Protein mobilisation and proteolytic activities in root tubers of Asphodelus aestivus

Abstract

We studied protein mobilisation in Asphodelus aestivus Brot. (Liliaceae) during a 1-year period. The activities of 3 proteolytic enzymes, endopeptidase (EP), leucine aminopeptidase (LAP), and carboxypeptidase (CP), together with soluble protein levels and total nitrogen and water content in root tubers were investigated. We found that protein mobilisation continued throughout the year. The highest levels of the 3 proteolytic enzymes were found in different months: LAP in December (1.19 perpendicular to 0.19 mu mol pNA/g FW), CP in February (14.19 +/- 1.13 mu mol Leu/g FW), and EP in May (5.18 +/- 0.12 U/h). Activities of LAP and CP generally reached their higher levels in January-April, namely in spring, but EP activity was higher in March-May. Activities of all 3 enzymes remained at lower levels during the asphodel's inactive life phase. The soluble protein contents were associated with the proteolytic activities. The total N contents were generally constant, but decreased in April. Our results show that the proteolytic activities in root tubers of Asphodelus aestivus continue to increase up to the start of flowering in early spring, and they can be an important nitrogen resource at the beginning of the generative development phase.