Previous Research

Cold Stress exerts Adaptation Phenomenon in Rice: Involvement of Aquaporin expression levels in Root Hydraulic Conductivity

Previous works:

  • We evaluated the effect of Low Root Temperature (LRT) on rate of phosphorylation of Aquaporin by using anti-phosphorylated aquaporin antibody. It was revealed that LRT induces phosphorylation as soon as 10 minutes, decreases a bit on day 2 and increases again.
  • In order to evaluate the mechanism of aquaporin signal transduction we examined the effect of Phosphatase inhibitor (Okadaic acid) and of Protein Kinase inhibitor (K252a, Staurosporine).
  • Effect of Abscisic Acid (ABA) on aquaporin expression levels were evaluated; we found that treating the rice root with 1M ABA shows an up regulation in all aquaporin mRNA expression levels. The rate of evaporation in long term (7 days) ABA treatment showed a decrease in dry weight as well as increase in the exudation sap.

Recent works:

figure 1 The involvement of acclimation process of root hydraulic conductivity (Lpr(os)) in rice aquaporin was being evaluated. We showed that at 10ºC, the (Lpr(os)) increased gradually after day 1 and reached a maximum of more than 10 times higher at day 5 compared to the control. figure 2 Among the root-specific Aquaporins (AQP), OsPIP2;5 showed the most dramatic increase in the expression level with a maximum increase of 3 times at day 3. In order to evaluate the acclimation process as well as the signal transduction mechanism in AQP expression levels in root, both long-term and short-term chilling responses were observed using root only chilling and whole plant chilling technique. The mRNA expression levels of AQPs showed that root only chilling increased the AQP expression levels whereas, whole plant chilling resulted in a drastic down regulation of AQP. This surprising data opened the possibility of involvement of shoot signal transport is a prerequisite for root aquaporin signal trigger. Moreover, total AQP level of OsPIP2;5 was found to be increased at root only chilling giving it a status of ‘Rescue AQP’ during cold stress.

figure 3 We also tried to evaluate the aquaporin expression level in the root tip. It is said that aquaporin protein is among the 10 most highly expressed genes in the root tip and other parts of the roots. The root aquaporin expression levels were compared between the root tip, elongation zone and the mature zone including the lateral roots. It was found that OsPIP2;6 plays an important role at the root tip in root development during the growing phase at younger age. Lateral roots showed increased level of aquaporin expressions, especially OsTIP2;1 which shows a significantly higher expression level compared to the other zones. Immunostaining also shows a high level of OsTIP2;1 in the lateral roots but almost no presence in mature part of the main root. This data suggests that OsTIP2;1 plays an important role in root water uptake in the lateral root.

figure 5 Abiotic stress induces a unique acclimation process which is involved in AQP signal transduction for the plants to survive in adverse environments. Furthermore, shoot signal is a vital factor for root water uptake capacity. OsPIP2;5 is considered as the cold stress induced aquaporin where as OsPIP2;6 is believed to play an important role in the root tips that involves the root cell growth and development whereas OsTIP2;1 plays an important role in water uptake in the lateral roots.

August 2015