Gas exchange of ears of cereals in response to carbon dioxide and light

Abstract

One cultivar each of spring wheat (Triticum aestivum L. cv. Arkas), oat (Avena sativa L. cv. Lorenz), and barley (Hordeum vulgare L. cv. Aramir) was chosen in order to study the relative contributions of individual bracts to the gas exchange of whole ears. The distribution and frequency of the stomata on the bracts were examined. Gas exchange was measured at normal atmospheric CO2 (330 μbar) and at high CO2 (2000 μbar) on intact ears and on ears from which glumes or lemmas and pleae (wheat and oat) or awns (barley) had been removed.The relative contribution to the gas exchange of the whole organ is highest for the awns of barley ears. In wheat, the contribution of the glumes is slightly higher than that of the inner bracts before anthesis. Two weeks after anthesis the inner bracts contribute more than the glumes. This tendency of increasing importance of the inner bracts is also found in oat ears, but the relative amount of CO2 uptake by the glumes is higher than in wheat. These changes during ontogeny result from the better supply of light to the inner bracts caused by opening of the ears' structures during grain filling, which in part compensates for the decreasing photosynthetic capacity.The ratio of the photosynthesis rate at high CO2 to that at normal CO2 is lower for the glumes of oat and for the awns of barley than for the other bracts.

Photosynthesis in non‐foliar tissues: implications for yield

“…Although stomata are almost absent in the growing endosperm, suggesting limited gas-exchange capacity, immunocytochemical analysis showed chloroplasts and Rubisco co-localization in the green pericarp with elevated photosynthetic capacity (Kong et al, 2016), which can account for up to 42% of the total photosynthetic activity of the ear (Evans and Rawson, 1970). Recent work reported that genes specific for the C4 pathways such as PEPC, NAD-ME and NADP-MDH are expressed in the cross and tube-cell layer of the pericarp (Rangan et al, 2016), agreeing with earlier studies that had already suggested the presence of C4 or C3-C4 intermediate metabolism in the ear (Ziegler-J€ ons, 1989;Imaizumi et al, 1990;Li et al, 2004;Jia et al, 2015), potentially induced under waterstress conditions. On the other hand, the following observations suggest limited evidence for a C4 pathway in the green pericarp and other ear organs: (i) oxygen sensitivity of CO 2 assimilation rate of the ear (increased by up to 45% under conditions of 2% O 2 ; Tambussi et al, 2005;Tambussi et al, 2007); (ii) high rates of CO 2 assimilation through the CBC rather than conversion into C4 malate or aspartate (Bort et al, 1995); and (iii) a lack of the specific C4 anatomy (Tambussi et al, 2005), although future analyses are required to confirm this and it remains a topic of debate.…”

Developmental Changes in Composition and Morphology of Cuticular Waxes on Leaves and Spikes of Glossy and Glaucous Wheat (Triticum aestivum L.)

“…Besides functioning as inflorescence and protectors of the growing grains, spikes play a major role in the production of assimilates for grain filling [ 34 ]. To this end, there is no information available on changes of wheat spike wax constituents with different growth stages.…”

Wheat and barley cultivars show plant traits acclimation and increase grain yield under simulated shade in Mediterranean conditions

“…The relationship between leaf area and grain yield was weaker in barley, whose leaves tend to be smaller than wheat. While flag leaf photosynthesis seems important for grain filling in wheat (Thorne, 1965), ear (spike and awns) photosynthesis does for barley (Biscoe et al., 1975; Ziegler‐Jöns, 1989), but this was not measured in our study. Further studies should assess the effects of shading on ears, especially in Mediterranean conditions, where the shading of spikes and awns could reduce to a larger extent grain yield than shading flag leaf (Merah & Monneveux, 2015).…”