Transport of 14C‐Assimilates to Cottonseed: Integrity of Funiculus During Seed Filling Stage1

Abstract

Early work suggested the vascular connection from the ovary wall to the ovules in cotton plants (Gossypium hirsutum L.) degenerates 32 days after fertilization. A minimum of 50 days after fertilization is required for the maturation of cottonseed. From a yield viewpoint, it is important to establish if leaf assimilates are transported to the developing cotton ovules throughout the seed maturation period.The incorporation of 14C‐assimilates into ovules in different age cotton bolls was measured by: (i) pulse‐labeling cotton plants (which contained a wide distribution of different age cotton bolls at a plant stage of maximum fruit load) with l4CO2 for 10 min, and (ii) allowing photosynthetically assimilated 14CO2 to be transported to the different age bolls for 20 hours.The rate of incorporation of 14C‐assimilates into fibers in different age cotton bolls was similar to the rate of dry weight increase in the different age bolls. The 14C‐assimilate was incorporated into the fibers during a period of active cellulose deposition in these fibers. 14C‐assimilate was incorporated into ovule wall, sugars, amino acids, organic adds, oil, and protein in 1‐ to 45‐day‐old bolls. This incorporation of photosynthate into the ovules probably reflects transport of 14C‐assimilate through the vascular connection. An alternate route of assimilate transport through the carpel wall, into the locule cavity, and absorption by the ovules, is not important because (iii) the carpel wall chloroplasts do not fix 14CO2 into 14C‐assimilate, and (iv) the transport of leaf and bract 14C‐assimilate to the carpel wall is completed in 30‐ to 35‐day.old bolls.The boll opening period for these cotton plants was 49 to 56 days after anthesis. The results in this paper show that assimilates are transported to cottonseed throughout the maturation period. The majority of this incorporation occurs through the vascular connection and the funiculus does not break 32 days after fertilization.