Photosynthesis, Dark Respiration, and Growth of Rumex patientia L. Exposed to Ultraviolet Irradiance (288 to 315 Nanometers) Simulating a Reduced Atmospheric Ozone Column

Net photosynthesis, dark respiration, and growth of Rumex patientia L. exposed to a ultraviolet irradiance (288-315 nanometers) simulating a 0.18 atm·cm stratospheric ozone column were determined. The ultraviolet irradiance corresponding to this 38% ozone decrease from normal was shown to be an effective inhibitor of photosynthesis and leaf growth. The repressive action on photosynthesis accumulated through time whereas leaf growth was retarded only during the initial few days of exposure. Small increases in dark respiration rates occurred but did not continue to increase with longer exposure periods. A reduction in total plant dry weight and leaf area of approximately 50% occurred after 22 days of treatment, whereas chlorophyll concentrations remained unaltered.     

SHORT-TERM RESPONSES OF NUTRIENT-DEFICIENT ALGAE TO NUTRIENT ADDITION1

Changes in net photosynthesis, dark respiration, ATP content, and some other aspects of composition were measured following phosphate or ammonium addition to cultures of the green alga Scenedesmus quadricauda (Turp.) Bréb. deficient in phosphorus or nitrogen. The deficient nutrient was rapidly taken up. Light-saturated net photosynthesis was depressed below the pre-addition rate during nutrient uptake and did not increase markedly above that rate until several hours after uptake was complete. Dark respiration, on the other hand, was markedly stimulated during uptake of the deficient nutrient and to a lesser extent after uptake was complete. Phosphate addition to P-deficient cells caused a large increase in the ATP content within 2–4 h of addition, whereas ammonium addition to N-deficient cells caused much less or no increase in ATP content. Short-term enrichment experiments to detect nutrient limitations are evaluated in the light of these and similar results taken from the literature. The available evidence shows that photosynthetic responses cannot reliably be used in short-term enrichments but changes in respiration or ATP content may be useful in certain circumstances.     

Alternative Path Mediated ATP Synthesis in Roots of Pisum sativum upon Nitrogen Supply

Changes in the efficiency of root respiration were examined on intact plants of Pisum sativum L. cv Rondo after addition of nitrate or ammonium to the culture solutions. Nitrate was absorbed immediately after addition and elicited a respiratory rise (O₂-uptake as well as CO₂-production) to 160% at most. This occurred both in roots of plants fixing N₂ and in those of non-nodulated plants pregrown for 1 or 2 weeks on a nitrogen-free culture solution. In older plants, used after 2 weeks of N-free growth, the full capacity of the cytochrome path was engaged in root respiration. This was demonstrated by the absence of an effect of the uncoupler carbonylcyanide m-chlorophenylhydrazone in the presence of 25 millimolar salicylhydroxamate, an inhibitor of the alternative path. In these plants more than 90% of the nitrate-induced stimulation of root respiration was salicylhydroxamate-sensitive. In young plants, used after 1 week of N-free growth, the cytochrome path was not saturated. Its activity increased instantaneously at the expense of alternative path activity, which initially dropped to zero and subsequently increased to 160% of the control 7 hours after nitrate supply. The rate of photosynthesis rose to 120% of the control, but not before 1 hour after nitrate supply, suggesting that the stimulation of root respiration was not due to a higher rate of photosynthesis. Experiments with plants grown with a split-root system showed that respiration rate and alternative path activity only increased in the root halves exposed to nitrogen. Ammonium was equally effective as nitrate in stimulating root respiration. These results lead to the conclusion that alternative-path mediated root respiration contributes to synthesis of ATP during at least the first 24 hours following nitrogen supply.     

The Regulation of Photosynthesis in Leaves of Field-Grown Spring Wheat (Triticum aestivum L., cv Albis) at Different Levels of Ozone in Ambient Air

Wheat (Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O₃), nonfiltered air (0.03 microliters per liter O₃), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic ¹⁴CO₂ uptake was measured in situ. Net photosynthesis, dark respiration, and CO₂ compensation concentration at 2 and 21% O₂ were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO₂ compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO₂ to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase.     

Diel phytoplankton periodicity in Mikołajskie lake,Poland, as determined by different methods in parallel

Photosynthetic rates as measured by the oxygen light and dark bottle method were highly correlated with estimates using the ¹⁴C technique. The high O₂/¹⁴C ratios found are explained by algal respiration and extracellular release which are included in photosynthetic measurements by the oxygen technique, while the ¹⁴C method yields values close to net photosynthesis. Separation of net- and nannoplankton using a 50 μm plankton net for filtration was not comparable to distinctions made by microscopic examination. Separation of both by filtration caused a significant decrease in the photosynthetic activity of nannoplankton in 24-hour incubations, but had no detectable effect after 4 hours of exposure. “Bottle effects” in 24-hour measurements of photosynthesis were similar using both methods. Asymmetric photosynthetic time-curves as well as vertical phytoplankton migrations were the main reasons for errors in estimates of daily photosynthetic rates from part-day incubations which were extrapolated to the entire day.     

The influence of phosphate deficiency on photosynthesis, respiration and adenine nucleotide pool in bean leaves

The decrease in inorganic phosphate (Pi) content of 10-d-old Phaseolus vulgaris L. plants did not affect rates of photosynthesis (PN) and respiration (RD), leaf growth, and adenylate concentration. Two weeks of phosphate starvation influenced the ATP content and leaf growth more than PN and RD. The ATP concentration in the leaves of 15- and 18-d-old phosphate deficient (-P) plants after a light or dark period was at least half of that in phosphate sufficient (+P, control) plants. Similar differences were found in fresh and dry matter of leaves. However, PN declined to 50 % of control in 18-d-old plants only. Though the RD of -P plants (determined as both CO2 evolution and O2 uptake) did not change, an increased resistance of respiration to KCN and higher inhibition by SHAM (salicylhydroxamic acid) suggested a higher engagement of alternative pathway in respiration and a lower ATP production. The lower demand for ATP connected with inhibition of leaf growth may influence the ATP producing processes and ATP concentration. Thus, the ATP concentration in the leaves depends stronger on Pi content than on PN and RD.     

Endogenous rhythmic activity of photosynthesis, transpiration, dark respiration, and carbon dioxide compensation point of peanut leaves

At 14-hour day length, 25 C leaf temperature, 9 mm Hg vapor-pressure deficit, and 1.17 joules cm⁻² min⁻¹ irradiance, the diurnal change in daily photosynthesis of the cultivated peanut (Arachis hypogaea L.) is a result of an endogenously controlled circadian rhythm in net photosynthesis which peaks near noon and troughs near midnight. By resetting the day-night light regime, the rhythm rephased in continuous light. The free-running rhythm approximates 26 hours. Both transpiration and dark respiration show similar rhythmicity, with transpiration closely in phase with the rhythm in photosynthesis. The rhythm in carbon dioxide compensation point is approximately 12 hours out of phase, peaking at midnight and troughing at midday. Endogenous changes in stomatal aperture seemed to be the major control of the rhythm in photosynthesis. The activity of ribulose-1,5-diphosphate carboxylase increased during the normal photoperiod, leveling off after 12 hours; however, the activity was not correlated with the rhythmic change in photosynthesis.     

Effect of glycolysis on the metabolism of adenylates in human erythrocytes

The ATP content in human erythrocytes depleted without glucose falls down to half of the initial value within 2-3 hours and reaches practically zero within more than 10 hours. The ADP content increases 2-3-fold during the 1st hour after depletion and then slowly decreases. The AMP content increases 10-fold during several hours, but the rate of this process constantly decreases. The adenylate pool decreases at a constant rate ranging from 0.13 to 0.25 mmol/l cell. h; this is accompanied by accumulation of IMP. Addition of glucose to depleted erythrocytes results in partial recovery of the ATP level within 1-2 hours. The sooner glucose addition after the depletion, the greater the recovery. Simultaneously the ADP and AMP levels drastically decrease to new constant values. The decline of the adenylate pool ceases and the rate of IMP accumulation increases. Normally, the [ATP]/adenylate pool ratio lies within the small interval 0.85-0.94 irrespective of significant individual differences in the absolute values of [ATP]. This ratio is decreased during depletion and restored to the initial value after glucose addition. The mass-action ratio of the adenylate kinase reaction changes greatly during depletion and restoration of erythrocyte ATP.     

Ethrel (Ethylene Releaser)-Induced Increases in the Adenylate Pool and Transtonoplast DeltapH within Hevea Latex Cells

The treatment of rubber tree (Hevea brasiliensis) bark with chloro-2-ethyl phosphonic acid (ethrel), an ethylene-releasing chemical, induced, after a lag period of 13 to 21 hours, a marked increase in the total adenine nucleotides (essentially ATP and ADP) of latex cells. This rise in the latex adenylate pool was concomitant with a marked decrease in the [ATP]/[ADP] ratio without significant changes in the adenylate energy charge. The apparent equilibrium constant for the adenylate kinase, which appeared to behave as a key enzyme in maintaining the adenylate energy charge in the latex, was considerably reduced, probably as a consequence of the alkalinization of the latex cytosol induced by the treatment with ethrel. To reduce the “sink effect” and activation of the metabolism induced in Hevea bark by regular tapping, the latex was collected by micropuncture (few drops) at increasing distance (5-50 centimeters) above and below an ethrel-treated area on the virgin bark of resting trees. The effect of ethrel was shown to spread progressively along the trunk. The increase in the adenylate pool (essentially ATP) was detectable as early as 24 hours after the bark treatment and was maximum after 6 or 8 days, 5 centimeters as well as 50 centimeters above and below the stimulated bark ring. The correlative vacuolar acidification and cytosolic alkalinization, i.e. the increase in the transtonoplast ΔpH, induced in the latex cells by ethrel were shown to be concomitant with the rise in ATP content of the latex. This suggests that the tonoplast H⁺-pumping ATPase, which catalyzes vacuolar acidification in the latex, is directly and essentially under the control of the availability of its substrate (i.e. ATP) in the latex. The results are discussed in relation to energy-dependent activation of metabolism, and increased rubber production, as induced by the stimulation of rubber trees with ethrel.     

A bimodal germination response to temperature in cocklebur seeds. II. ATP and adenylate pool

Abstract. The mechanism involved in a bimodal germination-temperature response in pre-soaked cocklebur (Xanthium pennsylvanicum Wallr.) seeds was studied with special reference to adenylate metabolism. Exposure to either low (optimal at 8°C) or high (optimal at 34°C) temperature which was effective in inducing the germination of the seeds brought about the accumulation of ATP in them. The ATP level remained unchanged at temperatures around 23°C. Pretreatment with KCN, stimulating germination even at 23°C, subsequently increased the ATP content, total adenylate pool and energy charge (EC) in the axial tissue prior to germination above those of the untreated controls. The lower the treatment temperature, the greater the inhibitory effect of KCN on ATP formation. An increase in germination following an increasing duration of pre-soaking at 8°C was comparable to increasing both the ATP content and total adenylate pool of axes, but not the EC value. Similarly, changes in germination following an increased exposure duration at 8°C correlated with changes in ATP content rather than EC value in the axes. Unlike the case of chilling, an increase in ATP level in response to 34°C was greater in the early period of water imbibition, during which times its germination-stimulating effect appeared more striking than in the later period, and it occurred without a concomitant rise in EC value because of the increased supply of AMP. Such a supply of AMP was reduced in the presence of benzohydroxamic acid or propyl gallale, inhibitors of an alternative respiratory pathway. It was thus concluded that both low temperature, coupled with warm temperature, and high temperature, by itself, can induce seed germination by increasing the ATP level as well as the total adenylate pool, but not the EC value, in the axial tissue. Further, that increases in both the ATP level and the adenylate pool especially are required for seed germination to proceed, probably depending on the activities of the cytochrome and alternative respiration pathways, respectively.     

Changes of Adenine Nucleotide in the Course of Mitochondrial Development of Mung Bean Cotyledon and Their Effect on Cellular Energy Status

The changes of adenine nucleotide and adenylate energy charge (AEC) during the development of mitochondria in imbibed mung bean cotyledons and the relationship between these changes and cellular energy status are studied. After cotyledons were imbibed in water for two hours, mitochondrial cristae were not observed, but for 12 hours, they appeared obviously on the inner membrane. With the structural integrity of the mitochondria, the functional mitochondria were graduately shown. For instance, the activity of H+-ATPase of cotyledons imbibed for 24 hours was about twice higher than that of 2 hours. The ATP content and the AEC value in the cotyledons imbibed for 24 hours increased sharply and the AMP decreased, but these were not observed in the mitochondria of the cotyledons imbibed either for 24 hours or 2 hours. When the cotyledons were imbibed in 1 × 10-4 mol/l or 5 × 10-4 mol/l DNP solution for 24 hours, the ATP and the AEC in the Cells exhibited a rapid decrease, but in the mitochondria they remained canstant. In the same DNP solution with cotyledons for 24 hours, the activity of mitochondrial adenylate kinase (AK) not only was not decreased but also increased by about 50% over the control. This result shows that the energy equilibration in the mitochondria seems likely to be regulated by adenylate kinase locating between inner and out membranes of the mitochondria.     

Cultivar-specific impairment of strawberry growth,photosynthesis, carbohydrate and nitrogen accumulation by ozone

In a 2-year study, fruiting plants of strawberry (Fragaria × ananassa Duch.) cv. ‘Korona’ and ‘Elsanta’ were exposed for 2 months to 78 ppb ozone on average or filtered air without ozone in controlled environment chambers. Plant growth, photosynthesis, carbohydrate accumulation, and macronutrient concentrations were investigated in order to demonstrate cultivar-specific differences in the ozone sensitivity of ‘Korona’ and ‘Elsanta’ on the whole plant level. Moreover, the hypothesis was tested whether properties of the root system in strawberry were involved in ozone tolerance, for example, the roots’ ability to store or make available carbohydrates and their capacity to secure plants’ supply with nitrogen during a stress situation. In strawberry, ozone reduced leaf area by reducing leaf number. Moreover, specific leaf area (SLA) and relative leaf water content were reduced. Net photosynthesis was only slightly impaired, but activity of Rubisco and chlorophyll content in older leaves of cv. ‘Elsanta’ were significantly reduced. The most important, indirect impairment of photosynthesis was the reduction of plants’ total leaf area, which resulted in a decrease in plant biomass. The reduction of root biomass, the root/shoot ratio, and also the distribution of carbohydrates indicated a partitioning priority of the shoot at expense of the root system. Cultivar ‘Elsanta’ was characterized by significantly lower carbohydrate levels in ozone-exposed leaves, whereas levels remained fairly stable in ‘Korona’ leaves. In addition, nitrogen concentrations in leaves and roots decreased significantly in ‘Elsanta’, not in ‘Korona’. The reduced nitrogen concentration in leaves may be related with the more distinct reduction in Rubisco activity and chlorophyll content in older leaves of ‘Elsanta’.     

Effects of abscisic Acid on growth, RNA metabolism, and respiration in germinating bean axes

The effect of abscisic acid on growth, respiration, the ATP pool, and rate and amount of RNA synthesis in aseptically cultured axes of Phaseolus vulgaris during the first 24 hours of germination has been measured in experiments where the duration of abscisic acid application and its concentration have been varied. At concentrations from 10(-7) to 10(-4)m, abscisic acid inhibits synthesis of RNA with maximal inhibition (80%) at 10(-5)m. RNA synthesis is inhibited by abscisic acid at all times examined (12, 18, and 24 hours), but the extent of inhibition is maximal at 18 hours. In 18-hour axes RNA synthesis is inhibited 42%, ATP pool size is reduced 3%, and O(2) consumption is decreased by 6% after 75 minutes of abscisic acid treatment. Inhibition of RNA synthesis is complete by 2 hours of treatment with abscisic acid, and recovery to near control levels occurs by the 3rd hour after removal from abscisic acid.     

Relationship between ATP and energy charge during lethal metabolic stress of the marine isopod Cirolana borealis

The relationship between ATP and energy charge was studied in individuals of Cirolana borealis under heavy metabolic stress caused by anoxia or exposure to toluene. Prolonged anoxia led to a lowering of the ATP content to about 10% after 4 days, with a simultaneous decrease in energy charge to about 0.25. A lowering of the total adenylate pool reduced the fall in energy charge somewhat, but this effect was marked only in late anoxia when the individuals had become inactive. Exposure to 0.14 mM toluene for 8 days led to a similar decrease in ATP and energy charge. Exposure to 1.4 mM toluene for 24 h led to only slight changes in the adenine nucleotide pool, although the individuals became narcotized within a few hours. The energy charge associated with moribund individuals thus varied much. The mechanism of energy charge stabilization through reduction of the adenine nucleotide pool as ATP declined seemed to be of little significance for the survival of the individuals.     

Nitrogenase activity, nodule respiration, and o(2) permeability following detopping of alfalfa and birdsfoot trefoil

Gas exchange measurements and noninvasive leghemoglobin (Lb) spectrophotometry (nodule oximetry) were used to monitor nodule responses to shoot removal in alfalfa (Medicago sativa L. cv Weevlchek) and birdsfoot trefoil (Lotus corniculatus L. cv Fergus). In each species, total nitrogenase activity, measured as H₂ evolution in Ar:O₂ (80:20), decreased to <50% of the initial rate within 1 hour after detopping, and net CO₂ production decreased to about 65% of the initial value. In a separate experiment in which nodule oximetry was used, nodule O₂ permeability decreased 50% within 5 hours in each species. A similar decrease in the O₂-saturated respiration rate (V_max) for the nodule central zone occurred within 5 hours in birdsfoot trefoil, but only after 24 hours in alfalfa. Lb concentration, also measured by oximetry, decreased after 48 to 72 hours. The decrease in permeability preceded the decrease in V_max in each species. V_max may depend mainly on carbohydrate availability in the nodule. If so, then the decrease in permeability could not have been triggered by decreasing carbohydrate availability. Both oximetry and gas exchange data were consistent with the hypothesis that, for the cultivars tested, carbohydrate availability decreased more rapidly in birdsfoot trefoil than in alfalfa nodules. Fractional Lb oxygenation (initially about 0.15) decreased during the first 24 hours after detopping but subsequently increased to >0.65 for a majority of nodules of each species. This increase could lead to O₂ inactivation of nitrogenase.     

PHOTOSYNTHESIS AND RESPIRATION RATES OF LEAVES OF NICOTIANA GLUTINOSA INFECTED WITH TOBACCO MOSAIC VIRUS AND OF N. TABACUM INFECTED WITH POTATO VIRUS X

The rates of respiration and of photosynthesis of tobacco leaves infected with potato virus X were not affected until the leaves showed symptoms; the respiration rate was then increased by more than 30% and the photosynthesis rate decreased by 20%. When local lesions appeared on the leaves of Nicotiana glutinosa infected with tobacco mosaic virus, but not before, the respiration rate was increased by an amount, up to 30%, that varied with the number of lesions. The photosynthesis rate was decreased by 20%, but there was no effect on photosynthesis or respiration until symptoms appeared. These results differ from those previously reported for tobacco leaves infected with tobacco mosaic virus, in which both respiration and photosynthesis were affected within 1 hr. of inoculation. The validity of extrapolating arguments based on the results obtained with other combinations to this commonly used combination and vice-versa is questioned.     

Photoperiodic Regulation of Photosynthate Partitioning in Leaves of Digitaria decumbens Stent

In leaves of pangolagrass (Digitaria decumbens Stent.), the proportion of photosynthate partitioned into starch adjusts to a change in daylength within 24 hours. After a single 14-hour long day, the relative starch accumulation rate is approximately 50% of that under 7-hour short days. This rapid response was exploited to study the light requirement for the perception of changes in daylength. It was found for short day-grown plants that: (a) 7-hour daylength extensions with dim white light (below the light compensation point for photosynthesis); (b) 7-hour daylength extensions with dim far red light (wavelengths greater than 690 nanomoles); or (c) 0.5-hour night-break irradiations with bright white light were all capable of producing about one-half of the effect of a 7-hour daylength extension with bright light. However, long periods of bright light were not required for a complete effect, since a 7-hour shifted short day (i.e. beginning 7 hours later than usual) was as effective as a 14-hour-long day itself. There was also a critical daylength between 11 and 12 hours for the transition between short-day and long-day partitioning patterns. Photoperiod determination depends, at least in part, on a nonphotosynthetic photoreceptor sensitive to both visible and far red irradiation. The duration of the photosynthetic period, as shown in experiments with low-pressure sodium lamps, does not by itself determine the response to daylength.     

Effect of ethanol and ethylene glycol on the circadian rhythm of adenylic nucleotide levels in muscles]

The 24-hour's changes in ATP content in the gastrocnemiuses of intact rast are not significant. Both the ADP and AMP content is subjected to 24-hour's variations. It reaches its maximum within the time period from 12 to 15 o'clock p.m. for ADP and at 18 o'clock p.m. for AMP. Intragastric administration of ethanol and ethylene glycol to rats in a dose of 1/3 LD50 once per 24-hour period at 9 a. m. during a 7-days-long period dramatically changes the 24-hour's rhythm of adenylic nucleotide content in the rat gastrocnemius. It has been found that ethanol increases the average 24-hour's content of ATP, but decreases that of ADP. It increases the range of their 24-hour period variations and changes the acrophase. Ethylene glycol decreases the average 24-hour content of the both ATP and ADP, but it increases that of AMP. It changes their acrophases and increases the ranges of 24-hour-period variations of ATP.     

Metabolism of carbon and nitrogen by soybean seedlings in response to vegetative apex removal

Short-term (31-hour diurnal) growth-chamber studies were conducted to determine the effects of removing the vegetative apex (meristem and developing trifoliolate leaves) on net photosynthesis (changes in plant dry weight), on distribution of metabolites among plant parts, and on nitrate metabolism and reduced-N accumulation by soybean [Glycine max (L.) Merr.] seedlings. Roots and stems served as alternate sinks for dry matter accumulation in the absence of the vegetative apex. Sugar concentration in roots increased (42%) within 4 hours of vegetative apex removal, and remained higher than for the controls during the 31-hour experimental period. Nitrate assimilation (nitrate reductase activity and total accumulation of reduced-N) was also enhanced in response to vegetative apex removal. Although dry matter accumulation was similar between treated and control plants (113 versus 116 milligrams per plant) over the 31-hour sampling period, more nitrate (1.31 versus 0.79 milligrams per plant) and more reduced-N (3.96 versus 3.45 milligrams per plant) accumulated in treated plants during the same interval. It was concluded that vegetative apex removal had little effect on overall net photosynthesis of soybean seedlings during the 31-hour treatment period, but did alter partitioning of photosynthate and enhanced uptake, transport, and reduction of nitrate. Implications are that uptake and metabolism of nitrate by soybeans may be limited by flux of carbohydrate to the roots, although hormonal effects due to vegetative apex removal cannot be ruled out.     

Rapid Increase in Adenosine 5'-Triphosphate during Early Wheat Embryo Germination

The ATP content of isolated wheat (Triticum aestivum L. var. Polk) embryos increases 5-fold during the first 30 minutes and 10-fold during the first hour of germination to 80% of maximum. The ATP level remains at approximately 800 nanomoles per gram of tissue during the next 15 hours. ADP, AMP, and total adenosine phosphates decrease between 1 and 6.5 hours, while adenylate energy charge increases from 0.6 to 0.8 and remains constant. The rapid increase in ATP during imbibition is consistent with the energy requirement for polyribosome formation and protein synthesis during the first hours of germination. A method for determining nanomole quantities of ATP in tissue extracts by isotopic dilution of γ-³²P-ATP in the hexokinase reaction is outlined.