Source-Sink Relationships And Leaf Senescence And The Regulation Of 6-Benzylaminopurine In Wheat (Triticum Aestivum L.)

The source —Sink relationships of nitrogen (N) and phosphorus (P) tranfer and the principle of leaf senescence as well as the regulation of 6—Benzylaminop-urine (BA) during grain — filling period of wheat (Triticum aestivum L. ) under natural condition were reported in this paper. The principal findings are as follows :1. From anthesis to maturity,roots,stem and leaves exported 47%..43%and 75% of their total N, respectively. Their contributions to the ear N accumulation were 3%, 11% and 18%,respectively. The other 67% of ear N accumulation come from the soil N absorped currently. 82% of total plant N was found in the ear at maturity,¹⁵N traced experiments using penultimate leaf internode per-fusion system indicated that ear and leaf are absolute sink (absorbed both endogenous N and exogenous N) ,and other organs are relative sinks (exogenous N absorbed more than endogenous N exported) during anthesis stage;After anthesis stage, ear is the only absolute sink, and other organs are relative source (exogenous N absorbed less than endogenous N exported). That BA treated different organs in different stages influences absorption and tranfer of N. While what the most significantly increased ear N accumlation was BA treated ear in milky stage.2. After anthesis, P was accumulated in grains and glumes continuously, and other organs showed a rapid decrease in P content. Finally, ear possessed 90% of total plant P. Redistribution of P also showed significant diurnal changes in various organs. There are different P distribution focuses at different time in 24 hours. These changes of P distribution focus in consistent with the functional changes of various organs. That BA treated wheat plant could alter the diurnal change pattern and decreased the range of diurnal change of P distribution.3. During flag leaf senescence, the specific activities of acid proteinase andcarboxypeptidase increased in parallel with the decrease of protein and chlorophyll contents. That BA treated flag leaf delayed the rate of protein degradation and the increasing of specific activities of acid proteinase and carboxypeptidase during flag leaf senescence. But the specific activity of aminopeptidase was almost constant and was increased by BA during flag leaf senescence. Therefore, we concluded that acid proteinase and carboxypeptidase must play an active role in wheat flag leaf senescence.4. We investigated the changes of chloroplast ultrastructure with electron microscopy and stereological methods, and have obtained a series of geometry parameters during flag leaf senescence. The results showed that during flag leaf senesconce:(I) Chloroplast shape changed from oval into sphere, the volume, the surface and the number of chloroplast per unit cell volume decreased continuously;(2) Grana volume decreased and lost their integrity;Granal thylakoids swell and were progressively dismantled;But grana number per chloroplasl increased in the early senescence stage;? There was an increased in the number and diameter of osmiophilic granules per chloroplast. That BA treated flag leaf could in-flueuce various stereological parameters of chloroplast. As a result, BA could preserved the stability of chloroplast shape and structure.Finally the physiological adaptability and integral unity of various wheat plant levels during grain — filling period were also discussed.