Preventive mechanisms of gibberellin4+7 and light on low-temperature-induced leaf senescence in Lilium cv. Stargazer

Lilium cv. Stargazer plants were held for 2 weeks at 4°C, either in darkness or in light (40 mmol m s). Another series of plants was held in darkness after pre-treatment with 100 mg l GA4+7. Changes in major senescence parameters were determined during storage at 4°C and during 6 days after transferring the plants to 22°C. Foliar sprays of GA4+7 or supplemental light prevented rapid leaf senescence induced by dark low-temperature storage. During storage at 4°C, basal leaves showed no significant changes in concentrations of chlorophyll, soluble proteins, lipid peroxidation, and activity of catalase. However, shifting from 4 to 22°C induced a series of changes in basal leaves of dark-held plants including rapid loss of chlorophyll, proteolysis, increased lipid peroxidation and loss of catalase activity. Both light and GA4+7 treatments prevented these changes. Total soluble carbohydrates decreased gradually during 4°C dark storage and after transferring to 22°C. GA4+7 treatments did not prevent the decline in carbohydrate levels at 4°C, but prevented it upon transferring to 22°C. Supplemental light during 4°C storage significantly increased soluble carbohydrate concentration. The abrupt increases in metabolic activities by shifting from 4 to 22°C accompanied by oxidative stress in leaves already depleted in reserves during 4°C storage seem to induce leaf senescence in dark-held plants. © 2000 Elsevier Science B.V. All rights reserved.