Maturation Pathway for Ribosomal RNA in the Hela Cell Nucleolus

The maturation pathway for ribosomal RNA in Hela cells has been confirmed by RNA sequencing methods.     

Enhanced assimilation rate and water use efficiency with latitude through increased photosynthetic capacity and internal conductance in balsam poplar (Populus balsamifera L.)

In outdoor common gardens, high latitude populations of deciduous tree species often display higher assimilation rates ( A ) than low latitude populations, but they accomplish less height. To test whether trends in A reflect adaptation to growing season length or, alternatively, are garden growth artefacts, we examined variation in height increment and ecophysiological traits in a range-wide collection of Populus balsamifera L. populations from 21 provenances, during unconstrained growth in a greenhouse. Rooted cuttings, maintained without resource limitation under 21 h photoperiod for 90 d, displayed increasing height growth, A , leaf mass per area and leaf N per area with latitude whereas stomatal conductance ( g _s) showed no pattern. Water-use efficiency as indicated by both gas exchange and δ ¹³C increased with latitude, whereas photosynthetic nitrogen-use efficiency decreased. Differences in δ ¹³C were less than expected based on A/g _s, suggesting coextensive variation in internal conductance ( g _m). Analysis of A – C _i curves on a subset of populations showed that high latitude genotypes had greater g _m than low-latitude genotypes. We conclude that higher peak rates of height growth in high latitude genotypes of balsam poplar are supported by higher A , achieved partly through higher g _m, to help compensate for a shorter growing season.     

Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.)

Plant phenology is expected to be sensitive to climate warming. In boreal trees, spring flush is primarily temperature driven, whereas height growth cessation and autumn leaf senescence are predominantly controlled by photoperiod. Cuttings of 525 genotypes from the full range of balsam poplar were planted into two common gardens (Vancouver and Indian Head, Canada) at similar latitudes, but with differing winter temperatures and growing seasons. There was clinal variation in spring and, particularly, summer and fall phenology. Bud flush and, despite milder climate, bud set and leaf drop were earlier at Vancouver than at Indian Head by 44, 28 and 7 d, respectively. Although newly flushed growth is insensitive to photoperiod, many genotypes at both sites became competent before the summer solstice. At Vancouver, high‐latitude genotypes set dormant terminal buds in mid‐spring. Most other genotypes grew until midsummer or set bud temporarily and then experienced a second flush. In both gardens and in a growth chamber experiment, earlier bud set was associated with reduced height growth and higher root/shoot ratios. Shoots attained competency ～5 weeks after flushing, which would normally prevent dormancy induction before the solstice, but may be insufficient if spring advances by more than a few weeks.     

Pressure-Induced Water and Solute Flow Through Plant Roots

Water and salt flows through detopped sunflower, tomato andred kidney bean roots under applied pressure were studied usinga pressure chamber. Values of J_v for these root systems weremeasured applying variable pressure on the root medium, andL_p calculated. The K, Na and Cl fluxes under applied pressure were comparedwith those in intact plants at the same water flow rates. Tento 100 times higher Na and Cl fluxes were observed through detoppedroots under pressure as compared to those in the unpressurized,intact plants. It is suggested that the roots under pressureare not completely analogous to intact plant roots, and thatpressure-induced flow may not be a reliable method of determiningcharacteristics of ion flow in roots in relation to water flow. Key words: Volume flow, Hydraulic conductivity, K selectivity     

The Relationship Between Cell Size and Cell Number and the Distance from the Root Tip to the Region of Phloem Initiation in Groundnuts (Arachis hypogea. L. var. Bukene Red)

The effects of cell size and number on the distance from theroot tip to phloem inception in groundnuts have been investigated.The roots were treated with a number of plant growth regulatorshaving a wide range of effects on the growth rate. Increasing the growth rate of roots increased the distance ofphloem initiation and lignification from the apex. In all treatments,the average distance to phloem inception varied from about 590to 885 µm behind the root apex. The average lengths of the cortical and epidermal cells, whichwere 16 and 20 µm respectively, remained constant regardlessof the distance from the root tip.     

Genomic diversity,population structure,and migration following rapid range expansion in the Balsam Poplar,Populus balsamifera

Rapid range expansions can cause pervasive changes in the genetic diversity and structure of populations. The postglacial history of the Balsam Poplar, Populus balsamifera, involved the colonization of most of northern North America, an area largely covered by continental ice sheets during the last glacial maximum. To characterize how this expansion shaped genomic diversity within and among populations, we developed 412 SNP markers that we assayed for a range‐wide sample of 474 individuals sampled from 34 populations. We complemented the SNP data set with DNA sequence data from 11 nuclear loci from 94 individuals, and used coalescent analyses to estimate historical population size, demographic growth, and patterns of migration. Bayesian clustering identified three geographically separated demes found in the Northern, Central, and Eastern portions of the species’ range. These demes varied significantly in nucleotide diversity, the abundance of private polymorphisms, and population substructure. Most measures supported the Central deme as descended from the primary refuge of diversity. Both SNPs and sequence data suggested recent population growth, and coalescent analyses of historical migration suggested a massive expansion from the Centre to the North and East. Collectively, these data demonstrate the strong influence that range expansions exert on genomic diversity, both within local populations and across the range. Our results suggest that an in‐depth knowledge of nucleotide diversity following expansion requires sampling within multiple populations, and highlight the utility of combining insights from different data types in population genomic studies.