PHOTOSYNTHESIS OF COTYLEDONS OF SOYBEAN SEEDLINGS

Abstract

S ummary The rate of net photosynthesis in each of the foliar organs present on seedlings of Glycine max (L.) Merrill was measured by infrared gas analysis on the fourth day after sowing and every third day thereafter until 5 d after cotyledon abscission. Dark respiration rates for the whole seedling were also measured. Estimates of the daily net carbon assimilation were made using the sum of the net CO 2 assimilatory rates for each foliar organ present and the dark respiration rate for the whole seedling. Rates of cotyledon photosynthesis were very low in comparison to the leaves, whether expressed per unit chlorophyll or unit area. Although the cotyledon contribution to seedling assimilation remained small throughout their lifetime, it was enough to balance seedling respiratory losses during days 7 to 10 prior to leaf expansion. Marked increases in the CO 2 budget only occurred once primary leaf photosynthesis began on day 10. Net assimilation then increased rapidly as first, second and third trifoliate leaves expanded.