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The functional significance of different photosynthetic CO2 fixation pathways is a question which can be answered in many ways, each being appropriate to certain scales of enquiry. In physiological ecology our purpose should be to integrate these different scales of enquiry as comprehensively as possible, and to show how photosynthesis contributes, directly or indirectly, to performance and survival of plants in diverse habitats. Studies of photosynthetic CO2 fixation were afflicted with a post-Calvin cycle chauvinism in the 1950’s, which may have been responsible for the slow and tentative revelation of the C4 pathway of photosynthetic carbon assimilation in the USA and USSR (Burr et al. 1957; Karpilov 1960; Kortschak et al. 1965). Elucidation of this pathway undoubtedly stimulated new interest in the carbon metabolism of photosynthesis in the next decade (Hatch and Slack 1966, 1970; CC Black 1973) and led to an upsurge in comparative studies of higher plant photosynthesis (Black 1971; Bjorkman 1973). Largely as a result of this stimulus, the peculiar dark CO2 fixation processes of succulent plants, known as crassulacean acid metabolism (CAM), were also recognized as a distinctive photosynthetic process (Kluge and Ting 1978; Osmond 1978). It also led to the present revival of interest in the photosynthesis of aquatic plants.

Mass spectrometric techniques were used to trace the incorporation of [(18)O]oxygen into metabolites of the photorespiratory pathway. Glycolate, glycine, and serine extracted from leaves of the C(3) plants, Spinacia oleracea L., Atriplex hastata, and Helianthus annuus which had been exposed to [(18)O]oxygen at the CO(2) compensation point were heavily labeled with (18)O. In each case one, and only one of the carboxyl oxygens was labeled. The abundance of (18)O in this oxygen of glycolate reached 50 to 70% of that of the oxygen provided after only 5 to 10 seconds exposure to [(18)O]oxygen. Glycine and serine attained the same final enrichment after 40 and 180 seconds, respectively. This confirms that glycine and serine are synthesized from glycolate.The labeling of photorespiratory intermediates in intact leaves reached a mean of 59% of that of the oxygen provided in the feedings. This indicates that at least 59% of the glycolate photorespired is synthesized with the fixation of molecular oxygen. This estimate is certainly conservative owing to the dilution of labeled oxygen at the site of glycolate synthesis by photosynthetic oxygen. We examined the yield of (18)O in glycolate synthesized in vitro by isolated intact spinach chloroplasts in a system which permitted direct sampling of the isotopic composition of the oxygen at the site of synthesis. The isotopic enrichment of glycolate from such experiments was 90 to 95% of that of the oxygen present during the incubation.The carboxyl oxygens of 3-phosphoglycerate also became labeled with (18)O in 20- and 40-minute feedings with [(18)O]oxygen to intact leaves at the CO(2) compensation point. Control experiments indicated that this label was probably due to direct synthesis of 3-phosphoglycerate from glycolate during photorespiration. The mean enrichment of 3-phosphoglycerate was 14 +/- 4% of that of glycine or serine, its precursors of the photorespiratory pathway, in 10 separate feeding experiments. It is argued that this constant dilution of label indicates a constant stoichiometric balance between photorespiratory and photosynthetic sources of 3-phosphoglycerate at the CO(2) compensation point.Oxygen uptake sufficient to account for about half of the rate of (18)O fixation into glycine in the intact leaves was observed with intact spinach chloroplasts. Oxygen uptake and production by intact leaves at the CO(2) compensation point indicate about 1.9 oxygen exchanged per glycolate photorespired. The fixation of molecular oxygen into glycolate plus the peroxisomal oxidation of glycolate to glyoxylate and the mitochondrial conversion of glycine to serine can account for up to 1.75 oxygen taken up per glycolate.These studies provide new evidence which supports the current formulation of the pathway of photorespiration and its relation to photosynthetic metabolism. The experiments described also suggest new approaches using stable isotope techniques to study the rate of photorespiration and the balance between photorespiration and photosynthesis in vivo.

Judged against the variable background of evolutionary and systematic relationships of Atriplex discussed in the previous three chapters, and the very diverse viewpoints adopted by different authors who have prepared monographs describing regional floristic and vegetation types, there are many ways of preparing a coherent account of Atriplex communities on a global basis. Just as we have taken a rather liberal and pragmatic approach to the systematics of the genus, we shall in this chapter explore some of the more generally recognized vegetation types (“communities”) and environments in which species of Atriplex commonly occur. The difficulties of generalization are exaggerated if one attempts to categorize Atriplex communities in terms of the definition offered by Walter, since it seems unlikely from our field experience that many species of Atriplex are found in “stable combinations” or indeed in “ecological equilibrium” with their environments. Initially we will consider some of the apparent, qualitative relationships between the vegetational and environmental features of these communities, and attempt to distinguish in very general terms the principal environmental factors that appear to be most significant in each vegetation type. In the latter part of this chapter we shall examine some approaches that have been made toward a quantitative analysis of these relationships, approaches that seek to provide a preliminary coupling between states and processes of the vegetation and environment appropriate to nodes in the span 106–1011 of our space-time scale.

Photosynthetic metabolism in plants capable of Crassulacean acid metabolism (CAM) may involve the net fixation of CO2 in the preceeding dark period or the net fixation of CO2 in the light. The properties of these two carboxylation reactions have been examined and evidence suggesting that dark fixation is essentially a C4-like process and light fixation is essentially a C3-like photosynthetic process is presented.

The C4 dicarboxylic acid pathway of photosynthetic carbon metabolism is a major elaboration of the photosynthetic carbon reduction cycle (PCR-cycle) which has stimulated a great deal of new research into all levels of carbon metabolism in higher plants in recent years (Hatch and Slack, 1970; Hatch, Osmond and Slatyer, 1971; Black, 1973; Hatch, 1975). The unique features of the C4 pathway centre around leaf anatomy and the location and activity of enzymes involved in the carboxylation and decarboxylation of C4 acids. There is now good evidence that these acids are synthesised in one cell layer (the mesophyll) and decarboxylated in another (the bundle sheath). This seemingly pointless exercise is believed to utilise C4 acids as CO2 carriers to bundle sheath cells and to result in an increase in CO2 concentration in the vicinity of RuDP3 carboxylase in these cells. The higher intracellular concentration of CO2 is believed to optimise the carboxylation activity of this enzyme and to effectively abolish the inhibition of the carboxylase due to atmospheric levels of O2.

By and large, studies of photosynthesis in response to stress have pursued the reductionist philosophies of biochemistry and biophysics, and have not sought to provide integrated accounts of photosynthetic processes in successful wild plants or among the successful products of pragmatic plant breeding. Integration of biochemical, physiological and ecological aspects of photosynthesis is essential if we are to further improve upon these successful experiments. Natural selection, which is responsible for the successful plants now found in what we regard as stress environments, acts not on isolated components (such as osmoregulation) which may respond to random mutations, but upon whole integrated physiological processes which are products of the total genetic potential of the organism. Waddington (1972) reminds us that “it remains true enough to say the ultimate units, the pebbles in the concrete or genes in the organism, have been produced by random processes, (but) this is almost irrelevant to the engineering of a bridge and, in many cases, not much more relevant to the anatomical or physiological construction of the organism.”

In this chapter we will review the available information on genetic relationships among various taxa of Atriplex as determined by cytogenetic methods, and the attempts to hybridize these taxa both at the intra- and inter-specific levels. Such studies are of utmost importance in understanding the evolutionary processes operating in speciation. In Atriplex, they also serve as a unique tool in elucidating the evolutionary and genetic aspects of an especially interesting example of adaptive differentiation, namely the C4 pathway of photosynthesis which is present in certain taxa but absent in others.

At constant cladode temperature the stomatal resistance of O. inermis increased when the cladode-air vapor pressure difference was increased and stomatal resistance decreased when the cladode-air vapor pressure difference was lowered. Net CO

The time courses of some Photosystem II (PS II) parameters have been monitored during in-vivo and in-vitro photoinhibition of spinach chloroplasts, at room temperature and at 10 °C or 0 °C. Exposing leaf discs of low-light grown spinach at 25 °C to high light led to photoinhibition of chloroplasts in-vivo as manifested by a parallel decrease in the number of functional PS II centres, the variable chlorophyll fluorescence at 77K (F v /F m ), and the number of atrazine-binding sites. When the photoinhibitory treatment was given at 10 °C, the former two parameters declined in parallel but the loss of atrazine-binding sites occurred more slowly and to a lesser extent. During in-vitro photoinhibition of chloroplast thylakoids at 25 °C, the loss of functional PS II centres proceeded slightly more rapidly than the loss of atrazine-binding sites, and this difference in rate was further increased when the thylakoids were photoinhibited at 0 °C. During the recovery phase of leaf discs (up to 9 h) the increases in F v /F m preceded that of the number of functional PS II centres, while only a further decline in the number of atrazine-binding sites was observed. The recovery of variable chlorophyll fluorescence and the concentration of functional PS II centres occurred more rapidly at 25 °C than at 10 °C. These results suggest that the photoinhibition of PS II function is a relatively temperature-independent early photochemical event, whereas the changes in the concentration of herbicide-binding sites appear to be a more complex biochemical process which can occur with a delayed time course.

In the previous chapter it was emphasized that, after the utilization of the nutrient and ionic reserves of the seed, the autotrophic activities of land plants depend on the absorption of mineral ions from the soil just as they depend on the harvest of solar energy and atmospheric carbon. This dependence on ion absorption is expressed both in the requirement for nutrient ions, which are incorporated into or complexed with organic molecules in the cytoplasm and metabolic machinery of living cells, and in the requirement for nonnutrient ions which do not participate directly in metabolism, but which play a role in turgor regulation and ionic balance. Some nonnutrient ions may have distinctly unfavorable effects on plant growth due to their interference with metabolism or with the absorption of nutrient ions.

Water plays an essential role in the function and survival of plants. It serves as a reactant in numerous metabolic processes, including photosynthesis, as a medium for stabilization and functioning of biological membranes and enzymes, and for ionization and transport of metabolites. It also serves to inflate and thus maintain structural rigidity of cells and tissues. Growth is therefore necessarily associated with water uptake. In autotrophic terrestrial plants the requirement for water is at least an order of magnitude higher than in heterotrophic organisms, since in order to permit CO2 to enter the leaf during photosynthesis the leaf must have a high permeability to gases. This inevitably results in an escape of water vapor from the wet cell surface in the leaf to the drier atmosphere, the process of transpiration. No membrane exists that would permit CO2 to pass freely while at the same time impeding the loss of water vapor. In all higher land plants the leaf epidermis is covered by a cuticle having a very low gas permeability and gas exchange between the leaf and the atmosphere occurs almost exclusively through the stomatal openings in the leaf epidermis. The stomata function as mechanical valves that are able to regulate this gas exchange. Typically, about 99% of the total water taken up by a plant is lost by transpiration.

In this chapter we are concerned for the first time with detailed discussions of states and processes as they relate to individual plants. Although the systematic state (Chap. 2) is deduced from analysis of individual plant specimens; although selective pressures leading to the survival of a new species (Chaps. 3, 4) act upon the individual; and although the survival of individual plants through a severe drought determines the response of a plant community (Chap. 5), the states and processes discussed previously were primarily abstractions based on populations of organisms. Birth rate is a key parameter of population ecology, yet in many ecological studies emphasis is given to interactions between adult plants. Similarly, during germination one encounters many fundamental problems of plant physiology in their most simple form, yet ecophysiological studies also concentrate upon the more accessible adult plants. By considering germination and establishment in the present context we hope to draw attention to the neglect of these processes by physiologists, as well as to assess the significance of germination and establishment in larger scale ecological processes. It is true that studies of metabolism in germinating seeds and of the control of morphological development in seedlings have been responsible for major advances in plant physiology. It is also true that understanding of these processes in other than idealized laboratory conditions is negligible. There is no doubt, however, that the period between successful seed set and seedling establishment is the most precarious in the life cycle of angiosperms.

The daily course of CO2 and H2O exchange in cladodes of Opuntia inermis was studied at four sites in Eastern Australia. On most occasions cladode water contents were high and nocturnal stomatal opening resulted in substantial uptake of CO2 and synthesis of about 130 μ equiv cm-2 of malic acid during the night. Under water stress nocturnal stomatal opening was confined to the latter part of the night and acid synthesis was reduced to about 40 μ equiv cm-2. Night temperature had little effect on acid synthesis, which responded primarily to rainfall and changed from the stressed condition within 2–3 days in irrigation experiments. On many occasions following summer rainfall stomata opened for 4 h in the late afternoon permitting net CO2 fixation which may contribute about 25% of the total carbon assimilated. This CO2 fixation was insufficient to have a marked impact on the δ13C value of the Opuntia cladodes. CO2 fixation in the light occurred in conjunction with maximum dark CO2 fixation under mesic conditions. Dark CO2 fixation rates were 3 to 5 times greater than those recorded in desert cacti under favorable conditions. Relative growth rates calculated on the basic of CO2 exchange correspond to measured relative growth rates of 0.05 g g-1 dry wt day-1 which prevailed for 60–90 days in summer. The capacity for very active CO2 fixation in the dark and light following summer rainfall and the capacity to persist at low levels of metabolic activity through summer drought are discussed in relation to the success of this introduced species in this habitat.

The C4 dicarboxylic acid pathway of photosynthetic carbon assimilation (the C4 pathway) is a complex biochemical and physiological elaboration of the common photosynthetic carbon reduction cycle (PCR cycle, C3 pathway; Bassham and Calvin, 1962). We define the C4 pathway as the complete reaction sequence in which CO2 is transferred via the C-4 carboxyl of C4 acids to the reactions of the PCR cycle and there reduced to the level of carbohydrate (Hatch and Slack, 1970; Hatch et al., 1971; Black, 1973; Hatch, 1976a). The distinctive biochemical features of this process are the carboxylation and associated reactions leading to the synthesis of C4 acids, and those concerned with the subsequent decarboxylation of these C4 acids to supply CO2 for the PCR cycle. Unlike the PCR cycle, in which carboxylation and carbon reduction is restricted to the chloroplast, the C4 pathway involves the operation of reactions in cytoplasm, mitochondria, and chloroplasts, and the transport of intermediates between intracellular compartments. In this sense it may be compared with another well-established elaboration of the PCR cycle, the glycolate pathway of photorespiration (see Chap. II,5). However, an additional and distinctive feature of the C4 pathway is the mandatory exchange of photosynthetic intermediates between adjacent cells. These exchanges constitute one of the most rapid and complex forms of symplastic transport known.

There is little doubt that the survival of an autotrophic plant is based on its ability to maintain a positive carbon balance even under severe stress conditions, and also that its reproductive potential is dependent on its ability to gain carbon and energy by photosynthesis. These relationships are complex and it is not necessarily true that selection pressure has always favored maximization of productivity as such. Survival obviously depends on a combination of a number of characteristics, only a few of which may be fully exploited. Nevertheless, we share the view of Fischer and Turner (1978) that maximization of photosynthetic efficiency in terms of a limited resource (such as water) remains central to maximization of survival. But we wish to again re-emphasize the importance of considering characteristics of possible adaptive significance in the proper time and space perspective. As Eckardt (1975) has pointed out … “activities of living beings seem to be directed towards the attainment of goals that lie in the future, [but] their behaviour just reflects the fact that they have evolved under changing conditions which favoured great variability.” Having discussed the responses and adaptations of the photosynthetic characteristics we shall how examine the difficult subject of the relationship between productivity and the success and survival of plants in natural environments.

The labeling patterns in malic acid from dark (13)CO2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and (13)C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12-14 h dark (13)CO2 fixation the ratio of [4-(13)C] to [1-(13)C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The (13)C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87-89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following (13)CO2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of [(13)C] malic acid ((13)CO2 or [1-(13)C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to (13)CO2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284-291). In the shortest times, only singly-labeled [4-(13)C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.

The absorption of inorganic ions by cells of higher plants involves ionic interaction with the enzymes and intermediates of metabolism at several levels. The primary interaction involves energy metabolism in the membrane-bound enzyme systems responsible for active ion transport across the cell membranes and preceding Chapters have comprehensively reviewed the way in which energy metabolism may fuel ion transport.

Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO2 partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO2 partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy.

The essence of crassulacean acid metabolism (CAM) as reviewed by Osmond and Holturn (1981), Ting and Gibbs (1982), and its relationship to C3 and C4 photosynthesis can be summarised as shown

The study of physiology — “science of the normal functions and phenomena” — of living plants should be inseparable from the study of their ecology which is concerned with “the habits, modes of life, and relations to their surroundings” (Fowler and Fowler, 1949) of individual plants in communities and ecosystems. Physiological plant ecology serves to bridge physiology and ecology which represent a continuum of biological research method and philosophy, and this bridging discipline has proved a possible and profitable exercise, generating new insights into both physiology and ecology. However, the canvas of physiological ecology is so vast and the scale of the exercise is so immense that there is a real danger of themes being lost and contributors becoming increasingly unable to relate their individual efforts to those of others. Each of us, like Niggle, has a clear concept of how particular leaves should be represented. Yet in striving to paint these within a particular context we too are frequently reduced to tacking our canvasses to the dimly perceived tree. It is this dilemma, the dilemma of context, relevance, and relationship between the different contributions, which poses the greatest challenge to physiological plant ecology.

When grown with adequate water and nitrogen (12 mM NO 3 - ) four clones of Solanum dulcamara from sun or shade habitats in Europe showed similar potential for acclimation of photosynthesis to irradiance level during growth. When grown with limiting nitrogen (0.6 mM NO 3 - ) all clones showed a low potential for acclimation of photosynthesis to irradiance during growth. If limiting nitrogen was accompanied by water stress at high irradiance, the initial slope of the irradiance response curve, and the irradiance saturated rate of photosynthesis were depressed, especially in a clone from a shaded habitat. These interactions are discussed in terms of earlier reports on the sunshade responses and sun-shade ecotypic differentiation in this species.

The objective of ecological plant physiology is to explain processes in plant ecology, such as plant performance, survival, and distribution, in physiological, biophysical, biochemical, and molecular terms. It is a relatively young discipline and we are aware of only a few basic textbooks that have been written (Larcher 1973, 1980a, b; Kreeb 1974; Bannister 1976; Etherington 1975, 1978). Physiological plant ecology was first reviewed as a separate discipline by Billings (1957), but the knowledge since gained in ecological-physiological studies has been rapidly integrated into and has strongly influenced the parent disciplines of plant physiology and ecology. Nearly a century ago the necessity of ecophysiological work was recognized by Schimper in the introduction to his classical text (1898) Pflanzengeographie auf physiologischer Grundlage and was expressed succinctly: „Nur wenn sie in engster Fuhlung mit der experimentellen Physiologie verbleibt, wird die Oekologie der Pflanzengeographie neue Bahnen eroffnen konnen, denn sie setzt eine genaue Kenntnis der Lebensbedingungen der Pflanzen voraus, welche nur das Experiment verschaffen kann.“ (In the original English translation: “the oecology of plant-distribution will succeed in opening new paths on condition only that it leans closely on experimental physiology, for it presupposes an accurate knowledge of the conditions of the life of plants which experiment alone can bestow.”) When introducing our perspectives as editors of four volumes dealing with physiological plant ecology in the New Series of the Encyclopedia of Plant Physiology, one of our tasks should be to consider the extent to which Schimper’s prediction has been fulfilled.

When isolated intact chloroplasts or cells from spinach (Spinacia oleracea L.) leaves are incubated in the light in the absence of CO2, their capacity for subsequent CO2-dependent photosynthetic oxygen evolution is drastically decreased. This inhibition is light and oxygen-dependent and can be prevented by addition of bicarbonate. It is concluded that the normal dissipation of photosynthetic energy by carbon assimilation and in processes related to photorespiration is an essential condition for the physiological stability of illuminated intact chloroplasts and cells.

The gas exchange characteristics of photosynthetic tissues of leaves and stems of Eriogonum inflatum are described. Inflated stems were found to contain extraordinarily high internal CO

The coupling of ion transport to energy sources in the light and in the dark in green cells ofAtriplex spongiosa leaves was investigated using light of different qualities, an inhibitor of electron transport (dichlorophenyl dimethyl urea), and an uncoupler (p-CF3O-carbonyl cyanide phenylhydrazone). Two different mechanisms of ion uptake were, distinguished. (1) A light-dependent Cl(-) pump which is linked to light-dependent K(+) uptake. The energy for this pump is probably derived from photosynthetic electron transport or from nicotinamide adenine dinucleotide phosphate, reduced form. This mechanism is dichlorophenyl dimethyl urea-sensitive and enhanced by uncouplers. (2) A mechanism independent of light, which operates at the same rate in the light and in the dark. This mechanism is sensitive to uncouplers. It is probably aK-Na exchange mechanism since K(+) and Cl(-) uptake and a small net uptake of H(+) are balanced by Na(+) loss.

Malic acid isolated from Bryophyllum pinnatum (Lamk.) Oken (B. calycinum Salisb.), Bryophyllum tubiflorum Harv., Kalanchoë diagremontiana Hamet et Perrier and Sedum guatamalense Hemsl. after dark (14)CO(2) fixation was degraded by an in vitro NADP-malic enzyme technique. In the short term (5 to 30 seconds) the malic acid was almost exclusively labeled in the C-4 carboxyl carbon (greater than 90%). The percentage of (14)C in the C-4 carboxyl of malic acid declined slowly with time, reaching 70% in B. tubiflorum and 54% in B. pinnatum after 14 hours of exposure to (14)CO(2). It was found that malic acid-adapted Lactobacillus arabinosus may seriously underestimate the C-4 carboxyl component of label in malic acid-(14)C. The amount of substrate which the bacteria can completely metabolize was easily exceeded; there was a significant level of randomization of label even when beta-decarboxylation proceeded to completion, and in extended incubation periods, more than 25% of label was removed from malic acid-U-(14)C. The significance of these findings in relation to pathways of carbohydrate metabolism and malic acid synthesis in Crassulacean acid metabolism is discussed.

Beet discs aged in 0.5 mM CaSO(4) develop a capacity to absorb K(+) and Cl(-) from solutions of low concentration. The initial influx of these ions is described by a hyperbolic relationship with concentration in the range 0.01 to 0.5 mM KCl, which is identical with the system 1 absorption isotherm found in other tissues. A second hyperbolic isotherm, attributable to system 2, is found at higher concentrations (1-50 mM KCl).When the transport of labeled ion to the vacuole is studied by wash-exchanging the bulk of the cytoplasmic label following the absorption period, it is noted that in the range of system 1, isotope influx to the vacuole increases with time as the concentration of labeled ions in the cytoplasm increases, while in the range of system 2, influx to the vacuole is constant from the beginning. Diminution of the cytoplasmic specific activity during radio-isotope absorption by prefilling the cytoplasm with the analogous unlabeled salt, markedly reduces subsequent radioisotope uptake to the vacuole only in the range of system 1. These experiments suggest that the cytoplasm serves as a mixing chamber, and that the plasma membrane controls ion uptake to the tissue at low concentrations, indicating that the system 1 isotherm reflects ion movement into the cytoplasm through the plasma membrane. Flux experiments support this conclusion, showing that development with age of the system 1 isotherm corresponds to a quantitatively similar increase in plasma membrane influx in 0.2 mM KCl.At higher concentrations the outer membrane no longer rate-limits entry of ions to the vacuole. Isotope influx under these conditions, described by the system 2 isotherm, presumably reflects movement across the tonoplast.

A method is described for separating mesophyll and bundle sheath chloroplasts from the leaves of C 4 plants. The agranal bundle sheath chloroplasts are inactive in the Hill reaction, whereas granal bundle sheath and granal mesophyll chloroplasts exhibit normal photosystem II activity. The agranal bundle sheath chloroplasts are deficient in photosystem II; they lack cytochrome b -559 and the fluorescence bands associated with photosystem II. All the chloroplasts exhibit photosystem I activity.

Enzymes which are affected by the addition of inorganic salts during in vitro assay were extracted from salt-sensitive Phaseolus vulgaris, salt-tolerant Atriplex spongiosa, and Salicornia australis and tested for sensitivity to NaCl. In each case malate dehydrogenase, aspartate transaminase, glucose 6-phosphate dehydrogenase, and isocitrate dehydrogenase showed NaCl responses similar to those found for commercially available crystalline enzymes from other organisms. Enzymes extracted from plants grown in saline cultures showed no important changes in specific activity or salt sensitivity. Interaction of pH optima and NaCl concentrations suggests that enzymes may differ in the way they respond to salt treatment.

St Michael9s NICU (StMH) provides pre and postoperative care for all newborns with an ante/postnatal diagnosis of congenital diaphragmatic hernia (CDH) in South-West England. A consistent care bundle is followed for antenatal diagnoses: delivery at StMH, sedation and muscle relaxation at birth, elective intubation, high frequency oscillatory ventilation (HFOV), inotropic support, pulmonary vasodilators and delayed surgery. ECMO is only considered for reversible pulmonary hypertension when conventional management fails. Objectives To review clinical management and evaluate survival/morbidity in infants with CDH over a 12 year period. Methods A retrospective case note review of all CDH cases managed at StMH(1998–2010). A review of the South-West Congenital Anomaly Register. Results 79 cases were identified, including 45 identified antenatally. 16 (20%) had additional major malformations/genetic syndromes; 2 lethal. Overall survival was 60/79(76%). The anomaly register identified 4 additional CDH deaths in local hospitals for this population. 100% of infants delivered at StMH received the full care bundle (91% received HFOV). No cases received ECMO. 10/79(12.6%) had pneumothoraces. 13/60(21%) of survivors required additional oxygen at 28 days of life and 3/60(5%) were discharged on oxygen. Domiciliary oxygen was not required for any infant delivered at StMH (where the complete care bundle was followed). Conclusion Our survival rate compares favourably with recent large published series and is not significantly biased by ‘hidden mortality’ in the South-West Region. Pneumothorax and chronic lung disease rates are significantly lower than recently published studies using HFOV. Our consistent approach delivers favourable survival rates with a low pulmonary morbidity burden in survivors.

SUCCULENT plants capable of Crassulacean acid metabolism (CAM) show extremely variable carbon isotope discrimination ratios1,2. This ratio, usually expressed as a δ13C value referred to a standard3, has emerged as a useful diagnostic criterion to determine photosynthetic pathways in higher plants3–5. Species with the C4 photosynthetic pathway6 show less negative δ13C values than do species with the C3 photosynthetic pathway. The difference in isotope discrimination is believed to be a result of the different fractionation characteristics of the primary phosphoenolpyruvate (PEP) carboxylase of C4 plants and primary ribulosediphosphate (RuDP) carboxylase of C3 plants7. Within a species, the δ13C value for total carbon does not usually vary by more than ±0.5‰ and it is largely insensitive to environmental conditions during growth8, although the soluble components within a particular leaf may show some variation9. Examples of the constancy of δ13C values are shown in the genus Atriplex, where C4 species have less negative values (for total carbon) of −8 to −12‰ than C3 species which range between −25 and −27‰ (ref. 8).

CATION absorption in Atriplex species is partly balanced by concurrent chloride absorption1,2, and, in all species so far examined, organic acid anions, principally oxalate, balance most of the residual cation excess. Atriplex has been known for some time to contain considerable deposits of calcium oxalate crystals in leaf tissue3 and this communication discusses the quantitative significance of oxalates in the genus.

The effect of oxygen concentration on oxygen exchange in six species of the Chlorophyta, one of the Cyanophyta, one of the Rhodophyta, three of the Phaeophyta, zooxanthellae from Tridacna maxima (clam) and Pocillopora damicornis (coral), and a marine angiosperm was investigated with a polaro- graphic oxygen electrode. The rate of photosynthesis in air-saturated sea water ranged from 14 to 248 micromoles of oxygen evolved per hour per milligram of chlorophyll. Photosynthesis was inhibited by 15-85% in sea water adjusted to between 65 and 90% of oxygen saturation. A post- illumination burst of oxygen uptake was observed on darkening and the size of this burst was in- fluenced by oxygen concentration. Steady-state rates of oxygen uptake in the dark were enhanced at higher oxygen tensions. The likelihood that the dissolved oxygen content of sea water may regulate the productivity of reef communities is discussed.

Fully expanded intact attached leaves of Zea mays and other C4 plants illuminated at 2000 �E m-2 s-1 in CO2-free N2 containing 10 mbar O2 for a 3-h treatment period showed substantial inhibition of the capacity for both CO2-dependent and light-dependent CO2 assimilation. This photoinhibition was reflected at the chloroplast level as substantial inhibition of photosystem II activity of the mesophyll chloroplasts. Photoinhibition was largely insensitive to the O2 partial pressure maintained throughout the treatment period. This result suggests that internal CO2 generation by photorespiration with subsequent carbon cycling, or O2 uptake in a Mehler-type reaction are largely unable to alleviate photoinhibition. The extent of photoinhibition was, however, markedly affected by the CO2 partial pressure present throughout the treatment period. This result is consistent with the CO2-concentrating function of C4 photosynthesis, which allows substantial rates of CO2 assimilation even at low mesophyll CO2 partial pressures. Apparently, a certain level of CO2 turn- over is beneficial in providing a sink for photochemically generated energy, thereby maintaining the ability of illuminated leaves to transduce and dissipate light energy.

Pyruvate, PI dikinase (EC 2.7.9.1) was present in crassulacean acid metabolism (CAM) plants that lack phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.32) but was not detected in plants that contain PEP carboxykinase or in C3 plants. It is suggested that, during deacidification in CAM plants that contain NAD and NADP malic enzymes (EC 1.1.1.38 and EC 1.1.1.40) but not PEP carboxykinase, pyruvate, P*i dikinase reverses the glycolytic reaction catalysed by pyruvate kinase (EC 2.7.1.40) and converts pyruvate to PEP as the first step in the gluconeogenic conservation of pyruvate as storage carbohydrate. The enzyme is not required by CAM plants that contain PEP carboxykinase and produce mainly PEP during decarboxylation. Leaf slices from Kalanchoe daigremontiana and CAM Mesembryanthemum crystallinum, two species that possess pyruvate, PI dikinase, transfer label from exogenous [3-14C]pyruvate to carbohydrates more rapidly than either Stapelia gigantea, a PEP carboxykinase CAM plant, or C3 Mesembryanthemum crystallinum, which lack the dikinase. Label from [2-14C]- and [3-14C]pyruvate is converted to carbohydrate at the same rate in K. daigremontiana while in S. gigantea label from [2-14C]pyruvate accumulates in carbohydrates twice as rapidly as label from [3-14C]pyruvate. The patterns observed for K. daigremontiana and for CAM M. crystallinum are consistent with the gluconeogenic anabolism of pyruvate whereas the patterns observed for S. gigantea and for C.3 M. crystallinum suggest pyruvate is oxidized possibly via the tricarboxylic acid cycle in these species. Deacidification in Aloe arborescens, a PEP carboxykinase CAM plant that also possesses NAD and NADP malic enzyme activity, was inhibited 80% by 0.1 mM 3-mercaptopicolinic acid (3-MPA), an inhibitor of PEP carboxykinase. It is thus likely that, in this species and probably also in other CAM plants with high PEP carboxykinase activities, a small proportion of the malic acid may be decarboxylated by malic enzymes. However, as 0.5 mM 3-MPA inhibited deacidification in K. daigremontiana by 40%, the inhibitor is probably only specific at low concentrations. 14CO2 fixation in the light by mesophyll cells isolated from K. daigremontiana was stimulated by 20-50% in the presence of 10 mM pyruvate, but there was no increase in 14CO2 fixation by mesophyll cells isolated from S. gigantea.