Distribution of Assimilate During Stem Elongation in Wheat

Abstract

During the phase of stem extension in plants of Triticum aestivum L. cv. Stewart, the distribution of assimilated 14C appeared to be related to sink size, proximity to the source, and a canalizing effect imposed by the vascular system on the movement between leaves. Evidence was found of a greater resistance to export from a leaf in the upward than in the downward direction and this is consistent with the observed arrangement of the sieve elements linking the bundles at the nodes. The cross· sectional area of the phloem did not appear to impose a limitation on the amount of material transported to the apex. The bulk of carbon imported by a growing leaf was consistently transported from the second lamina below. Import from other leaves continued after the emergence of a lamina and accounted for some 80% of its final dry weight and 50% of that in the attached sheath. The elongating internodes 81ther side of the leaf formed large sinks for its photosynthate. Ear growth, prior to its emergence, was supported by the upper three leaves. After emergence the flag leaf was the main supplier.

Tansley Review No. 27 The control of carbon partitioning in plants

“…However more recent data have shown that specific mass transfer can be much greater than the earlier estimates suggested (Patrick, 1972;Lush & Evans, 1974;Passioura & Ashford, 1974). In castor bean Kallarackal & Milburn (1984) showed that a fruit on an intact inflorescence had a SMT through the pedicel of up to 6 g cm~^ sieve tube area h~^ and this could be increased to 12 g cm"ŝ ieve tube h~^ when other fruits on the inflorescence were removed (a change from source to sink limiting growth).…”

Effects of irrigation and fertiliser on the yields of ‘Arawa’, ‘Aotea’, and ‘Karamu’ wheats

“…Before anthesis 'Karamu' plots had lower leaf area indices (Table 2) and plants may have had higher net assimilation rates and, presumably, higher soluble carbohydrate status than the New Zealand cultivars (Scott et al 1973). During grain set there should also have been considerably less competition for assimilates from the stem sink of the semi-dwarf (Patrick 1972) and more grains may have formed as a result.…”

“…Three cultivars, the relatively tall 'Arawa', intermediate 'Aotea', and the semi-dwarf 'Karamu', were sown to provide crops with potentially different source -sink relationships. Ear differentiations occur when the primary competing sink is the extending stem and, consequently, the semi-dwarf was expected to have a weaker sink (Patrick 1972). Irrigation treatments were also intended to modify source -sink relationships.…”

Levels of water-soluble carbohydrate in the pre-anthesis ear of wheat, and grain set per spikelet

“…This deficiency may limit the supply of assimilate to the ear, for, as Patrick (1972) observed, the ear is supplied from the three uppermost leaves and sheaths before ear emergence and by the flag leaf after its emergence. Until pollination the ear remains a minor sink (Lupton 1968) and, although it usually competes successfully with stem extension, the growth of the ear primordium appears limited by the availability of substrate (Patrick 1972).…”

“…The stage of development of wheat which is the most sensitive to shading and water stress with respect to grain set has been identified as that of rapid ear growth, approximately 2 weeks before anthesis when competition for substrates, particularly from stem internodes, is likely to be intense (Patrick 1972;Fischer 1973;Bingham 1972;Lupton et al 1974). Wardlaw (1970) has shown that grain set is also sensitive to assimilate supplies for 10 days after anthesis.…”