Grafting has been widely used in orchard management because the rootstock can make the tree more tolerant to environmental stresses. Iron deficiency is one of the major limiting environmental factor in apple production worldwide. Systematic research has been made about iron-deficiency adaptive responses in the level of organs, cells, and subcells, whereas the interactions between Fe and other divalent cations in tissue level are little known. Synchrotron radiation X-ray fluorescence (SR-μXRF) was used to map the location of selected elements Fe, Zn, Mn, Ni, and Co in the longitudinal and latitudinal root samples of Malus xiaojinensis. Iron deficiency induced a significant increase in the relative contents of five micronutrients in epidermis and cortex. The ratio of element contents of roots under Fe-deficient condition and Fe-sufficient condition at same position increased obviously in the section of 1000- to 2000-μm distance from the root tip in xylem. Expression analysis of iron absorption- and transport-related genes in roots showed that MdNramp3 and MxCS1 increased significantly. These results indicated that iron deficiency promoted the long-distance transport of micronutrients in xylem, and MdNramp3 and MxCS1 might play an important role in this process. Importantly, this study directly provides visual divalent metals distribution in tissue level for an improved understanding of metal absorption process in apple rootstock.
As one of the most important fruit tree crops, apple (Malus ×domestica), is faced with the serious impact of soil salinization. However, the underlying genetic and regulatory network remains elusive. Here, we adopted time-course RNA sequencing to decipher the genetic basis and regulatory module of apple in response to salt stress. Among a series of intense changes in genes at each time point, the critical genes in the mitogen-activated protein kinase signaling pathway were highly consistent with the duration of the stress treatment. Moreover, Salt Overly Sensitive 1 (SOS1) genes were identified and predicted to play important roles in the response process. We constructed coexpression modules and explored modules significantly associated with stress. SOS genes were identified in the hub genes, suggesting a critical role. Interestingly, transcription factors were also identified and predicted to cointeract with SOS genes in the hub genes of the coexpression module [e.g., HB7 (MD01G1226600), WRKY33 (MD12G1181000), and ERF106 (MD07G1248700)]. Collectively, our exploration and findings provide a reference and data resource for the study of genetic and salt regulatory networks in apple.
As a wild apple species native to central Asia, Malus sieversii (Ledeb.) Roem. is distributed in a wide region covering most of the Tienshan Mountains. Malus sieversii is a useful genetic pool for apple breeding since rich with diversity. In this paper, we first describe the species range of this endangered species. We then describe an in situ reserve that has been established. We also investigated some reproductive characteristics of M. sieversii including pollen germination, seed dormancy, and seed viability. Both stratification and seedcoat removal efficiently released seed dormancy and accelerated seed germination. Pollen germination rate is around 60%. Our data suggest that injurious insects and human activities, rather than reproductive characters, limit the renewal of M. sieversii.