Studies on the Metabolism of Aspergilli

Studies were made on the endogenous respiration of Aspergillus sojae K.S. Observing the changes of Kjeldahl-nitrogen in each fraction of the mycelial components, the author concluded that pool amino acids, bound amino acids, protein, nucleic acids and nucleotides covered whole of the nitrogenous reserves available for endogenous respiration in the mycelia. A study was carried out on the effect of preincubation with glucose or amino acids on endogenous respiration. Stimulation of either oxygen uptake, protein breakdown or ammonia formation was observed during respiration of the mycelia incubated with a suitable concentration of azide, 2,4-dinitrophenol, potossium fluoride, monoiodoacetic acid or ethylenediaminetetraacetic acid. Ammonia formation accompanied with endogenous respiration seemed to proceed inversely by the influence of energy yielding reaction.     

Some Effects of Temperature and Substrate Content upon Respiration and the Carbon Balance of Field Beans (Vicia faba L.)

The effects of substrate content and temperature upon the productionof carbon dioxide in the dark were investigated in Vicia fabaand Sorghum vulgare, using the time courses for carbon dioxiderelease. No endogenous rhythms were found. With V. faba at highsubstrate contents, a steady rate of respiration was measuredat low temperatures, suggesting that the rate of respirationis limited by a third factor such as enzyme activity. This steadyrate eventually decreased rapidly. There was a first order rateof decrease with time at higher temperatures. Low substratecontents gave a complex decay. The rate of decrease of the rateof respiration was affected by the initial state of the plantsover the same range of rates. Reasons for this are discussed.The temperature sensitivity of respiration was investigated.The respiration of plants with high substrate contents had alower temperature sensitivity than those with low substratecontents. This was further investigated by measuring the stoichiometryof carbon dioxide production in the dark from total solublecarbohydrate (as hexose equivalent). It is likely that incompletehexose respiration, which occurs at high substrate contents,is less temperature sensitive than complete hexose respirationor the respiration of some other substrate. Vicia faba, Sorghum oulgare, carbon dioxide, respiration, temperature, substrate content     

The Effects of Light, Osmotic Potential and Atmospheric Gases on Germination of the Mistletoe Amyema preissii

The high osmotic concentration of the viscid layer and non-volatilegermination inhibitors cannot account for the prolonged dormancyof the seeds of Amyema preissii while they remain within theintact fruit. Once excised, however, germination could not beprevented by depriving the seed of an external supply of water,oxygen or light. Elongation of the hypocotyl, bearing the primaryhaustorium of the young seedling, was enhanced by conditionsthat favoured photosynthesis as well as respiration. The pericarpis considered to prevent germination by acting as a barrierto influx of exogenous O₂ (critical under dark conditions),and efflux of endogenous CO₂ (critical under light conditions).     

Metabolic Systems in the 'Root' of Brassica napus L.

This is a study of the effects of possible intermediary metaboliteson the respiration of root tissue from Brassica napus usingthe Warburg micro-manometric technique. It is concluded thatascorbic acid is oxidized by two systems, one of which appearsto be a direct oxidase and the other a dehydrogenase. No evidenceof peroxidase activity was secured. A substantial fraction ofthe total respiratory activity was insensitive to cyanide andazide. The biologically important organic acids were oxidizedwith the production of carbon dioxide. Glutamic and asparticacids were metabolized with great rapidity, glycine and alaninemuch more slowly. A scheme integrating these results is outlinedand compared with the respiratory systems existing in potato.     

Differential Effect of Selected Phenoxy-acid Compounds on Oxidative Phosphorylation of Mitochondria from Vicia faba L.

The effect of six phenoxy-acid herbicides, 4-chloro-2-methylphenoxyaceticacid (MCPA), 4-(4-chloro-2-thylphenoxy)butyric acid (MCPB),2, 4-dichlorophenoxyacetic acid (2, 4-D), 4-(2, 4-dichlorophenoxy)butyricacid (2, 4-DB), 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T),and 4-(2, 4, 5-trichlorophenoxy)butyric acid (2, 4, 5-TB) onoxidative phosphorylation of mitochondria isolated from younghypocotyls of Vicia faba L. has been investigated. When NADHwas used as substrate all the test herbicides were found tostimulate state 4 respiration with the loss of phosphorylationand respiratory control in varying degrees. When malate andsuccinate were used separately as substrates, treatment with2, 4-DB, 2, 4, 5-T, and 2, 4, 5-TB at low concentration resultedin a marked stimulation of state 4 respiration; this effectwas not obtained with MCPA, MCPB, or 2, 4-D. At higher concentrationsall herbicides strongly inhibited respiration. These compoundsreleased oligomycin inhibition during NADH oxidation in varyingdegrees, stimulated mitochondrial adenosine-triphosphatase activity,and induced swelling of isolated mitochondria. In many respectsand in differing degrees they resemble 2, 4-dinitrophenol (DNP)in their action as uncouplers. Phenoxy-butyric acids were foundto be more toxic in vitro as uncouplers than their correspondingphenoxyacetic acids. Phenoxyacetic acids were very active as uncouplers in vivo whilephenoxybutyric acids had negligible effect. It is concludedthat in vivo, non-activity of phenoxybutyric acids is due totheir restricted entry into plants and that if available atthe site of action they would be inherently toxic.     

Respiration and Carbohydrate Accumulation in the Water-Stressed Wheat Apex

The effect of water stress on the respiration of the immaturefloral apex of wheat was studied in a controlled environmentand related to changes in water relations, growth, protein synthesis,and solute accumulation. Apex respiration measured in vitropolarographically showed no wounding response and was cyanide-and malonate-sensitive. It decreased with each decrease in apexwater potential _a reaching 40% of the non-stress control rateat –5·0 MPa, irrespective of whether the waterstress was induced by droughting in vivo or non-permeating osmoticain vitro. Apex respiration was not quantitatively related toturgor potential. During drought stress there was a conservation of ethanol-insolubledry matter and water in the apex while ethanol-soluble carbohydratesand amino acids accumulated. The calculated daily import ofsoluble carbohydrate into the apex during the whole droughtstress period remained nearly constant despite falling waterpotential. Respiration of the apex during a drought period wasnot limited by the suistrate supply within the apex.     

Physiological Studies on Germination of Phaseolus mungo Seeds: I. DEVELOPMENT OF RESPIRATION AND CHANGES IN THE CONTENTS OF CONSTITUENTS IN THE EARLY STAGES OF GERMINATION

Changes in respiration rate and in the contents of various constituentsduring the early period of germination of Phaseolus mungo seedswere studied. The course of the respiration developed in threephases. A sharp rise was observed in the first phase (Phasea), followed by the second phase (Phase b) of fairly constantrespiration rate. The respiration rate increases again in thethird phase (Phase c). The O² uptake in Phases a and b was notinhibited by iodoacetate and fluoroacetate, while that in Phasec was inhibited. The contents of aspartic and glutamic acidsand amides were very high. A decrease of aspartic acid contentwas notable during the first few hours of germination. Citricand malic acids were the major organic acid constituents. Citricacid content in the seeds decreased, while that of malic acidremained unchanged. The leaching of malic acid into the soakingmedium was remarkable during the first 6 h of imbibition     

Influences of Light Quality, Growth Regulators and Inhibitors of Protein Synthesis on Respiration of Protoplasts from Meristematic Cells in Barley Seedlings

The influences of light of different wavelengths and plant growthregulators on the respiration of protoplasts isolated from tissue0 to 5 mm above the basal intercalary meristem of barley (Hordeumvulgare L. cv. Patty) leaves were studied. Respiration was measuredusing oxygen electrodes and a Cartesian-diver technique. Red,far-red and blue light all stimulated respiration in the protoplastsbut not in mitochondria isolated from them. Gibberellic acid stimulated respiration in protoplasts but abscisicacid had the opposite effect. Physiological concentrations ofindole-3-acetic acid and kinetin had no influence in eitherdirection. Combinations of gibberellic acid with light of anywavelength always increased respiration. Red or far-red light treatments in the presence of abscisicacid decreased dark respiration and only blue light significantlyreversed the inhibitory effect of abscisic acid. Cycloheximidemarkedly increased dark respiratory activity; chloramphenicolwas without effect. These results indicate that mitochondrialactivity in the leaf basal intercalary meristem was partiallycontrolled through phytochrome and a blue light receptor, andby gibberellic and abscisic acids. Changes in cytosolic proteinsynthesis were important for the initiation of enhanced mitochondrialactivity in meristems. Hordeum vulgare L., barley, abscisic acid, Cartesian-diver microrespirometry, gibberellic acid, meristematic respiration, protoplasts     

Respiration and Mitochondrial Activity in Zea mays Roots As Affected by Osmotic Stress

Studies were made of metabolism in highly vacuolated and slightlyvacuolated Zea mays root tissue both during and after plasmolysis. Plasmolysis resulted in decreased respiration and carbon dioxideevolution from glucose and an increased sucrose synthesis. Inhibitionof respiration during plasmolysis in both the highly vacuolatedand slightly vacuolated tissue was not relieved by supply ofglucose, organic acids, or uncouplers of oxidative phosphorylation.Mitochondria isolated from plasmolysed tissue were tightly coupled,but activity in vitro was inhibited by exposure to a high negativeosmotic potential. It is suggested that low TCA cycle activityin vivo must be due either to inhibition of mitochondrial activityor to reduced flow of carbon through the glycolytic pathway. A low potential for TCA cycle activity after deplasmolysis issuggested, as addition of pyruvate stimulated carbon dioxideevolution but not oxygen uptake, which was severely decreased.This was presumably due to severe mitochondrial damage as shownby their activity in vitro. However, it is not clear whetherrespiration in vivo is rate limited by rapid leakage of metabolicintermediate (reported earlier) or by lysis of mitochondria. Deplasmolysis did not damage mitochondria from slightly vacuolatedtissue, a result which was consistent with respiratory measurementsmade in vivo. The data show that mitochondria in vacuolated tissue are damagedduring and after deplasmolysis and not before. It is suggestedthat lysis of mitochondria occurs in vivo as a result of a sharpincrease in the osmotic potential of the cell fluids.     

Coenzyme Q releases the inhibitory effect of free fatty acids on mitochondrial glycerophosphate dehydrogenase

Data presented in this paper show that the size of the endogenous coenzyme Q (CoQ) pool is not a limiting factor in the activation of mitochondrial glycerophosphate-dependent respiration by exogenous CoQ(3), since successive additions of succinate and NADH to brown adipose tissue mitochondria further increase the rate of oxygen uptake. Because the inhibition of glycerophosphate-dependent respiration by oleate was eliminated by added CoQ(3), our data indicate that the activating effect of CoQ(3) is related to the release of the inhibitory effect of endogenous free fatty acids (FFA). Both the inhibitory effect of FFA and the activating effect of CoQ(3) could be demonstrated only for glycerophosphate-dependent respiration, while succinate- or NADH-dependent respiration was not affected. The presented data suggest differences between mitochondrial glycerophosphate dehydrogenase and succinate or NADH dehydrogenases in the transfer of reducing equivalents to the CoQ pool.     

STUDIES ON RESPIRATION IN DEVELOPING POPPY SEEDS

The excised ovules of Papaver somniferum have been used to investigatethe endogenous uptake of oxygen during their maturation intoseeds. Effect of some activators and inhibitors and the activityof succinic dehydrogenase have been studied. There appears tobe an intimate correlation between respiration and the anatomicalchanges in the ovule. There is an increased oxygen uptake duringor immediately preceding the events of (a) pollination, (b)divisions of the endosperm nuclei, (c) cell wall formation inthe endosperm, and (d) elongation of cotyledons. The activityof succinic dehydrogenase follows a curve essentially similarto that of oxygen uptake. The low intensity of respiration duringcertain period of development appears not to be due to exhaustionof endogenous substrates. Endogenous substrates do, however,appear to be limiting on the days when maximum respiration occurssince added sugar does significantly enhance oxygen uptake.The results with two inhibitors, iodoacetate and fluoroacetate,suggest the operation of glycolysis and tricarboxylic acid cycleduring the earlier phase of seed development when the rate ofgrowth is highest. (Received September 1, 1964; )     

Effects of Ascorbate on the Oxidation of Derivatives of Hydroxycinnamic Acid and the Mechanism of Oxidation of Sinapic Acid by Cell Wall-Bound Peroxidases

A cell wall fraction isolated from epicotyls of Vigna angularis,which contained both ionically and covalently bound peroxidases,rapidly oxidized p-coumaric, caffeic and ferulic acids and slowlyoxidized sinapic acid. The oxidation of sinapic acid was greatlyenhanced in the presence of p-coumaric, caffeic or ferulic acid.Ascorbate (20 µM) inhibited the oxidation of ferulic acidby about 70% and completely inhibited the oxidation of p-coumaricand ferulic acids. The cell wall fraction was capable of bindingferulic and sinapic acids but not caffeic acid. p-Coumaric acidbound only slightly to cell walls. The oxidation of p-coumaricand ferulic acids by KCl-washed cell walls was inhibited byabout 60% and 10%, respectively, by 20 µM ascorbate, butthe oxidation of caffeic acid was completely inhibited by ascorbateat less than 20 µM. The oxidation of derivatives of hydroxycinnamicacid by peroxidases released from cell walls by washing with1 M KCl was completely inhibited by ascorbate. These resultssuggest that the inhibition by ascorbate depends on the substituentgroup of the phenyl ring of the derivatives of hydroxycinnamicacid when the oxidation reaction is catalyzed by cell wall-boundperoxidases and that the oxidation of sinapic acid is mediatedby phenoxyl radicals of derivatives of hydroxycinnamic acidother than sinapic acid. (Received December 2, 1993; Accepted March 3, 1994)     

Desiccation and Free Radical Mediated Changes in Plant Membranes

Senaratna, T., McKersie, B. D. and Borochov, A. 1987. Desiccationand free radical mediated changes in plant membranes.—J.exp. Bot. 38: 2005-2014. In vitro treatment of microsomal membranes from the axes ofsoybean (Glycine max (L.) Merr.) seeds with free radicals simulatesthe type of membrane injury observed following a lethal desiccationstress—the accumulation of free fatty acids in the membranebilayer, the loss of lipid-P, and the formation of gel phasedomains. The major phospholipids in the microsomal fractionwere phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol.Although these treatments induced an extensive loss of totalphospholipid from the microsomal fraction following desiccation,the ratio of the major phospholipids remained unchanged. Neitherlysophosphatides nor phosphatidic acid accumulated in the fraction,but free fatty acid levels increased. Therefore, cleavage ofboth acyl chains from the phospholipid molecule occurred followingdesiccation of the axes and in vitro free radical treatmentof the membrane. Both treatments also promoted formation of gel phase domainsas shown by wide angle x-ray diffraction and increased microviscosityas determined by the fluorescent probe, DPH (1,6-diphenyl-1,3,5-hexatriene).This could be simulated in liposomes prepared from the totalmicrosomal lipid fraction by the addition of saturated freefatty acids (16:0 and 18:0) at the levels observed followingstress. In contrast, the addition of unsaturated fatty acidsperturbed the bilayer and reduced microviscosity. The inclusionof both saturated and unsaturated free fatty acids as observedin vivo promoted a response similar to that observed with onlythe addition of the saturated free fatty acids. Desiccation of the axes also promoted a loss of microsomal protein,which was recovered in the 165 000 x g supernatant, and an apparentloss of thiol groups from the membrane as determined by a thiolspecific fluorescence probe, dansylaziridine. This loss of thiolgroups could also be simulated by exposure of the membranesto gamma irradiation, which was used as a non-enzymatic sourceof free radicals. Collectively, these data support the hypothesisthat membrane disassembly following desiccation stress is mediatedby a free radical mechanism, and that the consequent de-esterificationof membrane phospholipid and accumulation of saturated freefatty acids alter the physical properties of the membrane. Key words: Membrane microviscosity, membrane fluidity, free fatty acids     

The Assimilation of Nitrate-nitrogen by Nitrogen-starved Cells of Platymonas (Tetraselmis) striata (Prasinophyceae)

Nitrate refeeding of nitrogen-starved cells of Platymonas striataresulted in approximately a doubling of average cellular nitrogenwithin 24 h. All the nitrate-nitrogen removed from the culturemedium could be accounted for as non-nitrate nitrogen withincells. Thus no significantly sized nitrate pool existed in Platymonasstriata and no assimilated nitrogen was lost from the cellsto the medium over the 48 h period studied. The slight fallin average cellular nitrogen which occurred from 24 to 36 hcould be attributed to cell division. The majority (70–80per cent) of the assimilated nitrate was recovered in the trichloroaceticacid (TCA)-insoluble fraction. There was some increase in thepercentage of nitrogen found in the TCA-soluble fraction duringthe period of most rapid nitrate assimilation (0–24 h).This presumably reflects an inability of the cells to assimilatelow-molecular-weight metabolic intermediates into macromoleculesat the same rate at which they were being formed. The majorityof the TCA-soluble fraction could be accounted for in termsof amino acids, purine and pyrimidine bases and ammonia. Cellswith adequate nitrogen nutrition seemed to maintain amino acidand purine + pyrimidine base nitrogen pools of about 0.8–0.9and 0.3–0.4 pg per average cell respectively. Algal amino acids, algal purine and pyrimidine bases, algal ammonia     

Respiration of Malate and Glutamate in Symbiotic Frankia Prepared from Alnus incana

Frankia vesicle clusters were prepared from root nodules ofAlnus incana (L.) Moench inoculated either with a local sourceof Frankia or with Frankia Cpll. The capacity of vesicle clustersto respire was investigated by respirometric and enzymologicalstudies. Simultaneous addition of malate, glutamate, and NAD⁺supported respiration in both types of Frankia, though at asmaller rate compared to the substrates NADH or 6-phosphogluconate.The saturating concentrations of malate and glutamate were alsomuch higher than with the other substrates. No respiration wassupported by succinate. Activity of the enzymes malate dehydrogenase(EC 1.1.1.37 [EC] ) and glutamate oxaloacetate transaminase (EC 2.6.1.1 [EC] )was demonstrated in crude extracts from both types of symbioticFrankia. Their maximum rates were high enough to account forthe respiration of malate and glutamate. This respiration wasinhibited by mersalylic acid, an inhibitor of the dicarboxylateshuttle in mitochondria, but it was shown that inhibition ofrespiration could be due to a direct effect on the enzymes.We conclude that respiration of malate and glutamate is mostlikely mediated by malate dehydrogenase and glutamate oxaloacetatetransaminase, but no explicit evidence for or against the presenceof a dicarboxylate carrier was found. The utilization of respiratorysubstrates was largely similar in the two types of Frankia,except for some differences in maximum rates and cofactor dependency. Key words: Actinorhizal symbioses, Alnus, dicarboxylate shuttle, Frankia, reducing power, respiration     

Effect of Fatty Acids and Methyl Octanoate on Resting Mycelium of Boletus variegatus

The endogenous respiration of resting, submerged grown Boletus variegatus mycelium has been determined. In young cultures the intensity of the endogenous oxygen uptake was subject to great variations during the first few hours of starvation. However, by using six to eight days old mycelium the Qo₂ values could be kept at a relatively low and constant level for at least nine hours. Inhibition of the endogenous respiration was found after addition of n-saturated C-2 to C-12 fatty acids (2 × 10^-3M, pH 4.85). The inhibitory effect of the compound was dependent on the length of the carbon chain. Maximum effects were obtained for acids with eight to twelve carbon atoms per molecule. The inhibition was also dependent on the amount of undissociated acid present. By raising the pH so that the fatty acid dissociated the established inhibition was partly reversed. The effect of the neutral compound methyl octanoate was in essence identical to that obtained with octanoic acid. After fatty acid addition a close correspondence was found between the degree of inhibition of the oxygen uptake and the amount of UV absorbing substances leaking out from the cells. This extracellular material had an absorption maximum at 260 nm and a minimum around 240 nm. The leaking was ascribed to interaction between fatty acids or methyl octanoate and lipophilic substances of the cytoplasmic membrane. It is suggested that the inhibitory action on the endogenous respiration is due to similar effects on intracellular membrane systems.     

Depletion of Oxygen in Roots of Wheat and Maize by Respiration Following Encasement in Olive Oil

The extent to which isolated root systems of 14-d-old seedlingsof wheat (Triticum aestivum) and maize (Zea mays) were depletedof oxygen by respiration was measured after immersing them inoutgassed olive oil to exclude oxygen entry from the air. Atintervals over 45 min, gas from the roots was removed underpartial vacuum and oxygen partial pressures measured by gaschromatography. Contrary to earlier findings (Erdmann and Wiedenroth,1988), roots were able to utilize almost all of their oxygenwithin 20 min at 25°C, including that dissolved in the thinwater covering interposed between roots and oil. The rate ofaerobic respiration could be estimated readily from the timecourse of oxygen depletion.Copyright 1993, 1999 Academic Press Triticum aestivum, Zea mays, roots, anaerobiosis, respiration, oxygen, methods     

Inhibition of nitrogenase activity and nodule oxygen permeability by water deficit

Short-term effects of water deficit on nitrogenase activitywere investigated with hydroponically grown soybean plants (Glycinemax L. Merr. cv. Biloxi) by adding polyethylene glycol (PEG)to the hydroponic solution and measuring nitrogenase activity,nodule respiration, and permeability to oxygen diffusion (P_o).These experiments showed a rapid decrease in acetylene reductionactivity (ARA) and nodule respiration. A consequence of thedecreased respiration rate was that P_o calculated by Fick'sLaw also decreased. However, these results following PEG treatmentwere in direct conflict with a previous report of stabilityin P_o determined by using an alternative technique. To resolvethis conflict, an hypothesis describing a sequence of responsesto the initial PEG treatment is presented. An important findingof this study was that the response to water deficit inducedby PEG occurred in two stages. The first stage of decreasednodule activity was O₂-limited and could be reversed by exposingthe nodules to elevated pO₂. The second stage which developedafter 24 h of exposure to PEG resulted in substantial loss innodule activity and this activity could not be recovered withincreased pO₂. Severe water deficit treatments disrupt noduleactivity to such a degree that O₂ is no longer the major limitation. Key words: Glycine max, N₂ fixation, soybean, oxygen permeability, water deficit     

Evidence for the involvement of cytokinins in the regulation of proteolytic activity in cotyledons of germinating beans

The proteolytic activity of an extract of cotyledons of Phaseolusvulgaris increased during the first 7 days of germination, bothwhen casein was the substrate and when the endogenous proteinserved as such. The increase was partially dependent on thepresence of the embryo axis. The effect of the axis was replaceableby kinetin or zeatin, but not by gibberellic acid or IAA. During the period of 3–6 days after the beginning of incubation,the level of amino acids in cotyledons attached to the embryoaxis was lower than in detached ones. No such difference couldbe detected in the first 2 days of incubation. On the otherhand, the influence of the axis on protease activity alreadywas clearly detectable on the second day of germination. Applicationof casein hydrolysate to the seeds brought about an increasein the concentration of amino acids in the cotyledons, but nosimultaneous decrease in the protease level could be detected.We concluded that these results do not confirm the hypothesisthat the influence of the axis on proteolytic activity is dueto its function as a sink for amino acids produced in the cotyledons. (Received August 9, 1979; )     

Response to Selection for Dark Respiration Rate of Mature Leaves in Lolium perenne and its Effects on Growth of Young Plants and Simulated Swards

Selections for slow and for fast rate of dark respiration ofmature leaves were made from within Lolium perenne cv. S23.Selected parents were pair-crossed to provide 15 F₁ familieswith slow respiration and 15 with fast. Dark respiration was inherited and families with contrastingrates were subjected to sequentially harvested growth analysesfrom the third leaf stage to that of 95 per cent light interceptionin a growth room. Seven periods of regrowth of simulated swardsof the families were then recorded. During development of theprimary canopy, growth of the selections did not differ untilthe final harvest interval. At this stage slow respiration familieshad faster (P < 0.05) net assimilation rate and greater plantdry weight (P < 0.05) and leaf area index (P < 0.05) thanthe fast respiration group. Relative growth rate followed thesame trend. In the swards after each regrowth dry matter yieldof the slow respiration group was greater than that of the fast. In another experiment, simulated swards of six slow respirationfamilies yielded more than swards of six fast respiration familiesover sequential regrowth periods in a glasshouse from May toNovember: S23 was intermediate. Differences were most duringAugust and September. Crop growth rate at each harvest correlated(P < 0.05 or P < 0.01) with previously determined leafrespiration at 25 °C. Leaf protein levels in August weaklycorrelated (r = +0.57, P < 0.05) with respiration rate perunit dry weight but there was a significant residual negativecorrelation (r = –0.67, P < 0.05) between the rateper unit protein and growth at that time. Results are discussedin relation to the concept of ‘maintenance-relàted’respiration. Lolium perenne L., perennial ryegrass, respiration, maintenance respiration, relative growth rate, leaf area ratio