Php guzzle send data via post method

<?php
/**
 * @file
 *
 * This document is only for testing purposes.
 *
 * @author Telaya Escobedo, Luis Eduardo
 */

// Let php show all erors.
error_reporting(E_ALL);
ini_set('display_errors', '1');

require 'vendor/autoload.php';
use Guzzle\Http\Client;

$client = new Client();
$request = $client->post('http://200.31.114.39/Servicio-Rest/STMPOST_SMAR.svc/Registrar_Postulante', null, array('CO_AREA_DESA' => 'test'));
$response = $request->send();
$data = $response->xml();

print_r($data);

?>