ABSTRACT
Corolla life span of undetached flowers of Nicotiana tabacum was divided into stages from the closed corolla (stage 1) through anthesis (stage 5) to death (stage 9). Senescence began around stage 6 in the proximal part, concomitantly with DNA laddering. Nuclear blebbing, DNA laddering, cell wall modification, decline in protein, water, pigment content and membrane integrity were observed during senescence and PCD. Transglutaminase activity was measured as mono- and bis-derivatives of putrescine (mono-PU; bis-PU) and bis-derivatives of spermidine (bis-SD). Bis-derivatives decreased with the progression of senescence, while mono-PU increased during early senescence; derivatives were present in different amounts in the proximal and distal parts of the corolla. In excised flowers, exogenous spermine delayed senescence and PCD, and caused an increase in free and acid-soluble conjugated PA levels. Bis-PU was the most abundant PA-derivative before DNA laddering stage; thereafter, bis-PU generally decreased and mono-PU became the most abundant derivative.
Subject(s)
Apoptosis/physiology , Cellular Senescence/drug effects , Nicotiana/cytology , Spermine/pharmacology , Transglutaminases/metabolism , Cellular Senescence/physiology , DNA Fragmentation/physiology , Endopeptidases/metabolism , Phthalic Anhydrides , Polyamines/metabolism , Nicotiana/anatomy & histologyABSTRACT
We have purified to homogeneity 6-Phosphogluconate dehydrogenase from leaves of silver beet (Beta vulgaris L.) by means of cation-exchange and affinity chromatography. The enzyme is a homodimer of 52 kDa subunits; it catalyzes NADP dependent oxidation of 6-P-gluconate with Michaelian substrate saturation. The activity is affected by some intermediates of carbohydrate metabolism, particularly erythrose-4-P. Subcellular fractionation studies indicate the cytosolic location of the enzyme.
