HORMONAL CONTROL OF TRANSLOCATION OF PHOTOSYNTHETICALLY ASSIMILATED 14C IN YOUNG SOYBEAN PLANTS

The normal supply of growth substances to a young soybean plant was altered by removing the plant's apical meristem and replacing this meristem with an aqueous solution of either indole-3-acetic acid (IAA), gibberellic acid (GA), or water. The length of each experiment was 1 hr. In the middle of it, ¹⁴CO₂ was administered to one of the primary leaves of the plant, and at the end distribution of ¹⁴C in various parts of the plant was determined. It was found that an addition of growth substances stimulated translocation in three different ways. Both IAA and GA increased the total amounts of sucrose-¹⁴C translocated, increased the rate of its translocation, and affected the distribution pattern of translocated sucrose throughout the plant. Experiments using IAA-¹⁴C have shown that the action of IAA is on the longitudinal translocation in the stem and not on the transfer of photosynthate from the mesophyll to the conducting tissues of the leaf.     

TRANSLOCATION IN MACROCYSTIS. III. COMPOSITION OF SIEVE TUBE EXUDATE AND IDENTIFICATION OF THE MAJOR C14-LABELED PRODUCTS1

The major C¹⁴-labeled substance in sieve tube exudate of M. pyrifera is D-mannitol, comprising 3.6% (w/v). No sugars are detectable. Certain amino acids also possess some C¹⁴-labeling and occur in significantly high concentrations in exudate. The exudate contains negligible ether-soluble lipid, but has a large amount of protein and a high concentration of K⁺ Neither protein nor lipid become labeled significantly in sieve tubes during short-term translocation experiments with C¹⁴. In general the chemical composition of the assimilate stream is comparable to that of vascular plants and does not, consequently, necessitate a different mechanism for translocation.     

TRANSLOCATION IN MACROCYSTIS. III. COMPOSITION OF SIEVE TUBE EXUDATE AND IDENTIFICATION OF THE MAJOR C14-LABELED PRODUCTS1

The major C¹⁴-labeled substance in sieve tube exudate of M. pyrifera is D-mannitol, comprising 3.6% (w/v). No sugars are detectable. Certain amino acids also possess some CWabeling and occur in significantly high concentrations in exudate. The exudate contains negligible ether-soluble lipid, but has a large amount of protein and a high concentration of K⁺. Neither protein nor lipid become labeled significantly in sieve tubes during short-term translocation experiments with C¹⁴. In general the chemical composition of the assimilate stream is comparable to that of vascular plants and does not, consequently, necessitate a different mechanism for translocation.     

TRANSLOCATION OF C14-LABELED PHOTOSYNTHATE IN NODULATED LEGUMES AS INFLUENCED BY NITRATE NITROGEN

Translocation of C¹⁴-labeled photosynthate was studied in nodulated pea and subterranean-clover plants which were grown either continuously without combined nitrogen or exposed to NaNO₃ in the nutrient solution for five days prior to C¹⁴O₂ assimilation. Supplying combined nitrogen decreased the proportion of photosynthate translocated to nodules with a corresponding increase in the proportion going to roots. Nodules on plants grown without combined nitrogen had a higher radioactivity than nodules on plants treated with sodium nitrate.     

THE EFFECT OF GIBBERELLIC ACID ON THE ABSORPTION AND TRANSLOCATION OF PHOSPHORUS-32 BY BEAN PLANTS

Linck , A. J., and Theodore W. Sudia . (U. Minnesota, St. Paul.) The effect of gibberellic acid on the absorption and translocation of phosphorus-32 by bean plants. Amer. Jour. Bot. 47(2) : 101—105. Illus. 1960.–Plants of Phaseolus vulgaris, variety ‘Black Valentine,‘ treated with 1 p.p.m. gibberellic acid supplied to the roots for 4 hr. were compared with nontreated. plants for phosphorus-32 uptake. Plants treated with gibberellic acid where transpiration was either rapid or restricted absorbed more phosphorus-32 than those not treated. More phosphorus-32 was recovered from plants free to transpire than from plants in high humidity. In plants free to transpire, significantly more phosphorus was present in the treated plants after 28 hr. and significantly more phosphorus-32 accumulated in treated plants in those parts actively growing, i.e., stem apex, second internode and first trifoliate leaf, and in the roots. For plants in high humidity atmosphere significantly more phosphorus-32 was absorbed by the treated plants at the end of 4 hr. than in the non-treated plants and this difference was maintained throughout all times of harvest. For plants in high humidity atmosphere, significantly more phosphorus-32 accumulated in the lower portions, i.e., roots, hypocotyl, first internode and primary leaves, of treated plants than of non-treated plants, while the differences for the second internode, the first trifoliate leaf and the stem apex were not significant between treated and non-treated plants.     

TRANSLOCATION OF 14C METABOLITES IN CARROT ROOT

Four-month-old carrot plants exposed to ¹⁴CO₂ for 1 hr in light were harvested successively at 1, 5, 10, 26, and 78 hr after initial exposure. Half-mm thick transverse slices from 3 and 10 cm below the crown were frozen quickly, freeze-dried, and autoradiographed on film. Radioactivity was first localized in a ring surrounding the cambium. The radioactive region extended centrifugally along radii as discrete loci to half the phloem thickness in 10 hr, in a pattern similar to radial rows of callose-stained sieve elements. Median longitudinal sections stained for callose demonstrated the presence of anastomosing sieve tube strands between the more vertical sieve tubes of differing age. Radioactive materials did not move across the cambium for 5–10 hr. These data fit with the decreased growth, in earlier studies, of uniform phloem explants removed from increasing distances from the cambium and of the lesser growth than phloem of similar xylem explants.     

AN ANALYSIS OF THE GROWTH RESPONSE OF YOUNG TOMATO PLANTS TO INFECTION BY VERTICILLIUM ALBO-ATRUM

Infection of seedling tomatoes with Verticillium albo-atrum checked growth but did not result immediately in leaf yellowing. Localized wilting occurred in some plants 2 weeks after the check to growth was evident. 8 weeks after inoculation, dry weights of leaf, stem and root were decreased by 72, 70, and 65% respectively.
Of the growth attributes studied, leaf area was most reduced by infection and this was due to a failure of the leaves to expand rather than to a fall in the rate of leaf production. Neither water nor nitrogen appeared to be limiting factors in this respect. The water content of infected leaves was not reduced until 6 weeks after inoculation, when leaf yellowing and necrosis had also appeared. The percentage N contents of stem, root and leaf of infected plants exceeded those of the healthy controls 24 days after inoculation. N uptake was not seriously impaired until 21 days later.
The photosynthetic efficiency of the green leaves of infected plants was reduced. The mean values for net assimilation rates were: Healthy 0.47 and infected 0.39 g./dm.²/week.
Plants, in which two-thirds of the root system had been killed by crushing, were placed in contact with mycelium in soil. This initial root injury did not significantly affect the growth of infected plants.
The data accord with a toxin theory of damage to infected plants, but the slow development of chlorosis and wilting symptoms in the young plants suggested a greater tolerance to the toxin than is found in older plants.