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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.
- Photosynthetic responses of Lupinus albus to soil water fluctuationsPublication . Barrote, Isabel; Osório, Maria Leonor; Osório, Júlio; David, Maria Manuela; Correia, Maria JoãoLupinus albus plants were grown in 3 dm3 pots in a semi-controled greenhouse. Two water regimes were imposed: water deficit (S, 47% of soil capacity), and control (T, 86% of soil capacity). Plants water status was monitored through foliar relative water content (TRA) and pre-dawn (ypd) and midday water potential (ymd). Gas exchanges, chlorophyll a fluorescence and photosynthetic capacity (Amax) were measured. Pigments and soluble protein were quantified and antioxidant system enzymes activity was determined. Plants under water deficit were rehydrated and the same measurements and sampling were done again after 48 h (R1) and 72 h (R2). Albeit water availability has diminished from 86% to 47% of soil capacity, there weren’t any remarkable changes on S plants. R1 plants which haven’t shown any alterations neither in Amax nor in stomatal conductance (gH2O), exhibited a significant decrease on net photosynthesis (A), reaching negative values, along with a raise in non-photochemical quenching (NPQ). Presumably this raise should be related with an increase in the xanthophyll cycle deepoxidation state. The significantly increase in Superoxide dismutase (SOD) specific activity in R1 and R2 plants might be related with the activation of Mehler-peroxidase reaction which provokes lumen DpH raising. This can provide photosynthesis protection through VAZ cycle and may justify the NPQ increase.
- Fotossíntese e acumulação de ácido abcísico em Lupinus albus sujeito a stress hídricoPublication . Correia, Maria João; David, Maria Manuela; Barrote, IsabelThe objective of the present work was to assess whether the depression of photosynthetic activity in droughted Lupinus albus L. plants was more closely associated with carbohydrate build-up or ABA accumulation. With that purpose we have measured the concomitant drought-induced changes in photosynthetic capacity and the concentrations of Rubisco, chlorophylls, non-structural carbohydrates and ABA in young and old leaves of white lupin plants. Although Rubisco and chlorophylls contents did not decrease with water stress, the photosynthetic capacity was decreased by soil drying, the decline in photosynthesis being more tighly related with ABA accumulation than with sugar content. In contrast to droughted plants, ABA feeding to intact plants resulted in a significant decrease in Rubisco and chlorophyll content. However, no increase in shoot ABA content was detected in ABA-fed plants. Therefore this work is not conclusive as to the correlation between photosynthetic capacity and ABA accumulation in droughted white lupin plants being causal or not.