Mouthpart adaptations of antlion larvae facilitate prey handling and fluid feeding in sandy habitats

Antlion larvae are fluid-feeding ambush predators that feed on arthropods trapped in their funnel-shaped pits built in sandy habitats; however, details are lacking about their feeding mechanism. Here we tested the hypothesis that the antlion, Myrmeleon crudelis, has adaptations that facilitate fluid feeding in sandy habitats. We measured contact angles of water droplets and used the capillary-rise technique to assess mouthpart wettability. A structural organization was discovered that provides a hydrophobic-hydrophilic wetting dichotomy that would simultaneously support self-cleaning and fluid uptake and is enabled by antiparallel movements of the maxillae. The mouthparts also are augmented by their mechanical properties, including maxillae and mandible tips that might be heavily sclerotized, as determined by confocal microscopy, which likely facilitate piercing prey. Our findings provide insight on how antlion larvae have overcome the challenges of fluid feeding in sandy habitats, which likely contributed to their success and widespread distribution.

Maize root responses to drought stress depend on root class and axial position

In this study we tested the hypotheses that root classes would exhibit distinctive anatomical and architectural responses to drought stress, and that those responses would vary along the root axes. The root systems of four maize (Zea mays L.) sweet corn genotypes designated SC1, SC2, SC3 and SC4 were phenotyped under well-watered and drought treatments in greenhouse mesocosms, permitting increasing stratification of moisture availability as the drought progressed. Anatomical and architectural responses to drought were evaluated for each root class. Lignin distribution was assessed by image processing of UV-illuminated root cross-sections acquired by laser ablation tomography. The two cultivars with less biomass reduction under drought, SC3 and SC4, substantially enhanced lateral root development along the apical segments of axial roots when plants were grown with drought stress. These segments grew into the deeper part of the mesocosm where more moisture was available. Apical segments of the axial and large lateral roots from drought-stressed plants were thicker and had greater theoretical axial water conductance than basal segments, especially in SC3 and SC4. Basal segments of crown roots of SC3 and SC4 showed increased lignification of the stele under drought. Root anatomical and architectural responses to drought are complex and vary among cultivars and root classes, and along root axes. Drought-induced proliferation of lateral roots on apical segments of axial roots would be expected to enhance deep water acquisition, while lignification of axial roots could help preserve axial water transport.

Three-dimensional imaging reveals that positions of cyst nematode feeding sites relative to xylem vessels differ between susceptible and resistant wheat

Resistance conferred by the Cre8 locus of wheat prevents cereal cyst nematode feeding sites from reaching and invading root metaxylem vessels. Cyst nematodes develop syncytial feeding sites within plant roots. The success of these sites is affected by host plant resistance. In wheat (Triticum aestivum L.), 'Cre' loci affect resistance against the cereal cyst nematode (CCN) Heterodera avenae. To investigate how one of these loci (Cre8, on chromosome 6B) confers resistance, CCN-infected root tissue from susceptible (-Cre8) and resistant (+Cre8) wheat plants was examined using confocal microscopy and laser ablation tomography. Confocal analysis of transverse sections showed that feeding sites in the roots of -Cre8 plants were always adjacent to metaxylem vessels, contained many intricate 'web-like' cell walls, and sometimes 'invaded' metaxylem vessels. In contrast, feeding sites in the roots of +Cre8 plants were usually not directly adjacent to metaxylem vessels, had few inner cell walls and did not 'invade' metaxylem vessels. Models based on data from laser ablation tomography confirmed these observations. Confocal analysis of longitudinal sections revealed that CCN-induced xylem modification that had previously been reported for susceptible (-Cre8) wheat plants is less extreme in resistant (+Cre8) plants. Application of a lignin-specific stain revealed that secondary thickening around xylem vessels in CCN-infected roots was greater in +Cre8 plants than in -Cre8 plants. Collectively, these results indicate that Cre8 resistance in wheat acts by preventing cyst nematode feeding sites from reaching and invading root metaxylem vessels.