Shabala Sergey, Pang Jiayin, Zhou Meixue, Shabala Lana, Cuin Tracey A, Nick Peter, Wegner Lars H
School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tas. 7001, Australia.
Plant Cell Environ. 2009 Feb;32(2):194-207. doi: 10.1111/j.1365-3040.2008.01914.x. Epub 2008 Nov 17.
Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1-2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from -18 to -12 nmol m(-2) s(-1)) and K+ uptake (approximately 2 nmol m(-2) s(-1)) reverted to efflux (approximately -3 nmol m(-2) s(-1)). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a approximately 3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 mm NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (-50 nmol m(-2) s(-1)). Kinetin (2-4 microM), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.
成熟根区的养分获取受地上部和根尖的系统控制。在玉米中，地上部暴露于光照下会对根表面的净钾离子（K⁺）和氢离子（H⁺）转运产生短期（1 - 2分钟内）影响。氢离子外流减少（从 -18降至 -12 nmol m⁻² s⁻¹），钾离子吸收（约2 nmol m⁻² s⁻¹）转变为外流（约 -3 nmol m⁻² s⁻¹）。木质部探测显示，木质部导管与外部电极之间的跨根（电）电位降在光照强度逐步增加后数秒内就会做出反应；木质部压力在大约3分钟的延迟后开始下降，这有利于电信号而非液压信号。在低盐培养基中，将玉米和大麦的根从基部切断会减少氢离子外流并停止钾离子内流；木质部压力迅速升至大气水平。向浴液中添加100 mM氯化钠后，切断时的压力跃升更为显著，但通量仍未受影响，这进一步证明了离子吸收不受液压调节。切除大麦根尖后，内流转变为大量外流（-50 nmol m⁻² s⁻¹）。激动素（2 - 4 μM），一种合成细胞分裂素，可逆转这种效应。本文讨论了根尖合成的细胞分裂素对离子转运的调节作用。
