Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 4, 1998
Publication Date: N/A
Interpretive Summary: Broccoli florets that are yellow are not acceptable by the consumers. Yellowing is due to the degradation of chlorophyll, which is a poorly understood regulated process. A better understanding of the biochemical and ultrastructural changes would aid in future studies in genetic engineering broccoli lines that do not yellow rapidly. This study was undertaken to examine the ultrastructural changes of chlorophyll in senescing broccoli florets. The study showed sequential and interrelated processes within chlorophyll, which will be examined with the biochemical findings to better understand the regulatory process of chlorophyll degradation. These findings will be beneficial to other scientists who are studying the physiology of chlorophyll to develop methods for providing quality product to consumers.
Technical Abstract: Structural changes in chloroplasts of broccoli (Brassica oleracea L.) florets during senescence were examined using light microscopy, and scanning and transmission electron microscopy to better understand the senescence of the organelle. Light microscopy revealed that chloroplasts were initially intact and green, but the shape became obscure and the color faded during senescence. Scanning and transmission electron microscopy disclosed that stroma thylakoids in the chloroplast were initially parallel to each other and grana thylakoids were tightly stacked. As senescence advanced, the grana thylakoids degenerated and the parallel alignment of stroma thylakoids was lost. As the grana thylakoids continued to degenerate, small electron opaque globules and large spherical electron translucent spherical bodies appeared in the stroma. Finally, the limiting membrane of the chloroplast was lost and the globules and spherical bodies were expelled into the cytoplasm. Thus, the grana and stroma thylakoids underwent gradual degenerative changes during senescence that eventually led to the destruction of the chloroplast.