Nitrogen control of transpiration in grapevine

Transpiration per unit of leaf area is the end-product of the root-to-leaf water transport within the plant, and it is regulated by a series of morpho-physiological resistances and hierarchical signals. The rate of water transpired sustains a series of processes such as nutrient absorption and leaf evaporative cooling, with stomata being the end-valves that maintain the optimal water loss under specific degrees of evaporative demand and soil moisture conditions. Previous work provided evidence of a partial modulation of water flux following nitrogen availability linking high nitrate availability with tight stomatal control of transpiration in several species. In this work, we tested the hypothesis that stomatal control of transpiration, among others signals, is partially modulated by soil nitrate ( NO3- ) availability in grapevine, with reduced NO3- availability (alkaline soil pH, reduced fertilization, and distancing NO3- source) associated with decreased water-use efficiency and higher transpiration. We observed a general trend when NO3- was limiting with plants increasing either stomatal conductance or root-shoot ratio in four independent experiments with strong associations between leaf water status, stomatal behavior, root aquaporins expression, and xylem sap pH. Carbon and oxygen isotopic signatures confirm the proximal measurements, suggesting the robustness of the signal that persists over weeks and under different gradients of NO3- availability and leaf nitrogen content. Nighttime stomatal conductance was unaffected by NO3- manipulation treatments, while application of high vapor pressure deficit conditions nullifies the differences between treatments. Genotypic variation for transpiration increase under limited NO3- availability was observed between rootstocks indicating that breeding (e.g., for high soil pH tolerance) unintentionally selected for enhanced mass flow nutrient acquisition under restrictive or nutrient-buffered conditions. We provide evidence of a series of specific traits modulated by NO3- availability and suggest that NO3- fertilization is a potential candidate for optimizing grapevine water-use efficiency and root exploration under the climate-change scenario

Leaf treatments with a protein-based resistance inducer partially modify phyllosphere microbial communities of grapevine

Protein derivatives and carbohydrates can stimulate plant growth, increase stress tolerance, and activate plant defense mechanisms. However, these molecules can also act as a nutritional substrate for microbial communities living on the plant phyllosphere and possibly affect their biocontrol activity against pathogens. We investigated the mechanisms of action of a protein derivative (nutrient broth, NB) against grapevine downy mildew, specifically focusing on the effects of foliar treatments on plant defense stimulation and on the composition and biocontrol features of the phyllosphere microbial populations. NB reduced downy mildew symptoms and induced the expression of defense-related genes in greenhouse- and in vitro-grown plants, indicating the activation of grapevine resistance mechanisms. Furthermore, NB increased the number of culturable phyllosphere bacteria and altered the composition of bacterial and fungal populations on leaves of greenhouse-grown plants. Although, NB-induced changes on microbial populations were affected by the structure of indigenous communities originally residing on grapevine leaves, degrees of disease reduction and defense gene modulation were consistent among the experiments. Thus, modifications in the structure of phyllosphere populations caused by NB application could partially contribute to downy mildew control by competition for space or other biocontrol strategies. Particularly, changes in the abundance of phyllosphere microorganisms may provide a contribution to resistance induction, partially affecting the hormone-mediated signaling pathways involved. Modifying phyllosphere populations by increasing natural biocontrol agents with the application of selected nutritional factors can open new opportunities in terms of sustainable plant protection strategie

Laser microdissection of grapevine leaves reveals site-specific regulation of transcriptional response to Plasmopara viticola

Grapevine (Vitis vinifera) is one of the most important fruit crops in the world and it is highly susceptible to downy mildew, caused by the biotrophic oomycete Plasmopara viticola. Gene expression profiling has largely been used to investigate regulation processes of grapevine-P. viticola interaction, but all studies have involved the use of whole leaves. However, only a small fraction of host cells is in contact with the pathogen and highly localized transcriptional changes of infected cells may be masked by the large portion of not-infected cells when analysing the whole leaf. In order to characterise the transcriptional regulation of the plant reaction with spatial resolution, we optimized a laser microdissection protocol to harvest stomata and surrounding cells from leaves of in vitro-grown grapevines at early stages of P. viticola infection. The expression levels of seven P. viticola responsive genes were greater in microdissected cells than in whole leaves, highlighting the site-specific transcriptional regulation of the host response. The gene modulation was restricted to the stomata cells and to the surrounding areas of infected tissues, indicating that short-distance signals are implicated. The high sensitivity of the laser microdissection analysis showed significant modulations of three genes that were completely masked in the whole tissue analysis. These results highlight that the transcriptional regulation of the host response to a biotrophic pathogen is mainly located to the infection sites. The optimized protocol for the laser microdissection analysis is suitable to increase the sensitivity of further high-throughput transcriptomic studies of the grapevine-P. viticola interaction

Natural variation in stomatal dynamics drives divergence in heat stress tolerance and contributes to the seasonal intrinsic water-use efficiency in Vitis vinifera (subsp. sativa and sylvestris)

Stomata control CO2 uptake for photosynthesis and water loss through transpiration, thus playing a key role in leaf thermoregulation, water-use efficiency (iWUE) and plant productivity. In this work, we investigated the relationship between several leaf traits and hypothesized that stomatal behavior to fast (i.e. minutes) environmental changes co-determines along with steady-state traits the physiological response of grapevine to the surrounding fluctuating environment over the growing season. No relationship between iWUE, heat stress (HS) tolerance and stomatal traits was observed in field grown grapevine, suggesting that other physiological mechanisms are involved in determining leaf evaporative cooling capacity and the seasonal ratio of CO2 uptake (A) to stomatal conductance (gs). Indeed, cultivars that in the field had an unexpected combination of high iWUE but low sensitivity to thermal stress, displayed a quick stomatal closure to light, but a sluggish closure to increased vapor pressure deficit (VPD) levels. This strategy aiming both at conserving water under a high-to-low light transition and in prioritizing evaporative cooling under a low-to-high VPD transition, was mainly observed in Regina and Syrah. Moreover, cultivars with different known responses to soil moisture deficit or high air VPD (isohydric vs anisohydric) had opposite behavior under fluctuating environments, with the isohydric cultivar showing slow stomatal closure to reduced light intensity but quick temporal responses to VPD manipulation. We propose that stomatal behavior to fast environmental fluctuations can play a critical role on leaf thermoregulation and water conservation under natural field conditions in grapevine

Plant Hosts of Apple Proliferation Phytoplasma

In the last years the cooperation between the Fondazione Edmund Mach (Trentino) and the Laimburg Research Center (South Tyrol) was intensified to bundle the expertise of both research institutions. The cooperation in the field of apple proliferation (AP) disease became exemplary of how good scientific collaborations between the partner institutions is supposed to be. Both provinces - Trentino and South Tyrol - have large areas of apple cultivation, which were affected by recurrent outbreaks of apple proliferation disease. It was therefore evident that relevant discoveries can only be achieved in close collaboration and exchange. We discussed, planned, worked together, argued, but altogether and most important we grew as a team. The complexity of the topic is reflected by the different scientific and technical backgrounds of the researchers involved in the projects. This work was also possible thanks to the external contribution of prestigious national and international researchers known for their studies on apple proliferation. It should thus not be concealed that we are proud of what we achieved together in the last years. These achievements are reflected by numerous scientific publications, presentations and by this book that we edit as a joint work. The book is aimed at scientists in the field, local farmers, students and anyone who is interested in apple proliferation. We provide an overview of the current state of apple proliferation related research (with a focus on Trentino and South Tyrol) and provide an extended list of references for further reading. The book is available in three languages, Italian, German and English to make its content accessible to national and international readers. Our collaboration is ongoing and we are curious to see which interesting discoveries the future will bring.https://scholar.dominican.edu/books/1157/thumbnail.jp