. Paclobutrazol [(2 RS ,3 RS )-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice ( Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA 3 induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA 3 treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA 3 -treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality.

代謝阻害剤および抗オーキシンがトウモロコシ根皮層より酵素的に単離されたプロトプラストの2, 4-D吸収に及ぼす影響を細胞内pH (pHi) に及ぼす影響と関連して検討した. 作用機作の異なる5種類の代謝阻害剤はプロトプラストによる2, 4-D吸収を阻害した. これらの化合物はすべて5, 5-ジメチルオキサゾリジン-2, 4-ジオン分配法により測定されるpHiを低下させ, 2, 4-D吸収阻害は阻害剤の作用機作にかかわらずpHi低下と密接に関連していた. このことは原形質膜を介するpH勾配が2, 4-D吸収の重要な要因であることを示唆する. 一方, 抗オーキシンp-クロロフェノキシイソ酪酸 (PCIB) はpHiに影響を及ぼすことなく2, 4-D吸収を阻害した. 別の抗オーキシンN-1-ナフチルフタラミン酸 (NPA) は2, 4-D吸収, pHiいずれにも影響を及ぼさなかった. これらの結果は, トウモロコシ根プロトプラストによる2, 4-D吸収機構が二つの成分, すなわち, 1) 弱酸仮説に従う未解離2, 4-D分子の受動的な拡散と, 2) PCIB感受性でNPA非感受性のH+/オーキシンアニオン共役輸送体に媒介される解離2, 4-Dアニオンの能動輸送から成ることを示唆する.

トウモロコシ根皮層より酵素的に単離されたプロトプラストの2, 4-D吸収を細胞内外のpHと関連して検討した. 2, 4-D吸収は細胞外pH (pHo) の低下とともに増大した. プロトプラスト外部に対する内部の2, 4-D濃度比(ci/co) はpHo7.5, 6.5, 5.5, 4.5において75分以内の培養でおのおの約1.2, 4.0, 10～12, 30～40に達した. pHo3.5, 2.8においては15分以内にci/co比がおのおの約90, 150に達したが, 吸収された2, 4-Dはその後プロトプラストの死により速やかに放出された. 5, 5-ジメチルオキサゾリジン-2, 4-ジオン分配法による細胞内pH (pHi) 測定の結果, pHo変化 (7.5～4.5) によるpHi変化は比較的小さかった (6.9～6.6). これらのpHi測定値を用いて各pHoにおける理論的ci/co比を弱酸仮説に基づいて推定した. pHo変化に対する理論値の傾向は大まかには実測値の傾向を反映したが, pHo6.5および7.5におけるci/co比実測値はおのおのの理論的最大値を顕著に上回っていた. これらの結果は. プロトプラストによる2, 4-D吸収が単に弱酸仮説のみでは説明されえず, 少なくともpHo6.5および7.5においては能動的な輸送の関与していることを示唆する.

In current agricultural practices the foliar application of pesticides for the control of unwanted pests plays a major role in economic crop production. T h e penetration of foliar-applied pesticides is strongly influenced by the plant surface, the spray solution, and the environmental conditions before, during, and following application. T h e biological activity of a herbicide has been shown to be influenced by the physico-chemical properties as well as the rate and manner in which it was applied to the leaf (11). T h e interactions between the plant and the pesticide will govern the quanti ty that will enter the plant. T h e question of why some pesticides are translocated within the plant, and others are not, is of considerable importance and could be used to predict the systemic properties of pesticides. Many pesticides are incapable of being transported in the symplast from external applications because the physico-chemical properties, such as polarity, inability to move across membranes, adsorption to various cellular components, etc., prevent their entry into the symplasm. If they do enter, their movement is prevented. Translocat ion of assimilates (photosynthates) in plants involves both a metabolically active source (area of synthesis or high concentration) and a metabolically active sink (area of utilization or storage). Thus, assimilates will move through the sieve elements in the direction of the sink and at a rate determined by the sink strength. A unique feature of the phloem is the ability of the materials in the phloem to move out of the sieve elements or into the sieve elements at any point along the system. This report will present some of the current ideas or hypotheses currently be-

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The potential losses from spray applications of glyphosate [ N -(phosphonomethyl)glycine] with and without the inclusion of a polymer thickening agent were evaluated in field tests, applied under identified weather conditions with a boom-nozzle ground sprayer, helicopter, and fixed-wing aircraft. The downwind transport and diffusion of the spray loss was assessed by means of Mylar fallout sheets, high volume air samplers, and 4-leaf wheat (Triticum aestivum L. ‘Anza’) plants. Lowest drift losses occurred, under 0.01 g/ha on fallout sheets at 100 m, with deflector fan nozzles (KGF) operating at a low pressure (7 kPa) on the ground sprayer. Drift losses from a helicopter equipped with micro-jet nozzles were only slightly higher, less than 0.03 g/ha on fallout sheets at 100 m. Drift losses from 8003 nozzles mounted on a ground sprayer and D-6 jet nozzles directed back on fixed wing aircraft produced much higher drift deposits, from 0.2 to 1.0 g/ha on fallout sheets at 100 m. The highest levels of drift losses were obtained with D-4 jet nozzles directed down on a helicopter, 5 g/ha on fallout sheets at 100 m. Some evidence of reduced airborne drift was apparent where the polymer thickening agent was used with aircraft and ground equipment. The test results indicate that significant reduction in drift losses were obtained with proper application equipment; however, the use of a polymer thickening agent reduced drift only slightly for certain applications.

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