Effects of Exogenous 1,3-Diaminopropane and Spermidine on Senescence of Oat Leaves

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Abstract
Excision and dark incubation of oat (A. sativa L., cv. Victory) leaves cause a sharp increase in protease activity, which precedes Chl [chlorophyll] loss. Both these senescence processes are inhibited by exogenously applied 1,3-diaminopropane (Dap), which occurs naturally in leaf segments. The inhibition of protease activity is much greater in vivo than in vitro, suggesting inhibition of protease synthesis as well as protease action by Dap. Chl breakdown in leaves of radish and broccoli, which also senesce rapidly in the dark, is only slightly inhibited by DaP. These differences between cereal and dicotyledonous plants are correlated with the natural occurrence of Dap in cereals. In the light, Dap promotes, rather than retards, the loss of Chl in oat leaves. This resembles previously described effects of other polyamines. Addition of Mg2+ to the medium does not antagonize this effect. In the dark, the accumulated Dap also inhibits ethylene production and decreases titer of other polyamines. Addition of Ca2+ to the incubation medium containing Dap competitively reduces the effects of Dap. Dap, like other polyamines, seems to require an initial attachment to a membrane site shared with Ca2+ before exerting its antisenescence action.