Effects Of Soil Moisture Stress On Translocation Of Assimilates And Grain Filling In Rice And Wheat During Grain Filling Period And Its Mechanism

In this study, typical rice (Oryza sativa L.) and wheat (Triticum aestivum L.) cultivars were used asmaterials, and pot, shed and field culture experiments were conducted. Treatments of different soil waterpotentials (? soil) and N levels at grain filling period were designed for each experiment. Effects of soilmoisture stress and various N levels on translocation of assimilate and grains filling and their physiologicalmechanism were investigated. The main results are as follows:1. If a moderate water deficit was imposed during the mid and late grain filling period (from 9 d afteranthesis to maturity), plants could rehydrate overnight, and photosynthesis could not be heavily inhibited.This practice could enhance the remobilization of pre-stored carbon from vegetative tissues to the grainsand accelerate the grain-filling rate. The grain yield was not significantly reduced at a normal N level.When senescence of plants was unfavorably delayed by heavy use of N fertilizer, the gain from theenhanced remobilization and accelerated grain-filling rate could outweigh the loss of photosynthesis andshortened grain-filling period, leading to increase of grain yield, under the moderate water deficit.2. A moderate water deficit imposed during the grain filling period enhanced activities of sucrosesynthase (Susase), starch synthase (StSase), and starch branching enzyme (BE or Q-enzyme) in grains,whereas high amount N applied at heading time reduced the activities of the enzymes. Soil moisture and Nlevels had no significant effect on the activities of adenosine diphosphoglucose pyrophosphprylase(AGPase) and acid invertase in the grain. Increase in grain filling rate was closely associated with theenhancement in the activities of SuSase, StSase, and Q-enzyme in grains under the moderate water deficit.3. The evolution rate of ethylene of the wheat grains descends with days after anthesis increasing atgrain filling period, but the each period descends the speed was different, The evolution rate of ethylenewhile arriving the maturation already extremely minute. Although the same position grains of the evolutionrate of ethylene at each treatments expose no significant different, the evolution rate of ethylene of the thirdposition grain exceed the first or second position grain at each treatment from 9 days after anthesis to 30days after anthesis, but the first and second grain reveal no significant difference. The evolution rate ofethylene of wheat grains releases the same regularity during 72 hours at 6 days after anthesis.