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Open access

B. W. Poovaiah

Abstract

The role of Ca as an intracellular messenger is beginning to be unraveled as a result of recent research on calmodulin, a ubiquitous protein that binds Ca ions and regulates various biochemical processes in plants. Experimental evidence suggests that certain cell functions in plants are regulated, in part, by Ca and calmodulin. Changes in cell wall rigidity, membrane permeability, and enzyme activation are known to influence various aspects of cell physiology and have a significant influence on the growth and development of plants. Deficiency of Ca is known to induce physiological disorders in fruit and vegetables. We hope that this article will stimulate further studies and provide new insights into how these problems may be controlled. The role of Ca ions in signal transduction and cell function is beginning to be understood at the molecular level, and we have embarked on a new phase of the old subject of mineral nutrition, especially as it applies to Ca and plant growth and development.

Open access

B. W. Poovaiah

Abstract

Calcium is known to be a second messenger in many developmental processes in animal systems, but it has only recently become evident that Ca is an important intracellular messenger in plants as well (9, 15, 22, 32-35, 41). The level of free Ca concentration in the cytoplasm is extremely low, and it is influenced by extracellular signals such as light, gravity, and hormones. Investigations from our laboratory indicated that Ca and its binding protein, calmodulin, play an important role in stimulus-response coupling by regulating enzyme activities, especially through protein phosphorylation (33, 34, 48). In vivo and in vitro protein phosphorylation studies have revealed Ca-dependent changes in various plant tissues (18, 37–39, 49, 50). We have also been able to influence various physiological processes such as cell elongation, abscission, senescence, and tuberization by altering extracellular and intracellular Ca levels (33). Other examples of Ca-mediated processes in plants are as follows: a) cell division, b) geotropism, c) protoplasmic streaming, d) stomatal control, e) chloroplast movement, f) secretion, g) hormone-dependent changes, h) enzyme activation, and i) protein phosphorylation (9, 33).

Open access

B. W. Poovaiah

Abstract

Treatment of beet root slices (Beta vulgaris L.) with (2-chloroethyl)phosphonic acid (ethephon) at 100 ppm increased membrane permeability 7-fold as indicated by betacyanin leakage. Leakage was much greater at higher concentrations of ethephon. Divalent and trivalent cations (Ca++, Mg++, La+++) prevented the effects of ethephon on membrane leakage without altering the rate of ethylene evolution. The monovalent cations (K+, Na+, NH4 +) were not effective in relieving the ethephon effect.

Free access

Gregory M. Glenn and B.W. Poovaiah

Changes in texture, cell wall structure and composition during storage of Ca-treated and untreated `Golden Delicious' apple fruit (Malus domestics Borkh.) were investigated. The cell wall region of Ca-treated fruit showed no swelling during storage and cell-to-cell contact was maintained, whereas regions of the middle lamella in untreated tissue stained lightly, appeared distended, and eventually separated. In control fruit, microfibril orientation was lost in distended regions of the cell wall, especially in the outer wall region adjacent to the middle lamella. Furthermore, the middle lamella was fenestrated and in some cases was completely degraded. These changes during storage of control fruit were accompanied by a decrease in arabinose and galactose moieties of the cell wall and an increase in soluble pectin. Calcium treatment of fruit inhibited solubilization of polyuronide and arabinose moieties and reduced the loss in galactose content during storage. Tensile strength and firmness were positively correlated to Ca content of the fruit cortex. Excessive tensile stress caused tissue failure in control fruit when cells of the cortical tissue separated at the middle lamella. In contrast, cylinders of Ca-treated fruit fractured through cortical cell walls.

Open access

B. W. Poovaiah and K. Veluthambi

Abstract

Extracts of strawberry (Fragaria × ananassa Duch.) receptacles contain a soluble invertase and a bound invertase which can be extracted with 1 m NaCl. Both soluble and salt-extracted invertases had a pH optimum of 4.6. The soluble invertase was more sensitive than salt-extracted invertase to inhibition by I2 and HgCl2. The soluble invertase activity was high at an thesis and decreased markedly during receptacle growth. In contrast, salt-extracted invertase activity increased 80% to 100% during receptacle growth induced either by pollination or by the application of NAA. The possible role of salt-extracted invertase in establishing sink activity during auxin-induced strawberry receptacle growth is discussed. Chemical names used. 1-naphthaleneacetic acid (NAA).

Open access

Richard N. Arteca and B. W. Poovaiah

Abstract

Root systems of potato plants (Solanum tuberosum L. var. Russett Burbank) were treated with 14CO2 and translocation was evaluated by autoradiography. Treatments of less than 1 hour showed little radioactivity in the leaves. Between 1 and 6 hours, there was a substantial increase in radioactivity in both roots and leaves. The 14CO2 was translocated to the leaves as 14CO2 dissolved in the xylem sap and as components fixed in the roots then transported. Plant tissues were analyzed spearately for radioactivity as extractable, basic (amino acids), neutral (sugars), insoluble (starch), and acidic (organic acids and sugar phosphates) fractions. Between 70 and 80% of the total extractable radioactivity was in the acidic fraction; of this, 96% was found in malic acid with the remainder containing other organic acids, amino acids, and sugars.

Open access

K. W. Mudge, K. R. Narayanan, and B. W. Poovaiah

Abstract

The control of fruit set and development in strawberries (Fragaria X ananassa Duch.) was investigated by exogenous application of auxins to unpollinated flowers or receptacles from which achenes had been removed. Addition of 2% dimethylsulfoxide (DMSO) to aqueous naphthaleneacetic acid (NAA) sprays or dips increased fruit set from ca. 50% to 100%, thus providing a simple and dependable method to induce parthenocarpic fruit set in strawberries. Strawberry fruits were found to be less sensitive to auxin than coleoptiles when auxin-induced strawberry receptacle growth was compared with corn or oat coleoptile elongation. Suboptimal NAA concentrations induced parthenocarpic fruit set with limited fruit growth. Such fruits remained auxin-responsive and viable for 30-45 days when a second NAA treatment resumed their normal growth and development, thus doubling the life span of strawberry fruit from 30 to 60 days. In contrast, unpollinated flowers treated with optimal NAA concentrations in DMSO behaved like pollinated flowers and ripened within 25-30 days. Fifteen auxin analogs and structurally related non-auxins were tested for their ability to stimulate growth of strawberry receptacles following achene removal. The relative effectiveness of these compounds in inducing receptacle growth was very similar, with a few exceptions, to their relative effectiveness in stimulating corn coleoptile elongation.

Open access

Gregory M. Glenn and B. W. Poovaiah

Abstract

The influence of stomata, the stylar scar, cuticular fractures, and Ca2+ on susceptibility of ‘Bing’ sweet cherry fruit (Prunus avium L.) to water injury was studied. Water injury was first detected as an increase in cell turgor. Water penetration caused separation of the cuticle from the epidermal cell wall. Swelling in the epidermal cell wall region resulted in cuticular fracturing that generally preceded fruit cracking. Uncracked fruit that had cuticular fractures softened rapidly. Stomata were sparsely distributed on the fruit surface and were often fixed in an open or partially open position. Water injury was not visible at stomata even when injury occurred adjacent to the stomatal region. Initial signs of injury were commonly visible near the stylar scar. Histochemical studies revealed that the surface of the stylar scar was devoid of a cuticle covering and was rich in insoluble carbohydrates. Greater penetration of solute containing 45Ca2+ occurred at the stylar scar. Fine fractures in the cuticle surface were observed in fruit at harvest time in 1985 and 1986. Cherry fruit with cuticular fractures had a higher water absorption rate than unfractured fruit. In immersion tests, Ca2+ reduced cherry cracking. EGTA increased fruit cracking; this increase was negated by adding Ca2+. Neither Ca2+ nor EGTA affected the water absorption rate of the fruit. EGTA decreased the cracking threshold of the fruit, while Ca2+ increased it. Soluble pectin content of the immersion solution rose with increasing incubation times. EGTA increased while Ca2+ markedly decreased soluble pectin concentration in the immersion solution. Histochemical studies indicated a breakdown of the cell wall structure in the epidermal region of water-injured fruit. Autoradiographs of fruit immersed in a solution containing 45Ca2+ showed the epidermal region to be the site of Ca2+ action in altering fruit cracking. Chemical name used: Ethyleneglycol-bis-(β-aminoethyl ether) N,N,N,N-tetraacetic acid (EGTA)

Open access

Stephen M. Southwick and B.W. Poovaiah

Abstract

NAA at 10–3 m concentration plus 2% dimethylsulfoxide (DMSO) in lanolin paste, applied to apices of unpollinated strawberry (Fragaria × ananassa Duch. ‘Ozark Beauty’) flower receptacles, promoted growth and receptacle elongation resulting in full-sized fruit. Movement of [14C]NAA occurred predominantly in a basipetal direction from the treated apex to the receptacle base. Growth occurred only at the site of application when NAA was applied to the receptacle base or longitudinal half. Acropetal or lateral movement of [14C]NAA in receptacles was minimal. Movement of [14C]NAA out of receptacles and into pedicels was basipetal in nature and was slower than that noted within the receptacles. These data demonstrate that polar auxin movement in strawberry receptacles appears to promote uniform growth at some distance from the point of application. Chemical names used: 1-naphthaleneacetic acid (NAA); indole-3-acetic acid (IAA); and 2,3,5-triiodobenzoic acid (TIBA).

Open access

G. M. Glenn and B. W. Poovaiah

Abstract

Isolated cuticles from ‘Golden Delicious’ apples (Malus domestica Borkh.) were mounted in a flow-through diffusion cell. Donor solutions containing 0.5m Ca chloride, Ca acetate, Ca nitrate, and two commercial formulations of Ca were allowed to flow over the outer surface of the cuticle. Calcium that permeated the cuticle was collected and analyzed by atomic absorption spectrophotometry. The effect of temperature and pH on Ca penetration also was investigated. Calcium chloride permeated the cuticle significantly faster than other organic or inorganic forms of Ca tested. The Ca penetration rate decreased with decreasing temperature as predicted by the temperature coefficient for diffusion of strong electrolytes. The decrease in the rate of diffusion at low temperatures seemed to be due to the increase in viscosity of the solution. Uptake of CaCl2 tended to be higher at pH 3 than at pH 11. The pCa was also higher at pH 3 than at pH 11. Solutions of CaCl2 dried significantly slower than other forms of Ca tested. Cuticular Ca movement and the potential advantages of the system for screening cuticular permeability of various forms of Ca were investigated.