(2)O(2) could kill the leaf cells and cause leaf necrosis in the treated plant. Therefore, the high toxicity of lantana leaf extract to water hyacinth might be due to oxidative stress.

A proteomic approach to analysing responses of Arabidopsis thaliana callus cells to clinostat rotation.

Callus cells of Arabidopsis thaliana (cv. Landsberg erecta) were exposed for 8 h to a horizontal clinostat rotation (H, simulated weightlessness), a vertical clinostat rotation (V, clinostat control), or a stationary control (S) growth condition. The amount of glucose and fructose apparently decreased, while starch content increased in the H compared with the V- and S-treated cells. In order to investigate the influences of clinostat rotation on the cellular proteome further, the proteome alterations induced by horizontal and vertical clinostat rotation have been comparatively analysed by high-resolution two-dimensional (2-D) gel electrophoresis and mass spectrometry. Image analysis of silver-stained 2-D gels revealed that 80 protein spots showed quantitative and qualitative variations that were significantly (P <0.01) and reproducibly different between the clinorotated (H or V) and the stationary control samples. Protein spots excised from 2-D gels were analysed by microbe high performance liquid chromatography-ion trap-mass spectrometry (LC-IT-MS) to obtain the tandem mass (MS/MS) spectra. 18 protein spots, which showed significant expression alteration only under the H condition compared with those under V and S conditions, were identified. Of these proteins, seven were involved in stress responses, and four protein spots were identified as key enzymes in carbohydrate metabolism and lipid biosynthesis. Two reversibly glycosylated cell wall proteins were down-regulated in the H samples. Other proteins such as protein disulphide isomerase, transcription initiation factor IIF, and two ribosomal proteins also exhibited altered expression under the H condition. The data presented in this study illustrate that clinostat rotation of Arabidopsis callus cells has a significant impact on the expression of proteins involved in general stress responses, metabolic pathways, gene activation/transcription, protein synthesis, and cell wall biosynthesis.