赤霉素对亚高温胁迫下番茄花柱外露及相关基因表达的影响

Effects of gibberellin on tomato stigma exsertion and hormone-related gene expression under moderate heat stress

研究在亚高温胁迫下生长素(indole-3-acetic acid,IAA)、赤霉素(gibberellin A3,GA3)、茉莉酸(jasmonic acid,JA)及2,4-表油菜素内酯(2,4-epibrassinolide,EBR)等4种植物生长调节剂在番茄开花前后喷施花蕾对花柱外露的生理影响。结果表明:在亚高温胁迫下对花蕾喷施GA3加速了番茄花柱的外露,且外露率增加,外露程度增大,而用赤霉素生物合成抑制剂多效唑(paclobutrazol,PAC)处理可以减轻花柱的外露程度,此外,在亚高温胁迫下喷施GA3提高了番茄的坐果率;喷施JA的番茄花蕾与对照(无激素处理)相比花柱外露率提高,外露程度变化不明显;而喷施IAA与EBR对番茄花柱外露率及坐果率无明显影响。进一步利用实时荧光定量聚合酶链反应技术分析了在亚高温胁迫下经激素处理后生长素、赤霉素、脱落酸等激素信号特征基因及逆境信号传导基因SlPIFs在番茄雄蕊和雌蕊中表达水平的变化。结果表明,在亚高温胁迫下外源GA3或PAC处理使得番茄雄蕊和雌蕊中赤霉素生物合成基因的相对表达水平与无激素处理相比发生了明显不同的变化。在雌蕊中,外源GA3处理使得SlGA20ox1相对表达量显著上升,而赤霉素生物合成途径抑制蛋白基因SlDELLA相对表达量下调,从而增加了赤霉素的合成。此外,GA3处理导致SlPIF1-1、SlPIF4基因在雌蕊中下调表达,而在雄蕊中相对表达水平变化不显著。在雄蕊中,外源GA3处理使得SlGA3ox1相对表达量上调,同时,脱落酸8’-羟化酶代谢基因SlCYP707A1与9-顺式-环氧类胡萝卜素加双氧酶基因SlNCDE1在雄蕊中也上调表达。以上结果表明,赤霉素参与了番茄雄蕊和雌蕊的伸长生长,对番茄在亚高温胁迫下花柱外露有重要调控作用,且这一过程是通过赤霉素生物合成途径发生作用,而光敏色素相互作用因子(phytochrome interacting factors,PIFs)可能参与了亚高温胁迫下赤霉素诱导的番茄花柱外露过程的调控。该结果为深入探索植物激素参与调控高温诱导的番茄花柱外露的分子机制提供了研究基础,并为番茄抗高温栽培技术的完善提供了理论依据。

Summary Tomato, one of the most important vegetable crops, is widely cultivated around the world. Blossom drop is a common growing problem that can be extremely frustrating to the tomato production. The most frequent cause of tomato blossom drop is inappropriate temperature. In hot season, the stigma exsertion often occurs and causes the unsuccessful self-pollination, and finally markedly lowers fruit-setting. In this study, exogenous spray of indole 3 acetic acid （IAA, natural auxins）, gibberellin Aa （GA3）, jasmonic acid （JA） and 2, 4 epibrassinolide （EBR） with different concentrations on tomato flower buds was conducted under controlled heat stress conditions using tomato cv. ＂Micro-Tom＂, aiming to evaluate the influence of plant hormones on the heat-induced stigma exsertion. The growth of stamen and pistil was compared among different treatments. Meanwhile, using quantitative real-time polymerase chain reaction （qRT-PCR）, the changes of expression levels of some important genes involving auxin （IAA）, gibberellin （GA）, and ahscisic acid （ABA） signaling pathways, as well as phytochrome interacting factor （PIF） family genes were examined as exposed to exogenous GA3 or paclobutrazol （PAC） under moderate heat stress. The results indicated that tomato grown under the moderate heat stress developed the flowers with longer style and protruding stigma. Spraying GA3 under the moderate heat stress accelerated the tomato stigma exsertion, and the percentage of flowers for the stigma exsertion increased, whereas PAC, the inhibitor of gibberellin biosynthesis, could rescue the extent of stigma exsertion to some degree. Moreover, continuous GA3 application on the flower buds could significantly increase the tomato fruit setting. Furthermore, JA treatment showed similar effects on increasing the percentage of flowers for stigma exsertion, but the exsertion extent was not obvious. However, the effect of IAA and EBR treatments on stigma exsertion also was not obvious. The expression analysis on eight hormone-related genes as well as four SlPIF genes in tomato stamen and pistil showed that the relative expression level of the gibherellin biosynthesis genes SlGA2Oox2, encoding the main GA20ox in tomato, was significantly up-regulated in pistil when the flower buds were treated with GA3 under the moderate heat stress, whereas the gene SIDELLA, a repressor in the gibberellin signaling pathway, was down-regulated. In contrast, in stamen, SlGA3oxl, expected to be a negative feedback regulation in the gibberellin signaling pathway, was significantly up-regulated. The genes SlNCDE1 encoding a 9-cis-epoxy-carotenoid dioxygenase and SICYP707A1 participating in putative （＋） ABA 8＇ hydroxylase metabolism were up-regulated in stamen. Moreover, SIPIF1 1 and SlPIF4 were down-regulated in pistil. In conclusion, under the moderate heat stress, gibberellin participates in the stamen and pistil elongation growth and has an important regulatory role in tomato stigma exsertion through gibberellin biosynthetic pathway, and the PIF may be involved in the regulation of gibberellin inducing tomato stigma exsertion event. Our study may provide some helpful information for further elucidating the precise roles of plant hormones on tomato stigma exsertion as well as enhancing fruit yields under the moderate heat stress.