Effects of Chemical Treatments upon Photosynthetic Parameters in Soybean Seedlings

Synthesis and characterization of (Z)-5-arylmethylidene-rhodanines with photosynthesis-inhibiting properties

A series of rhodanine derivatives was prepared. The synthetic approach, analytical and spectroscopic data of all synthesized compounds are presented. Lipophilicity of all the discussed rhodanine derivatives was analyzed using the RP-HPLC method. The compounds were tested for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts and reduce chlorophyll content in freshwater alga Chlorella vulgaris. Structure-activity relationships between the chemical structure, physical properties and biological activities of the evaluated compounds are discussed. For majority of the tested compounds the lipophilicity of the compound and not electronic properties of the R¹ substituent were decisive for PET-inhibiting activity. The most potent PET inhibitor was (5Z)-5-(4-bromobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC₅₀ = 3.0 μmol/L) and the highest antialgal activity was exhibited by (5Z)-5-(4-chlorobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC₅₀ = 1.3 μmol/L).

Detection of chemicals inhibiting photorespiratory senescence in a large scale survival chamber

A large scale survival chamber was developed as a screen for detecting chemical treatments that extend the survival time of illuminated soybean seedlings at CO(2) concentrations below the compensation point. In theory, extended survival should indicate potential for improved crop performance via decreased photorespiration and increased photosynthetic efficiency. An automated control system regulated CO(2) concentrations, temperature and plant watering during a continuous CO(2)-removal photoperiod of 72 hours. An endogenously controlled circadian rhythm of net photosynthesis occurred throughout the continuous light treatment.Spray applications of 3.49 millimolar 2-(4-chlorophenoxy)-2-methylpropanoic acid (CPMP) significantly decreased leaf chlorophyll loss, compared with the control, after 72 hours of subcompensation-point stress. Treatment with CPMP also consistently increased leaf chlorophyll per unit area under nonstress greenhouse conditions. These effects may be due to increases in specific leaf weight produced by CPMP although the compound did not consistently act as a height retardant. The compound, 3-butyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one (BHPP), inhibited senescence under low CO(2) conditions but did not decrease leaf light transmission at ambient CO(2) levels. The cytokinin N(6)-benzyladenine (BA) retarded low CO(2) stress senescence although greening effects were not observed. Neither 2-hydroxy-3-butynoic acid (HBA) nor its butyl ester, inhibitors of glycolate oxidase, influenced low CO(2) survival. Cyclohexanecarboxylic acid (CHCA) and sodium naphthenate had no effect upon subcompensation-point senescence.Antisenescence effects of CPMP, BHPP, and BA do not appear to be directly attributable to effects upon the competing carbon paths of photosynthesis and photorespiration. Protection against low CO(2) stress and increased chlorophyll synthesis under nonstress conditions may represent separate effects upon plastids by some of the compounds. This screen will identify compounds which inhibit photorespiratory senescence without decreasing the CO(2) compensation point.