Apical Dominance in Vicia faba

Apical dominance phenomena have been studied in seedlings ofVicia faba particularly in relation to the movement about theplant of uracil-2-¹⁴C applied to the cotyledons. Decapitationjust below the second node releases the growth of the lowermostlateral bud and inhibition is completely reimposed by applicationof indole-3-acetic acid (IAA) to the cut surface. Uracil-2-¹⁴Capplied in solution to the cotyledons is distributed in thestems of all experimental seedlings with no consistent differencesdue to decapitation or IAA application. On the other hand, decapitationresults in a rapid increase in uracil-2-¹⁴C content in the lateralbuds which far exceeds their promoted growth. This uptake iscompletely suppressed by IAA application. A ring of tri-iodobenzoicacid (TIBA)-lanolin paste around the stem above the bud suppressesIAA action both in bud growth and on uracil-2-¹⁴C uptake, andalso on the movement of IAA-1-¹⁴C down the stem. TIBA-application to the base of the bud does not prevent IAAaction on bud growth, but also does not prevent the movementof IAA-1-¹⁴C (or a water soluble product of its metabolism)into the bud. Direct application of kinetin to the lateral bud of intact plantscauses a short-lived release of growth. Gibberellic acid producesa smaller and scarcely significant increase which is additiveto the kinetin effect. Neither has any effect on uracil-2-¹⁴Cmovement into the bud. The implications of these findings are discussed in relationto various existing theories of the mode of auxin action inapical dominance and it is concluded that their strongest supportis for a mechanism involving the suppression of phloem differentiationin the vascular supply to the bud.     

Toxicity of parathion-methyl to cells, akinetes and heterocysts of the cyanobacterium Cylindrospermum, sp. and the probit analysis of toxicity

The toxicity of a commercial formulation of the insecticide parathion‐methyl to the N2‐fixing filamentous cyanobacterium (blue‐green alga) Cylindrospermum, sp. was studied. A concentration of parathion‐methyl of 0.5 ppm caused growth increase in liquid growth media. The minimum inhibitory concentration of parathion‐methyl for both types (N₂, fixing and nitrate supplemented) of liquid and solid media was 1.0 ppm. LC₅₀ values were: 4.4 ppm (liquid, N₂, fixing), 5.5 ppm (liquid, nitrate supplemented), 3.3 ppm (agar, N₂‐fixing) and 4.0 ppm (agar, nitrate supplemented). LC100 values for N₂‐fixing liquid and both types of agar media were 10.0 ppm, while for the liquid nitrate supplemented medium the LC₁₀₀ was 12.0 ppm. Both akinete (spore) formation and germination were inhibited below the highest permissive concentration of 8.0 ppm, with the insecticide incorporated in the agar media. In soil, the LC50 and LC100 values for parathion‐methyl were 13.6 and 30 ppm, respectively. Both the dehydrogenase activity of heterocysts (monitored by 2,3,5‐triphenyl tetrazolium chloride reduction) and the nitrogen concentration of cultures (estimated by the micro‐Kjeldahl method) were affected by the insecticide, but the latter (N₂‐fixation) was more sensitive. The Kruskal‐Wallis H test on the numbers of vegetative cells in the filaments revealed that the insecticide significantly affected the division of vegetative cells. The cyanobacterium could detoxify the growth medium containing high levels (30 and 40 ppm) of the insecticide in short‐term exposures at the expense of cell viability.     

Seed morphology of Rotala L., Ammannia L., Nesaea Kunth and Hionanthera Fernandes & Diniz (Lythraceae)

PANIGRAHI, S. G., 1986. Seed morphology of Rotala L., Ammannia L., Nesaea Kunth and Hionanthera Fernandes & Diniz (Lythraceae) . Seed-surface characteristics of Ammonia lalifolia L., Rotala verticillaris L., Nesaea triflora Comm. ex Kunth and Hionanthera garciae Fernandes & Dinz were studied using the SEM. Seeds from herbarium specimens moistened in water produce cracks along the intercellular walls and distinctive types of invaginating 'hairs'. These 'hairs' are mucilaginous in nature and diagnostic at the species level. They are released in profusion from the upper convex surface of the testa. Viable seeds of Ammonia baccifera L., similarly treated, exude, in addition to the 'hairs', mucilaginous globules from the lower concave surface during germination. The invaginating 'hairs' arise diagonally from the roof of the epidermal cells of the testa and protrude to the lumen of the epidermal cells. A sac of mucilage is observed swelling out on the inner flat surface of the developing seeds. The biological functions of these 'hairs' and mucilage globules in germinating seeds in relation to seed dispersal and regulation of germination in appropriate habitats is discussed.