Cereal Husks: Versatile Roles in Grain Quality and Seedling Performance

Gideon Grafi,Jeevan R. Singiri

doi:10.3390/agronomy12010172

Gideon Grafi, Jeevan R. Singiri

Open Access

https://doi.org/10.3390/agronomy12010172

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Abstract

The seed is the fundamental unit of the dispersal of dry, dehiscent fruits, in which the fruit splits open at maturity to allow for seed dispersal. However, dry fruits may be indehiscent and therefore represent the dispersal unit (DU). Cereals possess a one-seeded fruit, whereby the seed coat and the fruit coat are fused together to generate the caryopsis. This caryopsis may be covered by floral bracts to generate two types of DUs, namely florets, whereby the caryopsis is enclosed by the lemma and the palea (e.g., Avenasterilis) or spikelet, whereby the floret(s) is further covered by the glumes (Triticum turgidum var. dicoccoides). Here, we highlight the dead coverings enclosing the caryopsis in cereals, namely the husks as an integral component of the dispersal unit that play multifaceted roles in grain biology. Thus, besides protection and dispersal means, the husks function as a rich maternal supply of proteins and metabolites for enhancing growth and development, combat potential pathogens as well as confer tolerance to abiotic stresses. These attributes might have broad implications for crop performance, plant population dynamics and diversity in ecological systems, and for conservation of genetic resources in seed banks.

Highlights

The dispersal unit (DU) in cereals can be composed of the fruit only (e.g., Sporobolus species, commonly called ‘dropseeds’), florets in which caryopses are enclosed by lemma and palea (e.g., Avena species), spikelets where the florets are further enclosed by the glumes (e.g., Triticum turgidum var. dicoccoides; Hordeum spontaneum) and the whole spike may serve as a DU (Aegilops species)
The germination of Japonica rice was higher for intact seeds than de-husked seeds [25], while seedlings of Brachypodium hybridum emerged from husked grains display better growth than seedlings of de-husked grains [26]
Seeds represent the fundamental unit of dispersal in higher plants, yet a large variety of dispersal units have been developed where the seed is further enclosed by maternally derived dead organs, such as pericarps or floral bracts in cereals

Summary

Introduction

Seed quality is the sum of all characteristics that contribute to seed fate and performance. It is commonly determined by several parameters including genetic, physical and physiological qualities and storability [1]. Cereals have evolved unique and variable DUs in which the fundamental unit is the caryopsis, a fruit containing a single seed, which can be further enclosed by the dead floral bracts, lemma, palea and glumes. The DU in cereals can be composed of the fruit (caryopsis) only (e.g., Sporobolus species, commonly called ‘dropseeds’), florets in which caryopses are enclosed by lemma and palea (e.g., Avena species), spikelets where the florets are further enclosed by the glumes While the term dispersal unit highlights its major role in seed dispersal, it carries multiple functions including embryo protection, moisture adsorption, light filtering, regulation of seed respiration and seed dormancy [9]

The Role of Husk and Other Dead Coverings in Seed Biology and Ecology

Husks Function as Long-Term Storage for Beneficial Substances

The Husk and Storability of Seeds in Seed Banks

Findings

Conclusions