Studies on the Growth in Culture of Plant Cells: I. GROWTH PATTERNS IN BATCH PROPAGATED SUSPENSION CULTURES

Techniques are described for following increases in total cellnumber, fresh weight and dry weight, and changes in mean cellsize, and in the relative number of free cells to cell aggregatesduring the growth of batch-propagated suspension cultures oftissues derived from several species of angiosperms. When totalcell number is plotted against time it is seen that there canbe distinguished in sequence a lag phase, phases of acceleration,maximum rate, and negative acceleration of cell division and,finaly, a stationary phase. Studies with Parthenocissus tricuspidatacrown-gall tissue, growing in a synthetic liquid medium, haveshown that the total cell production per culture in the firstinstance is limited by nitrate supply rather than by the supplyof other inorganic ions, sucrose supply aeration, or the releaseof endogenous inhibibors. Studies, particularly with Acer pseudoplatanustissue, have shown that during the period of high cell-divisionrate, mean cell size reached its minimum value and average numberof cells per cell aggregate its maximum value. Cell separationdoes not occur to a significant extent until cell-division activityhas almost ceased and it is dependent upon cell expansion. Thebalance between cell division and cell expansion determinesthe ‘cellular unit’ composition of the cultures.Refinement of the control of growth patterns in plant suspensioncultures calls for further study of the ‘conditioning’of media, of factors which limit the duration of the periodof high mitotic activity, and of the conditions necessary forfull and rapid cell expansion.     

Stereological Analysis of Cotyledon Cell Development in Phaseolus: II. THE DEVELOPING COTYLEDON

Quantitative changes in organelle volume, number, and area duringcotyledon cell development in Phaseolus vulgaris are describedduring the early period of reserve protein synthesis. RoughER undergoes a 400-fold increase in area per cell, and alsochanges in shape; changes in mitochondrial volume do not parallelthe changes which occur in respiration rate; nuclear volumeincreases, and relationships between cell and nuclear volume,DNA content, and cell weight are discussed; plastid divisionappears to occur in steps.     

A Comparison of Leek (Allium porrum) and Onion (Allium cepa) Seed Development

Leek and onion seed dry weight increased exponentially for thefirst 31 days after flowering (DAF) but thereafter the increasein dry weight was slower. Before maximum seed dry weight wasreached at 45 DAF in onion and 59 to 66 DAF in leek, seed moisturecontent, seed oxygen uptake and conductivity of the seed steepwater fell from initially high levels. Although some seeds germinated31 DAF in both species, full germination in both was not reacheduntil 66–80 DAF. Tolerance of the seed to artificial dryingimmediately after harvesting occurred 45 DAF in onion and 74DAF in leek. Free nuclear division continued in the endospermuntil 17–22 DAF in onion and until 31–35 DAF inleek but it was not until 45 DAF in onion and 66 DAF in leekthat the embryo and endosperm filled the cavity formed by thepericarp. After formation of cell walls in the endosperm thepattern of change in cell number in both species was similar.The shrunken appearance of the seed coat in leek, which occurredearly in seed development, was associated with the period offree nuclear division in the endosperm and, in addition, thepericarp was thinner than in onion. There was no evidence thatthe shrunken seed coat early in development was associated withself as opposed to open-pollination. Allium porrum, Allium cepa, seed development, endosperm, embryo, cell number, germination, respiration, seed leachates     

The Respiration Rate of Tomato Stem Tissue Infected by Tomato Aucuba Mosaic Virus

The oxygen uptake of stem tissue slices of Lycopersicum esculentumvar. ‘Stonor's Moneymaker’, in 0·035 M. Sorensonphosphate buffer was measured manometrically; the optimum pHwas found to be 5·2. With tomato-stem tissue systemicallyinfected by virus (tomato aucuba mosaic), the respiration ratewas always below that of healthy tissue when equal numbers ofrespiratory systems were compared. When the respiration ratewas expressed in terms of oxygen uptake per unit fresh or dryweight, the respiration rate of the virus-infected tissue couldbe greater or less than that of the healthy tissue dependingon the growth conditions of the experimental material. Underconditions favouring the complete development of disease symptoms,virus infection decreased the fresh and dry weight of the cell.For this reason fresh weight and dry weight were not consideredsuitable criteria to express the respiration rates as theseunits contained different numbers of respiratory systems inhealthy and virus-infected tissue.     

Studies on the Growth in Culture of Plant Cells: XXII. GROWTH LIMITATION BY NITRATE AND GLUCOSE IN CHEMOSTAT CULTURES OF ACER PSEUDOPLATANUS L.

The responses of steady-state cell populations of Acer pseudoplatanusL. (sycamore) in chemo-stats to changes in the nitrate concentrationof their environment was generally predictable by equationsderived for ideal, free-cell, nitrate-limited populations. Astep-down in nitrate concentration in the input medium of achemostat produced interlocking oscillations in spent-mediumnitrate, intracellular pools of nitrate and amino-N, proteinaccumulation, and cell division. The rate of nitrate uptakeinto the cell and thus the flow of nitrogen into protein (andultimately the specific growth rate) was seen to be finely regulatedby spent-medium nitrate concentration. Steady states of growth of sycamore cells were established withglucose as the limiting nutrient both from inoculation and afterswitching from nitrate to glucose limitation. Glucose-limitedcells produced by glucose step-down of a nitrate-limited populationsuffered major losses of cell material, including starch andcell wall polysaccharide, to the extent that protein then accountedfor c. 70% of cell dry weight.     

CHANGES IN CELL COMPOSITION AND LIPID METABOLISM MEDIATED BY SODIUM AND NITROGEN AVAILABILITY IN THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

The effects of nitrogen starvation in the presence or absence of sodium in the culture medium were monitored in batch cultures of the marine diatom Phaeodactylum tricornutum Bohlin. During nitrogen starvation in the presence of sodium, cell nitrogen and chlorophyll a decreased, mainly as a consequence of continued cell division. These decreases were accompanied by decreases in the rates of photosynthesis and respiration. There was no change in either cell volume or carbohydrate, but both carbon and lipid increased. During nitrogen starvation in the absence of sodium, cell division ceased. Cell nitrogen and chlorophyll a remained constant, and respiration did not decrease, but the changes in the photosynthetic rate and the lipid content per cell were similar to cultures that were nitrogen-starved in the presence of sodium. The carbon-to-nitrogen ratio increased in both cultures. Nitrogen, in the form of nitrate, and sodium were resupplied to cultures that had been preconditioned in nitrogen- and sodium-deficient medium for 5 d. Control cultures to which neither nitrate or sodium were added remained in a static state with respect to cell number, volume, and carbohydrate but showed slight increases in lipid. Cells in cultures to which 10 mM nitrate alone was added showed a similar response to cultures where no additions were made. Cells in cultures to which 50 mM sodium alone was added divided for 2 d, with concomitant small decreases in all measured constituents. Cell division resumed in cultures to which both sodium and nitrate were added. The lipid content fell dramatically in these cells and was correlated to metabolic oxidation via measured increases in the activity of the glyoxylate cycle enzyme, isocitrate lyase. We conclude that lipids are stored as a function of decreased growth rate and are metabolized to a small extent when cell division resumes. However, much higher rates of metabolism occur if cell division resumes in the presence of a nitrogen source.     

Effect of Pulp Cell Number and Assimilate Availability on Dry Matter Accumulation Rate in a Banana Fruit [ Musa sp. AAA group 'Grande Naine' (Cavendish subgroup)]

Fruit position on the bunch (inflorescence) is an importantpart of variability in banana fruit weight at harvest, as fruitsat the bottom of the bunch (distal fruits) are approx. 40% smallerthan those at the top (proximal fruits). In this study, therespective roles of cell number and cell filling rate in thedevelopment of pulp dry weight are estimated. To this end, thesource/sink ratio in the plant was altered at different stagesof fruit development. Leaf shading (reducing resource availability),bunch bagging (increasing sink activity by increasing fruittemperature), and bunch trimming (decreasing sink size by fruitpruning), applied once cell division had finished, showed thatthe pulp filling rate depends on resource availability. Bunchbagging and bunch trimming were also carried out before theend of cell division to estimate the role of pulp cell numberin the development of pulp dry weight. A sampling method wascalibrated to evaluate pulp cell number from the digestion ofa fixed portion of the pulp in a solution of chromic and nitricacids. A relationship was found between pulp cell number andfruit length at the end of cell division. It was observed thatpulp cell number is a determining factor in pulp dry weightvariability within a bunch. On the other hand, the cell fillingrate was identical for all fruits in the bunch and was influencedby the source/sink ratio. A Michaelis-Menten relationship wasinvoked to relate the cell filling rate in a bunch to the source/sinkratio during bunch filling. Copyright 2001 Annals of BotanyCompany Banana fruit, Musa sp., fruit growth, cell number, cell filling rate, source/sink ratio, temperature     

Studies on the Growth in Culture of Plant Cells: VI. NUCLEIC ACID METABOLISM OF ACER PSEUDOPLATANUS L. CELL SUSPENSIONS

Changes in the nucleic acid content of cell suspension culturesof Acer pseudoplatanus, L. have been investigated. Both RNAand DNA contents rise sharply early in the period of cultureand before any significant increase in cell number. With theonset of rapid cell division there is a rapid decline in DNAcontent per cell to reach the value which persists during thesubsequent period of growth. The high level of RNA establishedat the beginning of the phase of rapid cell division, declinesgradually as growth proceeded. More detailed investigation ofthe RNA revealed no signficant changes, during the 3-week periodof culture, in either its base composition or in the relativeamounts of its different constituent molecular species.     

The Absorption of Ions by Excised Root Systems: II. OBSERVATIONS ON ROOTS OF BARLEY GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Barley plants were grown in complete culture solution and indeficiencies of phosphorus, nitrogen, or potassium for a periodof about 6 weeks. Excised roots of these plants were treatedwith a complete, aerated culture solution at 25? C. for varyingperiods of time, and the changes in respiration rate, phosphorus,nitrogen, potassium, sugars, and starch contents measured.
2. Therewere changes in fresh weight and dry weight of the excisedrootsduring treatment. The dry weight decreased with time butthewater-content changes were variable. There was a gain orlossof water by the roots according to the treatment.
3. In all casesthe deficient roots increased in content of theelement in whichthey were originally deficient. The roots ofthe plants suppliedwith full nutrient usually decreased incontent of phosphorus,nitrogen, and potassium, but exceptionsoccurred and the reasonsare discussed.
4. In most of the experiments described simultaneousloss of oneion and gain of another occurred.
5. Nitrogen-deficientroots accumulated nitrate when exposed toa complete nutrientsolution, and some of this was assimilatedwith formation ofprotein. Under similar conditions nitrogen-richroots decreasedin nitrogen content and proteolysis took place.
6. There wasa rapid fall in sucrose and reducing sugar contentof the excise'roots. The starch content was initially verysmall and showedlittle change with time.
7. The respiration rate declined withtime in all treatments exceptwhere a nitrogen deficiency existed.Here the respiration rateincreased to a maximum value at about8 hours and then fell.This increase in rate is attributed toprotein synthesis. Noevidence of a ‘salt respiration’was observed evenwhen active uptake of phosphorus or potassiumwas occurring.
8. In most instances the carbon dioxide evolvedin respirationgreatly exceeded the carbon dioxide equivalentof the sugarconsumed in the same period. Exceptions were foundwith thenitrogen-deficient roots where less carbon dioxidewas evolvedthan the equivalent of sugar consumed. It is probablethat apart, at least, of the sugar unaccounted for was usedin proteinsynthesis.
9. Where the carbon dioxide of respirationwas in excess of theequivalent of sugar consumed, protein oramino-acid is the mostprobable substrate. Respiration rateis found to be relatedboth to nitrogen and sugar content.

     

The Absorption of Ions by Excised Root Systems: III. OBSERVATIONS ON ROOTS OF PEA PLANTS GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Pea plants were grown in complete culture solution and in deficienciesof phosphorus, nitrogen, or potassium for a period of about5 weeks. Excised roots of these plants were treated with a complete,aerated culture solution for varying periods of time and thechanges in respiration rate, phosphorus, nitrogen, potassium,sugar, and starch contents measured.
2. There were changes infresh weight and dry weight of the excisedroots during treatment.The dry weight decreased with time butthe water content changeswere variable. Uptake of water wascorrelated with uptake ofpotassium and sucrose content in someinstances.
3. There wasno evidence of a ‘salt respiration’ inthose caseswhere active accumulation occurred.
4. The rates of gain or lossof phosphorus, nitrogen, or potassiumat 0 hours, 8 hours, and16 hours were calculated and it wasfound that the rate dependedboth on content of element in theroot and the sugar cotent.There was very little evidence thatone element affected therate of uptake of another. Simultaneousloss of one elementand gain of another occurred in some instances.
5. The observationsappear to be best explained on the assumptionthat the absorbedions are fixed in the cells in the form ofloosely bound compoundsand that these compounds are formedfrom sugars.

     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

Studies on the Growth in Culture of Plant Cells: VII. EFFECTS OF KINETIN ON THE CARBOHYDRATE AND NITROGEN METABOLISM OF ACER PSEUDOPLATANUS, L CELLS GROWN IN SUSPENSION CULTURE

Aspects of the carbohydrate and nitrogen metabolism of Acerpseudcplatanus, L cell suspension cultures grown on a syntheticmedium containing 2 per cent glucose and 1.0 mg/l 2,4-dichlorophenoxyaceticacid and kinetin either at 0.25 mg/l (low kinetin) or at 2.5mg/l (high kinetin) are described. High kinetin inhibits growthas measured by increase in cell number, packed-cell volume,and cell dry weight. Although not inhibitory to glucose utdization,high kinetin inhibits the O₂ uptake of the cells. Such cellscontain only a trace amount of fructose and their rate of O₂uptake can be raised to that of the low kinetin cells by a periodof fructose feeding. The O₂ uptake of both kinds of cell issensitive to malonate but the stimulation of O₂ uptake inducedby bis(hexafiuoroacetonyl)-acetone (‘1799’) at 0.2mM is much less with the high-kinetin than the low-kinetin cells.The enzymes phosphoglucoseiseomerase and glucose-6-phosphatedehydrogenase are much less active in the high-kinetin cells.Mitochondria isolated from both kinds of cells show good respiratorycontrol although slightly lower values for Q_O2(N), ADP/O ratioand control ratio are recorded with mitochondria from the highkinetin cells. Kinetin at 2.5 mg/l slightly reduces the ADP/Oratio of isolated mitochondria but at 4.0 mg/l their responseto ADP is completely suppressed. Extracellular hemicelluloseformed in presence of high kinetin has a reduced content ofgalactose and xylose and an increased content of glucose. Theseobservations indicate that the inhibition of respiration byhigh kinetin is mainly due to suppression of glucose conversionto other sugars rather than to inhibition of glycolysis or terminalrespiration. High kinetin decreases the rate of protein but not of amino-acidsynthesis. Suppression of the synthesis of particular proteinsmay be an important factor responsible for the reduced cellyield of the cultures in presence of high kinetin. The significanceof these observations to our understanding of the critical metaboliceffects of cytokinina is discussed. Acer pseudoplatanus cells release amino acids into their culturemedium early in the period of batch culture and largely reabsorbthem as incubation proceeds.     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis I. Anatomy and Respiration in Triticum aestivum L.

Anatomical changes in roots of wheat seedlings (Triticum aestivumL. cv. Hatri) following oxygen deficiency in the rooting mediumwere investigated. The response of the plant to stress was testedat a very early developmental stage when the first adventitiousroots had just emerged. In order to analyze the adaptation ofdifferent roots, respiration rates of the roots 1–3 and4–n were compared with the respiration rates of the totalroot system. Oxygen deficiency was induced either by flushingnutrient solution with nitrogen or flooding of sand. In contrast to plants grown in well aerated media, both stressvariants led to a significant increase of the intercellularspace of the root cortex in seminal and first adventitious roots.Radial cell enlargement of cortical cells near the root tip,cell wall thickenings in flooded sand cultures and an increasein phloroglucinol-stainable substances were found to be furtherindicators of low oxygen supply. The roots 4–n which were promoted in growth under hypoxiashowed higher respiration rates; hence the total root respirationwas not restricted. Triticum aestivum L. cv. Hatri, wheat, roots, anatomy, anaerobiosis, stress, root respiration, intercellular space     

EUGLENA GRACILIS IN SYNCHRONOUS DIVISION I. DRY MASS AND VOLUME CHARACTERISTICS

Volume distributions and dry mass have been measured in synchronouspopulations of Euglena gracilis, grown in a salt medium at aconstant temperature. In keeping with the approximate doublingof cell number observed in each division burst, the averagedry mass and volume are doubled in each inter-division period. ¹ Present address: Department of Biology, Tokyo MetropolitanUniversity, Setagaya.ku, Tokyo. (Received February 17, 1961; )     

Studies in the Nitrogen Metabolism of Apple Fruits: THE CLIMACTERIC RISE IN RESPIRATION IN RELATION TO CHANGES IN THE EQUILIBRIUM BETWEEN PROTEIN SYNTHESIS AND BREAKDOWN

1. A close parallelism in the drift of the rate of respirationand the protein-N/ non-protein-N ratio is shown to occur bothin apple fruits attached to the tree and when detached fromthe tree at various stages of development and stored for severalmonths at 12 C.
2. In detached fruits the fall in respirationwhich occurs immediately(during the first 48 hours) after pickingis only accompaniedby a concomitant fall in net protein invery young fruits inwhich active cell division is taking place.Subsequently, infruit of all ages when a climacteric rise inrespiration occursit is accompanied by a net increase in protein.
3. It is argued that the climacteric rise in respiration is aresultof increase in the level of protein which will be expectedtoreduce the ATP/ADP ratio.
4. Over the climacteric period,although rate of respiration andnet protein content both rise,R rises more rapidly than proteinand, subsequently, falls ata faster rate than P. It is suggestedthat this may be due tothe ‘new’ protein containinga higher proportionof enzyme(s) directly involved in respirationand leading, forexample, to a reduction in the ATP/ADP ratio.

     

A Comparison of the Rate of Maintenance Respiration in Some Crop Legumes and Tobacco Determined by Three Methods

Carbon exchange was measured on whole plants of field bean,lucerne, chick pea, kidney bean, pea and tobacco. The maintenance respiration rate was measured in three ways:(i) by allowing the CO₂ efflux to decay in prolonged darknessto an asymptotic value which was then taken to be the maintenancevalue (the dark decay method); (ii) by plotting the dark CO₂efflux as a function of the net CO₂ uptake over a range of irradiancesand taking maintenance as the dark CO₂ efflux when the net CO₂uptake was zero (the dynamic method); and (iii) by plottingthe total CO₂ uptake as a function of the growth rate and takingmaintenance respiration as the CO₂ efflux when the growth ratewas zero (the zero growth rate method). The range of valuesfor the maintenance coefficient over all species was from 1.6to 2.1 per cent of the dry weight per day, 1.8 to 2.1 per centand 2.7 to 2.9 per cent as determined by these three methodsrespectively. There was a linear relationship, common to allspecies, between the maintenance respiration rate (dark decaymethod) and dry weight, total nitrogen and the organic nitrogencontent. The growth coefficient (0.69±0.01) was the samefor field bean, chick pea and lucerne and was unaffected bythe method of estimation. It was concluded that the dark decay method provided the bestestimate of the minimal maintenance requirements in the plantsstudied. Vicia faba L., Medicago sativa L., Cicer arientinum L., Phaseolus vulgaris L., Pisum sativum L., Nicotiana tobacum L., field bean, lucerne, chick pea, kidney bean, pea, tobacco, respiration, maintenance, growth, nitrogen content     

The relationship between nutrient status and chemical composition of Peridinium cinctum during the bloom in Lake Kinneret

Changes in water chemistry and the major chemical and elementalconstituents of Peridinium cinctum have been followed duringthe 1976 growth season (February-June) in Lake Kinneret. Thedecline of the bloom was not associated with changes in anysingle physical or chemical parameter of the lake water, althoughthe ambient N:P ratio was higher before the peak of Peridinium.Carbon, nitrogen and chlorophyll in the cells were almost constantover the growth season, averaging 48, 4 and 0.9% dry weight,respectively. There was an initial drop in cell phosphorus from0.7% to 0.2% dry weight which then remained stable after April.During the bloom period the carbohydrate and lipid content ofPeridinium decreased, nucleic acid increased, whereas proteinshowed no definite trend. The results suggest that (a) Peridiniumis not severely nutrient limited during most of the growth season;and (b) criteria based upon cellular composition used to definenutrient status in other groups of algae, may not be directlyapplicable to armoured dinoflagellates.     

Symbiosis of Leguminous Plants and Nodule Bacteria: IV. The Importance of the Oxygen Factor in Nodule Formation and Function

Nodulated plants of soya-bean have been grown in culture solutionslacking combined nitrogen and in continuous contact with oxygen/nitrogengas mixtures containing 21, 12, and 5 per cent. oxygen respectively.Reductions of oxygen content led to reductions in dry weightand in fixation of nitrogen. Somewhat similar but smaller effects on dry weight were observedwith non-nodulated plants supplied with ammonium-nitrogen, butsuch plants supplied with nitrate-nitrogen grew equally vigorouslyat all three oxygen levels, a result regarded with some reservation. The weight of nodules per plant was markedly reduced by curtailmentof oxygen, but the number was unaffected, indicating that theearlier stages in nodule formation are not specially sensitiveto oxygen supply. The greater effect of oxygen reduction onnodulated plants appears to be exerted on the process of fixationor on associated processes such as nodular respiration.     

Photosynthesis and photoassimilation of glucose during photomixotrophic growth of Marchantia polymorpha cells in suspension culture

Even in the presence of glucose the growth of Marchantia polymorpha L. (cell line HYH-2F) requires light, and growth is more sensitive to 10⁻⁶ M 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea than to 10⁻⁴ Antimycin A. The inability of the cells to grow in the dark is due to the low level of respiration. The respiration rate under light increased to four times the dark value. The values of the compensation ratio (the photosyntehtic rate/the respiration rate) for the oxygen exchange were below 1.0 daring the growth period, although oxygen evolution was found. At the early exponential phase, oxygen evolution was 0.373 μmol (mg cell dry weight)⁻¹ h⁻¹ [61.7 μmol (mg chlorophyll)⁻¹ h⁻¹]. M. polymorpha cells are unable to grow anaerobically in the light without a supply of carbon dioxide. When 1% carbon dioxide in nitrogen is supplied, photochemically produced oxygen and energy are sufficient for sustained growth although at significantly reduced yields in both cell dry weight and chlorophyll. Photosyntehtic CO₂ assimilation rate was 0.13 μmol (mg cell dry weight)⁻¹ h⁻¹[11.3 μmol (mg chlorophyll)⁻¹ h⁻¹]. At least one-third of the carbon atoms in cellular constituents seem to be derived from atmospheric carbon dioxide, which indicates that M. polymorpha cells grow photomixotrophicaily.     

Nitrogen and photosynthetic function of hermatypic corals. Oxygen exchange of Stylophora pistillata coral under artificial feeding

The change of Stylophora pistillata coral photosynthetic function (oxygen exchange and biomass of symbionts) under starvation and food enrichment was studied to understand the role of heterotrophy in nitrogen supplements of zooxanthellae. The starvation caused the decrease of frequency of zooxanthellae cells division in 7-10 times. The number of degraded algae cells increased in same proportion and, as a result, the density of zooxanthellae in corals decreased about two times during one-two weeks. Under starvation corals kept their photosynthetic capacity at the level of corals in situ by means of enhancing the zooxanthellae gross photosynthesis. The respiration rate of coral had tendency to increase and the dry mass of polyp tissue to decrease. Under artificial feeding which was following starvation the zooxanthellae density increased in 1.5-2 times, and particular food caused more intensive accumulation of zooxanthellae comparing to dissolved inorganic ammonium. The feeding regime did not affect dry mass of polyp tissue and chlorophyll content as well as respiration and gross productivity of the corals. The conclusion about high effectiveness of particular feeding for supplying symbiotic algae with nitrogen was made and trophic status of zooxanthellae in hospite was determined as unlimited by nitrogen.