Nutritionally enhanced cereals: A sustainable foundation for a balanced diet

Three nutrients, iron, zinc and pro-vitamin A, are widely deficient in humans, especially among low socioeconomic groups in developing countries, but they remain significant concerns in industrialized countries as well. Cereals provide the majority of the intake of these nutrients in low-income families. Moreover, these three nutrients may interact synergistically in absorption and function to such an extent that there are potentially huge advantages in providing all three together in the one staple food. Because of this, they may be more bioavailable to deficient individuals than current thinking allows. To do so would provide a sound basis on which to build a better balanced diet for nutritionally compromised individuals. Genetic variation in nutrient composition exists in cereals and can be exploited in conventional breeding programmes and through gene technology. Cultural techniques, including fertiliser technology and organic farming, have also impacted upon the nutrient composition of cereals. Human iron and zinc intake can be doubled at least, and essential carotenoid intakes can be increased dramatically. Preliminary feeding trials with nutrient-dense grains have been encouraging. Moreover, nutrient-dense seeds also produce more vigorous seedlings and higher grain yield in soils where these nutrients are poorly available, so that to a significant extent agronomic and health objectives coincide. New varieties are rapidly adopted, especially where there are yield advantages, ensuring maximum impact without new inputs. This approach is potentially more sustainable than fortification and supplementation programmes because intake is continuous, which is especially important for zinc because it is needed almost daily.

Ophthalmoscopic contact lenses for transpupillary thermotherapy

Ophthalmoscopic contact lenses for transpupillary thermotherapy (TTT) must provide effective visualization of retinal treatment sites and transmission of infrared diode laser radiation. Selection and proper use of retinal laser lenses requires knowledge of their lateral magnification, laser beam magnification factor, field of view and resolution. Optical performance is analyzed for Goldmann-type lenses and a series of inverted image lenses of differing magnification. Goldmann lenses have the highest resolution, but inverted image lenses of comparable magnification have 2.5 times or more their field of view. Inverted image lenses of similar magnification can differ in resolution. They require 2-4% more incident laser power to produce the same retinal irradiance as a Goldmann lens, but this difference is small in comparison to other clinical variables. Tilting an ophthalmoscopic contact lens up to 15 degrees causes little distortion in the circularity of the retinal spot formed by a laser beam or difference in retinal irradiance across the spot. Inverted image lenses produce higher anterior segment irradiances than Goldmann-type lenses, but anterior segment injuries are less likely in TTT than conventional visible light, short-pulse retinal photocoagulation because of the comparatively low irradiances used in TTT and the decreased absorption of diode laser infrared radiation in ocular media and melanin.

Comparing wheat grown in South Australian organic and conventional farming systems. 1. Growth and grain yield

Organic farming standards do not allow addition of water-soluble fertilisers and therefore it is likely that growth of organically grown crops will be limited by nutrient availability. However, in marginal rainfall conditions, when growth in conventional systems is limited by water availability, yields of organically grown crops could be comparable with those conventionally grown. Similarly, micronutrient-efficient plant varieties could be expected to perform comparatively better under organic farming conditions than they do in conventional systems, when compared with micronutrient-inefficient varieties.In this study, biomass and grain production of wheat from certified organic farming systems were compared with neighbouring conventional farming systems in 'across the fence' field trials in 1 moderate and 2 marginal rainfall areas of South Australia. Wheat varieties compared included 2 old wheat varieties developed under relatively low-input conditions (Baroota Wonder and Dirk-48) and varieties shown to be micronutrient-efficient (Janz and Trident) and inefficient (Yallaroi).The organic farming systems produced significantly less biomass than the conventional farming systems at late tillering in both the moderate and marginal rainfall areas. Grain yield was variable, but significantly lower in the organic farming system for 11 of the 14 comparisons. None of the varieties showed an adaptive advantage for 1 farming system over the other. The relative yield of the organic system, compared with the conventional system, was not associated with rainfall.

Breeding for nutritional characteristics in cereals

Extensive genetic variation within large species such as the major cereals can be confidently expected for any new trait of interest. This has now been extensively demonstrated for the nutrient content of cereal grains that is of interest under deficient conditions both to human nutritionists and to cereal agronomists. As cereals are eaten in large quantity by practically everyone, they are the ideal vehicles for changing the balance of nutrient intake of the whole human population. Doing so appears to be necessary as the World Health Organization has identified deficient micronutrient intake in well over half of all people globally, notably women and children. Of major concern are iron, zinc, selenium iodine, calcium and vitamin A-related carotenoids. Our results show that for any staple so far studied, the intake of iron, calcium and zinc from cereals can be doubled, and the content/intake of essential carotenoids can be increased by much greater factors. To prove to rigid scientific standards that greater intake results in greater absorption and measurable health benefits is quite difficult, but it is currently being pursued in various ways. This proof of bioavailability is all that impedes implementation in breeding programs.

A soil-based method to screen for zinc efficiency in seedlings and its ability to predict yield responses to zinc deficiency in mature plants

Nutrient efficiency measures the ability of a plant to grow and produce grain when the availability of a nutrient is low. Seedling tests for nutrient efficiency will be most useful if the results correlate well with grain yield responses. In two experiments, a diverse range of barley genotypes was screened for zinc (Zn) efficiency at the seedling stage and the relationship between vegetative and grain measures of Zn efficiency was examined. In Expt 1, 54 barley and 4 wheat genotypes were grown at 2 levels of Zn (0.02 and 0.8 mg/kg soil) for 21 days. Zinc efficiency ranged from 18% to 52%. The visual symptoms of Zn deficiency varied considerably between genotypes and was significantly correlated with Zn efficiency. Root:shoot ratio was increased by Zn deficiency and varied between genotypes, but these differences were not related to Zn efficiency. Zinc concentration and especially Zn content at 0.02 mg Zn/kg were significantly related to Zn efficiency. In Expt 2, 15 genotypes, selected on the basis of their response in Expt 1, were grown to maturity at either 0.1 mg Zn/kg or 2.4 mg Zn/kg. Zn efficiency, based on relative grain yield, ranged from 5% to 54%. High efficiency was associated with a large number of grains per plant and high kernel weight. Rankings of Zn efficiency in the experiment were significantly correlated with the rankings for visual scores in Expt 1. The 2 experiments suggested that deficiency symptoms at the seedling stage can identify efficient genotypes and could be useful for routine screening for Zn efficiency. Independent data from multisite comparisons over 8 years were used to examine the long-term performance of efficient and inefficient genotypes in the field. Hierarchical cluster was used to define efficient and inefficient groupings within the 56 genotypes examined in Expt 1, based on their responses to Zn. The Zn-efficient genotypes tended to yield more than the Zn-inefficient genotypes. The data provide prima facae evidence that high Zn efficiency may contribute to improved adaptation of barley in South Australia.

Kinetic analysis of boron transport in Chara

The permeability of biological membranes to boric acid was investigated using the giant internodal cells of the charophyte alga Chara corallina (Klein ex Will. Esk. R.D. Wood). The advantage of this system is that it is possible to distinguish between membrane transport of boron (B) and complexing of B by plant cell walls. Influx of B was found to be rapid, with equilibrium between the intracellular and extracellular phases being established after approximately 24 h when the external concentration was 50 microM. The intracellular concentration at equilibrium was 55 microM, which is consistent with passive distribution of B across the membrane along with a small amount of internal complexation. Efflux of B occurred with a similar half-time to influx, approximately 3 h, which indicates that the intracellular B was not tightly complexed. The concentration dependence of short-term influx measured with 10B-enriched boric acid was biphasic. This was tentatively attributed to the operation of two separate transport systems, a facilitated system that saturates at 5 microM, and a linear component due to simple diffusion of B through the membrane. Vmax and Km for the facilitated transport system were 135 pmol m(-2) s(-1) and 2 microM, respectively. The permeability coefficient for boric acid in the Chara plasmalemma estimated from the slope of the linear influx component was 4.4 x 10(-7) cm s(-1) which is an order of magnitude lower than computed from the ether:water partition coefficient for B.

Zinc deficiency up-regulates expression of high-affinity phosphate transporter genes in both phosphate-sufficient and -deficient barley roots

Phosphate (P) is taken up by plants through high-affinity P transporter proteins embedded in the plasma membrane of certain cell types in plant roots. Expression of the genes that encode these transporters responds to the P status of the plants, and their transcription is normally tightly controlled. However, this tight control of P uptake is lost under Zn deficiency, leading to very high accumulation of P in plants. We examined the effect of plant Zn status on the expression of the genes encoding the HVPT1 and HVPT2 high-affinity P transporters in barley (Hordeum vulgare L. cv Weeah) roots. The results show that the expression of these genes is intimately linked to the Zn status of the plants. Zn deficiency induced the expression of genes encoding these P transporters in plants grown in either P-sufficient or -deficient conditions. Moreover, the role of Zn in the regulation of these genes is specific in that it cannot be replaced by manganese (a divalent cation similar to Zn). It appears that Zn plays a specific role in the signal transduction pathway responsible for the regulation of genes encoding high-affinity P transporters in plant roots. The significance of Zn involvement in the regulation of genes involved in P uptake is discussed.

Validity of photoelastic strain measurement on cadaveric proximal femora

Rosette strain gages indicate shear and principal strains at specific points, whereas photoelastic coatings provide shear strain information over a broad area. Information regarding bone loading and load transfer from a prosthetic implant to adjacent bone can be obtained using either strain-measuring technique on loaded femora. This study compared proximal femoral strains derived from photoelastic coatings to those obtained from rosette strain gages applied directly to the bone in order to determine the relationships between photoelastic shear strains and rosette shear and principal strains. Photoelastic shear strains underestimated rosette shear strains and exceeded the larger of the rosette principal strains. Principal strains derived from photoelastic coatings augmented with strain separator gages underestimated their rosette counterparts in most instances. Correlation was strong and nearly linear for all measures, indicating that photoelastic coatings can accurately express proportional strain changes despite imperfect agreement in absolute strain magnitudes. The best agreement between absolute strain magnitudes occurred in the proximal medial, or calcar, region. Understanding the relationships between the various measures obtained using the two strain measurement methods will allow more accurate estimates of actual strains to be made from photoelastic coatings.

Effects of coronally slotted femoral prostheses on cortical bone strain

The photoelastic method was used to assess the effects on femoral cortical strain of total hip arthroplasty cementless femoral prostheses containing distal coronal slots. Eight cadaveric femurs were tested, although three were eliminated secondary to fractures. Loaded and unloaded cortical strains were determined at 72 points on the implanted femoral cortex and compared with the values obtained in the intact femur. Three different prostheses were sequentially implanted, in a random order, into each femur. The prostheses consisted of a standard solid stem, an identical stem with a coronal slot in its distal one fourth, and an identical stem with a coronal slot in its distal one half. The slotted stems did not enhance axial load transfer to the proximal medial femur but did result in increased proximal medial assembly strains and statistically significant (P < .05) decreased anterior and posterior assembly strains. The increased proximal medial assembly strains are hypothesized to enhance proximal medial femoral loading, while the decreased anterior and posterior assembly strains may minimize operative implantation fractures.

Treating mild-to-moderate hypertension: a comparison of lisinopril-hydrochlorothiazide fixed combination with captopril and hydrochlorothiazide free combination

The fixed combination comprising lisinopril 10 mg and hydrochlorothiazide 12.5 mg once daily (L/HCTZ) was compared with captopril 25 mg and hydrochlorothiazide 25 mg once daily (C/HCTZ) in a randomized, double-blind, parallel-group study. After a 2-4 week placebo run-in period patients were randomized to L/HCTZ (n = 82) or C/HCTZ (n = 83) for 8 weeks. After 8 weeks, peak blood levels of both treatments showed lowered sitting BPs (-22.8/-14.3 mm Hg for L/HCTZ vs -22.8/-14.0 mm Hg for C/HCTZ), and standing BPs (-22.6/-13.1 mm Hg vs -21.6/-12.8 mm Hg, respectively). Between-drug differences were not significant (ns). At trough blood levels L/HCTZ lowered sitting BPs more than C/HCTZ, -23.6/-14.9 mm Hg vs -16.0/-11.3 mm Hg (P less than 0.02/less than 0.03), respectively. The effect on standing BP was similar, -22.0/-13.8 mm Hg vs -15.1/-10.3 mm Hg (P less than 0.03/less than 0.05) for L/HCTZ and C/HCTZ, respectively. Both treatments slightly increased heart rate (ns). Serum potassium fell more with C/HCTZ than with L/HCTZ (P less than 0.005). The fasting glucose level rose with L/HCTZ and fell with C/HCTZ. Uric acid, triglycerides and fasting cholesterol levels rose in both groups (ns). There were no differences between treatments with respect to adverse events. L/HCTZ appears to be a well-tolerated combination with efficacy on once-daily dosing superior to that of C/HCTZ.

Increased manganese content of barley seeds can increase grain yield in manganese-deficient conditions

Manganese (Mn) deficiency which decreases barley (Hordeurn vulgare L.) yields can be difficult to eliminate by fertilizer applications. We hypothesized that higher Mn content of barley seed could decrease the severity of Mn deficiency and thus decrease yield loss due to that deficiency. Galleon barley with different amounts of Mn in the seed (low Mn seed: 0.08-0.26 8g per seed; medium Mn seed: 0.34-0 -62 8g per seed; high Mn seed: 0-74-1.208g per seed) was grown in field, glasshouse and growth cabinet experiments. In two experiments, seeds were soaked in MnS04 and had Mn contents of approximately 50 8g per seed. High Mn seed, either obtained artificially by soaking seed in MnSO4 before sowing, or naturally from the parent plant, increased grain yield of barley grown in Mn-deficient conditions. In both -Mn and +Mn treatments, barley grown from high Mn seed had a greater grain yield than that from low Mn seed. High seed Mn increased root dry weight, Mn content of both roots and shoots, shoot dry weight, number of early tillers, plant survival and number of grains per plant, but had no effect on weight per seed. Maximum grain yield was achieved by sowing seed with a high Mn content and applying Mn fertilizer; neither treatment completely corrected Mn deficiency on its own.

Application of different sources of manganese sulfate decreases take-all (Gaeumannomyces graminis var. tritici) of wheat grown in a manganese deficient soi

Two experiments tested the effectiveness of manganese (Mn) decreasing take-all of wheat. The first experiment was conducted under controlled environmental conditions. Mn sulfate was mixed through the soil at sowing or 2 weeks before, or applied to the seed or leaves, and manganese dioxide (MnO2) was mixed through the soil at sowing or 2 weeks before. Mixing manganese sulfate (MnSO4) through the soil was the most effective treatment at decreasing take-all, followed by seed applied Mn. MnO2 and foliar applied Mn had little effect on take-all. All Mn treatments, except foliar Mn, completely eliminated Mn deficiency in the plants. In the second experiment, which was conducted in the field at a Mn deficient site, Mn sulfate and MnO2 were applied to the soil at sowing. MnSO4 decreased take-all and increased grain yields in take-all inoculated plots nearly threefold, but increased yields only slightly in uninoculated plots. MnO2 was not effective in decreasing take-all or increasing grain yield. This is the first report of take-all infection being suppressed by MnSO4in the field. The results of these experiments support the hypothesis that Mn may be acting through the physiology of the wheat plant to decrease take-all.

Tolerance of wheat, barley, triticale and rye to manganese deficiency during seedling growth

The manganese (Mn) efficiencies, i.e. tolerances to Mn deficiency, of wheat, barley, triticale and rye seedlings, were compared, with emphasis on genotypic variation within wheat. Plants were grown in small pots containing a Mn-deficient calcareous sand, with and without Mn addition, over a 4-week period at 15�C.Barley proved to be the most Mn-efficient cereal, having the highest dry matter production, Mn uptake and utilization efficiency. The high rate of Mn uptake for barley was strongly associated with greater lateral root development. The severe Mn deficiency of this soil precluded any significant Mn uptake by the other cereals. Differences in growth between wheat cultivars without added Mn were associated with differences in the Mn content of sown seeds.The results obtained from the screening of wheat-barley addition lines suggested that Mn-efficiency characters could be transferred from barley to wheat, since relative growth at Mn 0 was significantly greater for some of the addition lines than for wheat.

Effects of Ni Deficiency on Some Nitrogen Metabolites in Cowpeas (Vigna unguiculata L. Walp)

Cowpeas grown in nutrient solutions, from which Ni had been removed by a ligand exchange technique, accumulated urea in most tissues. Urea levels were highest (up to 3.1 percent dry weight) in necrotic leaf tips. Urea accumulation in Ni-deficient cowpea tissues amounted to about 1 percent of the total N. The accumulation of urea was presumably associated with the catabolism of N compounds in older tissues and the redistribution of N catabolites within the plant during the reproductive growth. The exclusion of N salts from the nutrient media at a late stage of growth, either with or without added Ni, led to a general amelioration of urea accumulation and a lower level of the related amino acid, arginine, in root and stem tissue. Plant leaves that contained toxic levels of urea and displayed necrotic symptoms had tissue Ni levels ranging from less than 0.01 to 0.15 mug Ni per gram dry weight. Nickel concentrations in tissue from plants not treated with Ni, were initially very low, but increased as the cowpeas matured. Apparently, there was a source of Ni contamination in the Ni-deficient growth media which provided a source of Ni for uptake by the plants during growth. Ureide levels were low and unaffected by Ni deprivation. No evidence for free purines or uric acid accumulation in plant tissues could be found. It is hypothesized that Ni (and urease) participates in the normal N metabolism of these plants during the reproductive phase of growth.

Diagnosis and prognosis of manganese deficiency in Lupinus angustifolius L

Relationships diagnostic of manganese (Mn) deficiency in Lupinus angustifolius were examined in growth chamber experiments by studying the effects of Mn supply on plant growth and on photosynthesis and Mn concentrations in young leaves and whole shoots. A critical Mn concentration in youngest fully expanded leaves (YFEL) of 30 8g/g dry matter was found to be diagnostic of reduced dry matter production. A similar critical concentration was found for whole shoots, and the criteria were consistent over a wide range of ontogeny until at least early flowering. A less sensitive criterion of Mn deficiency was that for chlorophyll 'a' fluorescence characteristics of YFEL's (17 8g/g in YFEL), which estimates photosynthetic dysfunction in relation to Mn supply. The distal segments of lupin leaves best reflected changes in fluorescence in relation to their Mn status. The prognosis of impending Mn deficiency in maturing lupin plants was also examined in field and growth chamber experiments by studying the effects of Mn supply on the relationships between the concentrations of Mn in plant components at anthesis, and the subsequent appearance of Mn deficient ('split') seed on maturing plants. The absence of Mn deficient seed in main axis and first-order lateral inflorescences of maturing lupins could be predicted by Mn concentrations in stems at anthesis of >20 8g/g. Manganese concentrations of buds, leaves and tissues containing a high proportion of leaf, were found to be poor predictors of subsequent Mn deficiency in maturing lupins.

Photosynthetic dysfunction and in vivo changes in chlorophyll a fluorescence from manganese-deficient wheat leaves

Leaves on wheat plants growing in manganese-deficient media showed much higher constant-yield fluorescence (Fo) but greatly reduced variable fluorescence (Fv). Higher Fo was symptomatic of a stronger overall emission which derived from functional changes within photosynthetic membranes and was not simply attributable to differences in leaf reflectivity of wavelengths relevant to fluorescence measurements (710-720 nm). Topical application of 4 mM MnCl, to such deficient material restored photosynthetic activity (O2 evolution by leaf slices) and also led to correlative changes in fluorescence: increased Fv, and lower Fo. Original symptoms were therefore attributable to Mn-deficiency per se. Quantitative relationships between leaf Mn concentration and certain fluorescence characteristics (the ratio Fo/Fv) were then established on flag levels excised from field plants. Critical levels of leaf Mn were discernible as an abrupt increase in the Fo/Fv ratio, once leaf Mn was below a threshold concentration, which was the minimum requirement of this element for dry matter productivity, viz. 10-12 �g Mn g-1 dry wt.

The critical concentration of manganese in field-grown wheat

The critical concentration of manganese (Mn) in wheat tissues for optimal growth was determined from field experiments. In the youngest emerged blade showing a ligule (YEB), the critical concentration was 11 � 1 8g g-1 (DW). The critical concentrations for older blades and whole tops were: next leaf below YEB, 13 � 1 8g g-1 DW; older leaves, 16 � 1 8g g-1 DW; whole tops, 12 � 1 8g g-1 DW. The older blades were less sensitive determinants of the growth response and are not recommended tissues for analysis. Diagnosis using whole tops was less sensitive than with YEB, but analysis of whole tops may give an integrated picture of Mn deficiency where availability varies rapidly with time. The critical concentration of 11 � 1 8g g-1 in the YEB for growth is also the critical level for the appearance in that leaf of normal chlorophyll a fluorescence transients. The Fo/Fv ratio, a parameter of the leaf fluorescence transients, correlated well with the Mn concentration in the leaf and may prove suitable for the diagnosis of Mn deficiency in field-grown wheat. The critical level of Mn was the same for two genotypes differing in their ability to tolerate Mn deficiency in the soil. Grain yield responses and other relevant data collected over three years are presented. Analysis of grain was shown to be an unreliable method of diagnosing an earlier Mn deficiency in the crop.

The effect of soil- and foliar-applied manganese in preventing the onset of manganese deficiency in Lupinus angustifolius

The efficacy of the application of manganese, either applied to soil or as foliar sprays at three stages of flower development, in preventing the expression of manganese deficiency (ruptured seed coats ('split seed'); delayed maturity ('regreening'); and poor grain yield) in two cultivars of Lupinus angustifolius (cvv. Marri and Illyarrie) was assessed on sandy soils of the upper South East and Eyre Peninsula regions of South Australia. Six experiments were conducted during 1979 and 1980. A single foliar application of manganese (1.7 kg Mn/ha, in 200 litre water) when the upper-lateral shoots were in mid-flower, prevented the onset of the disorder. Applications of manganese to the soil at sowing at rates of up to 11.1 kg Mn/ha were usually less effective. The appearance of 'split-seed' symptoms in mature grain was a more sensitive indicator of manganese deficiency than was grain yield response to manganese fertilization. The degree to which these symptoms appeared increased markedly when the manganese concentration in intact seed became less than 8-10 �g/g dry seed, an observation which is consistent with other studies.

Responses of triticale, wheat, rye and barley to nitrogen fertilizer

A hexaploid triticale from Mexico and local cultivars of wheat, rye and barley, each at five levels of fertilizer nitrogen (0, 35, 70, 105 and 140 kg N/ha) with four replications, were grown in a field experiment at Mintaro, South Australia. A visually discernible response to nitrogen fertilizer by all four genotypes from an early stage was confirmed by quantitative sampling at tiliering, anthesis and maturity. Responses in plant dry weight to 105 kg N/ha were maintained until anthesis but grain yield responses were significant only at 35 kg N/ha. Total dry matter production responses at maturity to more than 35 kg N/ha were small. Numbers of tillers and heads were increased by nitrogen additions up to 140 and 105 kg N/ha, respectively, and plant height measurements showed general increases to 70 kg N/ha with significant lodging at higher nitrogen levels in both rye and triticale. For all genotypes, thousand grain weight decreased with increasing level of nitrogen supply while grain and straw nitrogen increased up to levels of 140 and 105 kg N/ha, respectively. Nitrogen supply had little effect on maturity, plants at 0 and 140 kg N/ha reaching anthesis less than a day apart. The lack of a significant nitrogen x genotype interaction in nearly all the data suggests that the triticale does not differ in its nitrogen nutrition from the traditional cereals. Triticale consistently outyielded the other cereals in total dry matter production followed by the rye, wheat and barley in that order. Grain yield was highest in the wheat and least in the rye, the latter also being the least responsive to nitrogen. The advantage of the triticale lay in its high grain protein and lysine content combined with good yield.

The sensitivity of hexaploid and octoploid triticales and their parent species to copper deficiency

The tolerance of two triticales to soil of low copper status was determined in deep pots in a glasshouse experiment, and compared with the tolerance of their wheat and rye parent types. Both tetraploid and hexaploid wheats were extremely sensitive to copper deficiency, producing no grain without copper added to the soil. In contrast, rye and the hexaploid triticale were completely tolerant of the copper-deficient soil, producing as much grain without added copper as at the highest rate of copper supply. The octoploid triticale produced about 60% of maximum grain yield in the unamended soil, a performance intermediate between its rye and hexaploid-wheat parents. The cause of grain failure in the wheats was pollen sterility induced by copper deficiency, and this was related to low uptake of copper into the shoot and heads of wheat from the unamended soil. The pattern of uptake of zinc was quite different from that of copper in these plants, which suggests that a specific uptake mechanism for copper exists in rye which is genetically controlled and transferable to triticale, its hybrid with wheat. The copper efficiency so conferred on triticale would appear to be adequate for most field situations where copper deficiency exists.

Potassium Deficiency-induced Changes in Stomatal Behavior, Leaf Water Potentials, and Root System Permeability in Beta vulgaris L

Studies of the water relations of potassium deficient sugarbeet plants (Beta vulgaris L.) revealed two factors for stomatal closure. One component of stomatal closure was reversible by floating leaf discs on distilled water to relieve the water deficit in the leaves; the other component was reversible in the light by floating the leaf discs on KCl solution for 1 hour or more. Potassium-activated stomatal opening in the light was observed when the guard cells were surrounded by their normal environment of epidermal and mesophyll cells, just as observed by previous workers for epidermal strips. Leaf water potentials, like stomatal apertures, appear to be strongly related to leaf potassium concentration. Potassium-deficient plants have a greatly decreased root permeability to water, and the implications of this effect on stomatal aperture and leaf water potential are discussed. In contrast, petiole permeability to water is unaffected by potassium treatment.