Annegret Schum

In vitro method for early evaluation of nitrogen use efficiency associated traits in potato

The objective of the present study was to characterize various traits associated with nitrogen uptake and utilization in a range of potato cultivars. For this purpose an in vitro test system was developed which allows analyzing specific stress responses in a highly controlled environment. Shoot tips were grown fixed in perforated stainless steel plates in 500 ml glass vessels in liquid culture medium at four nitrogen levels, i.e. 60, 30, 15 and 7.5 mmol L-1. At the end of a three weeks’ culture period plant developmental traits were determined and nitrogen uptake and assimilation were analyzed. Reduction of nitrogen in the culture medium differentially affected morphological and physiological features. Highly significant differences were found between different N-levels and cultivars as well as for genotype x nitrogen level interactions. Three groups of cultivars (high, low and intermediate) were distinguished with respect to biomass production and crude protein yield under nitrogen-sufficient conditions of 60 mmol L-1. Genotypes with a low biomass production at full nitrogen availability responded with increased root development under nitrogen deficiency stress and increased their nitrogen utilization capacity in relation to the other cultivars.

Comparative shoot proteome analysis of two potato (Solanum tuberosum L.) genotypes contrasting in nitrogen deficiency responses in vitro

Aiming at a better understanding of the physiological and biochemical background of nitrogen use efficiency, alterations in the shoot proteome under N-deficiency were investigated in two contrasting potato genotypes grown in vitro with 60 and 7.5mM N, respectively. A gel based proteomic approach was applied to identify candidate proteins associated with genotype specific responses to N-deficiency. 21% of the detected proteins differed in abundance between the two genotypes. Between control and N-deficiency conditions 19.5% were differentially accumulated in the sensitive and 15% in the tolerant genotype. 93% of the highly N-deficiency responsive proteins were identified by MALDI TOF/TOF mass spectrometry. The major part was associated with photosynthesis, carbohydrate metabolism, stress response and regulation. Differential accumulation of enzymes involved in the Calvin cycle and glycolysis suggest activation of alternative carbohydrate pathways. In the tolerant genotype, increased abundance under N-deficiency was also found for enzymes involved in chlorophyll synthesis and stability of enzymes, which increase photosynthetic carbon fixation efficiency. Out of a total of 106 differentially abundant proteins, only eight were detected in both genotypes. Our findings suggest that mutually responsive proteins reflect universal stress responses while adaptation to N-deficiency in metabolic pathways is more genotype specific. SIGNIFICANCE Nitrogen losses from arable farm land considerably contribute to environmental pollution. In potato, this is a special problem due cultivation on light soils, irrigation and the shallow root system. Therefore, breeding of cultivars with improved nitrogen use efficiency and stable yields under reduced N fertilization is an important issue. Knowledge of genotype dependent adaptation to N-deficiency at the proteome level can help to understand regulation of N efficiency and development of N-efficient cultivars.

Nitrogen Deficiency Induced Alterations in the Root Proteome of a Pair of Potato (Solanum tuberosum L.) Varieties Contrasting for their Response to Low N

Improving crop nitrogen use efficiency is important both from the economic and the environmental viewpoint. Here, the aim is to highlight differences between the proteomic response of the roots of two potato cultivars contrasting in their response to nitrogen (N) deficiency, in an effort to understand which proteins and metabolic pathways contribute to the tolerance of N deprivation. The two cultivars ‘‘Topas’’ (tolerant) and ‘‘Lambada’’ (sensitive) are grown under both an N sufficient and an N deficient regime, using an in vitro‐based cultivation system. Responsive proteins are identified and quantified using label‐free quantitative shotgun proteomics. The contrasting cultivars differed with respect to components of the glutamine synthetase/glutamine oxoglutarate aminotransferase pathway, tricarboxylic acid cycle, the glycolysis/gluconeogenesis pathway as well as protein and amino acid synthesis machinery. Additional differences are associated with protein catabolism and defense mechanisms.

Variation in Drought Tolerance of Perennial Ryegrass (Lolium perenne L.)

Global climate change is one of the biggest challenges for research in agricultural science. In Europe, expected temporary periods of reduced precipitation during the growing season will affect crop yields. Perennial ryegrass (Lolium perenne L.) is one of the most important forage grasses in Europe due to high yields and nutritional composition. Because perennial ryegrass has no distinct tolerance to drought, it is likely to be particularly affected by global climate change. Perennial ryegrass is found in many geographical regions across Europe, thus genetic variation for drought tolerance is likely. We have evaluated persistence under temporary drought conditions of 200 accessions, representing gene bank material from several countries with differing amounts of precipitation as well as breeding material. The evaluation was based on field trials at drought-prone locations. A contrasting drought response could be detected within the accessions and a representative subsample of 54 accessions could be identified for use in a two location rain-out shelter trial. Different methods for phenotyping recovery after drought stress were compared and traits were scored on a single plant basis in the semi-controlled environment rain-out shelter. A huge variation was found not only between, but also within accessions. It became obvious that the most important mechanism under Central European drought conditions is not maintenance of biomass production under severe drought stress but rather fast recovery after a limited period of water shortage. Single clones with contrasting recovery performance could be identified and will be used to investigate drought tolerance mechanisms and breed new varieties in future projects.