Differences in transport of photosynthates between high-and low-yielding Ipomoea batatas L. varieties

Abstract

Previous studies have focused mainly on the accumulation of photosynthates and less on their distribution in sweet potato (Ipomoea batatas L.). In addition, the effect of photosynthate accumulation in root tubers on photosynthate distribution was not considered. Thus, a field experiment was carried out from May to October (2011 and to clarify the differences in photosynthate transport between high-and low-yielding sweet potato. This study mainly focused on the photosynthetic capacities of leaves, photosynthate distribution, and characteristics of photosynthate accumulation in root tubers. Results showed the high-yielding varieties displayed the higher fresh root tuber yield and the economic coefficient than the low-yielding varieties. They also showed greater net photosynthetic rate with a pronounced increase at the early and middle growth stages (8.9% and 11.4%, respectively). After the growth peak, the leaf area index (LAI) of the highyielding varieties decreased with time and was maintained at 2~3 until harvest, whereas the LAI of the low-yielding varieties decreased slowly. The high-yielding varieties reached the 13 C distribution rate ≥ 50% at the early (2011, 2012) and middle (2011) growth stages, whereas the low-yielding varieties reached it at the late (2011) or middle (2012) growth stages. At harvest, the 13 C distribution rates in the branches and root tubers of the high-yielding varieties were 6.020.3% and 73.791.2%, respectively, whereas those of the low-yielding varieties were 29.634.7% and 60.763.5%, respectively. The high-yielding varieties showed the remarkable initial potential in root tubers, which was much better than that of the low-yielding varieties. The high-yielding varieties also produced heavier root tubers and the higher number of root tubers per plant at the early bulking stage. The root tubers also attained the greater content of soluble sugar and starch. The high-yielding varieties formed root tubers earlier, showed strong abilities to transport photosynthates into the root tubers, and exhibited a higher mean accumulation rate. These varieties could also reduce the photosynthate consumption in branch leaves and stems. Therefore, the high-yielding varieties established growth advantage for the root tubers earlier. It contributed to a reasonable distribution structure of photosynthates that led to the high root tuber yield. Based on our results, effective agricultural measures can be chosen to improve the root tuber yield of sweet potato.

Switch from Apoplasmic to Symplasmic Phloem Unloading during Storage Roots Formation and Bulking of Sweetpotato

“…Even high-yielding varieties are easily overgrown due to enhanced soil fertility (Duan et al, 2018), and when overgrowth appears, storage root yields are reduced. Our research group has demonstrated that differences in storage root yield were mainly caused by differences in assimilate unloading in storage roots; this was much more fluent in high-yielding varieties than in low-yielding varieties (Liu et al, 2015a). Our research group has demonstrated that differences in storage root yield were mainly caused by differences in assimilate unloading in storage roots; this was much more fluent in high-yielding varieties than in low-yielding varieties (Liu et al, 2015a).…”

“…Storage root formation is closely related to assimilate transportation from source to sink (storage roots), which is governed by loading of the phloem in source leaf, long-distance transport in the phloem, unloading in sink organs, and metabolism of unloaded sugars in sink cells (Patrick, 1997). Our research group has demonstrated that differences in storage root yield were mainly caused by differences in assimilate unloading in storage roots; this was much more fluent in high-yielding varieties than in low-yielding varieties (Liu et al, 2015a). However, the mechanism of phloem unloading in storage roots of sweetpotato is unclear, likely because of its inconvenience of investigation due to underground organ development.…”

“…Thus, storage root yield is notably decreased (Chen et al, 2012), mainly due to the low transportation rates of assimilates from leaves and stems to storage roots. Assimilate transportation from leaves and stems to storage roots is much faster in highyielding than in low-yielding varieties of sweetpotato, which results in a higher harvest index (Liu et al, 2015a). A further study indicated that the unloading of assimilates in storage roots is a major limitation for photosynthate transportation in sweetpotato varieties (Liu et al, 2015b).…”

“…Both high-yielding and low-yielding varieties are easily overgrown (Duan et al, 2018), especially under excessive fertilization, which is common in crop production. Assimilate transportation from leaves and stems to storage roots is much faster in highyielding than in low-yielding varieties of sweetpotato, which results in a higher harvest index (Liu et al, 2015a). Thus, storage root yield is notably decreased (Chen et al, 2012), mainly due to the low transportation rates of assimilates from leaves and stems to storage roots.…”

Differences between nitrogen-tolerant and nitrogen-susceptible sweetpotato cultivars in photosynthate distribution and transport under different nitrogen conditions

“…The leaves and petioles were collected, and stems and storage roots were cut, dried at 60°C in the oven and then ground to a powder using a Waring blender. The powder was analyzed using a stable isotope ratio mass spectrometer (IsoPrime 100, Elementar Analysensysteme GmbH Co. Ltd., Germany) [ 26 ].…”