La palabra y la fenomenología

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Effect of grafting on grapevine chlorosis and hydraulic conductivity

In a pot experiment the following grapevines were grown in a calcareous soil: Pinot blanc own-rooted and self-grafted, grafted on SO 4 and on 3309 C; SO 4 own-rooted, self-grafted and grafted on Pinot blanc; 3309 C own-rooted, self-grafted and grafted on Pinot blanc. The occurrence of chlorosis was strongly affected by graft combinations. In self-grafted 3309 C plants the specific conductivity was significantly reduced as compared to own-rooted ones. Own-rooted SO 4 plants showed the highest specific conductivity, associated with the highest rate of shoot growth and leaf chlorophyll content

Downward shoot positioning affects water transport in field-grown grapevines

Grape canopies (cv. Nebbiolo) were manipulated to obtain vines with alternatively upward and downward shoots on the same fruit-cane. Downward orientation reduced length and total leaf area of the shoot and water flow through the shoot, but did not modify shoot water potential. Shoot hydraulic conductivity, either evaluated on growing plants or on cut shoot portions, was lower in downward than in upward oriented shoots at all positions along the cane. This supports the hypothesis that downward shoot orientation causes a reduction of the hydraulic conductivity, which in turn reduces the availability of water and nutrients for the leaves growing downstream of the point of conductivity reduction. A mechanism which reduces growth in downward oriented shoots is proposed and practical consequences for viticulture, related to reduced water conductivity in downward-trained shoots, are discussed

The dynamics of embolism refilling in abscisic acid (ABA)-deficient tomato plants.

Plants are in danger of embolism formation in xylem vessels when the balance between water transport capacity and transpirational demand is compromised. To maintain this delicate balance, plants must regulate the rate of transpiration and, if necessary, restore water transport in embolized vessels. Abscisic acid (ABA) is the dominant long-distance signal responsible for plant response to stress, and it is possible that it plays a role in the embolism/refilling cycle. To test this idea, a temporal analysis of embolism and refilling dynamics, transpiration rate and starch content was performed on ABA-deficient mutant tomato plants. ABA-deficient mutants were more vulnerable to embolism formation than wild-type plants, and application of exogenous ABA had no effect on vulnerability. However, mutant plants treated with exogenous ABA had lower stomatal conductance and reduced starch content in the xylem parenchyma cells. The lower starch content could have an indirect effect on the plant's refilling activity. The results confirm that plants with high starch content (moderately stressed mutant plants) were more likely to recover from loss of water transport capacity than plants with low starch content (mutant plants with application of exogenous ABA) or plants experiencing severe water stress. This study demonstrates that ABA most likely does not play any direct role in embolism refilling, but through the modulation of carbohydrate content, it could influence the plant's capacity for refilling

Changes in air CO2 concentration differentially alter transcript levels of NTAQP1 and NTPIP2;1 aquaporin genes in tobacco leaves

The aquaporin specific control on water versus carbon pathways in leaves is pivotal in controlling gas exchange and leaf hydraulics. We investigated whether Nicotiana tabacum aquaporin 1 (NtAQP1) and Nicotiana tabacum plasma membrane intrinsic protein 2;1 (NtPIP2;1) gene expression varies in tobacco leaves subjected to treatments with different CO2 concentrations (ranging from 0 to 800 ppm), inducing changes in photosynthesis, stomatal regulation and water evaporation from the leaf. Changes in air CO2 concentration ([CO2]) affected net photosynthesis (Pn) and leaf substomatal [CO2] (Ci). Pn was slightly negative at 0 ppm air CO2; it was one-third that of ambient controls at 200 ppm, and not different from controls at 800 ppm. Leaves fed with 800 ppm [CO2] showed one-third reduced stomatal conductance (gs) and transpiration (E), and their gs was in turn slightly lower than in 200 ppm– and in 0 ppm–treated leaves. The 800 ppm air [CO2] strongly impaired both NtAQP1 and NtPIP2;1 gene expression, whereas 0 ppm air [CO2], a concentration below any in vivo possible conditions and specifically chosen to maximize the gene expression alteration, increased only the NtAQP1 transcript level. We propose that NtAQP1 expression, an aquaporin devoted to CO2 transport, positively responds to CO2 scarcity in the air in the whole range 0–800 ppm. On the contrary, expression of NtPIP2;1, an aquaporin not devoted to CO2 transport, is related to water balance in the leaf, and changes in parallel with gs. These observations fit in a model where upregulation of leaf aquaporins is activated at low Ci, while downregulation occurs when high Ci saturates photosynthesis and causes stomatal closure