P / O value

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Wind-pollinated species such as the hazel produce a lot of pollen per egg to make fertilization more likely.

In botany, the P / O value (also: P / O ratio or pollen-ovule ratio ) is the ratio of the number of pollen to the number of ovaries (egg cells). It was introduced by Robert William Cruden . It provides good information Pollination and fertilization mechanisms , with which it is very often correlated , based on the basic assumption that the more likely fertilization takes place, the less pollen has to be produced per ovary.

Pollen is rich in proteins (15–40%) and therefore also in nitrogen in the form of amino acids . Nitrogen (as a source) in the form of nitrate is essential for growth, but it is usually in short supply in the soil . It is therefore important for plants not to be too wasteful with this resource.

Typical P / O values ​​are:

  • at cleistogamous plants: from 2.5 to 54
  • with obligatory (exclusively occurring) autogamy (self-pollination): 18–40
  • in the case of facultative but predominant autogamy : 30–400
  • for facultative allogamy : 240–2600
  • with obligatory allogamy : 2100–200,000

Wind-pollinated species usually produce a particularly large amount of pollen, such as the common hazel ( Corylus avellana ) with a P / O value of up to 2.4 million.

Individual evidence

  1. RW Cruden: Pollen-ovule ratios: A conservative indicator of breeding systems in flowering plants . In: evolution . tape 31 , no. 1 , 1977, pp. 32-46 .