Changes of Water Potential in Rice Panicle under Increasing Drought Stress at Various Stages

Abstract

Experiments were conducted to examine whether the responses in panicle water potential under drought changes with panicle development. Twenty seedlings of two rice cultivars, Norin 20 and Milyang 23, were grown in a 4-liter pot under submerged-soil conditions. Tillers being removed weekly, only main culms were subjected to drought treatment. The treatment was imposed by withholding water at the different stages of panicle development : the spikelet differentiation stage in Norin 20, and the panicle differentiation stage, the meiosis stage and the early stage of grain growth in Milyang 23. Before heading the water potential of panicles changed little diurnally whereas it fluctuated markedly in concert with change in the potential evapotranspiration after heading. The decrease in panicle water potential during drought treatment was much less at the meiosis stage than at the earlier stages. Regardless of the developmental stage, the water potential of the panicles was lower than that of the soil when the soil was moist. With the increase of drought, the panicle water potential approached the soil water potential. These results suggest that water potential of panicles responds to transpiration under drought similarly as under submerged-soil conditions. The panicle water potential is also affected by drought through water flux for growth. Furthermore, during the meiosis stage the panicle undergoes a slower decrease in water potential probably due to its higher resistance to and/or capacitance of water flux. © 1993, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.