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University of Adelaide (1995)

Effects of water stress and partial soil-drying on senescence of sunflower plants

Wongareonwanakij, Sathaporn

Titre : Effects of water stress and partial soil-drying on senescence of sunflower plants

Auteur : Wongareonwanakij, Sathaporn

Université de soutenance : University of Adelaide,

Grade : M.Ag.Sc. Master of Science (Agriculture) 1995

Résumé partiel
The present thesis aimed to investigate the symptoms of leaf senescence in response to plant shoot water stress and explore the possibility of the involvement of a non-hydraulic root signal in the senescence response of mature leaves of sunflower. The effect of plant ¡eaf water status on mature leaf senescence of sunflower was evaluated from changes in the leaf water potential and soluble protein, total free amino acid and chlorophyll contents, and chlorophyll a/b ratio, following a regime of a single water stress cycle (15 days) and resumption of adequate tvater supply. The fall in leaf water potential accelerated the rate of loss of leaf soluble prote¡n content compared to that occurring in non-stressed senescing leaves. ln corresponding to the breakdown of soluble protein there was an accumulation of free amino acid¡including " p,._ryT"d proline  : accumulation. This phenomenon is different from that which occurred in attached naturally senescing leaves, in which the total amino acid content was found to decrease in company with the fall in leaf soluble protein content. The rate of loss of chlorophyll content was also accelerated by water stress. Chlorophyll degradation in response to water stress, however, was slower than the protein response. A similar pattern of response to that in total chlorophyll content was also achieved in the chlorophyll a/b ratio. Upon re-watsr¡ng, there was a recovery in the prote¡n content to the level found in control leaves coupled with a rapid disappearance of the total free amino acid accumulated. Total chlorophyll content and chlorophyll a/b ratio, on the other hand, did not recover to the control levels atter watering was resumed. However, there was a change in the rate of decline of both total chlorophyll content and chlorophyll a/b ratio to the normal senescence rate, subsequent to the recovery in leaf water potential.


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