COTYLEDON PHOTOSYNTHESIS DURING SEEDLING GROWTH OF COTTON,GOSSYPIUM HIRSUTUM L.

Respiration and net photosynthetic O₂ production by cotton cotyledons were determined from an early age through the senescent stage. Various treatments were applied to cotyledons to assess the importance of current photosynthesis as compared to translocation of reserves to seedling development. Rates of respiration and net photosynthesis per cm² were high on 1-day-old cotyledons, but the rates decreased sharply with rapid expansion to reach a fairly stable rate. Respiration per cotyledon decreased linearly with age until the onset of senescence, then exhibited a distinct climacteric rise followed by a sharp decrease. Net photosynthesis per cotyledon increased until expansion was completed and then decreased linearly and steeply with age. Excision of cotyledons, inhibition of photosynthesis either chemically or by covering, and removal of the terminal bud indicated that current photosynthesis is a potent force behind early epicotyl growth.