Abstract
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.
Highlights
ObjectivesThe objectives of this study were to (1) investigate the possible use of La as a fertilizer during switchgrass growth and the specific mechanism of its interaction with abscisic acid (ABA) and (2) determine whether La and ABA coregulate the chlorophyll content of switchgrass
It was seen that La and abscisic acid (ABA) had no significant effects on seed germination rate at day 5 and day 14 (Fig 1(a), S1a Table)
The results showed that the UV-Vis spectra of the control (Mg-chlorophyll A (MgCA) + Mg-chlorophyll B MgCB), ABA, La, and La + ABA treatments were similar to each other, and all of them had two strong absorption peaks at 413 and 649 nm in the visible region
Summary
The objectives of this study were to (1) investigate the possible use of La as a fertilizer during switchgrass growth and the specific mechanism of its interaction with ABA and (2) determine whether La and ABA coregulate the chlorophyll content of switchgrass
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