Boron Nutrition and Lignification in Sunflower and Tobacco Stems

Sunflower plants (Helianthus annuus L.) decapitated above the third node and tobacco plants (Nicotiana tabacum L.) decapitated above the tenth node were grown in plus- and minus-boron solutions in an attempt to determine whether boron plays a role in tissue lignification. After 18 days the stems of sunflower and after 82 days those of tobacco were harvested and analyzed for lignin. The percentage lignin in the stems of the minus-boron sunflower plants was higher, although there was no significant difference between the two series in total quantity of lignin. The percentage and total quantity of lignin in the seventh and eighth internodes of tobacco stems were lowest in the minus-boron plants; in the ninth internode these values were highest in the minus-boron plants. The present results seem to indicate that boron has some function in lignin production, but it was not established whether this is a direct role. Some of the factors which have resulted in the apparent discrepancies in the literature with res...