Devonian climate change, breathing, and the origin of the tetrapod stem group

The diversification of the tetrapod stem group occurred duringthe late Middle through the Late Devonian, that is from theGivetian to Famennian stages about 385–365 million yearsago. The relationships between the known taxa representing thisradiation have currently reached a reasonable consensus so thatinterpretations of the order of appearance of tetrapod charactersis possible. The immediate fish relatives of the earliest limbedtetrapods show what is interpreted as a progressive increasein the spiracular chamber and its opening to the outside. Here,this is inferred to be associated with an increased capacityfor air-breathing. Lungs are thought to have been present inmost early bony fishes, and were most likely ventilated by air-gulping.This could have brought about a facultative capacity for air-breathing,which the tetrapod stem group exploited to the greatest degree.These adaptations are shown not only in freshwater forms butalso in estuarine and marginal marine forms. Estimates of oxygenlevels during this period suggest that they were unprecedentedlylow during the Givetian and Frasnian periods. At the same time,plant diversification was at its most rapid, changing the characterof the landscape and contributing, via soils, soluble nutrients,and decaying plant matter, to anoxia in all water systems. Theco-occurrence of these global events may explain the evolutionof air-breathing adaptations in at least two lobe-finned groups,contributing directly to the rise of the tetrapod stem group.In contrast to recent studies, low atmospheric oxygen is notconsidered to be a causal factor in the lack of fossils documentingthe evolution of Early Carboniferous tetrapods.     

G proteins as regulators in ethylene-mediated hypoxia signaling

Waterlogging or flooding are frequently or constitutively encountered by many plant species. The resulting reduction in endogenous O₂ concentration poses a severe threat. Numerous adaptations at the anatomical, morphological and metabolic level help plants to either escape low oxygen conditions or to endure them. Formation of aerenchyma or rapid shoot elongation are escape responses, as is the formation of adventitious roots. The metabolic shift from aerobic respiration to anaerobic fermentation contributes to a basal energy supply at low oxygen conditions. Ethylene plays a central role in hypoxic stress signaling, and G proteins have been recognized as crucial signal transducers in various hypoxic signaling pathways. The programmed death of parenchyma cells that results in hypoxia-induced aerenchyma formation is an ethylene response. In maize, aerenchyma are induced in the absence of ethylene when G proteins are constitutively activated. Similarly, ethylene induced death of epidermal cells that cover adventitious roots at the stem node of rice is strictly dependent on heterotrimeric G protein activity. Knock down of the unique Gα gene RGA1 in rice prevents epidermal cell death. Finally, in Arabidopsis, induction of alcohol dehydrogenase with resulting increased plant survival relies on the balanced activities of a small Rop G protein and its deactivating protein RopGAP4. Identifying the general mechanisms of G protein signaling in hypoxia adaptation of plants is one of the tasks ahead.Key words: submergence, hypoxia, ethylene, G protein, reactive oxygen species, H₂O₂     

Oxygen isotope ratios between soil water and stem water of trees in pot experiments

Since the oxygen isotopic ratio of water extracted from stems reflects that of water taken up by roots, the stem water isotope ratio can be used to analyze the source of water for plant growth. However, it is known that the fractionation of isotopes during evaporation from the surface soil increases the isotope ratio in soil water drastically. In this study, it was experimentally confirmed that the stem water of Elaeocarpus sylvestris vs. ellipticus Hara seedlings is not isotopically similar to the water source in the case where evaporation from the soil occurs actively. However, since water in these plant bodies was replaced in about 2 days in the pot experiments, the 2-day-averaged values of the soil water isotope ratio approached the stem water isotope ratio. Thus, time-course samplings of the soil and stems, and measurements of the replacement time of water in the plant body (water volume in plant/transpiration rate) are recommended for correct interpretation of the isotopic signature of soil water and stem water.     

Quantitative Estimations of Downward Oxygen Transport from Aerial to Subterranean Parts in Intact Seedlings of Rice and Other Plants

Quantitative estimations of downward oxygen transport from aerial to subterranean parts in intact seedlings were carried out in the present investigation with the respiratory hydrometer specially designed by us for this purpose. The chief object of the investigation is rice, a crop which is notable for its marshy habitat and whose submerged roots are in particular demand of such transport. Some other common plants (wheat, pea, water cress, etc.), either of marshy or of mesophytic habitat, have also been included in the investigation for comparison. Although rice has long been known for its capability of downward oxygen transport, as has often been revealed by various qualitative demonstrations and indirect estimations; yet, data of direct quantitative measurement of the actual amount transported, so far as we are aware, have been very scanty. The few attempts of bringing about such quantitative measurement in an intact plant are made by enclosing its shoot and root in two adjoining compartments respectively, and gas analysis is made on samples taken from each compartment at intervals. The procedure is so elaborate and tedious that estimations on a large scale could not be readily carried out and the results have often been rendered unreliable by mishandling of the plant and air leakage between the compartments. Proposals to the path and mechanism of downward oxygen transport in higher plants have largely been based upon such scanty quantitative approximations and various qualitative observations, and the conclusions derived therefrom are contraversial and far from being convincing. The presentation in this communication of a simple yet accurate experimental method for the quantitative determination of this kind might be opportune and appropriate. The basic principle of the respiratory hydrometer employed in this investigation has been given previously (Lou et al., 1963). Seedlings raised in water culture are inserted into the vessel of the hydrometer (Fig. 1) with its aerial part in the air space above and roots in the water passage below. As the diffusion rate of oxygen in water is about 1/300,000 that in air, the submerged roots of an intact rice seedling practically have their immediate oxygen supply cut off and have to rely upon the oxygen transported from above. Downward oxygen transport in intact seedlings can be easily estimated through the following procedures and the results thus obtained are summarized below: 1. The difference between two consecutive determinations of the oxygen absorbed by the aerial parts of intact seedlings made before and after their roots are severed gives the amount of oxygen transported downwards to roots. For the marshy plant (rice, water cress), it is about 50% (range: 30%–70%) of the total amount absorbed; whereas for ordinary land plants raised in water culture (wheat, pea), it is 20%–30% of the total. 2. The above results are in good agreement with those obtained by determining the respiratory quotients of intact seedlings first in air (e.g.R.Q. ≌ 1 in case of rice seedling) and then with their roots submerged in water (R.Q. ≌ 0.5). The difference between the two consecutive determinations again gives the fraction of oxygen transported downwards. 3. Either by varying the oxygen supply to the aerial part (from 1/4 to twice the oxygen content in air) or by increasing the oxygen consumption of the root through temperature increase or DNP stimulation, the oxygen concentration gradient along the vertical axis of the plant can be steepened or lessened at will. When such experiment is carried out in rice seedlings, the amount of oxygen transported downwards increases with the gradient.     

Site of Oxygen Absorption for Downward Transport in Seedlings of Rice and Other Plants

Our earlier reports have shown that appreciable portions (ranging from 20% to 70%) of the total amount of oxygen absorbed by the aerial part can be transported downwards to roots in water cultured intact seedlings of rice, barnyard grass, wheat, pea, etc. By interrupting the alternative paths of transport, it has been demonstrated that oxygen moves downwards mainly through gaseous diffusion along the intercellularspaces in the cortex. The aim of the present investigation is to ascertain the site of oxygen absorption for downward transport in the aerial part and to show that such a transport does not necessarily involve active participation of the absorbing organ. The results are summarized below: 1. Provided that a small upper portion of the leaf is left exposed in air, flooding of the aerial part of the rice seedling does not reduce the amount of total oxygen absorption to any appreciable extent (Fig. 1). In agreement with field observation, the unflooded tip is capable of furnishing the submerged part with enough oxygen to keep it alive. 2. Nor does the complete or partial removal of leaves by cutting in seedlings of rice and pea affect downward oxygen transport appreciably, provided that the stem segment or a leaf sheath is left exposed in air. 3. The following common notion has been confirmed by actual measurement: The abnormal excessive elongation of the coleoptile in rice seedling germinated under water, which may easily extend itself above the water surface, is an adaptive device to furnish the seedling with the oxygen required for root development. 4. The "floating" roots developed at the later stage in rice culture have been demonstrated to be a possible site of oxygen absorption for downward transport. 5. When a rice seedling is held up side down, with its roots exposed in air and the shoot submerged, downward oxygen transport still takes place, although to a lesser extent than in its normal position.     

Growth and metabolism of Typha species in relation to cutting treatments

Container and field experiments, in which Typha latifolia L. and Typha angustifolia L. were cut either above or below the water level, were conducted to determine the physiological basis for reports that the latter treatment was more effective as a control measure. In containers, measurements of oxygen concentrations within the aerenchyma of the rhizome both with an oxygen electrode and by gas chromatography showed that oxygen could diffuse very readily to plant parts growing in an anoxic environment if there was a small amount of leaf or cut plant stem growing above the water level. When all shoots were cut below water, the oxygen in submersed plant parts was rapidly consumed and anaerobic respiration resulted in the production of ethanol. Lactate or elevated malate levels were not found. The below-water biomass decayed rapidly under these conditions and the plants had a much lower regenerative ability than plants cut above water where oxygen continued to reach the roots and rhizomes. In the field, three cuts during the growing season below water were sufficient to kill nearly all the underwater biomass; similar cuts above water reduced the total biomass compared with uncut plants, but much of the underwater biomass remained healthy and able to regenerate.     

Distribution of alcohol dehydrogenase in roots and shoots of rice (Oryza sativa) and Echinochloa seedlings

Abstract 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.     

Tolerance of crop plants to oxygen deficiency stress: fermentative activity and photosynthetic capacity of entire seedlings under hypoxia and anoxia

The study investigates the reactions of rice, wheat and maize to anoxia (plants without access to oxygen) and hypoxia (roots with very limited access to oxygen). We studied the adaptations of these intact crop plants because they are known to differ widely in their tolerance to oxygen deficiency. In hypoxia, there was an accumulation of sugars, especially in wheat and maize, although both flood-sensitive species significantly increased the activities of fermentative and glycolytic enzymes, clearly more than in rice. In rice, avoiding an oxygen limitation due to the effective aeration system (30% of root cross-sectional area) may have accounted for only a minor metabolic reaction to hypoxia. In anoxia, maize and wheat quickly lost viability and nearly all photosynthetic capacity, while most rice leaves stayed turgid and green, losing only 50% of the photosynthetic capacity. A strong metabolic arrest under anoxia was obvious for the sucrolytic, glycolytic and fermentative enzymes in all tested species, but was most pronounced in rice. Of the 14 enzymes studied, rice showed the lowest activity increase in hypoxia for 11 enzymes, and the strongest activity decrease in anoxia for 8 enzymes. However, rice was able even under anoxia to keep a 1/4 of the ATP level of the aerated control, while it was at the detection limit in maize and wheat. It appears that in anoxic rice, the switch to metabolic dormancy and maintenance of basic shoot meristems diminishes the needs for energy and substrate. Additionally, rice already has lower sugar demand under hypoxia, and sugar supply appears to be sustained under anoxia by a functioning anaerobic amylase and by the photosynthetically active shoot.     

Effect of gas pressure in the root and stem base zone on methane transport through rice bodies

Ebullition of gas bubbles from the soil surface is, in some cases (e.g., in early growth stage of rice), one of the major pathways for methane transport from rice paddies to the atmosphere. However, the role of the gas phase (entrapped gas) in the paddy soil in plant-mediated methane transport, which is the major pathway for methane emission, has not been clarified. To clarify the effect of the gas phase below ground on the methane emission rate through rice plants, we partly exposed the root and stem base of hydroponically grown rice to a high concentration of methane gas at various gas pressures, and immersed the rest of the roots in a solution with a high methane concentration. The methane emission rate was measured from the top of the rice plant using a flow-through chamber method. The methane emission rate drastically increased with a small increase in gas pressure in the gas phase at the root and stem base zone, with about a 3 times larger emission rate being observed with 10 × 10^-3 atm of extra pressure (corresponding to 10 cm of standing water in rice paddy) compared to no extra pressure. However, when alginate was applied to the stem near the base to prevent contact with the gas phase, the methane emission rate did not increase with increasing gas pressure. On the other hand, from observations in the rice paddy, it was found that the gas is entrapped near the surface (e.g., at a depth of 1 cm) and the gas entrapped in the soil would come into direct contact with a part of the stem near the base of the rice plant. Thus, the gas entrapped in the soil could enter into the rice body directly from the part of the stem near the base which is beneath the soil surface due to gas pressure in the gas phase resulting from the pressure exerted by the standing water. Hence, this mechanism involving the entrapped gas could play an important role in methane emission from rice paddy by affecting the plant-mediated methane transport as well as ebullition of gas bubbles.     

Ecology of deepwater rice-fields in Bangladesh 5. Mineral composition of the rice plant and other aquatic macrophytes

The mineral composition of deepwater rice (cultivar Kartik Sail) was studied during 1986 in a field near Sonargaon, Bangladesh, which is flooded by water from R. Meghna. Samples were taken four times, once prior to flooding and three times during the flood season. On two of the latter days (10 August = end of first flood peak, 23 September = second flood peak) the study was extended to other components of the ecosystem (sediments + soil, water, other aquatic macrophytes). On 23 September, 32% of the mass of the plant was out of water, 65% in water and 3% in sediment/soil. There were marked differences between elements in their pattern of accumulation by deepwater rice through the season. In comparison with the final totals for each element, about 48% of N, but only 11% of P and 10% of Na had been accumulated by the time the floodwater had arrived. The aquatic roots doubled in mass between the times of the two flood peaks and it is suggested that much of the P taken up by the plant may reach the plant via its aquatic roots after having becoming mobilized and released to the water when sediments become anaerobic. In comparison with other parts of the plant, Na was always much higher in the stem and Zn in the basal roots.Other aquatic macrophytes (weeds) increased from 0.40% of the mass (dry weight) of deepwater rice on 10 August to 4.0% on 23 September. However their content of each element (% dry weight) was considerably higher than that in deepwater rice, so they may at times compete effectively with the rice for nutrients. During the flood period (to 23 September) weeds accumulated 16% of the N accumulated by rice during the same period.     

Can small water level fluctuations affect the biomass of Nymphaea alba in large lakes?

In this study we investigated above-ground biomass and morphological responses of a floating-leaved plant species, Nymphaea alba, to small spring water level manipulations (0.1–0.5 m) in a large, shallow lake over a 9-year period (1995–2003). A year effect was found in mean annual above-ground plant biomass with higher values found in years of low water levels, 275–339 g DW m⁻² in 1995 and 2003 against 143–198 g DW m⁻² in 1996–2002 (no data transformation). No significant changes in biomass patterns were observed within each season (one summer peak), except in 1995 when a summer decline in biomass occurred. The amplitude and duration of exposure to high water levels affected the spring and annual above ground biomass of N. alba. The plant responded to high spring water levels by producing longer and thinner petioles to preserve leaves from flooding while no significant changes in leaf surface area (except in May) and leaf/petiole biomass ratio were obtained. The results are interpreted with regard to plant adaptations to changing environments (biomass allocation patterns in the different plant organs and stem density) and the effects of other abiotic factors relevant to the size of the system. We concluded that small deviations in spring water level can be driving forces in a large system in controlling the above-ground biomass of this floating-leaved plant.     

芽胞杆菌浸种对水稻内生细菌群落结构的影响

水稻内生细菌群落是反映植株内环境是否健康稳定的重要生物学指标,芽胞杆菌是防治水稻病害的重要生防微生物。为揭示芽胞杆菌浸种处理对水稻内生细菌群落结构的影响,采用Illumina MiSeq测序的方法对水稻内生细菌的16S rRNA基因进行测序,剖析了芽胞杆菌浸种处理对不同水稻组织内生细菌的微生态调控作用。结果表明,3种芽胞杆菌浸种处理可以提高水稻根和茎部内生细菌群落的丰富度和均匀度,降低叶部内生细菌群落的丰富度和均匀度,显著增加根部内生细菌群落多样性。变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)是水稻根部和茎部共有优势菌门,厚壁菌门和芽胞杆菌属(Bacillus)是叶部共有优势菌门和属。芽胞杆菌浸种处理显著提高了叶部内生厚壁菌门和芽胞杆菌属的相对丰度,增加了根系和茎部组织内生细菌的分类单元OTU(Operational Taxonomic Units)数量,对叶部组织影响不明显;降低了茎部和叶部中参与各种代谢通路的内生细菌丰度,显著增加了根部参与代谢通路的内生细菌丰度。因此,3种芽胞杆菌浸种处理可以显著改变水稻根部、茎部和叶部内生细菌群落结构,改善水稻生长的微生态环境。     

How insects overcome two‐component plant chemical defence: plant β‐glucosidases as the main target for herbivore adaptation

Insect herbivory is often restricted by glucosylated plant chemical defence compounds that are activated by plant β‐glucosidases to release toxic aglucones upon plant tissue damage. Such two‐component plant defences are widespread in the plant kingdom and examples of these classes of compounds are alkaloid, benzoxazinoid, cyanogenic and iridoid glucosides as well as glucosinolates and salicinoids. Conversely, many insects have evolved a diversity of counter‐adaptations to overcome this type of constitutive chemical defence. Here we discuss that such counter‐adaptations occur at different time points, before and during feeding as well as during digestion, and at several levels such as the insects' feeding behaviour, physiology and metabolism. Insect adaptations frequently circumvent or counteract the activity of the plant β‐glucosidases, bioactivating enzymes that are a key element in the plant's two‐component chemical defence. These adaptations include host plant choice, non‐disruptive feeding guilds and various physiological adaptations as well as metabolic enzymatic strategies of the insect's digestive system. Furthermore, insect adaptations often act in combination, may exist in both generalists and specialists, and can act on different classes of defence compounds. We discuss how generalist and specialist insects appear to differ in their ability to use these different types of adaptations: in generalists, adaptations are often inducible, whereas in specialists they are often constitutive. Future studies are suggested to investigate in detail how insect adaptations act in combination to overcome plant chemical defences and to allow ecologically relevant conclusions.     

短期干旱对水稻叶水势、光合作用及干物质分配的影响

采用盆栽水分试验,研究了不同生育期短期干旱处理对水稻叶水势、光合作用和干物质分配的影响．结果表明,干旱胁迫后,水稻叶水势低于对照,午后叶水势回升缓慢。凌晨叶水势随土壤含水量的降低而降低,表现为阈值反应。叶片净光合速率与凌晨叶水势密切相关,低于凌晨叶水势临界值,水稻叶片净光合速率急剧下降在水稻抽穗期和灌浆期叶片净光合速率显著下降的凌晨叶水势临界值为-1.04和-1．13MPa,对应的土壤含水量阈值分别为饱和含水量的61.0％和50．9％,土壤水势分别为-0．133和-0．240MPa干旱胁迫下单叶净光合速率的日变化规律表现为：胁迫较轻时,单叶净光合速率在正午附近出现低谷;胁迫严重时,净光合速率全天低于对照,且不及对照的一半。短期干旱后,水稻叶、根、穗的分配指数均降低,茎鞘的分配指数升高。本研究可为水稻节水灌溉管理和水分限制下水稻的生长模拟提供生理基础和理论依据。     

Insect eggs exert rapid control over an oxygen-water tradeoff

In terrestrial environments, the exchange of respiratory gases exacts a water cost: obtaining oxygen or carbon dioxide requires losing water. Insect eggs should be especially sensitive to this tradeoff-because they are unable to forage for water, have high surface area-to-volume ratios, and experience large temperature-driven changes in oxygen demand. Previous work from our laboratory, on eggs of a common hawk-moth, Manduca sexta, has shown that, during development, metabolic rate and water loss rates rise in parallel. These correlative data suggest that eggshell conductance increases to accommodate increasing metabolic demand. Here, we test this idea experimentally by subjecting eggs of M. sexta to 15, 21 (normoxia) and 35% oxygen for 24h, while measuring rates of metabolism (as carbon dioxide emission) and water loss. Hypoxia depressed egg metabolic rates, but led to pronounced, rapid increases in water loss. By contrast, hyperoxia had no significant effect on metabolism or water loss. These data demonstrate that insect eggs actively participate in balancing oxygen gain and water loss, and that they use tissue oxygen status, or some correlate of it, as a cue for increasing eggshell conductance. Rapid control over conductance may allow eggs to conserve water during an initial period of low metabolic demand, thereby deferring water costs of respiratory gas exchange until late in development.     

安徽禹会村遗址双墩文化时期农业发展的植硅体证据

本文利用植硅体分析方法,对安徽蚌埠禹会村遗址双墩文化时期44份土壤样品开展植物考古研究,重点关注典型农作物植硅体类型及其形态特征,以及敏感型与固定型植硅体组合特征等。结果显示,禹会村遗址大部分样品中皆发现有水稻特征型植硅体,并未发现粟、黍等旱地作物遗存;水稻扇型及双峰型植硅体形态特征分析显示,水稻遗存为驯化程度较高的粳型稻。以上研究结果表明,该遗址双墩文化时期的农业结构延续了顺山集文化时期以来种植粳型稻为主的传统。此外,通过水稻植硅体高密度样品中敏感型与固定型植硅体含量比值为0.7±0.2推测,该遗址水稻栽培环境属于“高地势-雨水供给”或“低地势-雨水供给”类型。本文研究结果为探讨淮河中游地区新石器时代农业发展、水稻栽培与驯化以及人类适应策略等问题提供了重要科学依据。     

Humid microenvironment prerequisite for the survival and growth of nymphs of the rice brown planthopper,Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

Nymphs ofNilaparvata lugens were experimentally reared from the 2nd instar in a cage covering part of the leaf sheath of an individual rice plant grown in a Wagner pot. Plants were covered with the cage from the water surface of the pot to 10 cm above the surface (lower cage-group) or from 10 cm to 20 cm above the surface (upper cage-group). Temperatures measured at three different parts of the cage remained fairly constant in both groups at around 25°C (23.7–25.2°C in mean value). In the lower cage-group, relative humidities measured at the three heights in the cage in (76.3–90.5% in mean value) markedly increased with the approach to the water surface. The nymphs of this group, particularly during the molting period, aggregated close to the surface. Eighty-two percent of the released nymphs emerged in this group. Relative humidities measured at three heights of the upper cage-group were 69.5–72.7% in mean value, and all the nymphs in this group died within 3 days after their release although half of them stayed on the rice plants within 6 h after their release. The role of relative humidity as a limiting factor on the range of the microhabitat and the population density ofN. lugens in rice fields was discussed on the basis of the results.     

Relationship Between Downward Oxygen Transport and Intercellular Spaces in Root Cortex in Water Cultured and Moist Cultured Seedlings

In the present investigation, seedlings of rice, pea, sorghum, and maize are raised both in water culture and moist culture. The former culture is to provide the roots with an oxygen deficient condition; while the latter, a direct access to air. The amount of oxygen transported downwards in the seedlings varies not only with the nature of plants but also with the way how they are raised: More oxygen is transported downwards in marsh plant (rice) than in land plants (pea, sorghum, maize); and, in case the same plant is concerned, more in water cultured seedlings than in moist cultured ones. Downward oxygen transport in the various seedlings is intimately correlated with the relative volume of the intercellular spaces in the root: the more the downward transport, the larger the air spaces in the cortex. The fractional volume of the intercellular spaces in a small plant segment can be conveniently estimated by determining the specific gravities of the fresh turgescent segment before and after it is filled with water by vaccum infiltration. The difference between the two consecutive measurements in specific gravity times 100 gives directly the percentage of the volume occupied by air spaces. When large root segments are used, the relative volume can also be determined by weighing before and after vaccum infiltration. To test whether oxygen diffusion in the intercellular spaces of roots could actually account for its downward transport, a model is built of capillary tubings with dimensions and oxygen pressure gradients similar to those found in roots. The amount of oxygen diffused in such a model is measured with a respiratory hydrometer (see Fig. 1) and fits closely that measured in roots. By comparing the amount of oxygen transported downwards in a seedling with that consumed by its excised roots in air, it can be shown that, in case of rice, it could meet (and at times may even exceed) 100% of that consumed by roots in water cultured seedlings, but is less in moist cultured ones. In land plants (pea, sorghum, and maize), however, the downward oxygen supply is far below its requirement, being 80%–100% in water cultured seedlings and 30%–60% in moist cultured ones. The above results, together with those obtained in previous communications, support the view that adaptation of a plant to flooded condition is primarily achieved by its capacity of providing adequate intercellular spaces for downward oxygen diffusion. The capacity depends not only upon the phylogeny of the plant concerned but also upon its ontogenic development.     

Diving behaviour and respiration in Blethisa multipunctata in comparison with two other ground beetles

ABSTRACT. The diving behaviour of Blethisa multipunctata (L.), a carabid species living on shores, is compared with that of two other hygrophilous carabid species. B. multipunctata enters the water spontaneously and is able to stay more than 1 h beneath the surface without renewing its respiratory air, In flooding experiments, c . 50% of submerged beetles do not leave the water after 2h. These animals emerge from time to time for a few seconds and then descend beneath the water again. Measurements of oxygen consumption and the volume of the respiratory air show that the underwater air-supply is sufficient for only a few minutes. B. multipunctata achieves maximum diving times of up to 97 min by using its air storage as a physical gill. In comparison with other Carabidae it shows neither morphological nor physiological adaptations, but only behavioural adaptations for its amphibious mode of life.