Plant regeneration of wildGlycine species from suspension culture-derived protoplasts

Protoplasts isolated from four-week old cell suspension cultures ofGlycine canescens F. J. Herm andG. clandestina Wendl. were cultured in 8P or modified 8P to a multicellular stage. Colonies of 0.5 to 1.0 mm diameter were transferred to solid media for callus growth and regeneration. Callus consisted of friable masses with compact green nodular areas. Organogenesis of both species occurred primarily from the green nodular areas. Shoot buds ofG. clandestina did not mature, but shoots ofG. canescens proliferated on MS medium, with B5 vitamins, 0.33 mgL^–1 each BA, KN, ZN, and 0.15 mgL^–1 NAA. Shoots failed to root after multiple subcultures on four different rooting media.In vitro grafting ofG. canescens scions ontoG. max root stocks allowed plants to be transferred to soil. An overall protoplast division efficiency of 48% was achieved with moderately efficient shoot regeneration inG. canescens. Division efficiencies forG. clandestina were lower (11%). Refinements of this protocol should result in high efficiencies of regeneration which would allowin vitro manipulations of these wild soybean relatives at the single cell level and would make the derivation of somatic hybrid plants possible within the genusGlycine.Abbreviations BA 6-Benzyladenine - KN kinetin - ZN Zeatin - NAA Napthaleneacetic acid - 2,4-D 2–4-dichlorophenoxyacetic acid - PIC Picloram - CH casein hydrolysate - Gln glutamine - Met methionine - MES 2[N-morpholine] ethanesulfonic acid     

The role of sediment type in growth and fecundity of mud snails (Hydrobiidae)

Summary We test the hypothesis that body size and population density of the deposit-feeding gastropod, Hydrobia truncata, are greater in muddy than in sandy habitats as a result of faster growth on fine- compared to coarse-grained sediments. We refute this hypothesis using a combination of field measurements and laboratory experiments. Three out of three populations tested had higher maximal growth rates and two of three populations approached their asymptotic size more quickly on sand than on silt-clay fractions of natural sediment. Growth decreased with increasing snail density and was as high or higher on sand as on silt-clay at all densities. Two populations were more fecund on sand than on silt-clay, and fecundity of the third population was not affected by sediment type. We show that the smaller body sizes observed in snails from the sandiest habitat result from late recruitment of these snails, relative to the other populations.     

The effect of soil compaction on the saprophytic growth of Rhizoctonia solani

The increase in bare patch of cereals associated with minimum tillage practices prompted an investigation of the relationship between soil compaction and saprophytic growth of Rhizoctonia solani. In soils wetter than 10 kPa there was a greater density of hyphae in compacted than in non-compacted soil. In relatively dry soil, however, there was wider exploration by hyphae in non-compacted than in compacted soil. The implications of these findings for disease management are discussed.     

A recombination event that redefines the Huntington disease region

We report both a recombination event that places the Huntington disease gene proximal to the marker D4S98 and an extended linkage-disequilibrium study that uses this marker and confirms the existence of disequilibrium between it and the HD locus. We also report the cloning of other sequences in the region around D4S98, including a new polymorphic marker R10 and conserved sequences that identify a gene in the region of interest.     

The Quaternary eolian sequence of Madeira: stratigraphy, chronology, and paleoenvironmental interpretation

A thick (ca. 40 m) sequence of coastal eolian sediments occurs on a narrow peninsula on the eastern end of the island of Madeira, located in the Eastern Atlantic at 33°N latitude. The sediments consist of black volcanic sands (with or without bioclasts) as well as clay units up to 2 m thick. A series of inceptisols (Eutrochrepts) and one alfisol (a Hapludalf) are developed in these sediments. Land snail shells and secondary carbonates, in the form of well-developed rhizoliths, calcretes, fissure-fills, and soil nodules, are present in abundance. The chronology of the sequence was determined by ¹⁴C and U---Th analyses of land snail shells and secondary carbonates and amino acid epimerization analysis of land snail shells. All sediments, including the clay units, are originally of eolian origin, derived from the beach to the south of the deposit, but some have been redeposited by colluviation. Temporal variation in the lithology of the sediments relates to variations in sea-level, with black sands being deposited during lower sea level stands and clays at the lowest. It is suggested that fine marine sediments, exposed during low sea-level stands, may also be the dominant source of silty or clayey units in other coastal eolian deposits in the subtropical Atlantic and Mediterranean.

The sequence spans from 200,000–300,000 years ago up to the 20th century. Sedimentation was discontinuous and often rapid; erosional hiatuses are present. During the Holocene, eolian sands started accumulating at 8200 yr B.P. during a transgressive phase and stopped at 4500 yr B.P. as sea level approached its present height. Colluviation increased dramatically following the first human settlement of the island in the 15th century and continued up to the 20th century, as dated by amino acid epimerization analysis of land snails. Earlier periods of colluviation were identified from the age distribution of land snail shells redeposited in younger colluvium.

Paleoenvironmental reconstruction was based mainly on soil and sediment features (including rhizolith morphology) and land snail faunas but also on stable isotope variations (¹³C, ¹⁸O) in land snails and secondary carbonates, pollen (generally not well preserved), and phytoliths. Most of the portion of the Middle Pleistocene represented in the sequence was characterized by moderately dry conditions, in comparison to the late Pleistocene and Holocene. During the last interglacial, relatively wet conditions occurred, wetter than during the Holocene interglacial. Moderately moist conditions were present during the accumulation of the thick unit dating to ca. 80,000 yr B.P. As sea level fell subsequent to this period, conditions appear to have become drier. Starting ca. 50,000–55,000 yr B.P., conditions were especially wet, but prior to the last glacial maximum, markedly arid conditions ensued. Toward the end of the last glacial, wet conditions returned and produced the best-developed soil preserved in the sequence. Moderately moist conditions occurred during the early to middle Holocene but apparently become slightly drier after 4500 yr B.P. The impact of human settlement can be seen in the loss of woody vegetation and enhanced gullying and colluviation during the last ca. 500 years.     

Phytochrome control of short-day-induced bud set in black cottonwood

In trees and other woody perennial plants, short days (SDs) typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud and bud dormancy. Phytochrome control of SD-induced bud set was investigated in two northern clones of black cottonwood (Populus trichocarpa Torr. & Gray) by using night breaks with red light (R) and far-red light (FR). For both clones (BC-1 and BC-2), SD-induced bud set was prevented when R night breaks as short as 2 min were given in the middle of the night. When night breaks with 2 min of R were immediately followed by 2 min of FR, substantial reversibility of bud set was observed for BC-1 but not for BC-2. By comparing the effects of the R night breaks on bud set and the length of specific internodes, we determined that the R night breaks influenced internode elongation in two opposing ways. First, the addition of a R night break to the SD treatment prevented the cessation of internode elongation that is associated with bud set. Those internodes that would not have elongated under SDs (and would have been found within the terminal bud) elongated in the R treatment. Second, the R night breaks decreased internode length relative to the long-day (LD) control. In contrast to the clonal differences in reversibility that we observed for bud set, the decrease in internode length (i.e. the second effect of R) was R/FR reversible in both clones. Based on these results, we conclude that internode elongation is influenced by two distinct types of phytochrome-mediated response. The first response is a typical response to photpperiod, whereas the second response is a typical “end-of-day” response to light quality. Our results demonstrate that SD-induced bud set in black cottonwood is controlled by phytochrome but that clonal differences have an important influence on the R/FR reversibility of this response. The availability of an experimental system in which SD-induced bud set is R/FR reversible will be valuable for studying the physiological genetics of photoperiodism in trees.     

A protocol for the efficient screening of putatively transformed plants forbar,the selectable marker gene,using the polymerase chain reaction

Amplification of thebar gene usingTaq DNA polymerase in PCR is often not successful, possibly due tobar's high GC content. We describe a PCR protocol in which reliable amplification at a sensitivity of one gene copy per genome (in this study, barley) present in the reaction was achieved using a novel pair of primers and Expand^tm High Fidelity DNA polymerase mix (Boehringer Mannheim). This method should allow for rapid screening of plants putatively transformed withbar.     

The adaptive acid tolerance response in root nodule bacteria and Escherichia coli

Root nodule bacteria and Escherichia coli show an adaptive acid tolerance response when grown under mildly acidic conditions. This is defined in terms of the rate of cell death upon exposure to acid shock at pH 3.0 and expressed in terms of a decimal reduction time, D. The D values varied with the strain and the pH of the culture medium. Early exponential phase cells of three strains of Rhizobium leguminosarum (WU95, 3001 and WSM710) had D values of 1, 6 and 5 min respectively when grown at pH 7.0; and D values of 5, 20 and 12 min respectively when grown at pH 5.0. Exponential phase cells of Rhizobium tropici UMR1899, Bradyrhizobium japonicum USDA110 and peanut Bradyrhizobium sp. NC92 were more tolerant with D values of 31, 35 and 42 min when grown at pH 7.0; and 56, 86 and 68 min when grown at pH 5.0. Cells of E. coli UB1301 in early exponential phase at pH 7.0 had a D value of 16 min, whereas at pH 5.0 it was 76 min. Stationary phase cells of R. leguminosarum and E. coli were more tolerant (D values usually 2 to 5-fold higher) than those in exponential phase. Cells of R. leguminosarum bv. trifolii 3001 or E. coli UB1301 transferred from cultures at pH. 7.0 to medium at pH 5.0 grew immediately and induced the acid tolerance response within one generation. This was prevented by the addition of chloramphenicol. Acidadapted cells of Rhizobium leguminosarum bv. trifolii WU95 and 3001; or E. coli UB1301, M3503 and M3504 were as sensitive to UV light as those grown at neutral pH.