Volatile profiling of cacti: a preliminary assessment of the taxonomic and evolutionary significance of volatile compounds in Cylindropuntia, Grusonia, Consolea, Opuntia, Quiabentia, and Tacinga

Abstract

Volatile analyses of cacti have previously been performed on the flowers, fruits, and consumed stems. During our own investigations, we and others have observed that the cut stems of certain species of the Graveolens clade of Cylindropuntia emitted odors similar to those of rancid butter or cyanoacrylate. Some species of Consolea, Opuntia, Quiabentia, and Tacinga were found to produce similar odors. Fresh samples of Cylindropuntia and these other genera were collected, and the volatile compound profiles were analyzed by solid phase micro-extraction gas chromatography mass spectrometry. Linear discriminate analysis found the compounds to be characteristic of the odiferous cacti as the aldehydes hexanal, 2-hexenal, and nonanal; the alcohol phenethyl alcohol; the terpene β-phellandrene; the ketone β-ionone; and the diol 5-pentyl-1,3-benzenediol. Compounds characteristic of the non-odiferous cacti are the ketones 6-methyl-2-heptanone, 2-octanone, and 1,3-dihydro-5-methyl-2H-benzimidazol-2-one; the alkanes undecane, tridecane, pentadecane, and heptadecane; the aromatics p-cymene and 1,2,3,5-tetramethyl benzene; the esters octyl formate, methyl benzoate, and methyl salicylate; the aldehyde 2-octenal; the alcohol cyclooctyl alcohol; the imine methoxy-phenyl-oxime; the terpene 1-methyl-2-(2-propenyl)-benzene; and nine unknown compounds. Putative hybrid cacti were found to have a unique volatile profile in comparison to the parents. Additionally, differing infraspecific chromosome races, diploids (n = 11) and tetraploids (n = 22), were found to have differing volatile profiles with some compounds increasing with an increase in chromosome number while other compounds decreased with an increase in chromosome number.