Poster: Hormones

Abs # 590: Quantitative changes of brassinosteroids and mRNAs of their biosynthesis, metabolism and receptor genes during seed growth and germination of pea

Presenter:	Yokota, Takao , yokota@nasu.bio.teikyo-u.ac.jp
Authors	Yokota, Takao  (A)   Ueno, Masaaki  (B)   Takatsuto, Suguru  (C)   Takeuchi, Yasutomo  (B)   Nomura, Takahito  (A)
Affiliations:	(A): Teikyo University (B): Utsunomiya University (C): Joetsu Univeristy of Education

To investigate the roles of brassinosteroids (BRs) during seed growth/maturation and germination, we quantified the endogenous BRs and the transcripts of BR synthesis (LKB, LK, DWF4, CPD, DDWF1, D), metabolism (BAS1) and receptor (LKA) genes in seeds and seedlings of pea (Pisum sativum L.). As pea seeds rapidly grow, the levels of brassinolide (BL) and castasterone (CS) were increased but, in fully-expanded seeds, were decreased drastically, indicating BL and CS are important for seed growth. In support of this, the D expression was increased in conjugation with the increase of CS and BL. 6-DeoxoCS was accumulated high in fully expanded seeds but rapidly decreased through desiccation presumably by the action of the BAS1 enzyme. The levels of upstream precursors, 6-deoxocathasterone, 6-deoxoteasterone, 3-dehydro-6-deoxoteasterone and 6-deoxotyphasterol were not changed much from immature to mature stages. 6-Deoxocathasterone was the major BR in mature seeds and is likely to be an important storage form. Through seed growth, the LK transcript levels remained constant but those of other genes were fluctuated. In mature seeds, the CPD gene level increased markedly while the levels of LKB, DDWF1, BAS1 and LKA were considerably high although much lower than in immature seeds, suggesting that the mRNAs of these genes may be stored as informosomes and utilized to generate BRs when seeds germinate. In imbibed seeds, neither CS nor BL were detected but the transcripts of D, DDWF1, DWF4, BAS1 and LKA were increased. One and three days after the imbibition, CS was detected in germinating seeds. In these plantlets, the level of CS as well as the D expression was high in shoots and roots but low in seeds, indicating that the D protein seems to be a key enzyme for seed germination.