Increases in 1,5-anhydroglucitol levels in germinating amaranth seeds and in ripening banana.
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To examine whether 1,5-anhydroglucitol (AG) is derived from starch degradation in plant tissues, we colorimetrically measured AG contents of germinating amaranth seeds and ripening banana pulp. In both cases, as starch degradation proceeded, AG levels were significantly increased, but were 1,700-5,000 times lower than those of total soluble carbohydrates. alpha-1,4-Glucan lyase activity, which is measured by the 1,5-anhydrofructose (AF) liberated from non-reducing glucose residues of starch or glycogen, was too low to be detected in amaranth or banana by the 3,5-dinitrosalicylic acid method. On the other hand, AF reductase, which reduces AF to AG, was detected in germinating amaranth seeds and banana pulp. Thus, the increases in AG levels are conceived to be derived from starch breakdown, although further investigation is needed to answer whether the starch degradation pathway via alpha-1,4-glucan lyase/AF reductase exists in plant tissues. (+info)
Preparation and root growth-modulatory activity of N-substituted 2-acetylamino-2-ethoxycarbonyl-3-(2-furyl)propanamides.
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N-Substituted 2-acetylamino-2-ethoxycarbonyl-3-(2-furyl)propanamides (8) were synthesized through the reaction of amines (13) with 2-acetylamino-2-ethoxycarbonyl-3-(2-furyl)propanoic acid (3b), which was prepared via condensation of 2-(bromomethyl)furan (10b) with diethyl acetamidomalonate, followed by partial hydrolysis of the resultant diethyl ester (3a) in the presence of barium hydroxide. However, bulky amines such as tert-butylamine or 2-trifluoromethylaniline did not afford the corresponding diamides (8). The biological activity of the prepared diamides (8) as root growth modulators was examined by germination assay using rape and leek seeds. N-(5-Bromo-2-thiazolyl)- and N-(4-chloro-2-benzothiazolyl)-2-acetylamino-2-ethoxycarbonyl-3-(2-furyl)propanami des (8h, i) both potently inhibited the root growth of rape seedlings, but were less effective in the case of leek seeds. The herbicide 2,4-dichlorophenoxyacetic acid completely inhibited root growth in both cases. (+info)
Molecular cloning, characterization, and expression of wheat cystatins.
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We cloned four kinds of cDNAs of wheat cystatins (WCs), WC1, WC2, WC3, and WC4, from the seed. They had 47-68% amino acid sequence similarities to other plant cystatins. WC1, WC2, and WC4 had 63-67% similalities to one another while 93% of amino acids were identical between WC1 and WC3. This suggested that WCI, WC2, and WC4 should be regarded as the isoforms of wheat cystatins. The mRNAs for WC1, WC2, and WC4 were all expressed in seed at an early stage of maturation and, after that, their quantities decreased gradually. However, each of the mRNAs was again expressed one day after the start of germination and the expression continued for the following five days. WC1 seemed to be expressed at a higher level than WC2 and WC4. Immunostaining for looking at site-specific expression of each WC demonstrated that both WC1 and WC4 existed in the aleuron layer and embryo, but in the endosperm the only existing species was WC1. Differences in mRNA level and tissue localization found for the WCs may suggest their differential physiological roles. (+info)
The TRANSPARENT TESTA12 gene of Arabidopsis encodes a multidrug secondary transporter-like protein required for flavonoid sequestration in vacuoles of the seed coat endothelium.
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Phenolic compounds that are present in the testa interfere with the physiology of seed dormancy and germination. We isolated a recessive Arabidopsis mutant with pale brown seeds, transparent testa12 (tt12), from a reduced seed dormancy screen. Microscopic analysis of tt12 developing and mature testas revealed a strong reduction of proanthocyanidin deposition in vacuoles of endothelial cells. Double mutants with tt12 and other testa pigmentation mutants were constructed, and their phenotypes confirmed that tt12 was affected at the level of the flavonoid biosynthetic pathway. The TT12 gene was cloned and found to encode a protein with similarity to prokaryotic and eukaryotic secondary transporters with 12 transmembrane segments, belonging to the MATE (multidrug and toxic compound extrusion) family. TT12 is expressed specifically in ovules and developing seeds. In situ hybridization localized its transcript in the endothelium layer, as expected from the effect of the tt12 mutation on testa flavonoid pigmentation. The phenotype of the mutant and the nature of the gene suggest that TT12 may control the vacuolar sequestration of flavonoids in the seed coat endothelium. (+info)
A postgermination developmental arrest checkpoint is mediated by abscisic acid and requires the ABI5 transcription factor in Arabidopsis.
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Seed dormancy is a trait of considerable adaptive significance because it maximizes seedling survival by preventing premature germination under unfavorable conditions. Understanding how seeds break dormancy and initiate growth is also of great agricultural and biotechnological interest. Abscisic acid (ABA) plays primary regulatory roles in the initiation and maintenance of seed dormancy. Here we report that the basic leucine zipper transcription factor ABI5 confers an enhanced response to exogenous ABA during germination, and seedling establishment, as well as subsequent vegetative growth. These responses correlate with total ABI5 levels. We show that ABI5 expression defines a narrow developmental window following germination, during which plants monitor the environmental osmotic status before initiating vegetative growth. ABI5 is necessary to maintain germinated embryos in a quiescent state thereby protecting plants from drought. As expected for a key player in ABA-triggered processes, ABI5 protein accumulation, phosphorylation, stability, and activity are highly regulated by ABA during germination and early seedling growth. (+info)
Polymorphism in rice amylases at an early stage of seed germination.
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A polymorphism in rice amylases at an early stage of seed germination is analyzed by zymogram. In non-glutinous cultivars of rice, alpha-amylase isozymes are mainly confirmed in germinating seeds. However, in glutinous cultivars, beta-amylase isozymes, which are not confirmed in nonglutinous cultivars, make up the major part of the total amylase activity and the expression of alpha-amylases are repressed. (+info)
Arabidopsis PLC1 is required for secondary responses to abscisic acid signals.
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The role of inositol 1,4,5-trisphosphate (Ins[1,4,5]P3) in transducing the abscisic acid (ABA) signal during seed germination and in the stress responses of mature plants is poorly understood. We have considered the contributions of the phospholipase C1 (encoded by AtPLC1) and an Ins(1,4,5)P3 5-phosphatase (encoded by AtIP5PII) to ABA signaling by using a modified version of the glucocorticoid-inducible system to regulate transgene expression. In the presence of the dexamethasone (Dex) inducer, transgenic lines expressing the AtPLC1 antisense and AtIP5PII sense transgenes showed no inhibition of germination and growth by ABA, whereas in the absence of the inducer they were sensitive. In the presence of Dex, these lines accumulated lower Ins(1,4,5)P3 levels upon ABA treatment compared with that of the control transgenic lines. RNA gel blot analysis revealed a decrease in the induction of the ABA-responsive genes RD29a, KIN2, and RD22 but not COR47 in the Dex-induced transgenic plants. In transgenic lines expressing the inducible AtPLC1 sense transgene, an increase in AtPLC1 expression was not sufficient to activate the expression of ABA-responsive genes in vegetative tissues. In vitro experiments demonstrated the induced PLC1 expression when extracts were assayed in the presence of calcium, but no increase in Ins(1,4,5)P3 levels in vivo was detected, suggesting that the PLC1 enzyme was latent. Our results indicate that although an increase in PLC1 activity and increased Ins(1,4,5)P3 levels are necessary for maximal gene induction by ABA, overexpression of AtPLC1 itself is not sufficient to trigger the expression of ABA-responsive genes. We propose that AtPLC1 plays a role in secondary ABA responses. (+info)
Small changes in the regulation of one Arabidopsis profilin isovariant, PRF1, alter seedling development.
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Profilin (PRF) is a low-molecular-weight actin binding protein encoded by a diverse gene family in plants. Arabidopsis PRF1 transcripts are moderately well expressed in all vegetative organs. A regulatory mutant in PRF1, prf1-1, was isolated from a library of T-DNA insertions. The insertion disrupted the promoter region of PRF1 100 bp upstream from the transcriptional start site. Although steady state levels of PRF1 transcripts appeared normal in mature prf1-1 plants, the levels in young seedlings were only one-half those observed in wild type. Reactions with a PRF1 isovariant-specific monoclonal antiserum and general anti-profilin antisera demonstrated that PRF1 protein levels also were one-half those found in wild-type seedlings, although total profilin levels were unaffected. Mutant seedlings no longer could downregulate PRF1 levels in the light, as did wild type. Consistent with their molecular phenotypes, young mutant seedlings displayed several morphological phenotypes but developed into apparently normal adult plants. Their initial germination rate and development were slow, and they produced excessive numbers of root hairs. Mutant seedlings had abnormally raised cotyledons, elongated hypocotyls, and elongated cells in the hypocotyl, typical of phenotypes associated with some defects in light and circadian responses. A wild-type PRF1 transgene fully complements the hypocotyl phenotypes in the prf1-1 mutant. The ability of profilin to regulate actin polymerization and participate directly in signal transduction pathways is discussed in light of the prf1-1 phenotypes. (+info)