Effect of Fruits on Dormancy and Abscisic Acid Concentration in the Axillary Buds of Phaseolus vulgaris L.

The mechanism regulating the growth of adult plants in two determinate bean (Phaseolus vulgaris L.) cultivars was investigated. "Redkloud" plants flowered, formed fruits, and ceased shoot growth earlier than "Redkote" plants. Redkloud attained a smaller plant size, compared to Redkote, by imposing dormancy on axillary buds at an earlier age. In both cultivars, cessation of bud growth coincided with maximum combined fruit length per plant. Removal of fruits caused resumption of axillary bud growth within 4 to 5 days. The amount of new growth induced by fruit removal depended on the cultivar and plant age. In fully developed Redkloud plants, where shoot growth had already ceased, total leaf and shoot number per plant nearly doubled within 2 weeks following fruit removal. A much smaller response was observed in the still growing Redkote plants. Fruits, therefore, are assumed to play a major role in the regulation of shoot growth and total plant size through the control of axillary bud dormancy. It seems that smaller plant size, earlier maturity, and earlier senescence of Redkloud, compared to Redkote, were the result of earlier flowering, and accomplished in part through the growth-inhibiting action of fruits.The endogenous abscisic acid (ABA) concentration of axillary buds was higher in Redkloud than in Redkote. It increased with plant age in both cultivars. Five days after fruit removal the ABA level in bud tissue dropped to approximately 10 to 30% of the control level. When buds were treated with a solution of ABA containing 5 nanomoles of ABA per bud, growth was substantially inhibited. Fifteen days after ABA application the mean length of growing buds on intact and defruited plants was reduced by 40 and 62%, respectively, compared to the untreated controls. A role for ABA in axillary bud growth regulation was not firmly established, but these data suggest correlation between the growth potential of axillary buds and their ABA concentration.

Effect of Older Fruits on Abortion and Abscisic Acid Concentration of Younger Fruits in Phaseolus vulgaris L.

In two cultivars of bean (Phaseolus vulgaris L., Redkloud and Redkote) the older fruits growing at the base of racemes aborted less frequently than the younger ones above them. When older fruits at the base of racemes were removed, the abortion rate of the younger ones was reduced and their abscisic acid (ABA) concentration was lowered. Thirteen days after fruit removal, 36 to 45% of the younger fruits remained viable on treated plants while less than 12% of the younger fruits were viable on control plants. On these intact controls the ABA concentration of young fruits was at least twice that of defruited plants. A similar difference was found when the ABA content was expressed on a per fruit basis, suggesting a direct regulatory influence of older fruits over the ABA content of younger fruits.

Mesophyll Resistance and Carboxylase Activity: A Comparison under Water Stress Conditions.

The response of several leaf gas exchange parameters were monitored with decreasing leaf water potential in Phaseolus vulgaris L. leaflets. These included photosynthesis, transpiration, CO(2) compensation point, ribulose 1,5-diphosphate carboxylase activity, boundary layer plus stomatal, and mesophyll resistance to diffusion of CO(2). Mesophyll resistance was calculated under two assumptions: (a) the CO(2) concentration at the chloroplast was zero, and (b) it was equal to the CO(2) compensation point.Contrary to some reports on bean, the estimates of mesophyll resistance (both models) increased with decreasing leaf water potential. Concurrently, the CO(2) compensation point increased and ribulose 1,5-diphosphate carboxylase activity decreased as internal water stress increased.It is suggested that the mesophyll resistance term has been too liberally interpreted in the past and that future use be verified by an indicator of biochemical response to environmental stress such as the assay for ribulose 1,5-diphosphate carboxylase activity.

The occurrence and ultrastructure of chloroplasts in the phloem parenchyma of leaves of C4 dicotyledons.

Chloroplasts were found to be common within the phloem parenchyma of leaves of dicotyledons, although they were not observable, at the light microscope level, in the vascular cells of any grasses examined. The phloem-cell chloroplasts of Boerhaavia paniculata L. and Portulaca oleracea L. (both C4 plants) were structurally similar to each other, even though the chloroplasts of their surrounding bundle sheaths were of different types. They were also similar to the phloem-cell chloroplasts of Phaseolus vulgaris L. (C3 plant). Although consistently small, all vascular plastids appeared normal. The extent of their functionality is unknown.

Effects of Ammonium Nutrition on Water Stress, Water Uptake, and Root Pressure in Lycopersicon esculentum Mill.

Ammonium (NH(4) (+)) nutrition inhibits water uptake and root exudation and decreases leaf water potential of tomato plants grown in solution culture. This inhibition is readily reversible by NO(3) (-) for short term exposures to NH(4) (+); however, recovery is delayed following long term exposures.

Influence of Translocation of Photosynthetic Efficiency of Phaseolus vulgaris L.

Measurements of net photosynthesis show that in Phaseolus vulgaris L. the cultivar Michelite-62 exceeds the cultivar Red Kidney in net CO(2) uptake by 23 to 31%. Data on translocation of pulse label indicate that export of a pulse of photosynthetically assimilated (14)C from the source leaf of either M-62 or Red Kidney follows an exponential pattern and shows an initial rapid phase followed by a second slower phase. The steeper slope for both phases in M-62 suggests its rate of translocation of pulse label is higher than that of Red Kidney. Furthermore, only 38% of the (14)C remains in the leaf of M-62 after 8 hours, while Red Kidney retains up to 60% of the label. Leaf autoradiographs obtained after pulse labeling demonstrate a much faster rate of vein loading in M-62 and are considered evidence for the higher translocation efficiency of M-62. These results provide evidence for a positive correlation between photosynthetic efficiency and translocation efficiency in M-62 and Red Kidney and give support to our hypothesis that translocation is one of the important physiological factors controlling the varietal differences in photosynthetic efficiency in Phaseolus vulgaris.

Starch Synthetase, Phosphorylase, ADPglucose Pyrophosphorylase, and UDPglucose Pyrophosphorylase in Developing Maize Kernels.

Soluble ADPglucose-alpha-glucan 4-alpha-glucosyltransferase (starch synthetase), ADPglucose pyrophosphorylase, UDPglucose pyrophosphorylase and phosphorylase were assayed in extracts from developing kernels of maize (Zea mays). Normal, waxy and amylose-extender maize at stages of development ranging from 8 days to 28 days after pollination were studied. Shrunken-4 maize at the 22-day stage was also studied. There is adequate activity of both ADPglucose pyrophosphorylase and starch synthetase at all stages of development to account for the synthesis of starch. Thus all starch could be synthesized via the ADPglucose pathway. High levels of UDPglucose pyrophosphorylase and of phosphorylase activities were also found at all stages of development. The possible role of phosphorylase in starch synthesis could not be discounted. The levels of phosphorylase, ADPglucose pyrophosphorylase, starch synthetase, and UDPglucose pyrophosphorylase activities in shrunken-4 kernels were about 20 to 40% of that found in normal maize kernels. It appears that the mutation in shrunken-4 affects the activities of more than one enzyme. The defective starch synthesis seen in this mutant could be due to the low activities of ADPglucose pyrophosphorylase and starch synthetase rather than the low activity of phosphorylase.

Intraspecific measurements of photorespiration.

The relative magnitudes of (a) CO(2) compensation concentration, (b) zero CO(2) intercept of the CO(2) response curve, (c) O(2) suppression of net photosynthesis, (d) differential (12)CO(2) and (14)CO(2) uptake, and (e) (14)CO(2) efflux into CO(2)-free air were determined in the dry bean (Phaseolus vulgaris L.) varieties Michelite-62 (M-62) and Red Kidney (RK). In comparing the two varieties for each of the above processes, there were three categories of response, M-62 > RK, M-62 = RK, and M-62 < RK. Since these processes did not give the same relative difference for the two varieties being studied, it was concluded that these phenomena cannot validly be used to estimate the magnitude of photorespiration, although they do identify its presence. The results suggest that photorespiration is but one component of O(2) inhibition of net photosynthesis and that photorespiration itself has two or more component metabolic pathways.

Soluble adenosine diphosphate glucose- -1,4-glucan -4-glucosyltransferases from spinach leaves.

Multiple forms of ADP-glucose-alpha-1,4-glucan alpha-4-glucosyltransferase were obtained from spinach leaves by gradient elution from a DEAE-cellulose column. In the presence of high concentrations of some salts and bovine serum albumin, unprimed activity was found in one (transglucosylase III) of the four fractions eluted from the column. In addition to having unprimed activity, transglucosylase III had a lower K(m) for ADP-glucose, a much higher K(m) for oyster glycogen, greater heat sensitivity and lower affinity for maltose, maltotriose and amylopectin beta-limit dextrin than fractions I, II and IV. In addition, the kinetics at low concentrations of amylose, amylopectin and rabbit liver glycogen were non-linear for transglucosylase III. The properties of transglucosylases I, II and IV were generally similar to each other. Rates of the unprimed reaction at physiological concentrations of ADP-glucose were greater than those found for the primed reaction of fraction III. The product formed by the unprimed reaction was a glucan containing principally alpha-1,4 linkages with some alpha-1,6 linkages. The primer, maltose, at a concentration of 0.5m inhibited the synthesis of the unprimed product.

Adenosine diphosphoglucose-starch glucosyltransferases from developing kernels of waxy maize.

TWO ADENOSINE DIPHOSPHOGLUCOSE: alpha-1,4-glucan alpha-4-glucosyl-transferases were extracted from kernels of waxy maize harvested 22 days after pollination and separated by gradient elution from a diethylaminoethyl-cellulose column. Both fractions could utilize amylopectin, amylose, glycogen, maltotriose and maltose as primers. The rate of glucose transfer from adenosine diphosphoglucose to rabbit liver glycogen of fraction II was 78% of the rate of glucose transfer to amylopectin, but with fraction I the rate of transfer of glucose to rabbit liver glycogen was 380% of that observed to amylopectin. Glucan synthesis in the absence of added primer was found in fraction I in the presence of 0.5 m sodium citrate and bovine serum albumin. The unprimed product was a methanol-precipitable glucan with principally alpha-1,4 linkages and some alpha-1,6 linkages, and its iodine spectrum was similar to that of amylopectin.

The association of carbohydrate changes in the shoot tip of cauliflower with flowering.

Changes in levels of sugars and starch in the shoot tip of cauliflower, Brassica oleracea L. var. botrytis D. C. cv. Main Crop were studied during periods of growth which were inductive or non-inductive to flowering. Flowering was induced by growing plants for 2 weeks under 16 hr of light at 5 degrees . During this period of floral induction there was a significant increase in sugar and starch content compared to that in vegetative plants grown at 20 to 26 degrees . Sugar and starch content did not increase and flowering was prevented when light and CO(2) were excluded during growth at 5 degrees . A 3-day dark period at 20 degrees or a high temperature treatment at 33 degrees with light following growth at 5 degrees reduced the carbohydrate level and prevented flowering.