Determination of senescence in plants
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Abstract
Senescence is interpreted by some authors to be a genetically controlled process; nevertheless, there is evidence that the internal and external environments are also involved in its control. Thus, for example, the increase in the C/N ratio, an alteration of living matter characteristic of senescence, could originate from an inhibition of nitrate reductase by high oxygen pressures. The evolution of senescence parameters under the action of oxygen pressure indicates that the process accelerates directly in correlation with the concentration of this gas. Likewise, free radicals and enzymes seem to be involved in the degradation of chlorophylls and proteins. In the case of chlorophylls, all known toxic species of oxygen (O₂, ¹O₂, HO·, H₂O₂) can bleach the pigment, and enzymatic degradation itself involves the participation of free radicals.In regards to proteolysis, four proteases have been detected in Avena chloroplasts, among them an endopeptidase whose activity increases under oxidative conditions. The sensitivity of some chloroplast proteins to the action of free radicals has also been established.
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