Variable responses of soybean chitinases to arsenic and cadmium stress at the whole plant level

Abstract

Plant chitinases (EC 3.2.1.14) are considered as typical defense components under various environmental stresses, including heavy metals. In addition, some of them play crucial role in normal plant growth and development. In this work the profile and activities of these enzymes were analyzed to study the variability of defense within soybean plants. For this, two cultivars with contrasting tolerance to metals were exposed to ecologically relevant doses of arsenic and cadmium. Enzyme profiles revealed a spatial distribution of chitinase activities throughout the individual plants, tending to decrease upwards to the top of the plants. Under metal stress, there was a single responsive isoform detected in roots that behaved opposingly in the studied soybean cultivars. In contrast, several isoforms were activated in aboveground tissue, predominantly in mature (older) leaves. Of these, two were identified (21 and 42 kDa) as more specifically involved in defense against metal stress in soybean. The 21 kDa isoform was concluded as possibly contributing to metal tolerance and deserves further investigations at molecular level. Nevertheless, no sound interaction was detected between leaf developmental stage and responsiveness to metals for either of the chitinase isoforms. Further studying the distribution of induced defense within plants is important in understanding the defense strategy of plants against environmental cues including metals.