(38(3):277-290)Comparison of Leaf Morphology and N Metabolism Among Rice Genotypes Differing in Grain Weight

本試驗以大粒型品種Pegonil、中粒型品種臺農67號與兩個粒重較高之臺農67號近同源系為主要材料，比較其間葉片形態性狀、氮素代謝酵素活性及維管束性狀的差異，藉以探討影響具不同粒重水稻種源光合及氮素代謝能力之機制。與大粒型品種比較，中粒型品種葉長自上位葉至下位葉顯著增加，葉寬減幅極小，田間透光度較佳，且下位葉比葉重較高，有利於光合作用表現。大粒品種葉片氮素濃度雖然較高，在穀粒充實期間葉綠素及可溶性蛋白質濃度降低的幅度與速率却高於中粒品種，亦即受老化影響，生理活性快速衰退。自抽穗期以後，glutamine synthetase活性逐漸降低，近成熟期時之活性以臺農67號為高，而Pegonil之proteinase活性則超過臺農67號三倍以上，顯示中粒型品種具有較高的氮素同化能力；glutamate dehydrogenase活性在穀粒充實期間的變化不大，推測對氮素代謝的影響較小。兩個回交系統的含氮化合物濃度及氮素代謝作用表現不受粒重影響，較趨近中粒親本臺農67號。造成品種間氮素代謝差異的主因，可能為穀粒對氮素需求的積儲強度。臺農67號葉脈數與葉脈頻度較Pegonil為高，篩管面積則較小，尚難據以判定輸導能力之強弱，但臺農67號篩管面積與維管束面積比值顯著較高，而兩個回交系統之維管束面積亦顯示雜種優勢，為具有利用價值之生理性狀，有必要對此變異性再加研究。 A medium-grain variety, Tainung 67 , a large-grain variety, Pegonil, and two each of their BC5 and BC6 offsprings with caryopsis weight about 28.5mg were used to study morphological, vascular, and N metabolism characters in their leaves. The purpose of this study was to clarify the mechanism governing the difference in photosynthesis and N metabolism among rice genotypes differing in grain weight. Compared to the large-grain Pegonil, leaf length of Tainung 67 increased significantly from upper to lower node positions, and decrease in leaf width was less significant, indicating higher light transmission ratio within canopy and hence a possible higher photosynthetic rate. Concentrations of leaf N and soluble protein at heading was higher for Pegonil, however, the decreases thereafter was also significant. A higher rate of senescence and loss of physiological activities were therefore suggested. Activity of glutamine synthetase decreased after heading, and it was higher for Tainung 67 as the plants approached maturity. On the other hand, proteinase activity of Pegonil was three times higher than that of Tainung 67. It was thus concluded that the capacity of N assimilation was higher for Tainung 67 during the grain-filling period. The two backcross offsprings-performed similar to Tainung 67 in terms of changing concentrations of N-containing compounds and N assimilation ability after heading, as no effect of grain-weight was observed in these genotypes. Tainung 67 was high in total vein number and vein frequency, but lower in phloem area than Pegonil. The data obtained failed to assess difference in vascular capacity between the two varieties. However, the highest phloem to vascular area ratio and heterosis in vascular area found in the two backcross offsprings are considered as superior physiological characters which might be of value for future variety improvement