The essentiality of boron for higher plants is well established although no definitive role proposed for this element has remained undisputed. So many processes are affected indirectly by boron that the primary effect(s) have remained obscure (9). Gauch and Dugger (9) suggest that a relatively specific role in carbohydrate translocation is indicated. Sucrose translocation is considerably reduced in boron deficient plants before morphological symptoms are evident. Gauch and Dugger (8) maintain that subsequent symptoms are simply the expression of carbohydrate deficiency resulting from the impaired translocation system. They suggest that a negatively charged sugar-boron complex might more easily traverse cell membranes than non-borated sugar molecules or that boron might be a constituent of the membrane site across which the sugar moves. Skok (20,21,22) points out that it is also possible for the relationship of boron to translocation to be indirect. He proposes that the boron effect on translocation is the result of the elements' essentiality to the metabolic activity of meristematic regions which have large substrate requirements. The effect of this particular metabolic activity including that associated with cell enlargement can be called sink effect; its relationship to translocation is now well established (3,12,23). If Skok is correct, cessation of growth would be the cause rather than the result of impaired carbohydrate translocation in boron deficient plants. Dugger et al. (4) proposed that boron affects the rate of translocation through its effect on the sugarstarch balance of the leaves. Scott (18) presents a similar hypothesis: "It appears that boron performs a protective function in plants in that it prevents excessive polymerisation of sugars at sites of sugar synthesis". It would appear, however, that boron

Benzimidazole has been studied previously by certain investigators as a growth regulator. This compound was found to promote various phases of growth in the gametophyte of the fern Thelypteris felix-mas. Concentrations of benzimidazole in the order of 0.01 mM, 0.02 mM, and 0.1 mM stimulated cell division, an increase in body size, and also rhizoid lengths of the gametophyte. A concentration of 1.0 mM was always inhibitory.Benzimidazole is a naturally occurring azole found as the 5, 6-dimethyl derivative and is part of the vitamin B12 structure. It has been previously studied as a growth regulator by several investigators.Galston et al. (2) discovered that benzimidazole inhibited a promotion of growth induced by auxins and adenine in the elongation of pea stems. Cortical cells of tissue treated with benzimidazole swelled tremendously in the transverse direction. This increase in diameter resulted from an increase in individual cell volumes rather than an increase in cell numbers.Work with Vicia faba by McCorquodale and Duncan (4) showed that benzimidazole resulted in a drop in mitotic frequency in the root meristem, an inhibition of root elongation, and a blackening pigmentation in the roots above the meristem. Since all three effects could be prevented by the presence of certain metals ions, it was suggested that the mechanism of action of benzimidazole is due to the formation of a strong chelate structure between the metal ions and the azole. Waygood (6) has shown that benzimidazole resulted in a delay of induced senescence of wheat leaves and in an increase in the Chl content. Changes in the chloroplast fine structure included more closely spaced intergrana and grana lamellae, more numerous electron dense particles, and an increase in NADP content. Dyar (1) found that benzimidazole resulted in an increase in both the fresh and dry weights of tobacco leaves, with an increase in the size of the leaves.Since benzimidazole has been found to have significant effects on cell metabolism and elongation, its effects on the gametophyte of the male shield fern (Thelypteris felix-mas) 1This work was supported by National Science Foundation College Science Improvement Program Grant GY5704.were studied. The fern gametophyte is morphologically simple as it is a single layer of cells, but as a multicellular organism still exhibits differentiation of cell types and structures. The gametophyte lends itself well to study because of its simple growth requirements and easy microscopic measurements and observations. These growth measurements, including cell number and size, can be carried out without disturbing the growth of the plants. The same plants can be observed throughout the course of the research. MATERIALS AND METHODSSpores of the fern Thelypteris felix-mas were sterilized by brief exposure to a 10% commercial Clorox solution. Three rinses in sterile-distilled water were accompanied by centrifugation to ensure spore separation. The spores were then used to inoculate a Bold's modified Bristol's solution in a was...

No abstract