Biomedical subjects

J E Mullet

Publications and source records attributed to J E Mullet.

At least 55 records · Page 3Linked to original sources

PubMed1992

The soybean vegetative storage proteins VSP alpha and VSP beta are acid phosphatases active on polyphosphates.

The soybean vegetative storage protein genes (vspA, and vspB) are regulated in a complex manner developmentally and in response to external stimuli such as wounding and water deficit. The proteins accumulate to almost one-half the amount of soluble leaf protein when soybean plants are continually depodded and have been identified as storage proteins because of their abundance and pattern of expression in plant tissues. We have shown that purified VSP homodimers (VSP alpha and VSP beta) and heterodimers (VSP alpha/beta) possess acid phosphatase activity (alpha = 0.3-0.4 units/mg; beta = 2-4 units/mg; alpha/beta = 7-10 units/mg). Specific activities were determined by monitoring o-carboxyphenyl phosphate (0.7 mM) cleavage at pH 5.5 (VSP alpha) or pH 5.0 (VSP alpha/beta and VSP beta) in 0.15 M sodium acetate buffer at 25 degrees C. These enzymes are active over a broad pH range, maintaining greater than 40% of maximal activity from pH 4.0 to 6.5 and having maximal activity at pH 5.0-5.5. They are inactivated by sodium fluoride, sodium molybdate, and heating at 70 degrees C for 10 min. These phosphatases can liberate Pi from several different substrates, including napthyl acid phosphate, carboxyphenyl phosphate, sugar-phosphates, glyceraldehyde 3-phosphate, dihydroxyacetone phosphate, phosphoenolpyruvate, ATP, ADP, PPi, and short chain polyphosphates. VSP alpha/beta cleaved phosphoenolpyruvate, ATP, ADP, PPi, and polyphosphates most efficiently. Apparent Km and Vmax values at 25 degrees C and pH 5.0 were 42 microM and 2.0 mumol/min/mg, 150 microM and 4.2 mumol/min/mg, and 420 microM and 4.1 mumol/min/mg, for tetrapolyphosphate, pyrophosphate, and phosphoenolpyruvate, respectively.

Acid Phosphatase↗

PubMed1992

Jasmonic acid/methyl jasmonate accumulate in wounded soybean hypocotyls and modulate wound gene expression.

Jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA), are plant lipid derivatives that resemble mammalian eicosanoids in structure and biosynthesis. These compounds are proposed to play a role in plant wound and pathogen responses. Here we report the quantitative determination of JA/MeJA in planta by a procedure based on the use of [13C,2H3]MeJA as an internal standard. Wounded soybean (Glycine max [L] Merr. cv. Williams) stems rapidly accumulated MeJA and JA. Addition of MeJA to soybean suspension cultures also increased mRNA levels for three wound-responsive genes (chalcone synthase, vegetative storage protein, and proline-rich cell wall protein) suggesting a role for MeJA/JA in the mediation of several changes in gene expression associated with the plants' response to wounding.

Acyltransferases↗

PubMed1992

Coregulation of soybean vegetative storage protein gene expression by methyl jasmonate and soluble sugars.

The soybean vegetative storage protein genes vspA and vspB are highly expressed in developing leaves, stems, flowers, and pods as compared with roots, seeds, and mature leaves and stems. In this paper, we report that physiological levels of methyl jasmonate (MeJA) and soluble sugars synergistically stimulate accumulation of vsp mRNAs. Treatment of excised mature soybean (Glycine max Merr. cv Williams) leaves with 0.2 molar sucrose and 10 micromolar MeJA caused a large accumulation of vsp mRNAs, whereas little accumulation occurred when these compounds were supplied separately. In soybean cell suspension cultures, the synergistic effect of sucrose and MeJA on the accumulation of vspB mRNA was maximal at 58 millimolar sucrose and was observed with fructose or glucose substituted for sucrose. In dark-grown soybean seedlings, the highest levels of vsp mRNAs occurred in the hypocotyl hook, which also contained high levels of MeJA and soluble sugars. Lower levels of vsp mRNAs, MeJA, and soluble sugars were found in the cotyledons, roots, and nongrowing regions of the stem. Wounding of mature soybean leaves induced a large accumulation of vsp mRNAs when wounded plants were incubated in the light. Wounded plants kept in the dark or illuminated plants sprayed with dichlorophenyldimethylurea, an inhibitor of photosynthetic electron transport, showed a greatly reduced accumulation of vsp mRNAs. The time courses for the accumulation of vsp mRNAs induced by wounding or sucrose/MeJA treatment were similar. These results strongly suggest that vsp expression is coregulated by endogenous levels of MeJA (or jasmonic acid) and soluble carbohydrate during normal vegetative development and in wounded leaves.

Journal Article↗

PubMed1992

Involvement of a lipoxygenase-like enzyme in abscisic Acid biosynthesis.

Several lines of evidence indicate that abscisic acid (ABA) is derived from 9'-cis-neoxanthin or 9'-cis-violaxanthin with xanthoxin as an intermediate. (18)O-labeling experiments show incorporation primarily into the side chain carboxyl group of ABA, suggesting that oxidative cleavage occurs at the 11, 12 (11', 12') double bond of xanthophylls. Carbon monoxide, a strong inhibitor of heme-containing P-450 monooxygenases, did not inhibit ABA accumulation, suggesting that the oxygenase catalyzing the carotenoid cleavage step did not contain heme. This observation, plus the ability of lipoxygenase to make xanthoxin from violaxanthin, suggested that a lipoxygenase-like enzyme is involved in ABA biosynthesis. To test this idea, the ability of several soybean (Glycine max L.) lipoxygenase inhibitors (5,8,11-eicosatriynoic acid, 5,8,11,14-eicosatetraynoic acid, nordihydroguaiaretic acid, and naproxen) to inhibit stress-induced ABA accumulation in soybean cell culture and soybean seedlings was determined. All lipoxygenase inhibitors significantly inhibited ABA accumulation in response to stress. These results suggest that the in vivo oxidative cleavage reaction involved in ABA biosynthesis requires activity of a nonheme oxygenase having lipoxygenase-like properties.

Journal Article↗

PubMed1992

A novel light-regulated promoter is conserved in cereal and dicot chloroplasts.

The chloroplast psbD-psbC genes encode D2 and cp43, a reaction center protein and chlorophyll-binding antenna protein of photosystem II, respectively. We have previously shown that differential accumulation of light-induced psbD-psbC mRNAs in barley chloroplasts is due to transcription from a blue light-responsive promoter (LRP). It is hypothesized that the light-induced mRNAs help to maintain levels of the D2 polypeptide, which is photodamaged and degraded in illuminated plants. To determine if light-induced accumulation of psbD-psbC mRNAs was a conserved phenomenon in chloroplasts, the expression of psbD-psbC operons from five cereals (barley, wheat, rice, maize, and sorghum) and three dicot (tobacco, spinach, and pea) species was examined. Cereal and dicot psbD-psbC operons differ due to several DNA rearrangements that moved psbK-psbI proximal to psbD-psbC, allowing cotranscription of these genes and production of several unique transcripts in cereals. Despite differences in the structure and expression of the cereal and dicot psbD-psbC operons, the accumulation of light-induced psbD-psbC mRNAs was conserved in all species studied. An unusual feature of the light-induced mRNAs was the occurrence of 5' end microheterogeneity. The multiple 5' termini were mapped to several consecutive nucleotides (8 to 25 bp) within a highly conserved (61%) DNA region that represents the transcription initiation site for the mRNAs in barley and tobacco. The novel LRP differs in sequence from typical plastid promoters that have prokaryotic "-10" and "-35" elements and is centered 570 bp (cereals), 900 bp (tobacco, spinach), or 1100 bp (pea) upstream from the psbD translational start codon. We propose that physiological and gene regulatory demands of the chloroplast act as constraints that preserved the linkage of the LRP with psbD despite DNA inversions involving the psbD upstream region.

Base Sequence↗

PubMed1991

Ribosomes pause at specific sites during synthesis of membrane-bound chloroplast reaction center protein D1.

Photosynthetic reaction center protein D1 contains five membrane-spanning alpha-helices which form binding sites for pheophytin, chlorophyll, carotenoids, quinone, Fe2+, and probably Mn2+. D1 translation intermediates of 15 to 28 kD were detected when isolated chloroplasts were pulse-labeled with [35S]methionine. The D1 translation intermediates were associated with membrane polysomes and can be chased into full length D1. The sites of translation pausing were determined by mapping the distribution of ribosomes on D1 mRNA using toeprint analysis. Clusters of toeprint signals were generated by D1 mRNA associated with membranes but not by D1 mRNA in nonpolysomal fractions of the soluble phase or phenol-extracted mRNA. The distribution of ribosomes on D1 mRNA determined by toeprint analysis was consistent with D1 translation intermediates observed with pulse-labeling. Ribosome pausing may facilitate co-translational binding of co-factors such as chlorophyll to D1 and aid the integration of D1 into thylakoid membranes.

Amino Acid Sequence↗

PubMed1991

Water deficit modulates gene expression in growing zones of soybean seedlings. Analysis of differentially expressed cDNAs, a new beta-tubulin gene, and expression of genes encoding cell wall proteins.

Transfer of soybean seedlings to low-water-potential vermiculite (psi w = -0.3 MPa) results in a reversible decrease in hypocotyl growth and modulation of several polysomal mRNAs (Plant Physiol 92: 205-214). We report here the isolation of two cDNA clones (pGE16 and pGE95) which correspond to genes whose mRNA levels are increased, and one cDNA clone (pGE23) which corresponds to a gene whose mRNA level is decreased in the hypocotyl zone of cell elongation by water deficit. In well-watered seedlings mRNAs hybridizing to pGE16 and pGE95 are most abundant in mature regions of the seedling, but in water-deficient seedlings mRNA levels are reduced in mature regions and enhanced in elongating regions. RNA corresponding to soybean proline-rich protein 1 (sbPRP1) shows a similar tissue distribution and response to water deficit. In contrast, in well-watered seedlings, the gene corresponding to pGE23 was highly expressed in the hypocotyl and root growing zones. Transfer of seedlings to low-water-potential vermiculite caused a rapid decrease in mRNA hybridizing to pGE23. Sequence analysis revealed that pGE23 has high homology with beta-tubulin. Water deficit also reduced the level of mRNA hybridizing to JCW1, an auxin-modulated gene, although with different kinetics. Furthermore, mRNA encoding actin, glycine-rich proteins (GRPs), and hydroxyproline-rich glycoproteins (HRGPs) were down-regulated in the hypocotyl zone of elongation of seedlings exposed to water deficit. No effect of water deficit was observed on the expression of chalcone synthase. Decreased expression of beta-tubulin, actin, JCW1, HRGP and GRP and increased expression of sbPRP1, pGE95 and pGE16 in the hypocotyl zone of cell elongation could participate in the reversible growth inhibition observed in water-deficient soybean seedlings.

Actins↗

PubMed1991

Chloroplast transcription is required to express the nuclear genes rbcS and cab. Plastid DNA copy number is regulated independently.

RbcL and rbcS mRNA levels and plastid transcription activity are low in the basal meristematic region of barley primary leaves and increase coordinately during leaf cell development with a similar time course in dark-grown or illuminated seedlings. The capacity of light to cause cab mRNA accumulation shows a similar dependence on leaf cell development. These results indicate that the initial activation of chloroplast gene expression and the expression of some nuclear genes encoding plastid proteins are coupled to leaf cell development. RbcL and rbcS mRNA levels and plastid transcription activity decline in older leaf sections of dark-grown or illuminated barley. The decreases in plastid transcription and rbcS and rbcL mRNA levels in older dark-grown seedlings could be reversed by plant illumination. Therefore, while the initial activation of plastid transcription and accumulation of rbcS mRNA are largely light-independent, these events become light-dependent in older leaves of dark-grown barley. If the initial increase in plastid transcription which occurs early in leaf cell development is prevented by tagetitoxin, a specific inhibitor of the plastid RNA polymerase, rbcS mRNA does not accumulate and cab mRNA accumulation cannot be induced by light. The effect of tagetitoxin is selective because this compound does not inhibit barley leaf growth, or the normal accumulation of nuclear-encoded actin and BN3 transcripts and plastid DNA which occurs during chloroplast development. Furthermore, a barley pigment-deficient mutant, alb-f17, and plants containing photo-oxidized plastids show parallel reductions in plastid transcription activity and levels of rbcS and cab mRNA. This suggests that the activation of plastid transcription during the early stages of chloroplast biogenesis is necessary for the expression of rbcS and cab.

Blotting, Northern↗

PubMed1991

Lipoxygenase gene expression is modulated in plants by water deficit, wounding, and methyl jasmonate.

Two classes of lipoxygenase (LOX) cDNAs, designated loxA and loxB, were isolated from soybean. A third lipoxygenase cDNA, loxP1, was isolated from pea. The deduced amino acid sequences of loxA and loxB show 61-74% identity with those of soybean seed LOXs. loxA and loxB mRNAs are abundant in roots and non-growing regions of seedling hypocotyls. Lower levels of these mRNAs are found in hypocotyl growing regions. Exposure of soybean seedlings to water deficit causes a rapid increase in loxA and loxB mRNAs in the elongating hypocotyl region. Similarly, loxP1 mRNA levels increase rapidly when pea plants are wilted. loxA and loxB mRNA levels also increase in wounded soybean leaves, and these mRNAs accumulate in soybean suspension cultures treated with 20 microM methyl jasmonate. These results demonstrate that LOX gene expression is modulated in response to water deficit and wounding and suggest a role for lipoxygenase in plant responses to these stresses.

Acetates↗

PubMed1991

Plastid DNA synthesis and nucleic acid-binding proteins in developing barley chloroplasts.

Activation of plastid DNA synthesis occurred early in barley leaf chloroplast development. High rates of DNA synthesis were observed in the leaf basal meristem of dark-grown plants where plastid transcription activity was low. DNA synthesis activity decreased in later stages of chloroplast development. Plastid nuclei acid-binding proteins were detected after lithium dodecylsulfate (LDS)-polyacrylamide gel separation and renaturation. One set of nucleic acid-binding proteins was associated with plastid nucleoids. A second set of nucleic acid-binding proteins co-sedimented with ribosomes and most probably corresponds to ribosomal proteins. Changes in the composition of the nucleic acid-binding proteins were characterized as a function of chloroplast development in dark-grown and illuminated barley plants.

Chloroplasts↗

PubMed1991

Abscisic Acid accumulates at positive turgor potential in excised soybean seedling growing zones.

Abscisic acid (ABA) accumulated in soybean (Glycine max [L.] Merr. cv Williams) hypocotyl elongating regions when seedlings were transferred to low water potential vermiculite (Psi = -0.3 megapascals) even though positive turgor is retained in this tissue. Accumulation of ABA in growing zones could occur from de novo biosynthesis within this tissue or transport from adjacent nongrowing zones. Both growing and nongrowing hypocotyl and root tissues accumulated significant levels of ABA when excised and dehydrated to reduce turgor. Surprisingly, excised growing zones (which experienced no water loss) also accumulated ABA when incubated in darkness for 4 hours at 100% relative humidity and 29 degrees C. Induction of ABA accumulation in the excised elongating region of the hypocotyl was not caused by disruption of root pressure or wounding. While excision of hypocotyl elongating regions induced ABA accumulation, no change in either extensin or p33 mRNA levels was observed. Accumulation of extensin or p33 mRNA required more severe wounding. This suggests that ABA is not involved in the response of these genes in wounded tissue and that wound signals are not causing ABA accumulation in excised tissue. Accumulation of ABA in excised elongating regions was correlated with growth inhibition and a decline in turgor to the yield threshold (Psi;(p) = 0.37 megapascals; R Matyssek, S Maruyama, JS Boyer [1988] Plant Physiol 86: 1163-1167). Inhibiting hypocotyl growth by transferring seedlings to lower temperatures or light did not cause ABA accumulation. We conclude that induction of ABA accumulation in growing zones is more sensitive to changes in turgor than the induction which occurs in mature tissues.

Journal Article↗

PubMed1990

In vitro synthesis of chlorophyll a in the dark triggers accumulation of chlorophyll a apoproteins in barley etioplasts.

An in vitro translation system using lysed etioplasts was developed to test if the accumulation of plastid-encoded chlorophyll a apoproteins is dependent on the de novo synthesis of chlorophyll a. The P700 apoproteins, CP47 and CP43, were not radiolabeled in pulsechase translation assays employing lysed etioplasts in the absence of added chlorophyll precursors. When chlorophyllide a plus phytylpyrophosphate were added to lysed etioplast translation assays in the dark, chlorophyll a was synthesized and radiolabeled P700 apoproteins, CP47 and CP43, and a protein which comigrates with D1 accumulated. Chlorophyllide a or phytylpyrophosphate added separately to the translation assay in darkness did not induce chlorophyll a formation or chlorophyll a apoprotein accumulation. Chlorophyll a formation and chlorophyll a apoprotein accumulation were also induced in the lysed etioplast translation system by the photoreduction of protochlorophyllide to chlorophyllide a in the presence of exogenous phytylpyrophosphate. Accumulation of radiolabeled CP47 was detectable when very low levels of chlorophyll a were synthesized de novo (less than 0.01 nmol/10(7) plastids), and radiolabel increased linearly with increasing de novo chlorophyll a formation. Higher levels of de novo synthesized chlorophyll a were required prior to detection of radiolabel incorporation into the P700 apoproteins and CP43 (greater than 0.01 nmol/10(7) plastids). Radiolabel incorporation into the P700 apoproteins, CP47 and CP43, saturated at a chlorophyll a concentration which corresponds to 50% of the etioplast protochlorophyllide content (0.06 nmol of chlorophyll a/10(7) plastids).

Apoproteins↗

PubMed1990

Light-induced transcription of chloroplast genes. psbA transcription is differentially enhanced in illuminated barley.

Transcription and Northern dot blot analyses were used to determine the relationship between light-induced changes in RNA levels and transcription in barley and maize plastids. Overall plastid transcription activity is near maximum and largely light independent in apical sections of 4.5-day-old dark-grown barley seedings. With continued development in the dark, transcription activity in barley plastids declined precipitously, but transcription could be reactivated if plants were illuminated. Illumination of 8-day-old dark-grown barley seedlings increased the transcription of psbA, rbcL, and 16 S rDNA; however, the stimulation of psbA transcription was 2-4-fold more than rbcL or 16 S rDNA. Differential enhancement of psbA transcription occurred when 4.5- or 8-day-old dark-grown seedlings were illuminated, and the influence persisted in plants illuminated for 72 h. Illumination of 8-day-old dark-grown barley caused an increase in psbA and rbcL mRNA levels, but the increase in psbA mRNA was greater than that of rbcL. Similarly, illumination of 9-day-old dark-grown maize increased plastid transcription activity and the levels of psbA and rbcL mRNA. These results indicate that light can modulate overall plastid transcription activity and differentially stimulate the transcription of genes including psbA.

Blotting, Northern↗

PubMed1990

Light-induced switch in barley psbD-psbC promoter utilization: a novel mechanism regulating chloroplast gene expression.

The synthesis of reaction center protein D2 and mRNAs which encode this protein are differentially maintained at high levels in mature barley chloroplasts. To understand the differential maintenance of psbD mRNA abundance, we have studied the transcription and the RNAs produced from the psbD-psbC operon in plastids of light and dark-grown barley seedlings. Ten psbD-psbC RNAs synthesized in dark-grown barley share four different 5'-ends, two of which arise by transcription initiation, and one of which is generated by 5'-processing of longer psbD-psbC transcripts. Illumination of dark-grown barley causes the decline of these ten transcripts, and the accumulation of two different psbD-psbC RNAs. Capping assays, in vitro transcription and RNA processing experiments and treatment of plants with tagetitoxin (a selective inhibitor of chloroplast transcription), indicate that the light-induced transcripts arise by transcription initiation. Run-on transcription and RNA quantitation experiments provide evidence that both light-induced transcription and RNA stability play roles in the accumulation of the light-induced RNAs. These data document a novel mechanism for regulating plastid gene expression involving a light-induced switch in psbD-psbC promoter utilization.

Base Sequence↗

PubMed1990

Turgor-responsive gene transcription and RNA levels increase rapidly when pea shoots are wilted. Sequence and expression of three inducible genes.

Reduction of turgor in pea shoots caused the accumulation of several poly(A) RNAs. cDNA clones derived from three different poly(A) RNAs which accumulate in wilted pea shoots were isolated, sequenced and expression of the corresponding genes examined. Clone 7a encoded a 289 amino acid protein. The C-terminal 180 amino acids of this protein were homologous to soybean nodulin-26. RNA hybridizing to cDNA 7a was abundant in roots, and induced in shoots by dehydration, heat shock and to a small extent by ABA. Hydropathic plots indicate that the protein encoded by cDNA 7a contains six potential membrane spanning domains similar to proteins which form ion channels. Clone 15a encoded a 363 amino acid protein with high homology to cysteine proteases. RNA hybridizing to cDNA 15a was more abundant in roots than shoots of control plants. Dehydration of pea shoots induced cDNA 15a mRNA levels whereas heat shock or ABA treatment did not. Clone 26g encoded a 508 amino acid protein with 30% residue identity to several aldehyde dehydrogenases. RNA hybridizing to cDNA 26g was induced by dehydration of shoots but not roots and heat shock and ABA did not modulate RNA levels. Levels of the three poly(A) RNAs increased 4-6-fold by 4 h after wilting and this increase was not altered by pretreatment of shoots with cycloheximide. When wilted shoots were rehydrated, RNA hybridizing to cDNA 26g declined to pre-stress levels within 2 h. Run-on transcription experiments using nuclei from pea shoots showed that transcription of the genes which encode the three poly(A) RNAs was induced within 30 min following reduction of shoot turgor. One of the genes showed a further increase in transcription by 4 h after dehydration whereas transcription of the other 2 genes declined. These results indicate that plant cells respond to changes in cell turgor by rapidly increasing transcription of several genes. Furthermore, the expression of the turgor-responsive genes varies with respect to the time course of induction and reversibility of the wilting-induced changes.

Amino Acid Sequence↗

PubMed1990

Sequence and transcriptional analysis of the barley ctDNA region upstream of psbD-psbC encoding trnK(UUU), rps16, trnQ(UUG), psbK, psbI, and trnS(GCU).

A 6.25 kbp barley plastid DNA region located between psbA and psbD-psbC were sequenced and RNAs produced from this DNA were analyzed. TrnK(UUU), rps16 and trnQ(UUG) were located upstream of psbA. These genes were transcribed from the same DNA strand as psbA and multiple RNAs hybridized to them. TrnK and rsp16 contained introns; a 504 amino acid open reading frame (ORF504) was located within the trnK intron. Between trnQ and psbD-psbC was a 2.24 kbp region encoding psbK, psbI and trnS(GCU). PsbK and psbI are encoded on the same DNA strand as psbD-psbC whereas trnS(GCU) is transcribed from the opposite strand. Two large RNAs accumulate in barley etioplasts which contain psbK, psbI, anti-sense trnS(GCU) and psbD-psbC sequences. Other RNAs encode psbK and psbI only, or psbK only. The divergent trnS(GCU) located upstream of psbD-psbC and a second divergent trnS(UGA) located downstream of psbD-psbC were both expressed. Furthermore, RNA complementary to psbK and psbI mRNA was detected, suggesting that transcription from divergent overlapping transcription units may modulate expression from this DNA region.

Amino Acid Sequence↗

PubMed1990

Chlorophyll regulates accumulation of the plastid-encoded chlorophyll apoproteins CP43 and D1 by increasing apoprotein stability.

Chlorophyll apoprotein accumulation in higher plant chloroplasts is controlled by light-dependent chlorophyll formation. Dark-grown plants lack chlorophyll and chlorophyll apoproteins. However, the plastid genes encoding the chlorophyll apoproteins are transcribed; chlorophyll apoprotein mRNA accumulates and associates with polysomes in plastids of dark-grown plants. Pulse-labeling assays revealed a population of short-lived proteins in plastids of dark-grown plants. One of these transiently labeled proteins was CP43, a chlorophyll apoprotein associated with photosystem II. Pulse-chase assays showed that newly synthesized CP43 was rapidly degraded in plastids of dark-grown plants, which lack chlorophyll. In contrast, CP43 synthesized in plastids from illuminated plants was stable. The synthesis of D1, a chlorophyll apoprotein of the photosystem II reaction center, was also analyzed in plastids of dark-grown and illuminated plants. Radiolabel accumulation into full-length D1 was only detected in plastids of illuminated plants. However, D1 translation intermediates of 15-25 kDa were detected in both plastid populations. Pulse-chase assays showed that the 15- to 25-kDa D1 translation products were precursors of mature D1 in plastids of illuminated plants. In contrast, in plastids of dark-grown plants, the 15- to 25-kDa translation intermediates were converted into a 23-kDa polypeptide previously suggested to be a proteolytic product of D1. These results indicate that chlorophyll produced in illuminated plants stabilizes D1 nascent polypeptides, which allows accumulation of mature D1.

Apoproteins↗

PubMed1990

Water Deficit and Abscisic Acid Cause Differential Inhibition of Shoot versus Root Growth in Soybean Seedlings : Analysis of Growth, Sugar Accumulation, and Gene Expression.

Roots often continue to elongate while shoot growth is inhibited in plants subjected to low-water potentials. The cause of this differential response to water deficit was investigated. We examined hypocotyl and root growth, polysome status and mRNA populations, and abscisic acid (ABA) content in etiolated soybean (Glycine max [L.] Merr. cv Williams) seedlings whose growth was inhibited by transfer to low-water potential vermiculite or exogenous ABA. Both treatments affected growth and dry weight in a similar fashion. Maximum inhibition of hypocotyl growth occurred when internal ABA levels (modulated by ABA application) reached the endogenous level found in the elongating zone of seedlings grown in water-deficient vermiculite. Conversely, root growth was affected to only a slight extent in low-water potential seedlings and by most ABA treatments (in some, growth was promoted). In every seedling section examined, transfer of seedlings into low-water potential vermiculite caused ABA levels to increase approximately 5- to 10-fold over that found in well-watered seedlings. Changes in soluble sugar content, polysome status, and polysome mRNA translation products seen in low-water potential seedlings did not occur with ABA treatments sufficient to cause significant inhibition of hypocotyl elongation. These data suggest that both variation in endogenous ABA levels, and differing sensitivity to ABA in hypocotyls and roots can modulate root/shoot growth ratios. However, exogenous ABA did not induce changes in sugar accumulation, polysome status, and mRNA populations seen after transfer into low-water potential vermiculite.

Journal Article↗