Effects of phosphorus and nitrogen on nodulation are seen already at the stage of early cortical cell divisions in Alnus incana.

GENTILI F; WALL LG; HUSS-DANELL K

ANNALS OF BOTANY

Año: 2006 vol. 98 p. 309 - 315

0305-7364

• The present work aimed to study early stages of nodulation in a chronological sequence and to study phosphorus and nitrogen effects on early stages of nodulation in Alnus incana infected by Frankia. A method was developed to quantify early nodulation stages in intact root systems in the root hair infected actinorhizal plant Alnus incana (L.) Moench. Plant tissue responses were followed every two days until 14 days after inoculation. Cortical cell divisions were seen already 2 days after inoculation with Frankia. Cortical cell division areas, prenodules, nodule primordia and emerging nodules were quantified as host responses to infection. • Seedlings were grown in pouches and received different levels of phosphorus and nitrogen. Four levels of phosphorus (range from 0.03 to 1mM P) and two levels of nitrogen (0.71 and 6.45 mM N) were used to study P and N effects on these early stages of nodule development. • Phosphorus at a medium concentration (0.1 mM) stimulated cell divisions in the cortex and number of prenodules, nodule primordia and emerging nodules as compared to higher or lower P levels. High N level inhibited early cell divisions in the cortex, and this was particularly evident when length of cell division areas and presence of the nodulation stages were related to root length. • We found extended cortical cell division areas that have not been previously shown in Alnus incana. • The results show that effects of phosphorus and nitrogen are expressed already at the stage when the first cortical cell divisions are induced by Frankia.