Frozen in time: a new method using cryo-scanning electron microscopy to visualize root-fungal interactions

• A new method of sample preparation for cryo-scanning electron microscopy was used to visualize internal infection of wheat (Triticum aestivum) roots by the pathogenic fungus Rhizoctonia solani AG-8. The new method retained fungal hyphae and root cell

Cryo-scanning electron microscopy (CSEM) in the advancement of functional plant biology: Morphological and anatomical applications

Cryo-scanning electron microscopy (CSEM) is reviewed by exploring how the images obtained have changed paradigms of plant functions and interactions with their environment. Its power to arrest and stabilise plant parts in milliseconds, and to preserve them at full hydration for examination at micrometre resolution has changed many views of plant function. For example, it provides the only feasible way of accurately measuring stomatal aperture during active transpiration, and volume and shape changes in guard cells, or examining the contents of laticifers. It has revealed that many xylem conduits contain gas, not liquid, during the day, and that they can be refilled with sap and resume water transport. It has elucidated the management of ice to prevent cell damage in frost tolerant plants and has revealed for the first time inherent biological and physical features of root/soil interactions in the field. CSEM is increasingly used to reveal complementary structural information in studies of metabolism, fungal infection and symbiosis, molecular and genetic analysis

Relative amounts of soluble and insoluble forms of phosphorus and other elements in intraradical hyphae and arbuscules of arbuscular mycorrhizas

Transport of phosphorus (P) into host plants and its release to root cells is an important function of arbuscular mycorrhizal fungi (AMF). However, relatively little is known about the forms and water solubilities of P compounds in specific locations in the intraradical fungal structures. We determined concentrations and solubility of P components in these structures in white clover (Trifolium repens L.). Plants were grown in the field (colonised by indigenous AMF) or in the glasshouse (inoculated with Glomus intraradices). Mycorrhizas were cryo-fixed in liquid nitrogen immediately (control) or after treatments designed to destroy cell membranes and extract solubles. Thirty to 70% of total P in hyphae and 100% in arbuscules was not extracted. The unextracted proportion of P was higher in the inoculated plants suggesting an environmental effect. It is proposed that the large component of non-extractable P in the arbuscules is involved in the tight regulation of inorganic P release to the host cells. In control roots magnesium, potassium and P were present in hyphae in molar ratios 1:2:4, further evidence that this relationship may be universal for AMF, and that other P-balancing cations are present but undetectable by the analytical technique

The management of extracellular ice by petioles of frost resistant herbaceous plants

• Background and Aims: Some frost-tolerant herbaceous plants droop and wilt during frost events and recover turgor and posture on thawing. It has long been known that when plant tissues freeze, extracellular ice forms. Distributions of ice and water i

The vascular system of maize stems revisited: Implications for water transport and xylem safety.

The plexus of vascular bundles in the nodes of grasses is notoriously complex, where long axial bundles pass through a network of transverse bundles. The xylem pathways for water in maize stems have been investigated anatomically and with dye and particulate tracers, revealing some of the details of this complexity. Only approx. 3 % of axial vessels pass through nodes without being interrupted by end walls. Axial bundles at nodes differ from those in internodes in having the metaxylem and protoxylem vessels connected by small tracheary elements. So it is only at nodes that exchange of sap occurs between the large vessels within a bundle. End walls, acting as filters for particles and gas bubbles, always separate axial vessels from vessels in transverse bundles. The high redundancy of bundle connections in the nodal plexus is interpreted as providing alternative water pathways to bypass embolisms and damaged or diseased sections of the xylem. The pores in the filters at the base of nodes and between axial and transverse vessels within nodes are < 20 nm in diameter. Where axial vessels connect to transverse vessels, a variety of unusual shapes of vessel elements mediate two- and three-way connections within the plexus. (C) 2000 Annals of Botany Company