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

Seabird colony effects on soil properties and vegetation zonation patterns on King George Island, Maritime Antarctic

Seabirds are among the most important vectors transferring biogenic compounds from the sea onto land in the polar regions and, consequently, influencing the properties of soil and vegetation. We studied the influence of bird colonies (Adélie penguin Pygoscelis adeliae, gentoo penguin P. papua and giant petrels Macronectes giganteus) on soil properties and plant communities on King George Island, Maritime Antarctic. We designated seven transects, each starting from the colony edge and running to a natural boundary feature, which were divided into contiguous sample plots where we identified specific plant taxa (Prasiola crispa, Deschampsia antarctica, Colobanthus quitensis, Usnea sp.), as well as hydrophilous and xerophilous ecological groups of mosses. Based on percentage contributions of each of these taxa, we distinguished six distinct vegetation zones along the transects, in which we measured physical (moisture, conductivity and pH) and chemical (NO3 −, NO2 −, NH4 +, K+ and PO4 3− content) soil parameters. Our study confirmed that, with increasing distance from bird colonies, the concentration of nutrients and soil conductivity decreased, while pH increased. The vegetation zones were clearly related to this gradient of seabird colony influence and occurred in the same sequence for all three bird species examined, although the largest colony of Adélie penguins had the strongest effect on vegetation. Similarly, the physical and chemical soil properties did not differ significantly between the colonie

Participation of labile and stabile phytochrome in the control of chlorophyll accumulation during the deetiolation of oat seedlings

The effect of the phytochrome system on the accumulation rate of chlorophyll-a and b in 96-hour-old oat seedlings during the first 3 hours of white light action was investigated. It was established that initial irradiation with red light stimulated the accumulation rate of both forms of chlorophyll. This effect depended on the level of the PFR form of phytochrome obtained during the initial irradiation and it reached the treshold value in the case of about 20% of PFR in relation to PR in etiolated seedlings. Far red light stimulated only the accumulation of chlorophyll-a. The effect of red light was reversible if far red light was applied directly after red light. The reversibility diminished gradually together with the extension of the dark period between red and far red light, disappearing completely after 6 hours. The results suggest the participation of two pools of phytochrome - a labile and a stabile one - in the reaction stimulating chlorophyll accumulation. A model of labile phytochrome action through the destruction products of phytochrome is proposed

Phytochrome and endogenous gibberellin-like substances in etiolated and irradiated oat seedlings

The level of gibberellin-like substances was investigated in oat coleoptiles with different stationary states of phytochrome and in leaf segments which had been etiolated and irradiated with red light. Etiolated coleoptiles and leaves containing maximum amounts of the PR form of phytochrome were characterized by an increased level of bound gibberellins. Irradiation with red light resulting in the photoconversion of phytochrome into the Pt R form caused the appearance of a high content of free gibberellins. It seems that the releasing the hormones from bound forms correlated with the formation of phytochrome PFR may be an important aspect of the mechanism of phytochrome action in the processes of seedling deetiolation. The interrelation between phytochrome and plant hormones in the control of photomorphogenesis of young monocotyledonous seedlings is also discussed

The effect of exogenous acetylcholine and other cholinergic agents on photoperiodic flower induction of Pharbitis nil

Exogenous acetylcholine (ACh), acetylcholinesterase (AChE) inhibitors, as well as agonists and antagonists of ACh receptors applied on the cotyledons of 5-day-old seedlings of Pharbitis nil during a 16-hour long inductive night or during a 12-hour long subinductive night, do not essentially influence the flower bud formation. Also the application of above mentioned substances to the seedlings growing under the conditions of 72 hours of darkness, 24 hours of light and then 24 hours of darkness does not influence in an essential way flowering of P. nil. On the other hand, applying these substances on the cotyledons of P. nil during 24-hour-long inductive night, preceded by 72 hours of darkness and then 24 hours of light of lowered intensity finished by 15-minute-long impulse of far red light which inhibit flowering, caused the reversion of the effect of far red light irradiation and stimulated the flowering. The obtained results suggest that endogenous system ACh/AChE could participate in the mechanism of a phytochrome controlled flowering of short day plants

IAA in the control of photoperiodic flower induction of Pharbitis nil chois

The endogenous content of IAA in the cotyledons of Pharbitis nil is low before and during the first half of the inductive 16-h-long dark period. From the 8th to the 12th hour the level of IAA increased and then again was going down at the end of a dark period. Exogenous IAA applied to the cotyledones before and during the first half of the inductive dark period inhibits flower bud formation. The application of IAA to shoot apex also resulted in the inhibition of flowering. Experiments with TIBA, an auxin polar transport inhibitor, and PCIB, an auxin action inhibitor, have shown that auxin polar transport in cotyledones and long-distance auxin transport from cotyledones to shoot apex play an important role in IAA inhibition of flower bud formation. It suggests that auxins play their role not only at the level of floral induction in cotyledones, but also in the later events of floral evocation and differentiation in shoot apex