Observations on the Senescence of a Mutant Non-yellowing Genotype of Phaseolus vulgaris L.

A non-yellowing mutant of Phaseolus vulgaris L. was used toinvestigate factors involved in chlorophyll breakdown duringfoliar senescence. The mutant showed physiological changes similarto those of the normal yellowing type during senescence exceptthat leaf chlorophyll did not decline. Transmission electronmicroscope studies did not reveal appreciable differences inchloroplast ultrastructure between the two genotypes, suggestingthat chloroplast membrane integrity was not the factor preventingchlorophyll degradation in the mutant. However, the lack ofplastoglobuli in senescent mutant chloroplasts suggested thatthe lipid environment may be different from that of senescentnormal chloroplasts. Banding patterns of total soluble protein,resolved by sodium dodecyl sulphate-poly aery lamide gel electrophoresisshowed few, if any, differences between mature non-senescentnormal and mutant leaves; however, bands at 14 kD and 58 kDdiminished in senescent normal leaves, but remained in senescentmutant non-yellowing leaves. Key words: Non-yellowing mutant, Phaseolus vulgaris, senescence, chlorophyll degradation     

Ethylene Production and Action during Foliage Senescence in Hedera helix L.

Detached leaves of Hedera helix remained green in the dark for20 d. Exogeneous ethylene increased respiration, endogeneousethylene biosynthesis and non-protein ninhydrin-positive compounds,while promoting losses of chlorophyll and sucrose. The sensitivityof the leaves to exogenous ethylene (1–100 mm³ dm^-3) variedgreatly with time of year. Ethylene treatment increased ADP,ATP, UDP and GTP appreciably but had no effect on other nucleotides.Leaves senescing naturally on the parent plant increased theirrates of ethylene evolution and oxygen uptake. These resultssupport the view that endogenous ethylene plays an integralpart in the senescence of detached and attached ivy leaves. Key words: Ethylene, leaves, senescence, nucleotides