AN AUTORADIOGRAPHIC STUDY OF THE MOVEMENT OF ¹⁴C‐LABELLED ASSIMILATES IN THE DEVELOPING WHEAT PLANT

Abstract

Summary. 14CO2 together with autoradiographic techniques was used to stuy the movement of labelled carbon within wheat plants at different stages in their development. Movement of 14C about the plain was found to be extensive in the early stages, gradually bccoming more localized until at a stage after ear emergence there was little transference of labelled carbon between tillers within a 24‐hour period. In the early stages of development 14C from leaves on the main shoot was transported throughout the plant but accumulated in greatest amounts in the meristematic regions. Assimilates produced by the leaves of newly formed tillers were distributed mainly to the meristematic regions of those tillers although labelled carbon was moved in into the rest of the plant. In the later stages of development of each tiller the labelled assimilate was restricted to the tiller itself and to any very young tillers associated with it. After car emergence the pattern of distribution of the labelled carbon from the youngest and second youngest leaves was found to differ. Movement was predominantly towards the ear from the flag leaf and towards the root system from the leaf below the flag. It was noticed that mature leaves accumulated some labelled material and the possibility that this occurred via the transpiration stream following migration from phloem to xylem, as is the case with some of the case with some of the translocated herbicides, was investigated, but no indication of xylem transference was obtained. The possible application of these studies to investigations into the relationship between the movement natural assimilates and of translocated herbicides is discussed.

Yield and Yield Components Response to Defoliation of Spring Wheat Genotypes with Different Level of Resistance to Helminthosporium Leaf Blight

“…On an average removal of penultimate leaves reduced TKW by 4% and 6% in grain yield. The result was consistent with reports showing very little role of penultimate leaf and ear receives assimilates exclusively from flag leaf (Quinlan and Sagar, 1962;Wardlaw, 1965;Lupton, 1966). Removal of flag leaf reduced grain yield by ≈ 12% and TKW by ≈ 10% with no yield loss to a maximum reduction of 23%.…”

Distribution of Assimilate During Stem Elongation in Wheat

“…Whether plant photosynthesis was sufficient to meet the demands for stem and ear growth is uncertain but it was clear that, under the experimental conditions, the ear competed successfully with the stem for 14C compounds. Following ear emergence, the contribution from these lower leaves declined rapidly and, as shown by other workers (Quinlan and Sagar 1962;Wardlaw 1965), the flag leaf was the sole supplier to the ear by the time of anthesis.…”

“…For example, in tobacco, there appears to be preferential transport between leaves on the same orthostichy (Jones, Martin, and Porter 1959). In cereals and grasses, 14C_ distribution patterns suggest that morphological restrictions on movement are unlikely (Doodson, Manners, and Myers 1964;Quinlan and Sagar 1962). However, few attempts have been made to explore the relationship between the pattern of distribution of photosynthate and the vascular network in the Gramineae.…”

“…A very young leaf imports all of its requirements; as it expands it enters a phase where it may be exporting photosynthate although still a net importer and then it becomes a net-exporting organ with virtually no import. In cereals and grasses, import into a leaf continues until it is fully emerged (Quinlan and Sagar 1962). Initially, most of the export goes to the apex but, with development of the leaves above it, an increasing amount moves downward (Rawson and Hofstra 1969).…”

Physiological observations of maize (Zea mays L.) hybrids differing in photosynthetic capability

“…Tiller ing is unproductive in maize and tillers serve as competitive sinks during vegetative development in wheat and sugarcane (Quinlan and Sager, 1962;Hartt et al, 1963Hartt et al, , 1964Lupton, 1966), and during grain filling in wheat (Wardlaw and Porter, 1967;Rhodes, 1973). In wheat, lateral tillers have a greater draw on main culm lower leaf assimilates than do developing ears on the main culm (Yoshida, 1972;Rawson and Hofstra, 1969).…”