Chemistry Reference
In-Depth Information
All phases are different in water content at tissues of newly developed seed [59] (Water
content increases in cell division phase together with total seed weight. In phase of cell
elongation water content is stable, but dry matter of seed increase thanks to stored reserves.
Quick decrease of water content characterizes maturation phase, till the level 10 - 15 % of
water, specifically for each plant species.
Desiccation phase is typical for orthodox seeds (mostly plants from temperate climate) and
necessary for overcoming adverse environmental conditions, evolved as adaptive
mechanism in time of plant phylogeny. Thanks to lower water content orthodox seeds can
be stored at normal conditions longer time without loss of theirs quality. This is very
important exactly for seeds of plants used as agriculture crops.
Development of seeds and fruits is controlled by phytohormones [57]. After fertilization
mainly cytokinins come to action to influence cell division in early stage of seed
development. Gibberellins are connected with phase of reserves deposition, when keep
endosperm in liquid state thanks to activation of α-amylase [81, 75]. Auxins control cell
elongation of newly formed seed. Influence of negative osmotic potential of surrounding
tissues, which prevent the embryo to next development [89], is substituted with increase of
absicic acid (ABA) level. ABA suppresses gibberellins' activity in the synthesis of -amylase
and by this mechanism prevents premature germination of new seed [13]. On the end phase
ABA level decrease too, together with decrease of water, when the seeds are becoming
quiescent. Regulation of ABA level in mature seed determines quiescent or dormant state of
seed [79]. During the seed development on mother plant the environmental conditions can
change and abiotic stress can appear. Seed development can be aborted in this case, when
environmental conditions are very adverse. In early phase of development the embryo is
very sensitive to lack of water [29]. Decrease of water potential more than above -1.6 MPa
[73] can imply damage of embryo or other tissues. Less favorable environmental conditions
can mean only formation of smaller seed, with smaller embryo or storage reserves, but
smaller seed size is obviously associated with shorter seed survival [68].
Seed quality is affected by location of seed on mother plant and related with flux of
assimilates to seeds. Each seed lot is heterogeneous group of seeds with similar
characteristics thanks to the same origin. But if we evaluate each seed in detail, we can find
differences between seeds.
Seed quality is influenced by sink: source ratio too. Buds, flowers and siliques of winter rape
fall down more from lateral branches than from terminal, which is more preferred [62].
Similarly fruit size decline from margin to the centre of capitulum as the result of resource
competition [86, 1]. Found that direct part of sunflower head is supplied from direct leaves.
[5] confirm different content of oil, fatty acids and total tocopherol content in different seeds
in sunflower head. We can suppose that similar differences exist between each seed in direct
content of stored reserves and in synthesis and reduction of phytohormones and other
metabolites. Stress conditions in time of seed development can these differences enhance.
All levels of adverse environmental conditions imply induction of stress response.
Acclimation starts as the first step, when mechanism of protective compounds synthesis
