Effect of bacterial polysaccharides in growth regulation of maize (Zea mays L.)

Abstract

Drouglll is one of the major abiolic stress affecting crop yie lds. Bacterial populations of stressed soils arc well adapted to stress and can be implicated as bio inoculant!,! to impart loler::mce to crops grown in stressed ecosystems. r'raduction of c:':opl)lysaccharides (EPS) is a major mechanism in bacteria to cope with drauglu stress. The present study deals with the isolation and charncleriL...1lion of exopolysacchnrides pl'Oduced by the PGPR from arid (Gholki Sindh) and semiarid (Ka ll a .. soydnn) regions of Pakistan. and to investigate the drought Lo lenlllcc potential of these PGPR 0 11 rnnize when lIsed as bio inoculant alone and in combination La their n:spccli\' c EPS. Three bacteria l strains S I (Pro/ell,\' pelllll.!rl\ S2 (Psetit/omolHls tlerugillo!taj and S3 (A /c:aligelt(!s fae lllb.~ were selected as exopolysaccharides (EPS)producing bllclcria on the basis of mucoid colony formal ion. All these str:lins we re gram negative. motile and positive for catalase. Strain SI was positive for oxidase and was phllsphalc solubilizcr. while S2 and S3 were ncgative. 'I hc isolated strains \'~·crc sequenced by using 16SrRNA. Biochemical characterization {solubility: quantilication of total slIgnr. protein and uronic acid; and emulsification uclivily) nnd Allenullled Total RcneClion Fourier Transformed lnfrll4Red spectroscopy ATR~F'T R of c:xopolysac:charides was done for determining functional groups of EPS. Drought stress induced by withholding water supply had signifkani adverse elTects 011 growth of maize seedlings. Seed bacterization of Illai zc with EPS producing bacleri nl slrninsin combinnlion to th!!ir respective EPS improved soil moist ure cantellts. plant biomass. rool, and shoot lengthand leaf area. The inoeultlled plants showed higher levels of relative water content. protein and suga rs under drought stress. As compared La uIl 4 inocuiaied seedlings. inoculated seedlings showed significantly lower activities of proline and ant iox idant enzymes. superoxide dismutase (SOD) peroxidase (POD) and calalase (CAT) under drought stress. The strain S2 (Pseudomonas aeFligitwstl) isolated from semi-arid region of Kallor Saydull was most potent PGPR under drought stress, In ull cases inoculum used in combinotion 10 their respective exopolysaccharides showed grc.lter potential to drought IOlcrancc as compared 10 inoculums alone. So exopolysaccharidcs production is the main mechanism and slower the desiccati on of rhizosphere soil during waler shortage. ix i:.1<opolysotcclmrides keep the soil moist and he lps the plDnts to cope with long period of drou&!ll. Inoculation studies of maize with EPS producing bacteria undcr drought stress improve lhe soil moisture content and relative water conlent RWC of leaves.