Calcium levels modulate embryo yield in microspore embryogenesis.

Calcium (Ca) is a universal signaling cation with a prominent role as second messenger in many different plant processes, including sexual reproduction. However, there is much less knowledge about the involvement of Ca during embryogenesis processes. In this work we performed a study of Ca levels during the different stages of microspore embryogenesis in , with special attention to how Ca can influence the occurrence of different embryogenic structures with different embryogenic potential. We also performed a pharmacological study to modulate Ca homeostasis during different stages of the process, using a series of Ca-altering chemicals (BAPTA-AM, bepridil, chlorpromazine, cyclopiazonic acid, EGTA, inositol 1,4,5-trisphosphate, ionophore A23187, W-7). This study shows that Ca increase can be considered as an early marker of induction of microspore embryogenesis. Besides, Ca levels are highly dynamic during microspore embryogenesis, influencing the final embryo yield. Increase of either extracellular or intracellular Ca levels improves embryo yield without altering the proportion of highly embryogenic structures formed, which suggests that elevated Ca levels increase the amount of microspores reaching the minimum Ca threshold required for embryogenesis induction. Conversely, inhibition of Ca uptake or signaling results in reduced embryogenic response. This allows to modulate embryo yield within a functional range, with lower and upper Ca thresholds beyond which embryo yield is reduced. There seems to be a relationship between Ca levels and embryo differentiation.