Changes Of Starch Grains In Lodicule Cells During The Flowering Time Of Rice And Sorghum

The common theory about floret opening of gramineous plants such as rice is that decreased water potential of lodicule cells causes lodicules to swell and the swelled lodicules push the floret open. Increased soluble sugar and other osmotic material in the lodicule cells decreases the water potential and the hydrolysis of starch in the lodicule cells is the main source of the osmotic material. So far, there are no systematic researches on the function of lodicules starch granules in the process of floret opening. In this study, conventional rice, male sterile rice and sorghum with different characteristics of floret opening were used for lodicules paraffin section researches. The dynamic changes of number of cells with starch granules, number of starch granules per cell, volume of starch granules, and the spatial distribution of starch granules in the lodicules were investigated, and the relationship of these changes and the floret opening is analyzed to elucidate the function of lodicules starch granules in the process of floret opening. The results are as follows:1. With the rice floret maturity increased, from3days before to the day of floret opening, the volume of lodicule cells, number of starch granules per cell, volume of starch granules and number of cells with starch granules increased gradually. Within2h before the floret opening of conventional rice, volume of starch granules decreased, number of starch granules per lodicule cell and number of lodicule cells with starch granules decreased rapidly. While in male sterile rice, number of starch granules per lodicule cell and number of lodicule cells with starch granules also decreased gradually in the period of2h before floret opening, but the decrement is smaller compared with that in the conventional rice, and there were no significant changes in volume of starch granules.2. When the conventional rice florets failed to open normally due to the cloudy or rainy weather conditions, the increment of the volume of lodicule cells and the decrement of number of starch granules per cell, volume of starch granules and number of cells with starch granules were smaller than that in lodicules of rice in the normal weather conditions. But in the afternoon, when the temperature increased, the florets opened. And in this case, the volume of lodicule cells increased and the number of starch granules per cell, volume of starch granules and number of cells with starch granules decreased rapidly before the floret opening.3. When the rice florets opened earlier due to the mechanical stimulation of the panicles, the volume of lodicule cells increased gradually and reached the maximum in2h after the mechanical stimulation. The number of starch granules per cell and number of cells with starch granules decreased gradually and reached the minimum within1.5h to2h after the mechanical stimulation, volume of starch granules decreased slightly. While in the control florets without mechanical stimulation, there were no significant changes in the corresponding time.4. In sorghum, with the floret maturity increased, the number of starch granules per cell and volume of starch granules increased3.2d before florets opening, but decreased rapidly in the period2h before floret opening.5. The above results suggested that the function of starch granules in the lodicule cells of rice and sorghum is to offer a mechanism of water potential regulation which regulates the timing of floret opening.6. Rice lodicules had an uneven spatial distribution of starch granules, starch granules mainly distributed in the outer2.3layers of cells of lodicules. While in the sorghum lodicules, starch granules were evenly distributed. The relationship between the difference of floret opening time and the difference of starch granule distribution of rice and sorghum need further investigation.