Primary and secondary induction requirements for flowering of Festuca rubra

Root and shoot temperatures were varied independently to determine the importance of root temperature during cold acclimation. Spinach ( Spinacia oleracea L. cvs Harbin and Bloomsdale) plants were subjected to 20/20°C. 20/5°C, 5/20°C, and 5/5°C (shoot/root) temperature treatments. Leaf freezing tolerance, water potential, stomatal resistance, osmotic potential, and water content were measured at 0.25. 1.25, 3.25, and 7.25 days of treatment. There was no change in freezing tolerance or the water relations of the 20/20°C treated plants during the course of the experiment. Freezing tolerance was increased by the 5°C shoot temperature treatments, but was not enhanced by water stress induced by the low root temperature. Leaf water potential and water content decreased and stomatal resistance increased within 6 h in the 20/5°C plants. By day 3, osmotic potential began decreasing in the 20/5°C plants. Leaf water content, osmotic potential, and water potential decreased more gradually in plants grown with 5°C shoot temperature, irrespective of root temperature. Decreased water content and osmotic potential were not correlated with increased freezing tolerance as reported for other herbaceous crop plants.     

Primary and secondary induction requirements for flowering in Alopecurus pratensis

The critical temperature for primary induction of flowering in two Norwegian eco-types of meadow foxtail ( Alopecurus pratensis L.) was about 21°C, with 6 weeks induction period. Inflorescence primordia were initiated with increasing effectiveness as the temperature was reduced below this level in both short days (SD) and long days (LD), although SD was the more effective photoperiod at all temperatures above 6°C. The degree of primary induction was closely negatively correlated with the length of basal leaves. Culm elongation and heading (secondary induction) were promoted by LD and high temperature and inhibited by the combination of SD and low temperature. The relationship between SD primary induction and vernalization is discussed in the light of these and other results.     

Dual induction control of flowering in Leucanthemum vulgare

The perennial herb Leucanthemum vulgare (oxeye daisy) has a dual induction requirement for flowering. The primary induction is a typical low temperature vemalization response. Temperatures up to 15°C are effective, and the optimum is 6–9°C. Short days (SD) during low temperature exposure enhanced primary induction, but SD could not fully substitute for low temperature in primary induction. At optimum temperatures about 6 weeks exposure were required for 100% flowering, but the flowering response increased with increasing exposure up to 12 weeks, especially at higher temperatures. Seedling have a short juvenile phase of about 4 weeks. Populations with origin ranging from 59 to 69°N in Norway did not vary in their primary induction requirements. Long days (LD) were required for inflorescence initiation and stem elongation at 9°C. At 21 and 15°C some plants initiated and developed inflorescences in SD, but the inflorescences were sessile and their development strongly delayed. More than 16 LD cycles were required for normal stem elongation (bolting).     

Gibberellin substitution for long day secondary induction of flowering in Poa pratensis

Plants of Poa pratensis cv. Holt initiate inflorescence primordia when exposed to short days (SD) and low temperature, but require a secondary induction by at least 4 long days (LD) for further inflorescence development and stem elongation. Single or double applications of 10 µg per plant of gibberellins A₁, A₃, A₅ and 16,17‐dihydro A₅ (DHGA₅) induced inflorescence development in a high proportion of plants in SD, but only if the plants were detillered to a single stem. Exposure to 2 LD cycles did not cause heading and flowering alone but enhanced the effect of exogenous gibberellins (GAs), bringing flowering to 100%. GA₅ and DHGA₅ were less effective than GA₁ and GA₃ in SD, especially with double applications, but were more effective than GA₁ and GA₃ when given together with 2 LD. The GAs had differential effects on vegetative growth and flowering, GA₅ and DHGA₅ causing much less leaf and stem growth than the other two GAs. Marginal induction, whether by LD or GA application, resulted in a high proportion of spikelets with viviparous proliferation. Thus, whereas GAs are inhibitory to the primary induction by SD, they can replace secondary induction by LD when vegetative growth is limited.     

Polyamine translocation following photoperiodic flowering induction in soybean

Radioactivity translocation after [¹⁴C]-spermidine application over the third trifoliate leaf of soybean plants ( Glycine max . [L.] Merr, cv. Williams) was checked during the first 72 h of short day (SD) treatment to study the involvement of polyamines (PAs) in photoperiodic flowering induction. PAs and/or their metabolites were translocated from the supplied leaf to all parts of the plant. Radioactivity reached its highest concentration in the upper portion of the stem, i.e. the apical bud and the youngest leaf. After the beginning of the first inductive night, the detected radioactivity showed two peaks of maximal concentration. The first arose after the first inductive night, coinciding with the proper flowering induction process; the second one arose after the third inductive night, coinciding with the first morphological symptoms of the transition of vegetative meristems to the reproductive condition. Soluble free PAs showed a different balance in the apical bud of SD-induced plants compared with LD-non induced control plants. Soluble conjugated PAs were detected as traces. It is suggested that under flowering inductive conditions, PAs play a different role according to the stage of the flowering process. Thus, their translocation from the leaves to the axillary and apical buds might be related, in a first step, to the fact that they were part of the complex mechanism of the flowering signal, and in a second step, to the flower transition of vegetative buds.     

Cytokinins in photoperiodic induction of flowering in Chenopodium species

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non-inductive for flowering in leaves, stems, roots and apical parts of short-day Chenopodium rubrum and long-day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum , has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far-red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.     

Potent induction of Arabidopsis thaliana flowering by elevated growth temperature

The transition to flowering is an important event in the plant life cycle and is modulated by several environmental factors including photoperiod, light quality, vernalization, and growth temperature, as well as biotic and abiotic stresses. In contrast to light and vernalization, little is known about the pathways that mediate the responses to other environmental variables. A mild increase in growth temperature, from 23 °C to 27 °C, is equally efficient in inducing flowering of Arabidopsis plants grown in 8-h short days as is transfer to 16-h long days. There is extensive natural variation in this response, and we identify strains with contrasting thermal reaction norms. Exploiting this natural variation, we show that FLOWERING LOCUS C potently suppresses thermal induction, and that the closely related floral repressor FLOWERING LOCUS M is a major-effect quantitative trait locus modulating thermosensitivity. Thermal induction does not require the photoperiod effector CONSTANS, acts upstream of the floral integrator FLOWERING LOCUS T, and depends on the hormone gibberellin. Analysis of mutants defective in salicylic acid biosynthesis suggests that thermal induction is independent of previously identified stress-signaling pathways. Microarray analyses confirm that the genomic responses to floral induction by photoperiod and temperature differ. Furthermore, we report that gene products that participate in RNA splicing are specifically affected by thermal induction. Above a critical threshold, even small changes in temperature can act as cues for the induction of flowering. This response has a genetic basis that is distinct from the known genetic pathways of floral transition, and appears to correlate with changes in RNA processing.     

Developing a cognitive evaluation method for serious game engineers

Serious game is an application that has been recently designed for a specific purpose in areas such as education, healthcare, management, and engineering with the core components in games. There have been recent attempts to evaluate the effects of serious games through cognitive aspects used in empirical research, yet there are struggles for application designers to apply these cognitive neuroscientific principles to validate their proposed programs. In this paper, simple tools in cognitive psychology are introduced for analyzing serious game designs through empirical testing. The experiment is designed to investigate the effects of a tangible walking game on attention, memory, and emotion. Results revealed that the group that directly played the tangible walking game showed a slightly better performance on word recall than the control group that just watched the game. We are proposing, in this paper, an experimental method for validating a tangible walking game that can be potentially applied to other serious games. A cognitive evaluation procedure has been developed showing how to exploit simple empirical testing to validate the effectiveness of the proposed tangible game through the cognitive aspects of information processing.     

Light conditions of photoperiodic induction of flowering inChenopodium murale L. ecotype 197 - Early flowering long-day plant

A method of cultivation and effectiveness of different light sources and light regimes in photoperiodic induction of flowering in non-rosette long-day plantChenopodium murale L. ecotype 197 are described. Under the described conditions of cultivation 5 days, of continuous light produced by incandescent bulbs (TESLA 74 3x40 W, red 4.9 μWcm-²nn-¹, far-red 7.4 μWcn-2nm-¹, blue 0.25 μW cm-²nn-¹) induced flowering in the majority of plants.     

Floral induction of vegetative plants supplied a purified fraction of deoxyribonucleic Acid from stems of flowering plants

It has been found that floral induced stems of flowering tobacco (Nicotiana tabacum cv. Wis. 38) plants contain large amounts of rapidly renaturing DNA, whereas noninduced stems of vegetative plants contain only small amounts. In addition, it has been shown that the striking qualitative difference in DNA between stems of flowering and vegetative plants mimics the over-all quantitative difference in DNA content (on a fresh weight basis). Therefore, the extra DNA in stems of flowering plants seems, at least in part, to represent preferential synthesis of rapidly renaturing DNA.     

Dual induction rather than intermediate daylength response of flowering in Echinacea purpurea

Echinacea purpurea cv. Bravado and Magnus have been reported to be intermediate daylength plants (IDP) which flower in response to photoperiods between 13 and 16 h. The present experiments with E. purpurea cv. Bravado show that E. purpurea is actually a dual induction short-long-day plant which flowers promptly and consistently when grown in short day (SD) followed by long day (LD) conditions, but not with the reverse sequence of photoperiods. The flowering response increased with increasing duration of both the SD and the LD treatments. A minimum of 4 weeks of SD followed by 12 LD was required for complete flowering. No flowering occurred in continuous SD or LD, whereas a high proportion of plants flowered in continuous 14-h daylength. However, flowering was more variable in intermediate daylength than after transition from SD to LD. Furthermore, photoperiods between 13 and 16 h could satisfy both the primary SD induction and the secondary LD induction requirements. As a number of dual induction plants, both short-long-day and long-short-day plants, have such an overlapping window of effective photoperiods that can trigger both the SD and LD responses, the rationale for maintaining IDP as a separate and genuine flowering response group is seriously challenged.     

Light requirement,phytochrome and photoperiodic induction of flowering of Pharbits nil Chois

The low chlorophyll content of cotyledons of Pharbitis nil grown for 24 h in far-red light (FR) or at 18° C in white light from fluorescent lamps (WL) allows spectrophotometric measurement of phytochrome in these tissues. The (A) measurements utilize measuring beams at 730/802 nm and an actinic irradiation in excess of 90 s. The constancy of the relationship between phytochrome content and sample thickness confirms that, under these conditions of measurement, a true maximum phytochrome signal was obtained. These techniques have been used to follow changes in the form and amount of phytochrome during an inductive dark period for flowering. Following exposure to 24h WL at 18° C with a terminal 10 min red (R), P_fr was lost rapidly in darkness and approached zero in less than 1 h; during this period there was no change in the total phytochrome signal. Following exposure to 24 h FR with a terminal 10 min R, P_fr approached zero in 3 h, and the total phytochrome signal decreased by about half. The relevance of these changes to photoperiodic time measurement is discussed.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Light requirement,phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois

For dark-grown seedlings of Pharbitis nil capacity to flower in response to a single inductive dark period was established by 24 h white, far-red (FR) or ruby-red (BCJ) light and by a skeleton photoperiod of 10 min red (R)-24 h dark-10 min R. FR alone was ineffective without a brief terminal (R) irradiation, confirming that the form of phytochrome immediately prior to darkness is a crucial factor for flowering in Pharbitis. The magnitude of the flowering response was significantly greater after 24 h FR or white light (WL) (at 18° C and 27° C) than after two brief skeleton R irradiations, but the increased flowering response was not attributable to photosynthetic CO₂ uptake because this could not be detected in seedlings exposed to 24 h WL at 18° C. Photophosphorylation could have contributed to the increased flowering response as photosystem I fluorescence was detectable in plants exposed to FR, BCJ, or WL, but there were large differences between flowering response and photosystem I capacity as indicated by fluorescence. We conclude that phytochrome plays a major role in photoresponses regulating flowering. There was no simple correlation between developmental changes, such as cotyledon expansion and chlorophyll formation during the 24-h irradiation period, and the capacity to flower in response to a following inductive dark period. Changes in plastid ultrastructure were considerable in light from fluorescent lamps and there was complete breakdown of the prolamellar body with or without lamellar stacking at 27 or 18° C, respectively, but plastid reorganization was minimal in FR-irradiated seedlings.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing from of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Pyridine nucleotides and redox-charge evolution during the induction of flowering in spinach leaves

In the long-day plant Spinacia oleracea changes in the pool size of pyridine nucleotides have been followed under different photoperiodic conditions. In short days (vegetative state), the dark and light phases of the cycle are characterized by specific reciprocal changes in NAD and NADP pool sizes. As a consequence, the ratios of NADH/NAD+NADH and NADPH/NADP+NADPH, which are respectively considered to represent the catabolic and anabolic state of metabolism, also show a characteristic pattern. Upon transfer to continuous light, i.e. during floral induction, a decrease in anabolic metabolism is paralleled by an increase in catabolic metabolism. In the floral state, both the catabolic and the anabolic couples of the pyridine nucleotides are considerably depressed, possibly reflecting the enhanced senescence of induced leaves. The results are discussed in relation to the involvment of the nucleotides in stoichiometric coupling of metabolic compartments at the cellular level in response to environmental signals.     

Gibberellic acid signaling is required for ambient temperature‐mediated induction of flowering in Arabidopsis thaliana

Distinct molecular mechanisms integrate changes in ambient temperature into the genetic pathways that govern flowering time in Arabidopsis thaliana. Temperature‐dependent eviction of the histone variant H2A.Z from nucleosomes has been suggested to facilitate the expression of FT by PIF4 at elevated ambient temperatures. Here we show that, in addition to PIF4, PIF3 and PIF5, but not PIF1 and PIF6, can promote flowering when expressed specifically in phloem companion cells (PCC), where they can induce FT and its close paralog, TSF. However, despite their strong potential to promote flowering, genetic analyses suggest that the PIF genes seem to have only a minor role in adjusting flowering in response to photoperiod or high ambient temperature. In addition, loss of PIF function only partially suppressed the early flowering phenotype and FT expression of the arp6 mutant, which is defective in H2A.Z deposition. In contrast, the chemical inhibition of gibberellic acid (GA) biosynthesis resulted in a strong attenuation of early flowering and FT expression in arp6. Furthermore, GA was able to induce flowering at low temperature (15°C) independently of FT, TSF, and the PIF genes, probably directly at the shoot apical meristem. Together, our results suggest that the timing of the floral transition in response to ambient temperature is more complex than previously thought and that GA signaling might play a crucial role in this process.