Derrick M. Oosterhuis

Influence of potassium deficiency on photosynthesis, chlorophyll content, and chloroplast ultrastructure of cotton plants

In cotton (Gossypium hirsutum L.) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied. After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (PN) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply. Decreased leaf PN of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves. Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading. K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues.

The effect ofAcremonium coenophialum on the growth and nematode infestation of tall fescue

The presence of the endophytic fungusAcremonium coenophialum Morgan-Jones et Gams in tall fescue (Festuca arundinacea Schreb.) induces toxicity when this grass is grazed by cattle; however, there is evidence that removing the endophyte reduces the stand vigor and longevity of fescue. A field trial was conducted to determine the effects of water supply and the presence of the endophytic fungus on plant growth, drought tolerance, and soil nematode populations in ‘Kentucky 31’ tall fescue. The design included two factors, level of endophyte infection (0 and 75%) and irrigation regime (none, low, and high). Where water deficits occurred, herbage yield and leaf area were lower, and percentage dead tissue and canopy minus air temperature were greater in endophyte-free compared with endophyte-infected fescue. Soil populations ofPratylenchus scribneri andTylenchorhynchus acutus were substantially higher in the noninfected than in the endophyte-infected plots. The endophyte apparently confers drought tolerance to Kentucky 31 tall fescue, and this effect may be at least partially mediated through enhanced resistance to soil-borne nematodes.

Physiological responses of cotton leaves and roots to water deficit induced by polyethylene glycol

Abstract The characterization of plant water relations is a prerequisite for subsequent selection and genetic manipulation for drought tolerance. To evaluate roots in addition to leaves, a method based on PEG was developed to obtain clean, stressed roots quickly while avoiding toxic effects associated with PEG treatment. A mild water deficit of −0.3 MPa was induced with polyethylene glycol (PEG 6000) around the roots of four cotton ( Gossypium hirsutum ) genotypes with different water deficit tolerances. Treatment with PEG during diurnal dark period avoided toxic effects observed with treatment during the light period. The genotypes examined included: (1) Siokra L-23, a drought-tolerant cultivar; (2) T-1521, a wild-type with significant osmotic adjustment capability; (3) CS-50, a moderately susceptible cultivar; and (4) Stoneville 506, a susceptible cultivar. The water potentials ( ψ w ) and osmotic potentials ( ψ s ) of roots and leaves of stressed and non-stressed plants were determined psychrometrically. In response to the water deficits Siokra L-23 and T-1521 showed 25 and 20% reductions in leaf ψ s , respectively, compared with unstressed controls. At the same time, ψ w of these two genotypes did not change significantly. Conversely, the decrease in the ψ s of CS-50 and Stoneville 506 was not significant, while their ψ w decreased significantly. By maintaining a higher ψ w during stress, the tolerant genotypes were able to maintain photosynthesis, stomatal conductance and relative water content near unstressed control levels. The use of PEG 6000 to maintain a constant ψ w in the root environment provides an efficient method for controlling ψ w while allowing for rapid sampling of clean root tissue for analysis. The results demonstrated that the empirically determined differences in drought tolerance of these cultivars can be related to measurable physiological parameters. These results suggest that physiological monitoring can be an effective tool in germplasm selection and improvement.

Physiological changes associated with potassium deficiency in cotton

Abstract Potassium (K) fertility recommendations based on cotton petiole diagnostic analysis results have been inconsistent in the past, partly because the lowest acceptable petiole K concentration is unknown. Therefore, cotton was grown in sand filled 8‐L pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, AR to determine the petiole K concentration that will impact leaf physiology. Chamber‐grown plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting two treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Measurements were taken 13, 19, and 26 days after treatment establishment (DATE). Organ K concentrations, leaf chlorophyll, photosynthesis, adenosine triphosphate (ATP), and nonstructural carbohydrate concentrations were monitored as plant K deficiencies developed. All organ K concentrations were much lower in the n...

Leaf photosynthesis and carbon isotope discrimination of cotton in response to potassium deficiency

Abstract Leaf photosynthesis and stable carbon isotope composition in response to potassium (K) deficiency was determined with cotton. Cotton plants were grown in sand-filled 8-l pots under two K treatments in a growth chamber at the Altheimer Laboratory in Fayetteville, Arkansas. Plants were watered every second day with nutrient solution and with deionized water on alternate days. At 14 days after planting (the fourth true leaf stage) the treatments were established consisting of (1) continued complete nutrient solution, and (2) nutrient solution containing no K. Leaf photosynthesis and related gas exchange measurements were taken 13, 19, and 26 days later. Leaf samples from each analysis date were then dried and reserved for nutrient and carbon isotope analyses. Photosynthesis declined as the K deficiency developed in the no-K treatment. Decreased ∂A/∂ci and increased Γ also resulted from declined leaf K concentration, which is attributed to changes in A and respiration in the light. Potassium deficiency also resulted in increased stomatal and non-stomatal limitations to A. Gas exchange studies showed stomatal conductance was most limiting to A at 13 days after treatment establishment (DATE), whereas instantaneous measurements at 19 and 26 DATE indicated non-stomatal conductances were most limiting. However, carbon isotope analyses, which integrated stomatal and non-stomatal conductances over the entire analysis period, indicated that the most limiting resistance to A was stomatal. We conclude from these studies that, during a mild K deficiency, increased stomatal resistance is first to result in a decrease in A and, as the deficiency becomes more acute, biochemical factors also contribute.

Effect of water stress on the epicuticular wax composition and ultrastructure of cotton (Gossypium hirsutum L.) leaf, bract, and boll

Abstract The epicuticular waxes (EW) of leaves, bracts, and bolls of cotton ( Gossypium hirsutum L.) were studied with respect to total accumulation, chemical composition, and their ultrastructure under well-watered and water-stressed conditions. Leaf, bract, and boll accumulated 91.71 μg cm −2 , 74.18 μg cm −2 , and 152.58 μg cm −2 of wax, respectively, under well-watered conditions, while water stress increased the wax concentration to 154.60 μg cm −2 , 108.91 μg cm −2 , and 158.53 μg cm −2 in the leaf, bract, and boll, respectively. Water stress increased the number and levels of long-chain, higher molecular weight alkanes in the leaf and bract wax, whereas the water-stressed boll wax contained only the long-chain alkanes. Among the long-chain alkanes, n -octacosane (2.70%), n -nonacosane (1.76%), n -triacontane (2.10%), dotracontane (4.60%), and n -tetratriacontane (24.50%) were the chief constituents of the water-stressed leaf wax. The bract wax contained n -octacosane (3.30%) and n -triacontane (38%). n -Octacosane (21.70%), n -nonacosane (8.60%), and n -triacontane (27.90%) were the long-chain alkane constituents of the boll wax. Alkanes constituted 65.94%, 51.00%, and 58.20% of the total wax in the water-stressed leaf, bract, and the boll, respectively, whereas wax from well-watered leaf, bract, and boll contained 10.53%, 25.70%, and 91.30% alkanes, respectively. Scanning electron microscopy revealed that the adaxial and abaxial surfaces of the leaf and bract, and the boll exterior surface had analogous wax morphology under both water-stressed and well-watered conditions. The results suggested that water stress increased the levels of long-chain alkanes in the epicuticular wax in which n -tetratriacontane was the major wax constituent of the water-stressed leaf, whereas the water-stressed bract and boll contained n -triacontane as the major wax component.

Physiological responses of two soybean [Glycine max (L.) Merr] cultivars to short-term flooding

Abstract Flooding of soybean plants [ Glycine max (L.) Merr] significantly reduces crop growth and yield, but the underlying physiological responses are poorly documented. The short-term physiological effects of flooding on soybean were studied in the field on a relatively impermeable soil classified as Typic Albaqualf. Flooding treatments were imposed on two soybean cultivars, Essex and Forrest, at a vegetative (V4) and a reproductive (R2) growth stage. Diurnal measurements of net photosynthesis ( P n ), stomatal conductance ( g s ), and components of leaf water potential were recorded on 4 consecutive days following flood application, and again at 14 days after the flood was removed. Photosynthesis of Essex was reduced significantly within 48 h of flooding by 33 and 32% for the V4 and R2 growth stages, respectively, while reductions of 16 and 22% in P n of Forrest were evident. Reductions in g s of 46 and 24% occurred within 48 h for Essex and Forrest in the V4 stage, although in the R2 growth stage, both cultivars experienced an approximate 48% reduction in g s . However, the decline in P n with flooding was only partially explained by changes in g s . Photosynthesis was correlated with stomatal closure at low g s ( −2 sec −1 ), but a higher values of g s an approximate 20% reduction in P n was observed presumably due to non-stomatal limitations. Flooding did not affect components of leaf water potential indicating that the decreases in P n and g s were not associated with plant water-deficit stress. Flooding of Essex and Forrest at either the V4 or R2 growth stage significantly reduced the dry matter accumulation during the flooding treatment and the subsequent growth. Final seed yields were reduced significantly by a mean of 52 and 40% for Essex and Forrest, respectively. Overall, Forrest appeared more tolerant to excess water than Essex.

Heat stress‐induced limitations to reproductive success in Gossypium hirsutum

Using in vitro systems, numerous authors have cited the sensitivity of pollen tube growth to high temperature as a major cause of low yields for crops with valuable reproductive structures. We investigated the hypothesis that in vivo fertilization efficiency would be negatively affected by heat stress-induced changes in energy reserves and calcium-mediated oxidative status in the pistil. Gossypium hirsutum plants exposed to optimal (30/20 degrees C) or high day temperature (38/20 degrees C) conditions during flowering were analyzed for fertilization efficiency via UV microscopic observation of pollen tube-containing ovules and for soluble carbohydrates, adenosine triphosphate (ATP), calcium, antioxidant enzyme activity and NADPH oxidase (NOX; EC 1.6.3.1) activity in the pistil. Leaf measurements included gas exchange, chlorophyll content, quantum efficiency and ATP content of the subtending leaf on the day of anthesis. In the pistil fertilization efficiency, soluble carbohydrates, ATP content and NOX activity declined significantly, whereas water soluble calcium and glutathione reductase (EC 1.8.1.7) activity increased, and superoxide dismutase (EC 1.15.1.1) activity remained unchanged. In leaves, heat stress decreased photosynthesis, quantum efficiency and chlorophyll content, but increased stomatal conductance. We conclude that decreased source leaf activity either inhibits pollen development, tube growth through the style or guidance to the ovules as a result of an insufficient energy supply to the developing pistil. We further conclude that a calcium-augmented antioxidant response in heat-stressed pistils interferes with enzymatic superoxide production needed for normal pollen tube growth and fertilization of the ovule.

Osmotic adjustment in tissues of tall fescue in response to water deficit

Abstract Understanding plant response to drought is important in evaluating mechanisms of drought tolerance. Osmotic adjustment was measured in various structures in the temperate grass tall fescue (Festuca arundinacea Schreb. cv. Kentucky 31) to characterize whole-plant response to water stress and to determine tissues most responsive to intermittent water deficit. A replicated greenhouse trial was conducted in which soil-grown tall fescue was watered or subjected to a series of drying cycles. Daily temperatures usually ranged from 20 to 32°C. Tissues sampled were youngest, fully expanded leaf blade, its sheath, emerged portion of expanding (immature) leaf blade, unemerged portion of same leaf blade, and all remaining basal tissue below the ligule inside the whorl. Plants osmotically adjusted (P

Photosynthesis of individual field-grown cotton leaves during ontogeny

Photosynthetic characteristics of field-grown cotton (Gossypium hirsutum L.) leaves were determined at several insertion levels within the canopy during the growing season. Single-leaf measurements of net photosynthesis (Pn), stomatal conductance to CO2 (gs·CO2), substomatal CO2, leaf area expansion, leaf nitrogen, and light intensity (PPFD) were recorded for undisturbed leaves within the crop canopy at 3–4 day intervals during the development of all leaves at main-stem nodes 8, 10, and 12. Patterns of Pn during leaf ontogeny exhibited three distinct phases; a rapid increase to maximum at 16–20 days after leaf unfolding, a relatively short plateau, and a period of linear decline to negligible Pn at 60–65 days. Analysis of the parameters which contributed to the rise and fall pattern of Pn with leaf age indicated the primary involvement of leaf area expansion, leaf nitrogen, PPFD, and gs·CO2 in this process. The response of Pn and gs·CO2 to incident PPFD conditions during canopy development was highly age dependent. For leaves less than 16 days old, the patterns of Pn and gs·CO2 were largely controlled by non-PPFD factors, while for older leaves Pn and gs·CO2 were more closely coupled to PPFD-mediated processes. Maximum values of Pn were not significantly different for any of the leaves monitored in this study, however, those leaves at main-stem node 8 did possess a significantly diminished photosynthetic capacity with age compared to upper canopy leaves. This accelerated decline in Pn could not be explained by age-related variations in gs·CO2 since all leaves showed similar changes in gs·CO2 with leaf age.