The Control and Branch Growth on Potato Tubers: I. ANATOMY OF BUDS IN RELATION TO DORMANCY AND CORRELATIVE INHIBITION

A study was made of the morphology of potato buds during thedormant period and of the anatomy of dormant, growing, and correlativelyinhibited buds. Lateral buds showed a progressive increase indevelopment with increasing number of nodes measured basipetally,and some further development in association with second-growthof the tuber. In dormant buds, or buds which had not grown afterthe end of the rest period, the cytoplasm of cells in the meristematicdome stained only lightly with Heidenhain's iron-hematoxylin,whereas cells of buds which had grown had densely staining cytoplasm.The xylem vessels leading to dormant buds were filled with tannin-likesubstances for a short distance below the bud. Buds which hadgrown after the end of the rest period had both old obstructedxylem vessels and new open vessels. The end of the dormant period was not reflected in the internalbud anatomy unless buds also commenced to grow. Thus, whiledormant buds had distinctive anatomical features, none of thestructures appeared to be primarily associated with dormancy.Correlatively inhibited buds showed the features either of dormantor of growing buds depending on whether or not they had grownat the end of the dormant period.     

The Control of Branch Growth on Potato Tubers: II. THE PATTERN OF SPROUT GROWTH

Following the end of dormancy or after desprouting, many budson a potato tuber start to grow. However, if the storage temperaturefavours rapid growth, a number may remain inhibited. After atime, the smaller sprouts stop growing. This inhibition affectsonly those sprouts below a certain length, which is proportionalto the length of the longest sprout. This critical length isrelatively greater for small tubers than for large ones (i.e.longer sprouts are inhibited); it is also greater for tubersstored under dry conditions than for those under moist conditions.The results are interpreted in terms of a correlative inhibitior,continuously produced under the influence of growing buds andcontinuously destroyed as it moves up into all stems. It issuggested that in the terminal bud of the stem there is a sensitiveregion which controls the growth of the other stem tissues andon which the inhibitor acts. It stems longer than the criticallength the inhibitor is possibly inactivated before it reachesthis sensitive tissue; in shorter stems the inhibitor acts onthe tissue and hence inhibits stem elongation.     

The Influence of Carbohydrate and Mineral Nutrient Supply on the Growth of Potato Tubers

The uptake and distribution of nitrogen, phosphorus, and potassiumhas been studied throughout the life of potato plants. Thereappears to be a net loss of all three elements from the plantduring emergence growth even though uptake occurs. When daughtertubers are formed they very quickly become the dominant sinkfor mineral nutrients, the concentrations of N, P, and K remainingsteady for a long period. These concentrations are maintainedin spite of decreasing rates of uptake, indicating the transferenceof mobile ions from the haulm to the growing tubers. ¹⁴C tracer experiments have shown that after tuberization thereis a greater export of recently incorporated photosynthate fromthe leaves than takes place before tuberization. There is nogood correlation between the size of individual tubers and theamount of photosynthate transported into them. This is thoughtto be because the largest tubers are not necessarily growingfaster than the smaller tubers. The most active sinks are alsomost active in converting the mobile ¹⁴C into storage compounds.The mother tuber continues to import ¹⁴C until it is detachedfrom the plant, but over much of this period there is no changein the tuber dry-weight, indicating that there is an equivalentexport from the tuber. The similarities between these distribution patterns and thosefound in tubers showing second-growth are described and theimplications with respect to the control of tuber growth discussed.     

QUANTITATIVE LAWS IN REGENERATION : III. THE QUANTITATIVE BASIS OF POLARITY IN REGENERATION.

It is well known that a long defoliated piece of stem of Bryophyllum calycinum forms shoots only at the apical or the two apical nodes, while when such a stem is cut into as many pieces as there are nodes each node produces shoots. It is shown in this paper that the dry weight of shoots produced in the apical nodes of a long piece of stem is approximately equal to the dry weight of shoots the same stem would have produced if it had been cut into as many pieces as it possesses nodes. Hence all the material which can be used for the growth of shoots goes into the most apical part of the stem and this accounts for the polar character of regeneration in this case. It seems that the mass of basal roots produced by a piece of defoliated stem also increases with the mass of the stem.     

STUDIES ON THE BIOCHEMICAL BASIS OF DISTAL AXONOPATHIES–I. INHIBITION OF GLYCOLYSIS BY NEUROTOXIC HEXACARBON COMPOUNDS

Abstract— Neurotoxic hexacarbon compounds 2,5-hexanedione (2,5-HD) and methyl n-butyl ketone (M n BK) inhibit crystalline and endogenous CNS and PNS glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Preincubation of the enzyme with the toxin was necessary for inhibition. The enzyme activity of GAPDH was preserved by the addition of dithiothreitol in the presence of either neurotoxin. By contrast, lactate dehydrogenase (LDH) activity was not inhibited by these neurotoxic chemicals. Neurologically inactive compounds 1,6-hexanediol and acetone failed to inhibit GAPDH. The present data indicate that 2,5-HD and M BK block energy metabolism by inhibiting glycolysis at the site of GAPDH. These observations may account for the known failure of GAPDH-dependent axonal transport and the axonal degeneration which occurs in hexacarbon neuropathy.     

THE CONTRACTILE BASIS OF AMOEBOID MOVEMENT : I. The Chemical Control of Motility in Isolated Cytoplasm

Cytoplasm has been isolated from single amoeba (Chaos carolinensis) in physiological solutions similar to rigor, contraction, and relaxation solutions designed to control the contractile state of vertebrate striated muscle. Contractions of the isolated cytoplasm are elicited by free calcium ion concentrations above ca. 7.0 x 10^-7 M. Amoeba cytoplasmic contractility has been cycled repeatedly through stabilized (rigor), contracted, and relaxed states by manipulating the exogenous free calcium and ATP concentrations. The transition from stabilized state to relaxed state was characterized by a loss of viscoelasticity which was monitored as changes in the capacity of the cytoplasm to exhibit strain birefringence when stretched. When the stabilized cytoplasm was stretched, birefringent fibrils were observed. Thin sections of those fibrils showed thick (150–250 Å) and thin (70 Å) filaments aligned parallel to the long axis of fibrils visible with the light microscope. Negatively stained cytoplasm treated with relaxation solution showed dissociated thick and thin filaments morphologically identical with myosin aggregates and purified actin, respectively, from vertebrate striated muscle. In the presence of threshold buffered free calcium, ATP, and magnesium ions, controlled localized contractions caused membrane-less pseudopodia to extend into the solution from the cytoplasmic mass. These experiments shed new light on the contractile basis of cytoplasmic streaming and pseudopod extension, the chemical control of contractility in the amoeba cytoplasm, the site of application of the motive force for amoeboid movement, and the nature of the rheological transformations associated with the circulation of cytoplasm in intact amoeba.     

The Effect of Gamma-Irradiation on the Sucrose Content in Sweet Potato Roots and Potato Tubers

The sucrose content in both potato tubers and sweet potato roots was considerably increased by gamma-irradiation. The maximum increase was achieved by an irradiation dose of 3 to 4 kGy for potatoes and 0.8 to 2 kGy for sweet potatoes. Cooling treatment (15°C, 2 weeks) for sweet potato roots also enhanced the sucrose content (almost 2 times) but was not additive to the irradiation treatment; the maximum sucrose content in irradiated sweet potato roots was in the range of 7 to 12% irrespective of the cooling treatment, depending on the variety of sweet potatoes. Irradiation made the sucrose content in the roots 2 to 4 times higher.     

NAD Malic Enzyme and the Control of Carbohydrate Metabolism in Potato Tubers

Potato (Solanum tuberosum) plants were transformed with a cDNA encoding the 59-kD subunit of the potato tuber NAD-dependent malic enzyme (NADME) in the antisense orientation. Measurements of the maximum catalytic activity of NADME in tubers revealed a range of reductions in the activity of this enzyme down to 40% of wild-type activity. There were no detrimental effects on plant growth or tuber yield. Biochemical analyses of developing tubers indicated that a reduction in NADME activity had no detectable effects on flux through the tricarboxylic acid cycle. However, there was an effect on glycolytic metabolism with significant increases in the concentration of 3-phosphoglycerate and phosphoenolpyruvate. These results suggest that alterations in the levels of intermediates toward the end of the glycolytic pathway may allow respiratory flux to continue at wild-type rates despite the reduction in NADME. There was also a statistically significant negative correlation between NADME activity and tuber starch content, with tubers containing reduced NADME having an increased starch content. The effect on plastid metabolism may result from the observed glycolytic perturbations.     

Apical Dominanace in Xanthium strumarium: A DISCUSSION IN RELATION TO CURRENT HYPOTHESES OF CORRELATIVE INHIBITION

The influence of the spectral distribution of illumination onthe gibberellin, cytokinin, auxin, and abscisic acid levelsand the correlation with the degree of branching in Xanthiumstrumarium is presented and discussed. Gibberellins do not appearto play a major role in apical dominance but may be importantfor bud extension following the initial release from dominance.The cytokinin level was much higher in inhibited buds than inreleased buds. It is suggested that the cytokinins present wereprobably not able to participate in bud growth because of anauxin-induced accumulation of abscisic acid in the buds themselves.The concentration of abscisic acid as measured by bioassay andgas-liquid chromatography was between 50 and 250 times thatoccurring in all other plants parts examined. This level felldramatically following release from apical dominance by decapitation.The results are discussed in relation to current hypothesesof apical dominance.     

Effect of Arachidonic Acid on Potato Tubers during Storage

Potato (Solanum tuberosumL.) tubers were treated with various concentrations (10^–9to 10^–4M) of biogenic elicitor arachidonic acid during storage (from October to June). The data showed that the resistance-inducing concentration of arachidonic acid was 10^–6M in autumn and 10^–9M in spring. The possible causes of the change in the immunizing concentration of arachidonic acid during storage of potato tubers are discussed.     

THE ROLE OF ANTIBIOTICS IN THE DECOMPOSITION OF SAWDUST: I. INHIBITION OF THE GROWTH OF CELLULOSE-DECOMPOSING BACTERIA

It has been shown that 'deal' sawdust contains substances which inhibit the growth of cellulose-decomposing bacteria of the genera Sporocytophaga and Cellulomonas , the former being the more sensitive. The substances can be extracted with water or a mildly alkaline solution of inorganic salts, the latter being rather more effective. The extracted material is acidic but still exhibits activity even after neutralization, especially towards Sporocytophaga. Sawdust which has been extracted with water or the alkaline solution, or neutralized by admixture with calcium carbonate, no longer prevents the growth of Cellulomonas on added filter paper cellulose, although there is a delay before the attack becomes evident, but Sporocytophaga is still completely inhibited under all three conditions.     

Influence of Phenolic Acids upon Ion Uptake: III. INHIBITION OF POTASSIUM ABSOBPTION

The influence of 12 naturally occurring phenolic acids on theuptake of potassium by barley (Hordeum vulgare L. cv. Karlsberg)was examined using ⁸⁶Rb-labelled potassium solutions. Withoutexception, all compounds tested, including both cinnamic acidand benzoic acid derivatives, caused a significant reductionof uptake. In addition, the inhibitory capacities of 15 variously substitutedbenzoic acids were determined over a range of different concentrationsof inhibitors. For each of these compounds an inhibition constant(K_i), defined as the concentration required to produce a 50per cent reduction of uptake, was determined. The K_i valueswere found to be strongly correlated with the octanol-waterpartition coefficients of the compounds under examination. Itis clear from this study and previous work upon phosphate uptakethat phenolic acids exert a generalized inhibitory effect uponactive ion-uptake which is almost certainly mediated throughreversible alterations in membrane permeability.     

Inhibition of Diabrotica Larval Growth by Patatin,the Lipid Acyl Hydrolase from Potato Tubers

Patatin, the nonspecific lipid acyl hydrolase from potato (Solanum tuberosum L.) tubers, dose-dependently inhibits the growth of southern corn rootworm (SCR) and western corn rootworm when fed to them on artificial diet. The 50% growth reduction levels are somewhat cultivar dependent, ranging from 60 to 150 [mu]g/g diet for neonate SCR larvae. A single patatin isoform also inhibits larval growth. Neonate SCR continuously exposed to patatin are halted in larval development. Treatment with di-isopropylfluorophosphate essentially eliminates patatin's phospholipase, galactolipase, and acyl hydrolase activities. SCR growth inhibition is eliminated also, indicating that patatin's serine hydrolase activity is responsible for the observed activities. Patatin-mediated phospholipolysis is highly pH and cultivar dependent, with specific activities up to 300-fold less at pH 5.5 than at pH 8.5. Esterase or phospholipase activities do not correlate with insect growth inhibition. Galactolipase activity, being cultivar and pH independent, correlates significantly with SCR growth inhibition. Insect-growth inhibition of patatin is significantly reduced with increased dietary cholesterol levels. In conclusion, patatin represents a new class of insect-control proteins with a novel mode of action possibly involving lipid metabolism.     

Probability of Globodera rostochiensis Spread on Equipment and Potato Tubers

The probability of spreading cysts of Globodera rostochiensis on farming equipment and potato tubers was investigated in naturally infested field plots. The number of cysts recovered from soil that adhered to equipment differed significantly between different pieces of equipment. These differences were related to initial nematode density and, in most cases, to the volume of soil that adhered to the equipment. At an initial density of 0.04 egg/cm³ of soil, significantly more cysts were recovered from a potato digger than from a potato hiller, cultivator, or plow. At an initial density of 0.90 egg/cm³ of soil, significantly more cysts were recovered from the plow than from the other equipment. Although the population density was 22 times greater, only 10 times more cysts adhered 3 to equipment used in soil with a density of 0.90 egg/cm³ of soil than when used in soil infested at 0.04 egg/cm³. The number of potato tuber samples (4.5 kg) that contained cysts with viable eggs was positively correlated with the initial densities of G. rostochiensis in soil in which they were produced. The percentage of tuber samples with cysts containing viable eggs was 10-12% for tubers harvested from soil with densities less than 1 egg/cm³ and 30-76% for tubers harvested from soil with densities greater than 4 eggs/cm³ of soil.