Histochemical examination of shoot initiation in cultured cotyledon explants of radiata pine

• Published in: Botanical gazette (Chicago, Ill.) Ill.), 1984-09, Vol.145 (3), p.312-322
• Main Authors: Patel, Kamlesh R., Thorpe, Trevor A.
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatases; Agronomy. Soil science and plant productions; Biological and medical sciences; Callus; Cell biochemistry; Cell physiology; Cell walls; cotiledones; cotyledon; Cotyledons; Cultured cells; DNA; Economic plant physiology; Enzymes; Fundamental and applied biological sciences. Psychology; In vitro culture; Nucleic acids; pinus radiata; Plant physiology and development; RNA; Starches; stems; tallo; tige
• ISSN: 0006-8071; 1940-1205
• DOI: 10.1086/337461

Histochemical events underlying the process of shoot initiation were studied in cotyledonary explants of Pinus radiata cultured in the presence of N6-benzyladenine (BA). The initial explant was mitotically active and showed intense staining for nucleic acids and for cytoplasmic as well as nuclear basic proteins. The cells of initial explants were rich in reserves such as lipids, proteins, and starch and also showed uniform localization of activity of various enzymes. The cotyledons cultured without BA showed a rapid decline in their reserves. The localization of nucleic acids, proteins, and enzyme activity was random, and the intensity of staining decreased in these cells. In contrast, in the cotyledons cultured in the presence of BA, the shoot-forming layers in contact with the medium showed increased staining for DNA, RNA, and cytoplasmic and nuclear proteins. Starch reserves declined in most cells of the explant, but the epidermal and subepidermal layers maintained abundant starch grains, which disappeared only as the meristematic tissue was formed. Lipase activity was confined to the shoot-forming layers during the initial stages of shoot formation but during the later stages was detected in cells underlying the meristematic tissue. Increased staining intensities for acid phosphatases, adenosine triphosphatase, succinate dehydrogenase, and peroxidase were found in shoot-forming regions of the cotyledons. These findings agree with the hypothesis that the initiation of organized development in vitro involves a shift in metabolism that precedes and is coincident with the process.