Wheat Vegetative Nitrogen Compositional Changes in Response to Reduced Reproductive Sink Strength

Abstract

N redistribution patterns and the N composition of vegetative tissues above the peduncle node of wheat (Triticum aestivum L.) plants with altered reproductive sink strength were evaluated to determine the role of vegetative storage proteins in the temporary storage of excess N destined for export. The degree of leaf senescence symptoms (loss of chlorophyll, total N, and ribulose-1,5-bisphosphate carboxylase/oxygenase) were quirements for N export or gene expression of VSP for the temporary storage of excess N.Leaf tissue of wheat (Triticum aestivum L.), as well as many other monocotyledon and dicotyledon species, induces proteins in response to MeJA treatment (6). The molecular mass and immunological properties of these induced proteins vary markedly among species, and considerable quantitative differences in the level of expression of MeJA-induced proteins apparently occur among barley (Hordeum vulgare L.) cultivars (6). In response to depodding, JA, MeJA, and other treatments given to soybean (Glycine max [L.] Merr.) plants, abundant levels of the same specific vegetative proteins (molecular masses of 27, 29, and 94 kD) accumulate predominantly in the vacuoles of PVM cells of leaves (5,7,18,19,21). The 94-kD protein was recently identified as a member of the vegetative lipoxygenase family and proposed to be a bifunctional zymogen capable of catalyzing the hydroperoxidation of lipids and storing excess N temporarily (21).The effects of an altered reproductive sink demand on accumulation of VSP have been limited to studies of soybean (5,18,19,25,26). Because depodding, JA, and MeJA elicit similar VSP accumulation responses in soybean, other monocarpic annuals that express MeJA-induced proteins also may accumulate proteins with VSP characteristics when reproductive sink demand is altered. In wheat, redistribution of vegetative N accumulated before anthesis normally provides the major source of grain N (1, 16, 22). During reproductive growth, the extent of vegetative N redistribution depends on sink size. Removal of all spikes from multiculm wheat plants delays physiological and biochemical processes associated with leaf senescence and net mobilization of N (2, 4, 15). Partial reduction of the reproductive sink, however, has a relatively small effect on the initiation and extent of N mobilization from the flag leaf of a partially degrained culm of wheat (9,10

Effect of sink manipulation on nitrogen accumulation and distribution among organs of gramineae and leguminosae

“…In contrast to Leguminosae, in Gramineae, special polypeptides like VSP were not detected in leaves and stems by the sink cut treatment. MacKown et al (1992) also reported that the special polypeptide was not detected in the flag leaf blade, flag leaf sheath and peduncle by the sink cut treatment in wheat.…”

Differences in Wheat Cultivar Response to Nitrogen Supply. II: Differences in N‐Metabolism‐Related Traits

“…It seems that more efficient integration of nitrogen into plant metabolism (Hageman 1979), together with a more rapid N turnover (Cox et al. 1985, Van Sanford and Mackown 1987) characterized Toronto during phase 2, which not only allowed to respond to higher sink capacity for plant‐available N (Mackown et al. 1992, Pugnaire and Chapin 1992) but at the same time to maintain higher levels of canopy N content.…”

Apoptosis-like DNA fragmentation in leaves and floral organs precedes their developmental senescence

“…Early degradation of DNA and proteins can be explained with the need of rdocating nutritional resources when the demand for nitrogen supply increases in the developing seeds (BARNEIX & GUITMAN, 1993). Other studies support the importance of the nitrogen translocation to the growing kernels (PEOPLES et al, 1980;MACKOWN et al, 1992;MARTIN DEL MOLINO et al, 1995). While nucleic acids and proreins are rapidly metabolised, the photosynthetic apparatus remains efficient as long as possible, because it can still provide an important source of nutrients.…”