Effects of Temperature on the Fine-Structural Responses in the Hypocotyl Regionof Alfalfa Lines to Ditylenchus dipsaci

摘要

Fine-structural analyses were made of the response of host tissue, Medicago sativa L. 'Ranger' and 'Lahontan', to infection by the stem nematode, Ditylenchus dipsaci (Kühn) Filipjev. Seedlings were grown at 15 and 25 C, and hypocotyl regions were sampled 1,3, or 7 days after inoculation. Electron micrographs of infected alfalfa tissue indicated that the same types of damage were inflicted on Lahontan (stem-nematode-tolerant)and Ranger (stem-nematode-susceptible). Only the infection rate and degree of damage differed between lines and temperatures, with the greater injury occurring at the higher temperatures. After 3 and 7 days of infection, the symptoms observed were: swollen and broken endoplasmic reticulum (ER), distended and broken chloroplasts, loss of nuclear material, and bulging and rupturing of nuclear envelopes. Cells with infected cytoplasm contained more ER, ribosomes, vesicles, and Golgi apparatuses, suggesting increased metabolic activities. Lobing nuclei were observed in all samples. Lipid contents varied with temperature in I-day-old seedlings. At 15 and 25 C, electron-dense substrances were commonly found along the tonoplast, and on the cell wall. Also, some cells with enlarged ER were noted in the noninfected controls at these temperatures.