Polyamine concentrations in four Poa species, differing in their maximum relative growth rate, grown with free access to nitrate and at limiting nitrate supply

摘要

The naturally fast-growing Poa annua and P. trivialis and the naturally slow-growing P. compressa and P. pratensis were grown with free access to nitrate, allowing plants to grow at their maximum growth rate (RGRmax), or were grown with relative nitrate addition rates of 100 or 50 mmol N (mol N)-1 day-1 (RAR100 and RAR50, respectively). The freely-occurring polyamines spermine, spermidine and putrescine were separated from their conjugates; the latter were further subdivided into a TCA-soluble anda TCA-insoluble fraction. Under nitrogen limitation, the total concentration of polyamines decreased in both leaves and roots of all species, whereas that in the stem remained more or less unchanged. These effects were to a large extent determined by thefree polyamines. For the conjugates there was more differentiation, both between plant organs and polyamine fractions. A positive correlation was found between polyamine concentration and RGR, leaf area ratio (LAR), specific leaf area (SLA), leaf mass ratio and stem mass ratio. The root mass ratio showed a negative correlation. No significant differences were found between the naturally fast- and slow-growing species. The putrescine:spermine + spermidine ratio in the leaves increased with decreasing nitrate supply, which was associated with a decrease in leaf expansion, accounting for a decrease in LAR and SLA. For the roots, this ratio tended to decrease with decreasing nitrate supply, whereas for the stems the results were somewhat more variable. There was no evidence for a crucial role of polyamines in the determination of inherent differences in growth rate in spite of a positive correlation of polyamines, especially the free polyamines, with growth parameters.