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Abstract In sweet potato, rational nitrogen (N) assimilation and distribution are conducive to inhibiting vine overgrowth. Nitrate (NO3 -) is the main N form absorbed by roots, and cultivar is an important factor affecting N utilization. Herein, a hydroponic experiment was conducted that included four NO3 - concentrations of 0 (N0), 4 (N1), 8 (N2) and 16 (N3) mmol L-1 with two cultivars of Jishu26 (J26, N-sensitive) and Xushu32 (X32, N-tolerant). For J26, with increasing NO3 - concentrations, the root length and root surface area significantly decreased. However, no significant differences were observed in these parameters for X32. Higher NO3 - concentrations upregulated the expression levels of the genes that encode nitrate reductase (NR2), nitrite reductase (NiR2) and nitrate transporter (NRT1.1) in roots for both cultivars. The trends in the activities of NR and NiR were subject to regulation of NR2 and NiR2 transcription, respectively. For both cultivars, N2 increased the N accumulated in leaves, growth points and roots. For J26, N3 further increased the N accumulation in these organs. Under higher NO3 - nutrition, compared with X32, J26 exhibited higher expression levels of the NiR2, NR2 and NRT1.1 genes, a higher influx NO3 - rate in roots, and higher activities of NR and NiR in leaves and roots. Conclusively, the regulated effects of NO3 - supplies on root growth and NO3 - utilization were more significant for J26. Under high NO3 - conditions, J26 exhibited higher capacities of NO3 - absorption and distributed more N in leaves and in growth points, which may contribute to higher growth potential in shoots and more easily cause vine overgrowth.

Abstract Background Due to unreasonable nitrogen (N) application and water supply, sweet potato vines tend to grow excessively. Early development of storage roots is conducive to inhibiting vine overgrowth. Hence, we investigated how N and soil moisture affect early root growth and development. Results A pot experiment was conducted using the sweet potato cultivars Jishu26 (J26, N-susceptible) and Xushu32 (X32, N-tolerant). Two N application rates of 50 (N1) and 150 mg kg− 1 (N2) and two water regimes, drought stress (DS) (W1) and normal moisture (W2), were applied to each cultivar. For J26, the lowest expansion root weight was observed in the N2W2 treatment, while for X32, the N1W2 and N2W2 treatments resulted in higher root weights compared to other treatments. The interaction between N rates and water regimes significantly affected root surface area and volume in J26. Root cross-sections revealed that N2W2 increased the percentage of root area covered by xylem vessels and decreased the amount of secondary xylem vessels (SXV) in J26. However, in X32, it increased the number of SXV. A high N rate reduced the 13 C distribution ratio in J26 expansion roots, but had no significant effect on X32. In J26, N2W2 inhibited starch synthesis in roots by downregulating the expression of AGPa, AGPb, GBSS I, and SBE I. Conclusion The observed effects were more pronounced in J26. For X32, relatively high N and moisture levels did not significantly impact storage root development. Therefore, special attention should be paid to N supply and soil moisture for N-susceptible cultivars during the early growth stage.

In recent years, the sweet potato cultivar Jishu 25 has exhibited good characteristics for starch processing in northern China. The storage root dry matter yields of this cultivar can exceed one ton per mu (1/15 of a hectare) at nitrogen (N) rates of 60-90 kg ha-1 based on soil nutrient content. However, the effect of N fertilizer on the physicochemical properties of starches isolated from this cultivar has not been reported. In order to evaluate these effects, three different N rates, 0 (control, N0), 75 (N1), and 150 kg ha-1 (N2), were selected for a field experiment in 2017. The results showed that N1 exhibited the highest storage root yield and starch yield. Compared to the control group, N fertilizer significantly increased the total starch content while no significant difference was found in these between the N1 and N2 groups. The amylose (AM) content was highest in the N2 group and lowest in the N0 group. In addition, N fertilizer exhibited no significant effects on the values of [D(v, 0.9)], D [4, 3] and D [3, 2]. Compared to the control group, N1 demonstrated significantly higher setback viscosity (SV), while N2 showed significantly higher peak viscosity (PV), cold paste viscosity (CPV) and SV. However, there were no significant differences in the hot paste viscosity (HPV), peak time and pasting temperature between the N1 and N2 groups. For the thermal properties of starch, there were no significant differences in peak temperature (Tp), conclusion temperature (Tc) or gelatinization enthalpy (ΔH) between the N1 and N2 groups. Overall, for the starch samples of cultivar Jishu 25, N fertilizer exerts significant effects on the starch content, AM content and viscosity properties but little effect on the particle size distribution and ΔH. 75 kg N ha-1 can easily lead to substantial planting benefits from the high storage root yield, dry matter yield and total starch content of this cultivar.

To characterize the differences in photosynthate distribution and transport between nitrogen(N)-tolerant and N-susceptible sweetpotato cultivars under different N conditions, three N levels, including 0 (N0), 120 (N120), and 240 kg ha-1 (N240), were used in field experiments with the Jishu26 (J26) and Xushu32 (X32) cultivars in 2015 and 2016. The results from both years revealed that high N application reduced the tuberous root yield, the tuber/vine rate of carbon-13 (13C), and top-to-base (three equal segments of stem divided from the fifth opened leaf of the shoot tip to the main stem, defined as the top, middle, and base parts, respectively) gradients such as sucrose, ammonia N and potassium along the stem. 'J26' showed a higher yield than 'X32' under N0 but lower yield than 'X32' under N120 and N240. It also exhibited a higher 13C distribution to tuberous roots compared with that of 'X32' under N0, and the opposite trend was observed under N120 and N240. Under N0, 'J26' showed a steep top-to-base amino acid gradient and a significantly lower top-to-base sucrose increase along the stem in the late growth stage. Under N120 and N240, 'X32' exhibited a greater top-to-base decrease in the ammonia N along the stem during the main growth stages, a steep top-to-base sucrose gradient along the stem in the early growth stage, and a lower top-to-base sucrose increase along the stem in the middle and late growth stages. The formation of a reasonable photosynthate distribution structure attributed to high yield was related to a desirable sucrose, ammonia N or K+ gradient downward along the stem. These results might help provide farmers with sweetpotato cultivars using less or no N fertilizer in soils of different fertility and enhance the knowledge of yield-related physiology.

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Copyright of Agricultural Science & Technology is the property of Hunan Academy of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objective] This study aimed to investigate the effects of uniconazole on physiological and biochemical properties of roots of different sweetpotato cultivars at seedling stage. [Method] Under hydroponic conditions in a greenhouse, the effects of exogenous uniconazole on physiological and biochemical properties of roots of different sweetpotato cultivars at seedling stage were analyzed under continuous drought stress simulated by PEG-6000. [Result] Compared with normal water supply treatment (N), drought treatment (D) decreased significantly root length, root surface area, average root diameter and root volume of Jishu 21 and Jihei 1; to be specific, compared with Jishu 21, root length, root surface area and average root diameter of Jihei 1 decreased greatly, but root volume of Jihei 1 decreased slightly. SOD, POD, APX activities and MDA content of Jishu 21 and Jihei 1 increased, and root vitality of two sweetpotato cultivars was reduced; to be specific, compared with Jihei 1, Jishu 21 exhibited significantly improved SOD, POD, APX activities, slightly improved MDA content and remarkably reduced root vitality. IAA, GAs and ZR contents of Jishu 21 and Jihei 1 declined at seedling stage; ABA content of two sweetpotato cultivars was improved; to be specific, compared with Jihei 1, IAA, GAs and ZR contents of Jishu 21 were reduced slightly, while ABA content of Jishu 21 was improved slightly. Under stress conditions, uniconazole treatment increased significantly root length and root surface area of Jihei 1 and increased slightly root volume of Jihei 1 compared with Jishu 21; uniconazole treatment increased significantly SOD, POD and APX activities and root vitality of Jihei 1 and declined remarkably MDA content of Jihei 1 compared with Jishu 21; uniconazole treatment increased significantly IAA, ZR and ABA contents of Jihei 1 compared with Jishu 21. [Conclusion] Drought-tolerant sweetpotato cultivar Jishu 21 exhibits high plasma membrane integrity and root vitality by increasing activities of antioxidant enzymes under drought stress and maintaining high contents of IAA, ZR and ABA. Unicona-zole exerts greater regulatory effects on physiological and biochemical properties of drought-sensitive sweetpotato cultivar Jihei 1 under drought stress. [ABSTRACT FROM AUTHOR]

To obtain large-volume non-thermal arc plasma (NTAP), a multiple NTAP generator with three pairs of electrodes has been developed. The arc plasma characteristics, including dynamic process, spatial distribution, and rotation velocity in the discharge zone, were investigated by high speed photograph and image processing methods. The results showed that the dynamic behaviors and spatial distribution of the arc plasma were strongly related to the electrode configuration. A swirl flow of multi-arc plasma was formed by adjusting the electrode configuration, and a steady luminance area was clearly observed in the center of the discharge zone. Moreover, the size of the luminance area increased by decreasing the gas flow rate. The electrical connection in series could be formed between/among these arc columns with their respective driving power supplies in the multi-arc dynamic evolution process. An approximately periodical process of acceleration and deceleration of the arc rotation velocity was observed in the multi-arc generator with swirl flow configuration. In general, the mean velocity of arc rotation was higher in the multi-arc generator with swirl flow configuration when a pair of electrodes driven by a power supply were opposite to each other rather than adjacent. [ABSTRACT FROM AUTHOR]