Elimination oftheLagPeriodinChloroplast Development ina Chlorophyll MutantofPeanuts
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Abstract:
Themutation ofanuclear geneinpeanut(Arachis hypogaea L.)plants results inareducedlight-dependent development of chloroplast finestructure, soluble protein, ribulose-1, 5-diP carboxylase, NADP-glyceraldehyde-3-P dehydrogenase, fructose1,6-diP aldolase, glycerate-3-P kinase, phosphoenolpyruvate carboxylase, malatedehydrogenase, anddarkrespiration during the72-hour lagperiod ofchlorophyll synthesis indark-grown leaves exposed tocontinuous light. Themutation haspleiotropic affects. Kinetic analysis showsthereisalso a72-hour lagperiod inthelight-dependent development ofNADP-glyceraldehyde3-Pdehydrogenase andfructose-1,6-diP aldolase inthemutant leaves, whereas there isnolaginthedevelopment ofNAD-malatedehydrogenase anddarkrespiration. Thereisminimaldevelopmentofthechloroplast during the72-hourmutationally inducedlagperiod, butthereispronounced cytoplasmic and mitochondrial activity during thisphase. Thereisa 24-hour lag period inthelight-dependent enlargement ofthemutantleaves. Atthecompletion ofleafenlargement, chloroplast differentiationisinitiated. Themutation doesnotresult inanychloroplast deletions, itonlyaffects thetiming ofthesynthesis ofthese components. Elimination ofthelagperiod inleafenlargement andchloroplast development (potentiation) requires apreliminary 72-to 96-hour darkperiod beforeexposing thedark-grown leaves to continuous light. Thereisextensive development oftheetioplasts during thisdarkperiod. Theseresults establish thatthe nuclear genemutation affects theearly stages ofplastid developmentandnotthelight-dependent synthesis ofplastid components. Thenuclear genemaycodefortheregulation ofthesynthesis ofacomponent (nutrient) inthedark(orduring thelag phaseinthelight) whichisessential forthedevelopment of mesophyll cells andplastids. Although, thechloroplast isasemiautonomousorganelie, nuclear genecontrol ofchloroplast differentiation maynotbeindependent ofcellular growth.Keywords:
Phosphoenolpyruvate carboxylase
Glyceraldehyde
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Light stimulated theactivation ofribulosebisphosphate carboxylase/oxygenase (rubisco) inabuffered lysed chloroplast system inthepresence ofsaturating concentrations ofATP.Thisindicatesarole forlight intherubisco activase activation systemin addition tothepreviously identified requirement forthesynthesis ofATP.Rubisco activation wasnearly asgreat atlowirradiance (10micromoles ofphotons persquare meterpersecond) asat highirradiance (1000micromoles ofphotons persquaremeter persecond). Light stimulation ofactivation occurred atbothlow bicarbonate (equivalent toairlevels ofC02) andhighbicarbonate (10mM)concentrations. Light activation wasinhibited byDCMU andglyoxylate. Methyl viologen didnotinhibit light activation, anddithiothreitol didnotstimulate activation inthedark, indicatingthattheferredoxin/thioredoxin systemwasnotinvolved. Following atransition ofthelysed chloroplasts fromlight todark, thelight-dependent increase inactivation ceasedimmediately. Theexperiments wereconducted withchloroplasts fromspinach (Spinacea oleracea L.), aspecies whichwaspreviously shown nottocontain theendogenous inhibitor ofrubisco, 2-carboxyarabinitol 1-phosphate. Assays oftotal rubisco activity inthelight anddarkconfirmed theabsence ofsuchatight binding inhibitor ofactivity. Theobservations reported herecannot beexplained bycurrent hypotheses oftheroleoflight inrubisco activation anddemonstrate thatinaddition toproviding ATPneededfor rubisco activase activity, atleast oneother light-dependent reaction isrequired forregulating theactivation state ofrubisco In vivo.
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Changes inglucose-6-P, fructose-6-P, fructose-1,6-diP, 6-phosphogluconate, phosphoenolpyruvate, 3-phosphoglycerate, andpyruvate levelsintheleaves oftheCrassulacean plant Kalanchoe daigremontiana HammetetPerrier weremeasured enzymicafly during transitions from CO2-free airtoair, air toCO2-free air, andthrougbout thecourse ofacid accumulation indarkness. Thedata arediscussed intermsoftheinvolvementofphosphoenolpyruvate carboxylase inmalic addsynthesis andin termsoftheregulation ofthecommencement ofmalic acid synthesis and accumulation through theeffects ofCO2onstorage carbobydrate mobilization andits termination through theeffects ofmalic acid onpbospboenolpyruvate carboxylase activity.
Kalanchoe
Phosphoenolpyruvate carboxylase
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Theammonium-inducible NADP-specific glutamate dehydrogenase of Chlorella sorokiniana wasshown torequire light forbothits induction by ammonia inuninduced cels, anditscontinuous accumulation infully induced cells. Addition ofammonia touninduced cells inthelight resulted ina35-minute induction lagfollowed bylinear andcoincident increases in enzyme activity andantigen. Enzyme activity wasnotinduced inthedark; however, transfer ofthese cells tothelight resulted inanimmediate increase inenzyme activity andantigen. Theabsence ofaninduction lag suggested that mRNAsequences and/or anenzyme precursor with differentantigenic properties thantheactive holoenzyme accumulated incells inthedarkinammonium medium. Whenfully induced cells weretransferred tothedark, theactivity oftheenzyme quickly ceased toaccumulate. Incontrast totheNADP-speclfic isozyme, thecells also contain aconstitutive NAD-specific isozyme which wasshown toaccumulate incells inthe darkineither ammonium ornitrate medium. synchronous cells growing inthecontinuous presence ofinducer foranentire cell cycle (10, 11). Thislatter experimental approach revealed theoperation ofaregulatory system whichalters the timing between genereplication andtheexpression ofnewly. replicated genes incells growing atdifferent rates inammonium medium. Underthese different cell cycle conditions, theactivity oftheNAD-GDHincreased inatypical steppattern during the last 0.5hofthecell cycle. Instudies onthecell cycle inducibility oftheNADP-GDH,it wasobserved that theinitial rate ofenzymeinduction (i.e., enzyme potential) wasproportional totherateofaccumulation oftotal cellular protein (21, 22). Since theaccumulation rateofcellular protein hasbeenobserved tobeproportional totheeffective light intensity percell (17, 19), itseemed possible that theinduction or accumulation oftheNADP-GDHmight belight-dependent. The experimental evidence described inthepresent paperisconsistent withalight requirement forboththeinduction andcontinuous accumulation oftheNADP-GDHinChlorella cells inammonium medium.
Chlorella sorokiniana
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