ISSN:
1432-2145
Keywords:
Self-incompatibility
;
S-ribonucleases
;
Pollen
;
Protein kinases
;
Phosphorylation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Solanaceous plants with gametophytic self-incompatibility produce ribonucleases in the transmitting tract of the style that interact with self-pollen and inhibit its growth. These ribonucleases are a series of allelic products of the S-locus, which controls self-incompatibility. Little is known about the pollen components involved in this interaction or whether a signal transduction pathway is activated during the self-incompatibility response. We have partially purified a soluble protein kinase from pollen tubes of Nicotiana alata that phosphorylates the self-incompatibility RNases (S-RNases) from N. alata but not Lycopersicon peruvianum. The soluble protein kinase (Nak-1) has several features shared by the calcium-dependent protein kinase (CDPK) class of plant protein kinases, including substrate specificity, calcium dependence, inhibition by the calmodulin antagonist calmidazolium, and cross-reaction with monoclonal antibodies raised to a CDPK from soybean. Phosphorylation of S 2-RNase by Nak-1 is restricted to serine residues, but the site(s) of phosphorylation has not been determined and there is no evidence for allele-specific phosphorylation. The microsomal fraction from pollen tubes also phosphorylates S-RNases and this activity may be associated with proteins of Mr∼60 K and 69 K that cross-react with the monoclonal antibody to the soybean CDPK. These results are discussed in the context of the involvement of phosphorylation in other self-incompatibility systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00230363
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