The Effects of Nutrient Dynamics on Root Patch Choice

Plants have been recognized to be capable of allocating more roots to rich patches in the soil. We tested the hypothesis that in addition to their sensitivity to absolute differences in nutrient availability, plants are also responsive to temporal changes in nutrient availability. Different roots of the same Pisum sativum plants were subjected to variable homogeneous and heterogeneous temporally – dynamic and static nutrient regimes. When given a choice, plants not only developed greater root biomasses in richer patches; they discriminately allocated more resources to roots that developed in patches with increasing nutrient levels, even when their other roots developed in richer patches. These results suggest that plants are able to perceive and respond to dynamic environmental changes. This ability might enable plants to increase their performance by responding to both current and anticipated resource availabilities in their immediate proximity

Egg production

Each row represents eggs laid by a group of fleas fed simultaneously on the same host

Emergence success

Each row represents a group of papae from the same clutch of eggs laid at the same day by a group of females fed on the same host individua

Data from: Use it or lose it: reproductive implications of ecological specialization in a haematophagous ectoparasite

Using experimentally induced disruptive selection, we tested two hypotheses regarding the evolution of specialization in parasites. The ‘trade-off’ hypothesis suggests that adaptation to a specific host may come at the expense of a reduced performance when exploiting another host. The alternative ‘relaxed selection’ hypothesis suggests that the ability to exploit a given host would deteriorate when becoming obsolete. Three replicate populations of a flea Xenopsylla ramesis were maintained on each of two rodent hosts, Meriones crassus and Dipodillus dasyurus, for nine generations. Fleas maintained on a specific host species for a few generations substantially decreased their reproductive performance when transferred to an alternative host species, whereas they generally did not increase their performance on their maintenance host. The results support the ‘relaxed selection’ hypothesis of the evolution of ecological specialization in haematophagous ectoparasites, while suggesting that trade-offs are unlikely drivers of specialization. Further work is needed to study the extent by which the observed specializations are based on epigenetic or genetic modifications

Pupation success

Each row represents a clutch of eggs laid at the same day by a group of females fed on the same host individua

N-glycosylation in Haloferax volcanii: adjusting the sweetness

Long believed to be restricted to Eukarya, it is now known that cells of all three domains of life perform N-glycosylation, the covalent attachment of glycans to select target protein asparagine residues. Still, it is only in the last decade that pathways of N-glycosylation in Archaea have been delineated. In the haloarchaeon Haloferax volcanii, a series of Agl (archaeal glycosylation) proteins is responsible for the addition of an N-linked pentasaccharide to modified proteins, including the surface (S)-layer glycoprotein, the sole component of the surface layer surrounding the cell. The S-layer glycoprotein N-linked glycosylation profile changes, however, as a function of surrounding salinity. Upon growth at different salt concentrations, the S-layer glycoprotein is either decorated by the N-linked pentasaccharide introduced above or by both this pentasaccharide as well as a tetrasaccharide of distinct composition. Recent efforts have identified Agl5–Agl15 as components of a second Hfx. volcanii N-glycosylation pathway responsible for generating the tetrasaccharide attached to S-layer glycoprotein when growth occurs in 1.75 M but not 3.4 M NaCl-containing medium

AglQ is a soluble protein.

<p><i>Hfx</i>. <i>volcanii</i> cells transformed to express GFP-AglQ were separated into membrane and cytosolic (supernatant) fractions and probed with anti-GFP (α-GFP) or anti-SRP54 (α-SRP54) antibodies, as was a total protein extract (cell). Alternatively, the position of the S-layer glycoprotein in the same fractions was identified by Coomassie staining. The proteins migrate with the following molecular masses in SDS-PAGE: S-layer glycoprotein, 180 kDa [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081782#B20" target="_blank">20</a>], SRP-54, 51 kDa [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081782#B16" target="_blank">16</a>], GFP-AglQ, 44 kDa.</p

Expression of AglQ mutants.

<p>The levels of the different versions of AglQ fused to GFP generated following site-directed mutagenesis and expression in Δ<i>aglQ</i> cells is shown. The protein content of equivalent amounts of <i>Hfx</i>. <i>volcanii</i> Δ<i>aglQ</i> cells expressing the various AglQ mutants were separated by SDS-PAGE subjected to immunoblot using anti-GFP and appropriate secondary HRP-conjugated antibodies. The positions of 55 and 40 kDa molecular weight markers are depicted on the right of each panel.</p

S-layer integrity in compromised in Δ<i>aglQ</i> cells.

<p>Parent strain (top panel) and Δ<i>aglQ</i> cells (lower panel) were challenged with 1 mg/ml proteinase K at 42°C. Aliquots were removed immediately prior to incubation with proteinase K and at 15-30 min intervals following addition of the protease for up to 3 h and examined by 7.5% SDS-PAGE and Coomassie staining. The S-layer glycoprotein band from each gel is presented.</p

S-layer glycoprotein N-glycosylation in compromised in Δ<i>aglQ</i> cells.

<p>Following trypsin treatment, the S-layer glycoprotein of Δ<i>aglQ</i> cells was examined by normal phase LC-ESI MS. Shown are profiles obtained for the ¹ERGNLDADSESFNK¹⁴ glycopeptide. Arrows indicate the positions of [M+2H]²⁺ ions corresponding to the peptide modified by (A) the first, (B) the first two and (C) the first three sugar residues of the pentasaccharide normally N-linked to this position. No [M+2H]²⁺ ion peaks corresponding to the same peptide modified by the first four pentasaccharide residues (D) nor the complete pentasaccharide (E) were detected in the <i>aglQ</i> deletion strain, despite such species being readily detected in the same sample obtained from parent strain cells (insets of D and E, respectively). The identity of each pentasaccharide subunit is provided in the inset in (A).</p