Ultrastructural Effects of Water Stress on Chloroplast Development in Jack Bean (Canavalia ensiformis [L.] DC)

An ultrastructural study has been made to determine to what degree chloroplast differentiation is retarded in leaves of young jack bean (Canavalia ensiformis [L.] DC.) seedlings when they are subjected to mild water stress. Rapid chloroplast differentiation occurred when etiolated seedlings were allowed to green at relative humidities above 85% but not at a relative humidity of 25%. Response to a drop in humidity was rapid. Germination and early development in the dark occurred at 100% relative humidity. At the time of exposure to light, the etioplasts contained well formed prolamellar bodies. Under high relative humidity conditions, transformation of the prolamellar body was well advanced within 2 hours. Under low relative humidity conditions, however, prolamellar body differentiation was extremely retarded for more than 24 hours following the beginning of illumination.