Essential Concepts & Key Facts
High-yield conceptual summaries for competitive exams and rapid revision.
- Seed dormancy is a physiological adaptation where viable seeds fail to germinate despite favorable moisture, temperature, and oxygen.
- Dormancy acts as an evolutionary bet-hedging strategy, preventing synchronous germination that could be wiped out by sudden frosts or droughts.
- The biochemical control of dormancy is governed by the hormonal antagonism between Abscisic Acid (ABA) and Gibberellins (GA).
- Abscisic Acid (ABA) induces and maintains dormancy, arresting embryonic cell division and protecting tissues against desiccation.
- Gibberellins (GA) break dormancy by triggering the synthesis of alpha-amylase, which hydrolyzes stored starch into glucose for the embryo.
- A high ABA-to-GA ratio maintains dormancy; environmental cues reverse this ratio to stimulate seed germination.
- Physical Dormancy (hardseededness) is caused by a water-impermeable seed coat (testa) rich in suberin, cutin, or lignin (e.g. legumes).
- Scarification breaks physical dormancy through mechanical abrasion, microbial breakdown, freeze-thaw cycles, or animal digestive acids.
- Physiological Dormancy involves metabolic constraints in the embryo, broken by environmental cues like cold moist chilling (Stratification).
- Photodormancy (light-sensitive germination) is regulated by Phytochrome, a pigment that converts to active Pfr upon absorbing red light (660 nm).
- Phytochrome prevents deeply buried seeds from germinating in total darkness, where seedlings would exhaust energy reserves before reaching light.
- Karrikins are organic molecules found in wildfire smoke that trigger rapid germination of dormant seeds in fire-prone ecosystems.
- Soil Seed Banks are underground reserves of viable dormant seeds that allow plant communities to regenerate naturally after wildfires or tilling.
- Orthodox Seeds can survive extreme drying (down to 5% moisture) and sub-zero temperatures, remaining viable for decades (e.g. grains, legumes).
- Recalcitrant Seeds (mango, avocado, rubber, jackfruit) cannot tolerate desiccation or freezing, lacking dormancy and germinating immediately.
- Russian scientists in 2012 regenerated fertile Silene stenophylla plants from 31,800-year-old seeds buried in Siberian permafrost.
- Judean date palm (Phoenix dactylifera) seeds excavated from the ancient Masada desert fortress in Israel successfully germinated after 2,000 years.
- Sacred lotus (Nelumbo nucifera) seeds recovered from ancient lakebeds in Pulantien, China, germinated after roughly 1,300 years of dormancy.
- Vivipary is the precocious germination of seeds while still attached to the parent plant, seen as a survival adaptation in mangrove species.
- Agricultural domestication historically selected against seed dormancy, favoring crops that germinate synchronously upon sowing.
- Pre-Harvest Sprouting (PHS) occurs in domestic wheat and barley when wet weather triggers premature on-stalk grain germination, damaging flour quality.
- Seed priming techniques (hydropriming, osmopriming) partially hydrate commercial seeds to accelerate rapid, synchronized field emergence.
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