The mechanism behind lack-of-effect of lanthanum on seed germination of switchgrass

Abstract

Switchgrass ( Panicum virgatum L.) is a perennial warm-season C 4 grass identified as a model species for bioenergy feedstock production. Lanthanum (La) as a rare earth element can stimulate the physiological processes of plant growth. The purpose of this study was to investigate the effect of lanthanum on seed germination of switchgrass. However, no significant differences in seed germination were found. The energy dispersive X-ray analysis showed that abundant lanthanum deposits resided on the pericarp and testa of the seed while few lanthanum deposits were present on the aleurone and endosperm. This phenomenon demonstrates that a semi-permeable layer, which could restrict or impede solute exchange, while allowing the permeability of internal and external water and gas, may be located between the testa and aleurone. Light microscopy and histochemical analysis revealed that the main chemical composition of the semi-permeable layer would be expected to be suberin because the layer was stained yellow with aniline blue. The quantum chemical calculations predict that the intervals between adjacent carbon chains in suberin molecule are so small that lanthanum ([La(H 2 O) 8 ] 3+ ) cannot pass through the suberin molecule. In conclusion, the seed germination of switchgrass is not affected by lanthanum because the semi-permeable layer restricts the penetration of lanthanum into the embryo.

Lanthanum and abscisic acid coregulate chlorophyll production of seedling in switchgrass

“…Several studies have investigated the seed germination of switchgrass under La or ABA stress. Thomas et al [31] found that La had no effect on germination of switchgrass at any dose, which was consistent with our previous work [32]. Duclos et al [18] showed that ABA inhibited the germination of switchgrass at a dose equal to or larger than 10 μM.…”

“…In the present study, we observed that La and ABA had no significant effect on seed germination, suggesting that the caryopsis covering structure was somewhat restrictive to the movement of macromolecular substances [32], and that ABA could significantly promote the root growth of switchgrass, while La could not alleviate the promotion of root growth by ABA. The root is the major organ for the absorption of water and nutrients.…”