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Grapevine (Vitis vinifera L.) is the most economically important deciduous fruit crop in the world. Iron (Fe) is an essential micronutrient for plant development since its active form is involved in several biochemical processes, e.g., chlorophyll synthesis. The uptake of the elements depends on individual elements' interactions. Iron (Fe) nutrition of plants can be significantly affected by different nitrogen (N) forms through altering the uptake ratio of cations and anions, and changing rhizosphere pH. It is known, that most crop species grow best with access to nitrate (NO3 -) as well as ammonium (NH4 +) nitrogen, but little attention has been paid to changes in iron uptake under supply of different nitrogen (N) forms. The presented study aimed to decipher the specific interaction of different nitrogen (N) forms on Iron uptake of different grapevine rootstocks on the physiological as well as on the biochemical and molecular level. Four NH4 +: NO3 - ratios (0:1,1:5, 1:3, 1:1) were tested with a modified half-strength Hoagland solution with and without FeNa(III)-EDTA, summing up to eight treatments within a hydroponic system (Kick-Brauckmann, 7.5 L) under semi-controlled climatic glasshouse conditions in 2021. Rooted woody cuttings of the rootstocks Fercal (V.berlandieri x V. vinifera) and Couderc 3309 (V. riparia x V. rupestris) were used for the experiment. The results could differentiate iron deficiency effects, nitrogen form effects and rootstock effects. Biomass of leaves was negatively influenced by iron absent in both rootstocks with nitrate as only N source. This effect was observed for 3309C for all NH4 +: NO3 -ratios, while with Fercal the biomass of leaves increased with increasing amount of NH4 +. A similar trend was overserved for root biomass, promoting in Fercal with increased NH4 + amount and not response in 3309C. The efficiency of the photsystem II (Y(II)) decreased under iron deficient conditions in both rootstocks showing the strongest effect with only nitrate as N source especially with rootstock 3309C. Increasing ammonium levels in the nutrient solution lead to a higher pH reduction by the rootstocks probably enhancing the Fe2+ availability and uptake. The ferric chelate reductase (FCR) activity was specifically increased in Fercal under irondeficient conditions, while no effect was observed for 3309C in comparison to control plants. These first results of the study indicate that rootstocks differ in their preference on both the physiological and molecular level depending on the nitrogen form and in interaction with iron deficiency stress. In a next step the molecular mechanism will be analysed. [ABSTRACT FROM AUTHOR]

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Cyst nematodes induce specific syncytial feeding structures within the root which develop from an initial cell by successive incorporation of neighbouring cells through local cell wall dissolutions followed by hypertrophy of included cells. Expansins are known to induce cell wall relaxation and extension in acidic pH, and they are involved in many processes requiring wall modification from cell expansion to cell wall disassembly. We studied the expression pattern of tomato ( Lycopersicon esculentum L., cv. Money Maker) expansins during development of syncytia induced by the potato cyst nematode ( Globodera rostochiensis Woll.). Based on semi-quantitative reverse transcription–polymerase chain reaction, two expansin genes, LeEXPA4 and LeEXPA5, were selected for detailed examinations because their expression was either elevated in infected roots ( LeEXPA4) or specifically induced in the root upon nematode infection ( LeEXPA5). Both genes have distinct spatial and temporal expression patterns that may reflect their different roles in syncytium development. LeEXPA4 transcripts were localized predominantly in parenchymatous vascular cylinder cells surrounding syncytia. This finding suggests that LeEXPA4 might be involved in cell wall disassembly or relaxation, mediating syncytium expansion and/or development of conductive tissues. By contrast, LeEXPA5 transcripts were localized in enlarging syncytial elements. Similarly, in immunogold localization experiments, polyclonal antibodies localized the LeEXPA5 protein in cell walls of syncytial elements. This expression pattern suggests that LeEXPA5 gene is specifically involved in enlargement of cells incorporated into syncytium. [ABSTRACT FROM AUTHOR]