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Ethylene is known to play an essential role in mediating hypoxic responses in plants. Here, we show that in addition to regulating hypoxic responses, ethylene also regulates cellular responses in the reoxygenation stage after anoxic treatment in Arabidopsis. We found that expression of several ethylene biosynthetic genes and ethylene-responsive factors, including ERF1 and ERF2, was induced during reoxygenation. Compared with the wild type, two ethylene-insensitive mutants ( ein2-5 and ein3eil1) were more sensitive to reoxygenation and displayed damaged phenotypes during reoxygenation. To characterize the role of ethylene, we applied microarray analysis to Col-0, ein2-5 and ein3eil1 under reoxygenation conditions. Our results showed that gene transcripts involved in reactive oxygen species ( ROS) detoxification, dehydration response and metabolic processes were regulated during reoxygenation. Moreover, ethylene signalling may participate in regulating these responses and maintaining the homeostasis of different phytohormones. Our work presents evidence that ethylene has distinct functions in recovery after anoxia and provides insight into the reoxygenation signalling network. [ABSTRACT FROM AUTHOR]

Flooding, a natural cause of anaerobiosis, is often accompanied by high CO concentrations in the flood water. Plants need to respond to these environmental conditions. Strong anaerobic reporter gene activity in tobacco ( Nicotiana tabacum) controlled by the glycolytic glyceraldehyde-3-phosphate dehydrogenase ( GapC4) promoter from maize ( Zea mays) depends on the presence of CO and light. To identify factors required for CO regulated gene expression, promoter deletions fused to the β-glucuronidase reporter gene were studied in transgenic tobacco. Deletion of a 40 bp fragment directly upstream of the TATA box leads to increased anaerobic reporter gene activity both, in the presence and absence of CO. This deletion does not affect light specific anaerobic expression. A positive correlation between increasing CO concentrations and gene activity is observed. Electrophoretic mobility shift experiments indicate that tobacco nuclear extracts harbour proteins that bind to part of the 40 bp fragment. Database assisted as well as experimental analysis reveal a role for AP2/EREBP transcription factors for conferring the high CO specificity to the GapC4 promoter in tobacco leaves. This work highlights the importance for plants to respond to high environmental CO concentrations under anaerobic conditions. [ABSTRACT FROM AUTHOR]

The activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10−6 mol g−1 fresh weight s−1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1-week exposure to either dissolved oxygen at air-saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot-to-root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of 14C-labelled photo-assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high 14C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning. [ABSTRACT FROM AUTHOR]

ABSTRACTA new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy–pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark–light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology. [ABSTRACT FROM AUTHOR]

The responses of two aquatic plants, arrowhead (Sagittaria pygmaea Miq.) and pondweed (Potamogeton distinctus A. Benn), to anoxia were compared with those of rice (Oryza sativa L.). Shoot elongation of arrowhead tubers was enhanced at around 1 kPa O2, whereas that of pondweed turions was slight in air and reached a maximum in the absence of O2. Anaerobic enhancement of alcohol dehydrogenase (ADH) activity took place in rice coleoptiles but not in arrowhead and pondweed shoots. Shoots of both arrowhead and pondweed maintained a more stable energy status than did the rice coleoptile under anaerobic conditions. Total adenylate nucleotide contents of arrowhead and pondweed shoots were constant under anaerobic conditions. Adenylate energy charge in both shoots remained at a high and stable level of more than 0·8 for at least 8 d. Three forms of ADH from arrowhead shoots were separated by starch gel electrophoresis, showing that the activity of each ADH form was different under aerobic and anaerobic conditions. The incorporation of 35S-labelled Cys and Met into soluble proteins in arrowhead shoots showed active protein biosynthesis and an involvement of a special set of polypeptides in the anaerobiosis. [ABSTRACT FROM AUTHOR]

To study the transcriptional and translational responses that occur in rice (Oryza sativa L., cv. Arborio) coleoptiles and roots during the first hours of anoxia, we analysed the patterns of in vitro translational products and in vivo labelled newly synthesized proteins obtained from both organs grown in the presence or absence of O2. Analysis of the protein pattern obtained from nuclear-enriched subcellular fractions showed the enhancement of the synthesis of several proteins with molecular weights of 67-62,54 and 34 kD. In the cytoplasmic-enriched subcellular fractions, we found that the synthesis of polypeptides of relatively low molecular weight (13-16 kD) was strongly induced by anaerobiosis. In vitro translation analysis showed that this enhancement was mainly due to a rapid increase in the level of the corresponding mRNA species. These low- molecular-weight translational products were already detected after 1 h of anoxia in both rice roots and rice coleoptiles, but remained undetectable in aerobically grown organs. Additional anaerobic-specific transcrip- tional and translational changes were also observed. In particular, a specific reduction in the level of mRNAs coding for polypeptides of 38 kD occurred in both roots and coleoptiles after only 1 h of anoxia. [ABSTRACT FROM AUTHOR]

Plant gene expression is regulated during development and in response to environmental stimuli. For example, the pattern of gene expression in roots changes dramatically when seedlings are placed under low oxygen conditions. Roots respond to anaerobiosis by increasing cytosolic-glycolytic enzyme activity. Through the use of genetic and molecular techniques we have begun to characterize the differential expression of isozymes which show increased synthesis under anaerobic conditions and tissue specific expression during plant development. [ABSTRACT FROM AUTHOR]

Aerobically germinated seedlings of rice and Echinochloa were found to survive when placed in an anaerobic environment for 4 d, whereas pea and maize seedlings did not. Although root and shoot growth were inhibited in rice and Echinochloa under anaerobiosis, growth resumed when the seedlings were returned to aerobic conditions. Alcohol dehydrogenase (ADH) activity increased more, and protein synthesis was greater, in the shoots than in the roots under anaerobic conditions. These results suggest that, in anaerobiosis-tolerant species, ADH activity and protein synthesis in the shoots represents or results from metabolic adaptations to low oxygen. These results are discussed in terms of plant establishment and growth in a low oxygen environment. [ABSTRACT FROM AUTHOR]

A method is presented for the control of carbon dioxide concentrations within the roots of Fraxinus pennsylvanica Marsh. The results indicated a linear fit of the root CO2 concentrations to the CO2 levels of the treatment gases: y= 1.1x+105 (r=0.98, 18 d.f.). The method presented for controlling CO2 can be easily modified for other gas mixtures and plant species. [ABSTRACT FROM AUTHOR]

For Chlorella emersonii, plausible membrane potentials between -80 and -120mV were calculated from the distribution of the lipophilic cation tetraphenylphosphonium (TPP+) between the cells and the medium. Furthermore, these calculated membrance potentials were influenced in a way expected from the literature, by different metabolic conditions induced by light or dark, anaerobiosis, glucose, and by inhibition or uncoupling of electron transport. Nevertheless, the experiments presented here indicate that TPP+ is unsuitable as a probe for electrical potential, at least in Chlorella emersonii. The reasons for this conclusion are as follows: 1. Much of the incorporated TPP+-14C could not be exchanged against unlabelled TPP+. 2. The uptake of TPP+-14C was very slow and exhibited complex rather than simple saturation kinetics. 3. A large adsorption of TPP+-14C took place even after the cells were killed; the adsorption by living cells was only 20-60% higher than with killed cells. [ABSTRACT FROM AUTHOR]

The article presents an overview of papers on the role of molecular biology in studies of environmental physiology published in the July 1988 issue of the journal "Plant, Cell and Environment." The papers deal with the perception of or response to, important environmental factors such as light, temperature, anaerobiosis, wounding and fungal attack, heavy metals, nitrate assimilation and the symbiotic interaction of plants with bacteria to produce root nodules. The molecular approach provides a range of powerful methods that combined with the appropriate physiological, biochemical and ultra-structural studies, make it possible to shed some light on many environmental physiology.