Plant Science

Cyst and root-knot nematodes are sedentary biotrophic parasites that infect a wide range of plant species, causing significant annual yield and economic losses. Cyst nematodes (genera Heterodera and Globodera) induce specialized feeding structures called syncytia in host plant roots, while root-knot nematodes (Meloidogyne spp.) form galls containing feeding cells known as giant cells. This protocol describes the visualization of lignin in Arabidopsis roots infected by beet cyst nematode H. schachtii and root-knot nematode M. incognita using histochemical staining. We present two distinct approaches for lignin detection: direct staining of root segments containing syncytia and galls and histopathological detection in thin longitudinal sections of the feeding sites.

Rhizobia interact symbiotically with legumes to form root nodules, where by rhizobia fix atmospheric dinitrogen into ammonia in exchange for carbon produced via photosynthesis. The symbiotic interaction is agriculturally important by reducing the need for fertilizer containing nitrogen. The root and stem nodule bacteria commonly include bacteria in the genera Rhizobium, Mesorhizobium, Sinorhizobium (Ensifer), and Bradyrhizobium, although other genera of bacteria have now been shown to form root nodule symbioses with several legume species (Weir, 2012). Different rhizobial strains form different numbers of nodules on specific legume plant varieties (or cultivars), and the nitrogen fixing effectiveness of each rhizobial strain, its ability to fix nitrogen and transfer it to the plant, is also highly variable (Toro, 1996). Some native rhizobia are ineffective at fixing nitrogen yet form a majority of nodules in filed grown plants. This is referred to as the competition for nodulation problem (Triplett and Sadowsky, 1992). Competition studies are not feasible when evaluating a large number of different native strains. However, nodulation speed of individual strains correlates well with overall competiveness and can be used to identify native strains that overcome the competition problem (De Oliveira and Graham, 1990; Bhuvaneswari et al., 1980).