Shut your eyes and picture a seed. It is a miniature undeveloped plant containing stored food and an embryo, enclosed in a protective coat.
Cecilia’s research focuses on key events in seed development and dormancy, and how they relate to genetic changes. She also investigates how gymnosperms have evolved a simpler ovule and seed structure than angiosperms.
Germination is the process that turns a seed into a plant. Seeds require water and oxygen for germination. When they have this, they start to grow a root and shoot. They then use photosynthesis to harness the sun’s energy for growth. Once a seed has gone through all of these processes it is considered to have completed germination.
During germination, the seed is hydrated and enzymes inside are activated. These enzymes help to break down the tough coating of the seed and also convert insoluble food to soluble form. After a seed is fully hydrated it starts to grow a small root called a radicle and then shoots or plumules.
Different seeds have different optimum temperatures for germination, so they will only germinate under the right conditions. In addition to temperature and water, a seed also needs oxygen in order for it to respire. In some cases, if the seed is buried too deep in the soil then it may not be able to access enough oxygen and will never germinate.
Dormancy is an adaptive strategy of higher plants to withstand adverse environmental conditions by pausing seed growth and development. It is controlled by both genetic and environmental factors but has a wide range of biological responses ranging from the germination promoting hormone abscisic acid to the gibberellins which promote seed vigour and germination in some species.
Physiological dormancy (PD) is the most widespread class of dormancy and is found throughout the phylogenetic tree, from gymnosperms and basal angiosperms through to core eudicot Rosids. It is a key feature of seasonal dormancy cycling in seed soil banks and is the most likely candidate for allowing seeds to delay germination until favourable germination conditions appear.
Despite its wide occurrence, the biological mechanisms that control PD remain unknown. Several molecular studies have shown that there is considerable variation in the response to different environmental cues, particularly those related to slow seasonal change (e.g. temperature) which are integrated by seeds over time and can significantly alter dormancy status.
Seed dispersal is the primary route by which plant seeds move across landscapes. Abiotic dispersal mechanisms (e.g. wind) can have significant impacts on distances seed moves but biotic dispersal also significantly influences landscape structure and patterns of species distributions and biodiversity.
Seeds have adapted to be dispersed by animal vectors such as birds and mammals, with some having fleshy appendages that entice animal dispersers to consume them; others are able to attach to fur or feathers or to pass through digestive systems. These adaptations enable the spread of some species across large areas whereas other species remain restricted to their local habitats.
Intraspecific variation in dispersal is common, regardless of the mechanism by which seeds are moved. For abiotically dispersed plants, phenotypic factors such as fruit size and the height at which fruits are released are important for how far seeds are moved. For biotically dispersed plants, the preference of frugivore assemblages for different canopy heights can influence how far seeds are moved (Zwolak 2018). Averaging over space or time essentially removes any rare or location-dependent events that might impact dispersal distances – e.g. steep hill inclines or specific weather conditions.
Seeds contain an embryo and a store of food reserves wrapped in a protective shell. When conditions are right, most seeds “wake up” and start growing roots and leaves to become a plant. This process is called germination and is one of the keys to plant biodiversity. Seeds can only grow if they have the correct amount of water and oxygen. To achieve this, they need to absorb these nutrients from their environment through the seed coat and an area in the middle of the seed known as a micropyle.
Phytohormones such as gibberellins (GA) and abscisic acid (ABA) help break seed dormancy and promote germination. However, the ratio of GA to ABA controls the process and determines whether a seed will grow or not.