Preventive mechanisms of gibberellin(4+7) and light on low-temperature-induced leaf senescence in Lilium cv. Stargazer

Lilium cv. Stargazer plants were held for 2 weeks at 4 degrees C, either in darkness or in light (40 mu mol m(-2) s(-1)). Another series of plants was held in darkness after pre-treatment with 100 mg l(-1) GA(4 + 7). Changes in major senescence parameters were determined during storage at 4 degrees C and during 6 days after transferring the plants to 22 degrees C. Foliar s prays of GA(4 + 7) or supplemental light prevented rapid leaf senescence in duced by dark low-temperature storage. During storage at 4 degrees C, basal leaves showed no significant changes in concentrations of chlorophyll, sol uble proteins, lipid peroxidation, and activity of catalase. However, shift ing from 4 to 22 degrees C induced a series of changes in basal leaves of d ark-held plants including rapid loss of chlorophyll, proteolysis, increased lipid peroxidation and loss of catalase activity. Both light and GA(4 + 7) treatments prevented these changes. Total soluble carbohydrates decreased gradually during 4 degrees C dark storage and after transferring to 22 degr ees C. GA(4 + 7) treatments did not prevent the decline in carbohydrate lev els at 4 degrees C, but prevented it upon transferring to 22 degrees C. Sup plemental light during 4 degrees C storage significantly increased soluble carbohydrate concentration. The abrupt increases in metabolic activities by shifting from 4 to 22 degrees C accompanied by oxidative stress in leaves already depleted in reserves during 4 degrees C storage seem to induce leaf senescence in dark-held plants. (C) 2000 Elsevier Science B.V. All rights reserved.