Involvement of aba in flower induction of Pharbitis nil

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

The Mechanism of Calcium Action on Flower Induction in Pharbitis nil

Calcium ions, calcium ionophores A23187 and ionomycin, as well as caffeine, stimulated the flowering of Pharbitis nil when applied just before and 2 h after starting a subinductive, 14-h long dark period. Effectiveness of all the mentioned compounds decreased over successive hours and when used from 6 h after the onset of the dark period they had no effect or inhibited flowering. Intracellular calcium modulators, ryanodine and thapsigargicin, which are active in animal cells had no effect on flowering. These results suggest that an increase in free Ca2 + before and during the first 2 h of the dark period increases the flowering responses, whereas after the 6th hour it decreases it. We postulate that the targets for calcium action are stomata, which are open before the dark period and remain closed during the first 4 - 5 h of the dark period. The significance of stomata in flower induction was confirmed in experiments with abscisic acid (ABA), a plant hormone which regulates stomatal movements. Treating the cotyledons of plants with ABA at the 8th and 10th hour of the dark period, resulted in plants with about 50 % less flower buds than the control, however, this phytohormone had no effect on flowering when used before the subinductive dark period

Wounding stimulates ALLENE OXIDE SYNTHASE gene and increases the level of jasmonic acid in Ipomoea nil cotyledons

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

Auxin increases the InJMT expression and the level of JAMe – inhibitor of flower induction in Ipomoea nil

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

Genetic control of flowering of angiosperm plants

Plants have developed mechanisms to integrate both endogenous and environmental cues for regulation of flowering time. When environmental and physiological (e.g. photoperiod, temperature) (e.g. stage of development) conditions are appropriate plants undergo the floral transition and become reproductive. The timing of flowering initiation depends on the balanced expression of many different genes that are regulated by both endogenous and environmental factors. As a result of physiological, genetic, and molecular analysis of Arabidopsis thaliana mutants altered in flowering time the existence of a long-promotion pathway, a gibberellic-acid promotion pathway, as well as vernalization and autonomous pathway were discovered and characterized. A few dozen of genes invilved in flower induction of Arabidopsis were identified. Some of them can integrate two or three flowering pathways. Floral repression is likely to be the principal mechanism for maintaining vegetative development. Floral repressor inhibit the floral signaling pathways at various levels. Some of genes involved in vernalization and photoperiodic flower induction encode putative chromatin-associated proteins. They probably function as epigenetic silencers that repress promotion of flowering, and thereby maintain vegetative growth. The complete genome sequences of two plant species; Arabidopsis thaliana (long-day dicot) and Oryza sativa (short-day monocot) have been published recently. Since that time, comparative genomics andmolecular genetics on photoperiod-induced flowering process became possible. Using this approach some differences between long- and short-day plants were established at the molecular level