Growth and metabolism of cells and tissue of jack pine (Pinus banksiana). 4. Changes in amino acids in callus and in seedlings of similar genetic origin

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Abstract
Growth rates of callus from hypocotyls and radicles of jack pine (Pinus banksiana Lamb.) seedlings were associated with the differential release and adherence of daughter cells. From 18 to 40% of the N in the medium was assimilated through the increasing surface area of callus and contributed nearly 6% of the total gain in dry weight. Sequential changes in free amino acid N leading to final size were similar for callus from both plant parts. Changes in N correlated significantly with growth rates and callus density (dry weight per cubic centimetre). When free amino acid N was expressed as a percentage of the total soluble N, correlations signified the relative proportions of the amino acid pool that gave different growth-rate forms. The balance of N metabolism during the autocatalytic growth of hypocotyl callus was under the influence of free glutamine, whereas the exponential growth of radicle callus was dominated by the synthesis of asparagine N. In callus from both plant parts 80 to 87% of the net gain in N was recovered in the bound (protein and nucleic acid) fraction. Percentage of free glutamine N decreased with the increase in bound N.Ways in which free amino acid N interacted with growth rates indicated that final size may be usefully defined not merely as an extreme of a growth function but in more sequential kinetic terms supported by a series of correlation coefficients. Correlations revealed the specific points at which free amino acids interacted strongly with rates.When amino acid N in callus was compared with N in seedlings from which callus was derived, the trends were strikingly similar. In seedlings the succession of amino acids was linked more to the uptake of N from the gametophyte by cotyledons and daughter cells in growing tissues rather than to their morphogenesis. Differences related mainly to the greater ability of the seedling to synthesize protein and to maintain higher levels of total soluble N than in callus.

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