Fixation of 14Co2 by Flowering and Non-Flowering Glumes of the Wheat Ear, and the Pattern of Transport of Label to Individual Grains

Abstract

This paper explores the possible role of photosynthesis by individual glumes in influencing the growth rates of individual grains of the wheat ear. Specifically we determined: (1) the photosynthetic capacities of individual glumes (i.e. nonflowering glumes, lemmas, and paleas) of an awned wheat cultivar; (2) the pattern of translocation of 14C-Iabelled assimilate from individual glumes to individual grains; and (3) the time course of translocation of label from glumes and flag leaf to the grain.The lemmas were photosynthetically the most active of the glumes; over the greater part of grain filling they accounted for some 15% of whole-plant photosynthesis; non-flowering glumes and paleas accounted for 5-6% and 2-5% respectively. Towards maturity the lemmas decreased in importance in relation to other glumes, particularly paleas. The photosynthetic efficiency (as measured by 14C fixed per unit weight) of glumes was less than half of that of flag and penultinlate leaves in the early stages, but declined more slowly with time. The nearest grain was the preferred but not exclusive sink for the 14C-Iabelled assimilate from any glume. Movement of label was always towards the apex and on the same side of the spikelet as the glume, if there was a grain towards the apex on that side;if not, movement across the spikelet, still towards the apex, occurred. This caused an accumulation of label in the distal grains of spikelets. Labelled assimilate from the glumes was detected in the grains within 10 min of the commencement of exposure and the rate of increase in activity was maxinlal in about 1 hr; corresponding times for flag leaf label were 1 and 2-3 hr.The distribution of glume assimilate between the grains provided no explanation for differences in their growth rates; there was evidence that the grains themselves exerted a controlling influence.

Associations between geographical origin and morphological characters in bread wheat (Triticum aestivum L.)

“…Assimilate is generated mainly from the spike, the flag leaf and its sheath. Nonetheless, it has been long recognized that awns can substantially increase spike photosynthesis and yields under dry conditions (Atkins and Norris, 1955;Bremner and Rawson, 1972;Evans et al, 1972;Olugbemi et al, 1976). Our observations are consistent with this notion, since awnedness is much more prevalent in regions where severe drought stress is common (Fig.…”

The Weights of Individual Grains of the Wheat Ear in Relation to Their Growth Potential, the Supply of Assimilate and Interaction Between Grains

“…If we consider the curve for grain a in the absence of others (Fig. 2a), we see that it departs from the pattern of control ears in approximately the same spikelets as does the curve for c, and that there is a suggestion of a similar relation between the curves for b and d. The members of each pair occur on the same side of the rachilla, and there is some affinity between such pairs in their vascular connections (Bremner and Rawson 1972).…”

“…In all three treatments, ear photosynthesis was prevented by immersion of the ears in a 3 x M solution of DCMU [3-(3,4-dichloropheny1)-1,l-dimethylurea for 30 s; this was repeated whenever routine gas-analysis checks indicated any recovery of ear photosynthesis. The rationale for the DCMU treatment was that, as the distribution of assimilate originating in the ear favours distal grains (Bremner and Rawson 1972), ear photosynthesis might obscure the pattern of distribution of material from the remainder of the shoot which, as the main source of assimilate for grain filling, was our primary interest.…”

“…In this case, however, the limitation is at the lower end of the gradient-in the rachis. If the concentration here is reduced by preventing ear photosynthesis, the rate of translocation from the shoot is increased (Bremner and Rawson 1972) and the rate of photosynthesis in the shoot may also increase (King et al 1967;Rawson et al 1976). The role of grain potential for growth-particularly that part of it which derives from grain number-in promoting this state of affairs is self-evident.…”

Morphological characterization of wheat genetic resources from the Island of Madeira, Portugal

“…It has been long recognized that awns can substantially increase spike photosynthesis and subsequently yields under dry conditions (Bremner and Rawson 1972;Olugbemi et al 1976;Atkins and Norris 1955). Our data showed that the awned varieties including graecum Körn., erythrospermum Körn., ferrugineum (Alef.)…”