The partitioning of 14C between growth and differentiation within stem-deformed and healthy black spruce seedlings

Abstract

When containerized black spruce seedlings (Picea mariana Mill.) are grown rapidly, their stems can become deformed, i.e., they bend over, grow horizontally, and obtain a permanent crook. To determine what physiological differences exist between these stem-deformed and healthy seedlings, we fed labeled amino acid,14C-phenylalanine, a precursor of lignin and phenolics as well as a constituent of proteins, to both kinds of seedlings and followed the partitioning of this 14C after a chase period of 24, 48, and 72 h. For one group of seedlings, intact plants incorporated the l4C-phenylalanine through their root systems, whereas for a second group of plants, root systems were excised and the 14C-phenylalanine was incorporated directly by stems. When the 14C was incorporated by roots, stem-deformed seedlings partitioned more l4C to protein and less to lignin and phenolics. However, when the 14C was incorporated directly by stems, the differences between stem-deformed and healthy seedlings nearly disappeared. Furthermore, the distribution of 14C following root incorporation in stem-deformed seedlings was the same as that for stem incorporation in both types of seedlings. Thus, stem-deformed black spruce seedlings behave as if their root systems are not performing their normal role in metabolizing phenylalanine into lignin precursors. The ratio of 14C allocated to phenolic-containing compounds associated with growth to 14C allocated to those compounds associated with the differentiation of existing plant structures was 3.7 times higher in stem-deformed seedlings than in healthy ones. These results demonstrate that roots can play an important role in controlling the partitioning of carbon between growth and differentiation. Key words: black spruce, differentiation, lignification, phenolics, stem deformation, secondary metabolism.