Immunohistological localization of chitinase and β-1,3-glucanase in rhizomania-diseased and benzothiadiazole treated sugar beet roots

Accumulation of plant basic beta-1,3-glucanase (Glu2) and basic class IV chitinase (Ch4) was examined in rhizomania-diseased sugar beet roots and compared to plants treated with a synthetic inducer of systemic acquired resistance, benzothiadiazole (BTH). Spatial distribution of the enzymes was studied by means of immunohistology in root tissues. It was established that Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, induced accumulation of Glu2 and Ch4 in cell walls and extracellular spaces. The deposition of the enzymes was found predominantly in endodermis, cortical cells adjacent to endodermis (Glu2 and Ch4), and xylem vessels (Glu2 only). Resting spores and plasmodia of the BNYVV vector, Polymyxa betae, were formed mainly in rhizodermis and cortex parenchyma cells; the direct co-location of P. betae infectious structures with Glu2 and Ch4 was not confirmed. BNYVV was detected unevenly in cortex parenchyma and rarely in the xylem vessels. The results indicate, that the accumulation of the defence proteins Glu2 and Ch4 is most likely connected with BNYVV multiplication or induced in a systemic mode. Similarly to the pathogens, BTH induced the deposition of both Ch4 and Glu2 systemically in cortex and endodermis cells. The extracellular localization of these hydrolases suggests the potential of BTH for protection the sugar beet against soil-borne diseases. (C) 2003 Elsevier Ltd. All rights reserved.