ASPARAGINYL ENDOPEPTIDASE DURING MATURATION AND GERMINATION OF DURUM-WHEAT

Asparaginyl-endopeptidase activity was detected in endosperms of matur ing and germinating wheat seeds. The highest activity was found during maturation before the maximal accumulation of storage proteins. The e nzyme activity then decreased in the dry seeds and increased again dur ing germination. The increase of activity during germination required the presence of the embryo. In fact, the activity found in detached en dosperms was lower than that found in attached ones. The localization at tissue level of the enzyme reveals differences between maturation a nd germination: the enzyme was about equally located in the aleurone l ayer and starchy endosperm during maturation, but solely in the aleuro ne layer during germination. The asparaginyl enzymes from maturing and germinating seeds had many similar properties, such as pH optimum, pH stability, thermal stability and sensitivity to thiol reagents and to thiol compounds. The results suggest that asparaginyl endopeptidases may be involved in the modification of proproteins of storage proteins during seed maturation and in the degradation of storage proteins dep osited in the aleurone layer during germination.