Growth Substances in Relation the the Rooting of Salix fragilis Cuttings

An attempt has been made to correlate seasonal variations inthe rooting responses of Salix fragilis cuttings with theircontent of growth-promoting substances. Although they were bothlow in early dormancy and higher in late dormancy and in summerthere was not an exact correlation in all months. It was found that extracts of S. fragilis cuttings taken indormancy strongly inhibited the action of IAA on the growthof Avena coleoptile segments. This inhibitory influence wasless in extracts of cuttings taken at the end of dormancy andin summer. Extracts of cuttings which had been left in waterto root showed a striking decrease in their inhibitory actionon IAA.     

The Effect of Cooling on Translocation in Salix viminalis

Radioactive phosphate was applied externally to a small areaof the bark of the main stem below the point of insertion ofa leafy branch. When photosynthesis and hence translocationwas proceeding, phosphate was carried down the stem and wasmonitored externally by two Geiger counters spaced 10 cm apartfurther down the stem. Sudden cooling to 0 °C of the leaves,or the stem between the leaves and the point of applicationof the isotope, caused a rapid and seemingly simultaneous responseby the two Geiger counters. It is concluded that cooling atone point causes an instantaneous reduction of velocity alongthe whole pathway. If cooling is continued for several hoursthe rate of translocation of phosphate recovers. The evidencesuggests that this recovery is due to a compensatory increasein concentration of radioactive phosphate in the translocationstream rather than a recovery of velocity.     

Nomenclatural remarks on the Salix viminalis group in Norden

Larsson, G. 1995. Nomenclatural remarks on the Salix viminalis group in Norden. —Nord. J. Bot. 15: 343–346. Copenhagen. ISSN 0107–05513.
The taxa in the Salix viminalis group which have been found in Norden are lectotyp-ified: S. viminalis, S. dasyclados, S . x smithiana, S . x stipularis and S . x calodendron . Flora Nordica notes no. 12.     

P-protein and inclusion bodies in root protophloem of Salix viminalis

The formation of P-protein in the protophloem of 9- to 14-day-old adventitious roots of Salix viminalis was studied. In immature sieve elements a finely granular material was present. This was considered to be nascent P-protein. Small aggregations of tubular P-protein were observed 17 cells from the first cleared sieve element. In older cells the bodies were up to 7 μm long. Nondispersed and disaggregating P-protein bodies were present in mature sieve elements. P-protein bodies were also observed in parenchyma cells adjoining mature sieve elements. In addition, inclusion bodies of unknown origin are described. They had a granular content and were most often found in mature sieve elements.     

Genetic mapping of sex-linked markers in Salix viminalis L

A total of 88 selective primer combinations were screened using bulked males and females sampled from four families of Salix viminalis. A total of more than 1000 polymorphic fragments was obtained, of which only four cosegregated with sex. These four sex-linked markers were subsequently scored in individuals that were used for bulked sample preparation in additional individuals of the same families, and in individuals in other families. A pair of primers that amplified the sex-linked fragments was constructed from one of the sex-linked amplified fragment length polymorphism (AFLP) fragments. In hybridization of Southern blot filters with the sex-linked DNA fragments, the band was present in females and absent in males, but the opposite pattern of band segregation (a band found in males and no band in females) was never observed in either the AFLP or RFLP experiments. Two of the sex-linked markers were placed on a linkage map. They both map at the same location in a linkage group comprising other markers not segregating with sex. Our data suggest that a single locus governs the sex determination and that nonrecombining sex chromosomes are absent in S. viminalis. A close association was found between skewed sex ratio and segregation distortion at this locus.     

Heat shock proteins in willow (Salix viminalis)

The heat shock response in three vegetatively propagated clones of Salix viminalis L. was studied. In the clone 78198, synthesis of a total of 58 proteins was induced or increased by heat shock. Of these proteins, 39 were found in both leaves and callus, 8 only in leaves, and 11 only in callus. The number of heat shock proteins differed between the three clones studied. The molecular weights of the heat shock proteins ranged from 18000 to over 94000. The optimal synthesis of heat shock proteins took place at 37–40°C, but several proteins could be induced at 25–30°C. The synthesis of the majority of the proteins present at a normal growth temperature (20°C) was not completely blocked by the heat shock. More than 12 h was needed for the reappearance of the normal protein synthesis pattern after heat shock.     

Root-promoting Substances in Salix alba

Root-promoting substances were extracted from softwood cuttings of Salix alba L. by centrifuging them with water or by shaking the ground freeze-dried stems with water. Rooting substances were partitioned by paper chromatography or chemical fractionation and their rooting activity was tested by mung bean cuttings. Both extracts indicated three major root -promoting fractions at Rf 0-0.1, 0.7-0.8, and 0.3-0.4 in a decreasing order of their activities when paper chromatographed with isopropanol:ammonia:water 8:1:1 v/v. The strongest one indicated an apparent synergistic rooting effect with indol-3yl-acetic acid (IAA) regardless of the extraction method. These results indicate that water can extract from freeze -dried sample the similar rooting substances found in the centrifugal diffusates. The Rf 0–0.1 fraction consisted of at least four fractions and the strongest one did not move from the starting line on the chromatogram when isopropanol:ammonia:water 8:1:1 was used. This starting line fraction was extremely strong in rooting activity and its highest concentration resulted in 8.7 times as many roots as controls. More thain additive rooting effect between IAA and the fraction was found only at the highest concentration. The fraction was very soluble in water but insoluble in chloroform or ethyl ether and only stimulated rooting of mung bean cuttings when it was applied within 3 days after cuttings were made. It had no effect in lengthening roots. The starting line fraction was further found to have four root-promoting subfractions at Rf 0.05, 0.35, 0.65, and 0.85 when it was chromatographed in 60 % isopropanol. Among these four, the subfractions at Rf 0.65 and 0.35 were strongly root promotive and displayed more than additive root promotion with IAA at the highest concentrations studied.     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

Some Low-temperature Effects on Sieve Tube Translocation in Salix viminalis

The data presented on translocation of ¹⁴C-labelled compoundsin Salix viminalis show that above a temperature close to –4°C translocation occurs, whilst below –4 °C inmost cases it does not. Stoppages were irreversible when the temperature of the cooledstem was raised again to normal (approximately 20 °C) andappeared to involve some disruption of the phloem. The temperaturesat which the bark was found to freeze were found to be closelysimilar, with respect to level and variability, to the stoppingtemperature. Respiration measurements on isolated strips of bark at –2°C showed that oxygen uptake fell to approximately 5 percent of its value at 25 °C. The decreased level of radioactivity in the cooled regions ofthe stems is considered to be evidence that the exchange oflabelled compounds between the sieve tubes and the surroundingcells was slowed up at low temperatures.     

Characteristics of Action Potentials in Willow (Salix viminalis L.)

After application of electric stimuli (square DC pulses) extra-andintracellular potentials were recorded on willow shoots. Theall-or-nothing law, strength-duration relation, and generalcharacteristics of the action potential were investigated. Byusing inhibitors of ionic channels (tetraethylammonium, MnCl₂,LaCl₃), the excitability of willow could be completely blocked.Treatment with the phosphorylation uncoupler dinitrophenol induceda depolarization and disappearance of excitability, indicatingthe participation of a metabolic component of the membrane potential.By using energy-dispersive X-ray microanalysis, the distributionof chloride, potassium and calcium was measured in differenttissues of non-stimulated and stimulated willow shoots. It was shown that stimulation of the plant was followed by ionshifts which were most striking in the phloem cells. While theircontent of potassium and chloride was diminished after stimulation,the amount of cytoplasmic calcium increased slightly. Thesedisplacements lead to the conclusion that Ca²⁺ influx as wellas K⁺ and Cl^– efflux are involved in the propagation ofaction potentials. Key words: Action potential, electrical stimuli, energy-dispersive X-ray microanalysis, ion shifts, Salix viminalis     

Preformation of root primordia in shoots and root morphogenesis in Salix viminalis

Root primordia are formed in the stems of Salix viminalis L. during normal growth. Some of these primordia are produced at definite sites in the nodes. The initiation and early structural and ultrastructural development of the nodal primordia were studied in young shoots. In the fourth node below the terminal leaf cluster some parenchyma cells situated at the lateral leaf gaps formed a small group of initial cells. Derivatives of the newly formed interfascicular cambium added cells to that group, in which later on cell divisions in various directions occurred resulting in the formation of a root primordium. Root morphogenesis was studied in cuttings from one-season-old stems. The cells in the dormant primordia contained many lipid bodies but only a small amount of starch. After the cuttings had been 24 hours in water starch was accumulating in the plastids and lipid bodies were seen in the vacuoles. 48 hours after activation cell divisions occurred throughout the primordia and a layered apical mer-istem was organized. After 96 hours a root cap with amyloplasts was formed and the procambium was well developed. The amyloplasts were sedimented in response to gravity. After six days the first roots were ready to emerge from the stems. Their root caps had a well developed columella and endodermal and pericyclic cells were recognizable.     

Abscisic Acid and the Photoperiodic Induction of Dormancy in Salix viminalis L

A series of growth room experiments was carried out aiming to establish the role of abscisic acid on dormancy of Salix viminalis L. The inhibitor content and abscisic acid levels of extracts from roots, sap, leaves, and apical tissues of willow were measured using biological assay and gas-liquid chromatography.     

Morphogenesis of the root cap in adventitious roots of Salix viminalis

The preformed root primordia in stems of Salk viminalis L. consist of undifferentiated cells. Forty-eight hours after activation of the primordia in cuttings a root cap meristem was initiated four to five cell tiers from the surface of the primordia. The cells distal to the meristem divided only in an anticlinal plane, while in the meristem they divided mostly periclinally but sometimes anticlinally. After 72 hours a columella was established and the amyloplasts began to sediment in response to gravity. Shortly after this stage the roots began to bend slightly downward, probably as a geo-tropic response. Six days after activation the root cap consisted of up to 15 tiers of cells. The ultrastucture of the cap cells just prior to emergence was studied in more detail. The plastids in the cells adjoining the root proper were typical proplastids. Distal to this cell tier starch accumulated in the plastids. In the fifth tier the amyloplasts were fully sedimented to the lowermost cell walls. The amount of ER increased with the distance from the initial cells and most of it was located at the distal periclinal cell wall. The nucleus and the vacuoles in the geo-sensitive cells occurred in the space above the sedimented amyloplasts. The cytoplasm was less electron opaque than in the initial cells and the mitochondria had more cristae. In the distal cells of the columella and the lateral root cap secretion of mucilage seemed to have started. Numerous large dictyosomes were associated with large vesicles containing a fibrillar or granular material. The plasmalemma lining the distal periclinal cell wall had separated from the wall. A fibrillar material was present between the plasmalemma and the wall and also in intercellular spaces outside the root cap.     

Genetic relationships between growth characters in Salix viminalis grown in Sweden

From an eight by eight factorial crossing with Salix viminalis, 40 of the 64 families obtained were selected for further analysis. Fourteen seedplants from each of these 40 families were planted in two pairs of contrasting environments: sand and clay soil, and low and high nutrient supply. The material in the soil contrast was harvested after 1, 4 and 6 years of growth. The material in the nutrient contrast was harvested each year for 3 years and analysed after the first and the third harvests. The correlation between number of shoots and weight in the clay environment changed from being negative in the first harvests to positive at the last harvest, compared with the sand environment where this correlation was positive in all years. In the nutrient contrast this correlation was positive at the last harvest in the high nutrient environment, but no correlation could be detected in the low nutrient environment. The differences in correlations between environments may be due to a different allocation of nutrients in the plants, depending on whether the plant is under stress or not. The data suggests that the genetic relationship between growth components is the same over age and environments when the plants are grown without stress.     

Gas-exchange and sap flow measurements of Salix viminalis trees in short-rotation forest

Simultaneous field measurements of transpiration and sap flow were performed on short-rotation Salix viminalis trees ranging in diameter from 1.5 to 3.5 cm (2-year-old shoots on 8-year-old stumps). Transpiration was measured using an open-top ventilated chamber enclosing the whole foliage of a tree. Sap flow was measured using a tree-trunk heat balance (THB) technique with a constant temperature difference and variable heat input. Both the instantaneous and daily values of water flux measured by the two absolute techniques agreed well with a difference of up to about 5%. In July, the hourly transpiration reached a maximum of about 0.2 kg m^–2 (leaf area) or 0.45 kg tree^–1, whereas maximum daily integrals reached 4 kg tree^–1. The response of sap flow rate to abrupt flux change when inducing emboli by cutting-off the stem was very rapid: the registered signal dropped by 85% within 10 min for a specimen with a projected leaf area of 2 m². For S. viminalis trees, transpiration was linearly correlated with stem cross-sectional area and with leaf area.     

Efficiency of selected heavy metals accumulation by Salix viminalis roots

The efficiency of the absorption from the medium and accumulation by plant of ions of the heavy metals depends on many factors including plant age and its genotype. The heavy metals accumulation by 1-, 2- and 3-year-old plants was studied in the aspect of reclamation and revitalization effectiveness of demoted areas. Results of this study answer the question concerning the accumulation of seven heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) by willow cuttings (Salix viminalis) in environments with different concentrations of these elements. Cuttings used were originally grown on a substrate not contaminated with the metals and rich in nutrients. In order to eliminate the effect of soil physicochemical factors, the experiment was carried out using a hydroponic system. Results indicated significant effects of the investigated metal concentrations on their accumulation by willow. The extent of metal accumulation as an indicator of the remediation capacity of willow depended on the age of the cuttings used at planting.     

Sex determination and sex ratio in the dioecious shrub Salix viminalis L.

 Various ecological factors (e.g. herbivory, difference between males and females in colonising ability) have been invoked to explain female-biased sex ratios in populations of willow species. It was implicitly assumed that genetic factors would lead to a balanced sex ratio in the absence of ecological disturbances. In an experiment carried out in a homogeneous environment and in the absence of herbivores the progeny sex ratio of 13 crosses of basket willow (Salix viminalis L.) was observed to range from extreme female bias to extreme male bias. The observed sex ratio cannot be explained by the presence of sex chromosomes without assuming that additional loci are also involved in the sex determination. Alternatively, the sex ratios in this study can be explained by a sex determination mechanism governed by multiple independent loci. Received: 1 February 1996 / Accepted: 14 June 1996     

Nitrate availability and shoot area development in small willow (Salix viminalis)

Abstract. The effect of nitrate supply upon leaf area development in willow ( Salix viminalis ) was investigated. Rooted cuttings were grown in culture solution at two different rates of exponentially-increasing nitrate supply and with free access to other nutrients. During the lag-phase in attaining stable nutrition, the rate of production of unfolded leaves, in the treatment with poorer N-supply, decreased. After acclimation to the different N-availabilities, the rate of dry matter increase per plant nitrogen was constant and the same in both treatments. The ratio of total leaf area to total amount of nitrogen in the plant was slightly higher in the treatment with poorer nitrogen supply. During the exponential (stable) phases of growth, nearly all the increase in total leaf area was attributable to main-stem leaves; large numbers of leaves on axillary shoots in the treatment with better N-supply contributed little to the total area. During the stable growth phase, the rate of production of unfolded leaves was the same in both treatments. Higher maximum values of relative rate of increase in area of single leaves were found with a better N-supply and at higher leaf positions on the main stem. The duration of leaf expansion was not much affected by N-supply. Final leaf size was greater at higher positions on the main-stem. Within a treatment (investigated for poorer N-supply), differences in final leaf size were proportional to differences in numbers of epidermal cells. Final leaf size was greater, at the same node, in the treatment with better N-supply. Better N-availability had increased the final size but not the number of epidermal cells. It was concluded that the higher exponential rate of total area increase with a better N-supply was largely associated with higher rates of expansion in epidermal cells.     

Toxicity of 2,3,5,6-tetrachlorophenol to willow trees (Salix viminalis)

Chlorinated phenols have been intensively investigated from an eco-toxicological point of view, however almost nothing is known about toxicity of tetrachlorophenol (TeCP) to higher terrestrial plants. This article applied the willow tree acute toxicity test to study the toxicity of 2,3,5,6-TeCP to willows Salix viminalis (S. viminalis) at neutral and acidic conditions (roughly pH 7 and 4) with inhibition of transpiration as toxic endpoint. At neutral pH the EC₅₀ was >10 mg L^?1 while the EC₅₀ at acidic conditions was 0.32 ± 0.17 mg L^?1, clearly indicating that toxicity is exerted by the non-ionic chemical fraction. Standard tests running at neutral pH are therefore not capturing the full toxicity of weak acids and bases.     

Growth, herbivory and disease in relation to gender in Salix viminalis L.

Many species of dioecious plants show sex-related differences in growth rate and rates of attack by various herbivores and diseases. The common pattern is for males to grow faster than females and to be less well defended against herbivores. In willows (Salix spp.), the predominance of female-biased sex ratios has been ascribed in part to differential feeding by herbivores. In this study of Salix viminalis, seven families grown on agricultural land showed no gender-related variation in shoot biomass or rates of herbivory by insects (lepidopterans and cecidomyiids). However, Melampsora rust disease was found to be more severe on females than on males when the plants were in a non-reproductive stage. After flowering and seed-set females tended to be more affected in some families but less affected in others. Although, on average, there was a female bias in the sex ratio of S. viminalis, sex ratios differed significantly between families. These ratios were not related to any of the recorded biotic agents, but rather to relationships between families. These results are interpreted in terms of resource allocation between reproduction, growth and defence, and causes for divergence from the expected patterns are discussed. The results may have implications for S. viminalis breeding strategies where the aim is to produce biofuel. For instance, these findings suggest that gender can be ignored when selecting for a high growth rate and resistance to Melampsora and certain insect pests. Received: 2 November 1996 / Accepted: 8 February 1997