Seasonal changes in adenine phosphoribosyltransferase and adenosine kinase activities as markers of the dormancy and the growth of Fragaria × ananassa

Because of the potential involvement of adenosine in the winter re-acquisition of nucleotide synthesis capability of strawberry plants (Fragaria × ananassa Duch., Elsanta), the properties and the time-course activity of an adenosine kinase (EC 2.7.1.20) and an adenine phosphoribosyltransferase (APRTase, EC 2.4.2.7) of the adenosine recycling pathway were characterized. The results showed an increase in APRTase activity during winter re-acquisition of nucleotide synthesis capability and an increase in adenosine kinase activity during spring growth of strawberry plants. Western blot analysis, performed with polyclonal rabbit antibodies raised against peach bud adenosine kinase, showed a concomitant rise in the strawberry enzyme. These results suggest that APRTase activity could be a good marker of the break of strawberry plant dormancy and adenosine kinase a marker of subsequent spring growth.     

Cultivar-specific impairment of strawberry growth,photosynthesis, carbohydrate and nitrogen accumulation by ozone

In a 2-year study, fruiting plants of strawberry (Fragaria × ananassa Duch.) cv. ‘Korona’ and ‘Elsanta’ were exposed for 2 months to 78 ppb ozone on average or filtered air without ozone in controlled environment chambers. Plant growth, photosynthesis, carbohydrate accumulation, and macronutrient concentrations were investigated in order to demonstrate cultivar-specific differences in the ozone sensitivity of ‘Korona’ and ‘Elsanta’ on the whole plant level. Moreover, the hypothesis was tested whether properties of the root system in strawberry were involved in ozone tolerance, for example, the roots’ ability to store or make available carbohydrates and their capacity to secure plants’ supply with nitrogen during a stress situation. In strawberry, ozone reduced leaf area by reducing leaf number. Moreover, specific leaf area (SLA) and relative leaf water content were reduced. Net photosynthesis was only slightly impaired, but activity of Rubisco and chlorophyll content in older leaves of cv. ‘Elsanta’ were significantly reduced. The most important, indirect impairment of photosynthesis was the reduction of plants’ total leaf area, which resulted in a decrease in plant biomass. The reduction of root biomass, the root/shoot ratio, and also the distribution of carbohydrates indicated a partitioning priority of the shoot at expense of the root system. Cultivar ‘Elsanta’ was characterized by significantly lower carbohydrate levels in ozone-exposed leaves, whereas levels remained fairly stable in ‘Korona’ leaves. In addition, nitrogen concentrations in leaves and roots decreased significantly in ‘Elsanta’, not in ‘Korona’. The reduced nitrogen concentration in leaves may be related with the more distinct reduction in Rubisco activity and chlorophyll content in older leaves of ‘Elsanta’.     

Roles for Auxin, Cytokinin, and Strigolactone in Regulating Shoot Branching

Many processes have been described in the control of shoot branching. Apical dominance is defined as the control exerted by the shoot tip on the outgrowth of axillary buds, whereas correlative inhibition includes the suppression of growth by other growing buds or shoots. The level, signaling, and/or flow of the plant hormone auxin in stems and buds is thought to be involved in these processes. In addition, RAMOSUS (RMS) branching genes in pea (Pisum sativum) control the synthesis and perception of a long-distance inhibitory branching signal produced in the stem and roots, a strigolactone or product. Auxin treatment affects the expression of RMS genes, but it is unclear whether the RMS network can regulate branching independently of auxin. Here, we explore whether apical dominance and correlative inhibition show independent or additive effects in rms mutant plants. Bud outgrowth and branch lengths are enhanced in decapitated and stem-girdled rms mutants compared with intact control plants. This may relate to an RMS-independent induction of axillary bud outgrowth by these treatments. Correlative inhibition was also apparent in rms mutant plants, again indicating an RMS-independent component. Treatments giving reductions in RMS1 and RMS5 gene expression, auxin transport, and auxin level in the main stem were not always sufficient to promote bud outgrowth. We suggest that this may relate to a failure to induce the expression of cytokinin biosynthesis genes, which always correlated with bud outgrowth in our treatments. We present a new model that accounts for apical dominance, correlative inhibition, RMS gene action, and auxin and cytokinin and their interactions in controlling the progression of buds through different control points from dormancy to sustained growth.     

Dynamics of phytohormone and DNA methylation patterns changes during dormancy induction in strawberry (Fragaria?×?ananassa Duch.)

Changes in endogenous phytohormone levels, DNA methylation patterns, and expression levels of related genes during induction of dormancy in two strawberry cultivars, Darselect and All Star, were studied under controlled environmental conditions. At 12°C, regardless of day length, potted, runner-derived plants of both cultivars gradually exhibited morphological traits typical of dormancy after treatment for 8 weeks. These morphological changes were accompanied by a synchronous significant decline in indole-3-acetic acid (IAA) level and increases in abscisic acid (ABA) content and global genomic DNA methylation in young leaves. Exposed at 15°C and a short-day photoperiod, the changes in morphology, phytohormone levels and DNA methylation of both cultivars were similar to those observed at 12°C. Slight but non-significant changes in IAA and ABA levels and genomic DNA methylation occurred in young leaves at both 15°C with long days and 18°C with short days. These results indicated that temperature alone was sufficient to induce strawberry to enter the typical dormant phase, and day length had no impact at 12°C. The higher temperature permissible for dormancy induction in strawberry was 15°C, but at this temperature dormancy induction was modified by day length. The expression patterns of FaPIN1, FaNCED1, FaDRM and FaROS1 were coincident with the changes in phytohormone levels and DNA methylation. Although the two tested cultivars have different temporal responses with the different degree of cold tolerance and depth of dormancy, both the endogenous phytohormone and DNA methylation were changed when induced by external environmental factors.     

匍匐茎草本蛇莓对基质养分条件的克隆可塑性

A pot experiment with three levels of nutrient (N, P, K) supply was carried out to investigate clonal plasticity of stoloniferous herb Duchesnea indica Focke in response to nutrient availability. The plants had greater biomass at higher levels of nutrient availability. The root/shoot ratio of the plants changed with the nutrient availability in the following order: low level > high level > medium level. They had the largest biomass allocation to stolon at the medium level of nutrient availability. The biomass allocation to petiole did not respond to the treatments. The plants formed more stolons and ramets at the high and medium levels than the low level of nutrient availability. The petiole length, specific petiole weight（mg/cm）and stolon internode length of the plants did not respond to the treatments, while the specific stolon weight (mg/cm）of the plants was greater at the high and medium levels than the low level of nutrient availability. The results have been discussed in the context of adaptation of clonal plants to environmental heterogeneity.     

Ecotype-dependent control of growth,dormancy and freezing tolerance under seasonal changes in <Emphasis Type="Italic">Betula pendula</Emphasis> Roth

Woody plants in the temperate and boreal zone undergo annual cycle of growth and dormancy under seasonal changes. Growth cessation and dormancy induction in autumn are prerequisites for the development of substantial cold hardiness in winter. During evolution, woody plants have developed different ecotypes that are closely adapted to the local climatic conditions. In this study, we employed distinct photoperiodic ecotypes of silver birch (Betula pendula Roth) to elucidate differences in these adaptive responses under seasonal changes. In all ecotypes, short day photoperiod (SD) initiated growth cessation and dormancy development, and induced cold acclimation. Subsequent low temperature (LT) exposure significantly enhanced freezing tolerance but removed bud dormancy. Our results suggested that dormancy and freezing tolerance might partially overlap under SD, but these two processes were regulated by different mechanisms and pathways under LT. Endogenous abscisic acid (ABA) levels were also altered under seasonal changes; the ABA level was low during the growing season, then increased in autumn, and decreased in winter. Compared with the southern ecotype, the northern ecotype was more responsive to seasonal changes, resulting in earlier growth cessation, cold acclimation and dormancy development in autumn, higher freezing tolerance and faster dormancy release in winter, and earlier bud flush and growth initiation in spring. In addition, although there was no significant ecotypic difference in ABA level during growing season, the rates and degrees of ABA alterations were different between the ecotypes in autumn and winter, and could be related to ecotypic differences in dormancy and freezing tolerance.     

Impacts of NaCl stress on plant growth and mineral nutrient assimilation in two cultivars of strawberry

Two strawberry (Fragaria × ananassa Duch.) cvs Korona and Elsanta differing in their tolerance to NaCl salinity were exposed to 40 and 80 mmol NaCl L^?1 for over 4 months in the growing seasons of 2002 and 2003, respectively. However, the osmotic potential, i.e. the NaCl concentration of the root medium, varied during the experiments, because Hoagland solution and demineralized water were added usually once a week in order to push NaCl uptake on the one hand, but to allow leaching the soil after application of demineralized water on the other. Leaching the soil should quickly improve the water relations of the plant, but not affect salt levels within the plant. This strategy was chosen to reduce the effects of water stress and to focus onto the salt-specific impacts of NaCl stress. The salt stress reduced fresh and dry matter of the whole plants and photosynthetically active leaf area, especially in cv. Elsanta. Typical leaf symptoms of Na and Cl stress were detected in both cvs and the combined effects of both toxic ions resulted in the leaf scorching symptoms. Na uptake of both cvs was similar, but distribution of Na within plants was different. Korona was able to protect leaves more efficiently from Na accumulation.Under NaCl stress Korona plants achieved a significant increase of K content in leaves and crowns, while Elsanta showed an increase of K in fruits and petioles. The accumulation of K under evaluated NaCl levels suggests an efficient K uptake system in strawberry plants. Concentrations of Ca were not significantly affected, with the exception of rising levels in roots of Elsanta plants. Concentrations of Mg, Mn and Fe significantly decreased in leaves, while those of Mg and Mn remarkably rose in crowns of both cvs. N content in leaves, petioles, and roots of both cvs increased. In addition it rose in fruits and crowns in cv. Elsanta. A significant limitation of N uptake by competition with Cl did not occur in these plants. Concentrations of P increased in roots and petioles of both cvs, and in fruits of cv. Elsanta. With respect to Zn and Cu, significant concentration changes related to NaCl stress could not be detected.     

The Interaction of (2-Chloroethyl) trimethylammonium Chloride and Gibberellic Acid in Strawberry

Applications of (2-chloroethyl) trimethylammonium chloride (CCC), by foliar spray or to the soil, shortened petioles and decreased top and root growth of strawberry plants. Application of gibberellic acid increased petiole length and fresh weights of tops but not of roots. Applied together gibberellic acid overcame the depression of growth in weight of tops induced by CCC and countered the depression in petiole lengths. Gibberellic acid induced elongation of internodes of the vegetative stem and the elongation was increased substantially by concurrent application of CCC. This synergism in stem growth indicates a lack of antagonism between CCC and exogenous gibberellic acid in strawberry. The implications are discussed.     

Low stomatal density and reduced transpiration facilitate strawberry adaptation to salinity

Water and soil salinization are major constraints to agricultural productions because plant adaptation to hyperosmotic environments is generally associated to reduced growth and ultimately yield loss. Understanding the physiological/molecular mechanisms that link adaptation and growth is one of the greatest challenges in plant stress research since it would allow us to better define strategies to improve crop salt tolerance. In this study we attempted to establish a functional link between morphological and physiological traits in strawberry in order to identify margins to “uncouple” plant growth and stress adaptation. Two strawberry cultivars, Elsanta and Elsinore, were grown under 0, 10, 20 and 40 mM NaCl. Upon salinization Elsanta plants maintained a larger and more functional leaf area compared to Elsinore plants, which were irreversibly damaged at 40 mM NaCl. The tolerance of Elsanta was correlated with a constitutive reduced transpirational flux due to low stomatal density (173 vs. 234 stomata mm⁻² in Elsanta and Elsinore, respectively), which turned out to be critical to pre-adapt plants to the oncoming stress. The reduced transpiration rate of Elsanta (14.7 g H₂O plant⁻¹ h⁻¹) respect to Elsinore (17.7 g H₂O plant⁻¹ h⁻¹) most likely delayed the accumulation of toxic ions into the leaves, preserved tissues dehydration and consented to adjust more effectively to the hyperosmotic environment. Although we cannot rule out the contribution of other physiological and molecular mechanisms to the relatively higher tolerance of Elsanta, here we demonstrate that low stomatal density may be beneficial for cultivars prescribed to be used in marginal environments in terms of salinity and/or drought.     

Dormancy and Germination of Abscisic Acid-Deficient Tomato Seeds : Studies with the sitiens Mutant

The role of abscisic acid (ABA) in the dormancy induction of tomato (Lycopersicon esculentum) seeds was studied by comparison of the germination behavior of the ABA-deficient sitiens mutant with that of the isogenic wild-type genotype. Freshly harvested mutant seeds, in contrast to wild-type seeds, always readily germinate and even exhibit viviparous germination in overripe fruits. Crosses between mutant and wild-type and self-pollination of heterozygous plants show that in particular the ABA fraction of embryo and endosperm is decisive for the induction of dormancy. After-ripened wild-type seeds fully germinate in water but are more sensitive toward osmotic inhibition than mutant seeds. Germination of both wild-type and mutant seeds is equally sensitive toward inhibition by exogenous ABA. ABA content of mature wild-type seeds is about 10-fold the level found in mutant seeds. Nevertheless, it is argued that the differences in dormancy between the seeds of both genotypes are not a result of actual ABA levels in the mature seeds or fruits but a result of differences in ABA levels during seed development. It is hypothesized that the high levels of ABA that occur during seed development in wild-type seeds induce an inhibition of cell elongation of the radicle that can still be observed after long periods of dry storage.     

Nitrogen and methyl jasmonate induction of soybean vegetative storage protein genes

Vegetative storage protein (VSP) and VSP mRNA levels in soybean (Glycine max) leaves correlated with the amount of NH₄NO₃ provided to nonnodulated plants. The mRNA level declined as leaves matured, but high levels of N delayed the decline. This is consistent with the proposed role for VSP in the temporary storage of N. Wounding, petiole girdling, and treatment with methyljasmonate (MeJA) increased VSP mRNA in leaves 24 hours after treatment. The magnitude of the response depended on leaf age and N availability. N deficiency essentially eliminated the response to wounding and petiole girdling. MeJA was almost as effective in N-deficient plants as in those receiving abundant N. Inhibitors of lipoxygenase, the first enzyme in the jasmonic acid biosynthetic pathway, blocked induction by wounding and petiole girdling but not by MeJA. This supports a role for endogenous leaf jasmonic acid (or MeJA) in the regulation of VSP gene expression.     

Variations in leaf characteristics of six species of Sagittaria (alismataceae) caused by various water levels

Plants grown from seeds of Sagittaria falcata, S. lancifolia, S. platyphylla, S. rigida, S. isoetiformis and S. papillosa were grown in water-saturated soil or soil submerged to 4.5, 12, 19.5 or 27 cm. Length and width of leaves and petiole lengths were measured at anthesis of the first flower on the first inflorescence produced by each plant. In general, leaf width and length were decreased by submergence, and petiole length increased. The species × water depth interaction was significant for emersed leaf width, leaf length and petiole length except for S. lancifolia leaf length and S. papillosa leaf length and width. These trends indicate genetic differences among, and variability within, taxa. Leaf width, leaf length and petiole length of plants growing in seed source populations were measured. The means from these measurements, when compared to those from experimental plants, indicate that both groups of plants respond similarly to variations in water depth.     

Clonal variation in apical growth and content in vegetative storage proteins in Populus

Summary Apical shoot growth and storage protein content in various poplar species and clones were followed in trees growing in the field and in micropropagated plants cultivated in the growth chamber under a controlled environment. In autumn a 32 kD and a 36 kD vegetative storage protein accumulate in wood, bark and roots of poplar and comprise together about 25% of the soluble proteins. In spring, at the time of dormancy break, the storage proteins are degraded and 3 weeks after budburst these proteins are no longer immunologically detectable. As in autumn, short day exposure of black cottonwood plants (Populus trichocarpa Torr. and Gray) induces cessation of apical growth and accumulation of the 32 kD and 36 kD vegetative storage proteins in all clones studied. In order to simulate spring conditions, short day induced plants were transferred back to long days. Like the situation in spring, budburst and storage protein degradation occurred considerably earlier in clone 9/60 than in clone Muhle Larsen. The latter clone accumulates both in winter and after short day exposure more storage proteins than the former. Furthermore two P. trichocarpa clones differ qualitatively in storage protein content: they possess an additional 34 kD polypeptide which cross-reacts with the anti-32 kD antibody. In conclusion, apical shoot growth and the capacity to synthesize storage proteins can be easily followed in micropropagated poplar cultivated in the growth chamber under inducing photoperiods. This offers the major advantage of independence from the annual growth cycle. Within one species considerable clonal variance in storage protein content and in the induction times needed for dormancy and dormancy break were observed. The suitability of storage protein content and apical growth as early selection traits in breeding programs focusing on nitrogen efficient poplar and clones adapted to specific latitudes will be discussed.     

Unexpectedly high susceptibility of micropropagated rhubarb (Rheum rhaponticum L.) to spot disease caused by Ramularia rhei

Rapid, large-scale micropropagation of a Rheum rhaponticum (rhubarb) breeding line, selected for the absence of autumn dormancy, produces changes typical of somaclonal variation. Among these is enhanced susceptibility to foliar infection by the spot disease pathogen Ramularia rhei, with consequential increased spore production on infected leaves. This provides an increased level of inoculum in the late season, leading to commercially unacceptable petiole spotting as spores are washed from the lamina on to the petiole surface. Infection of conventionally propagated plants does not exceed market acceptability. Consequently, to maintain the commercial value of this rhubarb selection micropropagation must be avoided, at least until an acceptably modified protocol is available.     

Irregular Occurrence of Rhabdoviruslike Particles in Tissues of Fragaria vesca Plants Infected with Strawberry Crinkle Virus

When evaluated by electron microscopy, rhabdoviruslike particles (RLP) were found most frequently in petioles, less frequently in midribs, and not at all in roots or petals of Alpine strawberry plants leaflet graft-inoculated with strawberry crinkle virus (SCV). In graft-inoculated plants RLP were found only in mesophyll and phloem parenchyma cells and in sieve tubes. Numbers of RLP detected were highest within one week of the onset of symptoms, decreased with time, and were extremely variable, both among identically treated Alpine seedlings that showed similar crinkle disease symptoms and within Alpine clones. Through electron microscopy we were not able to predict if a given petiole sample from a graft-inoculated Alpine plant showing typical symptoms of crinkle disease would have no, moderate, or many RLP. The percentage of Alpine plants developing crinkle symptoms after leaflet graft inoculation with symptom-bearing leaves from a crinkle source was higher in summer than in winter. It was not increased after the source plants had broken dormancy in the spring, compared to plants kept vegetative all winter, and was not dependent on the length of time a symptom-bearing source plant had been infected. When symptomless leaves from SCV-infected Alpine plants were grafted to healthy Alpine indicator plants, no symptoms developed on the latter.     

Evidence for a Flower Inhibitor and Vegetative Growth Promoter in the Strawberry

Experiments with pairs of strawberry runner plants joined bythe stolon and acting as donor/receptor units are reported.Long photoperiods or a light-break treatment on donor plantsbrought about increased petiole length, increased leaf size,and delayed flower initiation in receptor plants themselvesin short photo-periods. The response of receptor plants wasincreased by exposing donor plants to illumination by full daylight3 hours earlier each morning than receptor plants. It is thoughtthat this earlier illumination increased translocation fromthe earlier to the later illuminated plants. In translocationexperiments, radioactive P32 moved more freely from the olderto the younger plant of each pair, except when the older plantswere partially defoliated or when the younger plants were exposedto full light for a longer period of time each day than theolder attached plants. The results are discussed and it is concluded that they aregood evidence for the existence of a growth-regulating substance(s)which promotes vegetative growth and inhibits flower initiation.It seems possible that the regulation of vegetative growth andthe control of flower induction is principally achieved in thestrawberry by a flower inhibiting, vegetative growth-promotingsystem.     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, during Winter: The Effect of Photoperiod and Temperature on the Induction of Dormancy and the Annual Cycle of Development

The effects of daylength and temperature on the induction ofdormancy in shoots of Calluna vulgaris were investigated usingcontrolled environment growth rooms. Short days did not induce dormancy in Calluna but floweringwas inhibited and shoots having a characteristic end-of-seasonmorphology were formed. Short days combined with low temperaturesarrested growth but the depth of dormancy was not as great asthat of plants in the field in late autumn. Long days combinedwith low temperature did not induce dormancy or the end-of-seasonmorphology. Results from the growth room experiments may be interpretedin relation to the annual cycle of development of Calluna underfield conditions. Calluna vulgaris (L.), photoperiod, temperature, dormancy, flowering, annual cycle of development     

Involvement of Endogenous Gibberellins in the Chilling Requirements of Strawberry (Fragariaxananassa Duch.)

Plants of Fragaria ananassa Duch. cvs Tioga and Fresno werechilled in a cold store at—1°C for 2–8 months,after which they were transferred to short-day (SD) and long-day(LD)) growth chambers. Chilling promoted subsequent vegetative development, as expressedthrough leaf area, petiole length and stolon production, butinhibited the formation of inflorescences. Leaf area and petiolelength responses appeared to be almost saturated by 2 months'chilling. The increase in stolon production and the reductionin inflorescence formation came into full expression with longerperiods of chilling. Application of gibberellin A₃ (GA₃ to plants pre-chilied for2 months had little effect on leaf area or petiole length butpromoted stolon production and retarded the formation of inflorescences.AMO-1618 applied to plants pre-chilled for 4 months antagonizedthe chilling responses. The level of diffusible gibberellin-like substances from crownapices remained low during most of the chilling period but increasedmarkedly after 6–8 months of chilling, when plants approachedspontaneous sprouting in the cold store. Plants pre-chilledfor 2 months had low levels of gibberellin-like substances whichincreased several fold upon transfer to the growth chambers.This increase was somewhat delayed in plants treated with AMO-1618. The role of gibberellins in the responses of strawberry plantsto chilling is discussed.     

Bacillus methylotrophicus M4-96 Stimulates the Growth of Strawberry (Fragaria × ananassa ‘Aromas’) Plants In Vitro and Slows Botrytis cinerea Infection by Two Different Methods of Interaction

Bacillus methylotrophicus M4-96 is a beneficial rhizobacterium that has been isolated from the rhizosphere of maize (Zea mays). In this study, we investigated its efficacy as a plant growth promoter for strawberry in vitro, as well as its ability to induce callose deposition in leaves to reduce the severity of Botrytis cinerea infection. Two methods of plant-bacterial interaction were used: inoculation near the root and emission of volatile compounds with no physical contact. Plant biomass increased under both treatments, but with developmental parameters of the plants differentially stimulated by each method. Root inoculation increased petiole number and root length, whereas bacterial volatiles increased petiole length and root number. A chemical analysis of the bacterial culture revealed the presence of indole acetic acid (0.21 μg L⁻¹) and gibberellic acid (6.16 μg L⁻¹). Acetoin was previously identified as the major volatile produced by the bacteria, and its application to strawberry explants increased their growth and development. Furthermore, when acetoin and both phytoregulators were added to the culture media, these positive effects were enhanced. The inoculation method also affected the size and quantity of callose deposits in the leaves. Treatment with volatiles increased callose deposition in the leaves by up to five-fold, which promoted a rapid defense reaction that inhibited the incidence of gray mold by reinforcing cell wall. Taken together, our results show that B. methylotrophicus M4-96 promotes growth and induces systemic resistance in strawberry plants.