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Flowering of plants is controlled by hormones among which both stimulators and inhibitors are present. The role of abscisic acid (ABA) in flower induction of the short day plant Pharbitis nil was shown in our experiments through exogenous applications and endogenous level determination of the hormone in cotyledons of seedlings grown under special light conditions. The application of ABA to cotyledons or shoot apices during the first half of a 24-h long inductive night inhibits flowering. The same compound applied towards the end of or after a 14-h long subinductive night increases the number of flower buds produced by these plants. Exposing P. nil seedlings at the beginning of a 24-h long inductive night to far red light (FR) decreases the level of endogenous abscisic acid in cotyledons and leads to flower inhibition. However, a pulse of red light (R) reversing the inhibitory effect of far red light on the flowering of P. nil increases the ABA content. The results obtained confirm previous observations that ABA may play a dual and an important role in the regulation of floral bud formation in P. nil. The flowering occurs when the level of endogenous abscisic acid is low at the beginning and is high toward the end of the inductive night.
MicroRNAs regulate gene expression by guiding the cleavage or attenuating the translation of target mRNAs. In Arabidopsis thaliana, the subset of class II TCP genes (plant-specific group of transcription factors) contains an miR319-binding site. One of them, AtTCP4, regulates negatively leaf growth and positively leaf senescence. In addition, miR319 targeting of TCP4 is critical for petal and stamen development and affects flowering time. The aim of this work was to identify the cDNA of InTCP4 gene and In-miR319 precursor in Ipomoea nil (Pharbitis nil). The cDNA sequence of InTCP4 shows a significant similarity to the cDNA members of the TCP family of other plant species and contains nucleotides complementary to miR319. The identified sequence In-premiR319 creates a long hairpin structure and mature miRNA sequence is located in a similar place as in precursors found in other plant species. Accumulation of InTCP4 mRNA and In-pre-miR319 was examined in various organs of I. nil plants. We found that the InTCP4 is strongly expressed in cotyledons of I. nil seedlings while the In-premiR319 accumulates mainly in the hypocotyls of seedlings. Moreover, we investigate the role of InTCP4 in the flowering induction, flower development and cotyledon senescence in I. nil. We indicate that the InTCP4 expression is controlled by both light/clock and miR319. Both InTCP4 and InMIR319 probably participate in the regulation of such processes as do their homologues in other plant species, the development of cotyledons, leaves and flower elements. The main function of InMIR319 seems to be the regulation of InTCP4 organ localization.
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.
Interactions between methyl jasmonate (JA-Me) and ethylene in the photoperiodic flower induction of shortday plant Pharbitis nil were investigated. Both JA-Me and gaseous ethylene applied during the inductive long night caused a decrease in the number of flower buds generated by P. nil. Application of ethylene did not affected niether the level of endogenous jasmonates in the cotyledons during the 16 h long inductive night, nor the inhibitory effect of JA-Me on the flowering of P. nil accompanied by variations in ethylene production. The application of acetylsalicylic acid (aspirin)—a jasmonate biosynthesis inhibitor—slightly stimulated flowering. Our results have shown that the mechanisms of P. nil flower inhibition by jasmonates and ethylene are independent.
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.
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