Transcriptome dynamics of rice in natura: Response of above and below ground organs to microclimate.

The long-term dynamics of the transcriptome under natural field conditions remain unclear. We conducted comprehensive gene expression analyses of rice leaves and roots grown under natural field conditions for a long period, from the tillering stage to the ripening stage. In this experiment, changes in the transcriptome were captured in relation to microclimatic parameters, particularly potential evaporation (Ep), which is a multiple meteorological factor and acts as an indicator of transpirational demand.

Aquaporins in developing rice grains.

During rice grain filling, grain moisture content and weight show dynamic changes. We focused on the expression of all 33 rice aquaporins in developing grains. Only two aquaporin genes, OsPIP2;1 and OsTIP3;1, were highly expressed in the period 10-25 days after heading (DAH).

Cold stress-induced acclimation in rice is mediated by root-specific aquaporins.

Cold acclimation process plays a vital role in the survival of chilling- and freezing-tolerant plants subjected to cold temperature stress. However, it remains elusive whether a cold acclimation process enhances root water uptake (a component of chilling tolerance) in chilling-sensitive crops such as rice. By analyzing the root hydraulic conductivity under cold stress for a prolonged time, we found that cold stress induced a gradual increase in root osmotic hydraulic conductivity [Lp(r(os))].

Transpiration from shoots triggers diurnal changes in root aquaporin expression.

Root hydraulic conductivity (Lp(r)) and aquaporin amounts change diurnally. Previously, these changes were considered to be spontaneously driven by a circadian rhythm. Here, we evaluated the new hypothesis that diurnal changes could be triggered and enhanced by transpirational demand from shoots.

Vacuolar proton pumps and aquaporins involved in rapid internode elongation of deepwater rice.

Rapid growth of the submerged shoots of deepwater rice is essential for survival during the rainy season. We investigated changes in the expression of vacuolar H(+)-ATPase (V-ATPase), H(+)-pyrophosphatase (V-PPase), and aquaporins under submerged conditions. The amounts of vacuolar proton pumps, which support the active transport of ions into the vacuoles, were maintained on a membrane protein basis in the developing vacuoles.

Effect of low root temperature on hydraulic conductivity of rice plants and the possible role of aquaporins.

The role of root temperature T(R) in regulating the water-uptake capability of rice roots and the possible relationship with aquaporins were investigated. The root hydraulic conductivity Lp(r) decreased with decreasing T(R) in a measured temperature range between 10 degrees C and 35 degrees C. A single break point (T(RC) = 15 degrees C) was detected in the Arrhenius plot for steady-state Lp(r).

Osmotic water permeability of plasma and vacuolar membranes in protoplasts I: high osmotic water permeability in radish (Raphanus sativus) root cells as measured by a new method.

Intra- and transcellular water movements in plants are regulated by the water permeability of the plasma membrane (PM) and vacuolar membrane (VM) in plant cells. In the present study, we investigated the osmotic water permeability of both PM (P ( f1)) and VM (P ( f2)), as well as the bulk osmotic water permeability of a protoplast (P ( f(bulk))) isolated from radish (Raphanus sativus) roots. The values of P ( f(bulk)) and P ( f2) were determined from the swelling/shrinking rate of protoplasts and isolated vacuoles under hypo- or hypertonic conditions.

Osmotic water permeability of plasma and vacuolar membranes in protoplasts II: theoretical basis.

Water permeability of the plasma membrane (PM) and the vacuolar membrane (VM) is important for intracellular and transcellular water movement in plants, because mature plant cells have large central vacuoles. We have developed a new method for measuring the osmotic water permeability of the PM and VM (P ( f1) and P ( f2), respectively) in individual plant cells. Here, the theoretical basis and procedure of the method are discussed.