EFFECTS OF POLYAMINES ON CHLOROPHYLL AND PROTEIN-CONTENT, PHOTO-CHEMICAL ACTIVITY, AND CHLOROPLAST ULTRASTRUCTURE OF BARLEY LEAF-DISKS DURING SENESCENCE

The polyamines putrescine, spermidine and spermine prevent the loss of chlorophyll normally associated with senescence of excised leaf tissue maintained in darkness on water (control). Retention of chlorophyll in barley [cv. Gateway] leaf discs was in the range of 90% 4 days after excision and placement on effective polyamine solutions. In contrast, the loss of soluble protein was hastened with 0.5 mM spermidine and spermine treatments but it was retarded by 0.5 mM putrescine. Photosystem I and II activities of chloroplasts from polyamine-treated leaf discs declined more rapidly as compared to the control. Chloroplast ultrastructural changes resulting from the polyamine treatments included the apparent destruction of the envelope, preservation of thylakoid membrane structure and reduced accumulation of osmiophilic bodies. The influence of polyamines on senescence-related processes may be due to their cationic nature.