odoo_source/addons/purchase_analytic_plans/purchase_analytic_plans_view.xml

<?xml version="1.0"?>
<openerp>
<data>

    <record model="ir.ui.view" id="purchase_order_line_form_inherit">
        <field name="name">purchase.order.line.form.inherit</field>
        <field name="model">purchase.order.line</field>
        <field name="type">form</field>
        <field name="inherit_id" ref="purchase.purchase_order_line_form"/>
        <field name="arch" type="xml">
            <field name="account_analytic_id" position="replace">
                <field name="analytics_id" domain="[('plan_id','&lt;&gt;',False)]" groups="base.group_extended"/>
            </field>
        </field>
    </record>

</data>
</openerp>