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- Leaf age effects on photosynthetic activity and sugar accumulation in droughted and rewatered Lupinus albus L. plantsPublication . David, Maria Manuela; Coelho, Dulce; Barrote, Isabel; Correia, Maria JoãoChanges in the photosynthetic rate (A), stomatal conductance (g), water relations, photosynthetic pigments, Rubisco and soluble sugars accumulation were studied in different aged leaves of white lupin during soil drying and following rehydration. In water-stressed plants, A and g sharply declined and recovered only partially after rewatering. The way Ci and A/gchanged with drought was strongly dependent on leaf age; only in the young leaves did A/g increase and Ci decrease. Drought induced accumulation of soluble sugars was also age dependent, decreasing as leaves aged. In response to soil drying, the contents of photosynthetic pigments, total soluble protein and Rubisco protein increased in the young leaves and were either not affected or slightly decreased in the older ones. Rehydration accentuated the losses in pigments and Rubisco in the old leaves of water-stressed plants. These results suggest that the contribution of mesophyll limitations to explain drought inhibition of photosynthesis increases with leaf age, decreasing the ability to recover after rewatering. In young leaves the tolerance of the photosynthetic apparatus to dehydration and rehydration episodes is high and it is associated with high contents of Rubisco and in soluble sugars, particularly hexoses.
- Response to seasonal drought in three cultivars of Ceratonia siliqua: leaf growth and water relationsPublication . Correia, Maria João; Coelho, Dulce; David, Maria ManuelaThe responses of leaf growth and leaf water relations to seasonal drought were monitored, during two successive years, in three cultivars of Ceratonia siliqua L. growing in the field, in the South of Portugal. In leaves from the current year growth bulk leaf water relations parameters were characterised using pressure-volume analysis, and morphometric measurements of xylem in petioles were undertaken. The three cultivars under study (Galhosa, Espargal and Mulata) differed as to the seasonal pattern of leaf initiation: in Galhosa a sharp peak of leaf initiation occurred in June, soon before the period in which the highest leaf expansion rates were determined; on the other two cultivars (Espargal and Mulata), not only the onset of leaf growth occurred earlier, but they continued producing new leaves throughout the summer period. The diurnal pattern of water relations determined in recently-expanded leaves indicated that Galhosa was the only cultivar in which, during midsummer, leaf water potential was not decreased below the turgor loss point and leaf relative water content remained above 90%. Although no conclusive evidence was found for the occurrence of osmotic adjustment in recently-expanded leaves, during the dry season following leaf formation a seasonal decrease in osmotic potential sufficient to maintain turgor was detected in the leaves of Galhosa but not for the other cultivars. As to the anatomy of the xylem at the petioles, the widest xylem conduits were recorded in Galhosa. This might contribute to explain why in this cultivar midday leaf water potential never decreased below –2.0 MPa even at the end of summer drought season.