Calcium-45 Mobility in Young Apple Trees Grown under Different nutrient-calcium Conditions

Abstract

Root-applied 45Ca was readily translocated to leaves of normal-Ca trees but was less readily translocated to leaves of high-K or low-Ca trees. Calcium-45 accumulated to a much greater extent in roots and stems of the latter than in the former trees. Root-applied 45Ca was translocated much more readily to apical young leaves than to basal old leaves of growing shoots. Shoot-applied 45Ca was rapidly translocated to all leaves of excised shoots through the xylem transpiration stream. Calcium-45 applied to trees at the later stages of fruit development scarcely entered the fruit but accumulated strongly in the leaves of the fruit truss, and especially in the attachment point of the fruit (future abscission zone). The general nutritional status of trees changes the mobility of Ca through its effect on Ca-fixing sites in the plant tissues. A hypothesis of continuously-developing calcium-fixing sites in growing plant tissues has been proposed. 施用於根部之鈣-45 在正常鈣營養之果樹比在高濃度鉀或缺乏鈣營養之果樹較容易運移至葉部。後者果樹比前者果樹鈣-45 聚積更多於其根部及莖基部，施用於根部之鈣-45 在生長中之枝條運移至上端新葉比至基部老葉為多。施用於切斷枝條之斷端之鈣-45 迅速的經過導管之蒸散流運移至枝條上所有的葉片。在果實生長後期，果樹所吸收之鈣-45 頗難進入果實內，而聚積於果責附近之葉片。一般果樹之無機營養狀態可影響其組織中之鈣吸附及固定能力，而改變鈣在植物體之移動性，生長中之植物組織有繼續產生固定鈣的基質。