A Protective Role for Accumulated Dry Matter Reserves in Seeds During Desiccation: Implications for Conservation

Abstract

We live in an unprecedented time of plant biodiversity loss. Current extinction rates are three orders of magnitude faster than extinction rates measured over geologic time. Similarly, 30% of plants are threatened with extinction. This information is startling when one considers that humans depend on plants for life. Fortunately, several systems exist to conserve plant genetic diversity. Seed storage within genebanks represents the most widely utilized system for plant conservation. One advantage of genebanking is that seed viability can be maintained for decades to centuries. Seeds must tolerate extensive post-harvest drying (5–10% moisture content) and cold (−18 °C) to maintain shelf-life for these periods. However, many important tropical seeds cannot tolerate drying to these levels thus precluding genebank storage. But what separates desiccation-tolerant from sensitive seeds? Previous hypotheses related to protective roles for certain sugars and proteins or the formation of intracellular glasses are insufficient. For instance, desiccation-tolerant and desiccation-sensitive seeds accumulate the same types and levels of protective molecules. Likewise, desiccation-sensitive seeds form intracellular glasses if dried sufficiently. Alternatively, using seeds of a tropical palm as a model, our work identifies a critical minimum level of cellular dry matter accumulation for appropriate desiccation tolerance. Our model suggests that cells must acquire >35% dry matter reserves to avoid lethal desiccation stress prior to genebanking. This level of dry matter accumulation may serve as a reference point for future breeding efforts or manipulation of the seed developmental program to enhance desiccation tolerance.