College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi Province, China.
PLoS One. 2020 May 5;15(5):e0232750. doi: 10.1371/journal.pone.0232750. eCollection 2020.
The rare earth element lanthanum (La) has been proven to be beneficial for plant growth with a low concentration, and abscisic acid (ABA) which is a plant hormone also can regulate plant growth. In the present study, we investigated the germination and seedling growth of switchgrass (Panicum virgatum L.) under La (10 μM), ABA (10 μM) and La + ABA treatments. The results showed that La, ABA and La + ABA treatments could not significantly affect the germination and shoot length as compared to the control (P>0.05). However, La treatment increased the root activity and chlorophyll content, and ABA treatment enhanced root length and root activity (P<0.05). La + ABA treatments demonstrated that La could not significantly alleviate the promotion of ABA in root length, while ABA reversed the increase of chlorophyll content caused by La. The coregulation of La and ABA on chlorophyll content was further explored by in vitro experiments and quantum chemical calculations. In vitro experiments revealed that La, ABA, and La + ABA treatments reduced the absorbance of chlorophyll, and quantum chemical calculations indicated that the reduction of absorbance was caused by the reactions between La, ABA and chlorophyll. In vivo and in vitro experiments, together with quantum chemical calculations, demonstrated that both ABA and La could stimulate the production of chlorophyll, while they also could react with chlorophyll to produce La-monochlorophyll, La-bischlorophyll, and ABA adsorbed chlorophyll, which had lower absorbance. La + ABA treatment significantly decreased the chlorophyll content in vivo. This phenomenon was due to the fact that La and ABA formed LaABA compound, which markedly reduced the concentrations of ABA and La, and the effect of promoting chlorophyll production was overcome by the effect of reducing chlorophyll absorbance.
稀土元素镧（La）在低浓度下已被证明对植物生长有益，而植物激素脱落酸（ABA）也可以调节植物生长。在本研究中，我们研究了镧（10 μM）、ABA（10 μM）和 La+ABA 处理对柳枝稷（Panicum virgatum L.）萌发和幼苗生长的影响。结果表明，与对照相比，La、ABA 和 La+ABA 处理对萌发和茎长没有显著影响（P>0.05）。然而，La 处理增加了根活力和叶绿素含量，ABA 处理则增加了根长和根活力（P<0.05）。La+ABA 处理表明，La 不能显著缓解 ABA 对根长的促进作用，而 ABA 则逆转了 La 引起的叶绿素含量增加。通过体外实验和量子化学计算进一步探讨了 La 和 ABA 对叶绿素含量的共同调控。体外实验表明，La、ABA 和 La+ABA 处理降低了叶绿素的吸光度，量子化学计算表明，吸光度的降低是由于 La、ABA 和叶绿素之间的反应所致。体内和体外实验，以及量子化学计算表明，ABA 和 La 都可以刺激叶绿素的产生，同时它们也可以与叶绿素反应生成 La-叶绿素、La-二叶绿素和 ABA 吸附叶绿素，这些物质的吸光度较低。La+ABA 处理显著降低了体内叶绿素含量。这种现象是由于 La 和 ABA 形成了 LaABA 化合物，显著降低了 ABA 和 La 的浓度，促进叶绿素产生的作用被降低叶绿素吸收的作用所克服。
