from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The first formed xylem that differentiates from the procambium.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The first xylem to form in a plant.

from The Century Dictionary and Cyclopedia

  • n. In botany, the first-formed elements of the xylem of a vascular bundle.


from Wiktionary, Creative Commons Attribution/Share-Alike License

proto- +‎ xylem


  • The researchers conducted the study in the root of Arabidopsis, a small flowering plant related to cabbage, where they took a closer look at the development of two types of root cells - protoxylem and metaxylem.


  • High dosage of these messenger RNA molecules lead cells to become metaxylem, whereas low dosage leads to protoxylem.


  • Using a combination of molecular and cellular techniques including high-resolution imaging, they discovered a complex sequence of events at the molecular level that creates the distinction between protoxylem and metaxylem cells.


  • Since microRNA 165/6 moves out from its source cells and dissolves their target messenger RNAs, in areas where there are high levels of microRNA 165/6, nearby cells are more likely to become protoxylem.



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