Rhizobium Induced Plant Proteins in Target Root Epidermal Cells of Vigna Unguiculata

Abstract

Recent studies have shown that invasion by Rhizobium is limited to a very narrow region above the root tip which does not possess root hairs at the time of inoculation (1,2). The cells in this region remain susceptible to infection for only a brief period of 3 to 4 h. At present, not much is known in biochemical, cytological or genetic terms regarding the events occurring at the root surface during such early stages of infection. An analysis of preinvasion events in cowpea (Vigna unguiculata) — Rhizobium symbiosis is reported here. Using rhizobia having different infection rates we have recently demonstrated the significant role of host in early intereactions. Cowpea roots under nitrogen deficiency, secrete substances which elicit faster nodulation response in rhizobia which otherwise possess slow infection status (3). Under the influence of host root exudate rhizobia show enhanced capsular polysaccharides (CPS) synthesis (4) and alteration in capsule topography and chemical composition (5). The newly synthesised host induced CPS (HI-CPS) increase the nodulation efficiency of Rhizobium. These observations prompted us to examine the effect of HI-CPS on the infectible zone of cowpea roots.