Gap regeneration in primary evergreen broad-leaved forests with or without a major canopy tree,Distylium racemosum,southwestern Japan: A comparative analysis

Gap regeneration was studied in a typical primary evergreen broad-leaved forest withoutDistylium racemosum, at the Kasugayama Forest Reserve, southwestern Japan and the results were compared with those from other primary evergreen broad-leaved forests in southwestern Japan, whereD. racemosum was the dominant species. Several common types of gap regeneration behavior were recognized among the major tree species and forests with or withoutD. racemosum consisted of three typical regeneration guilds which could be detected in the principal component analysis.Castanopsis cuspidata frequently regenerated in gaps from saplings recruited before gap formation in the forest withoutD. racemosum, although elsewhere, in forests withD. racemosum, it lacked advanced regeneration and regenerated in gaps from saplings recruited after gap formation. Some evergreenQuercus had their regenerations in gaps of the forest withoutD. racemosum, although elsewhere, in forests withD. racemosum, evergreenQuercus might not regenerate. The results indicate that tree species may change their regeneration behavior depending on the presence or absence of another key dominant species. This suggests that the presence and the dominance of a potential competitor induces shifts in the regeneration niche of other coexisting tree species.     

Elevated CO2 and drought alter tissue water relations of birch (Betula populifolia Marsh.) seedlings

The effect of increasing atmospheric CO₂ concentrations on tissue water relations was examined in Betula populifolia, a common pioneer tree species of the northeastern U.S. deciduous forests. Components of tissue water relations were estimated from pressure volume curves of tree seedlings grown in either ambient (350 l l^–1) or elevated CO₂ (700 l l^–1), and both mesic and xeric water regimes. Both CO₂ and water treatment had significant effects on osmotic potential at full hydration, apoplasmic fractions, and tissue elastic moduli. Under xeric conditions and ambient CO₂ concentrations, plants showed a decrease in osmotic potentials of 0.15 MPa and an increase in tissue elastic moduli at full hydration of 1.5 MPa. The decrease in elasticity may enable plants to improve the soil-plant water potential gradient given a small change in water content, while lower osmotic potentials shift the zero turgor loss point to lower water potentials. Under elevated CO₂, plants in xeric conditions had osmotic potentials 0.2 MPa lower than mesic plants and decreased elastic moduli at full hydration. The increase in tissue elasticity at elevated CO₂ enabled the xeric plants to maintain positive turgor pressures at lower water potentials and tissue water contents. Surprisingly, the elevated CO₂ plants under mesic conditions had the most inelastic tissues. We propose that this inelasticity may enable plants to generate a favorable water potential gradient from the soil to the plant despite the low stomatal conductances observed under elevated CO₂ conditions.     

Factors toxic to beech (Fagus sylvatica L.) seedlings in acid soils

The effects of highly and moderately acid soils on total biomass, biomass partitioning, fine root characteristics and nutritional status of beech seedlings (Fagus sylvatica L.) were studied in a growth chamber experiment. In Haplic Arenosols seedlings grew slowly but equally well without damage symptoms in a highly acid and a moderately acid soil horizon. The moderately acid A_h+B_w-horizon of a Eutric Cambisol was favourable to seedling growth. The fine root development was reduced in the highly acid A+B_w-horizon of a Dystric Cambisol and in the A_h+E-horizon of a Haplic Podzol, the latter of which also caused increased mortality. Seedling growth in the B₂-horizon of the Haplic Podzol was vigorous, in spite of a higher level of extractable Al and lower base saturation as compared with the A_h+E-horizon. These results are interpreted in relation to soil acidity, soil Al and nutritional status of the seedlings. We conclude that neither Al-toxicity nor nutrient deficiency cause the damage symptoms observed in the A_h+E-horizon of a Haplic Podzol and the fine root reduction in the A+B_w-horizon of a Dystric Cambisol. The damage symptoms of the PZh_A treatment seems to be more the result of H-toxicity or H-related factors other than nutrient shortage or Al-toxicity. Other pH-related toxic factors are discussed.     

Regeneration from intact and sectioned immature embryos of barley (Hordeum vulgare L.): the scutellum exhibits an apico-basal gradient of embryogenic capacity

Immature zygotic embryos from spring barley cv. Dissa were used to induce somatic embryogenenesis. Up to 158 germinated somatic embryos could be recovered per plated zygotic embryo. Critical factors for obtaining a high yield of regenerants were the size of the explant, the level of 2,4-D used for callus induction and the careful division of callus at each subculture. Use of microsections of immature embryos as explants revealed a pronounced gradient of callus formation and embryogenic response across the scutellum. Sections from the scutellar tissue at the coleoptilar end of the embryo gave the most callus and were highly embryogenic. The regeneration response of sectioned explants was comparable to that recovered from intact embryos of similar size.     

Somatic embryogenesis from callus cultures ofNardostachys jatamansi

Callus cultures ofNardostachys jatamansi DC, an endangered medicinal and aromatic plant, were established using petiole explants on MS medium supplemented with 16.1 µM -naphthaleneacetic acid and 1.16 µM kinetin. Embryogenesis in these callus cultures took place only upon sequential subculture of the callus on media having gradually decreasing auxin (16.1 to 1.34 µM NAA) and simultaneously increasing cytokinin (1.16 to 9.30 µM kinetin) concentrations over a period of 7 months. Somatic embryo to plantlet conversion took place on a medium containing 9.30 µM kinetin and 1.34 µM NAA.     

Plant regeneration through culture of isolated microspores of Triticum aestivum L.

Wheat microspores mechanically isolated from the anthers before culture and isolated from the anthers during the hole culture period in a chemically defined medium resulted in proembryos, embryos and finally plants. Of the four genotypes included, all responded with proembryos, and the two spring wheats Ciano and Walter gave rise to macroscopic embryos and plants. The frequency of embryo regeneration and the frequency of albino plants in both Ciano and Walter was in accordance with previously obtained results with anther culture derived material.Abbreviations 2,4-d 2,4-dichlorophenoxy acetic acid - NAA 1-naphthaleneacetic acid     

Plant regeneration from callus and explants of Sesbania spp.

Root, hypocotyl and cotyledon explants of Sesbania bispinosa, Sesbania cannabina, Sesbania formosa, and Sesbania sesban were cultured on Murashige and Skoog medium with benzyladenine (BA; 2.22, 4.44, 8.88 M) in combination with 2,4-dichlorophenoxyacetic acid (2,4-d; 2.26, 4.52, 9.05 M), indolebutyric acid (IBA; 0.25, 0.49, 4.92 M) or naphthaleneacetic acid (NAA; 2.69, 5.37, 10.74 M). Although all explant types developed some callus, callus occurred earliest and continued to grow fastest with hypocotyls. Media including 2.4-d or NAA gave the fastest growing callus. Callus was subcultured up to 10 times at 20-day intervals and retained a rapid growth rate. Shoots regenerated readily from both hypocotyls or cotyledons but not from roots. Shoot organogenesis was most frequent with IBA (0.25–4.92 M) in combination with BA (4.44–8.88 M) and did not occur with 2,4-d. With each species at least one medium induced shoot differentiation from more than 50 percent of the callus pieces. With one exception, media containing IBA that induced shoot organogenesis on explants also did so in callus, but media containing NAA, even when effective with explants, did not cause differentiation of callus. Shoots that differentiated were excised and cultured on MS medium without growth regulators or with IBA (2.46, 4.92, 9.84 M). Roots developed after 3–8 days on an appropriate rooting medium, often without IBA. Rooted plantlets were transplanted to pots in a greenhouse and developed into normal plants. Suitable media and protocols for initiating and subculturing callus and regenerating whole plants in vitro from callus and explants have thus been established for four species of Sesbania.     

Arrest of somatic embryo development in grapevine: histological characterization and the effect of ABA,BAP and zeatin in stimulating plantlet development

In an effort to understand the causes of arrest of somatic embryo development, generally observed in grapevine (Vitis sp.), histological studies were undertaken, using two cultivars (CH76 and 41B) which differ in their ability to develop into plants. Embryos with a high conversion rate (70%; CH76) formed a well-structured and functional shoot apex between two thread-like cotyledons. In contrast, embryos with a low conversion rate (10%; 41B) formed a normal root apex but lacked a well-structured shoot apex and developed a wide range of aberrant forms in the intercotyledonary area: uncontrolled cellular proliferation, formation of adventitious buds, over-growth of cotyledonary or leaf meristems. ABA increased the conversion rate of 41B embryos from 10% to 20%, but failed to improve embryo morphology. Zeatin and BAP promoted growth of 41B somatic embryos, but generated a high level of abnormalities and failed to improve conversion rate. Applied in combination with ABA, these PGRs increased the frequency of cotyledonary embryos, but decreased the conversion rate.     

Fertile plants regenerated from suspension culture-derived protoplasts of an indica type rice (Oryza sativa L.)

Calluses were induced from immature embryos of an indica type rice and finely dispersed cell suspension cultures were initiated from the callus using modified AA medium (S₁ medium). The suspension cultures were maintained alternatively (1–2 passages in each medium) in S₁ medium and S₂ medium, the latter containing KNO₃, NH₄NO₃, proline and glutamine as nitrogen source. Protoplasts of high quality were isolated form suspension cells cultured in S₂ medium supplemented with ABA. Embedding the protoplasts in agarose blocks containing NH₄NO₃-free modified KM8P(PM₁) medium and immersing the blocks in NH₄NO₃-containing modified KM8P(PM₃) medium were most effective for obtaining protoplast division and callus formation. The protoplast-derived calluses were precultured in potato extract-aand/or ABA-containing N₆(D₁, D₂ or D₃) media and many embryo-like structures were formed. These structures developed into plantlets after being transferred to N₆ differentiation (D₄) medium. The regenerated plantlets grew into mature plants and beard seeds normally.Abbreviations AA medium amino acids based medium - ABA abscisic acid - BA benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - DF division frequency - IAA indoleacetic acid - KIN kinetin - NAA naphthaleneacetic acid - PE planting efficiency     

Contrasting litter effects on old field tree germination and emergence

Because the fate of seeds is critical to understanding the invasion of old fields by trees, and plant litter is an important component defining the old field microsite of dispersed seeds, I investigated the effects of litter type (Solidago spp./goldenrod,Quercus spp./oak, mixed) and litter amount (100–800 g/m²) on tree seed germination and seedling emergence. I found that at all densities bothSolidago andQuercus litter greatly reduced emergence of the small-seeded, bird-dispersed species,Juniperus virginiana andCornus florida. For one of the large-seeded, mammal-dispersed species,Carya tomentosa, high densitySolidago litter and high density mixed litter treatments reduced emergence. For the other large-seeded species,Quercus rubra, the high density mixed litter treatment and all levels ofSolidago litter reduced emergence.Quercus seedlings emerged twice as often as the other three species in control pots without litter.Carya emerged before the other species but the high density oak treatment delayed the expansion of its cotyledons. My results suggest that litter may contribute to the slow rate of tree invasion and the low probability of tree establishment in old fields. However, old field litter studies taken together point to the difficulty in drawing general conclusions about any net effect of litter on old field tree establishment.