The Golgi apparatus is known to be involved in synthesis and transport of pectins and hemicelluloses. PATAg staining revealed positive reaction of cell wall and the Golgi apparatus in the differentiating xylem, indicating the Golgi apparatus involved in the synthesis of hemicelluloses. Although this method stained polysaccharides selectively, it is difficult to distinguish one hemicellulose from another one. Antibody raised against targeting hemicellulose is a powerful tool to label the hemicellulose selectively. Glucomannan and xylan are main hemicelluloses in softwood. We applied the immnolabeling to investigate how these hemicelluloses are synthesized in the Golgi apparatus and transported towards the developing cell walls in softwood. Materials and methods Differentiating xylem of Chamaecyparis obtusa compression wood was excised into very small pieces with a razor blade, and fixed by high-pressure freezing. Then the specimens were freeze substituted in acetone containing 4% osmium tetroxide and 8% 2,2-dimetoxypropane for 5 days at -80 degree Celsius, washed with acetone and embedded in epoxy resin. Ultrathin sections were cut and immunolabeled with LM11 for xylan, BGM C6 for glucomannan, and LM5 for galactan independently or in combination. Results and discussion In case of immunolabeling of glucomannan, more than sixty percent of the Golgi apparatus was labeled during secondary wall formation stages, suggesting glucomannan continuously synthesized in the Golgi apparatus and transported towards secondary cell wall. In case of immunolabeling of xylan, more than forty percent of the Golgi apparatus was labeled, suggesting xylan synthesized and transported in the same manner of glucomannan. In case of immunolabeling of galactan, more than seventy percent of the Golgi apparatus was labeled in outer S2 formation stage, suggesting galactan synthesized in the Golgi apparatus and transported towards cell wall mainly in outer S2 formation stages. In case of double immunolabeling of glucomannan and xylan, many Golgi apparatus showed double labeling. However, each Golgi vesicle was labeled independently with LM11 or BGM C6, namely, one Golgi vesicle was labeled with LM11, and another vesicle was labeled with BGM C6.Above results indicated that two or more hemicelluloses are simultaneously synthesized in the Golgi apparatus and each hemicellulose is independently packed in the Golgi vesicle.

Function of the Golgi apparatus in differentiating xylem in Chamaecyparis obtusa

255th National Meeting (2018)

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