Exploring the Physiological Basis for High Reproduction Sensitivity to Boron Deficiency in Plants
Plant reproduction has higher boron (B) requirements than vegetative growth and generally reproductive plant parts contain more B, but the form and function of the extra B remains unexplained. In this paper we review the literature on B in plant reproductive development and add to it recent results on B distribution and forms in reproductive parts (silks, pollen) and vegetative parts (youngest open leaves) of maize grown in B-buffered solution culture. Cell wall binding of B in the silk and pollen of maize does not explain the higher B concentrations in reproductive than vegetative tissue. Given the rather high proportion of B present in the non-cell wall fraction in pollen and silk, the high B requirement for plant reproduction suggests an additional role for B other than in cell wall formation. The identity of non-cell wall B binding substrates in pollen and carpel tissue awaits further study. The higher sensitivity of plant reproduction to B deficiency is also related to weaker B transport into floral organs, especially where transpiration is suppressed in reproductive plant parts by enclosure of sheaths (e.g. wheat ear) or husks (e.g. maize ear) during the critical stage of development.