Breeding Of Heat Tolerant Genotype And Mechanisms Of Heat Tolerance Induced By Salicylic Acid In Cool Season Turfgrass

Tall fescue (Festuca arundinacea Schreb) and Kentucky bluegrass (Poa pratensis L.) are widely used in turf industry in the transition zone. Both of the two species have long green period in shanghai, but they could not survive in the summer well. The objectives of this study are: 1) to screen and breed heat-tolerant and non-heat tolerant genotypes for application in turf industry and study of heat tolerance mechanisms, 2) to investigate the optimal concentration of salicylic acid (S A) on thermotolerance inducement, 3) to study the mechanisms of SA induced heat tolerance and its relation to antioxidation.4 new lines of turf type tall fescue, temporarily named 98-19, 98-20, 98-21 and 98-22, were bred by selecting desirable plants to be open pollinated in an isolated field plots. Results from field experiments and controlled high temperature tests showed that "98-22" is more heat tolerant as compared with "98-19" (Fig. 4-1, upper). Based on the results from the field experiments in the past 10 years and under artificial high temperature, Wabash is more tolerant to summer stress and HS than Nassau (Fig. 4-1, lower).The optimal concentrations of SA treatment for heat tolerance inducement were 0.5 mmol/L (Table 3-1, Fig. 3-3) and 0.25 mmol/L (Table 3-2, Fig. 3-10) in tall fescue and Kentucky bluegrass respectively. SA at 1.5 mmol/L (Table 3-1, Fig. 3-3, Table 3-2, Fig. 3-10) or at 10 mmol/L (Fig. 3-11) was over-optimal (excessive) to enhance heat tolerance. Relative water content (RWC) decreased (Fig. 3-11) and the cellular electrolytic leakage(EC, Fig. 3-4) increased in plants under heat stress (HS). SA at optimal concentration could alleviate the decrease of RWC (Fig. 3-11) and increase of EC (Fig. 3-4) under HS.Based on the results from the tests in tall fescue (cov. Triplea) and Kentucky bluegrass (cov. Wabash), it is reasonable to conclude that SA induced thermotolerance is related to antioxidation. Superoxide anion (02-) generation rate in plants increased under HS (Fig. 3-20). SA could scavenge 02- directly (Fig. 3-21) and increased SOD activity in vivo (Fig. 3-22) under HS. The effects of SOD and SA on 02- scavenging were accumulated (Table 3-4) and SA at or more than 50 u mol/L enlarged the value of SOD activity significantly (Table 3-22). Though SA could not degrade H2O2 directly (Fig. Omitted), it increased significantly CAT activity (Fig. 3-8, Fig. 3-9, Fig. 3-13, Fig. 3-28) but decreased APX (Fig. 3-14) and POD (Fig. 3-15, Fig. 3-7) activities, indicating that CAT is more important than any other 2 enzymes, POD and APX, in SA induced H2O2 degrading for maintenance of normal cellular processes under HS. Results from in vitro test stated that SA had absorbency at 240 nm (A24o) (Fig. 3-17) and SA at or more than 0.5 mmol/L disturbed or decreased significantly CAT activity (Fig. 3-18). H2O2 had accumulated to maximum level in plants treated with no (control), optimal or excess concentration of SA at early stage of HS (HS 0.5 h or HS 1 h) (Fig. 3-12). No significant differences among the peak values were observed (Fig.3-12). During the same HS stage, the activities of CAT (Fig.3-13), APX (Fig. 3-14), POD (Fig. 3-15) and SOD (Fig. 3-19) were increasing. These results indicated that the increase of H2O2 content was only associated with SOD, which was related to neither SA nor the changes in the 3 H2O2 metabolism enzymes. SA treatment enhanced the soluble protein content in leaves (Fig. 3-5), but showed no influence on the HSPs synthesis in Kentucky bluegrass (Fig.4-5) and unsteady in tall fescue (Fig.4-4). Concurrent with SAand HS (SA+HS) did not induce any new patterns of SOD (Fig. 3-25, Fig. 3-23), POD (Fig. 3-27) and CAT (Fig. 3-29) isozymes as compared with HS treatment. Super-optimal SA enhanced CAT (Fig. 3-13) and APX (Fig. 3-14) activities to the maximum level at early HS stage and reduced them to the minimum level at the late HS stage, hinting that excess SA induced disorder of H2O2 metabolism so that increased the HS injury to plants. It is obvious that SA induced heat tolerance is...