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Senescence‐induced loss in photosynthesis enhances cell wall β‐glucosidase activity
Author(s) -
Mohapatra Pranab Kishor,
Patro Lichita,
Raval Mukesh Kumar,
Ramaswamy Nemmara Krishnan,
Biswal Udaya Chand,
Biswal Basanti
Publication year - 2010
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2009.01327.x
Subject(s) - photosynthesis , senescence , thylakoid , biochemistry , chlorophyll , photosystem i , photosystem ii , biology , dcmu , chemistry , biophysics , chloroplast , botany , microbiology and biotechnology , gene
A link between senescence‐induced decline in photosynthesis and activity of β‐glucosidase is examined in the leaves of Arabidopsis . The enzyme is purified and characterized. The molecular weight of the enzyme is 58 kDa. It shows maximum activity at pH 5.5 and at temperature of 50°C. Photosynthetic measurements and activity of the enzyme are conducted at different developmental stages including senescence of leaves. Senescence causes a significant loss in total chlorophyll, stomatal conductance, rate of evaporation and in the ability of the leaves for carbon dioxide fixation. The process also brings about a decline in oxygen evolution, quantum yield of photosystem II (PS II) and quantum efficiency of PS II photochemistry of thylakoid membrane. The loss in photosynthesis is accompanied by a significant increase in the activity of the cell wall‐bound β‐glucosidase that breaks down polysaccharides to soluble sugars. The loss in photosynthesis as a signal for the enhancement in the activity of the enzyme is confirmed from the observation that incubation of excised mature leaves in continuous dark or in light with a photosynthesis inhibitor 3‐(3,4‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU) that leads to sugar starvation enhances the activity of the enzyme. The work suggests that in the background of photosynthetic decline, the polysaccharides bound to cell wall that remains intact even during late phase of senescence may be the last target of senescing leaves for a possible source of sugar for remobilization and completion of the energy‐dependent senescence program.