Transient Carbon Reserves in Barley: Malate, Sucrose and Starch Are the Main Players, Their Quantitative Involvement Being Light Intensity Dependant

Abstract

Under natural environment plants experience different light intensities which can affect photosynthesis and consequently the availability of carbohydrates for daytime growth and their transient storage to supply night growth. We grew a spring barley cultivar, Propino, under three different light intensities under warm days and nights, and evaluated the spatial and diurnal adjustments occurring in the transient carbon stores. Leaves under high light at the end of the day accumulated mainly sucrose (30%) and malate (35%), with lower content of hexoses (5%), starch (15%) and fructans (15%). Under low light, plants presented reduced photosynthesis, with lower metabolite contents at end of day. The malate represented 51% of the total carbon accumulated at end of the day, at the expense of sucrose (12%), other metabolite contributions remaining similar to high light. The percentage of metabolites consumed at night was similar for all light intensities with around 75% of the sucrose and starch being mobilized whilst malate and fructans were only partially mobilized with 56 and 44%, respectively. Altogether, sucrose and malate were the main contributors of the total carbon used at night by barley plants, sucrose being predominant under high light (35% vs. 27%), but malate being the major metabolite used under low light with 40% of the total carbon consumed. Interestingly, light intensity also influenced the location of the C transient stores, the plants under low light prioritizing the accumulation of the metabolites, mostly malate, in the youngest tissues. Therefore, light influences quantitatively, but also qualitatively and spatially the carbon stores in the spring barley cv. Propino, suggesting a tight regulation of the primary metabolism.

Analysis of durum wheat photosynthetic organs during grain filling reveals the ear as a water stress-tolerant organ and the peduncle as the largest pool of primary metabolites

“…This could be reinforced by the aforementioned increase in starch synthesis in these organs, which is only activated when the C status is optimal in the cell (Kolbe et al 2005). Malate content, which is another transient C reserve also involved in respiration (Finkemeier and Sweetlove 2009;Barros et al 2020), was not affected in the ear bracts by water stress or it was even increased at later stages (Fig. 5, Supplementary Fig.…”

“…Intriguingly, malate content was unique in remaining unaltered in ear organs under rainfed conditions. Nevertheless, its content was lower than in the non-ear organs and further research is required to discover whether ear organs preferably use other C intermediates (Finkemeier and Sweetlove 2009;Barros et al 2020). In contrast, the ears redirected more C towards starch than other organs, as discussed above.…”

Ear metabolism and genotype-by-environment interaction in field-grown durum wheat: identification of novel traits for crop improvement

“…This could be supported by the aforementioned increase in starch synthesis, which would be activated when the C status is optimal in the cell by high levels of suc which, through the signal molecule trehalose 6-phosphate, would lead to the posttranslational redox activation of ADP-glucose pyrophosphorylase (Kolbe et al, 2005). Malate, another transient C reserve, also involved in respiration (Barros et al, 2020), was reduced in several organs under rainfed conditions, including the awns. However, it was not affected or even increased in ear bracts, supporting their better C status.…”