Calcium-mediated signaling during sandalwood somatic embryogenesis. Role for exogenous calcium as second messenger.
The possible involvement of Ca(2+)-mediated signaling in the induction/regulation of somatic embryogenesis from pro-embryogenic cells of sandalwood (Santalum album) has been investigated. (45)Ca(2+)-uptake studies and fura-2 fluorescence ratio photometry were used to measure changes in [Ca(2+)](cyt) of pro-embryogenic cells in response to culture conditions conducive for embryo development. Sandalwood pro-embryogenic cell masses (PEMs) are obtained in the callus proliferation medium that contains the auxin 2,4-dichlorophenoxyacetic acid. Subculture of PEMs into the embryo differentiation medium, which lacks 2,4-dichlorophenoxyacetic acid and has higher osmoticum, results in a 4-fold higher (45)Ca(2+) incorporation into the symplast. Fura-2 ratiometric analysis corroboratively shows a 10- to 16-fold increase in the [Ca(2+)](cyt) of PEMs, increasing from a resting concentration of 30 to 50 nM to 650 to 800 nM. Chelation of exogenous Ca(2+) with ethyleneglycol-bis(aminoethyl ether)-N,N'-tetraacetic acid arrests such an elevation in [Ca(2+)](cyt). Exogenous Ca(2+) when chelated or deprived also arrests embryo development and inhibits the accumulation of a sandalwood Ca(2+)-dependent protein kinase. However, such culture conditions do not cause cell death as the PEMs continue to proliferate to form larger cell clumps. Culture treatment with N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide reduced embryogenic frequency by 85%, indicating that blockage of Ca(2+)-mediated signaling pathway(s) involving sandalwood Ca(2+)-dependent protein kinase and/or calmodulin causes the inhibition of embryogenesis. The observations presented are evidence to suggest a second messenger role for exogenous Ca(2+) during sandalwood somatic embryogenesis.
Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India.
V S
VS
Anil
K S
KS
Rao
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D007476:Ionophores / Q000494:pharmacology; D019684:Magnoliopsida / Q000196:embryology / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology*; D012639:Seeds / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology
D000001:Calcimycin; D002118:Calcium; D002121:Calcium Channel Blockers; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin; D002614:Chelating Agents; D004533:Egtazic Acid; D004791:Enzyme Inhibitors; D007476:Ionophores; D011494:Protein Kinases; D013449:Sulfonamides; C017967:W 7