Panicle Water Potential, a Physiological Trait to Identify Drought Tolerance in Rice

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<ul><li><p>Journal of Integrative Plant Biology 2007, 49 (10): 14641469</p><p>Panicle Water Potential, a Physiological Trait to IdentifyDrought Tolerance in Rice</p><p>Guo-Lan Liu1,2, Han-Wei Mei2</p><p>, Xin-Qiao Yu2, Gui-Hua Zou2, Hong-Yan Liu2, Ming-Shou Li2,</p><p>Liang Chen2, Jin-Hong Wu2 and Li-Jun Luo1,2 </p><p>(1Huazhong Agricultural University, Wuhan 430070, China;2Shanghai Agrobiological Gene Center , Shanghai 201106, China)</p><p>Abstract</p><p>Two upland rice varieties (IRAT109, IAPAR9) and one lowland rice variety (Zhenshan 97B) were planted in summer andtreated with both normal (full water) and drought stress in the reproductive stage. Panicle water potential (PWP) and leafwater potential (LWP) were measured every 1.01.5 h over 24 h on sunny days. Both PWP and LWP of upland varietiesstarted to decrease later, maintained a higher level and recovered more quickly than that of the lowland variety. Theresults show that PWP can be used as an indicator of plant water status based on the parallel daily changes, and the highcorrelation between PWP and LWP. Similar correlations were also observed between PWP, LWP and eight traits relatedto plant growth and grain yield formation. PWP seemed to be more effective for distinguishing the upland rice varietieswith different drought-tolerant ability. Differences in PWP and LWP between upland and lowland rice varieties were alsoobserved at noon even under normal water conditions, implying the incorporation of the drought-tolerant mechanism toimprove the photosynthesis and yield of traditional paddy rice.</p><p>Key words: correlation analysis; drought tolerance; leaf water potential; Oryza sativa; panicle water potential.</p><p>Liu GL, Mei HW, Yu XQ, Zou GH, Liu HY, Li MS, Chen L, Wu JH, Luo LJ (2007). Panicle water potential, a physiological trait to identify droughttolerance in rice. J. Integr. Plant Biol. 49(10), 14641469.</p><p>Available online at www.blackwell-synergy.com/links/toc/jipb, www.jipb.net</p><p>Application of drought-tolerant crop varieties together with awater saving culture seems to be the most effective approachto overcoming the challenges in both food and water safety.Development of drought-tolerant varieties is largely based onthe quick and precise screening of germplasm and breeding ma-terials in water-limited environments. A suggested approach isthe identification and incorporation of physiological mechanismsand morphological characteristics, conferring drought toleranceas selection criteria, into traditional breeding programs (Turner1986). So it is necessary to identify such characteristics and to</p><p>Received 7 Sept. 2006 Accepted 12 Mar. 2007</p><p>Supported by Grants from Chinese Ministry of Agriculture (948 plan 2001-</p><p>101, 2006-G1), Shanghai Municipal Science and Technology Commission</p><p>(2005DJ14008), Shanghai Municipal Agriculture Commission (2004-2-14,</p><p>2005-2-3) and the Rockefeller Foundation (2004FS071), New York, USA.These authors contributed equally to this work.Author for correspondence.</p><p>Tel: +86 0(21) 6220 0490;Fax: +86 0(21) 6220 4010;E-mail: .</p><p>C 2007 Institute of Botany, the Chinese Academy of Sciencesdoi: 10.1111/j.1672-9072.2007.00551.x</p><p>evaluate their contribution to drought tolerance (Jackson et al.1996) and yield in the target population of environments (Cooper1999).</p><p>Water in plant tissues can be estimated by measuring relativewater content, water potential and osmotic adjustment. Theseinterdependent parameters are obtained usually by measuringthe leaves. For instance, leaf water potential (LWP) is a widelyused criteria for improving drought tolerance in rice and isrecognized as an index for whole plant water status (Turner1982). Maintenance of high LWP is considered to be associatedwith dehydration avoidance mechanisms (Levitt 1980). Droughtstress in the reproductive stage will cause severe losses ingrain yield. The water status in grains and panicles probablyhave more direct effect in spikelet fertility, grain filling and finalyield. Pantuwan et al. (2002) reported that under severe droughtconditions, the maintenance of panicle water potential (PWP) ofgenotypes played a significant role in determining the final grainyield.</p><p>In the current study, we measured the daily changes in PWPand LWP of three varieties with different drought tolerance. Thecorrelation between PWP, LWP and several other traits werealso investigated in twenty lines in order to estimate the merit ofPWP as a drought tolerance screening criteria.</p></li><li><p>Identify Rice Drought Tolerance by Panicle Water Potential 1465</p><p>Results</p><p>Performance of rice varieties under water stressand normal conditions</p><p>The relative yields under drought stress of three rice varieties(IRAT109, IAPAR9 and Zhenshan 97B) were 0.98, 0.78, and0.59 respectively. In other words, there was hardly any loss ingrain yield of IRAT109 under drought stress, in comparison withabout 20% yield loss in IAPAR9, and 40% yield loss in ZS97B.Based on leaf rolling and leaf desiccation (Ying et al. 1993),the drought tolerance scores of IRAT109, IAPAR9 and ZS97Bwere 1, 3, and 5 respectively, where 1 means highest droughttolerance with no leaf rolling and senescence, and 9 means thematerial with leaves completely dried. From the results of bothrelative yields and drought tolerance scores, it was found thatIRAT109 had the strongest drought tolerance ability, followedby IAPAR9, and ZS97B was most sensitive to drought.</p><p>Daily changes of PWP and LWP</p><p>Both PWP and LWP had similar U-shaped daily changes insunny summer days along with the changes of solar radiationand respiration rates of plants, (i.e. maintained near zero</p><p>Figure 1. Daily changes of panicle water potential (PWP, in bar) and leaf water potential (LWP, in bar) of upland and paddy rice varieties under</p><p>drought stress and non-stress conditions.</p><p>at night, dropped in the morning to a low level (06.00 to09.00 hours), stayed at a low-water-potential flat until lateafternoon (09.00 to 16.00 hours or later), then came back tohigh water potential in the evening (16.00 to 18.00 hours orlater) (Figure 1).</p><p>In comparison of both PWP and LWP in plants under droughtstress with those under normal conditions, three significantvariances were observed in three time windows. First, bothPWP and LWP started to drop and reached the low-water-potential flat about 1 hour earlier under stress (before 05.00 to09.00 hours) than under normal condition (before 06.00 to 11.00hours). Two upland rice varieties (IRAT109 and IAPAR9) hadsimilar decline rates, but ZS97B had a higher rate to decreaseunder drought stress. Second, LWP started to recover at thesame time (16.00 hours), but PWP started to recover understress (17. 00 hours) 1 hour later than under normal conditions(16.00 hours). PWP and LWP restored to a high level undernormal condition (&gt;5.0 bar) before 18.0019.30 hours, muchearlier than that under stress (21.00 hours for LWP and 22.00hours for PWP). Third, much longer low-water-potential flatswere observed under stress than under normal conditions. Theabsolute values of PWP and LWP at this stage were at similarlevels for IRAP109 and IAPAR9 under water stress and normalconditions, but both PWP and LWP of ZS97B were significantlydecreased under stress than under normal conditions. Much</p></li><li><p>1466 Journal of Integrative Plant Biology Vol. 49 No. 10 2007</p><p>lower PWP and LWP were also observed for ZS97B even undernon-stress conditions during the solar noon.</p><p>Compared to LWP, PWP seemed to be the better indicatorof drought tolerance based on two reasons. First, PWP hada wider and stable low-water-potential flat stage in favor ofreliable measurement of the parameter, especially for large setsof populations. Second, PWP gave a better identification of thedifference between the drought tolerance levels of two uplandrice varieties in this study, while the daily changes of LWP werealmost the same between IRAT109 and IAPAR9. Furthermore,a quicker recovery was observed for LWP of IAPAR9 thanIRAT109, in contrast to the drought tolerance levels based onrelative yield and morphological judgments. During the low-water-potential flat, PWP of IRAT109 was lower than that ofIAPAR9 under normal conditions, but significantly higher underdrought stress. In other words, PWP of IRAT109 maintained atthe level of about the10 bar under both conditions, but PWP ofIAPAR9 dropped from about the8 bar under normal conditionsto the 12.5 bar under stress.</p><p>Correlation among PWP and LWP with yieldand some traits</p><p>The data of midday PWP, LWP and eight traits related with plantgrowth or grain yield components of different rice genotypesand control conditions are presented in Table 1. Highly positivecorrelations were detected between PWP and LWP under stressand normal conditions (r 0.80), indicating again the parallelchanging of water potential in leaves and panicles (Table 2).Under normal conditions, PWP and LWP were negatively cor-related with other characters, but positively correlated with 100-grain weight (HGW) The correlation coefficients were belowthe significant level at P0.05, except r = 0.516 betweenLWP and biomass (BM). This result showed that there werenot any positive contributions from high water potential inrice leaves or panicles to eight traits about plant growth andgrain development. Under drought stress, PWP and LWP werepositively correlated with leaf relative water content (RWC),spikelet fertility (SF), HGW and grains yield (GY), but stillnegatively correlated with plant height (PH), spikelet numberper panicle (SN), spikelet density (SD) and BM. There werethree noticeable points. First, PWP had a better correlationwith RWC than LWP. Second, positive correlations were foundbetween PWP and LWP under stress with three traits relatedto the development of rice grain, (i.e. grain setting, filling andfinal yield). Third, negative correlations were observed betweenwater potential under stress and the vegetative growth ofmaternal organisms (i.e. plant, spikelet and biomass), moreoverwith higher coefficients than under normal conditions.</p><p>So it was well judged via correlation analysis that PWP canbe used as an indicator of the water status in rice plants underdrought stress, at least equivalent to LWP.</p><p>Discussion</p><p>Measuring PWP for screening drought-tolerant rice</p><p>Leaf water potential was widely used as effective screeningcriteria, showing whole plant water status (Turner 1982) and as-sociating with dehydration avoidance mechanisms (Levitt 1980).Pantuwan et al. (2002) measured predawn (before 06.00 hours)PWP for 128 rice genotypes from four populations under grain-filling mild drought and flowering short severe drought in rainfedlowland. No significant differences in PWP were found betweengenotypes under mild drought as there was little variance amongpopulations (average 1.140.065 MPa) and among geno-types within any population. Under severe drought, there werehighly significant differences in PWP among the genotypes ineach population and significant difference between the highestand the lowest populations. Predawn PWP also associated withgrain yield, harvest index, filled grain, fertile panicle, plant height,total dry matter at flowering, and delay in flowering time undersevere drought. In this study, PWP were measured for twoupland rice and one paddy rice variety. Similar results wereobserved indicating that there were little differences in PWPfrom midnight to predawn (00.00 to 05.00 hours). But PWP ofpaddy rice began to drop at 06.00 hours under drought stress.Water potential at predawn presented the ability of the plantto restore from severe water deficit during the day time. Butplant water potential in the day time was much more sensitiveto drought stress. Highly parallel daily changes and correlationsbetween PWP and LWP implied the equivalent judgments fordrought tolerance of rice genotypes. The results showed thatboth PWP and LWP had large differences between uplandrice and lowland rice, but PWP was more sensitive to droughtstress so that the ability for drought tolerance of two upland ricevarieties can be distinguished, matching the relative yield andmorphological phenomena under stress of the varieties. Similarcorrelations were observed between PWP, LWP and eight traitsrelated to plant growth and grain yield formation. It could beconcluded that PWP was an equivalent or better characteristicin screening drought-tolerant rice genotypes compared to LWP.So PWP at midday was suggested as an alternative parameterindicating drought tolerance during the reproductive stage in thisstudy.</p><p>Water status of upland and lowland rice varietiesunder stress and non-stress conditions</p><p>Leaf water potential values between the 10 to the 12.5 barwere observed in IRAT109 and IAPAR9 under stress (Figure 1),and near the 15 bar in ZS97B. The former was associatedwith 222% yield loss, while the later was associated with 41%yield loss. So the critical LWP value in rice should be about the11 bar.</p></li><li><p>Identify Rice Drought Tolerance by Panicle Water Potential 1467</p><p>Tab</p><p>le1.</p><p>Mid</p><p>day</p><p>pani</p><p>cle</p><p>wat</p><p>erpo</p><p>tent</p><p>ial(</p><p>PW</p><p>P),</p><p>leaf</p><p>wat</p><p>erpo</p><p>tent</p><p>ial(</p><p>LWP</p><p>)an</p><p>dei</p><p>ght</p><p>trai</p><p>tsre</p><p>late</p><p>dw</p><p>ithpl</p><p>ant</p><p>grow</p><p>than</p><p>dgr</p><p>ain</p><p>yiel</p><p>dco</p><p>mpo</p><p>nent</p><p>sof</p><p>rice</p><p>geno</p><p>type</p><p>sun</p><p>der</p><p>drou</p><p>ght</p><p>stre</p><p>ssan</p><p>d</p><p>cont</p><p>rolc</p><p>ondi</p><p>tions</p><p>Gen</p><p>otyp</p><p>esP</p><p>WP</p><p>LWP</p><p>PH</p><p>RW</p><p>CS</p><p>NS</p><p>DS</p><p>FH</p><p>GW</p><p>GY</p><p>BM</p><p>Str</p><p>ess</p><p>Ctr</p><p>lS</p><p>tres</p><p>sC</p><p>trl</p><p>Str</p><p>ess</p><p>Ctr</p><p>lS</p><p>tres</p><p>sC</p><p>trl</p><p>Str</p><p>ess</p><p>Ctr</p><p>lS</p><p>tres</p><p>sC</p><p>trl</p><p>Str</p><p>ess</p><p>Ctr</p><p>lS</p><p>tres</p><p>sC</p><p>trl</p><p>Str</p><p>ess</p><p>Ctr</p><p>lS</p><p>tres</p><p>sC</p><p>trl</p><p>31</p><p>51</p><p>0.5</p><p>14</p><p>11.</p><p>562</p><p>66.8</p><p>88.6</p><p>5790</p><p>.769</p><p>87.0</p><p>94.3</p><p>24.</p><p>64.</p><p>673.0</p><p>364</p><p>.63</p><p>2.34</p><p>2.47</p><p>7.23</p><p>7.38</p><p>13.2</p><p>116</p><p>.51</p><p>121</p><p>2.5</p><p>7.5</p><p>12.</p><p>59</p><p>79.5</p><p>84.6</p><p>67.9</p><p>0683</p><p>.458</p><p>100.</p><p>210</p><p>8.33</p><p>5.3</p><p>5.8</p><p>17.2</p><p>031</p><p>.94</p><p>2.24</p><p>2.33</p><p>2.12</p><p>2.83</p><p>14.3</p><p>712</p><p>.86</p><p>241</p><p>8.5</p><p>13</p><p>17.</p><p>51</p><p>371.3</p><p>90.3</p><p>74.1</p><p>6089</p><p>.980</p><p>100.</p><p>011</p><p>1.60</p><p>55.</p><p>338.4</p><p>966</p><p>.40</p><p>1.85</p><p>2.13</p><p>5.87</p><p>14.8</p><p>321</p><p>.67</p><p>35.3</p><p>0</p><p>371</p><p>91</p><p>51</p><p>7.5</p><p>12.</p><p>572.5</p><p>83.4</p><p>79.0</p><p>1592</p><p>.056</p><p>100.</p><p>412</p><p>5.74</p><p>5.7</p><p>7.0</p><p>27.8</p><p>451</p><p>.00</p><p>2.11</p><p>2.40</p><p>3.83</p><p>10.7</p><p>016</p><p>.74</p><p>23.5</p><p>1</p><p>381</p><p>19</p><p>.51</p><p>11</p><p>0.5</p><p>85.5</p><p>86.5</p><p>94.5</p><p>64.1</p><p>14.</p><p>25.</p><p>167.6</p><p>071</p><p>.02</p><p>2.6</p><p>2.75</p><p>7.5</p><p>7.40</p><p>16.2</p><p>821</p><p>.81</p><p>411</p><p>3.5</p><p>13</p><p>14.</p><p>51</p><p>467.8</p><p>72.8</p><p>83.4</p><p>4886</p><p>.838</p><p>73.0</p><p>69.7</p><p>24</p><p>3.9</p><p>58.3</p><p>173</p><p>.73</p><p>2.42</p><p>2.54</p><p>6.91</p><p>9.70</p><p>16.6</p><p>419</p><p>.87</p><p>491</p><p>37</p><p>11</p><p>869</p><p>72.8</p><p>82.4</p><p>2392</p><p>.076</p><p>79.9</p><p>84.7</p><p>03.</p><p>63.</p><p>775.0</p><p>372</p><p>.49</p><p>2.92</p><p>2.99</p><p>8.41</p><p>8.53</p><p>17.8</p><p>518</p><p>.68</p><p>531</p><p>8.5</p><p>15</p><p>15.</p><p>51</p><p>366</p><p>70.0</p><p>83.1</p><p>80.1</p><p>24.</p><p>64.</p><p>560.0</p><p>072</p><p>.67</p><p>2.11</p><p>2.21</p><p>5.81</p><p>10.2</p><p>013</p><p>.15</p><p>16.4</p><p>1</p><p>591</p><p>4.5</p><p>71</p><p>58</p><p>73.8</p><p>84.3</p><p>82.5</p><p>7293</p><p>.056</p><p>136.</p><p>811</p><p>3.52</p><p>5.7</p><p>4.9</p><p>47.6</p><p>951</p><p>.66</p><p>2.07</p><p>2.32</p><p>5.19</p><p>10.4</p><p>811</p><p>.54</p><p>22.9</p><p>6</p><p>741</p><p>6.5</p><p>12.</p><p>51</p><p>3.5</p><p>9.5</p><p>65.8</p><p>75.8</p><p>68.2</p><p>7589</p><p>.464</p><p>72.6</p><p>77.3</p><p>03.</p><p>94.</p><p>071.5</p><p>079</p><p>.88</p><p>2.25</p><p>2.41</p><p>5.18</p><p>9.17</p><p>10.5</p><p>517</p><p>.65</p><p>751</p><p>3.5</p><p>6.5</p><p>13.</p><p>58</p><p>.574.8</p><p>87.8</p><p>81.8</p><p>8292</p><p>.463</p><p>72.4</p><p>100.</p><p>324</p><p>5.3</p><p>58.1</p><p>444</p><p>.02</p><p>2.48</p><p>2.50</p><p>7.76</p><p>11.5</p><p>718</p><p>.92</p><p>27.0</p><p>7</p><p>891</p><p>61</p><p>11</p><p>61</p><p>1.5</p><p>78.3</p><p>97.3</p><p>88.6</p><p>6497</p><p>.243</p><p>88.8</p><p>107.</p><p>854.</p><p>75.</p><p>521.2</p><p>840</p><p>.90</p><p>1.79</p><p>1.96</p><p>1.73</p><p>4.83</p><p>13.1</p><p>818</p><p>.48</p><p>901</p><p>71</p><p>41</p><p>71</p><p>475.5</p><p>120.</p><p>082</p><p>.805</p><p>91.9</p><p>4699.7</p><p>135.</p><p>814.</p><p>86.</p><p>731.5</p><p>769</p><p>.69</p><p>1.81</p><p>2.12</p><p>2.07</p><p>13.8</p><p>119</p><p>.79</p><p>37.4</p><p>5</p><p>108</p><p>16</p><p>10</p><p>14.</p><p>57</p><p>.561.3</p><p>73.0</p><p>82.6</p><p>4292</p><p>.505</p><p>60.4</p><p>103.</p><p>093.</p><p>86.</p><p>249.0</p><p>454</p><p>.89</p><p>2.18</p><p>2.39</p><p>3.64</p><p>5.17</p><p>10.5</p><p>914</p><p>.97</p><p>117</p><p>15.</p><p>56</p><p>.51</p><p>59</p><p>.573.9</p><p>86.5</p><p>86.4</p><p>1989</p><p>.075</p><p>80.8</p><p>75.3</p><p>04</p><p>3.9</p><p>49.2</p><p>174</p><p>.81</p><p>2.32</p><p>2.50</p><p>4.81</p><p>9.60</p><p>16.4</p><p>721</p><p>.64</p><p>187</p><p>15.</p><p>59</p><p>16.</p><p>51</p><p>0.5</p><p>68.6</p><p>78.0</p><p>79.9</p><p>3386</p><p>.068</p><p>81.0</p><p>97.1</p><p>94.</p><p>55.</p><p>269.3</p><p>461</p><p>.47</p><p>2.12</p><p>2.39</p><p>6.66</p><p>11.7</p><p>014</p><p>.74</p><p>25.3</p><p>7...</p></li></ul>

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