Characteristics of Carbohydrate Assimilation and Distribution in Walnut (Juglans regia L.)

Based on 13 C isotope tracer technology, we investigated the 13 C abundance (δ 13 C), 13 C content ( 13 Camount), and new fixed 13 C percentage ( 13 CPCT) in different organs and different metabolic components in girdled fruit-bearing shoots at different stages of fruit growth and development in walnut. Our aim was to analyze the dynamic characteristics of carbohydrate assimilation, transportation, and utilization in different stages of walnut fruit growth and development. The results showed that (1) at 0 h after the feeding, δ 13 C, 13 Camount, and 13 CPCT in sucrose from the leaves were the highest and positively correlated with net photosynthetic rate of leaves (p < 0.05); (2) at 24 h after the feeding, δ 13 C, 13 Camount, and 13 CPCT in sucrose from the carpopodium reached their peak values; (3) δ 13 C, 13 Camount, and 13 CPCT in sucrose from the peel were lower than those of hexose at 48 h after feeding in the fast-growing stage, but they all reached maximum levels in peel sucrose at 48 h after feeding in the oil conversion stage; and (4) the highest δ 13 C, 13 Camount, and 13 CPCT were recorded in all carbohydrates from the seed kernel 48 h after feeding, among which the highest δ 13 C, 13 Camount, and 13 CPCT were recorded in sucrose. These results suggested that sucrose was the main form of carbohydrate assimilation and transportation in walnut fruit, and large amounts of sucrose are accumulated in the peel and in the kernel, where it is also the base for the transformation of oil. Additional key words: 13 C isotope, carpopodium, fruit development, photosynthesis, seasonal changes