Cereal Germination under Low Oxygen: Molecular Processes

Abstract

Cereal crops can differ greatly in tolerance to oxygen shortage under germination and seedling establishment. Rice is able to germinate and elongate the coleoptile under submergence and anoxia. This capacity has been attributed to the successful use of starchy reserves through a molecular pathway activated by sugar starvation and low oxygen. This pathway culminates with the expression of α-amylases to provide sugars that fuel the sink organs. On the contrary, barley and wheat are unable to germinate under anoxia. The sensitivity of barley and wheat is likely due to the incapacity to use starch during germination. This review highlights what is currently known about the molecular mechanisms associated with cereal germination and seedling establishment under oxygen shortage with a special focus on barley and rice. Insights into the molecular mechanisms that support rice germination under low oxygen and into those that are associated with barley sensitivity may be of help for genetic improvement programs.

Keywords: Hordeum spp.; Oryza spp.; anoxia; barley; germination; hypoxia; rice; submergence.

Figure 1

Possible mechanisms of rice and barley response to prolonged submergence. In rice, the anaerobic germination is regulated by hypoxia-dependent signaling and sugar starvation. The main upstream regulator of this pathway is CIPK15 which activates a signaling cascade culminating with expression of subfamily 3 α-amylase. In barley, GA biosynthesis is dampened under low O₂ and ABA synthesis and signaling are promoted. As a consequence, GA-dependent α-amylases may not be expressed. Results obtained with Arabidopsis suggest that ERF-VIIs promote seed dormancy and ABA sensitivity through ABI5 regulation. Image created with BioRender.com (accessed on 14 December 2021).