Physiological Function Analysis Of GNP1 Gene Affecting Grain Number Per Panicle In Rice

Source–sink–flow relationship determines allocation of assimilation and ultimate grain yield.However,the physiological mechanism study on regulation of source and sink related traits relevant to grain number per panicle gene GNP1 has not been reported so far.Gene GNP1 can enhance the activity of rice cytokinins,thereby inhibiting the accumulation of active GA1 and GA3,thus increasing the number of grains per ear.We developed near-isogenic lines NIL-GNP1^TQ containing GNP1 chromosomal region?66.1Kb?derived from Teqing in Lemont genetic background.We compared physical function of GNP1 gene on source,sink and flow related traits using NIL-GNP1^TQ and its recurrent parent Lemont.The major results are summarized as follows:NIL-GNP1^TQ had more grain number per panicle and filled number per panicle,but less effective panicle number per plant and 1000-grain weight compared to Lemont.The decrease in seed setting rate of NIL-GNP1^TQ was mainly attributed to decrease seed setting rate of the inferior grains on the secondary branch.Grain yield of NIL-GNP1^TQ increased 6.8%⁷.5%.Compared with Lemont,flag leaf area,second leaf area and leaf area index of NIL-GNP1^TQ significantly increased.No significant difference in net photosynthetic rate between NIL-GNP1^TQ and Lemont from full heading date to full heading date after 21 day.NIL-GNP1^TQ had more stomatal density and size than those of Lemont.NIL-GNP1^TQ exhibited higher dry matter accumulation and transformation percentage of NSC than those of Lemont.The grain-filling processes of superior and inferior spikeletes in NIL-GNP1^TQ and Lemont were both asynchronous.NIL-GNP1^TQ had slower grain-filling rate,shorter grain filling period and lower grain plumpness.The starch content of superior and inferior spikelets in NIL-GNP1^TQ significantly decreased compare to Lemont.Compared with Lemont,NIL-GNP1^TQ had increase in phloem area,xylem area and total area of large and small vascular bundle,but decrease in total mesophyll area in flag leaf.NIL-GNP1^TQ had more large and small vascular bundles,and larger phloem area,xylem area and total area of large and small vascular bundle in peduncle and second node,hinting that NIL-GNP1^TQ exhibited efficient transporting system.The grain yield and total sink load per leaf area of NIL-GNP1^TQ were similar to those of Lemont.The spikelet number,grain yield and total sink load per area of vascular bundle and phloem of NIL-GNP1^TQ were significantly larger than those of Lemont.