Characteristic symptoms of photosynthesis inhibition by herbicides are expressed in photomixotrophic tissue cultures ofNicotiana

摘要

A photomixotrophic tissue culture system forNicotiana plumbaginifoliaandN. tabacumhas been developed in which a primary symptom (bleching) of the inhibition of photosynthetic electron transport by herbicides can be observed. Photomixotrophic cultures were initiated and maintained in the light on medium containing 0.2–0.3 sucrose or glucose (low-sugar medium) as sole source of respirable carbohydrate. The usual medium for growing heterotrophic cultures contains 2–3 sucrose or glucose (high-sugar medium). Callus grown on low-sugar medium achieved a fresh weight three to four times greater in the light than in the dark and reached about half that of callus grown on high-sugar medium. Carbon-dioxide fixation rates were an order of magnitude higher in cultures grown on low-sugar medium in the light than in those grown on high-sugar medium or in any of the dark-grown cultures. The lightdependent growth and CO2-fixation rates of cultures grown on low-sugar medium indicated that a major proportion of the weight increase resulted from photosynthesis. Under these photomixotrophic conditions it was found that a number of photosystem-II herbicides, at concentrations which inhibit photosynthetic electron transport, also inhibited the light-dependent component of callus growth, and caused bleaching. These effects could not be demonstrated on high-sugar med