Chlorophyll Formation in Excised Roots of Cucumber and Pea

The effects of red and blue light on the formation of chlorophyll in excised roots of cucumber and pea was investigated and compared with previously reported experiments on wheat roots. All three kinds of roots are similar in that in continuous red light no or very little chlorophyll is formed. and in blue light a considerable amount of chlorophyll is produced. Roots of cucumber and pea differ from those of wheat, in that red light is ineffective (or nearly so) even when combined with blue.     

The Presence of Gibberellins in Excised Tomato Roots

Substances having similar physiological properties to the gibberellins(located by the ‘Meteor’ dwarf pea bio-assay) havebeen detected in extracts from excised tomato root. The chromatographicbehaviour of the most active zone is similar to that of gibberellinA₁. Experiments using the d-1 and d-5 mutants of mazie did not indicatethe presence of substances with differential effects on thesetwo mutants.     

The Effects of pH and Carbon Dioxide on Ion Uptake by Excised Barley Roots

The effects of carbon dioxide concentrations up to 8 per centin air on uptake of potassium and chloride at two pH levels,nominally pH 6 and 8, werestudied. In all experiments, enhanced uptake of potassium occurred atthe higher pH level with carbon dioxidefree air, but chlorideuptake was generally unaffected. At nominal pH 6, 1 per cent carbon dioxide reduced and 6 percent increased potassium uptake. There was no effect on chlorideuptake except with 1 per cent carbon dioxide where a markedenhancement was recorded. At nominal pH 8, l and 2 per cent carbon dioxide increased potassiumuptake whereas 6 and 8 per cent were inhibitory. Chloride uptakewas favoured by 1 and 8 per cent concentrations of the gas.     

Lateral Root Development in Attached and Excised Roots of Zea mays L. Cultivated in the Presence or Absence of Indol-3-yl Acetic Acid

The initiation of lateral root primordia and their subsequentemergence as secondary roots have been examined in attachedand excised roots of Zea mays grown in the presence or absenceof indol-3-yl acetic acid (IAA). Exposure to IAA enhanced anlageinception in both batches of roots. In the attached roots, theIAA-induced stimulation of primordium initiation was followedby a similar increase in lateral emergence. IAA treatment, however,had no effect on the number of laterals produced, per centimetreof root, in the excised primaries. Thus, exposure to IAA didnot directly enhance lateral emergence in the attached rootsnor did it stimulate such emergence in the excised ones. Nocorrelation was found between proliferative activity in themeristem at the apex of the primary or the rate of root elongationon the one hand, and either the number of primordia initiated,or the number of laterals produced, per centimetre of primary,on the other. Zea mays, maize, root, primordium, lateral, indol-3-yl acetic acid, meristematic activity     

Growth Response to Cyanide by Plants Grown in the Presence or Absence of Iron

Seedlings of Phaseolux vulgaris were grown in media with and without iron. Growth was measured in terms of leaf length and fresh weight increase. Cyanide at & concentration of 0.05 mM was found to inhibit severely plants growing in complete media but failed to inhibit growth to (he same extent in those plants grown in media lacking iron. It was established that this result was obtained whether the plants were grown in an unchanged medium or if the growth medium was replaced at intervals. A number of suggestions were made in an attempt to account for this anomalous behavior.     

Interactions in the Absorption of Monovalent Cations by Excised Radish Roots

Preferential absorption of potassium over sodium has been observedwith excised radish roots using a wide range of concentrationsin the bathing medium. This result is contrary to the situationobserved in most other plants which have been investigated,where it is found that at high external concentrations (>1·0mM) the uptake of potassium is less specific and the rate ofsodium absorption exceeds that of potassium. In radish rootscalcium does not interact with the monovalent cation absorptionin the higher range of concentration and the sodium absorptionis not sensitive to chloride-sulphate substitution. These resultsare discussed in relation to salinity-tolerance and potassium:sodiuminteractions.     

Changes Induced by Salinity to the Anatomy and Morphology of Excised Pea Roots in Culture

Ann. Bot. 57, 811–818, 1986     

Thermal Inactivation of Susceptible and Multiantimicrobial-Resistant Salmonella Strains Grown in the Absence or Presence of Glucose

The heat resistance of susceptible and multiantimicrobial-resistant Salmonella strains grown to stationary phase in glucose-free tryptic soy broth supplemented with 0.6% yeast extract (TSBYE−G; nonadapted), in regular (0.25% glucose) TSBYE, or in TSBYE−G with 1.00% added glucose (TSBYE+G; acid adapted) was determined at 55, 57, 59, and 61°C. Cultures were heated in sterile 0.1% buffered peptone water (50 μl) in heat-sealed capillary tubes immersed in a thermostatically controlled circulating-water bath. Decimal reduction times (D values) were calculated from survival curves having r² values of >0.90 as a means of comparing thermal tolerance among variables. D_59°C values increased (P < 0.05) from 0.50 to 0.58 to 0.66 min for TSBYE−G, TSBYE, and TSBYE+G cultures, respectively. D_61°C values of antimicrobial-susceptible Salmonella strains increased (P < 0.05) from 0.14 to 0.19 as the glucose concentration increased from 0.00 to 1.00%, respectively, while D_61°C values of multiantimicrobial-resistant Salmonella strains did not differ (P > 0.05) between TSBYE−G and TSBYE+G cultures. When averaged across glucose levels and temperatures, there were no differences (P > 0.05) between the D values of susceptible and multiantimicrobial-resistant inocula. Collectively, D values ranged from 4.23 to 5.39, 1.47 to 1.81, 0.50 to 0.66, and 0.16 to 0.20 min for Salmonella strains inactivated at 55, 57, 59, and 61°C, respectively. z_D values were 1.20, 1.48, and 1.49°C for Salmonella strains grown in TSBYE+G, TSBYE, and TSBYE−G, respectively, while the corresponding activation energies of inactivation were 497, 493, and 494 kJ/mol. Study results suggested a cross-protective effect of acid adaptation on thermal inactivation but no association between antimicrobial susceptibility and the ability of salmonellae to survive heat stress.     

Changes Induced by Salinity to the Anatomy and Morphology of Excised Pea Roots in Culture

Excised pea roots were grown in culture in the absence or presenceof NaCl. Salinity induced anatomical and morphological changesin the roots, some of which could be observed after only 24h in culture. Roots became constricted just above the apex,the region above the constriction thickened and the root tipcurved through 90°. Cellular differentiation began nearerthe apex, cortical and epidermal cells shortened and mitoticactivity in the pericycle increased as a result of exposureto salinity. Some of the changes resemble those induced by ethylene,but ethylene probably was not the cause of the response to salinity.Root cultures seem to be a suitable model for studying the effectof salinity in plant roots. Pisum sativum cv. Alaska, salinity, roots, cortex, root culture, pericycle, growth and differentiation     

Salt-induced Changes in the Distribution of Amyloplasts in the Root Cap of Excised Pea Roots in Culture

The effects of 120 mM NaCl on the anatomy and ultrastructureof the root tip of cultured excised pea roots was investigatedafter 24 h exposure to salinity. In the meristematic cells mitochondrialdamage was apparent and these cells showed increased vacuolation.The root cap was already severely affected after 24 h exposureto salinity and clumping of the cap amyloplasts around the cellnuclei was apparent. The possibility that salinity may affectroot gravitropic responses is discussed. Pisum sativum L. cv. Alaska, salinity, roots, root culture, amyloplasts, ultrastructure     

Regulation of Elongation Growth of Excised segments of Vigna Hypocotyl under Osmotic Stress in the Absence or Presence of Absorbable Solute

The regulation of elongation growth in excised segments of Vignahypocotyl under osmotic stress was investigated by means ofthe xylem perfusion and pressure-jump method. When subjectedto osmotic stress in the absence of absorbable solutes (100mM sorbitol only) or in the presence of absorbable solutes (70mM sorbitol plus 30 mM sucrose, or 70 mM sorbitol plus 15 mMKC1), the hypocotyl segments immediately began to shrink. Thehyper-polarizations of the transmembrane potentials (V_px andV_ps) took place at once. Within 40–60 minutes, the segmentsresumed growth. In the presence of absorbable solute, therewas an obvious increase in the effective turgor (Pⁱ–Y'),but the physiological wall extensibility () increased only slightly.Conversely, in the absence of absorbable solute, increasedsignificantly but (Pⁱ–Y') decreased. The results suggestthat the recovery of growth of an excised segment under osmoticstress is mainly due to the change in in the absence of absorbablesolute, and to the change in (P¹–Y') in the presence ofabsorbable solute, and that the two respiration-dependent protonpumps play important roles in these recovery processes. (Received April 28, 1989; Accepted August 24, 1989)     

Inhibition of Ion Transport in Excised Barley Roots by Abscisic Acid; Relation to Water Permeability of the Roots

Previous papers have shown that abscisic acid can inhibit transportof ions across the root to the xylem vessels, resulting in reducedexudation from excised roots or inhibiting guttation from intactplants. However, it has not been established whether the inhibitionwas due to a reduction in salt transport (J_s) or in permeabilityof the roots to water (L_p). This paper investigates the effectof ABA on L_p and J_s separately. It is shown that L_p increasedin ABA and then fell, but was about the same as in control rootswhen transport was inhibited. The effect of ABA on exudationtherefore appeared to be mainly due to reduction in J_s. Inhibitionof J_s was also present in intact, transpiring plants and sowas not due to reduced water flow. The inhibition of ion releaseto the xylem affected Na⁺, Mg²⁺, Ca²⁺, and phosphate as wellas the major ion in the exudate, K⁺. It is concluded that ABAinhibits salt transport to the shoot by acting on ion transportinto the xylem, and not by reducing water flow coupled withsalt transport.     

The Regulation of the Synthesis of Glutamate Dehydrogenase in Excised Pea Roots by ExogenousL- aspartic andL- glutamic Acids

Exogenous L-aspartic and L-glutamic acids enhance glutamate dehydrogenase activity in isolated pea roots. The results obtained indicate that both ammo acids induce increased GDH synthesis.     

The Effect of Exogenous IAA and Kinetin on Nitrate Reductase,Nitrite Reductase and Glutamate Dehydrogenase Activities in Excised Pea Roots

Nitrate reductase (NO₃R) activity, nitrite reductase (NO₂R) activity and NADH₂ dependent glutamate dehydrogenase (GDH) activity were followed in extracts from excised pea roots incubated under aseptic conditions for 9 and 24 h in nitrate containing nutrient medium to which IAA was added in concentrations promoting lateral root formation (1 × 10^?5; 3 × 10^?5; 5 × 10^?5 M) and kinetin in concentrations which reduce lateral root formation (0.1; 1; 5 mg 1^?1, that is 4.65 × 10^?7;4.65 × 10^?6 and 2.3 × 10^?5 M). NO₃R activity was not influenced by IAA, NO₂R activity was slightly depressed by IAA after 24 h incubation and GDH activity was slightly increased after 24 h incubation in the presence of IAA. Kinetin decreased NO₃R activity significantly both after 9 h and 24 h incubation, slightly increased NO₂R activity after 9 h incubation but slightly decreased it after 24 h incubation, and did not affect GDH activity after 24 h incubation. However, when applied together with IAA, kinetin abolished the promoting effect of IAA on GDH activity. IAA neither reversed nor accentuated the effect of kinetin on NO₂R activity. Nevertheless the depressing effect of kinetin on NO₃R activity was emphasized by the presence of IAA after 9 h incubation. The results obtained indicate that reduced nitrate assimilation due to the depression of nitrate reductase activity caused by kinetin probably contributes to the negative growth effect of kinetin in pea root segments grown in nitrate medium.     

Boundary Layer Effects in Ion Absorption by Roots and Storage Organs of Plants

In plant nutrition studies with culture solutions it is tacitly assumed that replenishment of ions at the root surface is guaranteed by the turbulence of the stirred solution. That this belief may be erroneous is demonstrated in this study with barley roots and discs of beet roots and potato tubers. At very low concentrations of RbCl (in presence of CaCl₂) the uptake of Rb by roots is strongly controlled by the rate of stirring. The results are interpreted in the light of the Nernst hydrodynamic boundary film which surrounds solids and through which ions must diffuse to reach the root surface. “Film-controlled” and “root-controlled” ion uptake is visualized.