Sugars play an important role in grapevine flowering. This complex process from inflorescence initiation to fruit maturity takes two growing seasons. Currently, most of the available data concern the involvement of sugars as energy sources during the formation of reproductive structures from initiation of inflorescences during the summer of the first year, until flower opening during the following spring. Sugars devoted to the development of reproductive structures are supplied either by wood reserves or by photosynthesis in leaves or inflorescences, depending on the stage of development. Female meiosis appears to be a key point in the success of flower formation because (i) flowers are vulnerable at this stage and (ii) it corresponds in the whole plant to the transition between reserve mobilization from perennial organs (roots, trunk, and canes) towards efficient leaf photosynthesis. The perturbation of reserve replenishment during the previous year provokes perturbation in the development of inflorescences, whereas altering the photosynthetic sources affects the formation of flowers during the same year. In particular, a lack of sugar availability in flowers at female meiosis caused by various environmental or physiological fluctuations may lead to drastic flower abortion. Apart from energy, sugars also play roles as regulators of gene expression and as signal molecules that may be involved in stress responses. In the future, these two topics should be further investigated in the grapevine considering the sensitivity of flowers to environmental stresses at meiosis.

Sugars and flowering in the grapevine (Vitis vinifera L.)

The objective of this study was to evaluate the effect of deficit irrigation on intrinsic water use efficiency (A/gs) and carbon isotope composition (d 13 C) of two grape- vine cultivars (Moscatel and Castelao), growing in a commercial vineyard in SW Portugal. The study was done in two consecutive years (2001 and 2002). The treatments were full irrigation (FI), corresponding to 100% of crop evapotranspiration (ETc), rain-fed (no irrigation, NI), and two types of deficit irrigation (50% ETc): (i) by supplying the water either to one side of the root system or to the other, which is partial rootzone drying (PRD), or (ii) dividing the same amount of water by the two sides of the root system, the normal deficit irrigation (DI). The water supplied to the PRD treatment alternated sides approximately every 15 d. The values of predawn leaf water potential (Wpd) and the cumula- tive integral of Wpd (SW) during the season were lower in 2001 than in the 2002 growing season. Whereas differences in Wpd and SW between PRD and DI were not significantly different in 2001, in 2002 (a dryer year) both cultivars showed lower values of SW in the PRD treatment as compared with the DI treatment. This suggests that partial rootzone drying may have a pos- itive effect on water use under dryer conditions, either as a result of better stomatal control and/or reduced vigour. The effects of the water treatments on d 13 C were more pronounced in whole grape berries and pulp than in leaves. The d 13 C of pulp showed the best correlation with intrinsic water use efficiency (A/gs )a s well as with SW. In spite of the better water status observed in PRD compared with DI in the two cultivars in 2002, no statistical differences between the two treatments were observed in A/gs and d 13 C. On the other hand, they showed a higher d 13 C compared with FI. In conclusion, it is apparent that the response to deficit irrigation varies with the environmental condi- tions of the particular year, the driest conditions exacerbating the differences among treatments. The highest values of d 13 C found in the pulp of NI vines in

/pdf/impact-of-deficit-irrigation-on-water-use-efficiency-and-862s26bhuh.pdf

Impact of deficit irrigation on water use efficiency and carbon isotope composition (δ13C) of field-grown grapevines under Mediterranean climate

Validation of thermal indices for water status identification in grapevine

Aims All components of the soil-plant-atmosphere (sp-a) continuum are known to control berry quality in grapevine (Vitis vinifera L.) via ecophysiological interactions between water uptake by roots and water loss by leaves. The scope of the present work was to explore how the main hydraulic components of grapevine influence fruit quality through changes in liquidand gas-phase hydraulic conductance. Methods To reach our objectives, determinations of shoot growth, berry size and sugar content, leaf gas exchange, predawn leaf water potential (as a proxy of soil water potential), midday stem water potential and leaf water potential were performed in conjunction with anatomical measurements of shoot xylem. All measurements were conducted in two different cultivars (Cabernet franc and Merlot) and on three different soil types (clayey, gravelly, and sandy).

/pdf/impact-of-soil-texture-and-water-availability-on-the-4e9rqyy9x3.pdf

Impact of soil texture and water availability on the hydraulic control of plant and grape-berry development

Diurnal and seasonal changes in the leaf water potential (Ψ), stomatal conductance (gs), net CO2 assimilation rate (PN), transpiration rate (E), internal CO2 concentration (Ci), and intrinsic water use efficiency (PN/gs) were studied in grapevines (Vitis vinifera L. cv. Touriga Nacional) growing in low, moderate, and severe summer stress at Vila Real (VR), Pinhao (PI), and Almendra (AL) experimental sites, respectively. In VR and PI site the limitation to photosynthesis was caused more by stomatal limitations, while in AL mesophyll limitations were also responsible for the summer decline in PN.

Leaf Gas Exchange and Water Relations of Grapevines Grown in Three Different Conditions

The relationship of photosynthesis (A) of grapevine ( Vitis vinifera L.) sun and shade leaves of primary and secondary (lateral) shoots to insertion level was investigated over two seasons in the field. The leaf plastochron index (LPI) was used to denote leaf position on the shoot. Additionally, laboratory and field measurements of the response of A to CO 2 were conducted. An empirical model was developed to estimate carboxylation efficiency (CE) and stomatal limitations (1) of A. In sun leaves, the relationship of A to LPI changed little until the end of the season (October), whereas stomatal conductance (g) and the intercellular partial pressure of CO 2 (c i ) increased. Leaves acclimated to low light and leaves older than LPI 5 had 30 % lower A and were operating at a slightly higher ci as sun leaves. During September and October, lateral leaves had highest rates of CO 2 assimilation and CE. In mid-October, A and g decreased rapidly and simultaneously for all leaf types, leaf positions and both treatments (sun and shade). Photosynthesis responded similar to individual leaf age as to leaf position. A was linearly related to c i up to non-limiting conductances for sun and shade leaves, for all ages and at all times during the season. The CE and 1 were highest at the beginning of the season and strongly dependent on leaf position. Stomatal limitation declined continuously from about 55 % at the beginning to about 23 and 18 % for sun and shade leaves, respectively, at the end of the season.

/pdf/photosynthetic-duration-carboxylation-efficiency-and-4wl9hu9tqy.pdf

Photosynthetic duration, carboxylation efficiency and stomatal limitation of sun and shade leaves of different ages in field-grown grapevine ( Vitis vinifera L.)

W. Kiefer

Papers

Photosynthetic duration, carboxylation efficiency and stomatal limitation of sun and shade leaves of different ages in field-grown grapevine ( Vitis vinifera L.)