Minisymposium 8: Water & Salinity

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Abs # M0801: Genetic analysis of hydrotropism in Arabidopsis thaliana

Presenter:	Cassab, Gladys I.       Contact Presenter
Authors	Cassab, Gladys I. (A)   Ponce, Georgina  (A)   Saucedo, Manuel  (A)   Campos, Maria E (A)   Quiroz, Francisco  (A)   Hernandez, Elizabeta  (A)   Herrera, Berenice B (A)
Affiliations:	(A): Institute of Biotechnology-UNAM

The survival of terrestrial plants depends upon the capacity of roots to obtain water and nutrients from the soil. Directed growth of roots in relation to a gradient in moisture is called hydrotropism and begins in the root cap with the sensing of the moisture gradient. Even though the lack of sufficient water is the single-most important factor affecting world agriculture, there are few studies on hydrotropism. Recent genetic analysis of hydrotropism in Arabidopsis has provided new insights about the mechanisms that the root cap uses to perceive and respond simultaneously to moisture and gravity signals. Using a screening system with a water potential gradient, we isolated a no hydrotropic response (nhr1) semi-dominant mutant of Arabidopsis that continued to grow downwardly into the medium with the lowest water potential contrary to the positive hydrotropic and negative gravitropic response seen in wild type-roots. The root gravitropic response of nhr1 seedlings was significantly faster in comparison with those of wild type. The enhanced gravitropic of nhr1 roots might suggest that the reduction in the strength of hydrotropism increases the net effectiveness of the gravitropic response. Further, hydrostimulated nhr1 mutant roots maintained their amyloplasts in columella cells opposing to those of wild type and thus, nhr1 roots exhibited gravitropism with no interference from hydrotropism. Expression of the nhr1 phenotype by heterozygous nhr1 roots exhibited intermediate penetrance, typically 50% depending on the batch of seed. Addition of 10μM abscicic acid (ABA) increased penetrance of the nhr1 phenotype up to 100%. In addition, hydrostimulated nhr1 roots treated with ABA developed larger and sedimented amyloplasts in contrast to those of wild type roots. These results suggest that ABA might play an important role in hydrotropism. We have also developed a screening system for the isolation of putative super hydrotropic response (suh) mutants of Arabidopsis. The suh1 mutant roots continuously grew under water deficit for 10 days and reach the moderate water potential conditions present in the lower section of the Petri dish in contrast with wild type roots. These analyses indicate that the application of new genetic screens for dissecting complex signaling phenomena such as hydrotropism is promising. Supported by CONACyT: 46022Q and DeGAPA, UNAM: IN412203.