ENDOGENOUS POLYAMINE LEVELS AND FLOODING-ENHANCED LEAF SENESCENCE OF TOBACCO

Changes in levels of nicotine and polyamines in leaves and rates of leaf senescence in response to flooding treatment by a low-alkaloid line (LA 5) and normal alkaloid (Speight G-70) tobacco plants were compared. Leaves from LA 5 plants contained 12-, 13-, 2- and 6-fold less nicotine, putrescine, spermidine and spermine, respectively, than those from Speight G-70 at the start of the experiment (7 days after topping). Flooding treatment resulted in an increase in levels of putrescine in both LA 5 and Speight G-70 plants. Flooding did not affect the levels of spermidine and spermine. Leaf senescence of LA 5 and Speight G-70 was promoted by flooding. However, the senescence syndrome in untreated leaves of LA 5 was not as pronounced as that of Speight G-70. Neither was the rate of senescence of flood-treated LA 5 leaves faster than that of flood-treated Speight G-70 leaves. It appears that endogenous polyamines may not play a significant role in the control of leaf senescence or flood-enhanced leaf senescence of tobacco plants.