Boron mobility in peanut (Arachis hypogaea L.)

In most plant families, boron (B) is phloem immobile. For plants such as peanut which bury their fruit, the mechanism for B delivery and the B source for fruit and seed growth remains enigmatic. Therefore, this study aimed to establish evidence of B retranslocation in peanut and to identify its importance in plant development. In a sand culture experiment, the increase in B contents in new organs after B withdrawal and the corresponding decline in B contents in older organs was evidence of B redistribution. In a foliar 10B experiment, the 10B abundance of treated-leaves decreased and 10B was detected in leaves and flowers formed after the application of foliar B. Application of 10B to the roots for a period also provided evidence for the retranslocation of 10B accumulated during the first growth period. The 10B abundance in older plant parts declined and 10B appeared in new organs (flowers, pegs, leaves) that had developed after the 10B supply had been replaced by 11B. In the fourth experiment, foliar application of B reduced hollow heart, a symptom of B deficiency in seeds, in cv. TAG 24 from 39 to 8% and in Tainan 9 from 63 to 18%. These experiments all provide evidence for B retranslocation in peanut, but further work on the relative importance of the xylem and phloem pathways for B loading into the fruit is needed.