Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26°C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O₂, located in the seed coat, inhibits seed respiration and growth. The rate of O₂ uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26°C at various O₂ concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO₂ below air saturation (21 kilopascals), whereas separated seeds showed a decline of O₂ uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO₂, at both 20 and 26°C. In air at 20°C, separated and intact seeds showed similar rates of O₂ uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q₁₀ of 2.3 and was insensitive to pO₂ in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O₂ into the seed.     

Variations in the Alternative Oxidase in Chlamydomonas Grown in Air or High CO(2)

Chlamydomonas in the resting phase of growth has an equal capacity of about 15 micromole O₂ uptake per hour per milligram of chlorophyll for both the cytochrome c, CN-sensitive respiration, and for the alternative, salicylhydroxamic acid-sensitive respiration. Alternative respiration capacity was measured as salicylhydroxamic acid inhibited O₂ uptake in the presence of CN, and cytochrome c respiration capacity as CN inhibition of O₂ uptake in the presence of salicylhydroxamic acid. Measured total respiration was considerably less than the combined capacities for respiration. During the log phase of growth on high (2-5%) CO₂, the alternative respiration capacity decreased about 90% but returned as the culture entered the lag phase. When the alternative oxidase capacity was low, addition of salicylic acid or cyanide induced its reappearance. When cells were grown on low (air-level) CO₂, which induced a CO₂ concentrating mechanism, the alternative oxidase capacity did not decrease during the growth phase. Attempts to measure in vivo distribution of respiration between the two pathways with either CN or salicylhydroxamic acid alone were inconclusive.     

Effects of CO(2) Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans

During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO₂ per liter air, was 1.45 milligrams CO₂ evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO₂ per liter air). There was a higher foliar nonstructural carbohydrate level (e.g. sucrose and starch) in the CO₂ enriched compared with CO₂ normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO₂ enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO₂ enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO₂ adapted plants, but not in the control plants.

Mitochondria, isolated simultaneously from the leaves of CO₂ enriched and control plants, showed no difference in NADH or malate-glutamate dependent O₂ uptake, and there were no observed differences in the specific activities of NAD⁺ linked isocitrate dehydrogenase and cytochrome c oxidase. Since the mitochondrial O₂ uptake and total enzyme activities were not greater in young enriched leaves, the increase in leaf respiration rate was not caused by metabolic adaptations in the leaf mitochondria as a response to long term CO₂ enrichment. It was concluded, that the higher respiration rate in the enriched plant's foliage was attributable, in part, to a higher carbohydrate status.

     

The Responses of Cytochrome Redox State and Energy Metabolism to Dehydration Support a Role for Cytoplasmic Viscosity in Desiccation Tolerance

To characterize the depression of metabolism in anhydrobiotes, the redox state of cytochromes and energy metabolism were studied during dehydration of soaked cowpea (Vigna unguiculata) cotyledons and pollens of Typha latifolia and Impatiens glandulifera. Between water contents (WC) of 1.0 and 0.6 g H₂O/g dry weight (g/g), viscosity as measured by electron spin resonance spectroscopy increased from 0.15 to 0.27 poise. This initial water loss was accompanied by a 50% decrease in respiration rates, whereas the adenylate energy charge remained constant at 0.8, and cytochrome c oxidase (COX) remained fully oxidized. From WC of 0.6 to 0.2 g/g, viscosity increased exponentially. The adenylate energy charge declined to 0.4 in seeds and 0.2 in pollen, whereas COX became progressively reduced. At WC of less than 0.2 g/g, COX remained fully reduced, whereas respiration ceased. When dried under N₂, COX remained 63% reduced in cotyledons until WC was 0.7 g/g and was fully reduced at 0.2 g/g. During drying under pure O₂, the pattern of COX reduction was similar to that of air-dried tissues, although the maximum reduction was 70% in dried tissues. Thus, at WC of less than 0.6 g/g, the reduction of COX probably originates from a decreased O₂ availability as a result of the increased viscosity and impeded diffusion. We suggest that viscosity is a valuable parameter to characterize the relation between desiccation and decrease in metabolism. The implications for desiccation tolerance are discussed.     

Growth and some metabolic activities ofScenedesmus obliquus cultivated under different NaCl concentrations

The physiological response ofScenedesmus obliquus to salinity (NaCl concentration of 40, 80, 120, 60 and 200 mM) for 7 d (long-term experiments) or 2 h (short-term experiments) was followed. Cell number, dry matter and the content of photosynthetic pigments decreased with the rise of NaCl concentration. However, the photosynthetic O₂ evolution mostly increased with the increase of NaCl concentration up to 80 mM, and respiration (dark O₂ uptake) was markedly promoted. Photosynthesis/respiration ratio went in concomitance with the cell number, dry matter or chlorophyll content. Contents of soluble saccharides and soluble proteins increased with the rise of salinization, while the content of insoluble and total saccharides or proteins decreased. Proline content increased greatly with salinization, whereas of other free amino acids were mostly reduced, especially at higher salinities. Similarly, the lipoid contents of salinizedScenedesmus obliquus were obviously higher than those of the control cultures.     

Factors influencing respiration data in freshwater sediment

Sediment respiration (oxygen consumption and CO₂ evolution) was measured in freshwater sediment samples using both flask- and core-microcosms, and the estimates were compared. Oxygen consumption data were also compared in flask-microcosms constructed with sediment samples of different masses, sediment: water ratios, and storage times. Furthermore, sediment respiration was examined under different incubation conditions of temperature and agitation. O₂ consumption was markedly higher in flask-microcosms than in sediment core-microcosms, when compared on a per g dry weight basis. However, when the results were expressed as O₂ consumed per unit surface area, the values were more similar. CO₂ evolution was less dependent on surface area as evidenced by similar CO₂ values per g sediment in both microcosms. In addition, the effect of sediment mass on O₂ consumption and CO₂ evolution was examined. Both O₂ consumption and CO₂ evolution (expressed as µmole g^–1 dry weight sediment) decreased significantly with increasing sediment mass between 3 and 12 g dry weight. Maximum O₂ consumption per unit headspace was measured when a wet sediment mass between 10.0 and 20.0 g was used in the flask-microcosms. It was also shown that the sediment: water ratio, agitation, incubation temperature, and previous storage time of sediment all affected the respiration estimates. Initial O₂ consumption and CO₂ evolution in flasks were significantly higher in flasks with a decreased sediment: water ratio (1:1 versus 1:2), increased flask agitation, and increased incubation temperature (15 °C versus 5 °C). Also, respiration decreased significantly over the first 100 days of storage at 4 °C.     

Role of seagrass photosynthesis in root aerobic processes

The role of shoot photosynthesis as a means of supporting aerobic respiration in the roots of the seagrass Zostera marina was examined. O₂ was transported rapidly (10-15 minutes) from the shoots to the root-rhizome tissues upon shoot illumination. The highest rates of transport were in shoots possessing the greatest biomass and leaf area. The rates of O₂ transport do not support a simple gas phase diffusion mechanism. O₂ transport to the root-rhizome system supported aerobic root respiration and in many cases exceeded respiratory requirements leading to O₂ release from the subterranean tissue. Release of O₂ can support aerobic processes in reducing sediments typical of Z. marina habitats. Since the root-rhizome respiration is supported primarily under shoot photosynthetic conditions, then the daily period of photosynthesis determines the diurnal period of root aerobiosis.     

Dark respiration of the stipe of Ecklonia cava (Laminariales, Phaeophyta) in relation to temperature

Sporophytes of Ecklonia cava Kjellman (Laminariales, Phaeophyta) with a stipe length of 22–102 cm were collected at 6–9 m depth in Nabeta Bay, Shimoda, central Japan by scuba diving in February (winter) and in August (summer) 1998. Dark respiration of the intact stipe of E. cava was measured at various water temperatures ranging from 15 to 27.5°C in winter and 15–30°C in summer in a closed system by using a dissolved oxygen meter. The stipe respiration was compared on whole stipe, length, surface area, volume, wet weight and dry weight bases. On each basis, the stipe respiration always increased with a rise in water temperature within the temperature range investigated. The stipes showed similar respiration rates on each basis of length, surface area, volume, wet weight and dry weight at each temperature, irrespective of the stipe length. The mean respiration rates in winter (at 15–27.5°C) were: length, 16.7–32.5 μL O₂ cm^?1 h^?1; surface area, 3.2–6.2 μL O₂ cm^?2 h^?1; volume, 7.6–15.0 μL O₂ cm^?3 h^?1; wet weight, 6.2–12.2 μL O₂ g (wet weight)^?1 h^?1; and dry weight, 43.8–88.0 μL O₂ g (dry weight)^?1 h^?1. Those for summer (at 15–30°C) were: length, 17.1–32.0 μL O₂ cm^?1 h^?1; surface area, 3.6–6.8 μL O₂ cm^?2 h^?1; volume, 9.7–18.7 μL O₂ cm^?3 h^?1; wet weight, 7.6–14.6 μL O₂ g (wet weight)^?1 h^?1; and dry weight, 49.4–95.8 μL O₂ g (dry weight)^?1 h^?1. This is the first report of the intact stipe respiration of E. cava at various temperatures.     

Respiration and growth of Hyas araneus L. Larvae (Decapoda:Majidae) from hatching to metamorphosis

Rates of respiration and growth were measured for larvae of the spider crab Hyas araneus L., reared in the laboratory from hatching to metamorphosis. The moulting cycle was simultaneously monitored. In both zoeal instars individual respiration rate (R) increased as a linear function of time (t) of development, whereas growth, measured as dry weight (W), carbon (C), nitrogen (N), hydrogen (H), and energy content (E, calculated from C) followed a power function of t. Weight-specific respiration rate (QO₂) was in all instars maximum in early postmoult, and minimum in intermoult and early premoult. Zoea II and megalopa instars showed another conspicuous QO₂ increase during late premoult. Respiration (both R and QO₂)and growth of the megalopa could be described by non-linear (quadratic) functions of t. R and QO₂ during this larval stage were not correlated with W, but were controlled by events of the moulting cycle: R followed a similar pattern to QO₂ (minimum values in intermoult), whereas biomass of the megalopa changed conversely, with a maximum in intermoult and early premoult. The respiratory coefficient (i.e. the ratio of metabolic energy loss: energy gain by body growth) was far lower (<0.8) in the zoeal instars than in the megalopa (>5), suggesting a strongly reduced capability of energy conversion in the final larval stage of H. araneus.     

Respiration,energy balance and development during growth and starvation of Carcinus maenas L. larvae (Decapoda:Portunidae)

In all larval stages of Carcinus maenas L. oxygen consumption was measured at three temperatures (12,18,25 °C). Values increased during development and were in the range of 0.037 ± 0.01 (zoea-1, 12°C, $\text{x}\text{?}\text{± 95\% CL}$) to 0.734 ± 0.047 μl O₂ · h^?1 · ind^?1 (megalopa, 25 °C). Growing larvae showed temperature dependent trends in weight specific respiration rates (referred to dry wt; DW), with values between ≈2.4 and 9.4 μl O₂· h^?1·mg DW^?1. Increase in oxygen consumption of megalops did not differ much at temperatures between 18 and 25 °C. This points to an exceptional physiological position of this stage. Fed zoea-1 of C. maenas (18 °C) revealed growth rates in terms of 40% DW, 20% carbon (C), 30% nitrogen (N) and 65% hydrogen (H). At the same time larvae gained individual energy by 13% (J · ind^?1), while weight specific energy dropped by ≈ 19% (J · mg DW^?1) during the first day and remained constant until the moult. Starved zoea-1 of C. maenas (18 ° C) gained ≈ 20 % in DW through the first day, probably caused by inorganic salts which enter the organism after the moult of the prezoea. DW dropped to ≈ 25 % of initial value, when starvation continued. Single components decreased by ≈50% (C), 54% (N), 57% (J · ind^?1). Weight specific energy (J · mg DW^?1) decreased by 40% during the first 4 days of starvation, remaining constant thereafter. Individual respiration rate (R) dropped by 61 %, weight specific respiration rate (QO₂) by 55 %. Individual energy loss in starved zoea-1 was 0.077 J over a period of 11 days. In this period ≈ 9.3 μl O₂·ind^?1 were consumed. Thus effective oxygen capacity was lower than in growing larvae. It dropped to 5.3 J·mlO₂^?1 after 4 days and remained constant if starvation continued, i.e. 65 % of possible energy loss occurred during the first 4 days. Decrease in requirement for oxygen and its effective capacity were both recognized as independent components of survival during starvation. Partitioning of energy through individual larval development of C. maenas was investigated for all five larval stages. The cumulative budget could be calculated: consumption (C) = 28.23 J, growth (G) = 0.92 J, exoskeleton (Ex) = 0.20 J, metabolism (M) = 5.30 J, egestion and excretion (E) = 21.82 J. Mean gross and net growth efficiency were, K₁ = 3.3% and K₂ = 14.8%, respectively.     

CO(2) and O(2) Exchange in Two Mosses, Hypnum cupressiforme and Dicranum scoparium

Photosynthetic CO₂ and O₂ exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using ¹⁸O₂ to trace O₂ uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO₂, 21% O₂) the net photosynthetic rate was around 40 micromoles CO₂ per gram dry weight per hour in H. cupressiforme and 50 micromoles CO₂ per gram dry weight per hour in D. scoparium. The CO₂ compensation point lay between 45 and 55 microliters per liter CO₂ and the enhancement of net photosynthesis by 3% O₂versus 21% O₂ was 40 to 45%. The ratio of O₂ uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO₂ showed a high apparent K_m (CO₂) even in nonsaturating light. On the other hand, O₂ uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O₂ concentration (saturating level as low as 30% O₂), and by 65% by decreasing the CO₂ concentration to the compensation point. Although O₂ is a competitive inhibitor of CO₂ uptake it could not replace CO₂ completely as an electron acceptor, and electron flow, expressed as gross O₂ production, was inhibited by both high O₂ and low CO₂ levels. At high CO₂, O₂ uptake was 70% lower than the maximum at the CO₂ compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction.     

Wounding Stimulates Cyanide-sensitive Respiration in the Highly Cyanide-resistant Leaves of Bryophyllum tubiflorum Harv

The rate of respiration in sectioned leaves of Bryophyllum tubiflorum Harv. increases with decreasing section thickness. The rates of uninhibited respiration in 2- and 8-millimeter-thick sections are 74 and 46 microliters of O₂ per gram fresh weight of unruptured tissue per hour at 20 C, whereas the rate in the presence of cyanide is 31 microliters of O₂ in each case. The rates are unaffected by salicylhydroxamic acid, but cyanide and salicylhydroxamic acid together completely eliminate O₂ uptake. The capacity of the alternative respiratory pathway is thus initially high (estimated at 84% of the uninhibited respiratory rate in whole leaves) and remains constant but probably unexpressed subsequent to the rapid induction of wound respiration.     

Effect of photosynthesis and carbohydrate status on respiratory rates and the involvement of the alternative pathway in leaf respiration

In spinach (Spinacia oleracea Hybrid 102 [New World seeds]) and wheat (Triticum aestivum L. cv Gabo) leaves, O₂ uptake rates in the dark were faster after the plants had been allowed to photosynthesize for a period of several hours. Alternative path activity also increased following a period of photosynthesis in these leaves. No such effects were observed with isolated mitochondria. In spinach and wheat leaves, the level of fructose plus glucose decreased during a period of darkness. In pea (Pisum sativum cv Alaska) leaves, the level of these sugars did not vary significantly during the day, and respiratory rates were also constant. In slices cut from wheat leaves harvested at the end of the night, addition of sugars increased the rate of respiration and engaged the previously latent alternative oxidase. In pea leaves, O₂ uptake in the first few minutes following illumination was faster than that observed before illumination, but declined during the next 15 to 20 minutes. Adding the alternative oxidase inhibitor salicylhydroxamic acid, or imposing high bicarbonate concentrations during the period of photosynthesis, prevented the rise in O₂ uptake rate during the immediate post illumination period.

We conclude that the level of respiratory substrate in leaves determines their rate of O₂ uptake, and the degree to which the alternative path contributes to that O₂ uptake.

     

Respiration and photosynthesis in cones of Norway spruce (Picea abies (L.) Karst.)

Summary Dark respiration and photosynthetic carbon dioxide refixation in purple and green Picea abies cones were investigated from budbreak to cone maturity. The rate of dark respiration per unit dry weight and CO₂ refixation capacity decreased during cone maturation. At the beginning of the growing season, photosynthetic CO₂ refixation could reduce the amount of CO₂ released by respiration in green and purple cones by 50% and 40%, respectively. The seasonal performance of the components of the cone carbon balance was calculated using information on the seasonal course of respiration, refixation capacity and the light response curves of cone photosynthesis, as well as the actual light and temperature regime in the field. The daily gain of CO₂ refixation reached 28%–34% of respiration in green and 22%–26% in purple cones during the first month of their growth, but decreased later in the season. Over the entire growth period refixation reduced carbon costs of cone production in both cone colour polymorphs by 16%–17%.     

High Arctic Dry Heath CO2 Exchange During the Early Cold Season

Climate change may alter the terrestrial ecosystem carbon balance in the Arctic, and previous studies have emphasized the importance of cold season gas exchange when considering the annual carbon balance. Here, we examined gross ecosystem production (GEP), ecosystem respiration (R _eco) and net ecosystem exchange (NEE) during autumn at a high arctic dry open heath, over a period where air temperatures decreased from +9.8 to ?16.5°C. GEP declined by 95–100% during autumn but GEP significantly different from 0 was measured on October 8 despite sub-zero temperatures. R _eco declined by 90% and dominated NEE throughout the study as the ecosystem on all measurement days was a source of atmospheric CO₂. We estimated net September carbon losses (NEE) to be 17?g?CO₂?m^?2, emphasizing the importance of autumn in relation to annual carbon budgets. The study site has been subjected to 14 summers of water addition, and occasional pulses of nitrogen (N) addition in a fully factorial design. N addition enhanced GEP up to 17-fold during September, although there was no effect in October when GEP was very low. Summer water addition decreased autumn R _eco by up to 25%. Both N amendment and water addition decreased carbon loss, that is, increased NEE; N amendment increased NEE on all dates by 13–64% whereas water addition increased NEE by 20–54% late in September and onward, demonstrating the importance of nutrient and water availability on carbon balance in high arctic tundra, also during the autumn freeze-in.     

Comparative diel oxygen cycles preceding and during a Karenia bloom in Sarasota Bay,Florida, USA

The diel change in dissolved oxygen concentrations were recorded with an automated incubator containing a pulsed oxygen sensor in Sarasota Bay, Florida. The deployments occurred during a ‘pre-bloom’ period in May to June 2006, and during a harmful algal bloom dominated by Karenia brevis in September 2006. The diurnal (daylight) increase in dissolved oxygen concentrations varied from 16 to 104 μmol O₂ l⁻¹ with the corresponding nocturnal decrease in oxygen varying from 16 to 77 μmol O₂ l⁻¹. Nocturnal respiration consumed 42–113% of the diurnal net oxygen production with the minimum and maximum during the pre-bloom period. Hourly production rates closely followed fluctuations in irradiance with maximum rates in the late morning. Hourly oxygen utilization rates (community respiration) at night were highest during the first few hours after sunset.     

Cell Size,Macromolecule Composition,Nuclear Number,Oxygen Consumption and Cyst Formation During Two Growth Phases in Unagitated Cultures of Acanthamoeba castellanii1

SYNOPSIS. The size, composition and physiology of average cells have been studied in cultures of Acanthamoeba castellanii during the phases of logarithmic growth and population growth deceleration (PGD). Most of the features examined were relatively constant during log phase, but had significant changes during PGD. Average cell volume increased about 60% and total dry mass about 15–20% during the latter period. Total protein content remained constant thruout both growth phases, but cytochrome oxidase doubled during PGD. DNA, RNA and glycogen levels began to change during late log phase. DNA decreased about 50% and RNA increased about 75%. Glycogen decreased 50% during the RNA build-up and then increased to a plateau above the log phase level. A final decrease in glycogen followed an increase in the relative numbers of cysts in late PGD. It was found that PGD begins when O₂ becomes limiting and evidence that the subsequent changes in macromolecule composition are related to encystation is discussed.     

Effects of elevated carbon dioxide and/or ozone on endogenous plant hormones in the leaves of <Emphasis Type="Italic">Ginkgo biloba</Emphasis>

Four-year-old Gingko (Ginkgo biloba L.) trees were exposed to ambient and elevated concentrations of CO₂ and O₃, and their combination for 1 year, using open-top chambers in Shenyang, China in 2006. Growth parameters and endogenous plant hormones were measured simultaneously over the experiment period. Elevated CO₂ increased leaf area and leaf dry weight but had no effect on shoot length, increased indole-3-acetic acid (IAA), gibberellins A₃ (GA₃), zeatin riboside (ZR), dihydrozeatin (DHZR) and isopentenyl-adenosine (iPA) content but decreased abscisic acid (ABA) content. Elevated O₃ significantly decreased leaf area, leaf dry weight, shoot length, and decreased IAA, GA₃, ZR content but increased ABA content and had a little effect on iPA, DHZR content. Elevated CO₂ + O₃ decreased IAA, iPA and DHZR content while increased ABA and GA₃ content in the early stage of the exposure and then decreased in the late stage. The evidence from this study indicates that elevated CO₂ ameliorated the effects of elevated ozone on tree growth, and elevated CO₂ may have a largely positive impact on forest tree growth while elevated O₃ will likely have a negative impact.     

Environmental Parameters Affecting Dark Response of Rice Seedlings (Oryza sativa L.) to Triacontanol

Triacontanol applied to IR-8 rice (Oryza sativa L.) seedlings in nutrient solution caused an increase in dry weight during a 6-hour dark period. This increase was altered by atmospheric CO₂ and O₂ concentrations. The largest growth response occurred from 200 to 350 μliters/liter CO₂ with 5% O₂. The treated seedlings did not fix atmospheric CO₂ in the dark, and the immediate products of photosynthesis were not involved in the dry weight increase. The growth response was characterized by an increase in soluble and insoluble Kjeldahl-N, and soluble carbohydrates. The response curve for dry weight increase was a linear function of log presentation time of triacontanol. The response exhibited an apparent K_dose of 25 minutes in 10 μg/liter triacontanol in the dark and 18 minutes in the light. Concentrations of 50 μg/liter and higher inhibited growth.     

Physiological and biochemical energetics of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia : Teredinidae)

The biochemical composition of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia: Teredinidae) was examined throughout larval development at 23°C and 30–32%. salinity in the presence of the phytoplankton food Isochrysis aff. galbana (clone T-ISO), during a delay of metamorphosis in the presence of food but absence of a wood substratum and during periods of enforced starvation. Newly released Teredo navalis larvae had a mean length (L) and height (H) of 89.3 and 76.1 μm respectively. The first appearance of pediveliger larvae at 212.1 μm L and 230.0 μm H occurred 27 days after release. Larval dry weight increased from 0.29 μg to 1.96 μg during this period. Newly formed straight hinge larvae of Bankiagouldi had dimensions of 62.8 μm L and 49.8 μm H. Metamorphically competent B. gouldi larvae had dimensions of 230.0 μm L and 282.9 μm H and were first observed 20 days after fertilization. Larval dry weight increased from 0.06 μg to 2.20 μg during this period. During enforced delay of metamorphosis the ash-free dry weight of Teredo navalis larvae decreased whereas the ash free dry weight of Bankia gouldi larvae increased. During the early period of shelled larval development both species showed similar decreases in lipid, protein and carbohydrate levels (μg·mg dry weight^?1); however, this was reflected in a decrease in biochemical content (μg·larva^?1) only in Teredo navalis. During enforced starvation the major proportion of both the weight and caloric losses were due to protein. Lipid also contributes significantly to these losses whereas the contribution of carbohydrate was small. Larval oxygen consumption rates were determined directly by manometry and indirectly by estimates of decrease in caloric content during periods of enforced starvation. Direct and indirect determinations for T. navalis are described by the relationships R = 1.16 W^1.05 and R = 0.98 W^1.24 respectively where R is the respiration rate in nl O₂ · larva^?1 · h^?1 and W is dry weight inclusive of shell in μg. Direct and indirect determinations for Bankia gouldi are described by the relationships R = 1.37 W^1.25 and R = 1.81 W^1.25 respectively. When data for both assay procedures are combined for each species the relationships R = 1.10 W^1.07 and R = 1.44 W^1.18 are obtained for Teredonavalis and Bankia gouldi respectively.