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Title: EMBRYO-SPECIFIC GENE EXPRESSION IN MICROSPORE-DERIVED EMBRYOS OF BRASSICA NAPUS. AN INTERACTION BETWEEN ABSCISIC ACID AND JASMONIC ACID

Author
item Hays, Dirk
item WILEN, RONALD - UNIV OF SASKATCHEWAN, CAN
item SHENG, CHUXING - UNIV OF CALGARY, CANADA
item MOLONEY, MAURICE - UNIV OF CALGARY, CANADA
item PHARIS, RICHARD - UNIV OF CALGARY, CANADA

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: In plant canola, storage proteins deposited in the seed make up a large percentage of the storage reserves. These storage proteins are then used as energy for the germinating seedling. An understanding of the endogenous factors that regulate the deposition of storage proteins may help in the improvement of canola seed quality. To date, three factors are known to play a role in regulating the expression of the genes that encode storage proteins. These factors are osmotic stress, and the plant hormones abscisic acid (ABA and jasmonic acid (JA). In this study the induction of storage protein gene expression in canola embryos was studied to determine the possible interaction between ABA and JA. Addition of JA to embryos decreased the concentration of ABA required to maximally induce storage protein gene expression by ten fold. As well, an endogenous concentration of ABA was required for JA to have any effect on inducing gene expression when applied to embryos alone. The results from this study indicate that J (which is known to play a role in defense gene expression) may act to shorten the maturation time and reduce the time required for a seed to reach maturity via a mechanism that increases the embryo's sensitivity to ABA. They also suggest that JA may serve as an alternative to herbicides that are used to induce seed drying in canola prior to harvest.

Technical Abstract: The induction of storage protein gene expression in Brassica napus microspore-derived embryos (MDEs) was studied to determine the possible interaction between abscisic acid (ABA) and jasmonic acid (JA). Napin and oleosin transcripts could be detected sooner following treatment with ABA than JA, and ABA was more effective at a lower concentration than JA at inducing the expression of the two genes. Oleosin mRNA levels were greater following application of ABA than JA when the optimal concentration of each hormone was used. Treatment of MDEs with ABA plus JA resulted in a synergistic or additive induction of napin and oleosin mRNA accumulation, depending on the concentration of each hormone. Endogenous ABA levels were reduced by 10-fold following treatment with JA, negating the possibility that the observed synergism was due to JA-induced increase in ABA biosynthesis. JA did not significantly increase the uptake of 3**H-ABA from mthe medium into the embryos suggesting that the synergism was not due to a modulation in carrier-mediated ABA uptake by JA. Napin mRNA did not increase when JA was added to MDEs that had been treated with the ABA biosynthesis inhibitor, fluridone. In contrast, the addition of JA to MDEs that had increased endogenous ABA resulted in an increase napin and oleosin gene expression similar to that obtained when both hormones were added together.