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V. O. SADRAS*, L. ECHARTE and F. H. ANDRADE
Universidad de Mar del Plata-INTA Balcarce, CC 276, Balcarce 7620,
Argentina
Annals of Botany 85: 187±195, 2000
We investigated the effect of reproductive growth on
the profiles of leaf senescence in maize (Zea mays L.) and sunflower (Helianthus
annuus L.). Leaf senescence after flowering was assessed using both
structural (leaf chlorophyll, nitrogen and dry matter) and functional
(photosynthesis) variables in undisturbed plants (G) and in plants in
which grain set was prevented (-G). Two weeks after flowering, lack of
grain accelerated senescence in maize and delayed senescence in sunflower
as indicated by leaf chlorophyll; leaf nitrogen and dry matter were less
sensitive response variables. Lack of interaction between reproductive
treatment and leaf position indicates that the senescence signal, whatever
its nature, was equally effective throughout the plant in both species. In
both species, feedback inhibition of photosynthesis was first detected
30±35 d after flowering; excess carbohydrate in the leaves was therefore
an unlikely trigger of accelerated senescence in maize. As reproductive
development progressed, differences betweenG and -G plants were more
marked in sunflower, and tended to disappear or reverse in maize. In
sunflower, interactions between leaf position and reproductive treatment
-attributable to the local effect of grain- were detected around 20±27 d
after flowering.
Key words: Helianthus annuus, Zea mays, chlorophyll, light, nitrogen,
photosynthesis, reproductive growth,
senescence, source-sink, SPAD. |
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