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Abstract. One mature blade of each squash plant was continuously labeled with 1O. for 15, 30, or 70 minutes in light. The ethanol soluble materials from serial sections of petioles were extracted and separated by paper chromatography. The ratios of label in the various com'ponents of this fraction were determined. Stachyose, which contained the major portion of the label of this fraction, was hydrolyzed and the resultant hydrolysate was separated by paper chromatography. Specific activities of the hexoses derived from stachyose were determined. It was found that the glucose and fructose moieties of stachyose became labeled at the same rates; however, the galactose moiety became labeled more rapidly.

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The mechanism of cytokinin-induced cell expansion in cotyledons excised from dark-grown seedlings of radish (Raphanus sativus L.) and cucumber (Cucumus sativus L.) was studied. Cotyledons were incubated in dim light with or without 17 micromolar zeatin for periods up to 3 days. Fresh weights and osmotic potentials were measured daily. Cell wall extensibility properties were measured before and after the growth period. Also, experiments in which radish cotyledons were grown in mannitol solutions of various concentrations were performed. Comparisons of growth rates and increases of tissue osmotic potentials (toward zero) during growth without mannitol indicate that wall extensibility increased during the growth period and that this extensibility was enhanced by zeatin.Extensibility values derived from growth rates in mannitol provided indirect evidence of zeatin-increased wall extensibility. These conclusions were verified by direct measurements of plasticity with an Instron extensiometer. Thus, growth stimulation of excised cotyledons by cytokinins apparently involves wall loosening, in addition to previously demonstrated increases of K(+) absorption and formation of reducing sugars.

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Squash (Cucurbita pepo L. var. melopepo torticalis, Bailey) leaves were supplied with 14C-sucrose, then specific radioactivities of the glucose and galactose moieties of translocated stachyose were determined. In every case, the specific radioactivity of the galactose moiety was greater than that of the glucose moiety. It is condoded that the stachyose was not synthesized at either the phloem-loading site or subsequent to phloem loading, but rather in cells that were not a part of the translocation system, possibly the mesophyll cells.Loading of carbohydrate into minor veins of leaves is the process that controls both the qualitative and quantitative components of translocation. Until recently there has been little direct evidence regarding the pathway followed by carbohydrates as they move from the photosynthetic cells into the phloem. Recently, however, Geiger et al. (5) and Giaquinta (6) have presented strong evidence that this pathway involves the apoplast. This paper presents indirect evidence in support of this apoplastic theory of phloem loading; however, the main thrust of this paper relates to the elucidation of the chemical specificity of sites which load carbohydrates into the phloem from the apoplast.A number of Soviet workers (2, 3, 9, 10) concluded that the phloem-loading system is specific to hexoses. From this, one would presume that the translocated oligosaccharides are synthesized either during or subsequent to loading. Geiger et al. (5) have presented evidence that the loading site in sugar beet leaves is specific to sucrose.In this study 14C-sucrose was supplied to leaf blades of squash, a species which normally translocates primarily stachyose. After translocation had occurred, the labeling pattern of the galactose and glucose moieties of stachyose from the petioles was determined. These results, together with results from earlier work (5-8) are used to support the conclusion that the loading site is specific to the translocated carbohydrate. MATERIALS AND METHODSExcept for the hydrolysis of the stachyose and the analysis of the resultant hexoses, the procedures used were essentially the same as have been reported previously (8). Therefore, only a brief description is presented here.Plant Material. Cucurbita pepo L. var. melopepo torticalis, Bailey seeds were germinated in vermiculite, and the resultant seedlings were transferred to modified Meyer's solution (7) for growth in the greenhouse. When the second true leaf was fully expanded, the plants were transferred to a fume hood. Light from 300 w reflector flood incandescent bulbs was filtered through water, supplying 1,000 ft-c to the plants. The day before label was supplied to the plants, all leaves were removed except the youngest fully expanded leaf (labeled leaf) and leaves less than one-fifth fully expanded. Experimental Procedure. Uniformly labeled '4C-sucrose (5.2 mCi/mmol) was introduced through the second lateral vein from the leaf base by the reverse flap method of Biddulph (1). After an appropriate labeling period, the...