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Interactions among jasmonates and auxin in the photoperiodic flower induction of a short-day plant Ipomoea nil were examined. Therefore, we measured changes in jasmonic acid (JA) and jasmonic acid methyl ester (JAMe) levels in the cotyledons of I. nil during the inductive night, as well as the effects of indole-3-acetic acid (IAA) on their content. We noticed an interesting result, that IAA applied on the cotyledons of I. nil is an effective stimulator of JAMe production in seedlings cultivated under inductive night conditions. IAA treatment also significantly increased the transcriptional activity of InJMT (JASMONIC ACID CARBOXYL METHYLTRANSFERASE), while did not affect the expression of JA biosynthesis genes (lipoxyganease, allene oxide synthase, 12-oxophytodienoate reductase). These data, as well as the results of our previous research, suggest that exogenous IAA participates in I. nil flower induction process by stimulating InJMT expression and, as a consequence of that, enhancing the level of JAMe, a flowering inhibitor.
Allene oxide synthase (AOS) encodes the first enzyme in the lipoxygenase pathway, which is responsible for jasmonic acid (JA) formation. In this study we report the molecular cloning and characterization of InAOS from Ipomoea nil. The full-length gene is composed of 1662 bp and encodes for 519 amino acids. The predicted InAOS contains PLN02648 motif, which is evolutionarily conserved and characteristic for functional enzymatic proteins. We have shown that wounding led to a strong stimulation of the examined gene activity in cotyledons and an increase in JA level, which suggest that this compound may be a modulator of stress responses in I. nil.
The abscission of certain organs from the plant is part of the fulfilment of its developmental programs. The separation process occurs in a specialized abscission zone usually formed at the base of detached organ. The changing level of phytohormones, particularly ethylene, is the element responsible for coordinating anatomical and physiological transformation that accompanies organ abscission. The application of ethylene (ET) on Lupinus luteus stimulates flower abortion. However, the treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) – direct ET precursor – does not cause such a strong physiological response. In turn, when applied on the pedicels both ET biosynthesis (2-aminoethoxyvinylglycine; AVG) and action (norbornadiene; NBD) inhibitors reversed the stimulatory effect of ET on generative organ separation. In order to determine ET role in the flower abscission process in L. luteus, we identified the sequences coding for synthase (LlACS) and oxidase (LlACO) of ACC and measured their expression levels. Abscission zone activation is accompanied by a considerable increase both in LlACS and LlACO cDNAs and also ACC content, which is specifically localized in the dividing cells at the base of the flower being detached. Obtained results suggest that ET is a strong stimulator of flower abortion in L. luteus.
In this study, the first ACC oxidase (PnACO1) cDNA from model short-day plant Pharbitis nil was isolated. The expression pattern of PnACO1 was studied under different conditions (photoperiod and auxin), an adequate balance of which determines P. nil flowering. It was shown that the gene was transcribed in all the examined organs of the 5-day-old seedling and was strongly activated by auxin. Our results also revealed that PnACO1 transcript accumulation in the cotyledons showed diurnal oscillations under both LD and SD conditions. On the basis of presented and previously obtained data, we suggest that flowering inhibition evoked by IAA in P. nil results from its stimulatory effect on both ACC synthase and oxidase gene expression and, consequently, enhances ethylene production.
The great agronomic potential of Lupinus luteus, species widely cultivated in many European countries as well as Australia, is strongly affected by premature and excessive generative organ abscission, mainly flowers. The unwanted process takes place in a specialized group of cells, called abscission zone (AZ). During their development they become competent to respond to external and internal factors, including phytohormones. Recently it was shown that the formation of AZ cells in Arabidopsis thaliana is coordinated by transcription factors, BLADEON- PETIOLE (BOPs). There is no such data, excluding tobacco plants, about BOP-dependent regulation of organ abscission in crop plants. In this work, we examined LlBOP mRNA content during generative organs AZ development and functioning. The high accumulation of LlBOP transcript was accompanied by the differentiation of morphologically distinct cells at the base of the mature flower pedicel. Moreover, enhanced LlBOP expression was observed in the active AZ, and was regulated by factors, which can strongly affect generative organ abscission. All these data indicate that LlBOP is involved in the abscission zone formation and functioning in L. luteus.
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