CLOB in trigger for DB LINK

I have such a problem

TABLE a1 and b1 have the same structure,

ID CHAR(15);
STATUS CHAR(1);
CONTENT CLOB;

a1 in database db_a (in host A),
b1 in database db_b (in host B)


linka_b is Database Link ,which can operate tale b1
in database db_a



CREATE OR REPLACE TRIGGER instob
AFTER UPDATE OF status ON a1
FOR EACH ROW

BEGIN
IF (:NEW.status='3') THEN
INSERT INTO b1@linka_b
VALUES(:NEW.id,:NEW.status,:NEW.content);
END IF;
EN;

when update table a1,the error is follow:

ORA-22990 LOB locators cannot span transactions

What can i do for the error? Help me!