Karen K. Tanino

Temperature-driven plasticity in growth cessation and dormancy development in deciduous woody plants: a working hypothesis suggesting how molecular and cellular function is affected by temperature during dormancy induction

The role of temperature during dormancy development is being reconsidered as more research emerges demonstrating that temperature can significantly influence growth cessation and dormancy development in woody plants. However, there are seemingly contradictory responses to warm and low temperature in the literature. This research/review paper aims to address this contradiction. The impact of temperature was examined in four poplar clones and two dogwood ecotypes with contrasting dormancy induction patterns. Under short day (SD) conditions, warm night temperature (WT) strongly accelerated timing of growth cessation leading to greater dormancy development and cold hardiness in poplar hybrids. In contrast, under long day (LD) conditions, low night temperature (LT) can completely bypass the short photoperiod requirement in northern but not southern dogwood ecotypes. These findings are in fact consistent with the literature in which both coniferous and deciduous woody plant species’ growth cessation, bud set or dormancy induction are accelerated by temperature. The contradictions are addressed when photoperiod and ecotypes are taken into account in which the combination of either SD/WT (northern and southern ecotypes) or LD/LT (northern ecotypes only) are separated. Photoperiod insensitive types are driven to growth cessation by LT. Also consistent is the importance of night temperature in regulating these warm and cool temperature responses. However, the physiological basis for these temperature effects remain unclear. Changes in water content, binding and mobility are factors known to be associated with dormancy induction in woody plants. These were measured using non-destructive magnetic resonance micro-imaging (MRMI) in specific regions within lateral buds of poplar under SD/WT dormancing inducing conditions. Under SD/WT, dormancy was associated with restrictions in inter- or intracellular water movement between plant cells that reduces water mobility during dormancy development. Northern ecotypes of dogwood may be more tolerant to photoinhibition under the dormancy inducing LD/LT conditions compared to southern ecotypes. In this paper, we propose the existence of two separate, but temporally connected processes that contribute to dormancy development in some deciduous woody plant: one driven by photoperiod and influenced by moderate temperatures; the other driven by abiotic stresses, such as low temperature in combination with long photoperiods. The molecular changes corresponding to these two related but distinct responses to temperature during dormancy development in woody plants remains an investigative challenge.

Warm temperature accelerates short photoperiod-induced growth cessation and dormancy induction in hybrid poplar (Populus × spp.).

There is increasing evidence that temperature, in addition to photoperiod, may be an important factor regulating bud dormancy. The impact of temperature during growth cessation, dormancy development, and subsequent cold acclimation was examined in four hybrid poplar clones with contrasting acclimation patterns: ‘Okanese’—EARLY, ‘Walker’—INT1, ‘Katepwa’—INT2, and ‘Prairie Sky’—LATE. Four day–night temperature treatments (13.5/8.5, 18.5/13.5, 23.5/8.5, and 18.5/3.5°C) were applied during a 60-day induction period to reflect current and predicted future annual variation in autumn temperature for Saskatoon, SK. Warm night temperature (18.5/13.5°C) strongly accelerated growth cessation, dormancy development, and cold acclimation in all four clones. Day temperature had the opposite effect of night temperature. Day and night temperatures appeared to act antagonistically against each other during growth cessation and subsequent dormancy development and cold acclimation. Growth cessation, dormancy development, and cold acclimation in EARLY and LATE were less affected by induction temperature than INT1 and INT2 suggesting that genotypic variations exist in response to temperature. Separating specific phenological stages and the impact by temperature on each clone revealed the complexity of fall phenological changes and their interaction with temperature. Most importantly, future changes in temperature may affect time to growth cessation, subsequently altering the depth of dormancy and cold hardiness in hybrid poplar.

Plant cold hardiness: from the laboratory to the field.

Section One The Freezing Process Section Two Molecular Basis for the Acquisition of Freezing Tolerance Section Three Linkage Between Developmental Arrest and Cold Hardiness Section Four Genetic Basis of Superior Cold Tolerance Section Five Impact of Global Climate Change on Plants Section Six From the Lab to the Field: Bridging the Gap Section Seven Photosynthesis and Signalling Section Eight Systems Biology.

Hormones and Endodormancy Induction in Woody Plants

Summary The scope of this review is limited to hormonal involvement in the induction of woody bud endodormancy and does not address dormancy maintenance or release. Knowledge of hormonal regulation of processes has become increasingly more complex, particularly with recent findings of auxin- and ethylene-triggered abscisic acid induction revealing many more responses mediated by ABA than originally considered. The intent of this review is to provide an account of the current state of knowledge of hormones in bud dormancy research within an historical context with a focus on promising avenues of research. While hormones are undoubtedly involved at some point during dormancy induction, meaningful progress in unraveling the mechanism of endo-dormancy-induction is difficult through this hormone-centered approach. The path to dormancy acquisition is a continuum. In many plants, this path begins far earlier than the traditionally-examined autumn period. Aside from more useful hormonal localization studies within the bud and utilization of mutants, continued gross analysis of hormone presence/absence during dormancy induction may not be fruitful. Examining the regulation of the early molecular switch within key cells of the apical meristem or subtending tissues may provide greater insight into dormancy induction. Turgor pressure-dependent cellular differentiation within the apical meristem and the extrinsic and intrinsic factors regulating turgor may be central to that molecular switch. Simpler model systems may need to be utilized to test these hypotheses. Only then can the potential role of hormones in endodormancy induction be more clearly articulated.

Synchrotron Radiation Sheds Fresh Light on Plant Research: The Use of Powerful Techniques to Probe Structure and Composition of Plants

While synchrotron radiation is a powerful tool in material and biomedical sciences, it is still underutilized in plant research. This mini review attempts to introduce the potential of synchrotron-based spectroscopic and imaging methods and their applications to plant sciences. Synchrotron-based Fourier transform infrared spectroscopy, X-ray absorption and fluorescence techniques, and two- and three-dimensional imaging techniques are examined. We also discuss the limitations of synchrotron-based research in plant sciences, specifically the types of plant samples that can be used. Despite limitations, the unique features of synchrotron radiation such as high brightness, polarization and pulse properties offer great advantages over conventional spectroscopic and imaging tools and enable the correlation of the structure and chemical composition of plants with biochemical function. Modern detector technologies and experimental methodologies are thus enabling plant scientists to investigate aspects of plant sciences such as ultrafast kinetics of biochemical reactions, mineral uptake, transport and accumulation, and dynamics of cell wall structure and composition during environmental stress in unprecedented ways using synchrotron beamlines. The potential for the automation of some of these synchrotron technologies and their application to plant phenotyping is also discussed.

The Method of ABA Application Affects Salt Stress Responses in Resistant and Sensitive Potato Lines

The phytohormone abscisic acid (ABA) has been proposed to act as a mediator in plant responses to a range of stresses, including salt stress. Most studies of ABA response apply ABA as a single dose. This may not resemble the prolonged increasing endogenous ABA levels that can occur in association with slowly increasing salinity stresses in nature or field situations. Salt stress response based on method of ABA application was examined in four potato genotypes of varying salt stress resistance: the sensitive ABA-deficient mutant and its normal sibling, a resistant genotype line 9506, and commercial cultivar ‘Norland’ of moderate resistance. ABA was applied by root drench at 0, 50, 75, or 100 μM concentrations through a single dose, or by slowly increasing multiple ABA doses in a sand-based growing system under greenhouse conditions. Salt tolerance was then evaluated after 2 weeks of exposure to 150–180 mM NaCl stress. The method of ABA application had a marked effect on the responses to salt stress. Plant responses to the method of ABA application were differentiated according to (1) growth rate, (2) root water content, and (3) apparent shoot growth response. Under a single dose, growth rate increased in all genotypes under salt stress, whereas slowly increasing multiple ABA applications generally maintained stable growth rates except in the ABA-deficient mutant where there was an upward growth trend. Percent root water content was elevated only under slowly increasing multiple ABA doses in two genotypes, whereas none of the single-dose treatments induced any change. The single ABA dose enhanced vertical growth, whereas the slowly increasing multiple ABA dose applications enhanced lateral shoot growth. Because exogenous application is still an artificial system, endogenous ABA was supplied through grafting of ABA-deficient mutant scions onto rootstocks with known elevated ABA levels. Multiple exogenous ABA applications as low as 50 μM elicited similar shoot water content responses as grafting treatments without ABA application in the mutant genotype but had no effect on the ABA normal sibling. Shoot dry weight was significantly increased through grafting over all exogenous ABA treatments. Our study further indicates that the method of ABA application regime in itself can alter plant responses under salt stress and that certain application regimes may reflect responses to elevated endogenous levels of ABA.

Paclobutrazol enhances minituber production in Norland potatoes

The effect of two plant growth regulators, paclobutrazol and kinetin, on minituber yield in greenhouse-grown “Norland” potatoes was investigated. Plants were treated with paclobutrazol at 450 mg/L, kinetin at 10 mg/L, or a combination of paclobutrazol at 450 mg/L + kinetin at 10 mg/L as single foliar applications at early stolon initiation. A set of plants sprayed with water served as the control. The experiment was conducted twice. In both cases, paclobutrazol nearly doubled the number of usable tubers/plant without affecting total tuber yield. Kinetin had no effect either on tuber number or tuber weight. Kinetin applied as a combination with paclobutrazol decreased the effectiveness of paclobutrazol on tuber number by 13–20%. Paclobutrazol treatments prolonged tuber dormancy by approximately 3 weeks. The results suggest that paclobutrazol treatment would be effective in enhancing potato minituber production under greenhouse conditions.

Abscisic Acid-Induced Cellular Alterations During the Induction of Freezing Tolerance in Bromegrass Cells

Summary Cellular alterations in bromegrass ( Bromus inermis Leyss cv Manchar) cell suspension cultures were characterized at different hardiness levels using fluorescence and transmission electron microscopy. After one day, when cells treated with abscisic acid (ABA) were 5 °C hardier than control cells, the hardier cells exhibited greater numbers of vacuoles and lipid bodies. However, no changes were observed in cell-wall thickness or cell size. Vacuole size in ABA-treated cells were equally distributed among three size classes, whereas control cells had a higher proportion of large vacuoles. Conversely, the lipid bodies in cells exposed to ABA treatment were consistently smaller than those in control cells. After 7 treatment days when hardiness had increased to -28 °C, the walls of ABA treated cells were significantly thicker than the control cells. The differences observed in lipid bodies after one day were accentuated in the hardier ABA treated cells after 7 days. The size of lipid bodies decreased and their numbers increased by a factor of ten. Osmiophilic granules and golgi apparati became more prevalent near the plasma membrane in the more frost tolerant cells. Cell-wall and protoplasm autofluorescence increased in response to ABA treatment and were quenched by methanol: chloroform extraction. These results show that ABA treatments at room temperature elicit ultrastructural changes associated with hardiness that are similar to those reported after low temperature acclimation.

Stomatal Responses to Drought Stress and Air Humidity

Water is one of the most important substances for both plant and animal survival. Plants require water for photosynthesis, nutrient uptake and transportation as well as cooling (Farooq et al., 2009). Plants are sessile organisms and in contrast to most animals they are unable to move when the environment becomes unfavorable. Accordingly, plants have to be able to respond and adapt to the local environmental changes. Since water is essential for plant survival, the ability to tolerate water stress is crucial. To be able to grow plants need to take up water from the soil and CO2 from the atmosphere and use it in photosynthesis. This is done by CO2 uptake through the stomatal pore, where water is simultaneously transpired. Water transpiration drives the water uptake by the roots and transport through the xylem. When the stomata are open CO2 is taken up while water is transpired. When the stomata are closed little CO2 is taken up and the transpiration is lowered. By opening and closing the stomata plants can regulate the amount of water lost, by sacrificing CO2 uptake, when the environmental conditions are unfavorable. Water stress can be defined as reduced water availability; either by water scarcity (drought) or osmotic stress (high salt concentrations) or water logging; too much water. Water stress may reduce photosynthesis, respiration and ion uptake, change the metabolic and growth patterns in the plant and in severe cases result in plant death (Jaleel et al., 2009a). In nature water stress is common either for long or short periods of time, depending on the local climate. Most plants therefore have some adaptation or response to enhance the growth and survival rate during water stress and subsequent recovery. In agriculture and horticulture drought stress is one of the major problems, causing major crop losses every year as well as loss of aesthetic value in ornamentals. In agriculture crop loss is due to reduced numbers of tillers, spikes and grains per plant and reduced grain weight (Farooq et al., 2009). With the global human population rapidly increasing, simultaneously as water scarcity increases, the loss of crop will be even more serious than before. The discovery and development of stress tolerant crops to avoid yield loss during water stress is therefore very important. In the greenhouse industry, energy saving for economic profit is important to be able, but it also affects the plants. To reduce the amount of energy needed for CO2 and heating in the greenhouses, energy-efficient semi-closed

Effect of Pot Size and Timing of Plant Growth Regulator Treatments on Growth and Tuber Yield in Greenhouse-Grown Norland and Russet Burbank Potatoes

Abstract. The effects of pot size, timing of the application of paclobutrazol (PTZ) and gibberellic acid (GA3), and the counteractive effect of these two compounds on growth and tuber yield of greenhouse-grown Norland and Russet Burbank potatoes were investigated. Plants were grown either in 1.5-liter pots (15 cm deep) or 3.0-liter pots (18 cm deep) and received a foliar application of either 1.5 mm PTZ or 9 × 10−3 mm GA3 at early or late stolon initiation. Some plants that had been foliar treated with 1.5 mm PTZ at early stolon initiation were foliar treated with 9 × 10−3 mm GA3 at late stolon initiation. PTZ reduced haulm length in both cultivars significantly, particularly when the treatment was applied at early stolon initiation, but the late treatment reduced haulm length only when growing in 3.0-liter pots. Irrespective of the timing of treatment, GA3 increased haulm length in Norland growing in both pot sizes, but the treatment increased haulm length in Russet Burbank only when applied at late stolon initiation. GA3 applied after PTZ did not overcome the growth-inhibiting effect of the PTZ treatment. The PTZ treatment effectively increased usable tuber number/plant (UTN) in Norland, but PTZ had no effect on UTN in Russet Burbank. PTZ reduced usable tuber weight/plant (UTW) only in Norland growing in 1.5-liter pots. By contrast, GA3 increased UTN only when treated at late stolon initiation of 1.5-liter pot-grown Norland, whereas the same treatment was effective when applied only at early stolon initiation for Russet Burbank. For Norland, the increase in UTN by early applied PTZ was reduced by the subsequent application of GA3. The use of 3.0-liter pots for minituber production in both Norland and Russet Burbank appears to have no advantage over growing in 1.5-liter pots, particularly when PTZ or GA3 is used to enhance tuberization.