Shoot-bud regeneration in subcultured callus of engelmann spruce

Summary Callus cultures ofPicea engelmannii (Parry, Engelmann spruce) were initiated and established from mature embryos cultured on von Arnold and Eriksson’s medium (AE) supplemented with N⁶-benzyladenine (10μM) and naphthalene acetic acid (10 μM). Cultures were maintained by subculture at 3-to-4-wk intervals. After three subcultures, callus was transferred to AE medium with only N⁶-benzyladenine (25 μM). Adventitious buds appeared on the surface of the callus after 2-to 4-wk and grew to adventitious shoots on AE medium without growth hormones or on AE medium with kinetin (0.1 μM). Shoot-forming capacity was maintained through 7 further subcultures. This study was supported by the Natural Sciences and Engineering Research Council of Canada grant G1438 to T. A. Thorpe and D. I. Dunstan.     

控制常绿针叶树叶量对树干生长的促进作用

一、前言近几年,在研究不同树种的修枝过程中,偶然发现,一些常绿针叶树的人工去叶能加快树干材积的生长,这引起了人们新的研究兴趣:控制常绿针叶树的叶量是否能促进树木生长?这一措施有多少可能的前途或弊端?多年来,人类为寻求促进林木生长的有效经营措施,利用各种手段进行了大量实验研究工作,获得了很有意义的成果,抚育间伐是其中的一项重要途径。由于世界各国的日益重视,60年代以来,很多学     

Physiological and growth responses of two African species, Acacia karroo and Themeda triandra, to combined increases in CO2 and UV-B radiation

The interactive effects of increased carbon dioxide (CO₂) concentration and ultraviolet-B (UV-B, 280–320 nm) radiation on Acacia karroo Hayne, a C₃ tree, and Themeda triandra Forsk., a C₄ grass, were investigated. We tested the hypothesis that A. karroo would show greater CO₂-induced growth stimulation than T. triandra, which would partially explain current encroachment of A. karroo into C₄ grasslands, but that increased UV-B could mitigate this advantage. Seedlings were grown in open-top chambers in a greenhouse in ambient (360 μmol mol^-1) and elevated (650 μmol mol^-1) CO₂, combined with ambient (1.56 to 8.66 kJ m^-2 day^-1) or increased (2.22 to 11.93 kJ m^-2 day^-1) biologically effective (weighted) UV-B irradiances. After 30 weeks, elevated CO₂ had no effect on biomass of A. karroo, despite increased net CO₂ assimilation rates. Interaction between UV-B and CO₂ on stomatal conductance was found, with conductances decreasing only where elevated CO₂ and UV-B were supplied separately. Increases in water use efficiencies, foliar starch concentrations, root nodule numbers and total nodule mass were measured in elevated CO₂. Elevated UV-B caused only an increase in foliar carbon concentrations. In T. triandra, net CO₂ assimilation rates were unaffected in elevated CO₂, but stomatal conductances and foliar nitrogen concentrations decreased, and water use efficiencies increased. Biomass of all vegetative fractions, particularly leaf sheaths, was increased in elevated CO₂. and was accompanied by increased leaf blade lengths and individual leaf and leaf sheath masses. However, tiller numbers were reduced in elevated CO₂. Significantly moderating effects of elevated UV-B were apparent only in individual masses of leaf blades and sheaths, and in total sheath and shoot biomass. The direct CO₂-induced growth responses of the species therefore do not support the hypothesis of CO₂-driven woody encroachment of C₄ grasslands. Rather, differential changes in resource use efficiency between grass and woody species, or morphological responses of grass species, could alter the competitive balance. Increased UV-B radiation is unlikely to substantially alter the CO₂ response of these species.     

Effect of various bud induction treatments on elongation and rooting of adventitious shoots of Canary Island pine (Pinus canariensis)

Three-day-old cotyledonary explants of Pinus canariensis were subjected to 30 induction treatments using half-strength Bornman's medium containing various combinations of N⁶- benzyladenine, zeatin, kinetin and 2-isopentenyl-adenine. The highest numbers of buds were obtained with 10 M 6-benzyladenine, but both kinetin and zeatin influenced shoot elongation. Shoots were maintained on half-strength Schenk and Hildebrandt medium with 2% sucrose and 0.05% activated charcoal. For rooting, shoots were pulsed for 4 h in a 100 M indole-3-butyric acid aqueous solution (pH 4.2–4.5), and planted in peat:vermiculite:perlite (1:1:1). After 8 weeks, the numbers of rooted shoots were similar for most treatments. Therefore, the bud induction treatments did not significantly influence rooting of adventitious shoots of Canary Island pine.     

Woody plant encroachment in granite barrens on the Frontenac Arch,eastern Ontario,Canada

Aims

Woody plant encroachment is a widespread phenomenon affecting treeless or sparsely treed habitats. We aimed to determine the extent and timing of tree and shrub encroachment into rock barrens of eastern Ontario over the last century, and to assess implications for their ongoing management.

Location

Queen's University Biological Station in the Frontenac Arch ecoregion.

Methods

We quantified the extent of change in woody vegetation in 290 rock barrens using aerial photography from 1925, 1965, and 2008. Composition and structure of woody plant communities in 10 barrens was subsequently quantified in the field using plot-based sampling. Cores or cross-sections were obtained from individuals >1.5 m height and dendrochronological techniques were used to determine their age and identify temporal patterns of any woody encroachment.

Results

Aerial photography indicated that the mean proportion of woody plant cover in barrens increased 22.5% from 1925 to 2008. Dendroecological analysis supported this. Few trees were present prior to 1900 and most established since 1960. Fraxinus americana, Juniperus virginiana, and Juniperus communis were the most common woody species colonizing the barrens. Remnants of large Pinus strobus stumps with extensive charring were found in 90% of the sampled barrens at a mean density of 22.6 stumps ha⁻¹.

Conclusions

Rock barrens on the Frontenac Arch have changed substantially over the past century; gradually being colonized by trees and shrubs and losing their distinctly open character. Active management — including prescribed fire and mechanical thinning — may be necessary if there is a desire to maintain these barrens and the rare species they support as components of the region's biodiversity. However, identification of a reference state for restoration is complicated by the fact that the structure and composition of these habitats were undoubtedly altered by European land clearance in the 19th century, and that some of these areas likely existed as pine woodlands before that.     

Actin distribution in somatic embryos and embryogenic protoplasts of white spruce (Picea glauca)

Summary Examination of unfixed immature somatic embryos of white spruce (Picea glauca) with fluorescent rhodamine-labeled phalloidin revealed an extensive network of fine actin microfilaments (MFs) in the embryonal region which were not detected in specimens fixed with formaldehyde. Transition cells linking the embryonal region and suspensor cells contained fine MFs as well as bundles of MFs. The large, highly vacuolated suspensor cells were characterized by actin MF cables only. Treatment of embryos with cytochalasin B (CB) removed the fine MFs from the embryonal region and transition cells, but many MF cables in suspensor cells were resistant. Full recovery from CB treatment was observed in most somatic embryos. Embryogenic protoplasts capable of regenerating to somatic embryos in culture were released from only the embryonal region of somatic embryos. Both uninucleate and multinucleate embryogenic protoplasts retained the extensive network of fine actin MFs. In contrast, protoplasts derived from vacuolated suspensor cells and vacuolated free-floating cells contained thick MF bundles and were not embryogenic. Distinct MF cages enclosed nuclei in multinucleate protoplasts and may be responsible for preventing nuclear fusion. Microspectrophotometric analyses showed that the DNA contents of embryonal cells in the embryo and embryogenic protoplasts were similar and characteristic of rapidly dividing cell populations. However, transition and suspensor cells which released nonembryogenic protoplasts appeared to be arrested in G₁, and suspensor cells showed signs of DNA degradation.     

Expression of ferredoxin-dependent glutamate synthase in dark-grown pine seedlings

Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark.     

The ecological impact of bush encroachment on the yield of grasses in Borana rangeland ecosystem

The ecological impact of woody encroachment and the responses of herbage yield to encroachment were assessed at three locations in Borana rangeland at the end of the growing season. The study was carried out in two communal grazing areas (Medhecho and Dubluk) and one Government ranch (Dida‐Tuyura) in bush and/or shrub encroached and non‐encroached sites. In each area, three altitude ranges were distinguished and in each altitude range one transect, covering both encroached and non‐encroached rangeland, was selected. The assessment was based on the yield and botanical composition of the herbaceous layer. The grasses Cenchrus ciliaris, Chrysopogon aucheri and Panicum coloratum were common or dominant in both encroached and non‐encroached sites. Pennisetum mezianum and Pennise‐tum stramineum were typically found in encroached vegetation. The relative yield increased with non‐encroached sites and varied at different altitude ranges from about 106% to about 150%, thus increases ranged from 75% in Medhecho to 350% in Dubluk as determined from the lower values of the ranges. The encroached vegetation had a significantly lower score for herbage yield than the non‐encroached vegetation for most of the sites, although the differences were small. Differences based on altitude range were also significant for Eragrostis papposa and Pennisetum stramineum, while the three areas showed a significant difference for the mean yield of Aristida adscensionis, Cenchrus ciliaris and Eragrostis papposa.     

Can we rely on forest reserves for primate conservation?

Tropical forests contain much of the world's biodiversity, yet their rate of decline is increasing. The strategy most frequently used to protect this biodiversity is to make parks and reserves. While there is a great deal of research on the effectiveness of parks for protecting biodiversity, there is little research on how well extractive reserves conserve biodiversity. Here, we evaluate the effectiveness of four forest reserves in western Uganda at maintaining populations of primates and compare census data from the reserves to data from the neighbouring well‐protected Kibale National Park. The relative abundance of the five most common primates in the park was approximately four times that of the forest reserves. In the forest reserves, evidence of new human encroachment was seen every 500 m, while in the park it was seen every 100,000 m. Two recommendations emerge from our research: (i) for forest reserves, such as those studied here, to have conservation value for primates, extraction must be reduced and (ii) until the long‐term viability of the populations in forest reserves can be ascertained, they should not be considered in estimates of the sizes of endangered species protected ranges.