Effects of Repetitive Acid Immersion, Red Light, and Gibberellin A3 Treatments on Phytochrome-mediated Germination Control in Skotodormant Lettuce Seeds

Dry lettuce seeds (Lactuca sativa L. cv. Grand Rapids), whichreceived 5 min far-red light (FR) 0.5 h after the onset of waterimbibition, showed 17% and 50% germination without and withacid immersion treatment (pH 0.1) for 1 h and rinsing with water,respectively. The acid treatment caused only 6% germinationor less in FR-treated seeds held for 10 to 30 d in dark storage.The 10 to 30 d skotodormant seeds did not respond to red light(R) or gibberellin A₃ (GA₃) singly, but showed 84% or higherpercentage germination if 1 h acid immersion was given beforeR or GA₃. The 20 d skotodormant seeds, which received R treatmentat day 10 but remained dormant showed 89% germination with onlyacid treatment. Similar values were obtained with 30 d skotodormantseeds which received one or two R treatments at day 10 or 20,i.e. the only requirement for these R-treated dormant seedswas an acid immersion. This releases the skotodormancy and rendersthe seeds more sensitive to R or GA₃, but the skotodormancywas initiated again if no light or hormone treatments were givenimmediately. The repetitive R or GA₃ treatments, which did notcause skotodormant seeds to germinate, lessened the degree ofskotodormancy. The germination of these skotodormant seeds canonly be induced by the synergistic action of R and GA₃. In thisstudy, GA₃ caused higher germination percentages in R-treatedskotodormant seeds than R stimulated in GA3-treated seeds. Itis suggested that (i) repetitive R or Ga₃ treatments maintaina high endogenous level of the far-red-absorbing form of phytochrome(P_fr) and GA activity, respectively, (ii) the accumulated stableintermediates of phytochrome persist in fully-imbibed skotodormantseeds for up to 20 d, without phytochrome expressing its functionuntil the seeds are acidified and (iii) a model is formulatedto interpret the results of acidification, growth promotersand R effects on germination of light-sensitive lettuce seeds. Key words: Phytochrome, Latuca saliva, seed germination, dark reversion of phytochrome, gibberellin A₃, acidification, skotodormancy     

Effects of Repetitive Drying, Acid Immersion, and Red Light Treatments on Phytochrome- and Gibberellin A3-mediated Germination of Skotodormant Lettuce Seeds

Ten-30 d imbibed skotodormant lettuce seeds (Lactuca sativaL. cv. Grand Rapids) showed no germination with water alone.However, following a single treatment of red light (R), gibberellinA₃ (GA₃) or 1 h acid immersion (pH 0–1) plus water rinse,7% germinated. These imbibed skotodormant seeds germinated 85%or higher if acid immersion was carried out before R or GA₃.Similar values were obtained with imbibed skotodormant seedsunder acid immersion plus drying treatment applied at day 10or 20 plus R or GA3 treatment applied 10 d later. One or twodrying treatments alone reduced the degree of skotodormancyand made seeds more responsive to R but not GA₃. Seeds withone R plus drying treatment at day 10 or 20 germinated about50% with or without an additional R, and 80% or more with GA₃on day 20 or 30. The 20 or 30 d skotodormant seeds having R(with or without drying) or acid plus R and drying treatmenton day 10 or 20 and additional dark incubation in water for10d showed 85 to 100% germination with only acid immersion.The skotodormancy was eliminated by the acid immersion but itwas initiated again if R or GA₃ treatment was not given immediately.It is concluded that the drying treatment, after eliminationof skotodormancy by acid or acid + R pretreatment, preventsthese seeds re-entering skotodormancy and maintains a high germinationpotential under dark storage for up to 20 d. Key words: Dark reversion of phytochrome, gibberellin A₃, acidification, skotodormancy, induction and breakage of seed dormancy     

The action of cyclic AMP on GA3 controlled responses VI. Characteristics of the promotion of light-inhibited seed germination in Phacelia tanacetifolia by GA3 and cyclic 3',5'-adenosine monophosphate

GA₃ and cyclic AMP were found to promote the germination (inlight) of light inhibited Phacelia tanacetifolia seed to thelevels obtained with dark controls. The GA₃ and cyclic AMP promotedgermination was inhibited by ABA and cycloheximide but not by6-methyl purine. The hormone and the nucleotide were not requiredfor the entire incubation period to obtain maximum germination. Theophylline and caffeine also promoted germination of theseseeds and 8-bromoadenosine cyclic AMP was found to be a betterpromoter of germination than cyclic AMP. Of a variety of nucleotidestested, only cyclic AMP promoted germination. This study supportsthe hypothesis that cyclic AMP is involved in some manner inGA₃-induced seed germination. (Received January 22, 1974; )     

The action of cyclic-AMP on GA3 controlled responses V. Similarities in the induction of isocitrate lyase in hazel seeds by gibberellic acid and cyclic 3',5'-adenosine monophosphate

Cyclic-AMP was found to promote the induction of isocitratelyase in hazel seeds. Similarities in the induction of thisenzyme by GA₃ and cyclic-AMP were found in the (1) total amountof enzyme produced, (2) the time course for the production ofthis enzyme, (3) the amount of enzyme secreted into the medium,and (4) the inhibition of enzyme production induced by ABA,cycloheximide and 6-methyl purine. Of a variety of nucleotidestested only cyclic-AMP consistently promoted high levels ofisocitrate lyase. Cyclic-AMP also promoted a similar increase in the fresh weightof the embryo to that obtained with GA₃ treated seeds. Thisinitial study is suggestive of the possibility that cyclic-AMPmay be involved in GA₃ mediated responses in hazel seeds. (Received May 4, 1973; )     

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; )     

The action of cyclic-AMP on GA3 controlled responses III. Characteristics of barley endosperm acid phosphatase induction by gibberellic acid and cyclic 3', 5'-adenosine monophosphate

Studies on the induction of barley endosperm acid phosphataseby GA₃ and cyclic-AMP revealed (1) acid phosphatase inductionby GA₃ and cyclic-AMP is inhibited in a similar manner by ABA,cycloheximide and 6-methyl purine, (2) combinations of GA₃ andphosphodiesterase inhibitors such as caffeine and theophyllinepromoted the level of acid phosphatase induction obtainablewith the hormone alone, and (3) cyclic-AMP and GA₃ may be actingas triggers in the induction of this enzyme. Some of the implicationsof these results are discussed. (Received May 25, 1972; )     

INFLUENCE OF INORGANIC NITROGENOUS COMPOUNDS ON TOBACCO SEED GERMINATION INDUCED BY GIBBERELLIN A3, KINETIN AND AMMONIUM SALTS OF ORGANIC ACIDS

1. Investigations were made on the influence of inorganic nitrogenouscompounds upon the the germination of tobacco seeds (Nicotianatabacum L. var. virginica (AGDH.) COM. "Bright Yellow") inducedby GA₃, kinetin and ammonium salts of organic acids. Potassiumnitrate, ammonium chloride, ammonium sulfate and ammonium nitrategreatly increase the germination of the seeds induced by theabove reagents, while these inorganic salts, given alone, arealmost ineffective in causing germination.
2. Kinetin was shownto induce germination of tobacco seeds inthe dark. The discrepancywith the results of previous investigationsin this respectwas discussed.
3. It was inferred that nitrogenous metabolismis involved in theprocess of dark-germination of tobacco seedsas induced by theabove-stated stimulating factors and promotedby inorganic nitrogenoussubstances.

(Received July 17, 1961; )     

Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

Ethylene (10 µ1^–1) caused about one-third of highlydark-dormant seeds of common purslane (Portulaca oleracea L.)to germinate in the dark. Attempts were made to increase germinationin the dark with nitrate and ethylene combinations. When applieddirectly to the seeds, KNO₃ did not stimulate germination andKNO₃ plus ethylene did not increase germination above that ofethylene alone. Pre-incubation of seeds in KNO₃ for 4 to 7 dbefore the ethylene applications significantly increased germination.The effects of the KNO₃ pre-incubation were additive at eachof four ethylene concentrations (0.1–100 µ11^–1).Potassium nitrate was effective only when ethylene followedthe KNO₃ pre-incubation period. Potassium nitrite stimulatedabout 25 per cent of the seeds to germinate without a pre-incubationperiod and without ethylene. Also, ethylene plus KNO₂ enhancedgermination above that achieved by either stimulus alone. Silvernitrate did not block the ethylene promotion of germination,but reversed the typical ethylene inhibition of seedling growthfollowing germination. The results support the views that nitrateexerted its effect via conversion to nitrite within the seedand that the rate of nitrate conversion may be a limiting factorin the dark germination of common purslane seeds. Ethylene mayfacilitate nitrite activity by increasing seed sensitivity tothe stimulus. Common purslane, Portulaca oleracea L., ethylene, nitrate, nitrite, germination, dormancy     

Effects of Chemicals Often Regarded as Germination Stimulants on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Gibberellin A₃ (GA₃), kinetin and zeatin promoted germinationof conditioned witchweed (Striga asiatica [L.] Kuntze) seedssimilar to dl-strigol and a natural stimulant from corn rootexudates. GA₃ promoted germination only with scarified seeds.However, these regulators, as well as dl-strigol and naturalstimulants, inhibited the conditioning of seeds and their subsequentgermination. On the other hand, abscisic acid induced 74% germinationof conditioned seeds but had no effect on seed conditioning.Other chemicals such as sucrose, NaNO₃, vitamin B₁, L-methionine,nicotinamide, indoleacetic acid and colchicine had no apparenteffect on seed conditioning, while sucrose, L-methionine andinositol induced about 30 % germination of conditioned seeds.Seeds generally required either a longer conditioning time ora higher terminal dl-strigol concentration to eliminate anyinhibition of seed conditioning induced by a compound. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica (L.) Kuntze, weed control, growth regulating substances     

The Effects of Gibberellic Acid on Organelle Biogenesis in the Endosperm of Germinating Castor Bean Seeds

Mature seeds of castor bean (Ricinus communis L.) were imbibedin tap water or 0.3 mM GA₃, planted in vermiculite moistenedwith tap water or 0.3 mM GA₃, and incubated at 32 ?C. Duringthe course of germination, GA₃ promoted marked increases inthe activities of the glyoxysomal marker enzyme isocitrate lyaseand certain mitochondrial marker enzymes, but did not affectthe ER marker enzyme choline phosphotransferase. Glyoxysomaland ER protein and phospholipid were not increased in amountby GA₃, whereas mitochondrial protein and phospholipid were.SDS-polyacrylamide gels of the glyoxysomal matrix polypeptidesfrom GA₃-treated beans exhibited two polypeptides additionalto those found to be common to both GA₃-treated and controltissue. Incorporation of CDP-(methyl ¹⁴C)-choline into intactendosperm tissue and the distribution amongst the glyoxysomes,mitochondria, and ER of newly synthesized phosphatidyl-(methyl¹⁴C)-choline was unchanged by GA₃.     

Gibberellin-Induced Suppression of Chloroplast Starch Formation from Exogenous Sucrose in Isolated Epidermis of Light-Grown Cucumber Hypocotyls

The effects of gibberellin A₃(GA₃) on chloroplast starch formationfrom exogenous sucrose in epidermal strips of light-grown cucumber(Cucumis sativus L. cv. Aonagajibai) hypocotyls were studied.Chloroplast starch formation was measured by counting microscopicallythe number of I₂KI stained chloroplasts. In the presence ofsucrose (1–50 mM) and in light, chloroplast starch formationoccurred rapidly for 5 hr and then the rate declined. GA₃ (100µM) simultaneously supplied with sucrose clearly suppressedboth the rate and the degree of starch formation. When the epidermiswas preincubated in the dark with sucrose in the presence orabsence of GA₃ and then post-incubated in light with bufferonly in the presence or absence of GA₃, starch formation wassuppressed to the same degree by GA₃ given either in the pre-or post-incubation period. When the epidermis was preincubatedin the dark with GA₃ alone and then transferred to light forpost-incubation with sucrose alone, GA₃ suppressed the initialrate of starch formation during the post-incubation period.The degradation of chloroplast starch formed in advance fromexogenous sucrose in light was not significantly affected byGA₃ These results are discussed in relation to the mechanismof the GA₃ action and also to the GA₃-induced decrease in theosmotic potential of the cell. (Received February 2, 1982; Accepted May 31, 1982)     

Effects of Temperature and Various Red or Far-red Irradiations on Phytochrome- and Gibberellin A3-mediated Germination Control in Partially Hydrated Lettuce Seeds

Dark reversion of phytochrome in partially hydrated lettuceseeds (Lactuca sativa cv. Grand Rapids) is temperature dependent.After initial red irradiation (R) the higher the storage temperature,the higher the dark reversion rate. Following dark moist storage(DMS) at 30 ?C for 15 d none of the seeds receiving initialR germinated, whereas seeds stored at 0 ?C germinated nearlyas well (about 80%) as unstored controls. The half-time fordark reversion at 20 ?C and 30 ?C is 9 d and 3 d respectively.Repeated R treatments given at 5 d intervals during DMS at 20?C and 30 ?C maintained a high germination capacity. With threeor more R treatments the effect of high temperature largelydisappeared. Dark reversion of phytochrome was not observed in partiallyhydrated lettuce seeds receiving continuous red irradiation(cont R) for two or more days. The promotive effect of contR could be reversed at any time with a brief far-red irradiation(FR), indicating that the phytochrome system remained fullyphototransformable. With continuous far-red light (cont FR)the ability of gibberellin A₃ (GA₃) to stimulate germinationdisappeared and response to GA₃ also diminished in cont R followedby FR but at a slower rate indicating the induction of secondarydormancy in these partially hydrated seeds. This induction ofdormancy was retarded by repetitive or cont R but was enhancedby cont FR. The results of this study suggest a role for theaccumulated stable intermediates of phytochrome transformationin partially hydrated seeds with repeated or continuous R treatmentsand different effects of GA₃ and R in the regulation of germination. Key words: Phytochrome, Lactuca sativa, Seed germination, Temperature, Dark reversion of phytochrome, Seed water content     

Possible effect of gibberellin on phytate degradation in germinating barley seeds

Changes in the contents of phytate (IP₆) and other phosphorus(P)-compoundsin germinating seeds of a huskless barley were investigatedin the embryo with scutellum (EM), the starchy endosperm (EN),and the aleurone layer with pericarp-testa (AL). More than 80%of the total P in the AL of 1-day germinated seeds was foundin acid-soluble organic P, most of which was IP₆. During germination,the IP₆ in AL decreased markedly with no accumulation of lessphosphorylated myo-inositols and Pi and acid-insoluble organicP increased in the EM. The total P in the EN of 1-day germinatedseeds was about one-third that in the AL, the greater part ofwhich was found in the acid-insoluble fraction and decreasedgradually during germination. Only a small amount of IP₆ couldbe detected in the EM and EN during the early stage of germination. IP₆ in AL of embryoless half-seeds incubated without gibberellicacid (GA₃) decreased slightly even after 6 days. Incubationwith 10 ppm GA₃ remarkably stimulated the IP₆ degradation. Thisstimulation was reduced, with no change in the Pi content, byabout 80–90% with 1 mM 6-methylpurine or 10 ppm cycloheximide.The addition of 0.1 M KH₂PO₄ caused a 4-fold increase in thePi content of AL in the presence of GA₃. In addition, it suppressedthe GA₃-dependent -amylase synthesis by about 20% and the GA₃effect on IP₆ degradation by about 50%. In light of these results, IP₆ seems to be hydrolyzed completelyinto Pi and myo-inositol within the aleurone tissue, and gibberellinseems to control this process. (Received August 24, 1979; )     

The action of cyclic-AMP on GA3 controlled responses II. Similarities in the induction of barley endosperm ATPase activity by gibberellic acid and cyclic 3',5'-adenosine monophosphate

The effect of cyclic-AMP and GA3 on ATPase production in embryolessbarley half-seeds was examined. Similarities in the responseinduced by 5 mM cyclic-AMP and GA₃ were observed in (1) thetotal amount of ATPase produced, (2) the time course for therelease of ATPase, and (3) the effect of abscisic acid on ATPaseinduction by these compounds. Of a variety of adenine nucleotidesexamined only cyclic-AMP was found to promote high levels ofATPase activity. Some of the implications of these results arediscussed. (Received May 11, 1971; )     

INTERACTION OF GIBBERELLIN A3, AND INORGANIC PHOSPHATE IN TOBACCO SEED GERMINATION

1. Investigation was made on the influence of inorganic phosphateupon the germination of positively photoblastic tobacco seed(Nicotiana tabacum L. var. uirginica (AGDH.) COM. "Bright Yellow")induced by GA₃, GA₃M, kinetin, red light, and ammonium saltsof various organic acids.
2. Inorganic phosphate increases theGAs-induced germination, andinhibits the germination causedby ammonium citrate, while itdoes not influence the germinationbrought about by GA₃M, kinetin,and red light.
3. The optimumpH for the GA₃-induced germination lies in the acidicpH range,indicating that the undissociated form of GA₃ is operative.The stimulatory effect of phosphate is, however, not ascribedmerely to the pH control in the mediurr. Phosphate exerts somespecific influence for which the presence of the free carboxylgroup of GAs is required.
4. The observed contrasting effectsof phosphate on the GA₃-inducedgermination (i.e., acceleration),on the one hand, and on theammonium citrate-induced germination(i.e., inhibition), onthe other, were explained by assumingthat the phosphate effectsultimately consist in acceleratingthe uptake of the carboxylicacid into the seeds.
5. GA₃M alsohas an activity of inducing the germination of tobaccoseedwithout light.

¹Present address: Department of Vegetable Crops, Universityof California, Davis, California, U.S.A. (Received March 12, 1962; )     

Light and temperature control of germination in Agropyron smithii seeds

In darkness, A. smithii seeds germinated poorly at constanttemperatures but well at alternating temperatures. Prolongedperiods on the high part of the temperature cycles reduced germination;the higher the temperature the shorter was the period requiredon the high part of the temperature cycles for optimum germination.Continuous, unfiltered, incandescent illumination and intermittentfar red at 15?–25?C alternation also inhibited germination;the inhibitory effects were similar to those caused by the highintensity reaction. Far red inhibited germination when appliedafter 1 and 2 complete 15?–25?C cycles in darkness butnot after 3 cycles. Less than 20% of the seeds were under phytochromecontrol at constant 20?C. When red light was applied directlyafter far red that was applied in intermittent cycles at 15?–25?C,however, 50% of the seeds caused to germinate by the alternatingtemperature were shown to be controlled by the reversible phytochromereaction. The induced high-temperature dormancy was overcome by gibberellicacid (GA₃) plus kinetin. The hormonal treatment was much moreeffective than light for breaking dormancy. Inhibition fromprolonged illumination was alleviated or eliminated by GA₃+kinetin.The failure of red light to promote good germination at 20?Cwas also overcome with GA₃+kinetin; effects of light plus thehormone treatments were more than additive. These data suggestthat optimum alternating temperatures facilitate a proper balanceand interaction of hormones, enzymes, substrates and possiblypreexistent P_fr so that the germination of A. smithii seedscan proceed without benefit of a light treatment. (Received July 7, 1976; )     

Effects of Gibberellins on Seed Germination of Phytochrome-Deficient Mutants of Arabidopsis thaliana

Experiments were carried out to explore the involvement of gibberellins(GAs) in the light-induced germination of Arabidopsis thaliana(L.) Heynh, using wild type (WT) and phytochrome-deficient mutants(phyA, phyB and phyAphyB deficient in phytochrome A, B and Aplus B, respectively). Seed germination of WT and phytochrome-deficientmutants was inhibited by uniconazole (an inhibitor of an earlystep in biosynthesis of GA, the oxidation of ent-kaurene) andprohexadione (an inhibitor of late steps, namely, 2rß-and 3rß-hydroxylation). This inhibition was overcomeby simultaneous application of 10^-5 M GA₄. The relative activityof GAs for promoting germination of uniconazole-treated seedswas GA₄>GA₁=GA₉>GA₂₀. The wild type and the phyA and phyBmutants had an increased response to a red light pulse in thepresence of GA₁, GA₄, GA₉, GA₂₀ and GA₂₄ but there were no significantdifferences in activity of each GA between the mutants. Therefore,neither phytochrome A nor hytochrome B appears to regulate GAbiosynthesis from GA₁₂ to GA₄ during seed germination, sincethe conversion of GA₁₂ to GA₉ is regulated by one enzyme (GA20-oxidase). However, GA responsiveness appears to be regulatedby phytochromes other than phytochromes A and B, since the phyAphyBdouble mutant retains the photoreversible increased responseto GAs after a red light pulse. (Received February 13, 1995; Accepted July 11, 1995)     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

獐牙菜种子萌发的研究

对温度、光照、植物激素（GA₃、NAA）条件对獐牙菜（Swertia bimaculata）种子萌发的影响进行了研究。结果表明,獐牙菜种子萌发的适宜温度为15～20℃,低温贮藏可促进其萌发,而有无光照对獐牙菜种子萌发没有明显影响,GA₃处理可提高其萌发势和萌发率,而NAA处理仅提高其萌发势。研究认为：獐牙菜种子具有休眠现象;激素及低温贮藏对打破种子的休眠具有重要作用。     

Effects of Gibberellins and Prohexadione on the Activities of Oryzain and {alpha}-Amylase in Rice Seeds

Oryzains, cysteine proteinases of rice seeds, are induced byGA₃ in germinating rice seeds [Abe et al. (1987) Agric. Biol.Chem. 51: 1509]. The effects of GA₁, GA₃, GA₄, GA₉, and GA₂₀on the production of oryzain and -amylase were investigatedin embryoless half- and whole-seeds of rice (cv. Nipponbare).When gibberellins (GAs) were incubated with embryoless half-seeds,GA₁, GA₃ and GA₄ induced oryzain and -amylase, but GA₉, andGA₂₀ did not. GA₉ and GAM induced oryzain and -amylase productionin whole seeds, but this production was inhibited by the simultaneousapplication of prohexadione, an inhibitor of 2ß- and3ß-hydroxylation of GAs. Prohexadione did not inhibitthe activities of oryzain and -amylase induced by GA₁. Theseresults suggest that GAs possessing the 3ß-hydroxylgroup induce activities of oryzain and -amylase in rice seedsand that GA₉ and GA₂₀ have activity only after they are convertedmetabolically to active GAs, probably GA₄ and GA₁, respectively.GA₁, was more active than GA₄ in both half seeds and wholeseeds incubation. Oryzain and -amylase activities induced byGA₄ were significantly inhibited in the presence of 10^–4M prohexadione. This suggests that the conversion of GA₁, toGA₄ (13-hydroxylation) might be inhibited at a high dose ofprohexadione in whole seeds. ⁴Present address: Institute of Food Development, Kyung Hee University,Suwon 449-701, Korea