During winter, asparagine is metabolised immediately, but other nutrients, especially phosphates and glutamine, are removed from the xylem sap and stored in mature stem, bark and leaf tissues for release back into the xylem just before shoot growth begins in mid summer. This is also the time when the oldest leaves senesce and die, returning nutrients to the plant at the time when they are needed most. When glutamine eventually reaches the leaves, it is broken down and used to synthesise protein and non-amide amino acids such as aspartate, threonine, serine, glutamate, glycine, alanine and cystine. Together with sucrose and other solutes, these are then circulated in the phloem. The phloem sap of "B. prionotes" is unusual in having an extremely low ratio of potassium to sodium cations, and very low concentrations of phosphate and amino acids compared to chloride and sulfate anions. The low levels of potassium and phosphate reflect the extremely low availability of these minerals in the soil. The unusually high levels of sodium and chloride—at concentrations usually only seen under saline conditions—may be due to the necessity of maintaining turgor pressure; that is, with so little potassium and phosphate available, and that needed in the building of new tissue, "B. prionotes" is forced to circulate whatever other ions are available in order to maintain turgor.