CHARACTERIZATION OF A WILTY SUNFLOWER (HELIANTHUS-ANNUUS L) MUTANT .1. ABSCISIC-ACID CONTENT, LIGHT-DARK CHANGES IN THE STOMATAL CONDUCTANCE AND GENETIC-ANALYSIS

The present study was conducted to characterize genetically and physio logically a spontaneous mutation in sunflower which confers a wilty ph enotype. The wilting condition of the mutant is due to abnormal stomat al behaviour. The mutant stomata resist closure in darkness. This abno rmality is associated with low levels of endogenous abscisic acid (ABA ). By artificially elevating the ABA content of the mutant plants by s pray treatments with 10(-4) and 10(-5) M solutions it proved possible to effect a phenotypic reversion of the mutant. It has, therefore, bee n proposed that the primary effect of this spontaneous mutation is to reduce the level of ABA. The genetic analysis has shown that the wilty phenotype is due to recessive nuclear mutation at a single locus.