Hugh Frick

Boron tolerance and accumulation in the duckweed, Lemna minor.

Abstract A sensitive measure of growth in the duckweed, Lernna minor, was used to demonstrate the tolerance of this higher plant to boron [B(OH)3] at levels of 10 to 20 μg/mL in the growth medium at pH 5.0. Growth inhibition by B in concentrations up to 100 μg/mL in the external medium was reversible after transfer to control medium. At pH 4.0 and in the presence of 20 μg/mL B for 7 days, the plants accumulated 93 μg B/g fresh weight (148% of the control) and this increased with pH up to pH 7.0 where the plants accumulated 257 μg B/g fresh weight (525% of the control). Only at pH 7.0 in the presence of B was growth inhibited. Thus, plants which had accumulated more than 100 μg B/g fresh weight still grew normally. This corresponds to about 800 μg B/g dry weight accumulated by this monocot without effect upon growth rate.

Callogenesis and Carbohydrate Utilization in Lemna minor

Summary Callus of Lemna minor L. was generated by fracturing whole plants which had been pre-conditioned to auxin containing callogenesis medium. Chlorophyll accumulation during callus growth and growth rate itself were sucrose-dependent. I have attempted to identify among common carbon-supplements those which support plant growth in vivo but not callus growth in vitro , and vice versa, with a view to recognizing «differentiated functions» for carbohydrate metabolism. Plant growth was not supported by galactose or sorbitol, whereas callus utilized each rather well. Obversely, plants utilized glucose, fructose, melibiose, starch, and mannitol, whereas callus growth was poorly supported by these in comparison to sucrose. Thus, there seem to be a number of differences between in vivo and in vitro gene expression in carbohydrate metabolism.

Heterotrophy in the Lemnaceae

Summary Lemna minor L. and Wolffia brasiliensis Weddell can use sucrose to support heterotrophic growth in darkness and photomixotrophic growth in the light, but each is killed by galactose in the medium. Spirodela punctata (G. F. W. Meyer) Thompson growth on sucrose and galactose was indistinguishable. L. minor, Wolffia , and Spirodela plants could not utilize lactose or sorbitol; Callitriche stagnalis Scopoli could not utilize galactose or sorbitol and made only marginal use of sucrose to drive growth in light or darkness. L. minor callus and Callitriche callus, on the other hand, utilized galactose effectively, and L. minor callus also utilized sorbitol. The specific reducing sugar content was lowered in Lemna callus during heterotrophic growth on galactose, bus not in Spirodela plants. The specific starch and sucrose contents were reduced in both when growing on galactose. Callitriche plants appeared to absorb galactose, but to not utilize it to drive growth, whereas the callus that did utilize galactose showed the Lemnacean pattern of diminished specific starch and sucrose pools. Catabolic sucrose synthase (EC 2.4.1.13) activity diminished during growth in darkness in all cases, consistent with an increase in the specific sucrose content. Invertase (EG 3.2.1.26) activity, alkaline and acidic, diminished in darkness (excepting heterotrophic Spirodela plants), consistent with the large increases in specific reducing sugar content being due to diminished alkaline invertase activity. L. minor callus not only showed lowered invertase and sucrose synthetase activities when growing on galactose or sorbitol, but also had lowered reducing sugar, sucrose, and starch contents. The enzymology of exogenous lactose, galactose, and sorbitol utilizasion is open to study with respect to primary carbon partitioning.

Micronutrient tolerance and accumulation in the duckweed, Lemna

Abstract Vegetative growth of the aquatic monocotyledon Lemna minor L. (duckweed) under continuous irradiation in photoheterotrophic medium is log‐linear with a frond doubling‐time of about 1.4 d. This steady‐state frond multiplication rate was not altered (through six days) by concentrations of micronutrients (Fe,Mn,B,Cu, Zn,Mo) between 28 and 1000 times that contained in the routine growth medium. Using high but not inhibitory concentrations, the effect on steady‐state growth of all possible 2‐, 3‐, 4‐, 5‐, and 6‐way combinations has been studied. Lerma growing in the presence of high concentrations of any other micronutrient is least tolerant to the addition of Mo. Growth inhibition due to 2‐way combinations of certain elements (eg. MnMo) was prevented by the presence of a third (eg. MnMoZn) in patterns suggesting selective interaction between the elements. Moreover, in the absence of Mo in high concentration the combination of the other 5 micronutrients was not inhibitory even though separate 2‐, 3‐, ...

Sensitivity of Lemna minor Growth to Osmotic Potential and Relative Tolerance of its Callus

Summary Growth of Lemna minor L. plants was blocked by 2.5 mM external proline, but growth of L. minor callus was only 50 % inhibited by 5 mM external proline. The growth rates of plants and callus decreased linearly with external Na 2 SO 4 , NaCl, mannitol, or PEG-8000 concentration, with the slope of decrease dependent upon the particular osmoticum, and the internal proline content generally increased as growth decreased. The correlations between decreased growth rate and proline accumulation were stronger for plants than for callus, and the callus showed a smaller growth decrease per unit external osmotic pressure. The accumulation of anions and cations as the external Na 2 S0 4 concentration increased was only linear for SO 4 ∔2 . The tissue content of SO 4 ∔2 was almost alone able to account for continued growth of plant or callus as [Na 2 SO 4 ] ext increased to 35.2 mM. A Callus Line Adapted To Fair Growth On 70.4 Mm Na 2 So 4 Showed The Same Rate Of Growth Declination In The Presence Of The Four Osmotica As Did The Unadapted Callus: the response curves were merely shifted to higher external osmoticum values. The relative tolerance to osmotic pressure of the Na 2 SO 4 -adaptedcallus could not be accounted for in terms of proline or sugar content.

Vitrification in vivo in lemna minor and its maintenance by isopentenyl adenine

Summary Clones of vitrified Lemna minor plants were recovered following heat and osmotic shock. Their growth in vivo was about two-thirds as rapid as glaucous plants, and they contained one-third as much chlorophyll. Reproduction of the vitrified state of plants in vivo was nearly complete over three fronddoublings in the presence of 0.5 mg · L -1 isopentenyladenine (2iP), and vitrification was lost immediately in the absence of 2iP. The correlation between in vivo maintenance of the vitrified plant state and cytokinin concentration was 0.989.

Inhibition of augmentation of potassium (86Rb) uptake in maize primary roots by the root apex

Summary The ability of the primary root of Zea mays L. seedlings to augment its rate of K + ( 86 Rb) uptake during submersion and aeration was not affected by excision from the kernel, but the presence of the attached apex partially suppressed augmentation development in basipetal regions. The root apex can have this influence whether attached or excised via an inferred water-soluble inhibitor. Kinetin and IAA each stimulate augmentation at low (5–10 nM), and inhibit at high (10, μM), concentration. An interaction of kinetin with IAA or with GA 3 in modulating aumentation could not be shown.

Potassium flux in Corn roots during augmentation of ion uptake

Abstract Aeration of submersed corn roots doubles the subsequent uptake rate of ions. This augmentation is accompanied by hyperpolari‐zation of membrane potential, depends upon aeration and protein synthesis, and is associated with changes in membrane proteins. Potassium uptake (86Rb) by excised and intact roots before and after augmentation was measured, and potassium losses by roots at different temperatures or in the presence of dinitrophenol was followed. Relevant effluxes of potassium follow excision and/or submersion or roots, and a metabolism‐dependent process must be carried out by roots in order to recover the control of membrane permeability. Moreover, we show that corn hybrids of different maturity classes differ not only for initial ion uptake rates but also for the ability to recover control of membrane permeability.

Augmentation of Ion Uptake in Maize Roots is Associated with the Biosynthesis of Plasma Membrane Proteins

Summary Aeration of excised submerged maize (Zea mays L.) roots augmented the rate of amino acid uptake, and incorporation into TCA-insoluble material. The plasma membrane fraction of augmented roots included 5.8 times higher specific 3H-leucine radioactivity than that of basal (non-aerated) roots. Proteins and radiolabel of the plasma membrane fraction were optimally (90 %) solubilized by zwitterionic sulfobetaine detergents with a carbon chain length of ten. Activity of the plasma membrane-associated, K-stimulated, pH 6.5, Mg-ATPase was not altered during augmentation. This enzyme activity appeared to be inhibited by the sulfobetaine detergent; less than 50 % of the activity could be recovered after solubilization. The solubilized plasma membrane proteins of both basal and augmented root extracts separated on Sephadex G-200 into six discrete peaks, ranging between about 15 and 700 kdaltons. Incorporated 3H-leucine coincided with a 500 kdalton class of proteins, and was incorporated in detectable quantities only into the plasma membrane fraction of augmented roots.

Photosynthetic capacity in potassium stressed soybean: Comparison of CO2 fixation and O2 evolution assays

Abstract Potassium deficiency in soybeans (Glycine max (L.) Merr.) may cause decreased photosynthetic capacity. Potassium‐stressed soybeans were compared by CO2 fixation and O2 evolution assays. Trifoliate leaves of potassium‐stressed soybean seedlings which did not show reduced chlorophyll content per unit fresh weight nor altered rates of light‐induced O2 evolution, fixed 38% less CO2 than did control leaves.