ATP Synthesis in Cell-Free Extracts of Peanut (Arachis hypogaea L.) Seeds

Cell-free extracts of peanut (Arachis hypogaea L., cv. Shulamit)seeds, incubated with various substrates, synthesized ATP. Significantsynthesis occurred in the presence of AMP + PEP, NADH₂ + PEPand NAD + PEP. When the activities were examined in extractsprepared with 0.3 M mannitol, the rates were 0.6, 0.1 and 0.04nmol min^–1 mg^–1 protein, respectively. The activitiesunder such conditions were linear with time up to 90 min incubationat 30 °C. In the presence of PEP + NADH₂ there was a higherspecific activity in extracts from non-dormant seeds than fromdormant seeds. No such difference was found when PEP + AMP orNAD + PEP was used as the substrate. The temperature dependenceof the activity showed a relatively high energy of activation(Ea) for AMP + PEP and a low one if NADH₂ + PEP or NAD + PEPwas used as substrate. In buffer extracts of seeds ATP was synthesizedin the presence of the above-mentioned substrate combinationsbut the rate of activity exhibited a lag phase at the earlytime of incubation, after which higher rates of activities (ascompared with mannitol extracts) were obtained. The activitieswere Co⁺-dependent, with a K_m of about 0.7 mM. In the bufferextracts relatively high activities of adenylate kinase (EC2.7.4.3 [EC] (AK) and pyruvate kinase (EC 2.7.1.50 [EC] ) (PK) were found.AK was stimulated by ethephon (ethylene). This effect is temperature-dependentand occurs in both directions: in the presence of ADP (ATP +AMP) as well as if ATP + AMP is used as substrate to synthesizeADP. PK is Co⁺-dependent, and unaffected by ethephon. Both activitieswere stimulated by malonate. Key words: Adenylate Kinase, Arachis hypogaea, ATP synthesis, Peanut, Pyruvate kinase, Seed     

Changes in Some ATP-Dependent Activities in Seeds during Treatment with Polyethyleneglycol and during the Redrying Process

During the imbibition of seeds in polyethyleneglycol (PEG),increasing amounts of ATP accumulated up to 24 h. Similar amountsaccumulated in the seeds during 4–5 h of imbibition inwater. Radioactive amino acids were increasingly incorporatedin the acid-insoluble fraction up to 24 h imbibition in PEG,as well as in water, after which a sharp decrease occurred upto 5 d of imbibition. If seeds were imbibed in PEG or waterin the presence of radioactive acetate, water-insoluble radioactivityincreased linearly in seeds during 5 d of imbibition. The amountsof incorporated amino acids or acetate were about double inPEG-imbibed as compared with in water-imbibed seed. The incorporationof AMP into the acid-insoluble fraction in seeds imbibed inPEG in the presence of radioactive AMP levelled off after 24h followed by a sharp decrease of up to 10% of the peak 5 dafter the start of imbibition. In water-imbibed seeds the incorporationof AMP continued to increase during at least 5 d of imbibition.During redrying of PEG-treated seeds (24 h), at least 80% ofthe accumulated ATP decreased during 18 d. The total radioactiveamino acids and nucleotide decreased during 3 d of redryingby 20% and 60%, respectively. At that time, the acid-insolubleincorporates increased by 20% and 50%, respectively. Some ofthe AMP was released as CO₂. Key words: AMP, Germination, Nucleic acid synthesis, Osmoconditioning, PEG, Protein synthesis     

The Effect of Ethylene and Temperature on ATP Accumulation from Various Substrates in Peanut (Arachis hypogaea L. ) Seeds

Peanut (Arachis hypogaea L. ) seed powder accumulated ATP fromAMP and phosphoenolpyruvate (PEP) at a rate of approx. 100 pmolmin^–1mg^– powder at 35° C. When peanut seed powderwas incubated with various substrates, which may result in PEPor AMP (ADP) synthesis, then ATP accumulated. The best substratecombinations examined so far were AMP + succinate, NADH₂, andAMP + malate + NAD, with activities of 33, 12 and 12 pmol min^–mg^–1powder,respectively; AMP + malate showed very low activity. Some combinationsexhibited linear activities with time, while others had an exponential-typeprofile. The temperature dependence of the ATP accumulationdemonstrated by the Ahrrenius plot had a double phase with atransition point at 25° C. The Ea values between 15°C and 25° C were 25 000–50 000 cal/mol, while above25° C the Ea values fluctuated between 6000 and 8000 cal/mol(depending on the substrate). The AMP + PEP combination exhibiteda single-phase profile between 15° C and 40° C, withan Ea value of 22 000 cal/mol. In the presence of some substrates,ethephon (ethylene) had a stimulatory effect and caused an increasein the Ea values at the high temperature phase. A comparisonof seed powder from dormant seeds with that from non-dormantseeds revealed that some substrate combinations accumulate ATPfaster in non-dormant seeds and others do so in dormant seeds. Key words: Arachis hypogaea, ATP, Ethylene, Dormancy, Peanut, Seed     

The Lack of Correlation between ATP Accumulation in Seeds at the Early Stage of Germination and Seed Quality

Seeds of various species were treated with polyethyleneglycolin the absence or presence of AMP and phosphoenolpyruvate, redriedand examined for ATP accumulation at the early stage of germinationand for the rate of germination under suboptimal temperatures.The pretreatments resulted in seeds with various levels of accumulatedATP but in most comparative experiments no correlation was foundbetween the ATP accumulation and the rate of germination. Similarpretreatments with naturally aged seeds led to the same conclusion.The fact that ATP accumulation is a result of ATP synthesisas well as ATP utilization was demonstrated by a protein inhibitionexperiment which showed a possibility to produce seeds withrelatively high ATP accumulation levels at the early stage ofgermination, but with very low germination ability. Key words: AMP, PEP, Polyethyleneglycol, Pretreatment     

Invigoration of Cotton Seedlings by Treatment of Seeds for Pregermination Activities

Incubation of cotton seeds (Gossypium hirsutum, cv. Acala S.J.2) at 20 °C and 95% r.h. for up to 12 d results in an increasein seed water content and in a higher rate of seedling development.When seed vigour is measured by tolerance to high temperaturestorage (aging conditions) or tolerance to low temperature andsalinity during germination, seeds incubated for up to 4 d aremore vigorous than the control seeds. Hence, such a presowingtreatment of seed could be used for seed invigoration. As theincubation proceeds, although a higher growth rate of seedlingsis obtained at optimal conditions, the tolerance to stress conditionsdeclines proportional to the duration of incubation. Results of chemical and biochemical examinations of the incubatedseeds are compared with those of seeds during normal imbibitionfor germination. The early stage of germination (up to 4 h)is accompanied by a decrease in reducing sugars and amino acids.At the later stage, an increase of these components and a decreasein the lipid fraction occur. During the first 4 h, an increaseand decrease of phosphoenolpyruvate carboxylase and of malicdehydrogenase occur. According to the chemical and biochemicalmarkers, it is evident that seed treatment at 20 °C and95% r.h. results in pregermination biochemical activities. Thefirst 4 d seem to be equivalent to the first 3 h of germinationunder normal conditons. At this period of time, degradationprocesses are taking place. If incubation is continued the resynthesisstage appears to be retarded by the low moisture available andtherefore degradation processes continue, resulting in lossof seed vigour. The resynthesis ability may therefore be a prerequisitefor the following steps in seed germination.     

The Effect of Accelerated Aging of Sorghum Seeds on Seedling Vigour

Six different levels of vigour of sorghum seeds from an identicallot were obtained through accelerated aging for various periodsof time. Vigour was estimated according to yielding abilityof the seed in the field. After 6 d of aging, seed invigoration,to the extent of a 20% increase in yield, was observed. However,this was followed by a gradual decrease in yield following agingof up to 48 d. All seed lots showed 88–92% germinationor emergence capacity when tested in the laboratory, which correlatespoorly with vigour. However, vigour correlated well with therates of germination and root emergence when tested in the laboratory,as well as with emergence rate in the field.     

ATP Accumulation in Peanut Seeds during Seed-Ripening and During the Dormancy-Breaking Process

Ripening and dormancy-breakage of peanut (Arachis hypogaea L.)seeds are accompanied by an increase, followed by a decrease,in the ability to accumulate ATP (from AMP + phospho-enolpyruvate(PEP)) in the embryonic axes as well as in the cotyledonarysegment powder. A similar increase and decrease profile in theconcentrations of the ATP precursors (AMP + ADP) in the embryonicaxes and in the cotyledonary segments is noted during dormancybreakage. The ability of the seeds to germinate during the ripeningprocess (after dormancy-breakage treatment) seems to correlatewith the decrease in the ability to accumulate ATP in the embryo,while dormancy breakage seems to be correlated with the samephenomenon in the cotyledon. Imbibition of seeds (as whole seeds or as embryonic axes andcotyledonary segments separately) causes a 10–40-foldincrease in the ability to accumulate ATP from AMP and PEP,and a decrease in the concentrations of the precursors of ATP.Ethylene has a stimulatory effect on ATP accumulation in embryonicaxes during imbibition. Key words: Arachis hypogaea, ATP, Dormancy, Peanut, Seed Ripening     

Biochemical Changes in Sorghum Seeds Affected by Accelerated Aging

Examination of the initial rates of enzyme activities in variousseed lots demonstrated that amylase, glutamic-pyruvic-transaminase,RNase, and glutamate decarboxylase follow the vigour profile,namely, an increase after 6 d of aging treatment followed bya decrease up to 48 d of aging time. Acid phosphatase, tetrazoliumreduction, and [¹⁴C]leucine incorporation decline directly withthe time of aging and no increase in those activities at 6 daging could be observed. Proteinase is the only enzyme foundso far that increases during accelerated aging. It is postulatedthat this enzyme may be the cause of the drop in all other enzymeactivities and therefore may play an important role in the lossof seed vigour. Examination of the components released from seeds into water,and of the rates of their leakage, led to the conclusion thatthe efflux reflects severely damaged seeds rather than vigourlessones.