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- Variation of carbon and isotope natural abundances (δ15N and δ13C) of whole-plant sweet potato (Ipomoea batatas L.) subjected to prolonged water stressPublication . Gouveia, Carla S.S.; Ganança, José F.T.; Slaski, Jan; Lebot, Vincent; Carvalho, Miguel Â. A.Sweet potato (Ipomoea batatas L.) is an important crop in the world, cultivated in temperate climates under low inputs. Drought changes the plant biomass allocation, together with the carbon and nitrogen isotopic composition (δ13C and δ15N), whose changes are faintly known in sweet potato crops. Here, we show the biomass allocation of eight sweet potato accessions submitted to drought during 3 months, using the δ13C, δ15N, carbon isotope discrimination (Δ13C), total carbon (TC) and water use efficiency (WUE) traits. The tolerant accessions had improved WUE, with higher TPB and TC. Storage roots and shoots had a heavier δ13C content under drought stress, with greater 13C fixation in roots. The Δ13C did not show a significant association with WUE. The δ15N values indicated a generalised N reallocation between whole-plant organs under drought, as a physiological integrator of response to environmental stress. This information can aid the selection of traits to be used in sweet potato breeding programs, to adapt this crop to climate change.
- Changes in oxalate composition and other nutritive traits in root tubers and shoots of sweet potato (Ipomoea batatasL. [Lam.]) under water stressPublication . Gouveia, Carla S.S.; Ganança, José F.T.; Lebot, Vincent; Carvalho, Miguel Â. A.BACKGROUND: The presence of insoluble calcium oxalate druse crystals (CaOx) in sweet potato (Ipomoea batatas) can negatively affect its nutritional quality. Photosynthesis, starch, and protein composition are linked with oxalate synthesis and tuber quality under water scarcity. Our main objective was the oxalate quantitation of sweet potato tubers and shoots and also to assess how drought changes their nutritional value. Eight sweet potato accessions from Madeira, the Canaries and Guinea-Bissau were analyzed for their response to drought stress. Tubers and shoots were analyzed for total (T-Ox), soluble (S-Ox) and insoluble (CaOx) oxalates, protein, chlorophyll content index (CCI), soluble starch, starch swelling power, and starch solubility in water. RESULTS: The S-Ox and CaOx content was higher in shoots. Six accessions were above maximum CaOx levels for raw consumption. Accessions with more favorable responses to drought had decreased CaOx with S-Ox increase content for osmoregulation. They also presented slightly decreased CCI and protein contents. These accessions also had an increased shoot starch content, for further tuber storage starch hydrolysis, and maintained the quality and functional properties of the tuber starch grain. Those with a less favorable response to drought had a higher T-Ox and CaOx content in both organs, hindering water absorption. They also had decreased protein and CCI, with a slight increase in tuber starch hydrolysis. CONCLUSION: Oxalate content was significantly related to carbohydrate metabolism, CCI, and protein synthesis. This study significantly contributed to the screening of the sweet potato stress response to drought, to adapt this crop to climatic change through breeding programs.
- Quantitation of oxalates in corms and shoots of Colocasia esculenta (L.) Schott under drought conditionsPublication . Gouveia, Carla S.S.; Ganança, José F.T.; Lebot, Vincent; Carvalho, Miguel Â. A. Pinheiro deOxalate (calcium oxalate) accumulation in taro plants (Colocasia esculenta (L.) Schott) impacts their nutritional quality, producing acridity, causing lips, mouth and throat tissues swelling if consumed fresh. The oxalate content is related to photosynthesis, through the glycolate–glyoxylate oxidation pathway. The plant’s photosynthetic rate usually increases in non-stressed conditions. Differences in photosynthetic rate are indirectly related to the chlorophyll content index. Protein accumulation and starch variation are also important traits to understand the taro oxalate synthesis caused by drought and how they affect corm quality. The purpose of this study was to quantitate oxalates in taro corms and shoots submitted to drought conditions and to evaluate how stress response can affect the nutritional quality of taro whole-plant. Seven taro genotypes from Madeira, Canaries and Pacific Community (SPC) collections were grown in greenhouse conditions and submitted to different watering regimes for drought tolerance screening. Corms and shoots were harvested and evaluated for oxalates (soluble, insoluble and total), chlorophyll content index (CCI), crude protein, starch, starch solubility in water and starch swelling power. All accessions had very high calcium oxalate content. Drought-tolerant genotypes showed good osmotic response by oxalate precipitation and mobilization through shoot to corm tissues, photosynthesis adaptation by increase of CCI, protein accumulation, and very low starch hydrolysis. Sensitive-drought genotypes showed less mobilization of calcium oxalate, decreased photosynthetic rate and protein synthesis, and slight increase of starch hydrolysis. Variation in taro oxalate content is consistent and significantly correlated with the photosynthetic rate, carbohydrate metabolism and protein synthesis.
- Stable isotope natural abundances (δ13C and δ15N) and carbon-water relations as drought stress mechanism response of taro (Colocasia esculenta L. Schott)Publication . Gouveia, Carla S.S.; Ganança, José F.T.; Slaski, Jan; Lebot, Vincent; Carvalho, Miguel Â.A. Pinheiro deTaro (Colocasia esculenta L. Schott) is an important staple food crop in tropical and developing countries, having high water requirements. The purpose of this study was to evaluate the feasibility of using carbon and nitrogen isotopic composition (δ13C and δ15N) as a physiological indicator of taro response to drought, and elucidation of the relationship between the water use efficiency (WUE) under drought conditions and carbon isotope discrimination (Δ13C). As an alternative to WUE determination, obtained by measuring plant growth and water loss during an entire vegetative cycle, we have used Δ13C to determine the tolerance of C3 taro plants to drought. Seven taro accessions from Madeira, Canary Islands and the Secretariat of the Pacific Community (Fiji) collections were grown under greenhouse conditions and subjected to different watering regimes during a one-year cycle. Total plant biomass (TPB), WUE and δ15N were determined at the whole-plant level (WP). Corms and shoots were evaluated separately for nitrogen content (N), δ13C, Δ13C and δ15N. WUE showed positive correlation with TPB (r = 0.4) and negative with Δ13C (r = -0.3); Corm δ15N showed positive correlations with WP δ15N (r = 0.6) and corm N (r = 0.3). Accordingly, the taro plants with enhanced WUE exhibited low Δ13C and δ15N values as a physiological response to drought stress. The approach used in the present study has developed new tools that could be used in further research on taro response to environmental stresses.