Browsing by Author "Ricardo, C. P."
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- How plants cope with water stress in the field : photosynthesis and growthPublication . Chaves, Maria Manuela; Pereira, J. S.; Maroco, J.; Rodrigues, Maria Luisa; Ricardo, C. P.; Osório, Maria Leonor; Carvalho, Isabel Saraiva de; Faria, T.; Pinheiro, C.Plants are often subjected to periods of soil and atmospheric water deficit during their life cycle. The frequency of such phenomena is likely to increase in the future even outside today's arid/semi-arid regions. Plant responses to water scarcity are complex, involving deleterious and/or adaptive changes, and under field conditions these responses can be synergistically or antagonistically modified by the superimposition of other stresses. This complexity is illustrated using examples of woody and herbaceous species mostly from Mediterranean-type ecosystems, with strategies ranging from drought-avoidance, as in winter/spring annuals or in deep-rooted perennials, to the stress resistance of sclerophylls. Differences among species that can be traced to different capacities for water acquisition, rather than to differences in metabolism at a given water status, are described. Changes in the root : shoot ratio or the temporary accumulation of reserves in the stem are accompanied by alterations in nitrogen and carbon metabolism, the fine regulation of which is still largely unknown. At the leaf level, the dissipation of excitation energy through processes other than photosynthetic C-metabolism is an important defence mechanism under conditions of water stress and is accompanied by down-regulation of photochemistry and, in the longer term, of carbon metabolism.
- Influence of water stress on the chemical composition of seeds of two Lupins (Lupinus albus and Lupinus mutabilis)Publication . Carvalho, Isabel Saraiva de; Chaves, C.; Ricardo, C. P.We have performed chemical proximate analysis and determined the carbohydrate profile of mature seeds of Lupinus albus, cv. Rio Maior and Lupinus mutabilis, cv. Potosi plants, either well watered (ww) or subjected to a water-stress period (imposed from the 15th to 35th day after anthesis). Protein content from lupin seeds was 450 and 320 g kg−1 of seed on dry weight basis, for ww plants, respectively, of L. albus and L. mutabilis. Water stress did not affect protein content. The oil content of ww plants was about 120 g kg−1 of seed dry weight for L. albus and 180 g kg−1 of seed dry weight for L. mutabilis. Water stress reduced those values of half. The sugar content was about 90 g kg−1 for L. albus and 50 g kg−1 of seed dry weight for L. mutabilis, in ww plants. Water stress led to an increase in sugar content to 200 and 130 g kg−1 of seed dry weight, respectively, for L. albus and L. mutabilis. The α-galactosides amounted to 70 % of the total sugars (raffinose being 30 % and stachyose, 40 %) and sucrose was about 20 % of the total sugars. Water stress increased total carbohydrates and increased the sucrose/α-galactoside ratio, although reducing raffinose content and increasing sucrose content.
- Quality and distribution of assimilates within the whole plant of lupines (L. albus And L. mutabilis) influenced by water stressPublication . Carvalho, Isabel Saraiva de; Ricardo, C. P.; Chaves, Maria ManuelaLupine crops (Lupinus albus and L. mutabilis) often experience water deficits during grain filling, thereby altering partitioning of assimilates. Water deficit, imposed at the beginning of seed production (15 days after anthesis, daa), brought about differences in assimilate partitioning and chemical composition within the whole plant. In both species, water stress (ws) was responsible for a significant decrease in plant water status and gas exchange. In spite of little effect on total biomass, leaf area was reduced for approximately half of the control treatment. The main effects of ws on chemical composition of different organs were a decrease in total oil and an increase in total soluble sugar content in leaves; an increase in both oil and soluble sugars in stems; and a decrease in total oil and total soluble sugar content in seeds. The data suggest that under ws conditions, imposed at flowering, lupine assimilates are stored in stems and pods and later retranslocated to the developing seeds.
- Sugar metabolism in developing lupin seeds is affected by a short-term water deficitPublication . Pinheiro, Carla; Rodrigues, Ana Paula; Carvalho, Isabel Saraiva de; Chaves, Maria Manuela; Ricardo, C. P.A short-term water deficit (WD) imposed during the pre-storage phase of lupin seed development [15–22 d after anthesis (DAA)] accelerated seed maturation and led to smaller and lighter seeds. During seed development, neutral invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1.13) have a central role in carbohydrate metabolism. Neutral invertase is predominant during early seed development (up to 40 DAA) and sucrose synthase during the growing and storage phase (40–70 DAA). The contribution of acid invertase is marginal. WD decreased sucrose synthase activity by 2-fold and neutral invertase activity by 5–6-fold. These changes were linked to a large decrease in sucrose (∼60%) and an increase of the hexose:sucrose ratio. Rewatering restored sucrose synthase activity to control levels while neutral invertase activity remained depressed (30–60%). A transient accumulation of starch observed in control seeds was abolished by WD. Despite the several metabolic changes the final seed composition was largely unaltered by WD except for ∼60% increase in stachyose and raffinose (raffinose family oligosaccharides). This increase in raffinose family oligosaccharides appears as the WD imprinting on mature seeds.