Chemical Induction and Repression of Haustoria in Orthocarpus Purpurascens (Scrophulariaceae)

A preliminary survey of compounds that induce haustoria in thehemiparasite Orthocarpus purpurascens suggests that cellulosefibre is one source of the active, water soluble factor(s).Haustoria are induced by extracts of soya bean seeds, flax seeds,plant roots, cotton string, cotton, paper towel, tissue paperand yeast extract. Sugars, hormones, nitrogenous compounds,microbial exudates, and citric and ascorbic acid do not inducehaustoria. Citric acid has a positive synergistic affect inthe presence of an inducing factor. Terramycin applied to seedlings 3 days of age had a detrimentaleffect on root development, while penicillin did not. Penicillinreduced the numbers of haustoria formed between 19 and 25 daysof age. The combined use of penicillin and inducing factorsmay provide an excellent experimental system for determiningthe temporal and developmental pattern of haustoria formation. haustoria, chemical induction and repression, Orthocarpus purpurascens, hemiparasite     

Nutritional studies of Hemiparasitic Orthocarpus (Scrophulariaceae)

Excised shoot tips from Orthocarpus attenautus and O. purpurascenswere cultured in vitro to ascertain whether the stem tips ofthese hemiparasites require complex organic substances for theirdevelopment, and to determine if the capacity for haustoriaformation is retained by the resulting plantlets. Explants consistedof the apical meristem plus the four smallest leaf primordia,having a volume of less than 0.5 mm3. A variety of mineral media,sucrose concentrations, root extract, soil extract, yeast extract,and malt extract were tested for effects on growth. Both speciescompleted development in sterile culture on simple media. Orthocarpusattenuatus grew best on Knop‘s minerals with Ball’smicroelements + 0.1 g ferric citrate 1–1+ 1% (w/v) sucrose,while MurashigeSkoog‘s minerals+ 2% sucrose provided thebest growth of the media tested for O. purpurascens. Haustoriaformed on the roots of all plantlets chemically induced by cottonstring. The mean number of haustoria per plantlet was abouthalf that of control plants raised from seed. Growth of intactO. Purpurascens seedlings was also compared on mineral agar,mineral agar supplemented with yeast extract, and in soil culturessupplemented with yeast extract and a host. While yeast extracthas variable effects on the growth of shoot tip explants andintact plants raised under axenic conditions, it is highly stimulatoryto the autotrophic growth of intact plants in soil culture.