Comparative leaf anatomy of Salix species and hybrids

Epidermal features, mesophyll differentiation and calcium oxalate characteristics of 19 species and 12 hybrids of Salix are described. The species and hybrids can be distinguished by the presence or absence of the following epidermal features: striated cuticle; stomata; covering trichomes; beaded anticlinal walls, and diosmin-like njstals. In or near marginal teeth, glandular trichomes are present in all cases. The leaf veins of all specimens examined have calcium oxalate prism sheaths and, with the exception of S. herbacea , cluster crystals in some cells of the mesophyll. Most sprcies studied in the subgenus Salix show: both adaxial and abaxial stomata; striated cuticle metopllyll of palisade cells, with little or no spongy mesophyll, but with a well-defined hypodermis, and absence of thick-walled, sinuous trichomes. Characteristic features of the subgenus Caprisalix are: abaxial stomata only; epidermal crystals; smooth cuticle; mesophyll diflerentiated into palisade cells and spongy mesophyll and without a hypodermis, and trichomes more numerous and varied than those of the subgenus Salix . Leaves of the two species of the subgenus Chaemelia examined and those of S. lapponum , have predominantly anomocytic stomata, whereas all the other leaves studied have predominantly paracytic stomata. The anatomical features described, in conjunction with the morphologiral characters, enable the species and hybrids of Salix studied to be autheenticated.     

Light effects on root formation in aspen and willow cuttings

The effect of light on rooting of leafy cuttings of aspen (Populus tremula × tremuloides) and a willow hybrid (Salix caprea × viminalis) was investigated under controlled conditions in water culture. Two levels of irradiance were used, 40 and 8 W m^?2. The lower level gave the best rooting of aspen cuttings, both when applied to the stock plants before the cuttings were taken and when given to the cuttings during the rooting period. Irradiation of the cutting base during the rooting period inhibited rooting almost completely in aspen and decreased the number of roots formed in the Salix hybrid. Net photosynthesis in the cuttings of Salix decreased considerably after excision and increased again after formation of roots. Indirect evidence indicated that photosynthesis was even more affected in aspen cuttings. The possible roles of carbohydrates and inhibitors in the light effects are discussed.     

Salix martiana,a regularly hermaphrodite willow

Sex distribution in a neotropical willow,Salix martiana Leybold, has long escaped the attention of botanists. Its catkins are regularly composed of female, hermaphrodite and male flowers. The present paper discusses some aspects of its possible morphological and/or evolutionary significance.     

Variation in the uptake of Arsenic, Cadmium, Lead, and Zinc by different species of willows Salix spp. grown in contaminated soils

The experiment assessed the variability of in seven clones of willow plants of high biomass production (Salix smithiana S-218, Salix smithiana S-150, Salix viminalis S-519, Salix alba S-464, Salix ’Pyramidalis’ S-141, Salix dasyclados S-406, Salix rubens S-391). They were planted in a pots for three vegetation periods in three soils differing in the total content of risk elements. Comparing the calculated relative decrease of total metal contents in soils, the phytoextraction potential of willows was obtained for cadmium (Cd) and zinc (Zn), moderately contaminated Cambisol and uncontaminated Chernozem, where aboveground biomass removed about 30% Cd and 5% Zn of the total element content, respectively. The clones showed variability in removing Cd and Zn, depending on soil type and contamination level: S. smithiana (S-150) and S. rubens (S-391) demonstrated the highest phytoextraction effect for Cd and Zn. For lead (Pb) and arsenic (As), the ability to accumulate the aboveground biomass of willows was found to be negligible in both soils. The results confirmed that willow plants show promising results for several elements, mainly for mobile ones like cadmium and zinc in moderate levels of contamination. The differences in accumulation among the clones seemed to be affected more by the properties of clones, not by the soil element concentrations or soil properties. However, confirmation and verification of the results in field conditions as well as more detailed investigation of the mechanisms of cadmium uptake in rhizosphere of willow plants will be determined by further research.     

Eighteen microsatellite loci in Salix arbutifolia (Salicaceae) and cross-species amplification in Salix and Populus species

Salix arbutifolia is a riparian dioecious tree species that is of conservation concern in Japan because of its highly restricted distribution. Eighteen polymorphic loci of dinucleotide microsatellites were isolated and characterized. Among these, estimates of the expected heterozygosity ranged from 0.350 to 0.879. Cross-species amplification was successful at 9-13 loci among six Salix species and at three loci in one Populus species.     

Parameters of photosynthesis light curve in <Emphasis Type="Italic">Salix dasyclados</Emphasis> and their changes during the growth season

A dependence of the photosynthesis rate on light is characterized by a number of parameters that are often used for comparison between plant species or for finding photosynthesis interconnections with other physiological processes. In order to properly assessed these parameters, we measured the maximum apparent photosynthesis rate (P _max), dark respiration rate (R _d), light compensation point (LCP), quantum yield corresponding to photosynthetic efficiency (QY), and the light saturation constant (K _s), taking into consideration the leaf plastochron index during vegetation of one of the willow species (Salix dasyclados Wimn.). The P _max value was the highest in the beginning of the growth season when the leaf reached 65% of its full area; after that P _max slowly declined. The most important cardinal value for R _d is its plateau reached by the end of leaf growth, i.e., later than the photosynthesis rate maximum. This plateau value also decreased during vegetation. The LCP value changed in the same way as R _d but reached its plateau simultaneously with the photosynthesis rate maximum. QY also reached its maximum at the same time with the photosynthesis rate; during vegetation it changed more than twofold. The K _s value also changed almost twofold during the season, reaching its maximum together or slightly later than the photosynthesis maximum and then remained constant. Thus, we have found significant changes in the parameters of the photosynthesis light curve during growth season. This shows that they can be used only after a thorough study of leaf development in each particular plant species. Usually performed measuring gas exchange parameters in fully developed leaves does not yield their maximum values and thus does not have any physiological sense.     

柳属植物化学成分研究概况

柳树是园林绿化的重要树种,各部位在民间药用历史悠久。对国内外柳属化学成分研究的相关文献资料进行了系统的整理,综述了柳属植物化学成分的研究进展,为柳属植物的进一步研究和开发提供资料参考。     

Pollen Morphology of Tundra Shrubs and Submarginal Plants from Barrow, Alaska

Investigation of plant morphological features, pollen, and habitat have been made for two shrub species from Barrow, Alaska, namely Dryas integrifoila M. Vahl and Salix rotundifolia Trautv., both of which are endemic to the Arctic floristic area. The former species has small lanceolate or plate leaves, whereas the latter has rounded leaves with distinct veins, rich in vitamin C. Both have dwarf and sprawling habits. Pollen studies showed that the pollen grains of the two species are spheroidal to sub-spheroidal or prolate. The type of aperture was tricolporate; pollen size 26.3-31.3 μm; ornamentation finely reticulate under a light microscope （LM） and strlate-reticulate under a scanning electron microscope （SEM） for D. integrafoila and finely reticulate under the LM and SEM for S. rotundifolia. Comparisons were made between the pollen from the same species from Arctic collections with those from China and Japan. Investigation of pollen morphology of tundra plants can provide significant data for comparative studies of fossil pollen and for the reconstruction of paleovegetation and paleoclimate in the Barrow area.     

Gibberellins and Subapical Cell Divisions in Relation to Bud Set and Bud Break in Salix pentandra

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA₁ action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA₁ levels. Application of GA₁ to short-day–induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA₁ application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4–6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA₁ content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA₁ affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues. Received February 26, 1999; accepted October 8, 1999