Proteolysis and expression of the cysteine protease gene in senescing cut leaves of Hosta ‘Undulata Erromena’ and Zantedeschia aethiopica Spr. treated with BA or GA₃

Abstract

Treatments with BA or GA₃ are known to extend the foliage display life of Hosta ‘Undulata Erromena’ and Zantedeschia aethiopica Spr., respectively. The effects of a 24hrs pulse conditioning with BA or GA₃ on the protein content, proteolytic activity and the expression of the cysteine protease gene were studied in senescing cut leaves of both species. A decrease in the soluble protein content in the untreated leaves was accompanied by an increased total proteolytic activity and the activity of the cysteine protease. The BA treatment in Hosta prevented such increases thereby preventing total protein loss. In Z. aethiopica, the GA₃ treatment delayed protein degradation but to a lesser extent than the BA treament of H. ‘Undulata Erromena’ leaves. No expression of the cysteine protease gene was observed in the freshly cut leaves of both species. The presence of the gene transcript was detectable in the senescing leaves of both species kept in water where significant increase in the cysteine protease activity was observed. No increase in the level of the cysteine protease mRNA was detected in the BA - conditioned leaves of Hosta but a slight increase in the transcript level was observed in Z. aethiopica regardless of whether the leaves were conditioned with GA₃ or were kept in water. Different reaction of the two species for two plant growth regulators inhibiting senescence suggest different mechanism of this process.