Early physiological flood tolerance is followed by slow post-flooding root recovery in the dryland riparian tree Eucalyptus camaldulensis subsp. refulgens.

We investigated physiological and morphological responses to flooding and recovery in Eucalyptus camaldulensis subsp. refulgens, a riparian tree species from a dryland region prone to intense episodic floods. Seedlings in soil flooded for 88 d produced extensive adventitious roots, displayed stem hypertrophy (stem diameter increased by 93%) and increased root porosity owing to aerenchyma formation. Net photosynthesis (Pn) and stomatal conductance (gs) were maintained for at least 2 weeks of soil flooding, contrasting with previous studies of other subspecies of E. camaldulensis. Gradual declines followed in both gs (30% less than controls) and Pn (19% less). Total leaf soluble sugars did not differ between flooded and control plants. Root mass did not recover 32 d after flooding ceased, but gs was not lower than controls, suggesting the root system was able to functionally compensate. However, the limited root growth during recovery after flooding was surprising given the importance of extensive root systems in dryland environments. We conclude that early flood tolerance could be an adaptation to capitalize on scarce water resources in a water-limited environment. Overall, our findings highlight the need to assess flooding responses in relation to a species' fitness for particular flood regimes or ecological niches.

Pattern of solutes accumulated during leaf osmotic adjustment as related to duration of water deficit for wheat at the reproductive stage.

This study examined expression of osmotic adjustment (OA) and accumulation of solutes in wheat (Triticum aestivum L.) leaves in response to water deficit (WD) imposed at the reproductive stage. Two contrasting cultivars, Hartog and Sunco (putatively high and low in OA capacity, respectively), were grown in deep (viz. 80 cm) pots in a controlled environment. In a sandy substrate, leaf OA was 5-times greater in Hartog compared with Sunco. At 21 d of WD treatment, K(+) only accounted for 12% of OA in Hartog and 48% in Sunco with less OA (i.e. tissue K(+) led to different proportions owing to different magnitudes of OA). Glycinebetaine and proline also increased under WD, but these were not significant osmotica on a whole tissue basis. Hartog accumulated dry matter faster than Sunco under WD, and this was consistent with greater water extraction by Hartog than by Sunco. In a second experiment on Hartog, with loam added to the sand to increase water-holding capacity and thus enable a longer draw-down period, leaf OA increased to 0.37 MPa at 37 d of withholding water. K(+) increased up to 16 d of drying and then decreased towards 37 d. Glycinebetaine, proline, glucose and fructose all increased during the draw-down period, although with different dynamics; e.g. glycinebetaine increased linearly whereas glucose showed an exponential increase. By contrast, sucrose declined. K(+) was the major contributor to OA (viz. 54%) up to 30 d of drying, whereas glycinebetaine, proline and glucose were major contributors later (at d 37 these organic solutes each accounted for 19, 21 and 21% of OA). Thus, the various solutes that contributed to leaf OA in wheat cv. Hartog accumulated at different times as WD developed.

Transfer of the barrier to radial oxygen loss in roots of Hordeum marinum to wheat (Triticum aestivum): evaluation of four H. marinum-wheat amphiploids.

• Wide hybridization of waterlogging-tolerant Hordeum marinum with wheat (Triticum aestivum) to produce an amphiploid might be one approach to improve waterlogging tolerance in wheat. • Growth, root aerenchyma and porosity, and radial oxygen loss (ROL) along roots were measured in four H. marinum-wheat amphiploids and their parents (four accessions of H. marinum and Chinese Spring wheat) in aerated or stagnant nutrient solution. A soil experiment was also conducted. • Hordeum marinum maintained shoot dry mass in stagnant nutrient solution, whereas the growth of wheat was markedly reduced (40% of aerated control). Two of the four amphiploids were more tolerant than wheat (shoot dry masses of 59-72% of aerated controls). The porosity of adventitious roots when in stagnant solution was higher in H. marinum (19-25%) and the four amphiploids (20-24%) than in wheat (16%). In stagnant solution, adventitious roots of H. marinum formed a strong ROL barrier in basal zones, whereas, in wheat, the barrier was weak. Two amphiploids formed a strong ROL barrier and two formed a moderate barrier when in stagnant solution. • This study demonstrates the transfer of higher root porosity and a barrier to ROL from H. marinum to wheat through wide hybridization and the production of H. marinum-wheat amphiploids.

Tolerance of combined submergence and salinity in the halophytic stem-succulent Tecticornia pergranulata.

BACKGROUND AND AIMS: Habitats occupied by many halophytes are not only saline, but are also prone to flooding. Few studies have evaluated submergence tolerance in halophytes. METHODS: Responses to submergence, at a range of salinity levels, were studied for the halophytic stem-succulent Tecticornia pergranulata subsp. pergranulata (syn. Halosarcia pergranulata subsp. pergranulata). Growth and total sugars in succulent stems were assessed as a function of time after submergence. Underwater net photosynthesis, dark respiration, total sugars, glycinebetaine, Na(+), Cl(-) and K(+), in succulent stems, were assessed in a NaCl dose-response experiment. KEY RESULTS: Submerged plants ceased to grow, and tissue sugars declined. Photosynthesis by succulent stems was reduced markedly when underwater, as compared with in air. Capacity for underwater net photosynthesis (P(N)) was not affected by 10-400 mM NaCl, but it was reduced by 30 % at 800 mM. Dark respiration, underwater, increased in succulent stems at 200-800 mM NaCl, as compared with those at 10 mM NaCl. On an ethanol-insoluble dry mass basis, K(+) concentration in succulent stems of submerged plants was equal to that in drained controls, across all NaCl treatments. Na(+) and Cl(-) concentrations, however, were elevated in stems of submerged plants, but so was glycinebetaine. Submerged stems increased in succulence, so solutes would have been 'diluted' on a tissue-water basis. CONCLUSIONS: Tecticornia pergranulata tolerates complete submergence, even in waters of high salinity. A 'quiescence response', i.e. no shoot growth, would conserve carbohydrates, but tissue sugars still declined with time. A low K(+) : Na(+) ratio, typical for tissues of succulent halophytes, was tolerated even during prolonged submergence, as evidenced by maintenance of underwater P(N) at up to 400 mM NaCl. Underwater P(N) provides O(2) and sugars, and thus should enhance survival of submerged plants.

Flooding tolerance: suites of plant traits in variable environments.

Flooding regimes of different depths and durations impose selection pressures for various traits in terrestrial wetland plants. Suites of adaptive traits for different flooding stresses, such as soil waterlogging (short or long duration) and full submergence (short or long duration - shallow or deep), are reviewed. Synergies occur amongst traits for improved internal aeration, and those for anoxia tolerance and recovery, both for roots during soil waterlogging and shoots during submergence. Submergence tolerance of terrestrial species has recently been classified as either the Low Oxygen Quiescence Syndrome (LOQS) or the Low Oxygen Escape Syndrome (LOES), with advantages, respectively, in short duration or long duration (shallow) flood-prone environments. A major feature of species with the LOQS is that shoots do not elongate upon submergence, whereas those with the LOES show rapid shoot extension. In addition, plants faced with long duration deep submergence can demonstrate aspects of both syndromes; shoots do not elongate, but these are not quiescent, as new aquatic-type leaves are formed. Enhanced entries of O2 and CO2 from floodwaters into acclimated leaves, minimises O2 deprivation and improves underwater photosynthesis, respectively. Evolution of 'suites of traits' are evident in wild wetland species and in rice, adapted to particular flooding regimes.

Oxygen dynamics in submerged rice (Oryza sativa).

Complete submergence of plants prevents direct O(2) and CO(2) exchange with air. Underwater photosynthesis can result in marked diurnal changes in O(2) supply to submerged plants. Dynamics in pO(2) had not been measured directly for submerged rice (Oryza sativa), but in an earlier study, radial O(2) loss from roots showed an initial peak following shoot illumination. O(2) dynamics in shoots and roots of submerged rice were monitored during light and dark periods, using O(2) microelectrodes. Tissue sugar concentrations were also measured. On illumination of shoots of submerged rice, pO(2) increased rapidly and then declined slightly to a new quasi-steady state. An initial peak was evident first in the shoots and then in the roots, and was still observed when 20 mol m(-3) glucose was added to the medium to ensure substrate supply in roots. At the new quasi-steady state following illumination, sheath pO(2) was one order of magnitude higher than in darkness, enhancing also pO(2) in roots. The initial peak in pO(2) following illumination of submerged rice was likely to result from high initial rates of net photosynthesis, fuelled by CO(2) accumulated during the dark period. Nevertheless, since sugars decline with time in submerged rice, substrate limitation of respiration could also contribute to morning peaks in pO(2) after longer periods of submergence.

Salt tolerance in a Hordeum marinum-Triticum aestivum amphiploid, and its parents.

Growth, grain production, and physiological traits were evaluated for Hordeum marinum, Triticum aestivum (cv. Chinese Spring), and a H. marinum-T. aestivum amphiploid, when exposed to NaCl treatments in a nutrient solution. H. marinum was more salt tolerant than T. aestivum and the amphiploid was intermediate, both for vegetative growth and relative grain production. H. marinum was best able to 'exclude' Na(+) and Cl(-), particularly at high external NaCl. At 300 mM NaCl, concentrations of Na(+) (153 micromol g(-1) dry mass) and Cl(-) (75 micromol g(-1) dry mass) in the youngest fully-expanded leaf blade of H. marinum were, respectively, only 7% and 4% of those in T. aestivum; and in the amphiploid the Na(+) and Cl(-) concentrations were 39% and 36% of those in T. aestivum. Glycinebetaine and proline concentrations in the youngest fully-expanded leaf blade of plants exposed to 200 mM NaCl were highest in H. marinum (128 and 60 micromol g(-1) dry mass, respectively), lowest in T. aestivum (85 and 37 micromol g(-1) dry mass), and intermediate in the amphiploid (108 and 54 micromol g(-1) dry mass). Thus, salt tolerance of H. marinum was expressed in the H. marinum-T. aestivum amphiploid.

Oxygen dynamics during submergence in the halophytic stem succulent Halosarcia pergranulata.

This study elucidated O2 dynamics in shoots and roots of submerged Halosarcia pergranulata (Salicornioideae), a perennial halophytic stem succulent that grows on floodprone mudflats of salt lakes. Oxygen within shoots and roots was measured using microelectrodes, for plants when waterlogged or completely submerged, with shoots in light or in darkness, in a controlled environment. Net photosynthesis (PN) when underwater, at a range of dissolved CO2 concentrations, was measured by monitoring O2 production rates by excised stems. The bulky nature and apparently low volume of gas-filled spaces of the succulent stems resulted in relatively high radial resistance to gas diffusion. At ambient CO2, quasi-steady state rates of PN by excised succulent stems were estimated to be close to zero; nevertheless, in intact plants, underwater photosynthesis provided O2 to tissues and led to radial O2 loss (ROL) from the roots, at least during the first several hours (the time period measured) after submergence or when light periods followed darkness. The influence of light on tissue O2 dynamics was confirmed in an experiment on a submerged plant in a salt lake in south-western Australia. In the late afternoon, partial pressure of O2 (pO2) in the succulent stem was 23.2 kPa (i.e. approximately 10% above that in the air), while in the roots, it was 6.2-9.8 kPa. Upon sunset, the pO2 in the succulent stems declined within 1 h to below detection, but then showed some fluctuations with the pO2 increasing to at most 2.5 kPa during the night. At night, pO2 in the roots remained higher than in the succulent stems, especially for a root with the basal portion in the floodwater. At sunrise, the pO2 increased in the succulent stems within minutes. In the roots, changes in the pO2 lagged behind those in the succulent stems. In summary, photosynthesis in stems of submerged plants increased the pO2 in the shoots and roots so that tissues experience diurnal changes in the pO2, but O2 from the H2O column also entered submerged plants.

Morphological and physiological responses of rice (Oryza sativa) to limited phosphorus supply in aerated and stagnant solution culture.

BACKGROUND AND AIMS: Rain-fed lowland rice commonly encounters stresses from fluctuating water regimes and nutrient deficiency. Roots have to acquire both oxygen and nutrients under adverse conditions while also acclimating to changes in soil-water regime. This study assessed responses of rice roots to low phosphorus supply in aerated and stagnant nutrient solution. METHODS: Rice (Oryza sativa 'Amaroo') was grown in aerated solution with high P (200 micro m) for 14 d, then transferred to high or low (1.6 micro m) P supply in aerated or stagnant solution for up to 8 d. KEY RESULTS: After only 1 d in stagnant conditions, root radial oxygen loss (ROL) had decreased by 90 % in subapical zones, whereas near the tip ROL was maintained. After 4 d in stagnant conditions, maximum root length was 11 % less, and after 8 d, shoot growth was 25 % less, compared with plants in aerated solution. The plants in stagnant solution had up to 19 % more adventitious roots, 24 % greater root porosity and 26 % higher root/shoot ratio. Rice in low P supply had fewer tillers in both stagnant and aerated conditions. After 1-2 d in stagnant solution, relative P uptake declined, especially at low P supply. Aerated roots at low P supply maintained relative P uptake for 4 d, after which uptake decreased to the same levels as in stagnant solution. CONCLUSIONS: Roots responded rapidly to oxygen deficiency with decreased ROL in subapical zones within 1-2 d, indicating induction of a barrier to ROL, and these changes in ROL occurred at least 2 d before any changes in root morphology, porosity or anatomy were evident. Relative P uptake also decreased under oxygen deficiency, showing that a sudden decline in root-zone oxygen adversely affects P nutrition of rice.

Root aeration in rice (Oryza sativa): evaluation of oxygen, carbon dioxide, and ethylene as possible regulators of root acclimatizations.

Adventitious roots of rice (Oryza sativa) acclimatize to root-zone O(2) deficiency by increasing porosity, and induction of a barrier to radial O(2) loss (ROL) in basal zones, to enhance longitudinal O(2) diffusion towards the root tip. Changes in root-zone gas composition that might induce these acclimatizations, namely low O(2), elevated ethylene, ethylene-low O(2) interactions, and high CO(2), were evaluated in hydroponic experiments. Neither low O(2) (0 or 0.028 mol m(-3) O(2)), ethylene (0.2 or 2.0 microl l(-1)), or combinations of these treatments, induced the barrier to ROL. This lack of induction of the barrier to ROL was despite a positive response of aerenchyma formation to low O(2) and elevated ethylene. Carbon dioxide at 10 kPa had no effect on root porosity, the barrier to ROL, or on growth. Our findings that ethylene does not induce the barrier to ROL in roots of rice, even though it can enhance aerenchyma formation, shows that these two acclimatizations for improved root aeration are differentially regulated.

How plants cope with complete submergence.

Flooding is a widespread phenomenon that drastically reduces the growth and survival of terrestrial plants. The dramatic decrease of gas diffusion in water compared with in air is a major problem for terrestrial plants and limits the entry of CO(2) for photosynthesis and of O(2) for respiration. Responses to avoid the adverse effects of submergence are the central theme in this review. These include underwater photosynthesis, aerenchyma formation and enhanced shoot elongation. Aerenchyma facilitates gas diffusion inside plants so that shoot-derived O(2) can diffuse to O(2)-deprived plant parts, such as the roots. The underwater gas-exchange capacity of leaves can be greatly enhanced by a thinner cuticle, reorientation of the chloroplasts towards the epidermis and increased specific leaf area (i.e. thinner leaves). At the same time, plants can outgrow the water through increased shoot elongation, which in some species is preceded by an adjustment of leaf angle to a more vertical position. The molecular regulatory networks involved in these responses, including the putative signals to sense submergence, are discussed and suggestions made on how to unravel the mechanistic basis of the induced expression of various adaptations that alleviate O(2) shortage underwater.

Response and adaptation by plants to flooding stress.

Stress on plants imposed by flooding of the soil and deeper submergence constitutes one of the major abiotic constraints on growth, species' distribution and agricultural productivity. Flooding stress is also a strong driver of adaptive evolution. This has resulted in a wide range of biochemical, molecular and morphological adaptations that sanction growth and reproductive success under episodic or permanently flooded conditions that are highly damaging to the majority of plant species. However, even seemingly poorly adapted species possess some short-term resilience that is important for overall success of these plants in various habitats. The papers contained in this Special Issue address these topics and emphasize molecular, biochemical and developmental processes that impact on flooding tolerance. Most of the articles are based on lectures given to the 8th Conference of the International Society for Plant Anaerobiosis (ISPA), held at the University of Western Australia, Perth, 20-24 September, 2004. Reviews and research papers are presented from the leading laboratories currently working on plant responses to flooding stress.

Morphology, anatomy and histochemistry of Salicornioideae (Chenopodiaceae) fruits and seeds.

BACKGROUND AND AIMS: The subfamily Salicornioideae (Chenopodiaceae) are a taxonomically difficult group largely due to the lack of diagnostic characters available to delineate tribal- and generic-level boundaries; a consequence of their reduced floral and vegetative features. This study examined the variation in fruits and seeds across both tribes of the Salicornioideae to assess if characters support traditional taxonomic sections. METHODS: Light microscopy, environmental scanning electron microscopy and anatomical ultra-thin sectioning were employed to examine variation in fruits and seeds. Sixty-eight representatives across 14 of the 15 genera currently recognized within the tribes Halopeplideae and Salicornieae were examined to determine whether characters support current taxonomic groups. KEY RESULTS: Characters such as seed coat structure, embryo shape, seed orientation, the forms of seed storage proteins and carbohydrates show variation within the Salicornioideae and may be phylogenetically useful. The campylotropous ovule typical of the Chenopodiaceae generally results in a curved embryo; however, many Halosarcia and Sclerostegia species have straight embryos and in Salicornia and Sarcocornia the large peripheral embryo appears bent rather than curved. Seed coat ornamentation of Microcnemum and Arthrocnemum is distinct from other Salicornioideae as the elongated epidermal cells of the exotesta have convex walls. Histochemical stains of anatomical sections of cotyledon cells showed protein bodies were variable in shape, and starch grains were present in some species, namely Salicornia bigelovii, S. europaea and Allenrolfea occidentalis. CONCLUSIONS: While fruits and seeds were found to be variable within the subfamily, no synapomorphic characters support the tribe Halopeplideae as these genera have crustaceous seed coats, curved embryos and abundant perisperm; features characteristic of many of the tribe Salicornieae. The endemic Australian genera are closely related and few seed and fruit characters are diagnostic at the generic level. Nineteen characters identified as being potentially informative will be included in future phylogenetic analyses of the subfamily.

Expression of alpha-expansin genes during root acclimations to O2 deficiency in Rumex palustris.

Thirteen alpha-expansin genes were isolated from Rumex palustris , adding to the six already documented for this species. Five alpha-expansin genes were selected for expression studies in various organs/tissues of R. palustris , with a focus on roots exposed to aerated or O2)-deficient conditions, using real-time RT-PCR. Several cases of differential expression of alpha-expansin genes in the various root types of R. palustris were documented, and the identity of the dominant transcript differed between root types (i.e., tap root vs. lateral roots vs. adventitious roots). Several genes were expressed differentially in response to low O2. In situ hybridizations showed expansin mRNA expression in the oldest region of the tap root was localized to cells near the vascular cambium; this being the first report of expansin expression associated with secondary growth in roots. In situ hybridization also showed abundant expression of expansin mRNA in the most apical 1 mm of adventitious roots. Such early expression of expansin mRNA in cells soon after being produced by the root apex presumably enables cell wall loosening in the elongation zone of roots. In addition, expression of some expansin mRNAs increased in 'mature zones' of roots; these expansins might be involved in root hair formation or in formation of lateral root primordia. The present findings support the notion that large gene families of alpha-expansins enable flexibility in expression for various organs and tissues as a normal part of plant development, as well as in response to abiotic stress.

Properties of several fly ash materials in relation to use as soil amendments.

Fly ash samples from five power stations in Western Australia and Queensland, and two soils used for horticulture in Western Australia, were evaluated for a series of physical and chemical properties. Soils were comprised primarily of coarse sand-sized particles, whereas most of the fly ashes were primarily fine sand- and silt-sized particles. Hydraulic conductivities in the fly ashes were 105- to 248-fold slower than in the soils. The water-holding capacities of fly ashes at "field capacity" were three times higher than those of the soils. Extractable P in the fly ashes (except Tarong and Callide) were 20- to 88-fold higher than in the soils. The pH showed considerable variation among the different sources of fly ash, with samples from Muja being the most acidic (pH = 3.8; 1:5 in CaCl2 extract) and from Gladstone the most alkaline (pH = 9.9). The toxicity characteristic leaching procedure (TCLP) values indicate that the potential for release of trace elements from the fly ashes was well below regulatory levels. When applied at sufficient rates (e.g., to achieve 10% w/w in surface layers) to sandy soils, fly ash altered texture and increased water-holding capacity. Depending on the source of fly ash used, such amendments could also provide P and aid nutrient retention by increasing the phosphorus retention index (PRI) and/or cation exchange capacity (CEC). The considerable variability in physical and chemical properties among the fly ash samples evaluated in the present study supports the notion that field trials are essential to the future development of soil amendment strategies making use of any particular source of fly ash.

De-submergence-induced ethylene production in Rumex palustris: regulation and ecophysiological significance.

Rumex palustris responds to total submergence by increasing the elongation rate of young petioles. This favours survival by shortening the duration of submergence. Underwater elongation is stimulated by ethylene entrapped within the plant by surrounding water. However, abnormally fast extension rates were found to be maintained even when leaf tips emerged above the floodwater. This fast post-submergence growth was linked to a promotion of ethylene production that is presumed to compensate for losses brought about by ventilation. Three sources of ACC contributed to post-submergence ethylene production in R. palustris: (i) ACC that had accumulated in the roots during submergence and was transported in xylem sap to the shoot when stomata re-opened and transpiration resumed, (ii) ACC that had accumulated in the shoot during the preceding period of submergence and (iii) ACC produced de novo in the shoot following de-submergence. This new production of ethylene was associated with increased expression of an ACC synthase gene (RP-ACS1) and an ACC oxidase gene (RP-ACO1), increased ACC synthase activity and a doubling of ACC oxidase activity, measured in vitro. Out of seven species of Rumex examined, a de-submergence upsurge in ethylene production was seen only in shoots of those that had the ability to elongate fast when submerged.

Responses by coleoptiles of intact rice seedlings to anoxia: k(+) net uptake from the external solution and translocation from the caryopses.

This study evaluated the effects of anoxia on K(+) uptake and translocation in 3-4-d-old, intact, rice seedlings (Oryza sativa L. cv. Calrose). Rates of net K(+) uptake from the medium over 24 h by coleoptiles of anoxic seedlings were inhibited by 83-91 %, when compared with rates in aerated seedlings. Similar uptake rates, and degree of inhibition due to anoxia, were found for Rb(+) when supplied over 1.5-2 h, starting 22 h after imposing anoxia. The Rb(+) uptake indicated that intact coleoptiles take up ions directly from the external solution. Monovalent cation (K(+) and Rb(+)) net uptake from the solution was inhibited by anoxia to the same degree for the coleoptiles of intact seedlings and for coleoptiles excised, 'aged', and supplied with exogenous glucose. Transport of endogenous K(+) from caryopses to coleoptiles was inhibited less by anoxia than net K(+) uptake from the solution, the inhibition being 55 % rather than 87 %. Despite these inhibitions, osmotic pressures of sap (pi(sap)) expressed from coleoptiles of seedlings exposed to 48 h of anoxia, with or without exogenous K(+), were 0.66 +/- 0.03 MPa; however, the contributions of K(+) to pi(sap) were 23 and 16 %, respectively. After 24 h of anoxia, the K(+) concentrations in the basal 10 mm of the coleoptiles of seedlings with or without exogenous K(+), were similar to those in aerated seedlings with exogenous K(+). In contrast, K(+) concentrations had decreased in aerated seedlings without exogenous K(+), presumably due to 'dilution' by growth; fresh weight gains of the coleoptile being 3.6- to 4.7-fold greater in aerated than in anoxic seedlings. Deposition rates of K(+) along the axes of the coleoptiles were calculated for the anoxic seedlings only, for which we assessed the elongation zone to be only the basal 4 mm. K(+) deposition in the basal 6 mm was similar for seedlings with or without exogenous K(+), at 0.6-0.87 micro mol g(-1) f. wt h(-1). Deposition rates in zones above 6 mm from the base were greater for seedlings with, than without, exogenous K(+); the latter were sometimes negative. We conclude that for the coleoptiles of rice seedlings, anoxia inhibits net K(+) uptake from the external solution to a much larger extent than K(+) translocation from the caryopses. Furthermore, K(+) concentrations in the elongation zone of the coleoptiles of anoxic seedlings were maintained to a remarkable degree, contributing to maintenance of pi(sap) in cells of these elongating tissues.

Aerenchyma and an inducible barrier to radial oxygen loss facilitate root aeration in upland, paddy and deep-water rice (Oryza sativa L.).

The present study evaluated waterlogging tolerance, root porosity and radial O(2) loss (ROL) from the adventitious roots, of seven upland, three paddy, and two deep-water genotypes of rice (Oryza sativa L.). Upland types, with the exception of one genotype, were as tolerant of 30 d soil waterlogging as the paddy and deep-water types. In all but one of the 12 genotypes, the number of adventitious roots per stem increased for plants grown in waterlogged, compared with drained, soil. When grown in stagnant deoxygenated nutrient solution, genotypic variation was evident for root porosity and rates of ROL, but there was no overall difference between plants from the three cultural types. Adventitious root porosity increased from 20-26 % for plants grown in aerated solution to 29-41 % for plants grown in stagnant solution. Growth in stagnant solution also induced a 'tight' barrier to ROL in the basal regions of adventitious roots of five of the seven upland types, all three paddy types, and the two deep-water types. The enhanced porosity provided a low resistance pathway for O(2) movement to the root tip, and the barrier to ROL in basal zones would have further enhanced longitudinal O(2) diffusion towards the apex, by diminishing losses to the rhizosphere. The plasticity in root physiology, as described above, presumably contributes to the ability of rice to grow in diverse environments that differ markedly in soil waterlogging, such as drained upland soils as well as waterlogged paddy fields.

Evidence for down-regulation of ethanolic fermentation and K+ effluxes in the coleoptile of rice seedlings during prolonged anoxia.

Ethanolic fermentation, the predominant catabolic pathway in anoxia-tolerant rice coleoptiles, was manipulated in excised and 'aged' tissues via glucose feeding. Coleoptiles with exogenous glucose survived 60 h of anoxia, as evidenced by vigorous rates of K+ and phosphate net uptake and growth of roots and shoots when re-aerated. In contrast, coleoptiles without exogenous glucose showed net losses of K+ and phosphates starting 12 h after anoxia was imposed and these did not recover fully when re-aerated after 60 h of anoxia. Ethanol production (micromol x g(-1) FW x h(-1)) declined from about 7.5 during the first 12 h of anoxia to 5 or 2.2 after 48-60 h, in coleoptiles with or without exogenous glucose, respectively. Carbohydrate concentrations changed only slightly in anoxic coleoptiles with exogenous glucose due to net glucose uptake at 2.6 micromol x g(-1) FW x h(-1). Ethanolic fermentation, and therefore ATP production, may have been down-regulated after an initial period of acclimation to anoxia in coleoptiles with exogenous glucose. Maintenance requirements for energy were assessed to be 3.4-7.6-fold lower in these anoxic coleoptiles than published estimates for non-growing aerated leaf tissues. A modest part of the required economy in energy consumption would have been derived from diminished ion transport; anoxia reduced K+ and phosphate net uptake by 70-90% in these coleoptiles. K+ efflux was 10-fold lower in anoxic than in aerated coleoptiles with exogenous glucose. Using the unidirectional efflux equation, the membrane permeability to K+ was estimated to be 17-fold lower in anoxic than in aerated coleoptiles, presumably due to predominantly closed K+ channels.

Simultaneous determination by capillary gas chromatography of organic acids, sugars, and sugar alcohols in plant tissue extracts as their trimethylsilyl derivatives.

A capillary gas chromatographic (GC) method for the simultaneous determination of organic acids, sugars, and sugar alcohols extracted from plant tissues is described. Plant leaves were extracted in 5% (w/v) perchloric acid and neutralized extracts were purified using C18 cartridges. Organic acids, sugars, and sugar alcohols in purified extracts were converted to their trimethylsilyl (TMS)/TMS-oxime derivatives prior to separation and detection by capillary GC with flame ionization detection (FID). Derivatization procedures were investigated in detail and the compounds of interest were readily converted to their TMS/TMS-oxime derivatives using hexamethyldisiazane reagent in acetonitrile solvent (1:6 v/v) at 100 degreesC for 60 min. The derivatives were sufficiently volatile and stable. The FID response to derivatized compounds was generally linear in the concentration range 30-300 microg ml-1, with detection limits in the order of 3-76 ng. The proposed method was demonstrated for the determination of organic acids, sugars, and sugar alcohols in leaf extracts of two native Australian plants.