A response of the imbibed dormant red rice caryopsis to biotic challenges involves extracellular pH increase to elicit superoxide production

Abstract

Seeds often survive in the soil in a dormant state, but their persistence is endangered by micro-organisms that could feed on them. Seed–microbe interactions in the soil are, however, poorly understood. We used dormant caryopses of red rice to study the defence response induced by pronase, a mixture of proteases secreted by Streptomyces griseus, a non-pathogenic bacterium. Pronase was shown to activate the plant immune reaction, indicating that its activity was recognized as a potential microbial attack. The defence reaction included extracellular alkalinization and superoxide production, and the former was necessary to activate the latter, since buffering at pH 6 inhibited the oxidative burst. Alkalinization was sufficient to trigger the oxidative burst, as superoxide production increased when caryopses were incubated in buffered solutions of increasing pH without pronase. Release of proanthocyanidins was observed, with or without pronase. These diverse mechanisms are hypothesized to cooperate in reinforcing seed protection. Finally, time profiles of superoxide production by dormant and non-dormant red rice caryopses during imbibition did not support a relationship between extracellular superoxide and dormancy breaking or germination. Thus, the role of this reactive oxygen species in red rice imbibed caryopses appears to be essentially aimed at defence against attacks by challenging micro-organisms.

The Caryopsis of Red-Grained Rice Has Enhanced Resistance to Fungal Attack

“…This is a physical-chemical defence, necessarily arrayed on the exterior of the seed, that favours long-term persistence in the soil [ 38 ]. In red rice, a red-grained, weedy type of rice whose spikelets (caryopses covered by the hull) can persist dormant in the soil for one or more years, accumulation of PAs and PA-associated compounds seems to be an important defence strategy providing protection against biotic challenges [ 41 ]. Skadhauge et al [ 10 ] also observed a moderate effect of extracts of PAs-accumulating barley testa layers on Fusurium growth, and concluded that the PAs and catechin in the testa layer of the mature barley grain are part of a passive resistance mechanism, acting as a physical barrier against pathogen attack.…”

A Travel through Landscapes of Seed Dormancy

“…Specifically, ROS that interact with wall polysaccharides and promote cell elongation in germinating seeds are produced in the cell walls of growing embryos at the time of radicle protrusion. ROS also have an important role in defence against attacks by challenging microorganisms [188,189].…”

Effects of salinity stress on proline content and expression ofΔ1-pyrroline-5-carboxylate synthaseandvacuolar-type H+subunit Egenes in wheat

“…Wheat ( Triticum aestivum L.) is the third most significant cereal in the world (Horvath et al ., 2009; Clifton and Keogh, 2018; Ghotbzadeh and Gianinetti, 2018; Wulff and Dhugga, 2018). The higher level of ploidy and the complexity of the hexaploid wheat genome have increased its physiological and ecological flexibility in comparison with the tetraploid and diploid ancestors (Dubcovsky and Dvorak, 2007; Feldman et al ., 2012).…”