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J E Mullet

Publications and source records attributed to J E Mullet.

At least 73 records · Page 4Linked to original sources
PubMed1990

Detection of endogenous gibberellins and their relationship to hypocotyl elongation in soybean seedlings.

Four gibberellins, GA(53), GA(19), GA(20), and GA(1), were detected by bioassay, chromatography in two HPLC systems, and combined gas chromatography-mass spectroscopy-selected ion monitoring (GC-MS-SIM) in etiolated soybean (Glycine max [L.] Merr.) hypocotyls. GC-MS-SIM employed [(2)H(2)]-labeled standards for each endogenous gibberellin detected, and quantities estimated from bioassays and GC-MS-SIM were similar. This result plus the tentative detection of GA(44) and GA(8) (standards not available) indicates that the early-C-13-hydroxylation pathway for gibberellin biosynthesis predominates in soybean hypocotyls. Other gibberellins were not detected. Growth rates decreased after transfer to low water potential (psi(w)) vermiculite and were completely arrested 24 hours after transfer. The GA(1) content in the elongating region of hypocotyls had declined to 38% of the 0 time value at 24 hours after transfer to low psi(w) vermiculite, a level which was only 13% of the GA(1) content in control seedlings at the same time (24 hours posttransfer). Rewatering seedlings following 24 hours growth in low psi(w) vermiculite resulted in a complete recovery in elongation rate, an increase in GA(1) (20% at 2 hours, two-fold at 8 hours, eightfold at 24 hours), and a decrease in ABA levels (tenfold at 2 hours). Treatment of well-watered seedlings with the GA-synthesis inhibitor tetcyclacis (TCY) resulted in lowered GA(1) levels and increased ABA levels. When seedlings grown 24 hours in low psi(w) vermiculite were rewatered with TCY, recovery of the elongation rate was delayed and reduced, and the decline in ABA levels was slowed. Addition of GA(3) restored the elongation rate inhibited by TCY. Seedlings were growth responsive to exogenous GA(3), and this GA(3)-promoted growth was inhibited by exogenous ABA. The data are consistent with the hypothesis that changes in GA(1) and ABA levels play a role in adjusting hypocotyl elongation rates. However, the changes observed are not of sufficient magnitude nor do they occur rapidly enough to suggest they are the primary regulators of elongation rate responses to rapidly changing plant water status.

Journal Article↗
PubMed1990

Expression of two soybean vegetative storage protein genes during development and in response to water deficit, wounding, and jasmonic acid.

The expression of vspA and vspB genes encoding soybean vegetative storage proteins was studied during seedling development and in response to water deficit, tissue wounding, and jasmonic acid treatment. vspA and vspB encode VSP-alpha and VSP-beta, 28-kilodalton and 31-kilodalton vacuole-localized polypeptides that are 80% homologous. vspA and vspB mRNAs could be distinguished on RNA blots using 3'-end probes. vspA mRNA was threefold to sevenfold more abundant than vspB mRNA in leaves, about equal expression was observed in stems, and vspB mRNA exceeded vspA in roots. Transcripts were not detected in dry seeds but appeared in intact or excised seedling axes between 12 hr and 24 hr after initiation of imbibition. Both transcripts were highly abundant in the meristematic region of seedling stems and in developing leaves but were rare in mature stems, leaves, and roots. In situ localization showed that vsp transcripts were found throughout the hypocotyl hook but were concentrated in cells associated with the epidermis and vascular bundles. Water deficit caused increased vsp mRNA levels in leaves and stems, which suggests that inhibition of growth necessitates temporary storage of amino acids. Wounding induced primarily vspB mRNA in etiolated seedlings, whereas both vspA and vspB mRNA levels increased in wounded leaves. Jasmonic acid and methyl jasmonate were potent inducers of vsp gene expression in cell cultures, developing axes, leaves, and roots. We hypothesize that jasmonic acid levels modulate vsp mRNA abundance in vivo.

Cyclopentanes↗
PubMed1989

Translation and stability of proteins encoded by the plastid psbA and psbB genes are regulated by a nuclear gene during light-induced chloroplast development in barley.

We have characterized a nuclear mutant of barley, viridis-115, lacking photosystem II (PSII) activity and compared it to wild-type seedlings during light-induced chloroplast development. Chloroplasts isolated from wild-type and viridis-115 seedlings illuminated for 1 h synthesized similar polypeptides and had similar protein composition. After 16 h of illumination, however, mutant plastids exhibited reduced ability to radiolabel D1, CP47, and several low Mr membrane polypeptides, and by 72 h, synthesis of these proteins was undetectable. Immunoblot analysis showed that plastids of dark-grown wild-type barley lacked several PSII proteins (D1, D2, CP47, and CP43) and that 16 h of illumination resulted in the accumulation of these polypeptides. In contrast, these polypeptides did not accumulate in illuminated viridis-115 seedlings, although mutant plastids accumulated two PSII proteins that participate in oxygen evolution, oxygen-evolving enhancers 1 and 3. Northern analysis showed that the levels of psbA and psbB mRNA in mutant plastids were equal to or greater than levels in wild-type plastids throughout the developmental period examined here. These results indicate that the nuclear mutation present in viridis-115 affects the translation and stability of the chloroplast-encoded D1 and CP47 polypeptides and that its influence is expressed after the onset of light-induced chloroplast development.

Blotting, Northern↗
PubMed1989

Blue light regulates the accumulation of two psbD-psbC transcripts in barley chloroplasts.

Synthesis of D2, a Photosystem II reaction center protein encoded by psbD, is differentially maintained during light-induced chloroplast maturation. The continued synthesis of D2 is paralleled by selective light-induced accumulation of two psbD-psbC transcripts which share a common 5' terminus. In the present study, we examine the nature of the photoreceptor and the fluence requirement for psbD-psbC transcript induction. The light-induced change in psbD-psbC RNA population can be detected between 1 and 2 h after 4.5 day old dark-grown barley seedlings are transferred to the light. Light-induced transcript accumulation occurs normally in the chlorophyll-deficient barley mutant, xan-f10, indicating that light-activated chlorophyll formation and photosynthesis are not required for RNA induction. High fluence blue light fully induces psbD-psbC transcript accumulation; low or high fluence red or far-red light do not. However, psbD-psbC transcript accumulation elicited by blue light pulses can be partially attenuated if far-red light is given immediately following the blue light treatment. Thus, although blue light is needed to initiate transcript accumulation, phytochrome modulates the amplitude of the response. Pretreatment of dark-grown plants with cycloheximide blocks light-induced psbD-psbC transcript accumulation. This could implicate a blue-light responsive nuclear gene in the light-induced accumulation of the two psbD-psbC transcripts.

4-Aminobutyrate Transaminase↗
PubMed1989

Plastid transcription activity and DNA copy number increase early in barley chloroplast development.

Plastid transcription activity and DNA copy number were quantified during chloroplast development in the first foliage leaf in dark-grown and illuminated barley (Hordeum vulgare L.) seedlings. Primary foliage leaves of seedlings given continuous illumination from 2 days post-imbibition reached a final mean length of 15 centimeters at 6.5 days, whereas primary leaves of dark-grown seedlings required 7 days to reach a similar length. Dividing cells were observed in the basal 0.5 to 1 centimeter of primary leaves until 5.5 days post-imbibition. Plastids isolated from cells located in the basal meristem of 4-day-old seedlings were small ( approximately 2 micrometers in diameter), exhibited low transcription activity and contained approximately 130 copies of plastid DNA per organelle. Cell size increased from 18 to 60 micrometers in a 1 to 3 centimeter region located adjacent to the leaf basal meristem. In this region, transcriptional activity per plastid increased 10-fold and DNA copy number increased from 130 to 210. Plastid transcriptional activity declined rapidly in illuminated plants with increasing leaf cell age and plastid DNA copy number also declined but with a slower time course. In dark-grown seedlings, plastid transcriptional activity declined more slowly than in illuminated plants while DNA copy number remained constant with increasing cell age. These data show that plastid transcriptional activity and DNA copy number increase early in chloroplast development and that transcriptional activity per DNA template varies up to 5-fold during barley leaf biogenesis.

Journal Article↗
PubMed1988

Light-dependent changes in psbD and psbC transcripts of barley chloroplasts: accumulation of two transcripts maintains psbD and psbC translation capability in mature chloroplasts.

The psbD and psbC genes encode two polypeptides of Photosystem II. These genes are adjacent in the barley chloroplast genome and are part of a 5.7 kbp transcription unit. In dark-grown barley, four large transcripts hybridize to psbD and psbC; two additional transcripts hybridize to psbC. Illumination of 4.5-day-old dark-grown seedlings causes a decrease in the six psbD--psbC transcripts found in etioplasts and the accumulation of two different transcripts of 4.0 and 3.2 kb which hybridize to psbD and psbC. The light-induced transcripts have a common 5' end approximately 600 nt upstream of psbD and 3' ends 1175 and 175 nt downstream of psbC. The shift in psbD--psbC transcript population occurs during a phase of chloroplast maturation when transcript levels and translation of chloroplast genes such as psaA--psaB and psbB decline approximately 3- to 5-fold. In contrast, translation of the psbD and psbC gene products declines to a lesser extent, suggesting that the light-induced accumulation of the 4.0 and 3.2 kb psbD--psbC transcripts is required to maintain psbD and psbC gene product translation in mature chloroplasts.

Chlorophyll↗
PubMed1988

Light-regulated translation of chloroplast proteins. I. Transcripts of psaA-psaB, psbA, and rbcL are associated with polysomes in dark-grown and illuminated barley seedlings.

We have previously observed (Klein, R. R., and J. E. Mullet, 1986, J. Biol. Chem. 261:11138-11145) that translation of two 65-70-kD chlorophyll a-apoproteins of Photosystem I (gene products of psaA and psaB) and a 32-kD quinone-binding protein of Photosystem II (gene product of psbA) was not detected in plastids of dark-grown barley seedlings even though transcripts for these proteins were present. In the present study it was found that nearly all of the psaA-psaB transcripts in plastids of dark-grown plants were associated with membrane-bound polysomes. Membrane-associated polysomes from plastids of dark-grown plants synthesized the 65-70-kD chlorophyll a-apoproteins at low levels when added to a homologous in vitro translation extract capable of translation elongation. However, when etioplast membranes were disrupted with detergent, in vitro synthesis of the 65-70-kD chlorophyll a-apoproteins increased to levels observed with polysomes of plastids from illuminated plants. These results suggest that synthesis of the chlorophyll a-apoproteins of Photosystem I is arrested on membrane-bound polysomes at the level of polypeptide chain elongation. In addition to the selective activation of chlorophyll a-apoprotein translation, illumination also caused an increase in chloroplast polysomes (membrane-associated and stromal) and induced a recruitment of psbA and rbcL transcripts into chloroplast polysomes. These results indicate that in conjunction with the selective activation of chlorophyll a-apoprotein elongation, illumination also caused a general stimulation of chloroplast translation initiation.

Cell Fractionation↗
PubMed1988

Polysomes, Messenger RNA, and Growth in Soybean Stems during Development and Water Deficit.

The polysome status and populations of polysomal mRNA were examined in different regions of dark-grown soybean (Glycine max [L.] Merr.) stems that contained either dividing, elongating, or mature (nongrowing) cells. There was a developmental gradient of polysome content in which the dividing tissue had the highest levels and the mature tissue the lowest. A few hours after transplanting the seedlings to vermiculite having low water content (water potential Psi(w) = -0.29 megapascals), stem growth rate decreased to 30% of well-watered controls and the polysome content decreased most in the dividing and elongating tissues. After 24 to 36 hours, stem growth and polysome content recovered gradually. In vitro translation products of polysomal mRNA from dividing, elongating or mature tissue were examined on two-dimensional gels. In well-watered controls, each of the stem regions was enriched in a small subset of the polysomal mRNA population, probably because of developmentally regulated gene expression. Exposing plants to low Psi(w) for 24 hours induced a change in the relative abundance of a small number of polysomal mRNAs in the elongating and mature tissues, but not in the dividing tissue. After 24 to 72 hours at low Psi(w), the changes in polysomal mRNA population were reversed in the elongating tissue. The data indicate that changes in stem growth at low water potential are associated with changes in polysome status and polysomal mRNA in the elongating tissue.

Journal Article↗
PubMed1988

Water deficit-induced changes in abscisic Acid, growth, polysomes, and translatable RNA in soybean hypocotyls.

Soybean seedlings (Glycine max L.) were germinated and dark-grown in water-saturated vermiculite (water potential = -0.01 megapascal) for 48 hours, then transferred either to water-saturated vermiculite or to low water potential vermiculite (water potential = -0.30 megapascal). A decrease in growth rate was detectable within 0.8 hour post-transfer to low water potential vermiculite. A fourfold increase in the abscisic acid content of the elongating region was observed within 0.5 hour. At 24 hours post-transfer, hypocotyl elongation was severely arrested and abscisic acid reached its highest measured level: 3.7 nanograms per milligram dry weight (74-fold increase). A comparison of the polyA(+) RNA populations isolated at 24 hours post-transfer from the elongating region of water-saturated and low water potential vermiculite-grown seedlings was made by two-dimensional (isoelectric focusing-sodium dodecyl sulfate) polyacrylamide gel analysis of in vitro translation products. It revealed both increases and decreases in the relative amounts of a number of translation products. Rewatering seedlings grown in low water potential vermiculite at 24 hours post-transfer led to a total recovery in growth rate within 0.5 hour, while abscisic acid in the elongating hypocotyl region required 1 to 2 hours to return to uninduced levels. Application of 1.0 millimolar (+/-) abscisic acid to well-watered seedlings resulted in a 48% reduction in hypocotyl growth rate during the first 2 hours after treatment. Plants treated with abscisic acid for 24 hours had a lower polysome content than control plants. However, hypocotyl growth inhibition in abscisic acid-treated seedlings preceded the decline in polysome content.

Journal Article↗
PubMed1988

Reduction of turgor induces rapid changes in leaf translatable RNA.

The turgor of pea (Pisum sativum) leaves was reduced by exposing excised pea shoots to a stream of 23 degrees C air for 20 min. Poly(A)(+) RNA was isolated from control and wilted shoots, translated in vitro and radiolabeled translation products separated by electrophoresis on two-dimensional (isoelectric focusing-sodium dodecyl sulfate) polyacrylamide gels. This analysis showed that the levels of several poly(A)(+) RNAs increased in wilted plants. Most of the poly(A)(+) RNAs induced in wilted plants did not accumulate in response to heat shock or exogenously applied ABA even though endogenous ABA levels were found to increase in shoots 30 min after wilting and by 4 h had increased 50-fold (1 versus 0.02 microgram per gram fresh weight). A lambdagt10 cDNA library was constructed using poly(A)(+) RNA from wilted shoots which had been incubated for 4 hours. Differential screening of the library identified four clones corresponding to poly(A)(+) RNAs which are induced in wilted shoots.

Journal Article↗
PubMed1988

Light-Dependent Accumulation of Radiolabeled Plastid-Encoded Chlorophyll a-Apoproteins Requires Chlorophyll a: I. Analysis of Chlorophyll-Deficient Mutants and Phytochrome Involvement.

The accumulation of radiolabeled plastid-encoded chlorophyll a-apoproteins is light dependent and is controlled at a posttranscriptional level. Illumination of dark-grown barley (Hordeum vulgare L.) with a brief pulse of red light induced the accumulation of radiolabeled chlorophyll a-apoproteins in subsequent protein synthesis assays. The induction of radiolabeled chlorophyll a-apoprotein accumulation was not affected by pretreatment of leaves with cycloheximide. Fluence response studies showed that a red light photoreceptor controls the accumulation of radiolabeled chlorophyll a-apoproteins with a threshold fluence of approximately 50 to 100 microeinsteins per square meter. While red light initiated chlorophyll a-apoprotein accumulation, this process was not reversed by a far red light treatment given immediately after the pulse of red light. The light pulse which initiated the accumulation of radiolabeled chlorophyll a-apoproteins also induced the rapid conversion of protochlorophyllide to chlorophyll a. A chlorophyll-deficient mutant, xan-f(10), which is blocked in chlorophyll biosynthesis prior to protochlorophyllide formation, failed to accumulate radiolabeled chlorophyll a-apoproteins in the light even though transcripts for these apoproteins were present. A second mutant, xan-j(64), which accumulates chlorophyllide in the light but only low levels of chlorophyll a, also showed reduced accumulation of radiolabeled chlorophyll a-apoproteins upon illumination. These results suggest that the light-induced conversion of protochlorophyllide to chlorophyll a is necessary for accumulation of the plastid-encoded chlorophyll a-apoproteins and one red light photoreceptor controlling this response is the protochlorophyllide holochrome.

Journal Article↗
PubMed1987

Characterization of the barley chloroplast transcription units containing psaA-psaB and psbD-psbC.

Four plastid genes, psaA, psaB, psbD and psbC, were localized on the barley plastid genome. PsaA was adjacent to psaB in one transcription unit and psbD was adjacent to psbC in a second transcription unit. The transcription units containing psaA-psaB and psbD-psbC are separated by approximately 25 kbp on the barley plastid genome and are transcribed convergently. Transcripts hybridizing to each transcription unit were characterized by northern blot analysis, S1 protection experiments and primer extension analysis. Two 5.3 kb transcripts hybridize to psaA-psaB. The two transcripts have a common 5' end but differ at their 3' ends by about 26 nucleotides. The transcription unit which contains psbD-psbC also includes trnS(UGA), trnG(GCC), and an open reading frame which codes for a 62 amino acid protein. Six large transcripts ranging from 5.7 kb to 1.7 kb hybridize to the psbD-psbC transcription unit as well as several RNAs of tRNA size. The large transcripts arise from three 5' ends and two clusters of 3' ends. The 3' ends map near trnG(GCC) and trnS(UGA) and could be generated by RNA processing or termination of transcription. Two of the six transcripts hybridize to psbC but not psbD suggesting that translation of psbD and psbC could occur on separate RNAs.

Biological Evolution↗
PubMed1987

Control of gene expression during higher plant chloroplast biogenesis. Protein synthesis and transcript levels of psbA, psaA-psaB, and rbcL in dark-grown and illuminated barley seedlings.

Etioplasts of 4.5-day-old dark-grown barley synthesize and accumulate most of the membrane and nearly all the soluble polypeptides of mature chloroplasts of light-grown seedlings. Etioplasts do not synthesize a limited set of chloroplast-encoded polypeptides which are major constituents of chloroplast thylakoid membranes: two chlorophyll apoproteins of photosystem I (68 and 65 kDa), two chlorophyll apoproteins of photosystem II (47 and 43 kDa), and a 32-kDa polypeptide which has now been identified as the psbA gene product. Throughout development in the dark, etioplasts were unable to synthesize the chlorophyll apoproteins of photosystem I and II or the psbA gene product despite the presence of significant transcript levels for psbA and psaA-psaB (encode for photosystem I chlorophyll apoproteins). Light was not required for the synthesis of ribulose bisphosphate carboxylase large subunit with the highest rate of large subunit synthesis occurring in young dark-grown seedlings. Illumination of 4.5-day-old dark-grown barley rapidly induced the synthesis of the chlorophyll apoproteins and the psbA gene product at a time when transcript levels for psbA and psaA-psaB did not increase appreciably. Therefore, during the early stages of light-induced development the synthesis of the chlorophyll apoproteins of photosystem I and psbA gene product is regulated at the translational level. With continued chloroplast development in the light, the synthesis of the chlorophyll apoproteins of photosystem I and II decline rapidly as does the synthesis of the large subunit of ribulose bisphosphate carboxylase. The decline in polypeptide synthesis correlated with a decline in rbcL and psaA-psaB transcript levels and a light-dependent decline in plastid rRNA content. In contrast, synthesis of the psbA gene product was maintained throughout light-induced chloroplast development which correlated with the maintenance of psbA transcript levels. However, light is not strictly required for psbA transcript accumulation since psbA transcript levels increased slightly with continued plastid development in dark-grown seedlings.

Chloroplasts↗
PubMed1987

Transcription and RNA stability are important determinants of higher plant chloroplast RNA levels.

Transcription in lysed barley plastids and Northern slot blot analyses were used to determine the relationship between changes in RNA levels and transcription during plastid development. Transcription in plastids of 4.5-9-day-old dark-grown or illuminated barley seedlings declined up to 10-fold as a function of plant age. Decreased transcription of some plastid genes (rbcL, psaA-psaB) was paralleled by decreased levels of mRNA. In other cases (16SrDNA, psbA) the changes in transcription were not followed by proportional changes in RNA levels indicating that RNA stability is important in establishing the amount of plastid RNA for these genes. Further analysis showed that transcription of the plastid rRNA transcription unit is regulated differently than the transcription of protein coding genes such as psbA or rbcL.

Journal Article↗
PubMed1987

Cell wall proteins at low water potentials.

We investigated the proteins extractable from cell walls of stem tissues when plants were subjected to low water potentials (low psi(w)). Dark-grown soybean seedlings (Glycine max [L.] Merr.) showed decreased stem growth when the roots were exposed to vermiculite having low water content (psi(w) = -3 bar). After a time, growth resumed but at a reduced rate relative to the controls. The extractable protein increased in the cell walls as psi(w) decreased, especially a 28-kilodalton protein in the young tissue. In contrast, a 70 kilodalton protein, mainly extractable from mature cell walls, appeared to decrease slightly at low psi(w). No hydroxyproline was present in either protein, which shows that neither protein is related to extensin. The level of the 28 kilodalton protein increased in the cell wall of the dividing region soon after the initial growth inhibition, and it appeared in the elongating tissue at about the time growth resumed. The correlation between growth and these protein changes suggests that the two events could be related.

Journal Article↗
PubMed1986

Inhibition of carotenoid accumulation and abscisic acid biosynthesis in fluridone-treated dark-grown barley.

Treatment of dark-grown barley with 0.1 mM fluridone inhibited carotenoid accumulation but did not alter plastid biogenesis. Plastids isolated from dark-grown control and dark-grown fluridone-treated plants were similar in size and protein compositions. Dehydration of dark-grown control barley caused abscisic acid levels to increase 30-40-fold in 4 h, while plants treated with 0.1 mM fluridone accumulated very little abscisic acid in response to dehydration. These results suggest that fluridone-treated plants do not accumulate abscisic acid because of carotenoid deficiency rather than plastid dysfunction. Dark-grown barley plants treated with 0.31 microM fluridone accumulated low levels of carotenoids. Dehydration of these plants resulted in a 4-8-fold increase in abscisic acid and a decrease in antheraxanthin, violaxanthin and neoxanthin, but no change in beta-carotene or lutein plus zeaxanthin levels. This result is consistent with the suggestion that xanthophylls are precursors to abscisic acid in dehydrated plants.

Abscisic Acid↗
PubMed1986

Regulation of chloroplast-encoded chlorophyll-binding protein translation during higher plant chloroplast biogenesis.

Etioplasts of 5-day-old dark-grown barley seedlings synthesize most of the soluble and membrane proteins found in chloroplasts of illuminated plants. Prominent among these proteins are the large subunit of ribulose bisphosphate carboxylase and the alpha- and beta-subunits of the chloroplast ATPase. However, etioplasts do not synthesize four chloroplast-encoded proteins which are major constituents of the chloroplast thylakoid membrane: two chlorophyll apoproteins of photosystem I (68 and 65 kDa) and two chlorophyll apoproteins of photosystem II (47 and 43 kDa). Pulse-labeling experiments show that the lack of radiolabel accumulation in the chlorophyll apoproteins in etioplasts is due to inhibition of synthesis rather than apoprotein instability. Illumination of 5-day-old dark-grown barley selectively induces synthesis of the plastid-encoded chlorophyll apoproteins and proteins of 32, 23, and 21 kDa. Synthesis of the chlorophyll apoproteins was significant in plants illuminated for 15 min and was near maximum by 1 h. The induction of photosystem I chlorophyll apoprotein synthesis was not accompanied by an increase in mRNA for these proteins. These results demonstrate that the synthesis of the plastid-encoded photosystem I chlorophyll apoproteins is blocked at the translational level in dark-grown barley. Translation of the chlorophyll apoproteins is induced rapidly by light with a time course which is similar to the light-dependent formation of chlorophyll from protochlorophyllide.

Chlorophyll↗