Transcription factors MhDREB2A/MhZAT10 play a role in drought and cold stress response crosstalk in apple.

Drought and cold stresses seriously affect tree growth and fruit yield during apple (Malus domestica) production, with combined stress causing injury such as shoot shriveling. However, the molecular mechanism underlying crosstalk between responses to drought and cold stress remains to be clarified. In this study, we characterized the zinc finger transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10) through comparative analysis of shoot-shriveling tolerance between tolerant and sensitive apple rootstocks. MhZAT10 responded to both drought and cold stresses. Heterologous expression of MhZAT10 in the sensitive rootstock 'G935' from domesticated apple (Malus domestica) promoted shoot-shriveling tolerance, while silencing of MhZAT10 expression in the tolerant rootstock 'SH6' of Malus honanensis reduced stress tolerance. We determined that the apple transcription factor DEHYDRATION RESPONSE ELEMENT-BINDING PROTEIN 2A (DREB2A) is a direct regulator activating the expression of MhZAT10 in response to drought stress. Apple plants overexpressing both MhDREB2A and MhZAT10 genes exhibited enhanced tolerance to drought and cold stress, while plants overexpressing MhDREB2A but with silenced expression of MhZAT10 showed reduced tolerance, suggesting a critical role of MhDREB2A-MhZAT10 in the crosstalk between drought and cold stress responses. We further identified drought-tolerant MhWRKY31 and cold-tolerant MhMYB88 and MhMYB124 as downstream regulatory target genes of MhZAT10. Our findings reveal a MhDREB2A-MhZAT10 module involved in crosstalk between drought and cold stress responses, which may have applications in apple rootstock breeding programs aimed at developing shoot-shriveling tolerance.

The transcription factor MhZAT10 enhances antioxidant capacity by directly activating the antioxidant genes MhMSD1, MhAPX3a, and MhCAT1 in apple rootstock SH6 (Malus honanensis × M. domestica).

Stress tolerance in apple (Malus domestica) can be improved by grafting to a stress-tolerant rootstock, such as 'SH6' (Malus honanensis × M. domestica 'Ralls Genet'). However, the mechanisms of stress tolerance in this rootstock are unclear. In Arabidopsis (Arabidopsis thaliana), the transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10) is a key component of plant tolerance to multiple abiotic stresses and positively regulates antioxidant enzymes. However, how reactive oxygen species (ROS) are eliminated upon activation of ZAT10 in response to abiotic stress remains elusive. Here, we report that MhZAT10 in the rootstock SH6 directly activates the transcription of three genes encoding the antioxidant enzymes MANGANESE SUPEROXIDE DISMUTASE 1 (MhMSD1), ASCORBATE PEROXIDASE 3A (MhAPX3a), and CATALASE 1 (MhCAT1) by binding to their promoters. Heterologous expression in Arabidopsis protoplasts showed that MhMSD1, MhAPX3a, and MhCAT1 localize in multiple subcellular compartments. Overexpressing MhMSD1, MhAPX3a, or MhCAT1 in SH6 fruit calli resulted in higher superoxide dismutase, ascorbate peroxidase, and catalase enzyme activities in their respective overexpressing calli than in those overexpressing MhZAT10. Notably, the calli overexpressing MhZAT10 exhibited better growth and lower ROS levels under simulated osmotic stress. Apple SH6 plants overexpressing MhZAT10 in their roots via Agrobacterium rhizogenes-mediated transformation also showed enhanced tolerance to osmotic stress, with higher leaf photosynthetic capacity, relative water content in roots, and antioxidant enzyme activity, as well as less ROS accumulation. Overall, our study demonstrates that the transcription factor MhZAT10 synergistically regulates the transcription of multiple antioxidant-related genes and elevates ROS detoxification.

Nano-Sized Antioxidative Trimetallic Complex Based on Maillard Reaction Improves the Mineral Nutrients of Apple (Malus domestica Borkh.).

The metallic complex is widely used in agricultural applications. Due to the oxidation of the metal and environmental unfriendliness of ligand, maintaining an efficient mineral supply for plants without causing environmental damage is difficult. Herein, an antioxidative trimetallic complex with high stability was synthesized by interacting Ca2+, Fe2+, and Zn2+ with the biocompatible ligands from the Maillard reaction. The composite structure elucidation was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR). Thermal stability was measured by thermogravimetric (TG). Antioxidative activities were evaluated by ferric reducing antioxidant power and radical scavenging activity assays. The three metals were successfully fabricated on the Maillard reaction products (MRPs) with contents of Ca (9.01%), Fe (8.25%), and Zn (9.67%). Microscopy images revealed that the three metals were uniformly distributed on the MRPs with partial aggregation of <30 nm. FTIR and XPS results revealed that the metals were interacted with MRPs by metal-O and metal-N bonds. TG and antioxidative activity assays showed that the trimetallic complex meets the requirements of thermodynamics and oxidation resistance of horticultural applications. Additionally, the results of the exogenous spraying experiment showed that the trimetallic complex significantly increased the mineral contents of the "Fuji" apple. By treatment with the complex, the concentrations of Ca, Fe, and Zn were increased by 85.4, 532.5, and 931.1% in the leaf; 16.0, 225.2, and 468.6% in the peel; and 117.6, 217.9, and 19.5% in the flesh, respectively. The MRP-based complexes offered a higher growth rate of the mineral content in apples than ones based on sugars or amino acids. The results of the spraying experiment carried out in 2 years show that the method has high reproducibility. This study thus promotes the development of green metallic complexes and expands the scope of agrochemical strategy.

[Multivariate analysis of relationship between soil nutrient factors and fruit quality characte-ristic of 'Fuji' apple in two dominant production regions of China]. / 两大优势产区'富士'è‹¹æžœå›­åœŸå£¤å »åˆ†ä¸Žæžœå®žå“è´¨å ³ç³»çš„å¤šå˜é‡åˆ†æž.

The objective of this experiment is to probe into the influence of soil nutrient contents on fruit quality features of 'Fuji' apple, screen major soil nutrient factors affecting fruit quality features, clarify the suitable soil nutrient content for good fruit quality indicators, and to provide theoretical basis in reasonable orchard soil fertilizer application for improving fruit qua-lity in the Circum-Bohai and Loess Plateau apple production regions in China. The soil nutrient contents and 'Fuji' fruit qualities were respectively analyzed at 66 commercial 'Fuji' apple orchards standard rootstock in the Circum-Bohai and Loess Plateau apple production regions of 22 counties in China from 2010 to 2011. The partial least squares regression (PLS) was used to screen major soil nutrient elements affecting fruit quality, and to establish regression equation of relationship between fruit quality and major soil nutrition factors. Linear programming was used to obtain optimum proposals of soil nutrient elements for good apple quality. The results showed that alkaline hydrolytic N, available P, Ca, Fe, and Zn of soil were significantly higher while pH and available K were significantly lower in Circum-Bohai region than in Loess Plateau apple production region. Soluble solid content in Loess Plateau was higher than in Circum-Bohai; moreover, ratio of soluble solids content and titratable acidity was lower. The soil available B in the Circum-Bohai and Loess Plateau apple production regions had positive effect on fruit mass, and total N had negative effect on fruit firmness. The soluble solid contents in the Circum-Bohai were mainly negatively affected by total N and positively by available B, while positively affected by available Ca and negatively by alkaline hydrolytic N in the Loess Plateau region. The desired soil nutrients for good fruit qualities were high avai-lable B, pH and suitable available K in the Circum-Bohai, and low total N, high alkaline hydrolytic N, available K, Fe and suitable available Zn and B in the Loess Plateau region. It was the key technical measures in soil nutrient management for good fruit quality to increase available B and pH, adjust available K in the Circum-Bohai, and to enhance alkaline hydrolytic N, available K, Fe, and to decrease pH, and adjust available Zn and B in the Loess Plateau region.

[Effects of different pruning modes on the light distribution characters and fruit yield and quality in densely planted 'Red Fuji' apple orchard].

This paper studied the effects of different pruning modes on the light distribution at different positions of canopy and the fruit yield and quality in different layers in a densely planted 'Red Fuji' apple orchard. Comparing with no pruning, both light and heavy pruning improved the light distribution in the canopy. Under light pruning, the canopy volume with a relative light intensity less than 30% occupied 14. 6% of the total, and that with a relative light intensity more than 80% accounted for 11.2%. Under heavy pruning, the two values were 12.8% and 28.8%, respectively. The fruit yield under light pruning increased in the first year, but that under heavy pruning decreased, with the fruit quality being both improved. The mean fruit mass, firmness, and soluble solid matter content decreased in the order of light pruning > heavy pruning > no pruning, the titratable acid content was in adverse, and the anthocyanin content was in the order of heavy pruning > light pruning > no pruning. From the viewpoint of fruit yield and quality, light pruning was the best modification mode for densely planted orchards.

[Effects of debagging time and picking off leaf on fruit quality of "Red Fuji" apple].

This paper studied the effects of debagging time and picking off leaves around fruits on the fruit quality and 1-year old shoots stored nutrition of "Red Fuji" apple. Properly advancing debagging time significantly increased the mean mass, anthocyanin content, and coloration area of the fruits (P < 0.05). Comparing with those of the fruits debagged on September 30, the mean mass, anthocyanin content, and coloration area of the fruits debagged on September 24 increased by 10.98%, 28.15%, and 13.44%, respectively, and the fruit firmness, soluble solid content, and titratable acidity had less differences. When the leaves within 15, 30, and 45 cm away from the fruits were wholly picked off, the light environment around the fruits improved significantly (P < 0.01), with the light intensity increased by 70%, 95%, and 115%, respectively, compared with no leaf picked off treatment. Picking off the leaves within 30-45 cm away from the fruits benefited the fruit coloration and anthocyanin accumulation. No significant effects were observed on the 1-year old shoots stored nutrition and their budding in next year among the treatments of picking off leaves. Advancing debagging time and picking off the leaves within 30-45 cm away from the fruits could improve fruit appearance and quality.

[Leaf photosynthetic potential in canopy layers of un-thinned and thinned apple orchards].

Through the comparison of leaf photosynthetic potential and of photosynthetically active radiation (PAR), leaf nitrogen concentration (Nl), and mass per unit leaf area (Ml) in different canopy layers of un-thinned orchard (UOD) and thinned orchard (TOD), this paper studied the effects of UOD rebuilding on the use efficiencies of PAR and nitrogen, and their relationships to the fruit yield and quality. Thinning obviously improved the radiation environment in canopy. The radiation distribution in TOD canopy was more uniformly than that in UOD canopy, and the invalid space with relative PAR (PARr) less than 30% in TOD approached to zero, while the minimum mean PARr in UOD was 17%, and the space under 0. 3 of relative canopy height was invalid. The leaf photosynthetic efficiency in TOD was notably improved. Comparing with that in UOD, the photsynthetic rate (Pn) at the middle and bottom of the canopy in TOD was increased by 7.8% and 10.2%, respectively. Meanwhile, the photosynthetic potential parameters such as maximum carboxylation rate (Vmax) and maximum electron transfer rate (Jmax) also increased remarkably in TOD. The leaf photosynthetic potential had significant correlation with Nl, and the Nl was strongly correlated with PARr. As a result, leaf photosynthetic potential and PARr could be estimated according to the spatial distribution of relative leaf nitrogen concentration (Nlr).

[Effects of alternative partial rootzone irrigation on peach growth, productivity, and water use efficiency].

Taking 12-year-old peach (Prunus persica L. Batsch cv. Ruiguang 5) as test material, this paper studied the effects of alternative partial rootzone irrigation (APRI) on its growth, productivity, and water use efficiency under semi-arid climate condition. The results showed that in APRI treatments, the soil water content in the wet side of peach tree decreased with increasing soil depth, while that in the dry side was in adverse, with the maximal difference appeared in 0-25 cm soil layer. In the treatments of APRI with an interval of 2 and 4 weeks, the leaf water potential at pre-dawn was lower than that in the control (sufficient irrigation), but with the time prolonged, this potential in all treatments tended to decrease, and had no significant difference in the afternoon. The peach yield in APRI treatments was 10% lower than that in the control, but the irrigation amount was reduced by 50%, and the water use efficiency was increased by 75%. APRI significantly limited the shoot growth of peach tree, but had no obvious effect on the fruit diameter.