Abscisic acid involvement in the induction of summer‐dormancy in Poa bulbosa, a grass geophyte

Summer‐dormancy occurs in geophytes that inhabit regions with a Mediterranean climate (mild, rainy winters and hot, dry summers). The environmental control of summer‐dormancy and the involvement of phytohormones in its induction have been little studied. Poa bulbosa L. is a perennial grass geophyte in which summer‐dormancy is induced by long days and by high temperature. Prolonged treatment with ABA (0.1‐1.0 m M ) under non‐inductive 8‐h short days (SD) resulted in cessation of leaf and tiller production and in the development of typical features of dormancy: bulbing at the base of the tillers and leaf senescence. Short‐term applications of ABA had similar effects but dormancy was transient, i.e. after a short while, leaf growth from the formed bulbs was resumed. ABA treatment of plants growing under an inductive 16‐h photoperiod (LD) enhanced the onset of dormancy. Endogenous levels of ABA in leaf blades and at the tiller base (where the bulb develops) increased markedly after the plants were transferred from SD to LD. This increase was greater in the tiller base, and concomitant with bulb maturation. High temperature (27/22 vs 22/17°C) accelerated both bulb development and ABA accumulation in leaf blades.
These results suggest that ABA plays a key role in the photoperiodic induction and development of summer‐dormancy in P. bulbosa .     

Regulation of summer dormancy by water deficit and ABA in Poa bulbosa ecotypes

BACKGROUND AND AIMS: Survival of many herbaceous species in Mediterranean habitats during the dry, hot summer depends on the induction of summer dormancy by changes in environmental conditions during the transition between the winter (growth) season to the summer (resting) season, i.e. longer days, increasing temperature and drought. In Poa bulbosa, a perennial geophytic grass, summer dormancy is induced by long days, and the induction is enhanced by high temperature. Here the induction of summer dormancy in a Mediterranean perennial grass by water deficit under non-inductive photoperiodic conditions is reported for the first time. METHODS: Plants grown under 22/16 degrees C and non-inductive short-day (9 h, SD) were subjected to water deficit (WD), applied as cycles of reduced irrigation, or sprayed with ABA solutions. They were compared with plants in which dormancy was induced by transfer from SD to inductive long-day (16 h, LD). Responses of two contrasting ecotypes, from arid and mesic habitats were compared. Dormancy relaxation in bulbs from these ecotypes and treatments was studied by comparing sprouting capacity in a wet substrate at 10 degrees C of freshly harvested bulbs to that of dry-stored bulbs at 40 degrees C. Endogenous ABA in the bulbs was determined by monoclonal immunoassay analysis. KEY RESULTS: Dormancy was induced by WD and by ABA application in plants growing under non-inductive SD. Dormancy induction by WD was associated with increased levels of ABA. Bulbs were initially deeply dormant and their sprouting capacity was very low, as in plants in which dormancy was induced by LD. Dormancy was released after 2 months dry storage at 40 degrees C in all treatments. ABA levels were not affected by dormancy relaxation. CONCLUSIONS: Summer dormancy in P. bulbosa can be induced by two alternative and probably additive pathways: (1) photoperiodic induction by long-days, and (2) water deficit. Increased levels of endogenous ABA are involved in both pathways.     

Photoperiodic control of dormancy in Sedum telephium and some other herbaceous perennial plants

The environmental control of dormancy and flowering of the herbaceous perennial Sedum telephium was studied in controlled environments. Short photoperiods induced growth cessation and the formation of resting buds in both seedlings and mature plants, whereas long photoperiods resulted in immediate growth activation of dormant buds. No chilling was required for dormancy release, even in plants induced to dormancy and maintained at high temperature (21°C) for more than 3 months. The critical photoperiod for dormancy release was about 15 h, a minimum of four long-day (LD) cycles (24 h) being required. The true photoperiodic nature of this response was ascertained by night interruption experiments. Flowering of S. telephium was found to have an obligatory LD requirement, with no requirement for vernalization. The critical photoperiod and minimum number of inductive cycles for floral induction were the same as for dormancy release. Dormancy release by long days was also obtained in preliminary experiments with three other herbaceous perennials. The eco-physiological significance of photoperiodic control of dormancy is discussed, and it is concluded that the mechanism ensures stability of winter dormancy, even under conditions of climatic warming.     

Proteomic analysis of shoot tissue during photoperiod induced growth cessation in <Emphasis Type="Italic">V. riparia</Emphasis> Michx. grapevines

Background  

Growth cessation, cold acclimation and dormancy induction in grapevines and other woody perennial plants native to temperate continental climates is frequently triggered by short photoperiods. The early induction of these processes by photoperiod promotes winter survival of grapevines in cold temperate zones. Examining the molecular processes, in particular the proteomic changes in the shoot, will provide greater insight into the signaling cascade that initiates growth cessation and dormancy induction. To begin understanding transduction of the photoperiod signal, Vitis riparia Michx. grapevines that had grown for 35 days in long photoperiod (long day, LD, 15 h) were subjected to either a continued LD or a short photoperiod (short day, SD, 13 h) treatment. Shoot tips (4-node shoot terminals) were collected from each treatment at 7 and 28 days of LD and SD for proteomic analysis via two-dimensional (2D) gel electrophoresis.     

Opposite effects of daylength and temperature on flowering and summer dormancy of Poa bulbosa

BACKGROUND AND AIMS: The timing of flowering and summer dormancy induction plays a central role in the adaptation of Mediterranean geophytes to changes in the length of the growth season along rainfall gradients. Our aim was to analyse the role of the variation in the responses of flowering and summer dormancy to vernalization, daylength and growth temperature for the adaptation of Poa bulbosa, a perennial geophytic grass, to increasing aridity. METHODS: Flowering and dormancy were studied under controlled daylengths [9 h short day (SD) vs. 16 h long day (LD)] and temperatures (16/10, 22/16 and 28/22 degrees C day/night) in four ecotypes originating in arid, semi-arid and mesic habitats (110, 276 and 810 mm rain year(-1), respectively) and differing in flowering capacity under natural conditions: arid-flowering, semi-arid-flowering, semi-arid-non-flowering and mesic-non-flowering. KEY RESULTS: Flowering and dormancy were affected in opposite ways by daylength and growth temperature. Flowering occurred almost exclusively under SD. In contrast, plants became dormant much earlier under LD than under SD. In both daylengths, high temperature and pre-chilling (6 weeks at 5 degrees C) enhanced dormancy imposition, but inhibited or postponed flowering, respectively. Induction of flowering and dormancy in the different ecotypes showed differential responsiveness to daylength and temperature. Arid and semi-arid ecotypes had a higher proportion of flowering plants and flowering tillers as well as more panicles per plant than mesic ecotypes. 'Flowering' ecotypes entered dormancy earlier than 'non-flowering' ecotypes, while the more arid the site of ecotype origin, the earlier the ecotype entered dormancy. CONCLUSIONS: Variation in the flowering capacity of ecotypes differing in drought tolerance was interpreted as the result of balanced opposite effects of daylength and temperature on the flowering and dormancy processes.     

Photoperiodic control of flowering in Dactylis glomerata, a true short-long-day plant

Flowering requirements of three Scandinavian cultivars of Dactylis glomerata L. have been studied in controlled environments. At temperatures ranging from 9 to 21°C optimal flowering required 10 weeks of exposure to short days (SD) followed by exposure to long days (LD). Only a few plants flowered in continuous LD and no primary induction took place in any daylength at 24 or 27°C. However, at a temperature of 3°C primary induction occurred also in 24 h LD, but more than 20 weeks of treatment were required for 100% flowering. The critical photoperiod for secondary induction was about 12–13 h, depending on the latitude of origin of the cultivar. A critical number of 12 to 16 LD cycles was required for 100% flowering, although some plants flowered after only 4 LD. A high proportion of viviparous proliferation resulted from marginal LD induction. Initiation of floral primordia did not take place in SD but required a transition from SD to LD. These results demonstrate that D. glomerata is a true short-long-day plant.     

Dual Floral Induction Requirements in Phleum alpinum

Flowering requirements of four Norwegian populations of Phleumalpinum were studied in controlled environments. A dual inductionrequirement was demonstrated in all populations. Inflorescenceinitiation had an obligatory requirement for short days (SD)and/or low temperature, while culm elongation and heading wereenhanced by long days (LD) and higher temperatures. At 3 and6 °C primary induction was almost independent of photoperiod,whereas SD was more effective than LD at higher temperatures.The critical temperature for primary induction was about 15°C in SD and 12 °C in LD. Saturation of induction required12 weeks of exposure to inductive conditions, although someheading and flowering took place with 6 weeks exposure to optimalconditions (9 °C/SD). Inflorescence development also tookplace in 8 h SD although it was delayed and culm elongationwas strongly inhibited compared with LD conditions. Only smalldifferences in flowering response were found between the populations. Phleum alpinum L., alpine timothy, dual floral induction, flowering, photoperiod, temperature     

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD-induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high-latitude population from 70°N ('Alta') had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high-latitude population.     

Influences of daylength and temperature on the period of diapause and its ending process in dormant larvae of burnet moths (Lepidoptera,Zygaenidae)

The onset of larval diapause in the burnet moth Zygaena trifolii is clearly characterized by the larva molting into a specialized dormant morph. In a potentially bivoltine Mediterranean population (Marseille) two types of diapause can occur within 1 year: firstly, a facultative summer diapause of 3–10 weeks, and secondly, an obligate winter diapause, which can be lengthened by a period of thermal quiescence to several months in temperatures of 5°C. For the first time, three successive physiological periods have been experimentally distinguished within an insect dormancy (between onset of diapause and molting to the next non-diapause stage), using chilling periods of 30–180 days at 5°C, and varying conditions of photoperiod and temperature. These stages are: (1) a continuous Diapause-ending process (DEP); (2) thermal quiescence (Q); and finally, (3) a period of postdiapause development (PDD) before molting to the next larval instar. The result of transferring dormant larvae from chilling at 5°C to 20°C depended on the length of the chilling period. After chilling for 120–180 days, molting to the next instar occurred after 6–10 days, independent of daylength. This period corresponds with the duration of PDD. After shorter chilling periods (90, 60, 30 days and the control, 0 days) the period to eclosion increased exponentially, and included both the latter part of the previous diapause process and the 6–10 day period of PDD. However, photoperiod also influences the time to eclosion after chilling. Short daylength (8 h light / 16 h dark: LD 8/16) lengthened the diapause in comparison to long daylength (16 h light / 8 h dark: LD 16/8). Short daylength had a similar effect during chilling at 5°C, as measured by the longer time to eclosion after transfer. The shorter time to eclosion resulting from longer chilling periods (30–90 days) demonstrates that the state of diapause is continuously shortened at 5°C, and corresponds to the neuroendocrine controlled DEP. Presumably the DEP has already started after the onset of diapause. When chilling was continued after the end of the DEP, which ranged between 90 and 120 days, thermal quiescence (Q) followed (observed maximum 395 days). Different photoperiodic conditions during the pre-diapause inductive period modified diapause intensity (measured as the duration of diapause), in that a photoperiodic signal just below the critical photoperiod for diapause induction (LD 15/9) intensified diapause. Experiments simulating the summer diapause showed that PDD occurred in the range of 10–25°C. Higher temperatures (15 and 20°C) shortened the DEP at LD 16/8, so that at 20°C many individuals had already terminated diapause after 10–40 days and had molted after the 6–10 days of PDD. A temperature of 25°C unexpectedly lengthened the DEP to 110 days in several individuals. The ecological consequences and the adaptive significance of variation in the duration of the diapause are discussed in relation to the persistence of local populations predictably variable and rare climatic extremes throughout the year.     

Periodicity of response to abscisic acid in lateral buds of willow (Salix viminalis L.)

Aseptically cultured lateral buds of Salix viminalis L. collected from field-grown trees exhibited a clear periodicity in their ability to respond to exogenous abscisic acid (ABA). Buds were kept unopened by ABA only when the plants were dormant or entering dormancy. Short days alone did not induce bud dormancy in potted plants but ABA treatment following exposure to an 8-h photoperiod prevented bud opening although ABA treatment of buds from long-day plants did not. Naturally dormant buds taken from shoots of field-grown trees and cultured in the presence of ABA opened following a chilling treatment. In no cases were the induction and breaking of dormancy and response to ABA correlated with endogenous ABA levels in the buds.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - HPLC high-performance liquid chromatography - LD long day - MeABA methyl ABA - PAR photosynthetically active radiation - SD short day     

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.     

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.     

Environmental control of flowering and morphology in the high-arctic Cerastium regelii, and the taxonomic status of C. jenisejense

Cerastium regelii has a distribution confined largely to regions north of 70° N but has retained a strong short-day (SD) response for primary flower induction despite the fact that it will hardly ever experience SD in a non-frozen condition in its natural environment. However, like many other high-latitude short-long-day plants it has also an alterntive long day (LD) pathway for floral initiation at low temperatures (<15°C). Floral primordia which are fully differentiated during SD have an absolute requirement for LD for flower development. The critical photoperiod for this LD response is about 16 h at 18°C and more than 20 h at 9°C. Plant morphology, including key characters for identification of the species, is greatly modified by environment and stage of plant development. At higher temperatures and LD C. regelii develops a striking resemblance to the sub-arctic C. jenisejense . Based on examination of authentic herbarium material it is concluded that the latter is merely a high-temperature morphotype of C. regelii .     

Temperature rather than photoperiod controls growth cessation and dormancy in Sorbus species

Environmental regulation of growth and dormancy of four Sorbus genotypes was studied in controlled environments. Emphasis was placed on assessment of the presence and nature of the deficient photoperiodic dormancy regulation system that has previously been reported for some woody Rosaceae species. Two genotypes of Sorbus aucuparia L. maintained indeterminate growth for 8 weeks and 9 weeks at temperatures of 15 °C and 21 °C in both 20 h and 10 h photoperiods, while at 9 °C, in the same photoperiodic conditions, they immediately ceased growing. At the higher temperatures, initiation of new leaves (nodes) was unaffected by photoperiod, while internode elongation was significantly enhanced by long days (LD). However, even after prolonged exposure to 9 °C, most plants resumed growth when moved to high temperature and LD, indicating a shallow state of dormancy. Seedlings of Sorbus intermedia (J. F. Ehrh.) Pers. and micro-propagated plantlets of S. commixta Hedl. 'Dodong' were also unaffected by photoperiod during primary growth, but failed to elongate and gradually became dormant regardless of temperature and day-length conditions. However, after chilling and breaking of dormancy, the plants elongated vigorously but changed to a determinate mode of growth. Furthermore, a temperature of 9 °C was found to be fully effective for breaking dormancy in S. intermedia plants. It is concluded that deficient photoperiodic dormancy control seems widespread in the Rosaceae and that, in such plants, both dormancy induction and release is brought about by low temperature. The potential impacts of climate change on such trees are discussed.     

Clinal variation of dormancy progression in apricot

The aim of this study was to determine the bud dormancy progression in apricot at different latitudes and altitudes. Six locations in regions with a Mediterranean climate in South Africa (SA) and Spain were chosen. The study was carried out during two consecutive years, 2007 and 2008, in SA and results were compared to those obtained in Spain in 2008. Locations ranged from low-chill areas, such as Ladismith and Villiersdorp in SA and Campotéjar in Spain, to high-chill areas, such as Ceres in SA and Barranda in Spain. A number of apricot cultivars comprising the range of chilling requirements in both countries were selected. In addition, a second, parallel study was performed to evaluate the paradormancy progression in ‘Palsteyn’ (SA) and ‘Rojo Pasión’ (Spain). Deeper dormancy was not observed in high-chill cultivars located in cold areas than in low-chill cultivars in warm areas. However, low-chill cultivars located in warm areas entered and released from dormancy earlier than high chill cultivars in warm areas. Thus, a clinal variation in dormancy progression under warm temperatures in apricot cultivars is suggested. The role of photoperiod and minimum temperatures is proposed to have a key role in dormancy onset. Paradoxically, an earlier maximum depth of dormancy was found in those areas with higher minimum temperatures at the end of summer. Before the beginning of winter, all cultivars showed an important increase of budburst rate, which indicated the end of endodormancy. Afterwards an ecodormancy period followed during winter, while chilling continued to accumulate. These results contrast with the assumed concept of the breaking of dormancy through chilling accumulation during winter and suggest a possible mediation by photoperiod in overcoming of dormancy. On the other hand, paradormancy exerted a reduction in budburst rate during dormancy entry, whereas decapitation increased the budburst rate throughout the dormant season, indicating interaction between different plant parts during this period.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

Flowering requirements in Bromus inermis, a short-long-day plant

Smooth bromegrass plants ( Bromus inermis Leyss.) have a dual photoperiodic requirement for flowering. At temperatures ranging from 6 to 24°C, short days (SD) are necessary for primary induction while a transition to long days (LD) is required for initiation of flower primordia, culm elongation and flower development (secondary induction). Critical photoperiods for primary induction (50% flowering) were 13.5 h (15°C) and 12 h (24°C) in the American cv. Manchar and 14.5 and 13 h, respectively, in the Norwegian cv. Löfar. For the secondary induction the respective critical photoperiods were 14 and 15 h in 'Manchar' and 16 and 17.5 h in 'Löar', which also appeared to be better adapted to low temperatures. Low temperature vernalization in LD for up to 16 weeks at 3°C was unable to cause primary induction and temperatures below 12°C also strongly reduced the SD effect. At optimum temperature (15-2TC) 4 to 6 weeks of 8-10 h SD treatments were needed for optimal primary induction effect. A minimum of 8 LD cycles of 24 h were required for complete secondary induction in 'Manchar', while more than 16 cycles were needed in 'Löfar'. Seedlings grown in SD developed a rosette type of growth with shoots growing in a decumbent position, while those in LD grew upright and formed elongated vegetative culms. Rate of leaf initiation was enhanced by about 60% by LD while tillering was promoted by SD.     

Influence of photoperiod on low temperature acclimation for cold-hardiness in Drosophila auraria

ABSTRACT. Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold-hardiness at low temperatures to a greater extent when exposed to a diapause-inducing photoperiod (LD10:14 h) than when exposed to a diapause-preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to -5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post-diapause females the ability to develop cold-hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non-diapause females. These results suggest that the physiological mechanism which promotes cold-hardiness under a diapause-inducing photoperiod is not directly linked to the process causing reproductive diapause.
In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.     

Changes in Tuberization and Assimilate Partitioning in Potato (Solanum tuberosum) During the First 18 Days of Photoperiod Treatment

Potato (Solanum tuberosum L.) plants were equilibrated under18-h days (LD) before a subset of the plants was transferredto 10-h photosynthetic periods with either a dark night (SD)or an 8-h dim photoperiod extension with incandescent lamps(DE). Plants were harvested at regular intervals for growthanalysis during the 18 d after transfer. Leaf area increasedrapidly under SD and LD but was inhibited under DE. Internodeelongation was similar under SD and LD, but much higher underDE. Stem d. wts were lowest under SD. Axillary branching wasgenerally greatest under LD. Total shoot weights were greatestunder LD. Total shoot weights were similar under SD to thoseunder DE, even though within 18 d of transfer as much as one-thirdof the biomass of SD plants was in tubers. Tuber initiationwas later under LD than under SD, and was delayed even moreby DE. High temperature increased the delay in tuberizationfrom LD. The early tuber initiation under SD was concurrentwith a rapid increase in leaf area under SD, not with an earlycessation of leaf growth. This was contrary to assumptions basedupon studies of long-term effects of photoperiod. The resultanthigh sink strength under SD contributed to the greater efficiencyof biomass production. Potato, Solanum tuberosum L. cv. Norchip, photoperiod, temperature, morphology, tuberization, growth analysis, biomass partitioning, sink strength, leaf area, short term effects     

Dormancy release in beech buds (Fagus sylvatica) requires both chilling and long days

Chilling and daylength requirements for dormancy release and budburst in dormant beech ( Fagus sylvatica L.) buds have been studied in cuttings flushing in controlled environments after different durations of outdoor chilling. Non-chilled buds sampled in mid October required long days (LD) only for budburst. Buds chilled until March still required LD for normal budburst, whereas buds sampled in November and December were unable to sprout regardless of daylength conditions and would do so only after a substantial period of chilling. Four ecotypes of distant latitudinal and altitudinal origin responded very similarly with a typical quantitative photoperiodic response. In fully chilled shoots sampled in March only 13 to 40% budburst took place in 8-h SD and only after three times as long time as in continuous light. It is concluded that this dual dormancy control system ensures optimum winter stability in trees under conditions of climatic warming. In the closely related Carpinus betulus L. budburst was unaffected by daylength.