Carbon Isotope Ratios in Ear Parts of Triticale

Abstract

Four triticale (xTriticosecale Wittmack) genotypes were grown under rainfed conditions with limited irrigation support in Lleida in northeast Spain. For each variety, samples consisting of 10 tillers with half-sterilized spikes were taken three times from anthesis to maturity. Carbon isotope ratios (513C) were then determined in water extracts from ear bracts (glumes, paleas, and lemmas), awns and flag leaves, and in powdered kernels. For the half-sterilized spikes, carbon isotope analysis was carried out separately in bracts and awns from fertile and nonfertile spikelets. The 613C in the water-soluble fraction of awns, glumes, and glumells from fruitless spikelets was significantly higher than that from fertile spikelets sampled at mid-grain filling. Differences in 613C among sterile and fertile spikelets were not significant in samples taken a few days after anthesis or at maturity. These results are in accordance with some degree of refixation by awns and ear bracts of the CO2 respired by grains during grain filling. There was progressively higher 63C from flag leaf blades to awns, glumes, and glumells. This variation in 613C along plant parts may be caused by differences in the ratio of assimilation rate to C02-diffusive conductance. Values of 613C of mature kernels were between the values at anthesis and mid-grain filling for the water-soluble fraction of flag leaves and inner bracts and were fairly similar to those of glumes and awns. Conservation of respired CO2 by an efficient recycling mechanism in fruit could provide a significant source of C for yield productivity (2). Cereal crops have received the greatest attention in this regard (4, 9, 16). For example, Kriedemann (9) studied the refixation of respired carbon dioxide in whole ears by measuring CO2 evolution of ears in a C02-free environment in the light and dark, reporting that evolution was lower in the light and suggesting that refixation was taking place. However, evidence of bracts and awns refixing the intemal CO2 released from growing grains remains to be elucidated.Carbon isotope ratios of plant tissue have been proposed as an indicator not only of water use efficiency or photosynthetic metabolism (5) but also of recycling of respired CO2 in

Immunocytochemical localization of phosphoenolpyruvate carboxylase and photosynthetic gas-exchange characteristics in ears of Triticum durum Desf.

“…In ears, PEPCase may be required, together with PEP, to recapture respiratory CO2 (Wirth et al 1977), a high proportion of which is reported to be refixed by the developing grain (Kriedemann 1966;Watson and Duffus 1988;Caley et al 1990) and another (probably lesser) proportion by the surrounding ear bracts (Singal et al 1986;Araus et al 1992;Araus et al 1993). In a recent review, Blanke and Lenz (1989) point out that PEPCase and possibly PEP carboxykinase refix parts of this accumulated CO2 in the cytosol via 13-carboxylation of PEP.…”

“…When the water-soluble fraction of ear bracts (i.e. current photoassimilates) rather than the total dry matter was analysed by carbon isotope composition (most of which probably comes from photoassimilates of vegetative organs), values of 813C for ear bracts from triticale (Araus et al 1992) and durum wheat (Araus et al 1993) were consistent with the presence of a C3-C4 intermediate photosynthesis pathway; however, this seems to be due to low diffusion of carbon dioxide through the bracts (Araus et al 1993). Recent experiments from our group on pulse labelling with 14C on ears of durum wheat and barley show insignificant labelling of C4 acids by photosynthetic tissue of ear parts when feeding 14C02 (data not shown).…”

Variations in the 13C/12C ratios of modern wheat grain, and implications for interpreting data from Bronze Age Assiros Toumba, Greece

“…From the data in Table 1 it appears that much of the 0.3 to 0.7‰ variation in (Abbad et al, 2004;Araus et al, 1992;Blum, 1998;Bort et al, 1996;Plaut et al, 2004). Much of the carbon may be derived from photosynthetic fixation occurring during grain filling, which utilises both atmospheric CO 2 and internally-respired CO 2 .…”

Carbon isotope discrimination of two-rowed and six-rowed barley genotypes under irrigated and non-irrigated field conditions

“…For personal use only. Dakheel et al 1994), common wheat (Botwright et al, 2002), durum wheat (Araus et al 1998) and triticale (Araus et al 1992). A proposed explanation for this ranking is that the CO 2 conductance of ear parts (awns and ear bracts) is fundamentally lower than the stomatal conductance for the flag leaf (Araus et al 1991).…”

“…Differences in physiological activity of different ear parts may explain some of the differences observed in grain filling between the two barley types. However, little attention has been given to the study of physiological differences and carbon/water metabolism between ear parts in C 3 cereals (Araus et al 1992).…”