Carbohydrate Metabolism ofCactus inaDesert Environment

Theconcentration ofglucan, mucilage, soluble carbohydrates, andmal;c acid weredetermined InOpuatia bigelovii EngehnL during a23-week period. Theexperiment began during thedrysummerbyirrigation tostimulate Crassulacean acid metaboUsm andwasfollowed by13weeks ofdrought. After the13-week drought period, theplants wereirrigated throughout a 10-week period until late December. Themaximumlevel ofmaicacid determined eachdayatdawndecreased throughout thedrought period and increased after irrigation. Hg levels ofmadcacid occurring atdawnare indicative ofactive Crassulacean acid metabolism. Soluble carbohydrates also decreased during drought andincreased after irrigation. Bothglucan andmuclage increased slihtly forabout 9weeksduring thedrought period andthen began todecrease. Irrigation wasaccniedbyafurther decrease inconcentration ofglucan andmucilage. Since bothglucan and mucilage changed inasimilar mannerandsince their concentrations inthe tissue arecorrelated, itishypothesized thatbothfunction asstorage carbohydrates. Whereas glucan isthenocturnal substrate formalic acid synthesis, there arenodatatosupport orrefute asimilar hypothesis for mucilage.