塩条件下で発生するイネ（Oryza sativa L.) 高節位分げつの成長とナトリウム蓄積

The mechanism of late-grown tillers which come out of the upper culm nodes in rice (Oryza sativa L.) under saline conditions was examined. A rice cultivar, Akihikari was grown in pots under flooding conditions. The panicles were excised below the neck node of the panicle at the heading stage. Salinity treatment consisted of adding 100mM sodium chloride to water of pot at the excision of panicle (Na0), and 14 days after the excision (Na2). Tillers on the upper clum nodes grew in NaO and Na2. Dry weight of tillers increased with decrease of dry weight of stock shoots that produced the tillers. So the sum of dry weights of the stock shoots and tillers did not change, indicating that tiller growth apparently depended on reserve of carbohydrate in the stock shotts. Sodium was accumulated gradually in the plant, while sodium content of internode and tiller were kept lower than those of leaa blade and leaf sheath. In the leaf blade and leaf sheath, the upper organs accumulated less sodium than the lower organs. The tillers on the upper nodes grow faster and had low sodium content in the early stages of tiller development in NaO. Therefore, it was concluded that tillers which come out of the upper culm nodes could grow under saline conditions because the sodium content of tiller, internode and the upper leaf sheath were kept at a relatively low level.

塩条件下において高節位分げつが成長する要因を調べた．水稲品種アキヒカリをポットに移植し湛水条件で栽培し，出穂期に穂を穂首節真下より切除した．ポットの水にNaCl濃度100mMとなるようにNaClを添加する処理を穂切除直後（Na０区）と14日後（Na２区）に行った．Na０とNa２区ともに高節位分げつが成長，乾物重が増加するとともに分げつを発生させた茎（母茎）の乾物重は低下した．分げつと母茎の乾物重の和は変化がなく，分げつの成長は母茎の貯蔵炭水化物によっていた．節間と分げつのNa含有率は葉身と葉より低く保たれ，葉身，葉鞘でも下位節に比べ上位節のNa含有率が低かった．またNa０区の分げつ成長初期では茎上部の分げつほど成長が早く，Na含有率が低かった．以上のことから塩条件下で高節位分げつが成長するのは分げつと乾物供給源である節間と上位葉のNa含有率が比較的低く抑えられるためであると考えられた．