Effects of calcium on embryogenic induction and the accumulation of abscisic acid, and an early cysteine-labeled metallothionein gene in androgenic microspores of Triticum aestivum.

摘要

A cloned cDNA to the wheat (Triticum aestivum) early cysteine-labelled metallothionein (EcMt) has been identified as a molecular marker for wheat pollen embryogenesis. This transcript is not detected in uninucleate microspores at the time of cultureor in pollen at any stage during normal ontogeny; its mRNA increases in embryogenic microspores within 6 h of culture, peaks at around 24 h, declines, then levels off through the next 21 days of development. Additionally, the accumulation of the embryoid-abundant EcMt gene transcript shows a direct and positive correlation with an increase in abscisic acid (ABA) in embryogenic microspores and developing pollen embryoids. External Ca2+ is required for in vitro pollen morphogenesis, since reduced Ca2+ concentrations in the medium suppressed EcMt transcript accumulation and the ability of microspores to form embryoids; however, endogenous ABA levels were unaffected by manipulating calcium concentrations in the medium. The calmodulin antagonist, W-7 alsosuppressed androgenesis and EcMt levels in treated microspores without altering ABA concentrations. It is suggested that ABA alone cannot maintain sporophytic differentiation of microspores and that Ca2+ may play a role in signal transduction during pollen androgenesis in bread wheat.