PLANT PHYSIOLOGY , Vol 105, Issue 4 1295-1300, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Chlorophyll Biosynthetic Reactions during Senescence of Excised Barley (Hordeum vulgare L. cv IB 65) Leaves
P. Hukmani and B. C. Tripathy
School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067 India
The chlorophyll (Chl) biosynthetic reactions were monitored during
senescence of dark-incubated excised barley (Hordeum vulgare L. cv IB 65)
leaves floated in double-distilled water or kinetin solution. Kinetin
abolished the degradation of Chl but failed to check the net degradation of
protochlorophyllide (Pchlide), suggesting that different sets of enzymes,
i.e. kinetin sensitive and insensitive, are responsible for the degradation
of Chl and Pchlide, respectively. Upon exposure of the leaves to light, the
dark-accumulated Pchlide was efficiently phototransformed to chorophyllide
(Chlide), even on the 7th d of dark incubation, demonstrating that the
activity of Pchlide reductase, one of the late enzymes of the Chl
biosynthetic pathway, is not substantially affected during senescence. The
senescing leaves continued to synthesize Pchlide and Chlide until the 7th
d, although at a reduced rate (20% of the 1st d). The decline of the rate
of synthesis of Pchlide and Chlide is due to the loss of activity of two
early enzymes of the Chl biosynthetic pathway, i.e. 5-aminolevulinic acid
dehydratase and porphobilinogen deaminase. Kinetin substantially checked
the loss of activity of these two enzymes.
