Awn contribution to gas exchanges of barley ears

Abstract

The effects of awn removal on ear gas exchange in four barley lines (Morex, Harrington, Steptoe, and TR306) were studied under a controlled environment using a Before-After Control-Impact Paired (BACIP) experimental design. From ear emergence to grain maturity, plants were grown in pots at either 60 or 90 % of soil water holding capacity. Gasexchange measurements of ears were made 9 and 10 d after anthesis (DAA). On 11 DAA, awn removal was performed on half of the ears in each pot, followed by measurements on both intact and de-awned ears on 12 and 13 DAA. Net photosynthetic (P N ) and transpiration (E) rates decreased significantly with awn removal, but dark respiration (R D ) rate was not affected. We estimated for each ear a temperature-adjusted respiration rate (R a ) from R D . When we corrected P N with R a , we found that rates of spikelet photosynthesis were largely underestimated. Moderate water stress had minimal effect on gas exchange of bracts and awns of the barley ear. Barley lines did not differ for any individual gas-exchange parameter.

Comparative Transcriptional Profiling Established the Awn as the Major Photosynthetic Organ of the Barley Spike While the Lemma and the Palea Primarily Protect the Seed

“…Overexpression of several of the genes in the mevalonate‐independent pathway as well as those in the actual synthesis of carotenoids and chlorophyll allows the awn to harvest more light energy than the other organs of the spike. Preferential expression of multiple genes for light harvesting, the light reaction and the Calvin cycle can explain the high rate of photosynthesis previously measured in the awn (Ziegler‐Jöns, 1989; Jiang et al, 2006).…”

“…The lemma and palea are the second most prominent photosynthetic organs of the barley spike. Because the lemma and palea tightly adhere to the seed and also recycle respiratory CO 2 released by the seed (Jiang et al, 2006; Tambussi et al, 2007), it is difficult to obtain an accurate measurement of photosynthesis in these organs. Difficulties in measuring gas exchange in the spike organs can underestimate photosynthesis of the lemma and palea and inflate that of the awn.…”

The fifth leaf and spike organs of barley (Hordeum vulgare L.) display different physiological and metabolic responses to drought stress

“…The few previous studies that examined drought response in cereal spikes either focused solely on the awn or on the entire spike as a collective unit [8–10, 50, 53, 54, 57, 58, 68]. Our goal in this study was to characterize the drought response of individual spike organs (awn, lemma, and palea) in barley during the early stage of grain filling and to compare those responses with that of a vegetative organ (i.e., the fifth leaf).…”

The contribution of the awns of bread wheat (Triticum aestivum L.) to grain filling: Responses to water deficit and the effects of awns on ear temperature and hydraulic conductance

“…Jiang et al, 2006;Li et al, 2006;Olugbemi et al, 1976), their contribution to grain filling is not well known, and even controversial (e.g. McKenzie, 1972;see Tambussi et al, 2007 and references therein).…”