AtROP1 negatively regulates potato resistance to Phytophthora infestans via NADPH oxidase-mediated accumulation of H2O2.

BACKGROUND: Small GTPases are monomeric guanine nucleotide-binding proteins. In plants, ROPs regulate plant cell polarity, plant cell differentiation and development as well as biotic and abiotic stress signaling pathways. RESULTS: We report the subcellular localization of the AtRop1 protein at the plasma membrane in tobacco epidermal cells using GFP fusions. Additionally, transient and stable expression of a dominant negative form (DN) of the Arabidopsis AtRop1 in potato led to H2O2 accumulation associated with the reduced development of Phytophthora infestans Montagne de Bary and smaller lesions on infected potato leaves. The expression of the Strboh-D gene, a NADPH oxidase homologue in potato, was analyzed by RT-PCR. Expression of this gene was maintained in DN-AtRop1 transgenic plants after infection with P. infestans. In transgenic potato lines, the transcript levels of salicylic acid (SA) and jasmonic acid (JA) marker genes (Npr1 and Lox, respectively) were analyzed. The Lox gene was induced dramatically whereas expression of Npr1, a gene up-regulated by SA, decreased slightly in DN-AtRop1 transgenic plants after infection with P. infestans. CONCLUSIONS: In conclusion, our results indicate that DN-AtROP1 affects potato resistance to P. infestans. This is associated with increased NADPH oxidase-mediated H2O2 production and JA signaling.

Implementing a soil ammonium N fertilizer management for synchronizing potato N demands.

Potatoes, as a high-nitrogen (N)-demand crop, are strongly influenced by both the quantity and form of N supply. Previous studies have demonstrated that applying nitrate N prior to tuber formation and ammonium N post-tuber formation can substantially enhance potato yields and improve N fertilizer use efficiency. However, the ammonium N introduced into the soil undergoes nitrification, creating challenges in aligning the N supply form with the needs of potatoes. This study explored novel N regulation strategies aimed at augmenting potato yields and improving N fertilizer use efficiency. Two field experiments were conducted from 2020 to 2022. Experiment 1 involved four N gradients, namely no N, 150 kg N ha-1, 300 kg N ha-1, and 450 kg N ha-1. Soil samples were collected regularly to determine the transformation patterns of soil ammonium N during potato growth. Experiment 2 included three N management practices: farmer practice (Con), "nitrate followed by ammonium" with nitrification inhibitor (N-NI), and optimization (the soil ammonium N transformation-based split application of N fertilizer, Opt). The potato yield and N fertilizer use efficiency were compared to assess the performance of the optimized strategy. The results showed that 90 % of the ammonium N transformed 20 days after the basal dressing of N. When N fertilizer was applied as top dressing during the tuber formation and bulking stages, more than 90 % of ammonium N was transformed after 10 days. The optimized strategy resulted in a 20 % increase in potato yield, a 20 % increase in N fertilizer partial factor productivity, and a 12-20 % reduction in residual inorganic N in the 0-60 cm soil layer. This suggests that ammonium N applied as base fertilizer exhibits a relatively slow transformation rate, while applying ammonium N as top dressing during the tuber formation and bulking stages accelerates the transformation rate. The split application of ammonium N based on soil ammonium N transformation patterns can improve the alignment between the N supply form with the specific demands of potatoes.

Class III peroxidases are activated in proanthocyanidin-deficient Arabidopsis thaliana seeds.

BACKGROUND AND AIMS: It has previously been shown that proanthocyanidins (PAs) in the seed coat of Arabidopsis thaliana have the ability to scavenge superoxide radicals (O2(-)). However, the physiological processess in PA-deficit seeds are not clear. It is hypothesized that there exist alternative ways in PA-deficient seeds to cope with oxidative stress. METHODS: The content of hydrogen peroxide (H2O2) and its relevance to the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidases was investigated in both wild-type and PA-deficit mutant seeds. A biochemical staining approach was used to detect tissue localizations of peroxidase activities in PA-deficit mutant seeds. KEY RESULTS: PA-deficient mutants possess significantly lower levels of H2O2 than the wild-type, despite their higher accumulation of superoxide radicals. Screening of the key antioxidant enzymes revealed that peroxidase activity was significantly over-activated in mutant seeds. This high peroxidase activity was mainly confined to the seed coat zone. Interestingly, neither ascorbate peroxidase nor glutathione peroxidase, just the guaiacol peroxidases (class III peroxidases), was specifically activated in the seed coat. However, no significant difference in peroxidase activity was observed in embryos of either mutants or the wild-type, although gene expressions of several candidate peroxidases were down-regulated in the embryos of PA-deficient seeds. CONCLUSIONS: The results suggest that enhanced class III peroxidase activity in the seed coat of PA-deficient mutants is an adaptive strategy for seed development and survival.

[Active crop canopy sensor-based nitrogen diagnosis for potato].

In the present study, two potato experiments involving different N rates in 2011 were conducted in Wuchuan County and Linxi County, Inner Mongolia. Normalized difference vegetation index (NDVI) was collected by an active GreenSeeker crop canopy sensor to estimate N status of potato. The results show that the NDVI readings were poorly correlated with N nutrient indicators of potato at vegetative Growth stage due to the influence of soil background. With the advance of growth stages, NDVI values were exponentially related to plant N uptake (R2 = 0.665) before tuber bulking stage and were linearly related to plant N concentration (R2 = 0.699) when plant fully covered soil. In conclusion, GreenSeeker active crop sensor is a promising tool to estimate N status for potato plants. The findings from this study may be useful for developing N recommendation method based on active crop canopy sensor.

Optimizing nutrient inputs by balancing spring wheat yield and environmental effects in the Hetao Irrigation District of China.

The Hetao Irrigation District is the primary spring wheat production region in China. However, overuse and unscientific use of chemical fertilizer have resulted in low nutrient use efficiency and potential risks to the environment. Balanced fertilization (BF), a 29.9-36.4% N fertilizer and 40% P fertilizer, was reduced, while a 72 kg K2O ha-1 K fertilizer was supplied and designed to resolve problems encountered during the field trial from 2019 to 2021. The results showed that the grain yield did not decrease significantly in the BF treatments compared in the local farmer practice (FP) treatment. The nitrogen fertilizer partial productivity (PFPN) and agronomic nitrogen efficiency (NAEN) increased 42.95-52.88% and 44.06-49.24% with BF compared to with the FP, respectively. Moreover, the BF treatments reduced nitrate leaching in the 0-100 cm soil layer and reduced the N surplus (Nsur) to approximately 160 kg N per hectare per year, dramatically reducing the environmental risk. The yield maintenance and nitrogen use efficiency increases were attributed to the lower nitrogen concentrations in the seedlings and the higher apparent N translocation efficiency (TR) from the stems and sheaths after anthesis in the BF treatments than in the FP treatments. Considering the yield, nutrient use efficiency, and environmental and economic benefits comprehensively, the BF1 treatment was considered the optimal fertilization scheme for Hetao spring wheat production.

Potato tuber degradation is regulated by carbohydrate metabolism: Results of transcriptomic analysis.

Tuber number is an essential factor determining yield and commodity in potato production. The initiation number has long been considered the sole determinant of the final total tuber number. In this study, we observed that tuber numbers at harvest were lower than at the tuber bulking stage; some formed tubers that were smaller than 3 cm degraded during development. Carbohydrate metabolism plays a crucial role in tuber degradation by coordinating the source-sink relationship. The contents of starch and sucrose, and the C:N ratio, are dramatically reduced in degradating tubers. Transcriptomic study showed that "carbohydrate metabolic processes" are Gene Ontology (GO) terms associated with tuber degradation. A polysaccharide degradation-related gene, LOC102601831, and a sugar transport gene, LOC102587850 (SWEET6a), are dramatically up-regulated in degradating tubers according to transcriptomic analysis, as validated by qRT-PCT. The terms "peptidase inhibitor activity" and "hydrolase activity" refer to the changes in molecular functions that degradating tubers exhibit. Nitrogen supplementation during potato development alleviates tuber degradation to a certain degree. This study provides novel insight into potato tuber development and possible management strategies for improving potato cultivation.

Physiological roles for aerenchyma in phosphorus-stressed roots.

Low phosphorus availability induces the formation of cortical aerenchyma in roots. The adaptive significance of this response is unknown. We hypothesized that aerenchyma may be helpful to low-phosphorus plants by reducing root respiratory and phosphorus requirements, thereby increasing the metabolic efficiency of soil exploration. To test this hypothesis we investigated aerenchyma formation, root respiration and tissue phosphorus concentration in maize and common bean genotypes in response to phosphorus availability and ethylene treatments. Genotypes differed substantially in their ability to form aerenchyma in response to low phosphorus. Aerenchyma formation was disproportionately correlated with reduced root respiration; roots with 30% cross-sectional area as aerenchyma had 70% less respiration than roots without aerenchyma. Aerenchyma formation was also proportionally correlated with reduced root phosphorus concentration. Variation in aerenchyma formation was correlated with root respiration and phosphorus concentration, regardless of whether such variation was caused genetically or by ethylene or phosphorus treatments. Results with isolated roots were confirmed by measurement of whole root respiration of intact maize plants. Our results support the hypothesis that aerenchyma formation reduces the respiratory and phosphorus requirements of soil exploration by roots, and thus, represents a useful adaptation to low phosphorus availability.