Physiological Study And Root Protein Expression Under Salinity Stress In Four Warm Season Turfgrasses

Salinity is one of the major abiotic factors limiting plant growth and inducesvarious changes in the growth, physiological and proteomic levels. Understanding themechanisms of salinity resistance and adaptation in turfgrass will provide the crucialreference to select suitable turfgrass variety for salinity soils and imformation forsalinity-tolerant variety development. In this study, existing turfgrass varieties werescreened for the salinity tolerance and the salt tolerance thresholds of fourwarm-season turfgrasses were determined. Salt seretion phenomenon was observedand salt secretion capacity was determinded in the four warm-season turfgrassesunder the salinity stress. Seashore paspalum, the most salt tolerance turfgrass species,and centipedegrass, the salt sensitive species, were selected for the studies ofdifferential photosynthetic responses to salt stress, and the differentially-expressedsalt-responsive proteins in the roots. The main contents and results of this study are asfollows:1. Salinity stress responses and thresholds in four warm-season turfgrassesFour warm-season turfgrass species including bermudagrass ‘Tifway’(Cynodondactylon×C. transvaalensis), centipedegrass‘Civil’(Eremochloa ophiuroides),seashore paspalum ‘Salam’(Paspalum vaginatum), and zoysiagrass ‘Matrella’(Zoysia matrella L.Merr) were grown in plastic pots under a series of NaClconcentrations to study the salinity stress responses in turfgrass growth andphysiological parameters. The results indicated that: sashore pspalum has the bestsalinity tolerance. The visual quality, relative growth rate, relative water content,chlorophyll index, Fv/Fm decreased52.2%、75.9%、62.1%、59.4%、72.9%respectively, at36d under600mM of NaCl, and electrolyte leakage increased to 71.5%. The cell membrane damage in seashore paspalum is the lowest whencompared to other three species. Zoysiagrass also showed the good salinity tolerance,with the visual quality, relative growth rate, relative water content, chlorophyll index,Fv/Fm decreased85.2%、68.8%、70.5%、73.9%、49.3%respectively, at36d under600mM of NaCl, and electrolyte leakage increased to81.8%. Bermudagrass andcentipedegrass showed the lowest salinity tolerance, for the treatment of600mMafter36d, both grasses were died. The critical salinity tolerance concentrations foreach parameter were calculated by the regression analysis and Least SignificantDifference (P<0.05). The salinity tolerance thresholds for each turfgrasses are:seashore paspalum261mM, zoysiagrass203mM, bermudagrass135mM andcentipedegrass131mM.2. Study of salt excretion ability in four warm-season turfgrassFour warm-season turfgrass species including bermudagrass ‘Tifway’(Cynodondactylon×C. transvaalensis), centipedegrass ‘Civil’(Eremochloa ophiuroides),seashore paspalum ‘Salam’(Paspalum vaginatum), zoysiagrass‘JD-1’(Zoysiajapomca) were grown in plastic pots under300mM NaCl concentration to study theirsalt secretion ability and made the microscopic observation for salt secretion process.The results indicated that: the most salt tolerant seashore paspalum and salt-sensitivecentipedegrass have no function of salt excretion, while zoysiagrass andbermudagrass have the salt excretion function. The salt secretion structures in bothturfgrass are salt glands, and the salt secretion capacity of bermudagrass is higher thanzoysiagrass. At20d of the salt treatment, the salt secretion content of bermudagrass is1.6times higher than zoysiagrass. Mainly due to the salt glands density ofbermudagrass is larger than zoysiagrass. The leaf salt gland number of zoysiagrassaveraged66/mm~2, while the leaf salt gland number of bermudagrass averaged169/mm~2, mermudagrass is2.6times higher than zoysiagrass.3. Differential photosynthetic responses to salinity stress between seashorepaspalum and centipedegrass in salinity tolerance This study was to examine photosynthetic responses to salinity stress in twowarm-season turfgrasses differing in salinity tolerance. Salt-tolerant species seashorepaspalum and salt-sensitive species centipedegrass were exposed to salinity at threeNaCl concentrations (0,300and500mM) in a growth chamber. Turf quality, RWC,and Fv/Fm declined while EL increased under the two NaCl regimes for both grassspecies, and the changes were more dramatic in centipedegrass than that in seashorepaspalum, as well as in the higher salinity concentration. Two grass species showeddifferent phytosynthetic responses to salinity stress. The earlier inhibition ofphotosynthesis in seashore paspalum was mainly associated with stomatal closure. Assalinity increased and salinity stress prolonged, the inhibition of photosynthesis inseashore paspalum was mainly associated with non-stomatal factors. The inhibition ofphotosynthesis in centipedegrass was associated with non-stomatal factors at bothsalinity levels. The SDS-PAGE analysis demonstrated the Rubisco large subunit hadno obvious decrease during the whole stress period under the300mM and500mMtreatments in seashore paspalum while significantly decreased in centipedegrass underboth the300mM and500mM treatments. The results indteicated that the superiorsalinity tolerance in seashore paspalum, compared to centipedegrass, could beattributed to its high Pn recovery capacity under salinity stress.4. Identification of differentially-expressed salt-responsive proteins in roots oftwo perennial grass species contrasting in salinity toleranceSeashore paspalum and centipedegrass were exposed to salinity stress bywatering the soil with300mM NaCl solution for20d in a growth chamber. Rootswere harvested at20d after salinity treatment. Proteins were extracted and separatedby two-dimensional electrophoresis (2-DE). Root electrolyte leakage (REL) increasedsignificantly while root osmotic potential and root viability decreased significantlyunder salinity treatment for both grass species. However, the extent of change in theabove physiological parameters in seashore paspalum was less pronounced than thosein centipedegrass. Under salinity stress, the abundance of8protein spots significantlyincreased and14significantly decreased in seashore paspalum, while19and16 protein spots exhibited increase and decrease in abundance in centipedegrass,respectively. By comparison of protein spots differentially accumulated between thetwo species,8protein spots that exhibited enhanced abundance in seashore paspalumunder salinity stress were excised from the2-DE gels and subjected to massspectrometry analysis. Seven protein spots were successfully identified. Two of themwere identified as the same protein: ATP synthase Delta chain (ATPS chain);5ofthem were previously confirmed as salt stress-responsive proteins: peroxidase (POD,2.36-fold), cytoplasmic malate dehydrogenase (cMDH,5.84-fold), asorbateperoxidase (APX,4.03-fold) and mitochondrial ATPS chain (2.26-fold and4.78-fold);2of them are novel ones: hypothetical protein LOC100274119(5.01-fold)and Flavoprotein wrbA (2.20-fold). Compared to the8enhanced salt-responsiveprotein spots in seashore paspalum,4corresponding protein spots (cMDH,2ATPSchain, LOC100274119) were expressed and3corresponding protein spots (POD,APX, Flavoprotein wrbA) were not expressed in centipedegrass. The expressedprotein spots in centipedegrass were not significantly changed in their abundance.Immunblotting analysis indicated that POD and ATPS chain were significantlyup-regulated in seashore paspalum at20d of salinity treatment while almost noexpression in both control and salt treatment of centipedegrass. The POD and APXactivities of seashore paspalum were markedly increased while centipedegrass weresignificantly declined at the end of salt treatment. These results indicated that thesuperior salinity tolerance in seashore paspalum, compared to centipedegrass, couldbe associated with its high POD, APX ability and energy metabolism.