Chemistry Reference
In-Depth Information
processes that determine dormancy and germination. Abscisic acid inhibits germination and
gibberellins and brassinosteroids promote germination.
The first phase of germination
If the seed gets into the soil initially only water uptake exist,
which start the first stage of germination, i.e. anaerobic processes, which is separated from
embryo germination and for which there isn't need oxygen. This phase is mostly regulated
by the amount of water in the seed, temperature and takes 24 -36 hours. Exactly imbibition
phase is regulated only by differences in water potential between seed and soil. For
example, in wet salted soil amount of water accessible for seed can be low, thanks to low
water potential of soil than seed. Anaerobic respiration is predominant in this phase - the
biological activity without oxygen (for example alcohol dehydrogenase activity).
The processes in the first phase can be affected by storage method, which affect the
structural changes in the seed. Seeds of some varieties may then quickly absorb water, but in
the case of drought loose of water is quicker too.
But transition from phase to phase is not sharp, for example embryo of maize seed can be
highly hydrated and endosperm have low amount of water. On the other hand, activation of
mRNAs in wheat seed was detected 2 hour after start of imbibition.
The second phase of germination
is also under influence of the seed storage way,
prolonged storage significantly affect mainly structural changes in the seed membranes and
reduced enzyme activity. The manifestation of this changes may be, for example, decrease of
germination energy (early germination) resulting in a field conditions in the low field
emergence). In this phase begin - aerobic respiration system, citrate cycle, oxidative
phosphorylation, and rapid activity of the mitochondria and lot of other biochemical
processes. The visual germination process begins. What happens during germination?
Metabolic activity in seed increases sharply, lipase, a-amylase, protease and peptidase -
hence they are broken down starches, proteins, lipids, and their metabolic products are
transported through the scutellum to the sprouting embryo - germination begins.
Prerequisite for good germination is low ABA levels, which resulted in the loss of dormancy
and increase the concentration of gibberellins thus promoting hormones, which creating a-
amylase that breaks down starch.
Germination process according to the latest information also contributes brassinosteroids.
Interactions between abscisic acid (ABA), brassinosteroids and gibberellins (GA) determine
the level of dormancy and germination energy. These plant phytohormones (GA) with
many functions in the plant during germination and seed sprouting are produced and
throught label penetrates the endosperm to the aleurone layer, where it promotes the
synthesis of α-amylase, thus accelerating the starch breakdown. The ratio of starch,
damaged starch, lipids and proteins like macro-elements can affect the germination rate.
Water uptake and efficiency of the water utilization are essential for enzyme activation, i.e.
for use of reserve seed storage material [23, 24, 25, 26]. This trait has also influence on the
root development at the begin of the vegetation period, but there is large variability in water
use efficiency of seeds between different species, cultivars from different conditions (seed
