Growth and metabolism of cells and tissues of jack pine (Pinus banksiana). 1. The establishment and some characteristics of a proliferated callus from jack pine seedlings

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Abstract
No more than 2% of the embryos from dry seeds of jack pine (Pinus banksiana Lamb.) produced callus on agar with a defined nutrient medium. When contact of the embryo with the nutritive female gametophyte was maintained during imbibition, callus production by excised seedlings on the medium increased to over 80%. Callus production was optimal with 5-day-old seedlings. Percentage callus formation was greater when the initial contents of the explant in dry weight, glutamate N, amide N, total nucleotides, RNA, adenylate energy charge, and oxygen uptake were also greater. Small initial increases in levels of these components over those found in dry embryos and resulting from imbibition substantially improved callus production. Subsequent increases, concomitant with germination and seedling development, gave only slightly more callus. By contrast, inverse or poor relations were observed with DNA, total soluble protein, and aminoacyl tRNA synthetase activity. In the initial explants the most conspicuous cytological events, leading to optimal callus production, were the onset of the first wave of mitosis and prominence of nucleoli. Seed reserves were nearly consumed and ribosome-like particles, which were associated with chromatin, appeared as new cytoplasm was being synthesized during the onset of proliferation of cells on the agar medium.