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.

A B S T R A C TThe changes in the composition of free and total amino aciak in wheat grain during development are described: the experiment was performed in a growth chamber with three varieties of winter wheat (Triticum aestivum L.): Splendeur, Hobbit and Maris Huntsman. The changes in the total composition of amino acids of the grain as development progressed were consistent with an increase in the proportion of storage proteins. A t 15 days after anthesis, the relative amount of glycine increased, suggesting that at this moment the proportion of gliadins was relatively low. The relative amount of arginine increased in mature grain, showing that at times close to maturity the relative proportion of synthesis of a protein fraction rich in this amino acid increased. Free glutamate, proline and arginine decreased at 15 days to a greater extent than the other amino acids and was present in low relative amounts during the period of maximum protein synthesis in the grain; these three amino acids could be the most limiting for protein synthesis in grain. In the free fraction the following showed a similar pattern of change during grain development: aspartate, arginine and histidine on the one hand, and on the other alanine, valine, leucine, isoleucine, threonine, phenylalanine and tyrosine; moreover both groups were inversely correlated. Glycine and lysine were directly related to each other and inversely to glutamate.

Photosynthesis and carbohydrate content of flag leaves were measured during the post‐anthesis period of three spring wheat (Triticum aestivum L.) varieties grown with two levels of nitrogen supply, with ears either left intact or with the upper halves removed at anthesis. With low nitrogen supply, removing the upper half of the ear increased photosynthesis in the varieties Shasta and Anza, but not in Yecora. With high nitrogen, removing half ears inhibited photosynthesis in Yecora but had no effect on the other two varieties. Early in grain growth, halving ears decreased the contents of glucose, fructose (hexose), fructans and starch in leaves of Shasta and Anza, and increased those of Yecora, grown with low nitrogen level. The treatment of the ear increased hexose content of leaves of the three varieties supplied with high nitrogen level but had no effect on fructan and starch contents. Neither with high nor with low nitrogen level was leaf sucrose content affected by the treatment of the ear. There were significant correlations among levels of carbohydrates, the level of hexoses being most closely related to that of fructans. The rate of photosynthesis showed a significant negative regression over hexose levels.

I. M. 1993. Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties. -Physiol. Plant. 89: 453-459.. ,Photosynthesis and carbohydrate content of flag leaves were measured during the post-anthesis period of three spring wheat {Triticum aestivum L.) varieties grown with two levels of nitrogen supply, with ears either left intact or with the upper halves removed at anthesis. With low nitrogen supply, removing the upper half of the ear increased photosynthesis in the varieties Shasta and Anza, but not in Yecora. With high nitrogen, removing half ears inhibited photosynthesis in Yecora but had no effect on the other two varieties. Early in grain growth, halving ears decreased the contents of glucose, fructose (hexose), fructans and starch in leaves of Shasta and Anza, and increased those of Yecora, grown with low nitrogen level. The treatment of the ear increased hexose content of leaves of the three varieties supplied with high nitrogen level but had no effect on fructan and starch contents. Neither with high nor with low nitrogen level was leaf sucrose content affected by the treatment of the ear. There were significant correlations among levels of carbohydrates, the level of hexoses being most closely related to that of fructans. The rate of photosynthesis showed a significant negative regression over hexose levels. = *;

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