Short-term boron deprivation enhances levels of cytoskeletal proteins in maize, but not zucchini, root apices

By using indirect immunofluorescence microscopy and Western blot analysis, we have demonstrated increased levels of actin and tubulin proteins as well as an altered polymerization pattern of their cytoskeletal assemblies in maize, but not zucchini root apices, as a response to early boron deprivation. Northern blot analysis, however, did not show significant increases in the amount of steady-state mRNAs of actin and tubulin. This finding indicates that these rapid cytoskeletal responses to boron removal are very likely regulated at translational/post-translational levels. Interestingly, these increased levels of cytoskeletal proteins coincided well with a reduction in the water-extractable, but not with the cell wall-bound, fraction of boron. This implicates that free boric acid, or other more labile boron complexes, might be involved in the activation of cytoskeletal responses in maize root apices. In fact, our experimental approach revealed that maize was suffering from boron deprivation as early as zucchini. This was evidenced by its slightly reduced root elongation rate recorded within 3-5 h of boron deprivation. Importantly, however, maize roots can recover from this early inhibition indicating an effective adaptation mechanism. In contrast, zucchini roots apparently lack this boron-deprivation response pathway and suffer extensively when exposed to boron-free environment. This leads to the tentative working hypothesis for an adaptive mechanism of maize roots to boron deprivation by enhancing its cytoskeletal protein levels and altering their polymerization patterns in order to mechanically reinforce the cell periphery complex of their cells. This testable hypothesis requires further experimental verification.