Proteolytic activity in germinating wheat seeds under heat stress

Proteolytic activity at pH 4.5 was recorded in various parts of 4-day-bid wheat (Triticum aestivum L.) seedlings heated at 42 degrees C for two hours. The highest activity of acid proteinases was found in caryopses at room temperature (25 degrees C); the activity was lower in roots, and only trace activity was detected in the shoots. Under heat stress (42 degrees C, 2-h treatment), proteolytic activity increased in seeds and decreased in roots. Stressed caryopses exhibited increased sensitivity of acid proteinases to inhibition by EDTA (an inhibitor of metalloenzymes), while stressed roots became more sensitive to p-chloromercuribenzoate an inhibitor of SH-groups of proteins. The acid proteinases in heat-stressed roots were activated by cysteine (activator of thiol proteinases). Our data suggest an increase in activity of metalloproteases in heat-stressed seeds and activation of thiol proteinases in roots.