Hydrotropism

Hydrotropism

Hydrotropism (hydro- "water"; tropism "involuntary orientation by an organism, that involves turning or curving as a positive or negative response to a stimulus")[1] is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration. A common example is a plant root growing in humid air bending toward a higher relative humidity level.

This is of biological significance as it helps to increase efficiency of the plant in its ecosystem.

The process of hydrotropism is started by the root cap sensing water and sending a signal to the elongating part of the root. Hydrotropism is difficult to observe in underground roots, since the roots are not readily observable, and root gravitropism is usually more influential than root hydrotropism.[2] Water readily moves in soil and soil water content is constantly changing so any gradients in soil moisture are not stable.

Root hydrotropism research has mainly been a laboratory phenomenon for roots grown in humid air rather than soil. Its ecological significance in soil-grown roots is unclear because so little hydrotropism research has examined soil-grown roots. Recent identification of a mutant plant that lacks a hydrotropic response may help to elucidate its role in nature.[3] Hydrotropism may have importance for plants grown in space, where it may allow roots to orient themselves in a microgravity environment.[4]

This behavior is thought to have been developed millions of years ago when plants began their journey onto dry land.[5] While this migration led to much easier consumption of CO2, it greatly reduced the amount of water readily available to the plants. Thus, strong evolutionary pressure was put on the ability to find more water.

  1. ^ condensed definitions, Webster's New Collegiate Dictionary
  2. ^ Takahashi N, Yamazaki Y, Kobayashi A, Higashitani A, Takahashi H (June 2003). "Hydrotropism interacts with gravitropism by degrading amyloplasts in seedling roots of Arabidopsis and radish". Plant Physiology. 132 (2): 805–810. doi:10.1104/pp.102.018853. PMC 167020. PMID 12805610.
  3. ^ Eapen D, Barroso ML, Campos ME, Ponce G, Corkidi G, Dubrovsky JG, Cassab GI (February 2003). "A no hydrotropic response root mutant that responds positively to gravitropism in Arabidopsis". Plant Physiology. 131 (2): 536–546. doi:10.1104/pp.011841. PMC 166830. PMID 12586878.
  4. ^ Takahashi H, Brown CS, Dreschel TW, Scott TK (May 1992). "Hydrotropism in pea roots in a porous-tube water delivery system". HortScience. 27 (5): 430–432. doi:10.21273/HORTSCI.27.5.430. PMID 11537612.
  5. ^ Cassab GI, Eapen D, Campos ME (January 2013). "Root hydrotropism: an update". American Journal of Botany. 100 (1): 14–24. doi:10.3732/ajb.1200306. PMID 23258371.