Relationships Between Lipid Changes and Plastid Ultrastructural Changes in Senescing and Regreening Soybean Otyledons

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Abstract
Lipid changes and plastid ultrastructursi changes were examined in senescing and regreening soybean cotyledons. The labelling data indicated that senescence commenced with increased activity of the cytoplasmic lipids while the chloroplast lipids experienced less change. The latter stages of senescence were accompanied by a decrease in the labelling of all the lipids. Labelling of the galactolipids indicated that mono-galactosyl cliglyceride (MGDG) activity more closely paralleled plastid structure than did that of di-galactosyl chglyceride (DGDG). Relationships between chlorophyll data and lamellar arrangement were also foand. Decapita tion of the epicotyls at the critical time resulted m the recovery of chlorophyll, lipid activity, and normal plastid structure. TJltrastructural observations revealed that plastids in regreened soybean cotyledons originated from chromoplast-chloroplast conversions. No proplastids were observed in the regreening tissues. It appears that the capability of soybean cotyledons to regreen depends partly on the ability to synthesize the galactolipids as well as on the integrity of the plastid envelope. Observations showed that the envelope played a dynamic role in the reconstruction of lamellar membranes.