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- Author or Editor: Victoriano Valpuesta x
Abstract
Indoleacetic acid (IAA) oxidase activity was measured in seeds of Prunus cerasus L. cv. Montmorency from full bloom to maturity. IAA oxidase activity reached a maximum at early Stage II of fruit development and decreased to trace levels during Stage III. The peak of IAA oxidase activity coincided with the time that the seed approached full size and endosperm was at a maximum volume and just prior to the rapid growth phase of the embryo. Inhibitors of IAA oxidase were coextracted (acetate buffer, 0.2 m, pH 4.0) with the enzyme. Low molecular weight compounds, which modified IAA oxidase activity, were separated from the enzyme extract with Sephadex G-25. The compounds from seeds of fruits in Stages I and III inhibited and from Stage II enhanced IAA oxidase activity. The possible role of IAA oxidase and the effectors in cherry fruit development are discussed.
Abstract
The distribution of indoleacetic acid (IAA) oxidase activity was determined in seeds of sour cherry (Prunus cerasus L. cv. Montmorency) fruits in mid-Stage II of development, 32 days after full bloom. The greatest activity was found in the integument tissue. No IAA oxidase activity was detected in the embryo or endosperm. When polyvinylpolypyrrolidone (PVP) was added to the extraction buffer (0.2 m acetate, pH 4.0), a trace of activity was detected in the embryo, but not in the endosperm. Inhibitors of IAA oxidase were coextracted with the enzyme and occurred in the greatest quantity in the integument tissue, an intermediate level in the embryo, and only a trace in the endosperm. The inhibitor from the integument and embryo tissues exhibited different kinetics when increasing concentrations were assayed against IAA oxidase isolated from the integuments. The possible significance of IAA oxidase and inhibitor distribution in the seed is discussed in relation to sour cherry fruit growth.
Rapid senescence of day lily flowers (Hemerocallis sp. cv. Cradle Song) has been shown to be associated with a rapid disappearance of proteins. Senescence was significantly delayed by pulsing developing flowers with cycloheximide, an inhibitor of protein synthesis. A cDNA library prepared from mRNA extracted from flowers in the very early stages of senescence was probed with mRNA from flowers at different stages of opening and senescence. Characterization of senescence-specific clones, and implications for the control of senescence in this non-climacteric flower will be discussed.
The metabolic pathway and function of ethylene during the senescence of many fruits and flowers have been extensively studied, the molecular basis of ethylene-insensitive flower senescence remains unknown. The ephemeral flowers of daylily (Hemerocallis) were used as a model system for the examination of ethylene-insensitive senescence. Senescence-associated cDNA clones were isolated from a cDNA library constructed from mRNA expressed in senescing tepals of daylily flowers. Up-regulated cDNA clones were identified by differentially screening the cDNA library. Sequence analysis of one of the clones, designated as SEN12, indicates that it contains a MADS box domain and an associated leucine-zipper K-box region and may be a transcription factor similar to floral homeotic genes. Northern analysis indicates that SEN12 encodes for a rare message. Therefore, reverse transcriptase polymerase chain reaction (RT-PCR) assays were used to quantitate the abundance of SEN12 transcripts during floral senescence. RT-PCR assays demonstrated that SEN12 transcripts significantly increase in abundance during the earliest stages of flower senescence and continue to increase until the end of senescence. We propose that SEN12 may be involved in controlling senescence in ethylene-insensitive flowers and we are continuing to investigate this hypothesis.
As in many commercially important flowers, especially the monocotyledonous geophytes, senescence of the ephemeral daylily flower (Hemerocallis) does not involve ethylene. By differentially screening a cDNA library constructed from mRNA extracted from daylily petals in the earliest stages of senescence, clones were isolated whose transcription is up-regulated coordinately with the onset of senescence. One of these clones, sen12, was found to be a transcription factor. The deduced amino acid sequence of sen12 contains a MADS-box and an associated K-box similar to transcription factors suggested to control floral morphogenesis in a variety of different species. Northern blot hybridization showed sen12 to be highly upregulated before and during visible flower senescence. The expression of homologous genes during senescence of other flowers will be reported.
In the present work, a set of eight new hexa-nucleotide simple sequence repeats (SSRs) is reported in olive (Olea europaea L). These SSRs loci were generated on the basis of expressed sequence tag (EST) sequences in the frame of an olive genomic project. The markers showed a high level of polymorphism when tested on a set of cultivars used as genitors in the olive breeding program of Córdoba, Spain. The long-core repeat motif of these markers allows a wider separation among alleles, thus permitting an accurate genotyping. Besides, these markers showed comparable levels of polymorphism to di-nucleotide SSRs, the only ones so far reported in olive. Selected on the basis of their discrimination capacity, four of the eight SSRs were used to test their ability for paternity testing in a total of 81 seedlings coming from 12 crosses. The paternity testing showed that seven crosses matched the alleged paternity and the remaining five were products of illicit pollinations. These results exactly matched with previous paternity testing performed with di-nucleotide SSR markers. These results demonstrate the usefulness of the developed hexa-nucleotide repeated motifs for checking the paternity of breeding progenies and suggest their use on variability studies.
Unlike other important crops analyzed so far for genetic diversity and population structure, the brief history and particularities of the genetics of the cultivated strawberry (Fragaria ×ananassa Duchesne) have limited its genetic characterization. The genomic composition and the pattern of inheritance have not been fully elucidated, although a number of studies have suggested a highly diploidized genome. In this study, the similarity relationships and structure of 92 selected strawberry cultivars with widely diverse origins have been established using simple sequence repeat (SSR) markers derived from expressed sequence tags (EST-SSR markers). Genetic analysis performed by the unweighted pair group method with arithmetic mean clustering revealed a distribution according to both date of cultivar release and breeding for a specific climatic adaptation. Additionally, a model-based clustering approach identified three populations among the strawberry cultivars with an overall FST value of 0.15 to 0.16. Both analyses support a limited differentiation of modern cultivars, most probably as a consequence of the methodology of strawberry breeding. Interestingly, the collection of strawberry cultivars here analyzed showed comparable genetic differentiation to that observed in natural populations of Fragaria chiloensis (L.) Mill., one of its wild ancestors. Our results suggest that breeding has produced a small but significant reduction on the genetic diversity of F. ×ananassa. The panel of 10 EST-SSRs described in this work provided an extremely low probability of confusion (less than 10−11), offering an efficient and accurate method for cultivar identification.