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

Kallyne A Barros,John Finnan,Alberto A Esteves-Ferreira,Helena Meally,Ronan Sulpice,Susanne Barth,Masami Inaba

doi:10.3389/fpls.2020.00209

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.

Highlights

Plants grown in the natural environment experience variation in both light quality and quantity
Plants grown under HL showed the fastest development, reaching three-leaf stage at 14 days after sowing (DAS), while plants grown under ML took 16 DAS and plants grown under LL 18 DAS
Photosynthesis was significantly reduced in plants under ML and LL compared to HL, while gs, Ci, E showed higher values only under HL, leading to a much lower water use efficiency (WUE) in these plants (Table 2)

Summary

Introduction

Plants grown in the natural environment experience variation in both light quality and quantity. The development of leaf primordia and flowering responses in barley are very sensitive to light intensity, quality and day length. Leaf development and Carbon Transient Stores in Barley flowering time are faster under higher light intensities and longer days, requiring far-red light as well (Aspinall and Paleg, 1963; Paleg and Aspinall, 1964). Light intensity and photoperiod can directly affect the light harvesting complexes and lead to changes in the abundance of chlorophyll and fluorescence parameters (Bailey et al, 2001; Kouril et al, 2013). Light intensity effects in barley include changes in chlorophyll a/b ratio within light-harvesting complexes, the levels of Qb and Cytf and electron transport rate (De la Torre and Burkey, 1990). In Arabidopsis, the activation state of Rubisco activase, which is controlled by the redox state of the cell, is responsive to light intensity, and the proper regulation of the activity of Rubisco activase is crucial to acclimation to light fluctuation and optimal growth (Carmo-Silva and Salvucci, 2013)

Methods

Results

Conclusion