02859naa a2200289 a 450000100080000000500110000800800410001902400350006010000200009524501640011526000090027950003500028852015710063865000240220965300250223365300190225865300270227765300310230470000130233570000230234870000150237170000150238670000180240170000170241970000180243677301150245410613452021-08-12       2021    bl uuuu     u00u1 u    #d7 adoi.org/10.1111/ppl.132022DOI1 aVANDEGEER, R.K.  aSilicon deposition on guard cells increases stomatal sensitivity as mediated by K+ efflux and consequently reduces stomatal conductance.h[electronic resource]  c2021  aArticle history: First published: 03 September 2020/Version of Record online:16 September 2020/Accepted manuscript online: 03 September 2020/Manuscript accepted:01 September 2020/Manuscript revised:27 August 2020/Manuscript received:30 June 2020/First published: 03 September 2020.  Corresponding author: e-mail: R.Vandegeer@westernsydney.edu.au  aAbstract: Silicon (Si) has been widely reported to improve plant resistance to water stress via various mechanisms including cuticular Si deposition to reduce leaf transpiration. However, there is limited understanding of the effects of Si on stomatal physiology, including the underlying mechanisms and implications for resistance to water stress. We grew tall fescue (Festuca arundinacea Schreb. cv. Fortuna) hydroponically, with or without Si, and treated half of the plants with 20% polyethylene glycol (PEG) to impose physiological drought (osmotic stress). Scanning electron microscopy (SEM) in conjunction with X-ray mapping (XRM) found that Si was deposited on stomatal guard cells and as a sub-cuticular layer in Si-treated plants. Plants grown in Si had a 28% reduction in stomatal conductance and a 23% reduction in cuticular conductance. When abscisic acid was applied exogenously to epidermal leaf peels to promote stomatal closure, Si plants had 19% lower stomatal aperture compared to control plants (i.e.increased stomatal sensitivity) and an increased efflux of guard cell K+ ions. However, the changes in stomatal physiology with Si were not substantial enough to improve water stress resistance, as shown by a lack of significant effect of Si on water potential, growth, photosynthesis and water-use efficiency. Our findings suggest a novel underlying mechanism for reduced stomatal conductance with Si application; specifically, that Si deposition on stomatal guard cells promotes greater stomatal sensitivity as mediated by guard cell K+ efflux.  aFESTUCA ARUNDINACEA  aLEAF WATER POTENTIAL  aPHOTOSYNTHESIS  aRELATIVE WATER CONTENT  aSCANNNG ELECTON MICROSCOPY1 aZHAO, C.1 aCIBILS-STEWART, X.1 aWUHRER, R.1 aHALL, C.R.1 aHARTLEY, S.E.1 aTISSUE, D.T.1 aJOHNSON, S.N.  tPhysiologia Plantarum, Volume 171, Issue 3, Pages 358-370,  March 2021. Doi: https://doi.org/10.1111/ppl.13202