Permanent address: Shanghai Institute of Plant Physiology, Academia Sinica, Shanghai 20032, China.
Received for publication 5 July 1985. This work was supported in part by research grants from the United States-Israel Agriculture Research and Development Fund (I-221-80) and the National Science Foundation (PCM-8414971). Appreciation is also extended to V. Found, R. Yastremski, M. Bacon, X.-Z. Jiao, and W.-K. Yip for their capable assistance. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.