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