Effects of cotyledon removal on apple seedling growth and distribution of 14C-labelled photosynthates
In very young apple (Malus domestica Borkh.) seedlings, cotyledon dry weight decreased during the 14-day period following cotyledon separation and development. Removal of both cotyledons at the time of cotyledon separation significantly reduced subsequent seedling development as measured by leaf area and leaf fresh and dry weights, but it did not alter established 14C-labelled photosynthate transport patterns. Cotyledon removal from seedlings with fully expanded cotyledons and four unfolded expanding true leaves did not affect subsequent seedling growth. Removal of one cotyledon in very young seedlings reduced retention and export and increased apparent metabolism of 14C-labelled photosynthate. Removal of one cotyledon in older seedlings to which 14CO2 was fed to the first true leaf did not influence retention, export, or metabolism of the 14C-labelled photosynthate in the fed leaf. In the early stages of seedling growth, assimilates were directed mainly to the lower stem and root system, then to the shoot apex and immature leaves, and finally again to the root system as the first true leaf assumed the function of supplying assimilates during cotyledonary senescence.