Plants grown in an environment of elevated CO2 and temperature often show reduced CO2 assimilation capacity, providing evidence of photosynthetic downregulation. The aim of this study was to analyse the downregulation of photosynthesis in elevated CO2 (700 µmol mol−1) in nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4°C) and water availability regimes in temperature gradient tunnels. When the measurements were taken in growth conditions, a combination of elevated CO2 and temperature enhanced the photosynthetic rate; however, when they were carried out at the same CO2 concentration (350 and 700 µmol mol−1), elevated CO2 induced photosynthetic downregulation, regardless of temperature and drought. Intercellular CO2 concentration measurements revealed that photosynthetic acclimation could not be accounted for by stomatal limitations. Downregulation of plants grown in elevated CO2 was a consequence of decreased carboxylation efficiency as a result of reduced rubisco activity and protein content; in plants grown at ambient temperature, downregulation was also induced by decreased quantum efficiency. The decrease in rubisco activity was associated with carbohydrate accumulation and depleted nitrogen availability. The root nodules were not sufficiently effective to balance the source–sink relation in elevated CO2 treatments and to provide the required nitrogen to counteract photosynthetic acclimation.

la Puente. L. 1995. Influence of nitrogen supply and sink strength on changes in leaf nitrogen compounds during sene.scence in two wheat cultivars. -Physiol. Plant. 95: 51-58.Changes in various nitrogen compounds during senescence of the fourth leaf were studied in two cultivars of spring wheat {Triticum aestivum L.). One of the cultivars (Yecora) was supplied with two N levels; the other (Tauro) was grown with the high N level and pruned above the fourth leaf, whereas the control was left intact. In both cultivars grown with high N supply, net nitrogen export from the fourth leaf did not occur until 35 days after sowing (DAS). Loss of leaf soluble proteins started earlier than that of chlorophylls, and coincided initially with an increase in insoluble protein. In N deficient plants the level of total N, soluble protein, and the activity of nitrate reductase (NRA, EC 1.6.6.1) started to decrease about 5 days earlier, and. along with chlorophyll, continued to decrease at a faster rate, than in high N plants. Also, with low N supph; the large subunit (LSU. 58 kDa) of ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco. EC 4.1.1.39) decreased in greater proportion than otiier soluble proteins, while with high N supply the decrease in Rubisco LSU was similar to that of other soluble proteins. Nitrogen deficiency caused a greater decrease in soluble proteins than in insoluble proteins, and NRA relative to soluble proteins. The faster senescinj Tauro cultivar had lower levels of most parameters, especially NRA, soluble protein and, after 35 DAS. Rubisco LSU as a proportion of soluble protein. The decrease in sink strength due to shoot pruning did generally not affect the level of the various nitrogenous compounds until 35 DAS: thereafter the levels of most parameters. especialTy soluble protein, Rubisco LSU and, at late stages of senescence, insoluble protein, were higher in pruned than in control shoots. Thus, shoot pruning slows down senescence. The 56-and 78-kDa polypeptides increased, rather than decreased with leaf age: the level of these two polypeptides showed a negative relationship with Rubisco LSU (r = -0.933 and r = -0.758. respectively).Ke\ words -Chlorophyll, cultivar, free amino N, nitrate, nitrate reductase activity, nitrogen supply, proteins, Rubisco. SDS-PAGE, sink strength, wheat. /. M. Martin del Molino (corresponding author) et al,, Instituto de Recursos Naturaiesganic nitrogen is mobilised to developing tissues (e.g.

Changes in various nitrogen compounds during senescence of the fourth leaf were studied in two cultivars of spring wheat (Triticum aestivum L.). One of the cultivars (Yecora) was supplied with two N levels; the other (Tauro) was grown with the high N level and pruned above the fourth leaf, whereas the control was left intact. In both cultivars grown with high N supply, net nitrogen export from the fourth leaf did not occur until 35 days after sowing (DAS). Loss of leaf soluble proteins started earlier than that of chlorophylis, and coincided initially with an increase in insoluble protein. In N deficient plants the level of total N, soluble protein, and the activity of nitrate reductase (NRA. EC 1.6.6.1) started to decrease about 5 days earlier, and along with chlorophyll, continued to decrease at a faster rate, than in high N plants. Also, with low N supply, the large subunit (LSU, 58 kDa) of ribulose‐1.5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) decreased in greater proportion than other soluble proteins, while with high N supply the decrease in Rubisco LSU was similar to that of other soluble proteins. Nitrogen deficiency caused a greater decrease in soluble proteins than in insoluble proteins, and NRA relative to soluble proteins. The faster senescing Tauro cultivar had lower levels of most parameters, especially NRA, soluble protein and, after 35 DAS. Rubisco LSU as a proportion of soluble protein. The decrease in sink strength due to shoot pruning did generally not affect the level of the various nitrogenous compounds until 35 DAS; thereafter the levels of most parameters, especially soluble protein, Rubisco LSU and, at late stages of senescence, insoluble protein, were higher in pruned than in control shoots. Thus, shoot pruning slows down senescence. The 56‐ and 78‐kDa polypeptides increased, rather than decreased, with leaf age; the level of these two polypeptides showed a negative relationship with Rubisco LSU (r = ‐0.933 and r = ‐0.758, respectively).

The single seed descent (SSD) method of selection has been evaluated in safflower {Carthamus tinctorius L.). The initial population of this study was a BCiF; from a cross between a well adapted and a high oil cultivar. Transgres.sive segregation for yieid and oil content producmg lines with considerably higher values than the better parent was observed in BCiFj and BC^Fj generations. These results and the great saving of time and effort makes the SSD method a very desirable tool for safflower breeders.