Effect of harvest date on the dormancy period of yam (Dioscorea rotundata)

Tuber dormancy enables yams to survive in the ground during the dry season and post-harvest storage. Three clones of Dioscorea rotundata were harvested after five intervals and then stored in a cooler (20.6°C) or at ambient temperature (27.8°C). The time from harvest to sprouting was shorter as harvest was delayed. The period from sowing to sprouting for each clone was similar for tubers harvested from 140 days after planting, but tubers harvested earlier took longer to sprout. The cooler temperature delayed sprouting. Tubers of two clones sprouted after only 70 days of crop growth. If the dormancy period of these young tubers can be broken, the generation time of yam crop improvement programmes could be considerably reduced.

Phases of dormancy in yam tubers (Dioscorea rotundata)

Background and Aims The control of dormancy in yam (Disocorea spp.) tubers is poorly understood and attempts to shorten the long dormant period (i.e. cause tubers to sprout or germinate much earlier) have been unsuccessful. The aim of this study was to identify and define the phases of dormancy in Dioscorea rotundata tubers, and to produce a framework within which dormancy can be more effectively studied. center dot Methods Plants of 'TDr 131' derived from tissue culture were grown in a glasshouse simulating temperature and photoperiod at Ibadan (7 degrees N), Nigeria to produce tubers. Tubers were sampled on four occasions: 30 d before shoot senescence (149 days after planting, DAP), at shoot senescence (179 DAP), and twice during storage at a constant 25 degrees C (269 and 326 DAP). The development of the apical shoot bud was described from tissue sections. In addition, the responsiveness of shoot apical bud development to plant growth regulators (gibberellic acid, 2-chloroethanol and thiourea) applied to excised tuber sections was also examined 6 and 12 d after treatment. center dot Key Results and Conclusions Three phases of tuber dormancy are proposed: Phase I, from tuber initiation to the appearance of the tuber germinating meristem; Phase II, from the tuber germinating meristem to initiation of foliar primordium; and Phase III, from foliar primordium to appearance of the shoot bud on the surface of the tuber. Phase I is the longest phase (approx. 220 d in 'TDr 131'), is not affected by PGRs and is proposed to be an endo-dormant phase. Phases II and III are shorter (< 70 d in total), are influenced by PGRs and environmental conditions, and are therefore endo-/eco-dormant phases. To manipulate dormancy to allow off-season planting and more than one generation per year requires that the duration of Phase I is shortened.

In vitro micro-tuber initiation and dormancy in yam

Dormancy is a mechanism that regulates the timing of sprouting (germination) of affected plant parts as well as ensures that the food quality of edible parts is maintained in storage until the following growing season. In yam, however, little is known about the control of tuber initiation or tuber dormancy. The objective of this study was to determine the effects of selected plant growth regulators (PGRs) on tuber initiation and dormancy, using an in vitro system. In two replicated experiments, 2-chloroethylphosphonic acid (ethephon, an ethylene source), abscisic acid (ABA) and gibberellin (GA3) – and their inhibitors silver nitrate, fluridone and 2-chloroethyl-trimethylammonium chloride, respectively – were added at two concentrations to the culture medium prior to explant culture. Dates of micro-tuber initiation and sprouting (end of dormancy) and tuber number were recorded. In the control (no PGR) in Experiment 1, micro-tubers were initiated at the base of the stem after 176 days and sprouted 235 days later, that is 411 days after culturing. Most PGR treatments had only small effects (±30 days) on the duration of dormancy and the time of micro-tuber initiation. However, in GA3 micro-tuber initiation occurred after 76 days, about 100 days earlier than in the control, whereas fluridone affected the position of micro-tubers and duration of dormancy. With fluridone treatments, tubers were found at the base of the stem (normal position) and on lower and upper nodes. Lower node tubers sprouted within 225 days of culturing compared with about 420 days after culturing at other nodal positions and in other PGR treatments. These data suggest an important role for ABA and gibberellic acid in yam micro-tuber initiation and the induction of dormancy.

Ecophysiology of seed dormancy and the control of germination in early spring-flowering Galanthus nivalis and Narcissus pseudonarcissus (Amaryllidaceae)

Seed dormancy induction and alleviation in the winter-flowering moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus are complex and poorly understood. Temperature, light and desiccation were investigated to elucidate their role in the germination ecophysiology of these species. Outdoor and laboratory experiments simulating different seasonal temperatures, seasonal durations, and temperature fluctuations; the presence of light during different seasons; and intermittent drying (during the summer period) over several ‘years’ investigated the importance of these factors in germination. Warm summer-like temperatures (20°C) were necessary for germination at subsequent cooler autumn-like temperatures (greatest at 15°C in G. nivalis and 10°C in N. pseudonarcissus). As the warm temperature duration increased so did germination at subsequent cooler temperatures; further germination occurred in subsequent ‘years’ at cooler temperatures following a second, and also third, warm period. Germination was significantly greater in darkness, particularly in G. nivalis. Dormancy increased with seed maturation period in G. nivalis, because seeds extracted from green capsules germinated more readily than those from yellow. Desiccation increased dormancy in an increasing proportion of N. pseudonarcissus seeds the later they were dried in ‘summer’. Seed viability was only slightly reduced by desiccation in N. pseudonarcissus but was poor and variable in G. nivalis. Shoot formation occurred both at the temperature at which germination was greatest and also if 5°C cooler. In summary, continuous hydration of seeds of both species during warm summer-like temperatures results in the gradual release of seed dormancy; thereafter, darkness and cooler temperatures promote germination. Cold temperatures, increased seed maturity (G. nivalis), and desiccation (N. pseudonarcissus) increase dormancy while light inhibits germination.

Gas exchange and ventilation during dormancy in the tegu lizard Tupinambis merianae

The tegu lizard Tupinambis merianae exhibits an episodic ventilatory pattern when dormant at 17 degrees C but a uniform ventilatory pattern when dormant at 25 degrees C. At 17 degrees C, ventilatory episodes were composed of 1-22 breaths interspaced by non-ventilatory periods lasting 1.8-26min, Dormancy at the higher body temperature was accompanied by higher rates of O-2 consumption and ventilation. The increase in ventilation was due only to increases in breathing frequency with no change observed in tidal volume. The air convection requirement for O-2 did not differ at the two body temperatures. The respiratory quotient was 0.8 at 17 degrees C and 1.0 at 25 degrees C. We found no consistent relationship between expired gas composition and the start/end of the ventilatory period during episodic breathing at 17 degrees C. However, following non-ventilatory periods of increasing duration, there was an increase in the pulmonary O-2 extraction that was not coupled to an equivalent increase in elimination of CO2 from the lungs. None of the changes in the variables studied could alone explain the initiation/termination of episodic ventilation in the tegus, suggesting that breathing episodes are shaped by a complex interaction between many variables. The estimated oxidative cost of breathing in dormant tegus at 17 degrees C was equivalent to 52.3% of the total metabolic rate, indicating that breathing is the most costly activity during dormancy.

On the germination and dormancy of dispersal units of Brachiaria decumbens STAPF

The effect of light and temperature on germination of Brachiaria decumbens as well as the action of some dormancy breaking chemicals were tested. Two seed batches stored different times were used. The results show that seeds failed to respond to alternating temperature regimes and different light qualities. Seeds were indifferent to white light at 25 degrees C. KNO3, ethanol and H2SO4 failed to break seed dormancy, whereas KCN and H2O2 partially reduced dormancy of two month stored seeds. The results suggest a metabolic character of dormancy in ''new'' (freshly collected) seeds and confirm the occurence of two types of dormancy in B. decumbens seeds.

On the germination and dormancy of dispersal units of Brachiaria decumbens staff

The effect of light and temperature on germination of Brachiaria decumbens as well as the action of some dormancy breaking chemicals were tested. Two seed batches stored different times were used. The results show that seeds failed to respond to alternating temperature regimes and different light qualities. Seeds were indifferent to white light at 25°C. KNO3, ethanol and H2SO4 failed to break seed dormancy, whereas KCN and H2O2 partially reduced dormancy of two month stored seeds. The results suggest a metabolic character of dormancy in new (freshly collected) seeds and confirm the occurence of two types of dormancy in B. decumbens seeds.

Germinative pretreatments to dormancy break in Guazuma ulmifolia Lam. seeds

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Cardiac hypertrophy and structural and metabolic remodeling related to seasonal dormancy in the first annual cycle in tegu lizards

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Dormancy breaking of the fig tree with hydrogen cyanamide and garlic extrate

The supply of cold hours needed to the dormancy breaking of shoots is the limiting factor for the cultivation of temperate climate fruit trees in warmer regions. In subtropical conditions, it is necessary to use chemical products to promote uniform sprouting. This research aimed at evaluating the effect of garlic extract and hydrogen cyanamide in sprouting, growth, production and production cycle of the fig tree. The experiment was conducted during the production cycles of 2011/12 and 2012/13. We used plants from the cultivar Roxo de Valinhos. Production pruning was made in the months of July/2011 and July/2012, and the following treatments were applied immediately after it: 2% hydrogen cyanamide and garlic extract in 4%, 8% and 12% doses, and a control treatment. Split plots were used as the experimental design, with five repetitions in blocks; each plot consisted of five treatments with hydrogen cyanamide, garlic extract and control; the subplots consisted of two production cycles. The use of hydrogen cyanamide promoted an anticipation of sprouting and the use of hydrogen cyanamide and garlic extract promoted a concentration of the productive period, when compared to the control. The estimated garlic extract dose that promoted the highest production per plant was 3%.

Phenolic compounds influence seed dormancy of palicourea rigida h.b.k. (rubiaceae), a medicinal plant of the brazilian savannah

Palicourea rigida H.B.K. (Rubiaceae), a medicinal species commonly known as douradinha, has wide distribution across ecosystems in Central and South America. This species exhibits seed dormancy delaying germination until optimal conditions for seedling growth and development are in place. While dormancy ensures species survival, it also presents a technical problem for developing P. rigida’s plant production program. Thus, the objective of this study was to investigate if secondary metabolites present in seeds influence the seed dormancy of P. rigida. Mature fruits were harvested from the native habitat, in the savanna region of the State of Minas Gerais during February 2009, 2010 and 2011. The content of phenolic compounds in the seed of P. rigida was measured, and the allelopathic effects were assessed using the germination of lettuces as model to detect phytotoxicity. The P. rigida seeds geminated at rates varying between 7% and 31% with a Seed Germination Index (SGI) of 0.09. Data suggest that the phenolic compounds present in the seeds may be responsible for seed dormancy.

Kiwifruit bud release from dormancy: effect of exogenous cytokinins

A new formulate containing citokinins, that is commercialized as Cytokin, has been introduced as dormancy breaking agents. During a three-years study, Cytokin was applied at different concentrations and application times in two producing areas of the Emilia-Romagna region to verify its efficacy as a DBA. Cytokin application increased the bud break and showed a lateral flower thinning effect. Moreover, treated vines showed an earlier and more uniform flowering as compared to control ones. Results obtained on the productive performance revealed a constant positive effect in the fruit fresh weight at harvest. Moreover, Cytokin did not cause any phytotoxicity even at the highest concentrations. Starting from the field observation, which suggested the involvement of cytokinins in kiwifruit bud release from dormancy, 6-BA was applied in open field condition and molecular and histological analyses were carried out in kiwifruit buds collected starting from the endo dormant period up to complete bud break to compare the natural occurring situation to the one induced by exogenous cytokinin application. In details, molecular analyses were set up on to verify the expression of genes involved in the reactivation of cell cycle: cyclin D3, histone H4, cyclin-dependent kinase B, as well as of others which are known to be up regulated during bud release in other species, i.e.isopenteniltransferases (IPTs), which catalyze the first step in the CK biosynthesis, and sucrose synthase 1 and A, which are involved in the sugar supplied. Moreover, histological analyses of the cell division rate in kiwifruit bud apical meristems were performed. These analyses showed a reactivation of the cell divisions during bud release and changes in the expression level of the investigated genes.

Characterization of a glycosylase family gene specifically expressed during winter dormancy in woody plants

Winter dormancy is the strategy used by perennial plants to survive the harsh conditions of winter in temperate and cold regions. This complex mechanism is characterized by cessation of the meristems activity, which is accompanied by the budset, the acquisition of a high tolerance to the cold temperatures and, in the case of deciduous trees, by the senescence and leaf abscission. In long-lived forest species, the length of the dormancy period limits the growing season, affecting wood production and quality. A Suppression Subtractive Hybridization (SSH) enriched in genes overexpressed during the process of winter dormancy in chesnut stems identified a DNA glycosylase gene. In order to study its role in the establishment and maintenance of the winter dormancy, a molecular characterization and seasonal expression were performed. Furthermore, we have obtained poplar transgenic plantlets overexpressing the chesnut gene.

Temporal variation, dormancy, and coexistence: A field test of the storage effect

Theoretical models suggest that overlapping generations, in combination with a temporally fluctuating environment, may allow the persistence of competitors that otherwise would not coexist. Despite extensive theoretical development, this “storage effect” hypothesis has received little empirical attention. Herein I present the first explicit mathematical analysis of the contribution of the storage effect to the dynamics of competing natural populations. In Oneida Lake, NY, data collected over the past 30 years show a striking negative correlation between the water-column densities of two species of suspension-feeding zooplankton, Daphnia galeata mendotae and Daphnia pulicaria. I have demonstrated competition between these two species and have shown that both possess long-lived eggs that establish overlapping generations. Moreover, recruitment to this long-lived stage varies annually, so that both daphnids have years in which they are favored (for recruitment) relative to their competitor. When the long-term population growth rates are calculated both with and without the effects of a variable environment, I show that D. galeata mendotae clearly cannot persist without the environmental variation and prolonged dormancy (i.e., storage effect) whereas D. pulicaria persists through consistently high per capita recruitment to the long-lived stage.

Urokinase Receptor and Fibronectin Regulate the ERKMAPK to p38MAPK Activity Ratios That Determine Carcinoma Cell Proliferation or Dormancy In Vivo

We discovered that a shift between the state of tumorigenicity and dormancy in human carcinoma (HEp3) is attained through regulation of the balance between two classical mitogen-activated protein kinase (MAPK)-signaling pathways, the mitogenic extracellular regulated kinase (ERK) and the apoptotic/growth suppressive stress-activated protein kinase 2 (p38MAPK), and that urokinase plasminogen activator receptor (uPAR) is an important regulator of these events. This is a novel function for uPAR whereby, when expressed at high level, it enters into frequent, activating interactions with the α5β1-integrin, which facilitates the formation of insoluble fibronectin (FN) fibrils. Activation of α5β1-integrin by uPAR generates persistently high level of active ERK necessary for tumor growth in vivo. Our results show that ERK activation is generated through a convergence of two pathways: a positive signal through uPAR-activated α5β1, which activates ERK, and a signal generated by the presence of FN fibrils that suppresses p38 activity. When fibrils are removed or their assembly is blocked, p38 activity increases. Low uPAR derivatives of HEp3 cells, which are growth arrested (dormant) in vivo, have a high p38/ERK activity ratio, but in spite of a similar level of α5β1-integrin, they do not assemble FN fibrils. However, when p38 activity is inhibited by pharmacological (SB203580) or genetic (dominant negative-p38) approaches, their ERK becomes activated, uPAR is overexpressed, α5β1-integrins are activated, and dormancy is interrupted. Restoration of these properties in dormant cells can be mimicked by a direct re-expression of uPAR through transfection with a uPAR-coding plasmid. We conclude that overexpression of uPAR and its interaction with the integrin are responsible for generating two feedback loops; one increases the ERK activity that feeds back by increasing the expression of uPAR. The second loop, through the presence of FN fibrils, suppresses p38 activity, further increasing ERK activity. Together these results indicate that uPAR and its interaction with the integrin should be considered important targets for induction of tumor dormancy.