[1] Trace gas exchange of NO 2 and O 3 at the soil surface of the primary rain forest in Reserva Biológica Jarú (Rondônia, Brazil) was investigated by chamber and gradient methods. The ground resistance to NO 2 and O 3 deposition to soil was quantified for dry and wet surface conditions using dynamic chambers and was found to be fairly constant at 340 ± 110 and 190 ± 70 s m À1 , respectively. For clear-sky conditions, the thermal stratification of the air in the first meter from the forest floor was stable during daytime and unstable during nighttime. The aerodynamic resistance to NO 2 and O 3 deposition to the ground in the first meter above the forest floor was determined by measurements of 220 Rn and CO 2 concentration gradients and CO 2 surface fluxes. The aerodynamic resistance of the 1-m layer above the ground was 1700 s m À1 during daytime and 600 s m À1 during nighttime. The deposition flux of O 3 and NO 2 was quantified for clear-sky conditions from the measured concentrations and the quantified resistances. For both trace gases, deposition to the soil was generally observed. The O 3 deposition flux to the soil was only significantly different from zero during daytime. The maximum of À1.2 nmol m À2 s À1 was observed at about 1800 and the mean daytime flux was À0.5 nmol m À2 s À1 . The mean NO 2 deposition flux during daytime was À1.6 ng N m À2 s À1 and during nighttime À2.2 ng N m À2 s À1 . The NO x budget at the soil surface yielded net emission day and night. The NO 2 deposition flux was 74% of the soil NO emission flux during nighttime and 34% during daytime. The plant uptake of NO 2 and O 3 by the leaves of Laetia corymbulosa and Pouteria glomerata, two typical plant species for the Amazon rain forest, was investigated in a greenhouse in Oldenburg (Germany) using branch cuvettes. The uptake of O 3 was found to be completely under stomatal control. The uptake of NO 2 was also controlled by the stomatal resistance but an additional mesophyll resistance of the same order of magnitude as the stomatal resistance was necessary to explain the observed uptake rate.

The formation of suberized and lignified barriers in the exodermis is suggested to be part of a suite of adaptations to flooded or waterlogged conditions, adjusting transport of solutes and gases in and out of roots. In this study, the composition of apoplasmic barriers in hypodermal cell walls and oxygen profiles in roots and the surrounding medium of four Amazon tree species that are subjected to long-term flooding at their habitat was analyzed. In hypodermal cell walls of the deciduous tree Crateva benthami, suberization is very weak and dominated by monoacids, 2-hydroxy acids, and -hydroxycarboxylic acids. This species does not show any morphological adaptations to flooding and overcomes the aquatic period in a dormant state. Hypodermal cells of Tabernaemontana juruana, a tree which is able to maintain its leaf system during the aquatic phase, are characterized by extensively suberized walls, incrusted mainly by the unsaturated C 18 -hydroxycarboxylic acid and the ␣,-dicarboxylic acid analogon, known as typical suberin markers. Two other evergreen species, Laetia corymbulosa and Salix martiana, contained 3-to 4-fold less aliphatic suberin in the exodermis, but more than 85% of the aromatic moiety of suberin are composed of para-hydroxybenzoic acid, suggesting a function of suberin in pathogen defense. No major differences in the lignin content among the species were observed. Determination of oxygen distribution in the roots and rhizosphere of the four species revealed that radial loss of oxygen can be effectively restricted by the formation of suberized barriers but not by lignification of exodermal cell walls.Suberin is a heterogeneous extracellular biopolymer closely attached to the inner primary cell wall (Schreiber et al., 1999). On the basis of chemical analysis of enzymatically isolated cell walls, the composition of suberin in the exodermis was shown to consist of long-chain aliphatic monomers esterified with aromatic compounds like ferulic and coumaric acids and cell wall carbohydrates (Zeier and Schreiber, 1997; Kolattukudy, 2001). Recently, glycerol has been identified as a new important structural element in the suberin macromolecule, which is supposed to cross-link the aliphatic and aromatic suberin domains (Moire et al., 1999; Pereira, 2000a, 2000b). The aliphatic monomers of suberin are synthesized via the fatty acid biosynthetic pathway, catalyzed by fatty acid elongases in the root cells (Domeregue et al., 1998;Schreiber et al., 2000). Hydroxylation is mediated by cytochrome P450-dependent enzymes, converting -hydroxyacids to either 1,-dicarboxylic acids or alcohols (Agrawal and Kolattukudy, 1978;Le Bouquin et al., 2001). The assembly of the aromatic moiety of suberin, in most cases cinnamic acid derivatives, proceeds via the general phenylpropanoid pathway with Phe ammonia-lyase as the central enzyme (Kolattukudy, 2001). Similar to suberin, lignin is a highly variable biopolymer synthesized in a complex pathway. The basic lignin molecule is derived from the oxidative polymerization of the ...

Fluxes of CO and HO vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35 µmol CO (ground) ms in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO uptake rates between the two periods was the larger respiration flux during LW due to the CO efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO and HO vapour fluxes and incident radiation. The daily CO fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996-1997 agreed closely with that previously estimated for 1985-1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions.

Regenerants of rice were examined by RFLP analysis to determine the occurrence and extent of somaclonal variation. DNA polymorphisms were observed both among plants regenerated from different callus cultures as well as among sibling plants derived from a single callus. Regardless of the basal medium, a higher degree of genetic instability was found among plants regenerated from callus cultures maintained for longer incubation periods (67 days) than among those from shorter incubation periods (28 days). Detailed analysis showed that in several regenerants, there was a close correlation among those plants exhibiting DNA rearrangements and those with apparent methylation changes. Such alterations were observed with both structural and housekeeping genes.

Vµrzeas are species-rich forest communities of the Central Amazon floodplains, inhabited by highly adapted tree species that can withstand long flooding periods. The leaf shedding behaviour and morphological traits that may contribute to adaptation to low oxygen levels were studied at the Ilha de Marchantaria on the lower Solimðes-Amazonas river, Brazil, and in greenhouse experiments with cuttings of six tree species typical of the Amazon floodplain. Comparison of deciduousness in situ revealed that four of the species under investigation, Salix martiana, Tabernaemontana juruana, Laetia corymbulosa and Pouteria glomerata, are able to maintain their leaf system during the aquatic period. Adventitious roots were formed by S. martiana and T. juruana, but anatomical characteristics differed between the species. Whereas S. martiana developed lysigenous aerenchyma in its roots during aerobic and anaerobic growth, only small intercellular spaces of schizogenous origin were formed in the root cortex of T. juruana. Similar to the latter species, such spaces were constitutively formed in the deciduous species Crateva benthami and Vitex cymosa. Suberin deposits were observed in tangential and radial cell walls of the hypodermis of roots from T. juruana, L. corymbulosa and P. glomerata. Suberin deposits were less pronounced in roots of S. martiana and absent in V. cymosa and C. benthami. The data show that different, almost contrasting, survival mechanisms have evolved in roots of plants with similar life forms in the same habitat. The results further suggest that the morphological traits of the investigated trees are causally linked with the in situ leaf shedding behaviour.

Adaptation to prolonged flooding was investigated using cuttings of two tree species from the Central Amazon white-water floodplain (V�rzea). Morphological features and oxygen distribution patterns were correlated with metabolic changes under hypoxia, such as alterations in alcohol dehydrogenase (ADH) activity and adenylate energy charge (AEC) of root cells. Salix martiana (Leyb.) was able to react to hypoxic growth conditions with formation of adventitious roots rich in lysigenous aerenchyma, which facilitates root aeration by longitudinal oxygen transport and rhizosphere oxidation by radial oxygen loss (ROL). The oxygen concentration on the surface of adventitious roots of S. martiana reached 2-3 mg O2 L–1. The low resistance to gas exchange in Salix roots was reflected by low ADH activities, which ranged between 0.03-0.1 μmol NADH mg –1 min–1, and AEC values of 0.8-1 under hypoxic conditions. Adventitious roots were also formed by Tabernaemontana juruana ([Markgr.] Schumann ex. J.F. Macbride) during growth under low-oxygen conditions, although at a later stage. The gas-space continuum in roots of T. juruana was less pronounced, resulting in a 10-fold lower oxygen concentration in the root cortex under oxygen stress compared with adventitious roots of Salix. The lower oxygen content was reflected in 6-fold higher ADH activities and decreased AEC values. ROL occurred only at the non-suberized root tip, suggesting that the suberized hypodermis functions as a barrier against gas exchange between the root and the rhizosphere. These findings indicate that different strategies of adaptation to low oxygen levels are realized in the two species under investigation that occur naturally in the same ecosystem but inhabit different elevation sites.

The adenylate energy charge, production of ethanol and lactate, and nitrate reductase activity were determined in order to study the influence of different nitrogen sources on the metabolic responses of roots of Carexpseudocyperus L. and Carex sylvatica HUDS. exposed to anaerobic nutrient solutions. Determination ofadenylates was carried out by means of a modified HPLC technique. Total quantity of adenylates was higher in Carex pseudocyperus than in Carex sylvatica under all conditions. In contrast, the adenylate energy charge was only slightly different between the species and decreased more or less in relation to the applied nitrogen source under oxygen deficiency. The adenylate energy charge in roots of plants under nitrate nutrition showed a smaller decrease under anaerobic environmental conditions than plants grown with ammonium or nitrate/ammonium. Roots of nitrate-fed plants showed a lower ethanol and lactate production than ammonium/nitrate-and ammonium-fed plants. Ethanol production was higher in C. pseudocyperus, formation of lactate was lower compared to that in Carex sylvatica. The activity of enzymes involved in fermentation processes (ADH, LDH and PDC) was enhanced significantly after 24 hours of exposure to anaerobic nutrient solutions in roots of both species. The induction of these enzymes was only slightly influenced by different nitrogen supply. In vivo nitrate reductase activity increased almost 3-fold compared to the aerobic treatment in both species and overcompensated loss of NADH reoxidation capacity caused by decrease of ethanol and lactate development. Induction of in vitro nitrate reductase activity was enhanced 313% in C. pseudocyperus and 349% in C. sylvatica under anaerobic environmental conditions and nitrate supply. These results indicate that nitrate may serve as an alternative electron acceptor in anaerobic plant root metabolism and that the nitrate-supported energy charge may be due to an accelerated glycolytic flux resulting from a more effective NADH reoxidation capacity by nitrate reduction plus fermentation than by fermentation alone.Abbreviations: ADH-alcohol dehydrogenase, AEC-adenylate energy charge, DMSO-dimethyl sulfoxide, EDTAethylen diamine tetraacetic acid, HPLC-high performance liquid chromatography, LDH-lactate dehydrogenase, NRA-nitrate reductase activity, PCA-perchloric acid, PDC-pyruvate decarboxylase, PVP-polyvinylpyrrolidone, PVPP-polyvinylpolypyrrolidone, TCA-trichloroacetic acid, Tris-tris(hydroxymethyl)aminomethane.

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