Input-output analysis of in vivo photoassimilate translocation using Positron-Emitting Tracer Imaging System (PETIS) data

The Positron-Emitting Tracer Imaging System (PETIS) is introduced for monitoring the distribution of (11)C-labelled photoassimilates in Sorghum. The obtained two-dimensional image data were quantitatively analysed using a transfer function analysis approach. While one half of a Sorghum root in a split root system was treated with either 0, 100, or 500 mM NaCl dissolved in the nutrient solution, tracer images of the root halves and the lower stem section were recorded using PETIS. From the observed tracer levels, parameters were estimated, from which the mean speed of tracer transport and the proportion of tracer moved between specified image positions were deduced. Transport speed varied between 0.7 and 1.8 cm min(-1) with the difference depending on which part of the stem was involved. When data were collected in the lowest 0.5-1 cm of the stem, which included the point where the roots emerge, transport speed was less. Rapid changes in NaCl concentration, from 0 to 100 mM, resulted in short-term increases of assimilate import into the treated root. This response represented a transient osmotic effect, that was compensated for in the medium-term by osmotic adaptation. Higher concentrations of NaCl (500 mM) resulted in distinctly less photoassimilate transport into the treated root half. The present results agree with earlier observations, showing that transport of (11)C-labelled photoassimilates measured with the PETIS detector system can be quantified using the method of input-output analysis. It is worth noting that with the PETIS detector system, areas of interest do not need to be defined until after data collection. This means that unexpected behaviour of a plant organ will be seen, which is not necessarily the case with conventional detector systems looking at predefined areas of interest.     

Apoplastic antioxidative system responses to ozone stress in strawberry leaves

Cell wall polysaccharides, pectin composition, as well as apoplastic superoxide dismutase and peroxidase activities were investigated in strawberry (Fragaria × ananassa) cultivars (cvs) Korona and Elsanta differing in their ozone sensitivity. Plants were exposed to 140–170 μg m⁻³ ozone either short-term for 7 days or long-term for 2 months in order to investigate whether differences in ozone sensitivity were due to differences in the apoplastic antioxidative systems. Cell wall polysaccharides were increased after 7 days and 2 months of ozone stress. While water-soluble pectins, low methoxy pectinates and NaOH-soluble pectinates were elevated after 7 days, their contents were unaffected (water-soluble pectins) or lower (low methoxy pectinates, NaOH-soluble pectinates) after 2 months. In cv. Elsanta, ozone treatment resulted in a significant reduction of superoxide dismutase activity after 7 days and 2 months, while it remained similar in cv. Korona. After 7 days, peroxidase activity was significantly higher in ozone-exposed leaves of cv. Korona, whereas after 2 months it was similar to or higher than in controls. Superoxide dismutase in cv. Korona detoxified ozone and its products in the apoplast, and the resulting elevated levels of H₂O₂ were balanced within 7 days by an increase in peroxidase activity. Long-term peroxidase activity may not play a comparably significant role in ozone defence, but the increase in cell wall polysaccharides and cell wall thickness measured after 2 months, resulting in a decrease in specific leaf area, reflected structural modifications that limited activities of reactive oxygen species efficiently. In contrast, the reduction of superoxide dismutase activity in cv. Elsanta indicated a less efficient apoplastic radical scavenging system, at least during the first 7 days of ozone stress, which was accompanied by membrane leakage and contributed to accelerated leaf senescence. Long-term, the reduction of intercellular air space volume in leaves contributed to ozone tolerance of cv. Elsanta as in cv. Korona.     

Use of transfer function and compartmental analysis to quantify 11C-labelled photoassimilate export from wheat leaves

Compartmental analysis of tracer loss from a leaf after pulse-labellingwith carbon isotopes has often been used to infer the flow ofphotosynthate through the leaf. Recently, a more general approachhas been suggested based upon estimation of the transfer functionusing data from pulse-labelling as well as continuouslabellingexperiments. A comparison of these two approaches shows thatwith the same data set they give equivalent physiological interpretations.The measured decline of ¹¹C activity from a wheat leaf after¹¹CO₂ pulse-labelling was extrapolated by compartmental as wellas transfer function analysis. Both methods estimated a 66.4%loss of the initially fixed ¹¹C due to export and respiration.The advantage of transfer function analysis, however, is itsapplicability to continuous-labelling experiments. The modelallows the use of the net photosynthetic rate as the reference(100%) value. Data from continuous-labelling experiments withwheat plants indicate diurnal variations in the export of freshlylabelled assimilate of between 32.7% and 43.6% of net photosynthesis. Key words: Triticum aestivum L, ¹¹CO₂, carbon partitioning, transfer function analysis, compartmental analysis     

Impacts of NaCl stress on plant growth and mineral nutrient assimilation in two cultivars of strawberry

Two strawberry (Fragaria × ananassa Duch.) cvs Korona and Elsanta differing in their tolerance to NaCl salinity were exposed to 40 and 80 mmol NaCl L^?1 for over 4 months in the growing seasons of 2002 and 2003, respectively. However, the osmotic potential, i.e. the NaCl concentration of the root medium, varied during the experiments, because Hoagland solution and demineralized water were added usually once a week in order to push NaCl uptake on the one hand, but to allow leaching the soil after application of demineralized water on the other. Leaching the soil should quickly improve the water relations of the plant, but not affect salt levels within the plant. This strategy was chosen to reduce the effects of water stress and to focus onto the salt-specific impacts of NaCl stress. The salt stress reduced fresh and dry matter of the whole plants and photosynthetically active leaf area, especially in cv. Elsanta. Typical leaf symptoms of Na and Cl stress were detected in both cvs and the combined effects of both toxic ions resulted in the leaf scorching symptoms. Na uptake of both cvs was similar, but distribution of Na within plants was different. Korona was able to protect leaves more efficiently from Na accumulation.Under NaCl stress Korona plants achieved a significant increase of K content in leaves and crowns, while Elsanta showed an increase of K in fruits and petioles. The accumulation of K under evaluated NaCl levels suggests an efficient K uptake system in strawberry plants. Concentrations of Ca were not significantly affected, with the exception of rising levels in roots of Elsanta plants. Concentrations of Mg, Mn and Fe significantly decreased in leaves, while those of Mg and Mn remarkably rose in crowns of both cvs. N content in leaves, petioles, and roots of both cvs increased. In addition it rose in fruits and crowns in cv. Elsanta. A significant limitation of N uptake by competition with Cl did not occur in these plants. Concentrations of P increased in roots and petioles of both cvs, and in fruits of cv. Elsanta. With respect to Zn and Cu, significant concentration changes related to NaCl stress could not be detected.