Abstract
Plants in semi-arid regions often have unique biochemical mechanisms to tolerate environmental stresses such as temperature extremes, draught, strong light, and salinity. In some cases, secondary metabolites have been shown to play an important role in such tolerance mechanisms. Phloroglucinol derivatives, grandinol and homograndinol, found in Eucalyptus grandis are inhibitors of germination and also of photosynthetic electron transport. Chemical modifications of these compounds afforded extremely potent photosystem II (PSII) inhibitors. These PSII inhibitors, however, are not herbicidal because they do not inhibit turnover of D1 protein. These phloroglucinol derivatives exhibit abscisic acid (ABA)-like, antiinflammatory, and anti-tumor-promotion activities. Seeds of root parasitic plants, Striga and Orobanche, require exogenous stimulants to germinate. Orobanchol and alectrol, germination stimulants for Orobanche minor, have been isolated and characterized from root exudates of its host, red clover. The production of these stimulants by red clover roots is promoted by nitrate but is inhibited by ammonium and phosphate. Amounts of orobanchol in the red clover root exudates were quantified by LC/MS/MS, and actively growing roots were found to be major parts of stimulant production.
