Influence of Abscisic Acid on Nitrate Accumulation and Nitrate Reductase Activity in Potato Tuber Slices

Abscisic acid (ABA) at concentrations of 1 to 10 µg.ml^–1suppressed development of nitrate reductase activity in freshtuber slices of Solanum tuberosum L. incubated in KNO₃. Suppressionof activity was evident after 3 hr and continued for 20 hr beforerecovery. This recovery may be due to inactivation of the hormone.Nitrate accumulation was enhanced by ABA. At exogenous NO₃ levelsof 0.1 to 5 mM, the hormone enhanced both NO₃ accumulation andnitrate reductase activity. When applied 24 hr after incubation in NO₃, ABA promoted a markeddecline in enzyme activity in the absence of exogenous NO₃,but was less effective in the presence of NO₃. Slices incubatedin NO₃ and ABA also exhibited increased loss of enzyme activityupon removal of NO₃. Preincubating slices in the hormone for24 hr in a NO₃- free medium resulted in stimulation of nitratereductase activity. Addition of NO₃ resulted in a marked stimulationof enzyme activity over a period of 8–10 hr. The ABA response is not related to tissue levels of free aminoacids and is not affected by different NO₃ sources. These resultssuggest the ABA effect on nitrate reductase activity is influencedby NO₃ status of the cells. Where external NO₃ levels are lowit stimulated NRA while it inhibited activity where NO₃ contentis high. (Received May 12, 1981; Accepted October 12, 1981)     

Variation in Nitrate Accumulation, Nitrate Reductase Activity and Nitrite Reductase Activity along Primary and Nodal Roots of Corn (Zea mays L.) Seedlings

Significant differences in NO₃ accumulation and nitrate reductaseactivity (NRA) were noted in the successive segments of developingyoung primary and nodal roots. This variation was also foundto be a function of root age. Nitrite reductase activity (NiRA)on the other hand had little variation among various segmentsof primary and nodal roots and also as a function of root age.These data suggest root NO₃ accumulation and root NRA are twoprocesses which are not directly linked. ¹ Present address: Division of Plant Physiology, Indian AgriculturalResearch Institute, New Delhi-110012, India. (Received December 3, 1983; Accepted June 18, 1983)     

Effect of Nitrate, Ammonium and Some Amino Acids on Growth and Nitrate Reductase Activity in Suspension Cultures of Atropa belladonna

Growth and nitrate reductase activity (NRA) of Atropa belladonnacells were studied in medium supplemented with NaNO₃, NH₄NO₃,and amino acid precursors to tropane alkaloids. Growth and NRAwere stimulated by NH₄⁺ and by proline, by proline plus ornithine,but not by glutamate, in NO₃^–-containing medium. Testedamino acids inhibited neither utilization of inorganic nitrogennor growth. (Received September 30, 1988; Accepted August 28, 1989)     

Inhibition of nitrate accumulation and in vivo nitrate reductase activity in potato tuber slices by dimethysuIfoxide

Dimethylsulfoxide at concentrations of 0.5 to 5.0% inhibitednitrate reductase activity and the accumulation of nitrate in"fresh" and "aged" potato tuber slices. Fresh slices were moresensitive to concentrations of 0.5 to 2.5% and suppression ofenzyme activity paralleled a decline in NO₃ accumulation. With aged slices concentrations of 0.5 to 2.5% progressivelysuppressed enzyme activity without affecting NO₃ accumulation.These results are discussed in relation to the known effectsof dimethylsulfoxide on the permeability of biological membranesand protein structure. (Received November 29, 1978; )     

Influence of Abscisic Acid on Phosphorus Metabolism and Respiration in Potato Tuber Discs. Comparison with the Cycloheximide Effect

Ageing of discs of potato tuber by incubation in an aerated medium, produces an increase in the rates of respiration and of phosphate uptake. The presence of cycloheximide (CHM) or abscisic acid (ABA) in the uptake medium, does not change uptake by fresh tissue over 3–4 h. On the other hand, CHM causes an inhibition of the rate of uptake by aged tissue although ABA does not. The addition of CHM or ABA to the ageing medium, prevents totally (CHM) or only partially (ABA) the increase in phosphate uptake. The analysis of ³²P-incorporation into the various phosphorylated fractions after 24 h of ageing with CHM or ABA show that CHM induces a large inhibition of the rate of uptake with an almost complete inhibition of ³²P-incorporation into the various phosphorylated fractions. By contrast, ABA produces equal inhibition of ³²P labelling of all fractions including all acid-soluble components. CHM prevents the increase in the rate of respiration, whereas ABA causes a slight stimulation. In both cases, no important effect on ATP content was observed. These results are discussed in terms of a comparison of ABA and CHM actions. They lead to the hypothesis of a specific effect of ABA on the development of the uptake mechanism.     

Effect of Plant Growth Regulators on Nitrate Utilization by Roots of Nitrogen-Depleted Dwarf Bean

We examined the effect of pretreatments (18 h at 5 µmoldm^–3) with abscisic acid, the ethylene-releasing substance‘Ethephon’, gibberellic acid, indoleacetic acid,kinetin and zeatin on nitrate uptake and in vivo nitrate reductaseactivity (NRA) in roots of nitrogen-depleted Phaseolus vulgarisL. Nitrate uptake showed an apparent induction pattern witha steady state after about 6 h, in all treatments. The nitrateuptake rate after 6 h was unaffected or at most 30% lower aftertreatments with the plant growth regulators. Gibberellic acid, kinetin and zeatin induced substantial NRAin roots in the absence of nitrate, whereas Ethephon enhancedNRA only during nitrate nutrition. Kinetin-induced NRA (Ki-NRA)was maximal after a pretreatment at 1 µmol dm^–3,and showed a lag phase of 6–8 h. Ki-NRA was additive tonitrate-induced NRA (NO^–₃-NRA) for at least 24 h, independentof the induction sequence. After full induction, Ki-NRA approximated20% of NO-₃-NRA. Abscisic acid counteracted the developmentof Ki-NRA, but not of NO^–₃-NRA. Cycloheximide and tungstatewere equally effective to suppress the development of nitratereductase activity after supply of kinetin or NO^–₃. Our data are consistent with the operation of two independentenzyme fractions (Ki-NRA and NO^–₃-NRA) with apparentlyidentical properties but with separate control mechanisms. Theabsence of major effects of plant growth regulators on the time-courseand rate of nitrate uptake suggests that exogenous regulators,and possibly endogenous phytohormones are of minor importancefor initial nitrate uptake. The differential effect of someregulators on nitrate uptake and root NRA furthermore indicatesthat the processes of uptake and reduction of NO^–₃ arenot obligatory or exclusively coupled to each other.     

Gibberellic Acid-stimulated de Novo Synthesis of a Particular Isozyme of Acid Phosphatase in Wheat Half-seeds

GA₃ stimulated incorporation of radioactive methionine intoan acid phosphatase isozyme possessing an isoelectric pH at4.0 (pI 4 isozyme). This effect of GA₃ was completely inhibitedby cycloheximide, but not by cordycepin. The results suggestthe existence of preformed mRNA coding for pI 4 isozyme in thewheat aleurone layer and the stimulation of its translationby GA₃. (Received April 7, 1981; Accepted July 1, 1981)     

The Heritability of Abscisic Acid Accumulation in Water-stressed Leaves of Pearl Millet [Pennisetum americanum (L.) Leeke]

Using detached leaves, two cultivars of pearl millet [Pennisetumamericanum (L.) Leeke], B282 and Serere 39, were assessed forvariation in the capacity to accumulate ABA in response to waterstress. Significant differences in ABA accumulation were detectedbetween cultivars and between different inbred lines withina cultivar, but within lines there was much less variation inthis character. In crosses between individual lines of B282(low ABA) and Serere 39 (high ABA), ABA accumulation in theF₁ was mid-way between parental values, indicating additivegenetic control and lack of dominance. Selfed progeny of a B282 x Serere 39 cross were selected forcontrasting ABA accumulation in the F₂ to F₄ generations. Asixfold range in ABA accumulation was found amongst 207 F₂ progeny.This increased to nearly ninefold at F₃ and F₄. Regression analysisindicated high heritability of ABA accumulation and rapid approachto homozygosity. As the cross studied involved a dwarf (B282) and a tall (Serere39) parent, segregation occurred for height as well as for ABA,though not entirely independently. Tall F₃ progeny had significantlyhigher ABA contents than dwarf progeny and high ABA was thereforeassociated with other traits (e.g. large leaves, high leaf percent d. wt) characteristic of tall plants. Nevertheless, therewas a substantial range of ABA content within both groups whichwas uncorrelated with height and other characters. The potential use of the selections in studies on drought responseis briefly discussed. Pennisetum americanum (L.), Leeke, pearl millet, abscisic acid accumulation, water stress, genetic differences, inheritance     

Effect of PGF2α on progesterone secretion and adenylate cyclase activity in ovine luteal tissue

Ovine luteal slices were used to study the effects of prostaglandins (PG) F₂α on luteinizing hormone (LH)-stimulated secretion of progesterone and adenylate cyclase activity. The accumulation of progesterone in incubation medium and adenylate cyclase activity was similar after incubation of luteal slices with Medium 199 alone or Medium 199 containing PGF₂α (250 ng/ml) for 3 hr. Addition of luteinizing hormone (LH; 100 ng/ml) resulted in a 2–3 fold increase in both the rate of progesterone accumulation and adenylate eyclase activity by 3 hr. When luteal slices were incubated in the presence of both LH and PGF₂α the rates of progesterone accumulation and adenylate cyclase activity were identical to those in flasks containing LH alone after 1 hr; however, after 3 hr both LH stimulated progesterone accumulation and adenylate cyclase activity were inhibited to levels similar to those observed in control slices.In a second experiment, after 60–120 min of exposure to PGF₂α the rate of progesterone accumulation in the medium was not different from that in untreated control slices. In addition, after this experiment the luteal slices were homogenized and the basal, sodium fluoride, LH, isoproterenol (ISO) and PGE₂ sensitive adenylate cyclase activities were determined to evaluate the hormonal specificity of the negative effect of the pretreatment with PGF₂α. Both LH and ISO stimulated adenylate cyclase activities were reduced after PGF₂α pretreatment. However, fluoride ion stimulated adenylate cyclase activity was not significantly effected by PGF₂α pretreatment and PGE₂ sensitive adenylate cyclase was effected only slightly.     

Seasonal Changes of GA1, GA19 and Abscisic Acid in Three Rice Cultivars

The levels of endogenous gibberellin A₁ and A₁₉ (GA₁ and GA₁₉)and abscisic acid (ABA) in three rice (Oryza sativa L.) cultivars,Nihonbare (normal), Tan-ginbozu (semid-warf) and Tong-il (semi-dwarf),were measured at various stages of internode elongation andear development. GA₁₉ was the main GA in Nihonbare and Tong-ilthroughout the life cycle but was not detected in Tan-ginbozu.The levels of GA₁ in the ears of all three cultivars were lowand reached their maxima after anthesis. Similarly, the earsof all three cultivars contained high ABA levels which peakedafter anthesis. Shoots contained low quantities of ABA throughoutthe life cycle. The roles of GAs and ABA are discussed withrespect to physiological phenomena, such as internode elongation,ear development and dwarfism. (Received May 9, 1981; Accepted July 18, 1981)     

Effects of in Vivo Treatment with Abscisic Acid and/or Cytokinin on Activities of Vacuolar H+ Pumps of Tonoplast-Enriched Membrane Vesicles Prepared from Barley Roots

We investigated the effects of in vivo treatment (1 day) ofbarley roots with abscisic acid (ABA) and/or a cytokinin (6-benzyladenine;BA) on the ATP- and PP_i-dependent H⁺ transport activities oftonoplast-enriched membrane vesicles prepared from the roots.Treatment with ABA significantly increased the two H⁺ transportactivities. By contrast, treatment with BA significantly decreasedPP_i-dependent H⁺ transport activity, while the change in ATP-dependentH⁺ transport activity was small. Increases in the two H⁺ transportactivities caused by treatment with ABA were suppressed duringtreatment with ABA and BA. Changes in the NO^–-inhibitableATPase activity and the Na⁺-inhibitable PP_iase activity of membranevesicles after treatment of roots with phytohormone(s) (ABA,BA, ABA + BA) were similar to changes in the ATP- and PP_i dependentH⁺ transport activities of the membrane vesicles, respectively.Immunoblot analysis with antibodies raised against the functionalcatalytic subunits of the vacuolar H⁺ pumps (H⁺- ATPase andH⁺-PP_iase) of mung bean revealed that only the level of thefunctional catalytic subunit of the H⁺-PP_iase of the membranevesicles was significantly increased by treatment with ABA aloneand in combination with BA. These results suggest that treatmentwith ABA has a stimulatory effect on the activities of the twoH⁺ pumps of the vacuolar membrane of barley roots, with increasein the level of the catalytic subunit of the H⁺-PP_iase, andthat treatment with BA has an inhibitory effect on the two H⁺pump activities of the vacuolar membrane without changes inthe levels of the catalytic subunits of either H⁺ pump, withthe limitation that treatment with BA has an inhibitory effectonly when the activity of the H⁺-ATPase has been increased bytreatment with ABA. ³Present address: Department of Biology, Faculty of Science,Hirosaki University, Hirosaki, 036 Japan     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Characterization pf Spring Wheat Genotypes Differing in Drought-Induced Abscisic Acid Accumulation: I. DROUGHT-STRESSED ABSCISIC ACID PRODUCTION

Abscisic acid (ABA) accumulation in response to drought stresswas studied in F₅ and F₆ progeny of a cross between two springwheat (Triticum aestivum L.) genotypes contrasting in ABA accumulation:TW269/9 (high ABA) and Highbury (low ABA). Selection in earliergenerations had been made on the basis of ABA accumulation indetached and partially dehydrated samples of the fourth leafof the main stem (MSL4). Detached-leaf tests with MSL4 from several low and high ABAselections at F₅ confirmed differences found in ABA accumulationin the F₄ generation. Approximately two-fold differences weremaintained at F₅ in both cabinet-grown and field-grown plants. Measurements of the ABA concentrations present in flag leavestaken from drought-stressed plants in the field gave variableresults. Several selections at F₅ which differed in ABA contentby about 70% in detached-leaf tests with MSL4, contained, overall,the same concentration of ABA in both low and high ABA selectionsas plants became water-stressed. However, low and high ABA F₆selections which were sampled on five occasions over severalweeks differed consistently in the level of ABA present fora particular degree of water stress. The high ABA selectionscontained c. 50% more ABA than low ABA selections.Possible explanationsare given for the inconsistencies between ABA levels from lowand high ABA selections in detached-leaf and attached-leaf tests. Key words: Wheat Triticum aestivum, Abscisic acid, ABA, Drought stress     

The Effect of Abscisic Acid on Amino Nitrogen and Protein Content of Potato Plants in Relation to the Inhibition of Nitrate Reductase Activity

Treatment of potato plants grown in nutrient solution with 3.8µM ABA resulted in reduced soluble protein in roots andin leaves at 24 h, but not in stems. This treatment reducedin vivo nitrate reductase activity in all organs for about 48h with the most pronounced reduction occurring in the roots.Excised root and leaf segments from plants treated with ABAfor 24, 48 and 72 h absorbed significantly more ¹⁴C leucine,compared to the control but the percent incorporation into proteinwas not altered in roots. In response to ABA total free amino nitrogen in leaves was lowerat 5 and 72 h and in stems at 72 h. Amino nitrogen content ofroots was enhanced by ABA at 5, 24 and 72 h due to generallyhigher levels of aspartate, serine, glutamate, proline and ammonia.There was no consistent relationship between ABA suppressionof nitrate reductase activity and ammonia or specific aminoacid (except proline) levels in leaves and stems. The increasedfree amino nitrogen levels in response to the hormone may bethe result of impaired NO₃– reduction rather than thecause. The results of protein synthesis studies and solubleprotein content suggest that ABA inhibition of nitrate reductaseis not due to general inhibition of protein synthesis and mayinvolve specific inhibition of nitrate reductase protein synthesis. ¹ Contribution No. 684, Department of Plant Science, Universityof Manitoba.     

Influence of abscisic acid on nitrogen partitioning, sucrose metabolism and nitrate reductase activity of chicory suspension cells

Batch suspension cultures of chicory cells (Cichorium intybusL. var. Witloof) possess a NADH-specific nitrate reductase activitythat peaks on day 3 of a 10 d growth cycle. When both nitrateand ammonium are used as nitrogen sources, chicory cells absorbnitrate irst. Ammonium uptake becomes predominant at day 3,even though NO₃^– was still present in the medium. Althoughabscisic acid impairs growth as well as ¹⁵NO₃^– uptakeand reduction, it promotes nitrate reductase activity as measuredboth in vivo and in vitro. Specific activity is 50% higher inABA-treated cells than in controls. These conflicting data maybe explained either in erms of nitrate reductase levels or bythe availability of reducing power and energy. Since NRA isgenerally controlled by the availability of the reducing power,the energy status of the cell, the adenylate nucleotide pools,were measured simultaneously with the carbohydrate levels withinthe cell and the growth medium. The energy charge was not modifiedduring the growth cycle, regardless of the rowth conditions.Yet ABA modified the intracellular carbohydrate metabolism andinhibited the acidic invertase, the sucrose synthase and thesucrose phosphate synthase activities. Modified assimilationrates of nitrate in chicory cells grown in the presence of ABA,were probably correlated to modified carbohydrate metabolismpathways leading to increased availability of reducing power,energy and C-skeletons. Key words: Abscisic acid, Cichorium intybus L, nitrate reductase, reductase, invertase, sucrose synthase, sucrose phosphate synthase     

Effectiveness of Lotus Root Nodules: III. EFFECT OF COMBINED NITROGEN ON NODULE EFFECTIVENESS AND FLAVOLAN SYNTHESIS IN PLANT ROOTS

When grown in a nutrient solution containing combined nitrogen(NH₄NO₃), Lotus pedunculatus and L. tenuis seedlings inoculatedwith a fast-growing strain of Rhizoblum (NZP2037) did neitherdevelop root nodules nor develop flavolans in their roots. Incontrast, the roots of nodulated seedlings growing in a nitrogen-freenutrient solution contained flavolans. Flavolan synthesis coincidedwith root nodule development on these plants. When added as a single dose, high concentrations of NH₄NO₃ (5and 10 mg N per plant) stimulated the growth of L. pedunculatusplants but suppressed nodulation and nitrogen fixation. In contrastthe continued supply of a low concentration of NH₄NO₃ (1?0 mgN d^–1 per plant) stimulated nitrogen fixation by up to500%. This large increase in nitrogen fixation was associatedwith a large increase in nodule fresh weight per plant, a doublingof nodule nitrogenase activity, and a lowering of the flavolancontent of the plant roots. The close relationship between nitrogendeficiency, nodule development, and flavolan synthesis in L.pedunculatus meant that it was not possible (by nitrogen pretreatmentof plants) to alter the ineffective nodule response of a Rhizobiumstrain (NZP2213) sensitive to the flavolan present in the rootsof this plant.     

Stimulation of the Flowering of Pharbitis nil Chois. by Gibberellin A3 : Time Dependent Action at the Apex

Gibberellin A₃ (GA₃) stimulated flowering when it was appliedto the shoot apex of seedlings of Pharbitis nil, dwarf strainKidachi; but, not when it was applied to the cotyledons. GA₃applied to the plumule before or shortly after the start ofan inductive dark period promoted both flowering and shoot elongation;but, the later the time of application during the dark periodless the promotion of flowering, although marked promotion ofshoot elongation always took place. The variation with time in the response of flowering to GA₃indicates that early floral processes at the apex are stimulatedby GA₃, but that subsequent processes are insensitive to it.The early processes of floral stimulus produced by a 16 hr inductivedark period probably are completed within 20 hr at 28°Cafter the end of the dark period. At low temperatures, suchas 15 and 20°C, early floral processes continued for morethan 40 hr. When cotyledons were removed at various times, the export ofthe floral stimulus to the shoot apex was apparent within hoursof the generation of the floral stimulus in the cotyledons,which started with the passage of the critical 9-hr dark period. (Received February 18, 1981; Accepted March 24, 1981)     

硝酸镧对碱胁迫下黑麦草幼苗生长和光合生理的影响

在150 mmol·L^-1 NaHCO₃胁迫下,研究了不同浓度硝酸镧对黑麦草幼苗生长的影响及其对叶片光合生理响应的调节作用。结果表明,叶面喷施低浓度硝酸镧(0.05 mmol·L^-1)预处理显著减小了碱胁迫下黑麦草幼苗生物量、叶片叶绿素和类胡萝卜素含量、叶绿体希尔反应、光合电子传递、光合磷酸化、Mg²⁺ ATP酶、RuBP羧化酶活性和光合效率的下降幅度,却对光呼吸调节酶乙醇酸氧化酶活性无明显影响。而高浓度硝酸镧(0.5 mmol·L^-1)预处理不仅对碱胁迫没有缓解作用,反而加重了碱胁迫伤害。因此,适宜浓度硝酸镧可以通过改善光合功能从而缓解碱胁迫对黑麦草幼苗生长的抑制作用。     

Mechanism for the induction of 3-hydroxy-3-methylglutaryl coenzyme A reductase in HgCl2-treated sweet potaso root tissue

No 3-hydroxy-3-methylglutaryl coenzyme A reductase activitywas detected in microsomal fractions prepared from healthy andwounded sweet potato root tissues. However, there was considerableenzyme activity in the tissue discs when Hgcl₂ was applied afterincubation at 30?C for 18 hr. This increase in the enzyme activitywas followed by furano-terpene accumulation. Application ofcycloheximide to discs immediately after preparation completelyinhibited the increase in the enzyme activity when HgCl₂ wasapplied after incubation. In contrast, the increase was delayedfor about 4 hr, then the activity was enhanced, when CHI wasapplied after preliminary incubation. CHI completely inhibitedprotein synthesis when applied to the discs after the preliminaryincubation, as judged by the inhibition of the incorporationof ¹⁴C-leucine into protein and the inhibition of the increasein peroxidase activity which is synthesized de novo. These resultssuggest that the inactive precursor of HMG-CoA reductase issynthesized during the preliminary incubation in response onlyto wounding then it is converted into the active form aftertreatment with HgCl₂. (Received January 11, 1979; )     

Respiration of Grand Rapids lettuce (Lactuca sativa L.) seeds in relation to chemical and photocontrol of germination

A 10-min irradiation with red light (R) of ‘Grand Rapids’lettuce (Lactuca sativa L.) seeds increased respiratory rates(QO₂ and QCO₂) over those of far red (FR)-irradiated seeds within2 to 3 hr. Differences in respiration between R- and FR-irradiatedseeds became more pronounced with time. The respiration, indarkness at 25?C, of seeds air dried after germination promotingimpregnation treatments with 1.0 mM GA₃+0.5 mM kinetin in acetonewas stimulated slightly by the 6th hour after planting and markedlyby the 12th and 24th hour. Results with seeds in GA₃+kinetindissolved in water were similar. ABA, which inhibits germinationand seedling growth, prevented stimulation in respiration oflight-induced seeds. ABA also repressed respiration when usedwith GA₃+kinetin. The germination and growth retardant, isopropylN-(3-chlorophenyl) carbamate (CIPC), did not affect the respirationof either R- or FR-treated seeds. A comparison of the effectsof chemical and light treatments on respiration indicate thatchemical and photocontrol mechanisms are not identical. (Received May 17, 1976; )