Are There Inter‐relations Between the Metabolic Role of Boron, Synthesis of Phenolic Phytoalexins and the Germination of Pollen?

SUMMARY The similarities between the effects of wounding, microbial infection and boron deficiency in bringing about alterations in phenolic and hormone metabolism in vascular plants are emphasized and attention drawn to gaps in available information. It is proposed that the similarities are due to induction of localized or systemic sequestration of endogenous borate by β‐l,3 glucans or other carbohydrates including glycoproteins (microbial elicitors and wound callose). In view of the morphological, physiological and biochemical parallels between fungal infection and pollination, it is further argued that there are common metabolic links between the effects of boron deficiency, wounding and infection and the presence of callose in pollen grains and tubes, the stigmatic deposition of callose in response to some incompatible pollinations and the boron requirement for the germination of pollen. A highly speculative but experimentally testable scheme is proposed.