Phenylheptatriyne variation in Bidens alba var. radiata leaves.

Variation of phenylheptatriyne (PHT) in leaves of Bidens alba (Linn.) var. radiata (Shultz-Bip.) was investigated across its Florida range, throughout the year, and in response to the photoenvironment. A survey of PHT in B. alba leaves was done at 13 sites in Florida and three sites throughout the year. PHT concentrations differed among populations (P < 0.001), but little of the variation was explained by latitude (R2 = 0.024) or longitude (R2 = 0.022). Leaf concentrations of PHT fluctuated throughout the year (P < 0.001); they were highest in October and lowest in January and April. Experimental manipulations of light quality and quantity caused increased PHT accumulation when UV wavelengths were filtered out and decreased accumulation under low R/FR treatments. Low light levels did not significantly influence the concentration of PHT on a dry weight basis, but did decrease leaf biomass and PHT levels on a leaf area basis. The results suggest that PHT in B. alba leaves varies in nature and that light quality affects PHT biosynthesis in situ.