Effect of salicylic acid on germination of Ocimum gratissimum seeds induced into dormancy by chlormequat
Abstract
The present work is to study the influence of salicylic acid in concentrations ranging from 0 to 1 mM on the germination of seeds of Ocimum gratissimum. This work is performed on non-dormant seeds and seeds induced into dormancy by chlormequat at a concentration of 550 mg / L. The study shows that salicylic seems to play an important role in acid stimulation of germination of non-dormant seeds that role varies with the concentration of salicylic acid: low concentrations lead to a small inhibition of germination whereas higher concentrations (greater than 0.5 mM) lead to stimulation of the germination. Furthermore, we found that the SA causes a dormancy dormant seeds. This dormancy is partial and slow at low concentrations (0.05 and 0.25 mM) and becomes complete when the concentration of SA increases. In this case, dormancy is very fast since the germination rate becomes important from the 3rd day.
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Introduction
Germination, transitional stage between the dry seed stage and the emergence of the radicle[1] is possible when the physiological and environmental conditions are favorable (no primary dormancy, oxygen availability, adequate temperature ...). Dormancy can be defined as blocking the germination of intact and viable seed despite favorable environmental conditions[2].
Changes in these factors influence the levels of endogenous plant growth regulators (PGR)[3]. Many chemically substances can be used to break seed dormancy. It has been suggested that at an acid pH, substances like cyanide, nitrate, salicyl hydroxamic acid, and aliphatic monocarboxylic acid, are physiologically active as dormancy-breaking compounds[4 ,5]. The positive relationship between lipophilicity and dormancy-breaking capacity of compounds like alcohols, aldehydes, esters and ketones has been demonstrated [6].
It has also been suggested that dormancy is due to decreased oxygen diffusion to embryos, and activation of the oxidative pentose phosphate pathway has been proposed to be the main step leading to germination [7]. However, convincing evidence supporting this hypothesis is missing [8].
Abscisic acid (ABA) plays an important role in induction and maintenance of seed dormancy [9,10,11,12]. During germination, gibberellin (GA), induces embryo growth and, therefore, stimulates the germination process. At the beginning of germination, ABA and GA act in an antagonistic manner [13,7]. Removal of the effects of ABA is essential for GA to function during germination [12]. In barley seeds, It was previously proposed that dormancy is determined by at least three factors, synthesis of the plant hormone abscisic acid (ABA) following imbibitions, (n) the lack of breakdown and/or removal of ABA, and (m) changes in sensitivity to ABA [12]. If this hypothesis is correct, various chemically dissimilar compounds that break dormancy might interfere with at least one of the aforementioned factors.
Several authors have indicated that the salicylic acid which is an endogenous growth regulators;has a stimulatory effect on germination[14], and that this effect depends on its concentration [15,16].
Furthermore, chlormequat is a plant growth regulator (PGR) which is applied to change the physiological processes of the plant [17],in particular to induce germination inhibition [18].
The present work was to evaluate the effect of AS on the dormancy of seeds induced secondary dormancy by chlormequat taking as model the seeds of Ocimum gratissimum.
Conclusion
According to this work, we can conclude that the chlormequat affects negatively the germination of Ocimum gratissimum seeds, but the application of increasing concentrations of SA on these dormant seeds stimulates germination. We have also shown that the application of high concentrations (0.5-1mm) of SA on non-dormant seeds, stimulate the germination.