ISSN:0032-0889    

DOI:10.1104/pp.113.1.1

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

ISSN:0032-0889    

DOI:10.1104/pp.113.1.5

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Completion of germination (radicle emergence) is an all-or-none developmental event for an individual seed. Variation in germination timing among seeds in a population therefore reflects variation among seeds in the rates or extents of physiological or biochemical processes prior to radicle emergence. For tomato (Lycopersicon esculentum Mill.) seeds, correlative evidence suggests that endo-[beta]-mannanase activity weakens the endosperm cap tissue opposite the radicle tip to permit radicle emergence. To test whether endo-[beta]-mannanase activity is causally related to germination rates, we have developed a sensitive assay suitable for use with individual radicle tips or endosperm caps. We show that endo-[beta]-mannanase activity varies at least 100-fold and often more than 1000-fold among individual inbred tomato seeds prior to radicle emergence. Other sources of variation (tissue size and experimental error) were evaluated and cannot account for this range of activity. Endo-[beta]-mannanase activity was generally 10-fold greater in leachates from endosperm caps than from radicle tips. Release of reducing sugars from individual endosperm caps also varied over a considerable (9-fold) range. These extreme biochemical differences among individual tomato seeds prior to radicle emergence indicate that results obtained from bulk samples could be misleading if it is assumed that all seeds exhibit the“average”behav

ISSN:0032-0889    

DOI:10.1104/pp.113.1.13

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Endo-[beta]-mannanase is hypothesized to be a rate-limiting enzyme in endosperm weakening, which is a prerequisite for radicle emergence from tomato (Lycopersicon esculentum Mill.) seeds. Using a sensitive, single-seed assay, we have measured mannanase activity diffusing from excised tomato endosperm caps following treatments that alter the rate or percentage of radicle emergence. Most striking was the 100- to more than 10,000-fold range of mannanase activity detected among individual seeds of highly inbred tomato lines, which would not be detected in pooled samples. In some cases a threshold-type relationship between mannanase activity and radicle emergence was observed. However, when radicle emergence was delayed or prevented by osmoticum or abscisic acid, the initial increase in mannanase activity was unaffected or even enhanced. Partially dormant seed lots displayed a bimodal distribution of activity, with low activity apparently associated with dormant seeds in the population. Gibberellin- and abscisic acid-deficient mutant seeds exhibited a wide range of mannanase activity, consistent with their variation in hormonal sensitivity. Although the presence of mannanase activity in the endosperm cap is consistently associated with radicle emergence, it is not the sole or limiting factor under all conditions.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.21

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Endogenous brassinosteroids (BRs) in the dwarf mutants lka and lkb of garden pea (Pisum sativum L.) and comparable wild-type plants were quantified by gas chromatography-selected ion monitoring using deuterated internal standards. In young shoots of the lkb mutant, the levels of brassinolide, castasterone, and 6-deoxocastasterone were 23-, 22-, and 9-fold lower, respectively, than those of wild-type plants. Applications of brassinolide, castasterone, typhasterol, 3-dehydroteasterone, and teasterone normalized internode growth of lkb seedlings. These findings indicate that the lkb plants are BR-deficient mutants, probably as a consequence of a block in the BR biosynthetic pathway prior to the production of teasterone. Young shoots of lka plants contained only 50% less brassinolide and 5 times more castasterone than the equivalent wild-type tissues. The lka seedlings were approximately 100 times less responsive to brassinolide than the lkb mutant, and application of castasterone had only a marginal effect on lka internode growth, suggesting that the lka lesion results in impaired sensitivity to BR.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.31

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Repair of cyclobutyl pyrimidine dimers (CPDs) in DNA is essential in most organisms to prevent biological damage by ultraviolet (UV) light. In higher plants tested thus far, UV-sensitive strains had higher initial damage levels or deficient repair of nondimer DNA lesions but normal CPD repair. This suggested that CPDs might not be important for biological lesions. The photosynthetic apparatus has also been proposed as a critical target. We have analyzed CPD induction and repair in the UV-sensitive rice (Oryza sativa L.) cultivar Norin 1 and its close relative UV-resistant Sasanishiki using alkaline agarose gel electrophoresis. Norin 1 is deficient in cyclobutyl pyrimidine dimer photoreactivation and excision; thus, UV sensitivity correlates with deficient dimer repair.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.39

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

The promoters of the hemoglobin genes from the nitrogen-fixing tree Parasponia andersonii and the related nonnitrogen-fixing Trema tomentosa both confer [beta]-glucuronidase reporter gene expression to the central zone of the nodules of a transgenic legume, Lotus corniculatus. [beta]-Glucuronidase expression was high in the uninfected interstitial cells and parenchyma of the surrounding boundary layer and was low in the Rhizobium-infected cells. This contrasts with the expression of both the P. andersonii hemoglobin protein in P. andersonii nodules and the endogenous Lotus leghemoglobins that are expressed in the infected cells at very high levels. The expression pattern of the P. andersonii and T. tomentosa hemoglobin promoters in L. corniculatus resembles that of a nonsymbiotic hemoglobin gene from Casuarina glauca, which was introduced into this legume, and suggests that only the nonsymbiotic functions of the P. andersonii promoter are being recognized. Deletion of the distal segments of both the P. andersonii and T. tomentosa promoters identified regions important for the control of their tissue-specific and temporal activity in Lotus. Potential regulatory elements, which enhance nodule expression and suppress nonnodule expression, were also identified and localized to a distal promoter segment. A proximal AAGAG motif is present in the P. andersonii, T. tomentosa, and nonsymbiotic Casuarina hemoglobin genes. Mutation of this motif in the P. andersonii promoter resulted in a significant reduction in both the nodule and root expression levels in L. corniculatus. Some of the regulatory motifs characterized are similar to, but different from, the nodulin motifs of the leghemoglobins.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.45

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

The differentiation of chloroplasts to chromoplasts in cucumber (Cucumis sativus L.) corollas parallels flower development. Chromoplast biogenesis involves chlorophyll degradation, carotenoid accumulation, and the appearance of a new set of proteins. To study factors involved in chromoplast biogenesis in floral tissues, a minor (in abundance) protein of about 14 kD, CHRD (chromoplast protein D), was isolated from cucumber corolla chromoplasts. Immunological characterization revealed that the protein is chromoplast-specific and that its steady-state level in corollas increases in parallel to flower development. The protein was not detected in cucumber leaves or fruits. Immunological analysis of corollas and fruits from a variety of other plants also did not reveal cross-reactivity with the CHRD protein antisera. Using an in vitro bud culture system, we analyzed the effect of phytohormones on CHRD expression. Gibberellic acid rapidly enhanced, whereas paclobutrazol down-regulated, the steady-state level of CHRD. Ethylene also down-regulated the protein's steady-state level. It is suggested that hormonal control of chromoplastogenesis is tightly regulated at the tissue/organ level and that mainly developmental signals control carotenoid accumulation in nonphotosynthetic tissues.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.59

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Two genomic sequences encoding 4-coumarate:coenzyme A ligase (4CL;EC 6.2.1.12) in loblolly pine (Pinus taeda L.) were cloned. Both sequences contained three introns and four exons with identical coding sequences predicting 537 amino acids. Two of the three introns in these two clones were different both in sequence and in length. Sequences of both 4CL clones were found in all nine megagametophyte DNAs tested, providing genetic evidence that these two 4CL genomic sequences are nonallelic genes. Our analyses suggest that there are at least two distinct, intron-containing 4CL genes, at least one of which is transcribed into 4CL mRNA in developing xylem tissue of loblolly pine. The levels of 4CL gene transcription in xylem were influenced by compressional stress, resulting in an elevated 4CL enzyme activity with 4-coumaric acid. 4CL enzyme activity with ferulic acid remained unchanged, whereas with caffeic acid it was significantly inhibited. Exogenously applied trans-cinnamic acid in the protein extracts from normal wood xylem caused inhibition of 4CL activity toward caffeic acid similar to that under compressional stress. The implications of this cinnamic acid-modulated effect on 4CL enzyme activities toward different substrates in regulating monolignol synthesis in xylem under compressional stress are discussed.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.65

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB

摘要:

Acetyl-coenzyme A carboxylase (ACCase) occurs in at least two forms in rapeseed (Brassica napus): a homomeric (HO) and presumably cytosolic isozyme and a heteromeric, plastidial isozyme. We investigated whether the HO-ACCase of Arabidopsis can be targeted to plastids of B. napus seeds. A chloroplast transit peptide and the napin promoter were fused to the Arabidopsis ACC1 gene and transformed into B. napus, with the following results. (a) The small subunit transit peptide was sufficient to provide import of this very large protein into developing seed plastids. (b) HO-ACCase in isolated plastids was found to be biotinylated at a level comparable to extraplastidial HO-ACCase. (c) In vitro assays of HO-ACCase in isolated plastids from developing seeds indicate that it occurs as an enzymatically active form in the plastidial compartment. (d) ACCase activity in mature B. napus seeds is normally very low; however, plants expressing the SSU/ACC1 gene had 10- to 20-fold higher ACCase activity in mature seeds, suggesting that plastid localization prevents the turnover of HO-ACCase. (e) ACCase over-expression altered seed fatty acid composition, with the largest effect being an increase in oleic acid. (f) The total oil content of seeds was increased approximately 5% by the expression of HO-ACCase in plastids.

ISSN:0032-0889    

DOI:10.1104/pp.113.1.75

出版商:American Society of Plant Biologists    

年代:1997

数据来源: ASPB