Halotropism in Turfgrass.

Turfgrasses are said to cover approximately 16 million hectares in the continental U.S. and to be largest irrigated crop in the country.  Global climate change and increasing demands for fresh water have resulted in decreased availability and increases in cost for freshwater irrigation.  While use of re-claimed water as an alternate irrigation strategy is on the rise, this water can contain large concentrations of salt.  Also, as less irrigation is being applied, due to restrictions, salts will aggregate in soils.  For turfgrass managers, salt stress is generally maintained through flushing with large volumes of freshwater, but this option may be forbidden by law in the future.  Cool season turfgrasses, in particular, are not tolerant to salts; an understanding of mechanisms of turfgrass adaption to salt stress is therefore needed.  Currently, salt exclusion and sequestration are well-understood mechanisms of salt tolerance.  However, a tropic growth response has also been recently defined in Arabidopsis, tomato, and sorghum.  Halotropism is a form of adaptive growth where upon exposure to a directional salt stress, roots will bend/grow away from the area of high salt concentration due to changes in auxin transport and metabolism.  As flavonoids have also been shown to interact with auxin transport and metabolism, flavonoids may modulate halotropism.  The objective of this study was to first determine if the turfgrass species rough bluegrass (Poa trivialis L.) exhibits halotropism, and to second determine the impact of flavonoid accumulation on halotropism.  Results show that rough bluegrass exhibits halotropic growth at 300 mM NaCl.  Halotropic growth was also shown to be modulated through flavonoid application and treatment with specific light regimes.