Biochemical and physiological comparison of heavy metal-triggered defense responses in the monocot maize and dicot soybean roots.

Defense responses against cadmium, arsenic and lead were compared in two crop plants such as the monocotyledonous maize (Zea mays cv. Quintal) and dicotyledonous soybean (Glycine max cv. Korada). The applied metals caused root growth retardation, membrane damage and subsequent loss of cell viability, while enhanced H(2)O(2) generation, lipid peroxidation and lignification were detected with respect to corresponding controls. The measured data suggest that soybean was in general more tolerant to tested doses of metals and showed more pronounced defense responses than maize. Concurrently, the total activity of β-1,3-glucanases, a subgroup of so called pathogenesis-related defense proteins, was comparable in root extracts of both plant types. Though in a view of previous comparative genome approaches the β-1,3-glucanases do not mirror the differences in the cell wall structure and architecture between the monocots and dicots, we show that in both plant types they clearly respond to metal stress. Accumulation patterns of different glucanase isoforms upon exposure to tested metals indicate that they do contribute to plant defense mechanisms during exposure to heavy metals and their biological role is more complex than expected.