The color of an apple is an important index of its appearance quality, which affects the fruit’s marketability and value. The green variety “Granny Smith” remains green when ripe, and the pigment in the peel is mainly chlorophyll. The chlorophyll in the peel of the yellow variety “Golden Delicious” degrades as the fruit ripens. To explore the different mechanisms of chlorophyll degradation in the “Golden Delicious” and “Granny Smith” varieties, transcriptomic analysis was performed on the mature peels of both cultivars. High-quality sequences totaling 48,206,940 and 48,796,646 raw bases, as well as 9632 differentially expressed genes (DEGs), were identified. A total of 1206 DEGs were classified in 118 KEGG metabolic pathways. Additionally, 3258 transcription factors from 428 gene families were predicted, and DEGs associated with chlorophyll degradation, including MdSGR2, MdNYC1 and MdHCAR, were identified. Subsequently, the MdSGR2 gene was isolated from the mature peel of “Granny Smith” apples. Subsequent subcellular localization analysis confirmed that MdSGR2 specifically targets chloroplasts. The transient overexpression of MdSGR2 was found to negatively regulate chlorophyll degradation, leading to the inhibition or deceleration of chlorophyll breakdown, thereby maintaining green coloration in the leaves and peel. Conversely, silencing MdSGR2 positively regulated chlorophyll degradation, resulting in chlorosis in the leaves and peel. These findings offer valuable insights into the regulatory mechanism governing apple fruit coloration and lays a solid foundation for further investigation in this field.

Objective In order to solve the problem of resource waste caused by the low quality of early harvest of fresh walnuts，this study explores the dynamic changes of various quality indexes of fresh walnut fruit at different growth stages.The analysis and evaluation of the comprehensive quality can clarify its growth and development law and propose a suitable fresh harvest period，which provides a reference for the timely harvest and resource utilization of fresh walnuts. Method In this experiment，the fresh walnut variety ‘Lipin No.2’ from Yicheng County，Shanxi Province was used as the test material.Samples were taken at 82 d，92 d，102 d，112 d，123 d and 133 d after flowering，for a total of 6 times.The contents of postharvest fruit quality indexes were determined by spectrophotometer，Kjeldahl nitrogen analyzer，soxhlet extraction，gas chromatography，amino acid analyzer.The LSD multiple comparison method was used to test the significance of the difference between the data at different growth stages，and the quality of walnuts at different growth stages was comprehensively evaluated by principal component analysis. Result With the growth of the fruit，the appearance indexes include three diameter mean of green fruit，three diameter mean of nuts，fresh weight of green fruit，fresh nut weight，the dry weight of the nut，the fresh weight of the walnut kernel，the dry weight of the walnut kernel and the ratio of the diameter of the kernel all increased first and then tended to be relatively stable.The appearance quality indexes reached a relatively high level at 112 days after flowering，the fruit size and quality were basically stable.In terms of sensory quality，the evaluation scores of taking kernel difficulty，seed coat color and seed coat peeling difficulty gradually decreased，the kernel plumpness score gradually increased，the kernel aroma and flavor scores first increased and then decreased.The comprehensive score of sensory quality （2.8~4.5 points） increased first and then decreased，the highest score was 4.5 points at 112 days after flowering，and the sensory quality was the best.In terms of nutritional quality，the contents of kernel rate，fat，protein，stearic acid and oleic acid showed an overall upward trend，while the contents of water content，palmitic acid，linoleic acid and linolenic acid showed an overall downward trend.The contents of soluble sugar，fructose，total amino acids，total essential amino acids，four kinds of flavor amino acids （umami，sweet，bitter and aromatic），P，Zn and Ca elements decreased first and then increased.The content of tannin showed a trend of increase-decrease-increase，and the content of Mg and Fe elements showed a trend of decrease-increase-decrease.At 112 days after flowering，the contents of some nutrients such as protein，soluble sugar，fructose，linoleic acid，P，Mg and Zn accumulated rapidly and reached a high level.The results of principal component analysis of the comprehensive quality of fresh walnut at different growth stages showed that the score was 0.53 at 112 days after flowering，which was close to the highest score of 0.57 at 133 days after flowering，and the comprehensive quality had reached a higher level. Conclusion 112 days after flowering is the suitable harvest time for fresh walnut of ‘Lipin No.2’.The visual index is that the color of inner fold wall and septum of core shell develops from white to yellowish brown，which can provide reference for fruit farmers to harvest fresh walnut.

The absorption and utilization of NH₄⁺ and NO₃⁻ by plant roots is closely related to soil moisture. In this study, we investigated the effect of short-time drought and rewatering on uptake and assimilation of NH₄⁺ and NO₃⁻ in 1-year-old Malus hupehensis plants, as well as transcription changes of ammonium transporters (AMTs) and nitrate transporters (NRTs). In roots, the NH₄⁺ and NO₃⁻ content and nitrate reductase activity decreased under drought and to some extent was restored after rewatering. Expression analysis indicated that most investigated AMTs and NRTs were down-regulated while MhAMT1;2 was significantly up-regulated in drought-stressed roots. Therefore, the function of MhAMT1;2 was further studied through bioinformatics analysis, tissue-specific expression, subcellular localization, and functional complementation in NH₄⁺ uptake-defective yeast and Arabidopsis mutants. Results showed that MhAMT1;2 was mainly expressed in roots and localized to the cell membrane. Moreover, MhAMT1;2 can mediate NH₄⁺ uptake in both yeast and Arabidopsis mutants, and the transport process was affected by external proton concentrations and ATP. The present study will create a basis for exploring the functional roles of plant AMT members and improving N uptake and use efficiency under drought condition in fruit trees.

Fruit color is a key quality indicator for apples and directly influences their market value. The process of fruit ripening encompasses various physiological and biochemical changes, such as the breakdown of chlorophyll and the buildup of anthocyanins and carotenoids. This study investigated the mechanism of chlorophyll degradation in apple peels using ‘Granny Smith’ varieties. The experiments involving the treatment with methyl jasmonate (MeJA) indicated that a concentration of 10 µM MeJA led to a reduction in chlorophyll degradation, while a higher concentration of 1500 µM MeJA enhanced this degradation, which aligned with the variations observed in the expression of genes associated with chlorophyll degradation. The key chlorophyll degradation gene MdSGR1 was cloned and found to be induced by methyl jasmonate. MdSGR1 encodes a 283-amino-acid protein belonging to the stay-green superfamily. The promoter possesses inducible cis-acting elements that respond to methyl jasmonate, low temperature and light, while the protein is localized to chloroplasts. Overexpression and silencing vectors were constructed. Overexpression of MdSGR1 induced chlorosis in tobacco leaves and ‘Granny Smith’ apple peels, decreased chlorophyll content, and upregulated related gene expression. Conversely, silencing MdSGR1 produced opposite effects. Arabidopsis thaliana plants overexpressing MdSGR1 exhibited low chlorophyll content, reduced photosynthetic rate, upregulated expression of genes associated with chlorophyll degradation. The results of yeast one-hybrid and dual-luciferase reporter assays indicated that the MdMYC2 transcription factor interacts with the promoter region of MdSGR1. In conclusion, MdSGR1 is crucial for the degradation of chlorophyll in apple peel, and it is regulated both by the MdMYC2 transcription factor and different concentrations of MeJA. This study preliminarily elucidated the regulatory mechanism of methyl jasmonate on chlorophyll degradation in fruit peel, and these findings provide an important theoretical basis for controlling degreening and color quality in apple fruit.