Abstract
Seed dimorphism (polymorphism) can be defined as the production of two (or more than two) different types of seeds by a single individual. The seeds may be different in morphological and/or physiological aspects. Seed dimorphism or polymorphism is found in many plant species of Asteraceae, Poaceae, Brassicaceae and Chenopodiaceae. Dimorphic seeds typically differ in the presence/absence of dispersal structures (e.g., pappus, trichomes). In members of Asteraceae, peripheral achenes are persistent, large, dormant and sensitive to light, temperature, water and salt; while central archenes are dispersible, small and non-dormant. Dormant seeds or the seeds which are sensitive to environmental factors are an essential part of a seed bank. Seedlings from dimorphic seeds differ at the early stage (40 days old for Hedypnois cretica), but the difference decreases quickly for H. cretica(no difference at 70 days old), while the difference persists during the life cycle for Atriplex Sagittata. Both kinds seedlings produce dimorphic seeds in next generation. Environmental factors such as water, salt, nutrient and density stress affect the ratio of dimorphic seeds. Genetic factors also affect this ratio with a heritability factor of 0.2～0.5. Seed dimorphism is a quantitative genetic character and is under the control of more than two genes (locus). In order to explain the causes of seed dimorphism, two models are proposed based ecological and ontogenetic constraints: bet-hedging (high risk/low risk) strategy and ontogenetic model. Dimorphic seeds from different individuals of the same species differ considerably in their structure, germination/dormancy characters, responses to environmental stresses, early seedling growth and genetic aspects. Generally, seed dimorphism (polymorphism) is a consequence of long-term (evolutionary) interactions between environmental and genetic factors - an ecological adaptation to variable environment. The underlying mechanisms of seed dimorphism are very complex and unclear. Four guidelines are proposed for future studies: biotechnology procedures to identify genetic mechanisms of seed dimorphism, molecular biology techniques to identify phytohormone differences in dimorphic seeds, the current ecophysiological studies to understand the relative importance of various environmental factors and life cycle research.
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Claims 8
Claim · model-written summary
Peripheral Asteraceae achenes are persistent, large, dormant and sensitive to environmental factors, whereas central ones disperse and lack dormancy.
- Taxon
- AsteraceaeAsteraceaee0
- Organ / stage
- achenese0
- Outcome
- persistent, large, dormant and sensitive to light, temperature, water and salte0
- Comparator
- central archenese0
Verbatim
e0“In members of Asteraceae, peripheral achenes are persistent, large, dormant and sensitive to light, temperature, water and salt; while central archenes are dispersible, small and non-dormant.”
Claim · model-written summary
Hedypnois cretica seedlings from dimorphic seeds differ at 40 days but not at 70 days.
- Taxon
- Hedypnois cretica
Hedypnois rhagadioloidese0 - Organ / stage
- Seedlingse0
- Outcome
- differencee0
- Direction
- differe0
- Value
- 40 days olde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Seedlings from dimorphic seeds differ at the early stage (40 days old for Hedypnois cretica), but the difference decreases quickly for H. cretica(no difference at 70 days old)”
Claim · model-written summary
Atriplex Sagittata seedlings from dimorphic seeds differ throughout the life cycle.
- Taxon
- Atriplex Sagittata
Atriplex sagittatae0 - Outcome
- differencee0
- Direction
- persistse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the difference persists during the life cycle for Atriplex Sagittata.”
Claim · model-written summary
Both seedling types produce dimorphic seeds in the next generation.
Verbatim
e0“Both kinds seedlings produce dimorphic seeds in next generation.”
Claim · model-written summary
Water, salt, nutrient and density stress change the ratio of dimorphic seeds.
Verbatim
e0“Environmental factors such as water, salt, nutrient and density stress affect the ratio of dimorphic seeds.”
e1“Dimorphic seeds typically differ in the presence/absence of dispersal structures”
Claim · model-written summary
Genetic effects on dimorphic seed ratio have reported heritability of 0.2～0.5.
Verbatim
e0“Genetic factors also affect this ratio with a heritability factor of 0.2～0.5.”
e1“Dimorphic seeds typically differ in the presence/absence of dispersal structures”
Claim · model-written summary
Seed dimorphism is described as a quantitative trait controlled by more than two loci.
Verbatim
e0“Seed dimorphism is a quantitative genetic character and is under the control of more than two genes (locus).”
e1“Dimorphic seeds typically differ in the presence/absence of dispersal structures”
Claim · model-written summary
Dimorphic seeds from individuals of one species vary in morphology, dormancy, stress response, early growth and genetics.
Verbatim
e0“Dimorphic seeds from different individuals of the same species differ considerably in their structure, germination/dormancy characters, responses to environmental stresses, early seedling growth and genetic aspects.”