The role of cotyledons in early development of pine seedlings

Abstract

The role of photosynthetically active cotyledons on development of young red pine (pinus resinosa Ait.) seedlings, and especially on growth of primary needles, was studied over a 30-day period. Photosynthesis of cotyledons, as measured with an infrared CO2 analyzer, was variously reduced by photosynthesis-inhibiting herbicides (atrazine, simazine, propazine, monuron), by reduced light intensity, or by combinations of these. When photosynthesis of cotyledons was completely eliminated shortly after seed germination, the primary needles failed to expand, and dry weight production by seedlings was inhibited. Partial reduction of photosynthesis by herbicides, low light intensity, or both of these was followed by proportional decrease in expansion of primary needles and reduction in dry weight increment of seedlings. Reduced photosynthesis in cotyledons inhibited expansion of primary needles rather than formation of their primordia which occurred early in ontogeny. Growth of cotyledons appeared to utilize carbohydrate reserves to a large extent as cotyledons of many plants emerged even in the dark.